Experimental study on the melting and solidification behaviour of a medium temperature phase change storage material (Erythritol) system augmented with fins to power a LiBr/H 2 O absorption cooling system Francis Agyenim a, * , Philip Eames b , Mervyn Smyth c a Room A10 Marmont Renewable Energy Centre, Department of The Built Environment, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK b Department of Electronic and Electrical Engineering, Loughborough University, Leicestershire LE11 3TU, UK c School of The Built Environment, University of Ulster, Newtownabbey, Co. Antrim, Belfast BT37 0QB, UK article info Article history: Received 13 February 2010 Accepted 4 June 2010 Available online 15 July 2010 Keywords: Erythritol phase change material (PCM) Temperature gradient LiBr/H 2 O absorption cooling system abstract Experimental studies using a concentric annulus storage system with Erythritol (melting point of 117.7  C) as a phase change material (PCM) and augmented with longitudinal fins on the shell side, have been conducted to assess the thermal behaviour and heat transfer characteristics of this system. The study forms part of a broader investigation of PCMs to store energy to operate a LiBr/H 2 O absorption cooling system which operates with generator inlet temperatures of 70  Ce90  C. The experiments investigated the effect of changing mass flow rates ð _ mÞ and inlet heat transfer fluid (HTF) temperatures (T in ) on the thermal behaviour of the PCM system. The results showed that the suitable mass flow rate and inlet HTF temperature for charging the system to power a LiBr/H 2 O absorption system are _ m ¼ 30 kg=min and T in ¼ 140  C respectively. The experimental programme also investigated the temperature gradient in the axial, radial and angular directions during charging to help predict heat transfer in the system during phase change of Erythritol. Isothermal plots and temperatureetime curves were used to analyse the results. Temperature gradients in the axial and angular directions were 3.6% and 9.7% respectively that of the radial direction, indicating essentially a two-dimensional heat transfer in the radial and angular directions during the phase change. The amount of energy recovered from the 20 kg store during solidification was 70.9% of the maximum energy charged, at an average temperature of 80  C. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Most PCMs have unacceptably low thermal conductivity, leading to slow charging and discharging rates, hence requiring heat transfer enhancement techniques. Several studies have been conducted to study heat transfer enhancement techniques in phase change materials (PCMs) and include finned tubes of different configurations [1e 11], bubble agitation [12], insertion of a metal matrix into the PCM [13,14], using PCM dispersed with high conductivity particles [15], multitubes [10,16], or micro-encapsu- lation of the PCM [17,18]. Results of numerical and experimental studies on phase change around isothermal finned cylinder have also been extensively reported in literature. Sparrow et al. [3] investigated the freezing of a finned vertical tube when either conduction in the solid or natural convection in the liquid controlled the heat transfer using n-eicosane paraffin as a PCM. The authors concluded that the presence of fins brings about an enhancement of freezing on the tube surface between the fins. An earlier experimental investigation of a finned tube using four fins by Sparrow et al. [1] had also concluded that the use of fins could delay the domination of natural convection during a solidification process. The presence of natural convection, according to the authors, could delay or interrupt the solidification process and was deemed undesirable for the solidification process. Horbaniuc et al. [8] studied the solidification of a PCM within a finned heat pipe phase change storage system by means of an analytical technique considering the radial heat propagation towards the heat pipe wall and the angular propagation towards the fin. Horbaniuc et al. [8] measured performances of fins in terms of the interface freezing stage and the time taken for complete solidification to be achieved using parabolic and exponential approximations. Velraj et al. [12] investigated four different heat transfer enhancement techniques including tube with fins in a latent heat storage system using paraffin. Velraj et al. [12] evaluated the enhancement of the heat transfer using the effective thermal conductivity taken from a two- * Corresponding author. Tel: þ44 (0) 115 8466 140; fax: þ44 115 9513 159. E-mail addresses: francis.agyenim@nottingham.ac.uk, aboffour@hotmail.com (F. Agyenim). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2010.06.005 Renewable Energy 36 (2011) 108e117