Numerical model of a cold storage tank containing paraffin as phase-change material

Autores UPV
Año
CONGRESO Numerical model of a cold storage tank containing paraffin as phase-change material

Abstract

The aim of this work is to develop and validate a numerical model of a PCM cold storage tank. This model reproduces the performance of a tank with around 235 l PCM immersed around the heat exchanger, which is a set of 8 spiral shaped coils placed parallel wise on horizontal planes. A 2D effective heat capacity model has been developed, where one dimension corresponds to the heat transfer fluid direction and the other is the radial direction of the tube along which the PCM solidifies. The volume of PCM is discretized in these two dimensions and the heat transfer between the nodes and their corresponding temperatures are calculated. These nodes are characterized by their temperature which is associated to a given enthalpy state. Hence, a key input to the model is the effective heat capacity-temperature curve of the tested PCM, which is the paraffin RT8 from RUBITHERM and has a phase-change temperature in the range 3-8ºC. The enthalpy-temperature curve has been measured by means of the T-history method, and an experimental validation has been carried out for the numerical model of the tank. The results have shown a good agreement between the predicted and measured thermal power of the tank. The model has helped to calculate the thermal resistances of the heat transfer inside the tank and to understand the limiting processes. The performance of the tank is particularly hindered during the solidification process by the low thermal conductivity of the paraffin. Once validated, the model has been used to predict the effect of different materials in the heat exchanger. The results indicate that despite the lower thermal conductivity of polymer materials, the latter are an interesting low cost solution given that the thermal power remains very similar to tanks with more conductive coils such as with copper or aluminium.