Abstract
Frost formation on and choking of evaporators are perplexing problems in heat-pump systems using ambient air as the heat source. In the present study, heat-and mass-transfer, frost formation and defrosting of single row cooled-tubes were investigated experimentally in a uniform humid air flow, an impinging air jet, and a fluidized bed with a multi-slit distributor and a static-bed height of 10 mm, respectively. The heat transfer performance for an impinging jet decreased with time, because of the frost formation. As for teflon coated tubes in the present fluidized bed using glass beads of 0.92 mm in diam., it was found that non-frost operation is possible under comparatively wide conditions of heat flux and superficial velocity, and that the heat transfer performance is about five times that for the uniform air flow.
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