Temperature Difference ΔTmax Research Articles

Lithium-ion battery pack thermal management under high ambient temperature and cyclic charging-discharging strategy design

To ensure the stable operation of lithium-ion battery under high ambient temperature with high discharge rate and long operating cycles, the phase change material (PCM) cooling with advantage in latent heat absorption and liquid cooling with advantage in heat removal are utilized and coupling optimized in this work. Based on the preferred hybrid cooling scheme, the two layers cold plates and fins are arranged, and the cold plate structure is redesigned to optimize cooling system. The coupling effects of composite PCM and water flow rate, as well as charging and discharging strategy, are numerically studied. The results show that the hybrid cooling is more suitable to high discharge rate of 5C and long-term cyclic operation at 40 °C. The two layers cold plate and fins arranged in hybrid cooling system can mitigate the temperature non-uniformity of batteries along the axis, and the maximum temperature Tmax and temperature difference ΔTmax are reduced by 4.44 °C and 4.17 °C, respectively. Also, the optimized cold plate can mitigate the temperature non-uniformity caused by battery dispersion, and the standard deviation of temperature of batteries is reduced from 0.48 to 0.37. Then, the composite PCM added with expanded graphite can further decrease the Tmax and ΔTmax by 2.18 °C and 1.79 °C, respectively. Lower charging rate offers more reliable cooling performance during continuous cyclic operations. In general, the designed fin-enhanced hybrid cooling system with composite PCM and two layers cold plate can control the Tmax and ΔTmax within 45.85 °C and 3.39 °C at 40 °C ambient temperature and 5C discharge respectively, and offers a reliable and desired cooling performance during continuous charging and discharging of 1C, 2C and 3C. During cyclic operation with 3C discharging and 1C charging, the Tmax and ΔTmax can be controlled below 44.39 °C and 2.64 °C, respectively.

Design method of multiple inlet/outlet air cooling frame of pouch lithium-ion battery based on thermal-fluid coupling topology optimization

The reasonable working temperature and maximum temperature difference are of critical importance for the electric vehicles. A design method of multiple inlet/outlet air cooling frame based on the thermal-fluid coupling topology optimization (TO) is developed to design novel air cooling frames of pouch lithium-ion battery (LiB) to improve the deficiency of low cooling efficiency and poor temperature uniformity found in the traditional air cooling structure. A 2D optimized flow channel of cooling frame is obtained based on TO, which is stretched to model the 3D optimized cooling frame for its cooling performance analysis. Then the influence of inlet/outlet location, width and number and multiple inlet/outlet layout on the heat exchanging performance is investigated to proposed the design criteria of multiple inlet/outlet air cooling frame. The design criteria is employed to obtain several new air cooling frames, in which the 3 inlet/outlet cooling frame with the alternative layout of inlet/outlet has the beat heat exchanging performance. This scheme improves the cooling performance of pouch LiB module by reducing the module maximum temperature Tmax and temperature difference ΔTmax, which will be promoted in the economical vehicles or small logistics vehicles.

Dimensionless Mathematical Model of a Thermoelectric Cooler: ΔTmax Mode

The thermal resistances on the cold and hot sides substantially affect the output characteristics of thermoelectric devices. A dimensionless mathematical model of a thermoelectric cooler, which makes it possible to calculate device parameters, such as the optimal thermal resistance ratio on the cold and hot sides as well as the optimal current taking into account the influence of thermal resistances, is presented. The maximal temperature difference ΔTmax mode is considered. It is shown that the optimal cooler parameters are different for implementation of the ΔTmax and Qmax modes. The determining factor for the ΔTmax mode is the influence of the thermal resistance on the hot side, and the optimal current is 0.4–0.7 of the maximal current in most cases for the material with ZT = 1. It is shown that an additional increase in ΔTmax of a cooler is attained with a decrease in the thermal conductivity of the thermoelectric material due to a decrease in the influence of the thermal resistance on the hot side besides the effect from an increase in ZT. An increase in the length of thermoelectric legs has the same positive effect of an increase in ΔTmax of a cooler, while a decrease in the leg length negatively affects ΔTmax.