Year: 2006
Type: dissertation
Abstract: Frost accumulation on an air cooler, a direct result of combined heat and mass transfer between the moist air flowing across a cold surface, causes heat transfer performance degradation due to the insulating effect of frost layer and the coil blockage as the frost grows.The complex geometry of finned tube air cooler leads to uneven wall and air temperature distribution inside the coil, and causes variations of frost growth rate and densification along the coil.In this study, a general distributed model with frost formation was developed.The equations for finned tube heat exchanger were derived in non-steady-state manner and quasisteady state in the frost model.In order to make the model more realistic, the variation of frost along fin due to uneven temperature distribution was included.The presented model is able to predict the dynamic behavior of an air cooler both under non-frost and frost condition.Results include frost accumulation and its effect on energy transfer, air off-coil temperature, refrigerant liquid dry-out position and propagation of frost formation along the coil.Comparisons were made based on the frost mass accumulation, pressure drop across coil and energy transfer coefficient, and results were found to agree well with reported experimental results.A field investigation was performed on the frost formation at an evaporator of a commercial full-scale refrigerated container that uses R-12 as the working refrigerant.Results show that the model is capable of predicting the dynamic behavior of a direct expansion evaporator under both non-frosting and frosting conditions.The air outlet and energy transferred compare well between experiment
DOI: 10.32657/10356/6557
Author: Yeong Chang Cheng
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W2272417089