Hydrothermal performance through multiple shapes of microchannels (MCHS) using nanofluids: an exhaustive review

Abstract

Hydrothermal performance through multiple shapes of microchannels (MCHS) using nanofluids is summarized as the previous studies in the present work. The enhancement of heat transfer dissipation in electronic equipment becomes more necessary where high heat can damage it and cause more problems, so the Microchannel heat sinks can be a solution fore these problems. The heat transfer enhancement through Microchannels can be acheived by a passive technique which includes using corrugated channels such as wavy, zigzag, and converge-diverge MCHS. Also, flow disruptions such as using MCHS with cavities, ribs, grooves, dimples, and offset strip pin fins. In otherside the fluid additives included using nanofluid with different MCHS shapes, and Secondary flow as an MCHS with oblique fins is another method fore passive techniques. Wavy microchannels with secondary channels have higher hydrothermal performance compared to other types. Zigzag MCHS could provide good heat transfer enhancement but with high pressure drops. Regarding flow disruptions, the hydrothermal performance of MCHS with ribs is better than pin fin. The results showed that using a hybrid nanofluid gives more enhancement heat transfer as well as higher pressure drops. Concerning single-phase fluid, the review results showed that using metal oxide nanofluid has higher thermal conductivity compared to carbon-based and dielectric nanofluids; therefore, the single phase of nanofluids can be arranged descending from the best to worst, according to its use as the cooling liquid in microchannels and their efficiency in heat transfer enhancement, metals (Ag, Cu), metal oxides (TiO₂–H₂O, CuO–H₂O, ZnO–H₂O, and Al₂O₃–H₂O), and dielectric nanofluid (SiO₂–H₂O). The specific application requirements and design considerations will guide the selection of the appropriate microchannel type for optimal heat transfer performance, so MCHS with mixing flow, higher thermal conductivity nanofluids, and low pressure drop are the most important factors that achieve hydrothermal efficiency.

Introduction

In most thermal engineering equipment, the excessive heat generated must be dissipated to keep it for a long time and work with more performance; hence, the microchannel heat sinks appear to be one of the solutions to achieve these demands. Microchannel heat sinks (MCHS) are a class of heat exchangers that contain small channels that have hydraulic diameter smaller or equal to 200 mm to give more enhancement in heat transfer between a fluid and solid surface. So the MCHS are used in various industries where efficient heat dissipation is essential, such as electronic cooling (microprocessors, power amplifiers, and LED arrays) [1], power generation systems such as solar and fuel cells to enhance the performance of energy conversion and maintain optimal operating temperatures of these systems [2], aerospace applications to manage the thermal loads experienced by components in aircraft and spacecraft systems [3], automotive cooling to give efficient cooling and manage higher heat loads for components such as engine control modules, battery systems in electric vehicles, and power electronics in hybrid vehicles [4], medical applications such as laser systems, medical imaging equipment, and diagnostics tools to prevent the overheating and ensure accurate operation [5], heat recovery systems in order to transfer waste heat from industrial processes for other applications, such as space heating or preheating of fluids and in bioengineering, aerospace, micropumps, microturbines, engines, microvalves, and microreactors [6]. So according to the above applications more cooling techniques are being used to reduce heat flux, but more research is still needed to extract heat flux greater than 800 W cm⁻². As a result, proper thermal management of microelectronics requires overcoming heat flux-related damages. Because of this, incorporating a reliable cooling system into the design of these devices has become crucial. So, microchannel configurations are one of the crucial techniques capable of dissipating high power densities (more than 1000 W cm⁻²) as opposed to traditional channels. The systems include a cooling medium (air or liquid) and thermal sinks in different shapes and designs. The rapid development of electronic chips has focused the attention on the flow of fluid and heat transfer researchers leading to improving cooling systems. However, the smooth, straight microchannel heat sinks mentioned above cannot cool electrical components properly; this can be attributed to the constantly increasing power density of high-density microelectronics, optical devices, instrumentation, and other devices. Advanced electronic systems cannot continue to evolve with their current level of heat dissipation. Numerous novel designs have been proposed for improving the heat transfer efficiency of MCHS. These designs include using “a secondary channel” [7, 8], “nanofluids” [9, 10], “a channel with curvatures” [11, 12], “dimples, porous” [13, 14], “ribs” [15,16,17,18,19,20,21,22,23,24], “cavities or ribs” [25,26,27,28,29,30,31], and “a combination of ribs and grooves” [32,33,34,35,36,37]. The geometry of the microchannels may not be sufficient to meet the demand for high thermal performance, so more researchers investigated the effect of using the cooling liquid on the hydrothermal performance of microchannels.

The novelty and needs of this work may be summarized as follows:

• 1. Study the techniques of heat transfer augmentation that can be used in MCHS.

• 2. A significant number of researchers have independently examined a study of the relationship between microchannel structure, hydrothermal performance, and the thermal properties of nanofluids. Few researchers have looked into how different MCHS shapes can affect the hydrothermal performance of a mixture of flowing nature, type of nanofluid, volume fraction, percentage of nanofluid, particle size, and MCHS shape.

• 3. The most mathematical equations and models related to calculating the thermal properties of most nanofluids used as cooling liquids are reviewed.

• 4. Predictive models that have high hydrothermal performance.

Hydrothermal enhancement in MCHS

Generally, hydrothermal enhancement techniques for any thermal engineering system can be classified into two types which are passive and active techniques. Passive techniques are those that do not require direct application of external power, while active techniques require external power. Figure 1 shows a schematic of methods used for heat transfer augmentation.

Fig. 1

Different methods of hydrothermal enhancement

Active methods

The passive technique has more attention than the active technique because of its role in enhancing the hydrothermal performance of MCHS due to its compact design of electronic devices. However, few researchers tried to enhance heat transfer performance using the active method. Flow-induced vibration is one method of active technique, Go [38] used this method to show the effect of flow-induced vibration of a microfin array on hydrothermal performance. The study proved that increasing the vibration displacement led to a high heat transfer rate. In another related work, Krishnaveni et al. [39] proposed heat transfer can be enhanced using the periodic electric field technique in rectangular MCHS due to chaotic mixing in a microchannel resulting in heat transfer augmentation. The magnetic field is one method of active techniques, in this field gives a rate of enhancement in heat transfer rate, Selimefendigil et al. [40] proved that the heat transfer factor is enhanced by 13.8% when using a magnetic field with nanofluid through a triangle-shaped cavity.

Hydrothermal enhancement for multiple shapes of MCHS using passive technique

Due to the significance of the passive technique in selecting the best MCHS design, the following methods for hydrothermal performance in MCHS will be reviewed in this paper:

• Developing the fluid flow by optimizing the design of MCHS such as in straight MCHS,

• Channel curvatures (corrugated channels) such as in wavy, zigzag, and converge–diverge MCHS [11, 52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76],

• Flow disruptions such as using MCHS with cavities, ribs, grooves, and offset strip fins, [32, 77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113]

• Fluid additives, such as using nanofluid with different shapes of MCHS [32, 74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172]

• Secondary flow such as in MCHS with oblique fins [59] or microchannel with an alternatively directed slanted secondary channel [61],

Straight microchannels

In the present topic, a passive method for enhancing the performance of MCHS is represented by optimizing the design, single phase (distilled water as a cooling liquid), laminar flow, and 3-D. Heat transfer enhancement can be achieved by breaking the thermal boundary layer and uniformity of temperature distribution with a low pressure drop in fluid flow. The straight MCHS whether single layer or multiple layers have different shapes of cross sections such as rectangular, triangular, and trapezoidal. Wang et al. [41] examined the effect of multiple shapes of MCHS, including rectangular, triangular, and trapezoidal. The findings show that thermal resistance was lowest in the RMCH and highest in trapezoidal. Moreover, the effect of the aspect ratio (AR = Hc/Wc) of RMCH on performance was investigated, where an (AR) between 8.904 and 11.442 resulted in the greatest performance (Fig. 2).

