Improved performance of latent heat energy storage systems utilizing high thermal conductivity fins: A review

Abstract

A review of the analytical, computational, and experimental studies directed at improving the performance of phase change material-based (PCM) latent heat energy storage systems that utilize high thermal conductivity fins is presented. Spanning over many decades, managing of heat generation associated with electronics utilized for early work on aeronautics and space exploration was emphasized, with later extensions to waste heat recovery, passive thermal management of computing platforms, and energy storage for solar thermal applications. The focus of this review is placed on investigations that deal with utilization of non-moving fins/extended surfaces with high conductivity. Aluminum, brass, bronze, copper, iron, mild steel, nickel, and stainless steel were the metal-based fin materials of choice utilized to promote heat transfer, whereas carbon fiber brushes were also used. A variety of phase change materials including pure/commercial paraffins, carbonate mixtures, polyethylene glycol, chloride mixtures, fluorides, asphalt, water, nitrite and nitrate mixtures, stearic acid, dodecanoic acid, and lauric acid, covering melting temperatures in the range of 0–735 °C, was used. Both freezing and thawing of phase change materials within a variety of thermal energy storage container geometries and heat exchange operating conditions were reported. More recent studies have highlighted the important role of convection, particularly in situations involving melting. The formation of thermally unstable fluid layers responsible for improved mixing and expedited thawing of PCM was also highlighted. It was found that the number of fins (or fin-pitch) and fin length have far stronger effects on the performance of the storage system than those caused by fin thickness and fin orientation. At the same time, insertion of fins will weaken buoyancy-driven convection, which is well-known to play an important role in the melting process. Therefore, the conflict between enhancement of the effective thermal conductivity and simultaneous suppression of the buoyancy effect should be considered by the designer through selecting the optimum positions and orientation of the fins. A generalized finding of these studies underlines that in employing fins with high thermal conductivity, minimum-distance conducting pathways that connect the extreme temperature of the heat storage system should be sought.