Heat Transfer Performance Potential with a High-Temperature Phase Change Dispersion

Ludger Fischer,Qi Li,Geng Qiao,Yulong Ding,Jörg Worlitschek,Silvan von Arx,Poppy O’Neill,Ernesto Mura

doi:10.3390/en14164899

Abstract

Phase change dispersions are useful for isothermal cooling applications. As a result of the phase changes that occur in PCDs, they are expected to have greater storage capacities than those of single-phase heat transfer fluids. However, for appropriate heat exchanger dimensions and geometries for use in phase change dispersions, knowledge about the convective heat transfer coefficients of phase change dispersions is necessary. A test unit for measuring the local heat transfer coefficients and Nusselt numbers of PCDs was created. The boundary condition of constant heat flux was chosen for testing, and the experimental heat transfer coefficients and Nusselt numbers for the investigated phase change dispersion were established. Different experimental parameters, such as the electrical wall heat input, Reynolds number, and mass flow rate, were varied during testing, and the results were compared to those of water tests. It was found that, due to the tendency of low-temperature increases in phase change dispersions, the driving temperature difference is greater than that of water. In addition, larger heat storage capacities were obtained for phase change dispersions than for water. Through this experimentation, it was acknowledged that future investigation into the optimised operating conditions must be performed.

Highlights

Phase change dispersions (PCDs) are two-phase heat transfer fluids (HTFs) that are comprised of a phase change material (PCM) that is dispersed into a continuous phase and stabilised with the help of surfactants [1]
The merit of using the PCD was shown in the evolution of the bulk temperatures along the length of the tube, whereby bulk temperature reductions of 1.5 and 2 K were observed for experiments 1 and 2, respectively, compared to water under the same operational conditions
The local heat transfer coefficients and local Nusselt numbers were higher for the PCD than for water, with Nusselt enhancements of 12% for the first set of experimental conditions and 23% for the second set of experimental conditions

Summary

Introduction

Phase change dispersions (PCDs) are two-phase heat transfer fluids (HTFs) that are comprised of a phase change material (PCM) that is dispersed into a continuous phase (generally water) and stabilised with the help of surfactants [1]. PCDs are designed so that the PCM within the PCD changes phase at a temperature where heat can be stored or isothermally released [2]. During this phase change, the PCD exploits the sensible heat of its relevant components (the PCM and water), and the latent heat of the phase change [1,3]. The PCD exploits the sensible heat of its relevant components (the PCM and water), and the latent heat of the phase change [1,3] This ensures that PCDs have considerably higher cooling capacities compared to standard cooling fluids, such as water. Wang et al [3] focused on highlighting the thermophysical, rheological, and heat transfer properties of PCDs, and

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