Keywords

1 Introduction

The air conditioning system in the vehicle refers to providing and maintaining desirable temperature and humidity for passenger comfort irrespective of external conditions. The working substance which is used in the air conditioning system to absorb and liberate the heat alternatively is called refrigerant. The name of refrigerant used is R134a [1]. An automobile air conditioning system works on the principle of vapour compression refrigeration (VCR) system [2]. In this system, a refrigerant R134a undergoes alternatively a change of phase from vapour to liquid and liquid to vapour during the working of the cycle. The refrigerant is circulated in a closed circuit through a compressor, condenser, expansion valve, and evaporator. The power required to run the compressor is given from engine power. It will increase fuel consumption and reduce the mileage of the vehicle by up to 35% [3]. The system should give a higher CoP in the working temperature range. This is necessary to reduce the running cost of the system in terms of reducing fuel consumption. The CoP is defined as the ratio of heat extracted from the cabin to the work done on the system [4]. The heat removal rate in the evaporator depends on the refrigerant temperature at the condenser exit. The evaporative cooling gives a decrease in exit temperature of refrigerant by additional removal of heat than the inbuilt air cooling condenser. Hence, CoP of the system increases for the same amount of compressor work [5]. This was understood from the p–h chart as shown in Fig. 1. In this Fig. 1, 3–3′ is the decrease in exit temperature of the refrigerant in the condenser due to evaporative cooling, and 4–4′ is corresponding to the increase in heat removal rate in the evaporator for the same compressor work of 1–2. Hence, the CoP of the system increases [6].

Fig. 1
An image depicts a graph between pressure and enthalpy in which black, red, and blue dashed lines are mentioned.

p–h chart of VCRS

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Many kinds of research [7] on VCR system are focussed to increase the CoP through either increase in heat removal rate (refrigeration effect) by subcooling or a decrease in compressor work input by superheating. Subcooling has a simple and more effective method rather than superheating [8]. Removing extra heat from the condenser through any method allows a higher amount of heat absorption in the next stages of the cycle. Hence, the CoP of the system increases with the same compressor work. Subcooling by liquid-suction method has been used in the past years to achieve better performance of the system [9]. These methods necessitate the exact and optimised design of the heat exchanger. The research gap of improving performance on the air conditioning system is to be fulfilled in this study through evaporative cooling of the condenser.

2 Experimental Facility

2.1 Evaporative Cooler Setup

The evaporative cooler was fabricated as shown in Fig. 2, and it consists of exhaust fan runs at 1300 rpm, three cooling pad of size 60 cm × 40 cm and a water pump. The steel frame was fabricated in such a way that to accommodate the fan and cooling pads. A separate water pump was used to supply water over the cooling pads through the multi-drilled PVC pipe at a different flow rate such as 0.03, 0.07, 0.08, and 0.1 kg/s, and the corresponding reduction of atmospheric air temperature was measured and found 4 °C temperature reduction from 31 to 27 °C at 0.08 kg/s flowrate. The velocity of cooled air blow over the surface of the condenser was measured using an anemometer. The distance between the cooler and condenser was adjusted to obtain a maximum reduction in condenser surface temperature. At a gap of 20 cm, the maximum decrease in surface temperature of the condenser was attained at 5.5 m/s velocity of air blow.

Fig. 2
An image is divided into two parts. (a) has a brown cooler with a gray-colored fan, and (b) has the same cooler fan but the condenser has some distance.

a Fabricated evaporative cooler. b Distance between cooler fan and the condenser

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2.2 Test Rig Setup

The experiment test rig was fabricated as shown in Fig. 3 using Hyundai, i-10 variant car air conditioning parts. A 1.5 HP three-phase induction motor was attached to the test rig set up to drive the compressor through the belt and pulley assembly. The electric power consumption was measured using an energy metre. The evaporator is enclosed by a rectangular duct of size 25 cm × 18 cm and 80 cm made up of a 3 mm thick acrylic sheet to prevent heat loss to the surrounding. The inbuilt condenser fan was replaced by an evaporative cooler fan. The velocity of cooled air blows in the duct was measured as 0.5 m/s.

