回收发动机余热的球内对称凝固过程参数分析

Parameter Analysis of Freezing in Spheres for the Recovering of Waste Heat of Engine

利用适当的相变材料,贮存汽车发动机冷却系统的低品位热能,能改善汽车低温环境下的冷启动。以球作为贮能单元,建立了球体内对称凝固过程的数学模型,并用Lighthill奇异摄动法给出了球体内对称凝固问题的近似分析解。以Ba(OH)2·8H2O为相变材料,得到了相变介质的温度分布规律,相变界面、冷却介质温度随凝固时间的变化规律,还讨论了球囊半径、外部冷却介质的对流换热系数对凝固过程的影响。从理论上证明了相变贮能装置用于回收发动机余热,改善车辆冷启动是可行的。

Proper phase change material can be chosen to store the waste heat of the vehicle engine, and release the stored heat of the engine when the vehicle is running. Thus the fuel can be saved, the emission of poisonous exhaust gases can be diminished and a good performance of the engine can be obtained during cold start. In this paper, spheres are taken as an units to store energy. The mathematical model, which could reveal the process of symmetrical freezing in spheres, is set up. Then a singular perturbation method is adopted to solve the freezing problem, and the analytical solution is obtained. With Ba（OH）2 · 8H2O as the phase change material, the variation laws of interface position, the temperatures of the phase change material and the cooling medium with freezing time are given. At the same time the effects of the sphere radius and convective heat transfer coefficient on freezing are obtained. These theoretically testify that energy storage device can be used to improve cold start of the engine by recovering the waste heat of engine is practicable. And these provide certain theoretical reference for the optimal design of the energy storage device.