Experimental and Theoretical Investigation of the Natural Convection Heat Transfer Coefficient in Phase Change Material (PCM) Based Fin-and-Tube Heat Exchanger

Saulius Pakalka,Kęstutis Valančius,Giedrė Streckienė

doi:10.3390/en14030716

Abstract

Latent heat thermal energy storage systems allow storing large amounts of energy in relatively small volumes. Phase change materials (PCMs) are used as a latent heat storage medium. However, low thermal conductivity of most PCMs results in long melting (charging) and solidification (discharging) processes. This study focuses on the PCM melting process in a fin-and-tube type copper heat exchanger. The aim of this study is to define analytically natural convection heat transfer coefficient and compare the results with experimental data. The study shows how the local heat transfer coefficient changes in different areas of the heat exchanger and how it is affected by the choice of characteristic length and boundary conditions. It has been determined that applying the calculation method of the natural convection occurring in the channel leads to results that are closer to the experiment. Using this method, the average values of the heat transfer coefficient (have) during the entire charging process was obtained 68 W/m2K, compared to the experimental result have = 61 W/m2K. This is beneficial in the predesign stage of PCM-based thermal energy storage units.

Highlights

Efficient use of renewable energy sources is usually linked to the practical ability to accumulate energy
This study focuses on the Phase change materials (PCMs) melting process in a fin-and-tube type copper heat exchanger
One of the main techniques for heat enhancement in latent heat storage (LHS) systems is the use of extended surfaces [9], e.g., fins [10] with shell and tube heat exchangers being the most widely used for this purpose [11,12]

Summary

Introduction

Efficient use of renewable energy sources is usually linked to the practical ability to accumulate energy. Many researchers have analysed various types of fins, their configuration, forms, used materials, manufacturing method thereof as well as the influence of the geometry of the storage tank [16,17] Various physical phenomena, such as natural convection, were studied separately or together. Deng et al [26] numerically analysed the influence of shell conductivity, fin length and heat transfer fluid temperature parameters on the melting of the PCM in a horizontal shell and tube HX. In order to contribute to a better understanding of natural convection process in shell and fin-and-tube HXs with PCM and practical design of LHS systems, we have carried out analytical calculations and experimental tests by expressing the heat transfer coefficient. The objective of the study is to present calculation methods that allow to determine the heat transfer coefficient for a PCM-based horizontal shell and fin-and-tube HX system as accurately as possible. The design of LHS systems could be cheaper, faster and facilitated

Experimental Setup

RkaLNS Su

Findings

Latin letters APCM cp ghkLm Nu Pr