Fig. 2

Schematic of a microchannel heat sink geometry and b cross section with its dimensions of different microchannels studied by Wang et al. [41]

Li and Peterson [42] performed a numerical study on the heat transfer capabilities of silicon-based parallel MCHS. The optimal geometric properties of the microchannel were verified and indicated there is an increase in the overall cooling capacity exceeding 20% at a pumping power of 2 W and that the thermal resistance was 0.068 C W⁻¹. On the other side, the pressure difference remains constant. Kou et al. [43] Provided a 3D numerical model of the MCHS to examine the effects of heat transfer characteristics caused by different channel heights and widths. The findings demonstrate that lower thermal resistance can be achieved with a bigger flow area, more flow power, and a thinner substrate.

A numerical analysis study by Chein and Chen [44] was used to examine the impact of various inlet and outlet configurations on the thermal behavior of microchannels. The results showed that the velocity and temperature homogeneity of the MCHS, with the supplying of coolant and collection occurring vertically via the flow path from inlet to outlet on the microchannel heat sink cover plate, were very well. Mansoor et al. [45] used Fluent commercial software to analyze the heat transfer performance in a rectangular microchannel by examining the Nusselt number at a range of Re from 500 to 2000. The model was a three-dimensional, laminar flow, and water was used as a cooling liquid. Thermal characteristics in a copper microchannel were investigated using a heat rate per unit area equal to 130 W cm⁻². The findings demonstrate that as heat flux continued to increase, the coefficient for heat transfer decreased. Also, the results showed that the $\overline{\mathrm{Nu} }$ increased with increasing Re ranging (from 500 to 2000) at heat rate per unit area ranging from 45 and 130 W cm⁻².

Shkarah et al. [46] investigated various shapes of rectangular microchannels with widths of 44–56 µm, heights of 287–320 µm, and lengths of 10 mm. Aluminum, silicon, and graphene were used as materials. A fully developed laminar water flow was used at different volumetric flow rates and heat flux values. The results showed that using graphene in the microchannel reduced thermal resistance. The numerical method treated the thermophysical properties of the materials as non-temperature-dependent, which impacted the results compared to the experimental setup, and the findings have yet to be verified experimentally.

The hydrothermal performance of microchannels was examined numerically by Feng et al. [47]. The authors used a wire coil placed at different locations of the microchannels to examine this effect on heat transfer performance as shown in Fig. 3. In the experiment work, distilled water was used as a cooling liquid. The study's findings demonstrated that the longitudinal vortex created by the wire coils effectively improved the MCHS's heat transfer capability, but at the same time, resistance of flow increased. At a heat flux of 400 kW m⁻², the MCHS with a long wire coil positioned at the center line of the microchannel exhibits the best heat transfer performance with a performance factor of 1.4–1.8.

Fig. 3

Different configurations of rectangular microchannels [47]

An algorithm of multi-objectives was used by Yildizeli and Cadirc [48] to optimize the conjugated heat transfer in MCHS. The best trade-off results from maximizing the transfer of pumping power and convective heat, which are mutually exclusive. Microchannel heat sinks with different AR had been optimized for thermal performance and power consumption for Reynolds numbers 13 to 360 using Fluent flow solver and MATLAB optimization. The results revealed that increasing the AR reduced pressure loss and improved thermal performance up to a certain point. Fluid flow type is one method of passive technique that enhances heat transfer and takes attention from researchers. The effect of fluid flow type (parallel and counterflow) in double-layer rectangular MCH has been investigated by Xie et al. [49]. The findings of this work are that the counterflow gives better performance at large flow rates and uniform temperature rise. On the other hand, superior performance is achieved with parallel flow at slightly higher values of flow rates. Conventional DLMCHS design enhances the uniformity of temperature. Findings showed that the temperature of the cooling liquid is high temperature compared to the cooling at the bottom at the inlet region of the bottom channels, resulting in inevitable heating. Leng et al. [50] optimized a unique DLMCH with truncated top channels. The optimization process involved maintaining a constant volumetric flow rate of coolant and a fixed pumping power while experimenting with various design configurations. Employing an alternation structure with the staggered flow with MCHS enhances its overall thermal performance by facilitating the flow switching between the two channels. Shen et al. [51] provided a new structure for parallel and counterflows that include various staggered flow patterns. This structure has led to better temperature uniformity in a DLMCHS. Table 1 shows summary of previous studies related to straight microchannel heat sink.

Table 1 The literature sources reporting studies related to straight microchannel

Corrugated microchannel heat sink

Undoubtedly, one of the key applications in the area of passive heat transfer augmentation techniques is corrugated channels. This method significantly improves the flow mixing between cooler fluid layers in the core region and hotter fluid layers near the channel wall. Dean vortices (DVs) and chaotic advection (CA) are thought to be the mechanisms responsible for the induction of high-flow mixing. It is typical to fully comprehend these mechanisms. Wavy and zigzag are the main shapes of corrugated microchannels; hence, in this part, an exhaustive review will be presented by focusing on the hydrothermal performance of different shapes of the corrugated microchannel and the main parameters that affect performance.

Configurations of Wavy MCHS (WMCHS)

The effectiveness of wavy microchannels in reducing temperature fluctuations in electronic devices was studied numerically by Ghorbani et al. [52]. The proposed wavy MCHS is schematically shown in Fig. 4. Five wavy patterns were taken into consideration, with an amplitude (A) range (62.5 to 250 µm) and wavelength (L) range (1250–5000) µm. The flow regime was laminar, and the heat flux varied at five values: 80, 120, 160, 180, and 240 W cm⁻². The outcomes showed that in geometries with larger (A/L) ratios, transverse flow amplification improved heat transfer. A wavy case with a 2500 µm as wavelength and 250 µm amplitude was the ideal geometry. Chips can operate at higher heat fluxes because of the improved heat transfer provided by the use of wavy patterns in heat sinks. The findings from this study are displayed in Fig. 5.

Fig. 4

Schematic of wavy channel and the desired boundary conditions Ghorbani et al. [52]

Fig. 5

Comparison for a “the average Nusselt number” and b “friction factor versus the Reynolds number.” Ghorbani et al. [52]

Sui et al. [53] presented a numerical study of heat transfer in 3-D wavy MCHS with rectangular cross sections under study conditions such as constant wall heat flu, constant wall temperature, and conjugate conditions with water laminar flow. In this research it can be noted, the Navier–Stokes equations were solved using FVM based on CFD. The dynamical system technology was used to analyze fluid mixing. According to the simulation results, chaotic advection, which occurs when liquid flows through wavy MCHS, can significantly improve the process of fluid mixing and heat distribution performance while incurring a significantly lower pressure drop penalty than straight-type microchannels. Following this study, heat transfer and flow friction were presented.

