Thermodynamic investigation of automotive air conditioning system performance using ejector as an expansion device

To enhance the performance of air conditioning (/AC), an ejector as expansion device can be applied to replace the conventional expansion device. The cooling capacity of A/C system influences the diameter of ejector motive nozzle. Meanwhile, the cooling capacity of car A/C system follows the engine rotation. Consequently, the diameter of ejector motive nozzle is not constant in the automotive A/C when the engine rotation changes. The present study determines the diameter of ejector motive nozzle used for automotive A/C system at three difference cooling capacities, i.e. 2.5, 3.5 and 4.5 kW with R134a as working refrigerant. These cooling capacities represent low, medium and high velocities of the automotive respectively. Besides varying the engine rotation, the study also varies the condensing temperatures at 40, 45 and 50°C. The numerical results showed that diameters of ejector motive nozzle for three velocities at the condenser temperature of 40°C are 1.529, 1.809 and 2.051 mm, respectively. Besides lowering input power, the use of ejector also decreases the cooling capacity of the A/C system. However, because decrease in input power is higher than that of cooling capacity, the COP of the system increases. In addition, higher ambient temperature also causes an increase in COP of the A/C. At the condensing temperatures of 40, 45 and 50°C, the COP improvements are 9.38, 22.49 and 33.20%. It indicates that the COP improvement is optimal at high ambient temperature.