Melting and solidification characteristics of a double-pipe latent heat storage system with sinusoidal wavy channels embedded in a porous medium

Abstract

The aim of this investigation is to explore the combined effects of porous medium and surface waviness on the melting and solidification of PCM inside a vertical double-pipe latent heat storage (LHTES) system. The results are compared with the cases of smooth channels and pure PCM. In the system, water is passed through the inner tube while composite PCM is placed in the annulus side. Different effective parameters including wavelength and wave amplitude of the sinusoidal wavy channels, porosity and pore size of the porous structure, Reynolds number and inlet temperature of water are examined to find the optimum geometric as well as operating conditions in both melting/solidification processes. The results show that utilizing both the high conductive porous structure and wavy channel reduces the melting/solidification times significantly. For the best case, the melting and solidification times of PCM reduce by 91.4% and 96.7%, respectively, compared with the smooth channels pure PCM system. The average rate of transferred heat for the wavy channel composite PCM are 10.4 and 18.9 times that for ACCEPTED MANUSCRIPT 2 the smooth channel pure PCM case. Comparing with the pure PCM system, the presence of copper foam reduces the effect of channel waviness significantly for both melting/solidification processes.

Thermal Performance of a PCM-Based Thermal Energy Storage with Metal Foam Enhancement

“…The numerical model is created under the following assumptions: (1) the water flow and liquid PCM flow are assumed to be laminar and incompressible, (2) the metal foam is considered homogeneous and isotropic, (3) the volume expansion of the PCM during phase change is neglected [2,17,18,21], (4) the Boussinesq approximation is used to account for the natural convection inside the PCM, and (5) the thermo-physical properties are constant. Based on the above assumptions, the governing equations can be expressed as: For the forced flow and heat transfer in the water flow side [2,24]: The numerical model is created under the following assumptions: (1) the water flow and liquid PCM flow are assumed to be laminar and incompressible, (2) the metal foam is considered homogeneous and isotropic, (3) the volume expansion of the PCM during phase change is neglected [2,17,18,21], (4) the Boussinesq approximation is used to account for the natural convection inside the PCM, and (5) the thermo-physical properties are constant. Based on the above assumptions, the governing equations can be expressed as:…”

“…Enthalpy-porosity method is adopted, and the liquid-solid mushy zone is treated as a pseudo porous zone. The variable γ is determined by the following formulas [17,18,21]:…”

“…Considering that the HTF/PCM temperature changes along the flow direction in an actual situation during the charging and discharging processes, a comprehensive model involving the flow and heat transfer both in the HTF and PCM sides should be built [2,[19][20][21][22]. Liu et al [19] developed a numerical model including the convective heat transfer of HTF and the melting process of PCM within metal foam.…”

“…It was found that melting time is decreased by 14% and 55% using the foam porosities of 0.9 and 0.7, respectively. A combination of surface waviness and porous medium was introduced by Shahsavar et al [21] into the double-pipe latent heat storage system, and the feasibility in decreasing the melting/solidification time was demonstrated, based on thermal equilibrium thermal model. Extra addition of metal foam into the HTF domain was first proposed by Yang et al [2], and it presented better performance in the melting charging process.…”

Effect of Porous Media on The Performance Characteristics of a Concentric Vertical Annular Tube

“…(ke) The total thermal conductivity of porous media is defined as a calculation method based on the thermal conductivity of fluid (water) and solid (balls) [17].…”