Sui et al. [54] performed experimentally. The authors study heat transfer in three types of wavy microchannels with rectangular cross sections. The test section has a width and depth of 205 µm and 404 µm, respectively. Different values of wavelength magnitudes (0, 138, and 259 µm) were studied. The number of channels in test section 60–62 wavy (sinusoidal) microchannels distributed in parallel. Reynolds' numbers range from 300 to 800. The researchers made a comparison between the performance in heat transfer between wavy microchannels' and straight microchannels. The results showed that wavy microchannels were more effective than straight microchannels in hydrothermal. Other types of 3D WMCHS heat sinks are raccoon and serpentine wavy MCHS, with rectangular cross sections and Dh of 500 µm studied by Kota et al. [55]. At three different Reynolds numbers (50, 100, and 150), the impact of wavelength, inverse aspect ratio, and amplitude on heat augmentation performance was examined. The heat transfer by the thickness of the thermal boundary layer and in both wavy microchannels was found to be improved by increasing the Reynolds number, wave amplitude, and decreasing the wavelength. Xie et al. [56] proposed a transversely wavy microchannel with a rectangular cross section. The effect of this design on thermal performance has been investigated numerically. The findings demonstrated that compared to a straight microchannel, a transversally wavy microchannel has a significant potential to reduce pressure loss, particularly for higher wave amplitudes at the same Reynolds number. The results showed that the transversal wavy microchannel outperformed the conventional straight, rectangular microchannel in terms of total thermal performance. Figure 6 shows a schematic of transversal wavy microchannels.

Fig. 6

a Transversal wavy microchannels, b single transversal wavy microchannel. Xie et al. [56]

A developed flow with heat transfer in rectangular cross section with periodic converging–diverging channels was investigated by Yong et al. [57]. This study presented three types of study (experimental theoretical and CFD simulations). The conditions of this study are liquid water as a cooling liquid and constant wall temperature conditions. This research demonstrates that the fluid behavior and formulation of recirculating vortices are controlled by the channel aspect ratio (AR), with an AR between 0.5 and 1.0 ideal. Furthermore, it looks into how converging–diverging channels with sinusoidal profiles and continuous curvature can outperform straight microchannels by as much as 60% in thermal–hydraulic efficiency.

Gong et al. [58] compared the three proposed designs of dimpled and undimpled wavy microchannels and a straight microchannel to conclude on their relative merits. Hydrothermal properties in WMCHS with dimples at the base of each microchannel were studied numerically. The findings showed that the hyper method of passive technique (wavy with dimpled) achieved high heat transfer enhancement compared to straight without dimples and straight with dimples.

Ghani [59] used the combined techniques (secondary flow and channel curvature) depicted in Fig. 7 to improve heat transfer in MCHS. This study investigated the effects of three structural parameters, with amplitudes ranging from 0.05 to 0.2 mm, secondary channel widths from 0.1 to 0.2 mm, and angles of inclination from 45° to 90°. The results were compared to those of WMCHS lacking secondary channels and straight MCHS has same conjugated area. The findings revealed that 0.1 mm amplitude, 0.2 mm secondary width, and a 45° angle of inclination were ideal structural parameters, and thermal performance rose by about 108%.

Fig. 7

Contours of temperature distribution a RMCHS, b WMCHS and c WMSC on x–z plane at y = 0.25 mm with Re = 600 [59]

Kumar et al. [60] investigated thermal and hydraulic performances of MCHS numerically and experimentally with air as a cooling medium. Straight, wavy, and wavy with secondary MCHS are the heat sinks investigated in this work. The main assumptions taken into consideration through the numerical study are 3-D, conduction, and convection as modes of heat transfer, and the flow is a laminar model. With respect to various airflow rates, the Reynolds number ranges from 300 to 1900. The experimental method was used to validate the numerical method. According to the study's findings, the wavy with secondary MCHS performed better in terms of thermal–hydraulic performance than the straight and wavy.

Figure 8 illustrates a model developed by Memon [61] that included parallel and trapezoidal secondary flow channels. In one design, the secondary flow passages were parallel, while in the other, they were regular trapezoidal. The “I-type, C-type, and Z-type” inlet–outlet configurations were used to test these designs. The results were calculated in terms of the temperature on the base plate of the heat sink as well as the velocity and pressure profiles within the flow domain. The results of the study demonstrated that compared to the “C-type and Z-type” configurations, the “I-type” inlet–outlet configuration achieves better flow velocity uniformity. Due to the high fluid distribution that can be achieved in “I-type,” this can be considered as the perfect model compared to other types.

Fig. 8

a Sectional view of the MCHS; b heat sink with trapezoidal secondary flow (heat sink A); c heat sink with parallel secondary flow [61]

Khan et al. [62] Numerically studied the cooling performance of the straight, wavy, and dual-wavy microchannels. Al₂O₃ nanofluids with different volume fraction of 1%, 3%, and 6% was as cooling liquid. The fluid is assumed to be an incompressible fluid, laminar flow. Effect of a secondary flow and thermal performance of WMCHS studied by Memon et al. [63]. This study studied many parameters at different flow rates, such as pressure drop, flow profile, temperature profiles, and Nusselt number. The results have been examined along with related trends and those for the standard design.

An asymmetric wavy, double-layer microchannel with porous fins was a design studied by Wang et al. [64]. The hydrodynamic and thermal characteristics of a three-dimensional fluid–solid conjugate model were computationally analyzed in order to make a comparison between two configurations which are “wavy and porous fin” designs. The results demonstrate that WMCHS can dramatically improve HTP and decrease drop of pressure when using the porous fin design. While the symmetrical layout results in a greater reduction in pressure drop, the parallel configurations produce a greater increase in thermal performance. As a result, the pressure drop penalty for two wavy designs using the porous design is roughly the same. Table 2 shows a summary of previous studies related to WMCHS.

Table 2 Summary of previous studies related to wavy MCHS

Zigzag MCHS

Previous studies on the zigzag microchannels are summarized in this section due to their importance in many industrial applications, such as cooling electronic systems. The existence of bends along the channel can increase the intensity of the turbulence of the fluid and enhance the mixing of the wall fluid and the main channel to strengthen heat transfer [65,66,67,68,69].

Mohammed et al. [70] investigated the HTP of MCHS in three different microchannel shapes, namely zigzag, curvy, and step MCHS. The cooling liquid was water in a laminar flow. The outcomes showed that while the temperature was smaller in the ZMCHS, the coefficient of heat transfer was greater. Results also showed that ZMCHS, followed by step and curvy MCHS, could be used to produce high pressure drops. Zheng et al. [71] investigated the hydrothermal characteristics of ZMCHS with cross sections as semicircle under steady-state laminar conditions. Re number ranges from 50 to 320, while the Prandtl number ranges from 0.7 to 20. According to the findings, a lower value for the half-unit length-to-diameter ratio (L/D) results in greater fluctuation in the thermal enhancement factor while simultaneously lowering the drop of pressure. The results also show that the rate that which heat is transferred and drop of pressure rise when the ratio of the radius of curvature to the diameter (Rc/D) is reduced.

Ma et al. [11] introduced a novel offset zigzag microchannel heat sink with 30 parallel channels and basic structural dimensions of 0.1 mm in width, 0.3 mm in depth, 5 mm in length, and 0.2 mm in pitch. The surface's maximum temperature decreases by 5.65 K, and the power of pumping is reduced by 1.4%. At a power of pumping equal to 0.167 W, R_t was also lowered by 17.4%. Because the porosity of the zigzag microchannel reduces the average fluid velocity, it was designed to improve heat transfer and lower flow resistance. [72].

Duangthongsuk [73] compares the thermal behavior of nanofluid flows in crosscutting zigzag heat sinks (CZHS) and crosscutting single zigzag flow channels “CCZHS.” SiO₂–H₂O nanofluid with 0.3, 0.6, and 0.8 vol% is used as a cooling liquid. “CZHS and CCZHS” are both made of copper. According to the experimental results, the thermal performance of the nanofluid as a cooling liquid with a heat sink was 3–15% better than that of the water-cooled heat sink. Findings showed that the heat transfer performances of the CCZHS were superior to CZHS by a margin of between 2 and 6% on average.

