Evaluation of ionic liquids as absorbents for absorption refrigeration systems using hydrofluoro-olefin refrigerant

In this study, we evaluate the use of ILs as absorbents in a double effect absorption refrigeration system using HFO refrigerant. By examining the properties of various refrigerant/absorbent mixtures, we identify the most efficient refrigerant/absorbent pair for the aforementioned absorption refrigeration system. First, we identify a suitable HFO refrigerant for the system. Among the candidates in this study, R1336mzz(Z) and R1234ze(Z) can be used in the absorption refrigeration system because both have low flammability and high critical points. Then, we analyze the characteristics of ILs as absorbents in the absorption refrigeration system. Imidazolium ILs have relatively low viscosities of approximately 20 mPa s at temperatures exceeding 50 °C and high stability. Next, we analyze the characteristics of refrigerant/absorbent pairs. When R1336mzz(Z) and R1234ze(Z) are used as the refrigerant, [OMIM][BF4] have the highest solubilities in oprating conditions. The solubility value of R1234ze(Z) with [OMIM][BF4] is 0.256 at 289.89 kPa and 80 °C, while the solubility value of R1336mzz(Z) with [OMIM][BF4] is 0.154 at 128.02 kPa and 80 °C. Finally, we analyze the performance of the refrigeration system. When the R1234ze(Z)/[OMIM][BF4] is used in the absorption refrigeration system, the COP and cooling capacity of the system exhibit the values of 0.516 and 0.549 kW, respectively

Experimental Study on Behavior of Coolants, Particularly the Oil-Cooling Method, in Electric Vehicle Motors Using Hairpin Winding

This paper analyzes the characteristics of oil behavior in the oil-cooling of motors with hairpin winding to understand how to maximize cooling performance. The oil cooling is performed by directly spraying oil onto the motor components. The results show that as the temperature of the oil increases, the viscosity decreases, and the oil film is formed more evenly; however, oil splashing also increases. Similarly, as the flow rate increases, oil splashing also increases, but the amount of oil forming the oil film increases. However, the oil film is not affected by the rotor’s rotation. In contrast, the immersed oil is found to be closely related to the rotor’s rotation. As the rotational speed increases, the immersion oil is mixed with the air, and oil churning occurs. The mixing phenomenon increases as the temperature and flow rate of the oil increases. The higher the oil level, the greater the oil churning. As the oil is mixed with air, the heat transfer coefficient decreases, which adversely affects the thermal management of the motor. As a result, when considering the oil film and the immersion oil, the optimal oil temperature, flow rate, and oil level are at 60 °C, 0.140 kg/s, and 85 mm, respectively. The results of this paper give important information about EV motor cooling and can contribute to the development of high-performance motors