Thermal network calculation model for phase change material with SPICE circuit simulator

Abstract

The SPICE model of phase change material (PCM) for thermal network transient calculation was investigated. The nonlinear behavior of PCM due to latent heat was modeled by using the voltage dependent current source and the capacitor. A latent heat is stored in the capacitor as electric charges. Corresponding to the PCM phase state, such as solid, liquid and mixed phases, the dependent current source is controlled with PCM temperature and the latent heat quantity of PCM. Since the melting point of PCM has a distribution, the model in which multiple PCM models having different melting points and capacitor capacities were connected in parallel was employed. To validate the numerical simulation model, the aluminum case with PCM sealed inside was prepared. The sample was heated with a rubber heater from the bottom with different heat quantities. The temperature changes of the upper and lower surfaces were measured with thermocouples. The results showed the error between simulated and measured values were below ±4 °C and the calculation time took below real-time. This simulation model can be applied to cooling system optimization and temperature control system. of the maximum latent heat quantity of PCM divided into 15 blocks. The lower melting point (thin line) and the higher melting point (dotted line) show the time changes of the endothermic and exothermic reactions up to the maximum latent heat amount of 35 J, which is half of the maximum latent heat amount of center melting point. It shows the relationship between the change of latent heat quantity for each melting point of PCM and the stepwise change of PCM temperature. It was confirmed that the PCM temperature was maintained while the latent heat was generated at each melting point of each layer. The analysis result with an applied heat flow of 8W shows the latent heat quantity of higher melting point of top PCM layer doesn’t reach the upper limit. It indicates that the third PCM layer was not completely melted. In this experiment, the aluminum case was heated from the bottom. Therefore, it was shown that in the temperature behavior of PCM when the temperature rose, when the amount of heat applied was small, PCM melts in order from the low melting point regardless of the layer. On the other hand, when the amount of heat applied increases, the internal temperature distribution of the PCM increases, which indicates that the lower melting part of PCM in the lower layer melts before the lower melting part of PCM in the upper layer. In the cooling process, it can be confirmed that the upper layer has exothermic reaction earlier than the intermediate layer, and there was also a heat dissipation from the upper surface. The developed model can estimate not only the temperature but also the transient of the latent heat inside the PCM. Thus, this model can be a very useful tool for cooling system optimization.