Fig. 3
An image depicts a setup of a test rig in which a brown box shapes a duct and has a green electric motor, a black compressor, a condenser, and an evaporative cooler with an evaporator.

Test rig setup

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2.3 Experimental Tests

The experiment was conducted on the test rig at three various cases viz., 1. using inbuilt fan, 2. exhaust fan, and 3. evaporative cooler. During the test trial, the amount of heat removed from one kg of water in the aluminium jug which is kept inside the duct at a regular interval of 10 min was measured. Besides that suction and delivery pressure of compressor; condenser and evaporator inlet and exit temperatures; and energy metre readings were noted for CoP calculation.

3 Results and Discussion

3.1 Condenser Exit Temperature

Figure 4 represents the exit temperature of the condenser against the running time of the system for the three cases. When running time increases, the exit temperature of the condenser increases in all trails. The increasing excess temperature for an entire test run was reduced in the case 2 and 3 compared to case 1. Most reduction in condenser exit temperature in case 3 was observed by blowing the cooled air over the entire surface of the condenser and placing the cooler at an optimised distance from the condenser. Trail 2 also reduces the exit temperature of the condenser to some extent compared to Trail 1 due to reduction of bypass volume of air blows over condenser surface even the exhaust fan speed (1300 rpm) is lower than inbuilt fan speed (1700 rpm).

Fig. 4
An image depicts a graph between condenser exit temperature and time in which the red circle line, blue circle line, and purple triangle line present their relationship.

Condenser exit temperature with a running time

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3.2 Heat Removal Rate

Figure 5 illustrates the amount of heat removed with running time for three trails. The amount of heat removed from the water was calculated using the formula m cp ∆T. Where m is mass of water, cp is the specific heat of water and ∆T is the decrease in temperature of the water after 10 min. An increasing trend of heat removal rate was observed in three cases. The more amount of heat was removed in case 3 followed with case 2 and case1. It is evident from Graph 4; there is a small drop of exit temperature of condenser give more amount of heat removal rate in case 3 due to evaporative cooling.

Fig. 5
An image depicts a graph between heat removal rate and time in which the red circle line, blue circle line, and purple triangle line present their relationship.

Amount of heat removed with a running time

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3.3 Coefficient of Performance

As explained in the introduction section, the higher CoP of the system reduces the running cost. The actual CoP of the three cases was calculated against the running time using the ratio between heat removal rate and electric power consumption for the motor. Theoretical CoP was also calculated using p–h chart of R134a and found that the actual CoP of three cases was lower than theoretical CoP. Figure 6 represents the comparison of the coefficient of performance with running time. From the calculation, the deviations of the power consumption of the compressor in the three trails are very small. Hence, work input was assumed as constant. But the variation of heat removal rate, the CoP has varied. The higher CoP was noted in case 3 during the test run due to more amount of heat was removed, it is evident from Graph 5.

Fig. 6
An image depicts a graph between the coefficient of performance and time in which the red circle line, blue circle line, purple triangle line, and green triangle line present their relationship.

Coefficient of performance with a running time

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4 Conclusion

Through experimental study, it was proved that the evaporative cooling process in the condenser increases the heat removal rate for the same compressor work which results in higher CoP of the system. The test results point out the following.

  • Through the fabricated evaporative cooler reduce the atmospheric air temperature up to 4 °C

  • By reducing the bypass of air blows over the condenser surface using an evaporative cooler increases the amount of heat removed rate up to 35%

  • A 5 °C temperature drop of the liquid refrigerant at condenser exit due to evaporative cooler increases the CoP system up to 22.5%

  • This method will put into operation in the vehicle reduces fuel consumption considerably.