To increase heat transfer performance Tang et al. [74] constructed a unique heat sink that comprises a zigzag microchannel and a serpentine channel. Also, it incorporated a manifold channel as the input channel to improve flow uniformity. Alnaqi et al. [75] Studied hydrothermal performance in (MCHS) with a zigzag shape under constant heat flux. The MCHS is cooled using hybrid nanofluids (HNFs) nanofluid compounds from “MWCNT/SiO₂/EG-H₂O.” Ongoing research investigates the effect of Hybrid nanofluids’ velocity (1–2 m s⁻¹), HNF volume fraction (0–0.5 vol%), and zigzag height (0 to 10 mm) on hydrothermal performance. As a result of the increases in velocity, the results showed that a greater amount of heat was removed from the microchannel. In addition, expanding the length of the channel's zigzag pattern helps improve heat transfer from the surface of the MHS, which is associated with an increase in the pressure of the fluid moving through the channel. Peng et al. [76] Conducted experiments on a new model with a zigzag serpentine microchannel heat sink (ZSMHS) shown in Fig. 9. The performance of the structure's heat transfer is examined using a zigzag microchannel with four different angles (300, 450, 600, and 900). Investigations were conducted on a number of variables, including pumping power, friction factor, pressure drop, heat transfer coefficient, thermal resistance, and temperature uniformity. The results showed that an angle of 300 could produce the lowest pressure drops, friction coefficients, and thermal resistance of the ZSMHS (Table 3).

Fig. 9

Incidence angle of the ZSMHS. Peng et al. [76]

Table 3 Summary of previous studies related to zigzag microchannel heat sink

Flow disruptions

It was one method of passive technique for heat transfer augmentation in MCHS by using MCHS with ribs, pin fin, dimples, obstacles, and curvature. The heat transfer enhancement can be achieved by interrupting of thermal boundary layer and creating vortices [77]. In the present topic, some of the studies related to flow were disruption studied.

Ribs in MCHS

Unfortunately, high-flow disturbances and the locking flow effect can significantly increase of drop in pressure when ribs are used [78, 79]. As a result, optimizing the geometric characteristics of the ribs is typically required to enhance the cooling of equipment while lowering $\Delta P$. Utilizing MCHS with ribs, grooves, or cavities to interrupt thermal boundary layers and reduce pressure drop is another frequently used method to improve heat transfer [80, 81]. Greater mixing between the hot water that is closest to the walls and the central flow of cold water is made possible by the jet and the throttling structure [27].

A combination of ribs and grooves or cavities effectively improves heat transfer while minimizing pressure drop and taking advantage of the lower pressure drop of grooves or cavities [32].

Ahmad et al. [82] numerically investigated the effect of rib surface refinements on the hydrothermal performance of MCHS. The pressure drop was reduced by as much as 85% and the Nusselt number was reduced by as much as 25% due to the ribs' surface refinement, leading to a thermal enhancement factor of 80%. The effectiveness of both the length and width of the ribs on the hydrothermal performance at different Reynolds numbers was examined by Paramanandam [83]. The main assumption in that study was water used as a cooling liquid with laminar flow and three-dimensional. The effectiveness of MCHS with ribs was measured by performance factor. Results indicate that the effect of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the dropping in pressure.

Zhang et al. [84] investigated the thermal performance of MCHS with new trefoil-shaped ribs. This study looked at three trefoil-shaped rib configurations: MC-AWTR, MC-SWTR, and MC-BWTR. At Re = 100–1000, the HTP, Rt, and entropy generation are used to measure the performance of MCHS. The results indicate that adding trefoil ribs to the walls of a smooth microchannel makes it better at handling heat, but it makes it worse at handling pressure. As the Reynolds number gets higher, it also affects the Nu and the h ̅. The efficient MCHS can be impacted by varying cross sections, and as a result, ribbed microchannel architectures have been developed. The ribs will disrupt the flow boundary layer and the thermal boundary layer, improving heat transmission. Figure 10a–c show different configurations of ribs and cavities. The most recent research on the effects of ribs and cavities on MCHS is compiled in Table 4.

Fig. 10

Different shapes of ribs and cavities: a shape of ribs [85]; b shape of truncated ribs [86]; c structure of cavities and ribs [87]

Table 4 Selected studies related to the microchannel heat sink with ribs

Pin fin MCHS

Later the design of the heat sink was a plate fin heat sink (PFHS), and the air was used as a cooling liquid. This design was considered one of the most traditional designs because of its ease of fabrication. Much research into PFHSs has gone into optimizing the fins' height, thickness, and separation, with the results being heated transfer predictions. Siu-ho et al. [88] studied a heat exchanger with staggered square pin fins to show that the heat transfer coefficient is highest close to the inlet and decreases along the flow direction. Liu et al. [89] carried out a test on a microsquare pin fin heat sink with pins in different places. It has been seen that as Reynold's number goes up, both pressure and average Nusselt go down. Three models of pin fins heat sink were studied numerically by Sajedi et al. [90] shown in Fig.  11. The models were circular pin fin heat sink (PFHS), circular pin fin with splitter, square pin fins, and square pin fin with splitter. According to the results, a circular pin fin heat sink with a splitter reduces pressure drop by 13.4%, thermal resistance by 36.8%, and profit factor by 20%. The same results are observed for square pins, with an 8.5% reduction in pressure drop, a 23.8% reduction in thermal resistance, and a 14% increase in profit factor.

Fig. 11

Configurations of pin fin heat sink a circular pin fin b circular PFHS with a splitter c rectangular PFHS d rectangular PFHS with a splitter. Sajedi et al. [90]

Yadav et al. [91] Three ways were used to put some cylinder-shaped microfins in a rectangular microchannel. The upstream finned microchannel worked best at a low Reynolds number (Re). At a high Re, the whole microchannel with fins worked best. The venting holes in the microchannel heat sink described by Yu et al. [92] make separating and removing fluids from the Piranha pin fins easier. Also, the Piranha pin fins disrupt the flow field. This causes the air to distribute, which makes the heat transfer better. Yang et al. [93] examined the heat transfer enhancement with five different configurations of microchannel heat sinks, including pin fin. The cross-sectional geometries of the pin fin have been chosen as circle, triangle, square, pentagon, and hexagon. The overall dimensions of all MCHS were designed to be the same, and a constant heat rate per unit area was applied at the bottom surface of the microchannel heat sink. Similar trends were observed in both the results and the simulations. To maximize the cooling efficiency of single-phase array microchannel heat sinks, the shape of the pin fin was critical in balancing pressure drop and heat transfer rate. The effect of geometry and the working fluid in laminar flow on heat transfer and flow characteristics was examined by Al-Asadi et al. [94]. The first is a heat sink with holes and pins (PPHS). The second is a new design for a uniform microchannel with vortex generators (VGs) of various shapes spaced out along the channel base. The constant volume flow rate of fluid is used to compare the triangle, circle, and rectangle VG shapes. The results show that using water to move heat in PPFHS does not make a big difference. It is also found that of the shapes suggested, circular VGs perform best when it comes to heat.

