Experimental study on immersion phase change cooling of lithium-ion batteries based on R1233ZD(E)/ethanol mixed refrigerant

To improve heat dissipation and temperature uniformity for the lithium-ion battery module of electric vehicle, the immersion phase change cooling characteristics of R1233ZD(E)/Ethanol mixed refrigerant were studied experimentally in a staggered battery module, which is composed of 50 batteries. At 101.3 kPa saturated vapor pressure, coupled wall boiling and forced convection heat transfer was analyzed under different discharge rates (1 C, 2 C, and 3 C), filling volume fractions of R1233ZD(E) (0.463, 0.540, 0.630, 0.735, and 0.857), and inlet volume flow rates (652.0, 1086.0, 1521.0, and 2172.0 mL min^{- 1}). Meanwhile, the outlet vapor quality of the two-phase flow was calculated according to energy conservation. The results show that the heat generation of the battery was dominated by the operating current. With the decrease of the output power of the battery, the heat generation first increases rapidly, then increases gently, and finally decreases sharply. When low boiling point R1233ZD(E) was mixed into ethanol, wall boiling heat transfer was effectively enhanced, and the temperature uniformity of the battery module could be improved by up to 57.0\%. However, the outlet vapor quality of the two-phase flow showed that when the volume fraction of R1233ZD(E) exceeded 0.803, wall boiling departed from the nucleate boiling regime as well as heat transfer and temperature quantities changed accordingly. Forced convection heat transfer of liquid-phase played a leading role in reducing the temperature rise of the battery module, and its contribution increased with the increase of refrigerant inlet flow rate. When the inlet flow rate increased from 652.0 mL min^{- 1} to 1086.0 mL min^{- 1}, the module temperature rise decreased by 14.8%. Nevertheless, forced convection of liquid-phase weakened battery wall boiling, which adversely affected the temperature uniformity of the battery module.