Numerical Simulation of a Composite Metal Foam-PCM Air Heat Exchanger Using Rod PTC Heating Elements

Abstract

The aim of this paper is to study the charging/discharging process in a Latent heat exchanger for the purpose of space heating by using a composite metal foam/PCM. The composite PCM-air system is modelled in a 3-D CFD approach for the purpose of 8h charging during the night and 16h discharging during the daytime using the non-equilibrium thermal model to simulate the presence of a porous medium in the domain. For the charging process, rod Positive Temperature Coefficient (PTC) heating elements with constant temperature are selected to heat the PCM based on the maximum operating temperature of the PCM. For the discharging process, a blower is assumed to pass the air from the middle of the PCM container and so the air can gain heat and its temperature rises which is used then for space heating. RT70HC is also selected as the PCM material due to the high capacity of latent heat and suitable melting point for domestic usage. The system is studied according to the average liquid fraction and temperature of the PCM during both charging and discharging as well as the outlet temperature of the air during discharging. The results show that by using two rod heating elements with the diameter of 1cm, length of 25cm and temperature of 95°C, the melting process is performed in less than 8h. Furthermore, a uniform output temperature of almost 29.5°C is also achieved in the next 16h during the discharging process with the air mass flow rate of 0.04 kg/s.