Keywords

1 Introduction

Spray drying is frequently utilized in the food and pharmaceutical sectors[1, 2]. The liquid is converted into particles, which are then dried with hot air[3, 4]. Percentage of particles hitting the wall more than coming out through the channel[5]. Small diameter particles come out earlier than the large-diameter [6, 7], with fixed droplet size in each configuration. The co-current flow of air is in the direction of the particle flow, the countercurrent flow is in the opposite direction, and the mixed flow is a combination of the two [8]. This study aimed to compare the residence times of particles in co-current and mixed flow spray dryers regarding variations in inlet temperature and particle diameter as boundary conditions. Conclusions from experimental comparison studies [3] and fluid dynamics calculations [1] the spray dryer is relatively the same; CFD analysis produces a pretty good prediction on the spray dryer compared to the experimental approach. The use of turbulence models affects the accuracy of airflow characteristics in the drying chamber [8]. Because the moisture content drops fast as the drying air temperature rises, drying time is reduced [7]. Modification of inlet dry airflow direction can reduce particle residence time.

2 Method

2.1 Basic Theory

Predict the tracking of individual particles in the spray dryer using the three-phase flow equation with the Eulerian-Lagrangian approach, calculated using the discrete phase model (DPM). Equations 1 and 2 are used to write the particles’ equations of motion [9].

$$\frac{{dx_{p} }}{{dt}} = {\mathop{u}\limits^{\rightharpoonup}}_{p}$$
(1)
$$\frac{{{d\mathop{u}\limits^{\rightharpoonup}} _{p} }}{{dt}} = F_{d} \left( {\mathop{u}\limits^{\rightharpoonup} - {\mathop{u}\limits^{\rightharpoonup}}_{p} } \right) + {\mathop{g}\limits^{\rightharpoonup}}_{x} \frac{{\left( {\rho _{p} - \rho } \right)}}{{\rho _{p} }}$$
(2)

Fluid velocity is \(\left( {\mathop{u}\limits^{\rightharpoonup} } \right)\), particle velocity is \( \left( {{\mathop{u}\limits^{\rightharpoonup}}_{p} } \right)\), \({x}_{p}\) denotes particle position, \({\mathop{g}\limits^{\rightharpoonup}}_{x} \) is gravitational force, \(\rho\) is fluid density, and \({\tau }_{p}\) denotes particle density. In Eq. (2), \(F_{d} \left( {\mathop{u}\limits^{\rightharpoonup} - {\mathop{u}\limits^{\rightharpoonup}}_{p} } \right)\) denotes drag per unit mass of particles. \({F}_{d}\) is calculated based on energy equation:

$${F}_{d}=\frac{1}{{\tau }_{p}}\frac{\left({C}_{d}-{Re}_{p}\right)}{24}$$
(3)

where (\({\tau }_{P}\)) is particle relaxation time, given by Eq. 4.

$${\tau }_{p}=\frac{{\rho }_{p}{d}_{p}^{2}}{18\mu }$$
(4)

2.2 CFD Modelling

Figure 1 geometric shape of a spray dryer with a co-current flow design, used based on research of Anandharamakrishnan et al.[3].

Fig. 1.
figure 1

The geometric of spray dryer.

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Dimensions of mixed flow (co-current flow) are: D1 = 600(600), D2 = 50(50), Dn1 = 40(81), Dn2 = 20(55), Dn3 = (20), Dp1 = 26(26), Dp2 = 24(24), a × b = 147 × 125, H1 = 900(900), H2 = 300(300), H3 = 480(480), Nozzle height 1 Hn1 = (35), Hn2 = (15), Hn = 20, Hp = 150(150), L = 1275(1275). This study simulates two geometries, and the governing equations are solved numerically using ANSYS FLUENT with a SIMPLE scheme for velocity-pressure coupling. The turbulent model of mixed flow causes rotating flow, which is more accurate using the k-SST method [10, 11], than the standard k-ε for wall co-current flow [1, 3, 6, 12]. The drying air velocity is eight m/s, the initial temperature is 100, 120, 140, 160, and 180 °C, the particle density is 816.4 kg/m3, and the gas density is 1,225 kg/m3, DPM spry dryer escape wall surface, and reflect pipe surface.

3 Results and Discussion

The residence time of the particle is the length of time the particle is in the drying chamber [3]. In a mixed flow spray dryer, the residence time of the particles decreases with in-creasing droplet diameter because droplets with a smaller diameter (10.30 mm) have small momentum. The particles follow the airflow around the drying chamber to the outlet so that the particle residence time is longer. Droplets with larger diameters (50, 70, 90, 110, and 130 m) have shorter residence times. In co-current flow, droplets with a larger diameter tend to last longer than droplets with a smaller diameter. Particles of larger diameter are recirculated to the walls of the drying chamber, the same as in the study of Anandharamakrishnan et al. [3], Sadripour et al. [6], and Roustapour et al. [7], giving the particles a longer residence time. Figure 2 shows the configuration condi-tions of the spray dryer flow model at (a) outlet temperature and (b) particle diameter concerning time.

Fig. 2.
figure 2

Characteristics spry dryer in drying chamber.

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4 Conclusion

This paper describes the results of multiphase modeling tracking residence time and particle inflow movement in a spray dryer. The residence time of particles changes with the change in droplet diameter; in mixed flow, the residence time of particles decreases with increased droplet diameter, whereas in the co-current flow tends to increase.