Study of Frosting Heat-and Mass-Transfer. Defrosting Mechanisms, and its Control by Impinging Solid Particles.

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The present research is divided into two parts. The first is an experimental study on heat-and mass-transfer of humid air flow in a parallel plate under various conditions covering condensation and frost formation. The other is an experimental study on defrosting of frost layers on cooled-tubes using a very shallow fluidized-bed and the heat/mass transfer. The obtained results are summarized as follows :1. Experimental Study on Heat/Mass Transfer and Frost Layer Growth. i) Growing thickness, mass, and density of the frost layer depend on the velocity of air stream ; the density increases with time, owing to the diffusion and solidification of water vapor in the frost layer. ii) Total heat flux and latent-heat flox of filmwise condensation are increased with increasing the humidity difference. iii) There exists a critical mass flux. at which the heat transfer coefficient of filmwise condensation has the maximum value.2. Experimental Study on Heat/Mass Transfer and Defrosting Mechanisms … More of Frost Layers around Cooled-Tubes in a Fluidized Bed. i) A novel jet distributor has been designed specially for defrosting in the fluidized bed, and a visualization technique has been developed to investigate the initiation of frost formation and the motion of fluidizing particles. ii) Observation using a high speed video system revealed that gas-solid impinging jets produced by the distributor strip effectively off the frost on the tubes. iii) The local heat transfer coefficient and frost area fraction were measured lowering the coolant temperature to -30^ﾟ C ; the effects of the DB temperature. tube temperature, static bed height of particles, and position of distributor and stabilizers on the defrosting performance and heat transfer characteristics were clarified. iv) The size distribution of stripped frost was measured with a Laser Doppler Particle Dynamics Analyzer System.In summary, the objectives of the present study have almost been achieved, and the results of present and successive research will make great contributions towards engineering and industries. Less