Numerical Study of Heat Conduction Enhancement of a Latent Heat Thermal Energy Storage (LHTES) Devise Using Finned Tubes

Abstract

The objective of this paper is to examine the thermal performance of a LHTES system comprised of a single tube, by means of a Computational Fluid Dynamics (CFD) computer code. Two different types of fins, straight and annular, were considered to enhance the heat conduction between the tube and the RT42 Phase Change Material (PCM). The dimensions of the fins were elected so that the total area of the fins to be almost equal, in both configurations. The RT42 PCM is a paraffin wax with medium to high thermal energy storage and chemically inert. Whereas possible, temperature dependent thermal properties, provided by the producer, used for the definition of the material model. Between the finless tube and the one with straight fins, the melting time reduction was approximately 56.7% and between the finless and the annular tube, the PCM melt time was reduced by 61.5%. Heat conduction was the driving heat transfer mechanism during the first seconds of the PCM melting process. On the other hand, natural convection was the lead heat transfer method as the liquid PCM was able to move due to density and temperature differences. The investigation of the liquid PCM travel revealed that in the finless model and the one with the straight fins the PCM movement was parallel to the axial direction whereas in the model with the annular fins the velocity of the PCM was parallel to the radial direction.