The objective of this research is to investigate microencapsulated phase-change materials as heat-transfer media in gas-fluidized beds. Microcapsules are small capsules, usually between 50 and 100 m diameter, consisting of an impervious shell of only a few microns' thickness enclosing a gaseous, liquid, or solid core material. Phase- change materials such as toluene, cyclohexane, or fluorocarbons are potential core material for these experiments. Convection coefficients for these materials are expected to be much larger than those for gas-fluidized beds of solid particles. Furthermore, pressure drops in such beds are expected to be small compared to conventional beds because of smaller densities for capsules compared to solid particles. Our approach includes both experimental and theoretical evaluations. An electrically heated probe is used to measure convection coefficients in temperature-controlled fluidized beds of microencapsulated phase-change material. Several theories of heat transfer in fluidized beds will be tested against our experimental data. Suitable theoretical refinements will be developed as appropriate for the microencapsulated phase-change materials. The improvements in heat transfer will expand the opportunities for using fluidized beds in such diverse applications as air-cooled microelectronics equipment, where pressure drop is critical; gas-liquid heat exchangers, where gas-side heat transfer is rate limiting but difficult to enhance; and liquid fluidized beds, where heat capacities of conventional bed materials are not enough larger than the liquid heat capacity to yield the order-of-magnitude enhancements typical of gas-fluidized beds.
