Elsevier

Powder Technology

Volume 98, Issue 3, 15 August 1998, Pages 217-222
Powder Technology

Article
Microencapsulated phase-change materials as heat transfer media in gas-fluidized beds

https://doi.org/10.1016/S0032-5910(98)00080-1Get rights and content

Abstract

The objective of this research is to investigate microencapsulated phase-change materials as heat-transfer media in gas-fluidized beds. The effective specific heat of an encapsulated material undergoing phase-transition is several-fold larger than the specific heat of the same material undergoing sensible heat changes. Because heat transfer coefficients in a fluidized bed increase with specific heat of the particulate phase, encapsulated phase-change materials are expected to enhance heat transfer rates in a fluidized bed. Several types of microencapsulated products were evaluated for their usefulness as heat transfer media in fluidized beds, including shells of polymethylene-urea, cross-linked nylon, and gelatin and cores of octadecane and paraffin. Microcapsules with shells of gelatin and cores of octadecane proved most useful in this study. Heat transfer enhancements of 30% were observed for these microcapsules although enhancements of at least 85% were expected based on the effective specific heats of the microcapsules. The thermal resistance of the gelatin shell or octadecane core may be responsible for these results. Another possibility is that particle residence times in the fluidized bed were shorter than estimated, which would reduce the effect of increasing thermal time constant of capsules.

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    Citation Excerpt :

    The GR50 was stable for only up to 15 melt-solidification cycles under fluidized conditions, which corresponded to approximately 75 h of operation. The only microencapsulated PCM study for fluidized bed is an earlier one by Brown et al (1998). The synthesized microcapsules for this purpose included shells of polymethylene-urea, cross-linked nylon and gelatin and cores of octadecane and paraffin.

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