Heat transfer performance of a micro heat pipe array for battery thermal management systems

Temperature is a key factor that affects the performance of power batteries, because excessive operating temperatures and uneven temperature distribution may accelerate the degradation rate of batteries and shorten their lifespans. Therefore, an efficient battery' thermal management system is required to keep the battery' temperature within the desirable operating range. Traditional cooling methods, including air cooling and liquid cooling, are limited in efficient heat extraction for a large amount of heat generation from fast charging batteries. Heat pipe technologies, especially micro heat pipe arrays, have attracted lots of attention due to the superior thermal conductivity. However, micro heat pipe arrays in battery thermal management need to be further studied under high heat power density conditions and need to be further developed in the structural optimization design. In this paper. a micro heat pipe array is adopted as a heat conduction element for a battery' thermal management system. Then, the temperature performance of the micro heat pipe array is analyzed and the equivalent thermal conductivity is calculated theoretically. To further enhance the heat transfer capability of the micro heat pipe array. the internal fluid flow and heat transfer characteristics are investigated by adjusting groove parameters. In addition, the thermal performance of micro heat pipe array is compared with that of a traditional sintered heat pipe group and latest published results. The experimental and theoretical studies show that when the heat power density is below 0.3658 W cm(-2). the surface temperature at the evaporator section of micro heat pipe array can be maintained at below 45 degrees C and the temperature difference can be controlled at below 1.3 degrees C. As the heat power density increases to 0.9176 W cm(-2). the equivalent thermal conductivity of the micro heat pipe array increases to 6027 m(-1) K-1, and the maximum temperature difference of the evaporator section is well controlled at 2.75 degrees C. Furthermore, increasing the height and width of the grooves in the micro channel has a positive effect on the equivalent thermal conductivity. The results show that the figure will increase by 129% when the height of the groove increases from 0.01 to 0.47 mm. However. changing the width of the groove can weaken the capillary force which drives liquid return inside the channel. In order to prove the potential capability in broad electric vehicles application, related experiments have been carried out under dynamic power conditions and at low temperature environments. The results revealed that the micro heat pipe array has a fast thermal response and stable performance to dynamic heat powers. At -4 degrees C environments, the temperature of the micro heat pipe array could reach 20 degrees C in 2 min if given a heat power of 0.36 W cm(2). Compared with the thermal performance of a traditional sintered heat pipe group, the micro heat pipe array can reduce the maximum temperature by 15.1 degrees C and the temperature difference by 14 degrees C. Overall, the micro heat pipe array shows excellent capability in controlling the temperature rise and minimizing the temperature difference, and the advantages become more obvious at high heat power densities. This shows that micro heat pipe arrays have broad application prospects in the future. All the results from the study could further support the development of battery thermal management systems and the heat transfer enhancement of micro heat pipe arrays.