Experimental investigation with feature interpretation of an ejector-based integrated thermal management system for HEVs with refrigerants R134a and R1234yf

An exhaust heat-driven ejector-based hybrid automotive air conditioning system (AACS) combined with a battery thermal management system (BTMS) is developed for hybrid electric vehicles (HEVs) to reduce the power consumption compared to conventional systems. The coolant flow rate and flow direction of a novel straight, parallel micro-channel cold plate integrated within the BTMS are optimized to maintain battery pack temperatures within safe limits between 25 °C and 40 °C by estimating the heat transfer rate, heat transfer coefficient, and j/f factor. To determine the optimal operating strategy, the performance of the developed system with and without activation of BTMS is assessed using R134a and R1234yf across the compressor and hybrid modes under varying compressor and refrigerant pump speeds. Further, a machine learning (ML) based explainable prediction modelling is employed to interpret the relative importance and influence of input features on each performance parameter. Results indicate that the coolant flow rate of 300 LPH with a counter flow arrangement direction 3 of cold plates delivers optimal performance and provides superior cooling, faster heat removal rate, and improved thermal-hydraulic efficiency. The BTMS activation increases power consumption due to additional cooling loads. Hybrid mode reduces total work input by up to 20.84 % with R134a and 24.99 % with R1234yf, increases cooling capacity by up to 3.37 % and 2.46 %, respectively, and ultimately enhances COP by 17.43 %–26.98 % with R134a and 18.66 %–33.88 % with R1234yf, compared to compressor mode. The secondary flow rate and compression ratio are identified as key input features, and their values below 0.035 kg/s and 3.2, respectively, maximize COP and cooling capacity while minimizing work input. Although R1234yf in hybrid mode exhibits marginally lower cooling capacity and COP than R134a, its low power consumption and generator heat requirements make it a promising and reliable alternative for HEV cabin and battery cooling.