An experimental study for improving the hydrothermal efficiency of the inclusive MCHS was proposed by Wang et al. [95]. The researchers conducted a new design consisting from PF and VG. The finding showed that fins as a pin and vortex generators on MCHS make it easier for the water flow to be disturbed and for efficient heat transfer. This structure is shown in Fig.  12. The results show that oval pin fins perform better than round and diamond pin fins when it comes to thermal and hydraulic performance. When considering Reynolds numbers between 340 and 640, the oval pin fin achieves the best overall performance factor with (0.4 mm) as spacing and (0.1 mm) as height, as shown in the Fig.  13. The vortices will increase the mixing operation of hot fluid cold fluid.

Fig. 12

The schematic diagram of pin fins and vortex generators in the microchannel heat sink Wang et al. [95]

Fig. 13

Variations coefficient of friction and Nu with Re for various cases. Wang et al. [95]

The local coefficient of heat transfer coefficient around a single pin fin in a microchannel was predicted by Wang et al. [96], to maximize the wake's trailing edge downstream of the pin fin. Comparing the heat transfer rates of open and closed heat sinks, Prajapati [97] found that heat sinks with a fin height of 75% to 80% were more efficient than those with a full height of fins. The author has also listed the other benefits of the open microchannel heat sink. The open-type microchannels were investigated experimentally by Kadam et al. [98]. This research focused on improving the heat transfer efficiency of a microchannel heat sink with single-phase flow. A plain MCHS and an extended MCHS configuration of the open type were built. The work studied at mass flow rate per unit area range (157–754 kg m⁻² s⁻¹) and an effective heat per unit area range (6.1–246 kW m⁻²). The maximum decrease in wall temperature was measured equal to 3.7 °C. According to the study's findings, fins in the plain open MCHS accelerate heat transfer performance by 15%. Bhandari and Prajapati [99], examined open microchannel configurations with a gap between the fin's top surface and the heat sink's top wall. Seven different heat sinks in the 0.5–2.0 mm range with a 0.25 mm increment were compared in this study. According to the prediction results, raising the heat sink's fin height will speed up heat transfer. Figure 14 show all models are analyzed.

Fig. 14

Sketch of various configurations of pin fin a square b circular c triangular d pentagonal e hexagonal f diamond g piranha h chevron i rectangular j cone k hydrofoil l elliptical m oblong n S-shaped o trapezoidal (Bhandari and Prajapati 2021) [99]

Bhandari and Prajapati [99] validated the average Nu with varying Reynolds numbers for the different values of heat fluxes, where this validation showed that the value of Nu was approximately 10–12% with the prediction relations of Shah and London [100]. Figure 15b proved that the pressure drop predicted by the Bhandari and Prajapati [99] model is in close agreement with the experimental findings of Qu and Mudawar [101].

Fig. 15

a Comparison of average Nu for a plane channel with the correlations given by Yu et al. [92] and Shah and London [100] b Pressure drop validation with Qu and Mudawar [101].

Pandey [102] presented the results of an experimental investigation into the efficiency of copper pin–fin heat sinks, and parallel microchannel heat sinks using DI water as a coolant at varying flow rates. Substrate temperature, pressure drop, pumping power, and thermal resistance are among the thermal and hydraulic features examined. The results showed that as pumping power increased, thermal resistance decreased for both heat sinks, albeit at different rates and amounts. Furthermore, increasing the Reynolds number decreased thermal resistance and increased pressure drop for both designs. In the same heat flux conditions, a parallel microchannel heat sink showed lower thermal resistance pumping power than a pin fin heat sink (Tables 5, 6).

Table 5 Selected studies related to pin fins MCHS

Table 6 Selected studies related to microchannels heat sink with dimple-type

Dimples with MCHS

Dimples have been shown in studies [103,104,105] to increase thermal transmission by disturbing the boundary layer. Microchannel heat sinks using nanofluid [106]. The efficiency of dimples in improving cooling performance was analyzed by Xu et al. [107]. Hydrothermal efficiency is computed numerically for a laminar flow with a Re equal to 500. Due to the dimple effect, the author has found that transverse convection improves convection heat transfer under laminar flow without significantly increasing pressure drop. Because the difference in flow behavior and pressure drop between a standard microchannel and one with dimples is small, the pressure drop is disregarded as negligible when discussing the impact of dimples on heat transfer. Li et al. [108] demonstrated that the depth of dimple and protrusion significantly impacted thermal performance, with the relative Nusselt number Nu/Nuo increasing with flow rate and depth of dimple/protrusion. Huang et al. [109] conducted a numerical study to determine how dimples affect the heat transfer performance of a microchannel heat sink with impinging jets. The authors utilize numerical simulation and the field synergy principle to examine the performance of MIJs with and without dimples of varying dimple structures, including convex, concave, and mixed dimples. Results indicate that IMJS with convex dimples exhibited the best cooling performance, followed by those without mixed and concave dimples. Gan et al. [110] suggested a new model with side outlets for microchannel heat sinks with impinging jets and dimples (MHSIJD). The performance of the MHSIJD with side outlets was studied using a simulation method based on CFD with an RNG k–e turbulence model. The analysis indicates that the MHSIJD with side outlets works better at transferring heat. Up to 17.51% more heat transfer capacity is possible. The MHSIJD with side outlets has a lower pressure drop, which can be reduced by nearly 22.39%. The MHSIJD with side outlets also performs better because it cools better and uses less pump power.

The effects of dimples, dimple positions, and dimple sizes on experimental heat transfer and flow friction were studied by Gupta et al. [111]. More heat is dissipated when the dimple diameter is larger. A larger dimpled heat sink with a staggered dimple pattern results in a higher Nu and a higher friction factor. Okab et al. [112] investigated numerically a new design to improve heat transfer. The new design features two dimple sizes (0.5 mm and 1 mm) that are systematically clustered along channels with and without filets at Re numbers ranging from 200 to 1200. Furthermore, the filet profile influences MCHS thermal performance without increasing the pressure drop penalty. The results showed that the construction of dimples with filet profiles significantly enhanced HTP. The Nusselt number of microchannel heat sinks with a 1 mm dimple size, and filet profile is 60% higher than a plain microchannel. A numerical study was conducted by Debbarma et al. [113]. The incorporation of dimples and protrusions improved the double-layer sink's overall performance. Utilizing double layers in the heat sink allows us to get around the problem of the extreme temperature difference. Research into deionized water as a coolant is conducted for the Re ranging from 89 to 924. The results show that dimples or protrusions, regardless of their number or positional pattern, always contribute to an increase in Nusselt number, indicating a higher heat release rate.

Nanofluid synthesis and characterization

Nanofluids can be defined as colloidal suspensions from nanoparticles in a base fluid (water, Ethylene glycol, oil, etc.). Thermophysical properties of conventional fluid improve dramatically when the incorporation of nanoparticles is done. These properties are represented by density, specific heat, thermal conductivity, and dynamic viscosity. The amount of nanoparticles suspended in the base fluid determines the degree of heat transfer enhancement. Metal oxides (Al₂O₃, CuO, TiO₂, ZnO, MgO, SiC, etc.) are preferred as high thermal conductivity nanoparticles. Base fluids that are commonly used are water (H₂O), ethylene glycol (EG), and engine oil (EO) [114]. Various engineering applications utilized nanofluids due to their tremendous potential in improving heat transfer enhancement. From these applications photovoltaic (PV) panels [115]. One promising avenue for their utilization is in microchannels, where the small dimensions present unique challenges and opportunities for enhancing heat dissipation and fluid flow. Research in this area aims to leverage the unique properties of nanofluids to optimize thermal management in microchannel systems, leading to advancements in fields such as electronics cooling, energy systems, and biomedical devices.

