The reliable simple one-dimensional 64-CPWTR model applied to the two-dimensional heat transfer problem of an insulated rectangular duct in an air conditioning or refrigeration system

The heat-transfer characteristics of an insulated long rectangular or square duct are analyzed by using the one-dimensional plane wedge thermal resistance (PWTR) model and plate thermal resistance (PTR) model in this study. It is found that the errors generated by the PWTR model are all positive and the errors generated by the PTR model are all negative. Thus, the combined plate wedge thermal resistance (CPWTR) model generated by paralleling PWTR and PTR models with the proportion factors of α=0.6 vs. β=0.4 (64-CPWTR model) can neutralize the positive and negative errors and obtain very accurate results in comparison with the two-dimensional numerical solutions analyzed by the CFD software. The errors generated by the one-dimensional 64-CPWTR model are within 1% for practical sizes and practical insulated thickness in air conditioning and refrigeration systems. Thus, the engineer can obtain very reliable heat transfer results when applying the one-dimensional 64-CPWTR model to an insulated rectangular duct.