Abstract Lithium-ion batteries are widely used in electric vehicles due to their advantages such as high capacity, long lifespan, and low self-discharge rate. However, these batteries generate a significant amount of heat during the charge/discharge process due to chemical reactions and internal resistance, leading to issues such as excessive heating, swelling, and even battery explosions. From a reliability standpoint, designing an efficient battery thermal management system becomes a crucial challenge in electric vehicles to control and eliminate the generated heat by the battery cells. This research focuses on the design of a combined battery thermal management system (combining heat pipes and phase-change material heat exchangers) for fast charging or supercharging conditions at a charge rate of C5 (which charges the battery in one-fifth of an hour). Heat pipes are small, compact and lightweight. Additionally, heat pipes act as passive thermal devices as they do not require external power supply to transfer their heat to the heat sink. The performance of a heat pipe depends on its structural design, working fluid, and wick structure. The 18650 cylindrical lithium-ion battery modules transfer heat through heat pipes to the evaporator section, and the heat is dissipated by the cooling fluid in the condenser part of the heat pipe. In the first part, the solution domain consists of a three-dimensional heat pipe with transient behavior, and the simulation was performed using COMSOL Multiphysics 6.0 software. Different physical domains, including heat transfer in the porous medium, laminar flow and the Brinkman equation for heat and fluid flow in the vapor chamber and wick were coupled and solved. The second part of this research focuses on an external heat exchanger located outside the battery pack and at the charging station, where the heat transfer fluid is cooled. This part is based on previous research conducted at the faculty on designing a novel PCM heat exchanger, and its coupling with the first part of the research is addressed.During the charging period, the proposed model is solved for specific parameters, including a wick thickness of 0.7 millimeters, a heat pipe wall thickness of 0.3 millimeters, a condenser length of 30 millimeters, and an adiabatic section length of 30 millimeters. The time-dependent solution reveals that the maximum temperature ranges from 31.8 to 32.8 degrees Celsius as the battery is charged for a duration of 720 seconds. It is concluded that increasing the length of the heat pipe condenser region and the thickness of the wick reduces the maximum temperature. Various models were eva‎luated to obtain a model where heat is received from the battery while maintaining the battery's operating temperature within the range of 15 to 35 degrees Celsius. It is found that increasing the heat transfer coefficient and achieving a lower maximum temperature requires an increase in the wick thickness. Ultimately, proposed models allow achieving temperatures below 35 degrees Celsius by increasing the wick thickness and placing fins on the condenser region. To achieve temperature uniformity throughout the battery pack, a single modular compartment was designed around the condenser part of the heat pipe. The compartment uses water as a fluid with a velocity of 0.05 meters per second, employing a reference heat pipe and a square shaped water inlet of 3 millimeters square at the end of the condenser and two circular outlet openings with a radius of 1.5 millimeters square on both sides of the heat pipe model. Keywords: Li-ion battery, Heat pipe, Fast charging, BTMS, Maximum temperature

محمدرضا سليم پور

علي اكبر عالم رجبي , ايمان چيت ساز