Nanofluid preparation

Nanofluids produced by dispersing nanoparticles in the base fluid require good dispersion, which can be improved by using surfactants, surface modification, and strong force. There are two basic methods for preparing nanofluids: one-step physical and two-step physical. Firstly, the percentage of volumetric concentration and the mass of nanofluid must be specific then the mass of nanoparticles determine. The percentage of volume concentration is calculated by Eq. (1). [114]

$${\text{Volume}}\;{\text{concentration}},\;\phi = \left[ {\frac{{\frac{{W_{{{\text{sp}}}} }}{{\rho _{{{\text{np}}}} }}}}{{\frac{{W_{{{\text{np}}}} }}{{\rho _{{{\text{pp}}}} }} + \frac{{W_{{{\text{bs}}}} }}{{\rho _{{{\text{bs}}}} }}}}} \right] \times 100$$

(1)

where W_np denotes the mass of the nanoparticles, W_bf is the mass of the base fluid, ρ_np is the density of the particle, and ρ_bf is the density of the base fluid.

One-step method

This method avoids some procedures, including drying, storing, moving, and dispersing nanoparticles. Physical vapor deposition (PVD) is used to create stable nanofluid. (PVD) technique in which the base fluid is used to carry out direct evaporation and condensation of nanoparticles. Pure and consistent nanoparticles are created using this technique. As a result, nanoparticle accumulation is decreased.

Two-step method

In the two-step method, the nanoparticles are produced using various techniques, and they are then mixed with the base liquid to create the desired nanofluid. This manufacturing procedure costs little and enormous. The two-step method's main flaw is the clumping together of nanoparticles. The use of surfactant is due to instability.

Analyzing the stability of nanofluids

Nanofluid stability is the resistance of nanoparticles against aggregation or sedimentation [116]. There are different methods to examine the stability of nanofluids, such as

• Sedimentation, in this technique the mass or volume of the sediment under external forces must be measured [117]. Sahooli et al. [118] investigated the stability of CuO nanofluid.

• UV–spectrum in this technique the absorbance of light by the nanofluids at different wavelengths must be measured. [116]

• Zeta potential: measuring the electrical charge on the surface of nanoparticles in the nanofluids [114]

• Dynamic light scattering: measuring the size distribution of nanoparticles in the nanofluids [114]

Mathematical relations of properties of nanofluids

Density of nanofluid

The classical mixture law is the formula most frequently used to calculate density. The density of a nanofluid can be described using the classical mixture law as,

$${\rho }_{\mathrm{nf}}={\rho }_{\mathrm{np}}\phi +\left(1-\phi \right){\rho }_{\mathrm{bf}}$$

(2)

Specific heat of nanofluid

Equation (3) is an expression for the specific heat of nanofluids based on the volume concentration and density of individual element equation [119].

$${{\varvec{C}}}_{\mathbf{n}\mathbf{f}}={{\varvec{C}}}_{{\mathbf{p}}_{\text{p}}}{\varvec{\phi}}+\left(1-{\varvec{\phi}}\right){{\varvec{C}}}_{{\mathbf{p}}_{\mathbf{b}\mathbf{f}}}$$

(3)

Zhou et al. [120] showed that Eq. (3) was used for small volume concentration. Assuming thermal equilibrium, Xuan and Roetzel [121] proposed Eq. (4)

$${{\varvec{C}}}_{{\mathbf{p}}_{\mathbf{n}\mathbf{f}}}=\frac{{\varvec{\phi}}{{\varvec{\rho}}}_{\mathbf{n}\mathbf{p}}{{\varvec{C}}}_{{{\mathbf{p}}}_{\mathbf{n}\mathbf{p}}}+\left(1-{\varvec{\phi}}\right){{\varvec{\rho}}}_{\mathbf{b}\mathbf{f}}{{\varvec{C}}}_{{\mathbf{p}}_{\mathbf{b}\mathbf{f}}}}{{{\varvec{\rho}}}_{\mathbf{n}\mathbf{f}}}$$

(4)

Thermal conductivity of nanofluid

Thermal conductivity is the principal property effect on heat transfer enhancement in all thermal engineering systems, so this property can be enhanced by using nanofluid (nanoparticle + suitable fluid). So, choosing appropriate nanoparticle is important. Table 7 demonstrates the thermal conductivity of different nanoparticles.

Table 7 Thermal conductivity of different nanoparticles

The following table shows the models used by researchers (Table 8):

Table 8 Previous studies related to thermal conductivity

Dynamic viscosity of nanofluid

Dynamic viscosity is an important property, the increasing or decreasing of its value effect on the hydrothermal performance of MCHS. When two adjacent layers of fluid moves each to other resistance force will be generated which is namely viscous force that dependent on dynamic viscosity. Theoretically dynamic viscosity considered as a ratio of shear stress to the shear strain rate. Experimentally, dynamic viscosity can be evaluated by using viscometer. So, for its important more than authors take attentions by it and predicted models to calculate the dynamic viscosity. Table 9 show previous literature studies related to calculate the dynamics viscosity.

Table 9 Previous studies related to dynamic viscosity equations

Using of mono-Nanofluid in MCHS

Hung and Yan [143] studied the effect of using microchannel as a double layer with Al₂O₃ as a nanofluid that increased thermal performance by 26%. The results show that using an Al₂O₃–water nanofluid will result in the greatest improvement in channel cooling, where Al₂O₃ (1%)–water nanofluid shows an average improvement in thermal performance of 26% over that of pure water for a given pumping power. Ahmed et al. [144] numerically investigated the effects of nanoparticle volume fraction on a two-dimensional wavy channel. The Reynolds number and the volume fraction of nanoparticles considered are, respectively, in the ranges of 100–800 and 0–5%. In this work, copper–water nanofluid was used as the working fluid. According to the research, nanoparticles' volume fraction, wavy wall amplitude, and Re were the most important hydrothermal variables. Wang et al. [145] used Al₂O₃ as a coolant liquid in a straight MCHS with a pin fin and vortex generator to increase flow disturbance and mixing flow. A 4% nanofluid with 20 μm Al₂O₃ nanoparticles size provided the best heat transfer. Selimefendigil and Öztop [146] studied numerically effect of pulsating and nanofluid for nanofluids, where pulsating fluid compared to the steady case. The findings show the combined effect of pulsation and inclusion of nanoparticles in the pulsating flow case at Re = 200 and ϕ = 1 vol % led to enhance heat transfer by 3%. Furthermore, heat transfer enhanced by 18.8% at Re = 200 and ϕ = 6 vol%. Sakanova et al. [147] used three nanofluids to cool straight and wavy microchannels, including (Diamond–H₂O, CuO–H₂O, and SiO₂–H₂O). The authors found that wavy channels enhance heat transfer more than straight channels. Also, it is noted that the use of (Diamond–water) as the nanofluid coolant in a wavy channel enhanced heat transfer; moreover, when compared with straight channels, diamond–water nanofluid ranked the highest performance. Uysal et al. [148] studied the effect of utilizing (ZnO–ethylene glycol (EG)) nanofluid through rectangular microchannels on the heat characteristics numerically. Akbari et al.[149] investigated the effect of varying the height of the ribs in a straight microchannel on heat transfer performance. Al₂O₃ nanofluids with volume fractions ranging from 0.00 to 0.04 are used as a coolant inside a two-dimensional rectangular microchannel 2.5 mm long and 25 mm wide. The friction coefficient, rate of heat transfer, and average Nusselt number increased as the rib heights and nanoparticle volume fractions were increased. Modifying the solid volume fraction and rib height also significantly changes the temperature and dimensionless velocity along the flow's centerline in the ribbed regions, according to the simulation results. display previous literature studies on calculating the dynamic viscosity.

