Date of Award

6-2009

Degree Name

MS in Mechanical Engineering

Department

Mechanical Engineering

Advisor

Jesse Maddren

Abstract

Frost accumulation on evaporator coils has been a serious problem that decreases the efficiency of refrigeration systems. Many defrost methods have been used and hot gas defrost is the most common for industrial refrigeration applications. However, it is not a simple task to run an efficient hot gas defrost system. The duration and frequency of the defrost cycle should be properly determined so that the frost is melted but no additional heat transfer is transferred to the refrigerated space.

An experimental investigation was conducted at the Classic Salads Facility in Salinas, California. A single coil was instrumented to study frost build up and defrost during normal operation.

The finite difference method is used to numerically model the temperature of the coil during a defrost cycle. A separate model was developed to determine the pressure drop across evaporator coil with and without frost. Both models are used to determine the presence of frost on the coil tested at Classic Salads.

The pressure drop data did not show an increase in the pressure drop over time, indicating there was no frost accumulation during testing at Classic Salads. Also, comparison between the finite difference model and the experimental temperature data indicate that there was minimal frost. These results indicate that energy savings could be achieved if an accurate defrost termination was implemented.

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