THE EFFECT OF FROST FORMATION ON THE PERFORMANCE OF A PARELLEL PLATE HEAT EXCHANGER
Abstract
In this study the frost formation process and its effect on the performance of a parallel plate heat exchanger were modeled and experimentally investigated. A frost growth model was developed which: (1) treated the frost layer as a porous media, (2) incorporated empirical relationships from previous studies for the thermal conductivity and tortuosity as a function of density and (3) estimated frost growth as a function of time, plate temperature, air temperature, air humidity, Reynolds number, and location on the plate. A heat exchanger test loop was built and tested to experimentally investigate the frost formation process and to verify the model. Test conditions were limited to plate temperatures fro -12 to -5(DEGREES)C, air humidity ratios from 0.00382 to 0.00514 kJ/kg(,a), Reynolds numbers from 4400 to 32400, and air temperatures from 5 to 12(DEGREES)C. Frost growth was found to be strongly dependent on the heat exchanger plate temperature and the air humidity. Frost growth was dependent on Reynolds number for Reynolds numbers less than 15900. Above this value frost showed no dependence on the Reynolds number. An empirical correlation relating frost height to time, Reynolds number, plate temperature, and air humidity was developed. Frost density was found to vary with the location on the plate and Reynolds number. The friction factor initially increased with time then remained constant for high Reynolds numbers. Empirical correlations relating both j-factors with Reynolds number, plate temperature, and air humidity were developed. The model overestimated frost growth by 10 to 40% over the range of conditions covered in this investigation. Both the sensible and enthalpy j-factors estimated by the model were approximately 28% lower than the experimental values. The model captured the trend of increasing frost density with increasing Reynolds number and estimated frost density within 13% of the measured values.
Degree
Ph.D.
Subject Area
Mechanical engineering
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