Sivakumar et al. [150] performed an experimental study to show the effect of nanofluids (Al₂O₃–H₂O and CuO–H₂O) on the forced convection heat transfer in a serpentine-shaped microchannel heat sink with a hydraulic diameter of 0.81 mm and volume fraction range (0–0.3%. The findings showed that when compared to distilled water and Al₂O₃–H₂O, CuO H₂O nanofluid has a higher heat transfer coefficient. Additionally, experimental results indicate that a higher volume fraction of nanoequal to (0.3%) will improve forced convective heat transfer.

Using the Eulerian and Lagrange methods, Nanofluids Al₂O₃ were used by Rostami and Abbassi [151] to evaluate heat transfer in a wavy microchannel. It is discovered that the wavy channel had a higher Nusselt number. While there was no discernible change in pressure drop, an increase in volume fraction resulted in a higher Nusselt number. Compared to a straight channel, heat augmentation, and drop of pressure were enhanced by 162.3 and 195.7%, respectively, when a wavy channel was used. Increases in pressure drops were observed to occur with the use of nanofluid. The $\Delta P$ by 2.4%, and the Nu increased by 11.6% for a volume factor of 0.02. Anbumeenakshi and Thansekhar, [152] used Al₂O₃ Nanofluids as the cooling fluid to indicate the performance of MCHS subjected to nonuniform heat flux. The experimental study employs three separate heaters of identical dimensions. A nonuniform heating condition is created by turning on any of the three heaters at the same time. For both uniform and nonuniform heat transfer, the average surface temperature dropped as volume concentration rose from 0.1 to 0.25%. Naphon et al. [153] studied experimentally using TiO₂ nanofluids on hydrothermal performance characteristics in the microchannel heat sink. This study uses three heat transfer enhancement techniques: microchannel heat sinks, jet impingement, and nanofluids. The obtained results demonstrated that at a nanofluid concentration of 0.015 vol%, suspending nanoparticles in the base fluid significantly increases convective heat transfer by 18.56%. Ali et al. [154] indicated experimentally and numerically the impact of various heat sink configurations and rates of working fluid flow using CuO–H₂O and Al₂O₃–H₂O with volumetric concentrations of 0.4% and 0.67%, respectively. Following the findings, Al₂O₃–H₂O nanofluid transferred heat faster than distilled water and CuO–H₂O nanofluid. The findings also showed that using nanofluids and increasing the flow rate decreased the base temperature. Heat transfer and hydrodynamic properties of a TiO₂–H₂O nanofluid used as a coolant through heat sinks with a wavy channel are investigated experimentally by Sajid et al. [155]. Performance of (TiO₂–H₂O) nanofluid at (0.006), (0.008), (0.01), and (0.012) vol% is compared to that of pure water in laminar flow with (25), (35), and (45) W heating capacity. The results demonstrate that, across all heat sinks, nanofluids outperformed distilled water regarding heat transfer characteristics.

Balaji et al. [156] studied the effect of using graphene nanoplatelets (GnP)/H₂O as nanofluid to improve thermal conductivity in a MCHS. Several heat transport metrics, including the coefficient of heat transfer, temperature drop, Nu, and $\Delta P$, were investigated and found to be affected by both the mass flow rate (from 5 g s⁻¹ to 30 g s⁻¹) and the concentration of GnP (from 0 to 0.2%). In experiments, using GnP–H₂O as nanofluids led to reduce the heat sink temperature by 10 °C, also the convective heat transfer coefficient increased by 71%, and increased the Nusselt number by 60%, respectively, In another side the pressure drop has been increased by 12% compared to water.

In a three-dimensional numerical study, Bazdar et al. [157] investigated heat transfer and turbulent flow in wavy MCHS with sinusoidal wavelengths. CuO–H₂O nanofluid has been used at Re numbers ranging from 3000 to 7500. The finding showed that by increasing Re to 7500, the HTP increased. While there is a little change in HTP approach to 3% at Re lower 7500 examined heat transfer and turbulent flow in a wavy microchannel with sinusoidal wavelengths in a three-dimensional numerical study. CuO–H₂O nanofluid was tested at Reynolds numbers from 3000 to 7500. The Nusselt number increased when the Reynolds number was greater than 7500 but did not change when it was less than 7500. Performance evaluation was worth 3%. Engineers and economists recommend nanofluids. Using a straight microchannel as a heat sink, Plant [158] utilized a variety of concentrations of Al₂O₃/H₂O nanofluid and porous media. Two and three channels have been used to assess different regions, with heat flow values ranging from 3.8328 to 10.3737 W cm⁻². Furthermore, the analyzed nanofluid was subjected to a range of flow rates. The results demonstrated a superior thermal enhancement of 24.5% for nanofluids with a 1% concentration compared to nanofluids with a 2% concentration. Heidarshenas et al.[159] conducted an experimental study to determine the impact of the various particle diameters of alumina nanoparticles Al₂O₃ (20, 50, 80, and 135 nm) on a forced convection coefficient of heat transfer in a cylindrical microchannel heat sink at different nanofluid flow rates. Their results demonstrated that increased particle size decreased the coefficient of heat transfer. At constant Reynolds number, the convective heat transfer coefficient increased for all particle sizes except 135 nm, where it decreased by 8.5%. For (20, 50, and 80 nm) a 21.9%, 21.1%, and 18.7% increase in Nu was observed. Alkasmoul et al. [160] presented a numerical study of the hydraulic and thermal performance of different nanofluids with different concentrations of nanoparticles in a microscopic heat sink for laminar flow. Based on previous work in cooling a microprocessor chip, a single rectangular microchannel is considered. The rectangular microchannel is silicon with a thermal conductivity of 130 W m⁻¹ K⁻¹, and the working fluid is common nanoparticles—Al₂O₃, CuO, TiO₂, and SiO₂—in water because of their stability in the base. Utilizing nanofluid as a cooling liquid in an MCHS decreases thermal performance due to it cannot be sustained under low-temperature ranges or because its pumping cost-effectiveness is inferior to that of water, according to the findings (Table 10).

Table 10 Previous studies related to using nanofluids

Hybrid nanofluids in MCHS

Hybrid nanofluids could have greater thermal conductivity and heat transfer capacity than either mono- or conventional coolants. Numerous numerical and experimental studies have been devoted to the hydrothermal performance and exergy features of nanofluids in MCHS [161,162,163,164]. Combining hybrid nanofluids and microchannel heat sinks (MCHSs) has enhanced heat removal from heat flux electronic chips. In copper heat sinks, the convective heat transfer coefficient of an Al₂O₃/Cu hydrophilic hybrid nanofluid was analyzed by Selvakumar and Sures [165]. Their results showed that the hybrid nanofluid had better heat transfer than water. Convective heat transfer increased by 24.35% and pumping power by 12.61%. Ho et al. [166] examined Al₂O₃ hybrid nanofluid thermal performance in mini-channel heat sinks. Al₂O₃ nanofluids cool better than hybrid nanofluids based on Al₂O₃/microencapsulated phase change material. Nimmagadda [167] examined how an Al₂O₃/silver hybrid nanofluid affected MCHS heat transfer. The author concluded that the convective heat transfer coefficient increased by 126–148%. A similar study tested the heat transfer of an Al₂O₃/Ag binary hybrid nanocoolant in a rectangular microchannel. In addition, it was demonstrated that the coefficient of convective heat transfer increases as the volume fraction of the hybrid nanofluid increases.

