Pergamon Int. Comm. HeatMass Transfer, Vol. 27, No. 8, pp. 1057-1065, 2000 Copyright © 2000 Elsevier Science Ltd Printed in the USA. All rights reserved 0735-1933/00/S-see front matter PII: S0735-1933(00)00193-7 FORCED CONVECTION HEAT TRANSFER IN A SLURRY OF PHASE CHANGE MATERIAL IN AN AGITATED TANK L. Royon, G. Guiffant, P. Perrot Laboratoire de Biorhtologie et d'Hydrodynamique Physicochimique CNRS, ESA 7057, Universit6 Paris 7, 2 pi. Jussieu, PARIS, FRANCE (Communicated by M. Lebouch6) ABSTRACT The heat transfer during the crystallisation in a slurry of a stable mixture of water with a water-soluble polymerised and cross-linked monomer, suspended in oil is investigated. Some experimental data are presented which eanphasize that such a suspension of millimetric particles of a phase change material allows both a high capacity of heat storage and limited super cooling phenomena. A phenomenological description of the crystallisation process is proposed which permits to predict the duration of the plateau of crystallisation as a function of the weight fraction and the temperature of the cold spring. The results compare very well with the experimental data thus giving a new impulse to the design of new complex fluids for both storage and heat transport. © 2000 Elsevier Science Ltd Introduction Owing to a wide variety of application, the concept of energy storage by using phase change material (PCM) has attracted a great interest in the framework of the recovery of low-level energy. The first possibility was to make use of fixed beds. Then an external fluid has to be used to ensure the heat exchange. In that case, the material had to be coated because of the transition solid-liquid (when using paraffin for example) which leads to additional heat transfer resistance. An alternative procedure, avoiding any coating, was to use water with a water-soluble polymerised and cross-linked monomer [I]. Here the technical difficulties arise mainly from the mechanical resistance of the samples of gel. The storage time is clearly one of the most important factors to consider when designing a storage process. The problem being governed by non-linear differential equations has to be solved numerically. Different methods were continuously proposed for PCM of macroscopic size ([2- 4] for example). Methods with a moving interface (fmite - element methods) permits to give the interface velocity of phase change front [5-8]. The second possibility is to make use of a dispersion of the PCM in a suspending fluid This new technology offers many advantages such as a high cooling capacity, the possibility of using the same medium for both energy transport and storage (thereby reducing losses during the heat exchange process), 1057