Efficacy of using slurry of metal-coated microencapsulated PCM for cooling in a micro-channel heat exchanger

Abstract

This paper provides a method of heat transfer enhancement using microencapsulated phase change material (MPCM) slurries, utilizing the latent heat of PCM during melting. The values of heat transfer coefficient obtained for water are in a good agreement with those estimated using heat transfer correlation available in the literature. Two types of PCM microcapsules, non-metal coated and metal coated, were tested through a short tube MCHE with different slurry concentrations (5 and 10 wt.% PCM) and fluid flow rates. The calculated melting times for PCM microcapsules are less than their resident time at the same flow rate; which confirm their melting in the MCHE. The results show that heat transfer coefficient, hf increases as slurry flow rate and MPCM concentration in it increases. The hf increased by ∼3.5 times of that of pure water when 10% non-metal coated MPCM slurry was used. The metal coated MPCM slurry showed a further 10% increase in hf compared to the non-metal coated at same MPCM concentration and Reynolds number. The results show that the major enhancement in hf is due to the increase in the fluid thermal capacity caused by PCM melting and also to less extend by micro mixing caused by the capsules. The use of MPCM slurry increases pressure drop, however the heat transfer enhancement override such increase in pressure drop.