Kumar and Sarkar [168] numerically examined a hybrid nanofluid's heat transfer and fluid flow characteristics based on Al₂O₃ multi-walled carbon nanotubes (MWCNTs) in mini-channel heat sinks under laminar flow conditions. The highest heat transfer coefficient enhancement was 15.6%, with no pressure drop. Hussien et al. [169] conducted an experimental study to assess the thermal performance and entropy generation characteristics of a microtube cooled with an MWCNT/GNP hybrid nanofluid with (Re) ranging from 200 to 500. In this case, the average coefficient of heat transfer was raised by 58%. In addition, increasing Re and vol% decreased thermal entropy production while increasing frictional entropy generation. Bahiraei et al. [170] conducted a numerical study of the thermohydraulic performance and entropy generation of various modified MCHSs cooled with a graphene–Ag hybrid nanofluid. Findings showed that surface temperatures dropped dramatically as volume fraction and inlet velocity increased. Increases in volume fraction and inlet velocity resulted in a significant boost in pumping power in a wavy microchannel. Pahlevaninejad et al. [171] examined the analysis of non-Newtonian nanofluid and rectangular ribs with five heights. As a working fluid, 0.5% carboxymethylcellulose and Al₂O₃ nanoparticles of varying volume friction and diameter were combined. In addition, ribs with different geometries are used as obstacles in the microchannels' middle wall. The Nusselt number increased as the proportion of nanofluid volume increased, and the greatest impediment produced the greatest friction factor. Souby et al. [172] explored a numerical study that used novel, reasonably priced binary/ternary hybrid nanofluids to assess how well MCHSs performed under the first and second laws. MgO/TiO₂ nanocomposite and CuO/MgO/TiO₂ nanocomposite are examples of binary and ternary hybrid nanofluids, respectively, that are based on water. When using hybrid nanofluids with high Re and vol. percent values, the convective heat transfer coefficient, pressure drop, and frictional entropy generation rate are all increased. Table 11 show a summary of studies related to using hybrid nanofluid.

Table 11 Summary of previous studies related to using hyper nanofluid as coolant liquid

Effect of nanoparticle mixture ratios on HTP

Also, the HTP of hybrid nanofluids is highly sensitive to nanoparticle mixture ratios. The effect of the nanoparticle mixing ratio on the thermal performance of an Al₂O₃–TiO₂ hybrid nanofluid was investigated by Charab et al. [173]. It was determined that a ratio of 2:3 provided the greatest improvement in heat transfer (35.3%). The influence of the nanoparticle mixing ratio of an Al₂O₃-MWCNT hybrid nanofluid on the HTP of mini-channel heat sinks was experimentally examined by Kumar et al. [174]. Their research shows that a combined ratio of about 3:2 yields the highest hydrothermal performance. By doing experimental research on the conducted heat coefficient of Al₂O₃–SiO₂/Water hybrid nanofluids, Moldoveanu et al. [175] found that the hybrid nanofluid has superior thermal conductivity to alumina nanofluids. The experimental study of the thermal conductivity and viscosity of hybrid nanofluids with varying particle ratios was conducted by Hamid et al. [176]. Maximum thermal conductivity improvement of up to 16% was seen at a 1:4 ratio of TiO₂–SiO₂, while maximum dynamic viscosity was at a 5:5 ratio. Kumar 2019 [31] conducted an experimental investigation on the cooling equipment's heat transfer performance with the same set of nanoparticles and observed a maximum boost of 35.3% for a 2:3 ratio. The experimental investigation of the viscosity of Graphite–SiO₂ hybrid nanofluid by Dalklç et al. [177] at various volume concentrations and mass ratios revealed an increase in viscosity from 0.65–36.32% with an increase in volumetric concentration. Based on their research into the thermal conductivity and stability of Cu–Al₂O₃ hybrid nanofluids with varying mixing ratios, Siddiqui et al. [178] concluded that a mixing ratio of 5:5 was optimal for achieving desirable hydrothermal parameters. Thermophysical properties of (Al₂O₃–SiO₂/EG) nanofluid were studied by Zawawi et al. [179], who discovered that a mixing ratio of 60:40 resulted in the lowest property enhancement ratio. By testing several quantities of MWCNT (30 vol%) and Al₂O₃ (70 vol%) in 5 W50 oil (from 0.05 to 1%), Esfe et al. [180] determined that the greatest viscosity improvement was 24%. The ratios of nanoparticles in the mixture affect the heat transfer coefficient and the pressure drop, as shown in Fig. 11a, b. Selimefendigil et al. [181] reported that the heat transfer average rate can be increased with the addition of the nanoparticles but the ratios of nanoparticles volume fraction limited the rate of heat transfer enhancement.

Fig. 16

a Variation of heat transfer coefficient with Re [182] b Variation of pressure drop with Re [182].

Summary

Methods of heat transfer augmentation can be classified as passive and active techniques. Passive technique is the more technique that studied in the present work. The hydrothermal performance in MCHS restricted by high heat transfer and low pressure drop with low thermal resistance. So, Table 12 shows a summary to pressure drop which indicated friction coefficient.

Table 12 Summary of heat transfer enhancement and pressure drop in different shapes of MCHS

Conclusions and recommendations

In this paper, an exhaustive review is presented of most configurations of the microchannel heat sink. Besides this, more than one type of nanofluid can be used as a cooling liquid. The main conclusions of the present work are as follows:

• With regards to corrugated MCHS the wavy MCHS outperforms the standard rectangular design when using water as a coolant. The heat resistance is lower in a wavy microchannel at a larger amplitude and a shorter wavelength.

• Wavy MCH with sinusoidal shape has superior HTP and low drop of pressure.

• Zigzag MCHS has good heat HTP but with high $\Delta P$.

• With regards to flow disruptions, the MCHS with ribs can significantly enhance heat transfer due its ability to interrupt thermal boundary layer due to creating of secondary flow and vortices.

• The high drop in pressure can be induced at MCHS with rib, so the appropriate dimensions of ribs must be choose attentionally.

• The hybrid techniques (active with passive techniques) or (more than methods of passive) can improve the hydrothermal performance of MCHS.

• “Al₂O₃/H₂O,” “CuO/H₂O,” and “TiO3/H₂O” can be considered the most nanofluids used as coolant liquids for cooling electronic types of equipment.

• There are few papers dealing with the hyper nanofluid as coolant liquids.

• There are serious limitations in the study type of fluid flow such as turbulent or pulsating flow.

• The design of the microchannel is related to the application that is used to cool it, so the numerical analysis is not enough to study the thermal performance of the microchannel.

• Nanoparticle mixture ratio and size of nanoparticle effect on the hydrothermal performance of MCHS.

• Thermal conductivity increases with increasing concentration and temperature.

• The combination of using nanofluids has high HTP as cooling liquid with an optimized MCHS structure lead to efficient cooling of the MCHS.

Recommendations

• The current study demonstrated that the majority of existing research findings on using nanofluid as a cooling liquid in various MCHS concurred that using a nanofluid with high thermal conductivity properties can improve heat dissipation. Fewer researchers are focused on the impact of other crucial nanofluid parameters like surface tension and contact angle, and stability of nanofluid on the cooling of MCHS, so in future research must give particular focus to how the characteristics of nanofluids, such as their surface tension and contact angle, affect MCHS cooling.

• Future studies must give attention to the combination between corrugated channels and

• flow disruptions technique.

• Effect of vibration induced in electronic system on MCHS performance.