130 An Analysis of the Feasibility of Photoelectric Technique Applied in Defrost-Control

This study has been carried out to investigate the feasibility of using the photoelectric method for defrost-control in refrigeration equipments. The new method originates from the principle of the photoelectric conversion. Photoelectric sensors were emplaced on the cold finned heat exchangers in natural convection regimes. Three frost and defrost cycles were performed. During these cycles, the photos of frost were taken by the microscope and the height of frost was measured on the photos. At the same time, the output-voltage of the photoelectric sensor was monitored. The experiment results present that the photoelectric signals experience three different periods during the frost process. Further more, the signals present two desirable characteristics, namely, “binary” and “linear”. These characteristics indicate that the photoelectric method is feasible to solve the problem of mis-defrost.