Experimental study of natural convection in the melting of PCM in horizontal cylindrical annuli

Abstract

Heat transfer characteristics, including the convective flow driven by melting of subcooled phase change material (PCM) in the horizontal annulus gap, were experimentally studied The inner cylinder was heated with a constant surface heat flux and the outer cylinder had a constant temperature. The history of the temperature field was measured with an infrared scanning system. It is shown in this paper that contribution of natural convection in the melt region becomes significant as the Stefan number increases. In recent years numerous experimental and numerical studies or analytical solutions, have been performed to explain the prinCipal mechanism of energy transfer occurring during the melting or solidification. In many of these practical cases natural convection effects, in the melted region, dominate over diffusion. Also an experimental and numerical investigation has been conducted at the Institute of Heat Engineering to study the characteristics of natural convection for the melting of n-octadecan inside a horizontal annulus gap [1-4]. Understanding and predicting the melt behavior of phase change material (PCM) is of special importance in designing cost-effective heat receivers of latent thermal energy storage (L TES). The temperature field and the solid-liquid interface boundary can be conventionally studied with the help of thermocouples. Another technique used in measurements of such kind is the application of thermochromic liquid crystals (TLC) suspended as small tracer particles. The Particle Image Thermometry (Pin is based on temperature-dependent reflectivity of TLC at visible light wavelengths [5]. Another sensor to study the solid-liquid interface is optical fiber [6]. This paper reports experimental results on the melting in a horizontal annulus gap using infrared (IR) thermography. This method has several advantages over measurements performed with usage of thermocouples, especially in experiments on natural convective melting/solidification heat transfer. Some advantages of IR thermography are: it is a non-intrusive measurement of temperature in the whole test cell (not only in the chosen points), it leads to simultaneous measurements of temperature and progress of the liquid-solid interface, it avoids disturbance of the heat flow caused by the presence of the numerous thermocouples.