루버핀 형 복합 유로 방열기의 열설계 모델 개발

Abstract

A computational model has been developed to predict thermal and hydraulic design parameters for high capacity radiators equipped in high power diesel engines. In this case, compact heat exchanger is usually used for smaller size and a compound flow arrangement and extended surface such as louvered, fin and offset-strip fin are used to maximize heat transfer rate. In this study, thermal design model of louvered fin heat exchangers with compound multi-pass flow arrangement has been developed to calculate heat transfer rate and pressure drops.

In the model, the heat exchanger core with compound multi-pass flow path is subdivided into a number of macro volumes along the coolant flow path, and each macro is divided into a number of cells. Each cell is regarded as a crossflow element and ε-NTU method is used to compute the heat transfer rate within a cell. The overall heat transfer coefficient(UA) and the NTU are calculated using the fin-tube design parameters and the heat transfer correlations for both coolant and air-side flow. The heat transfer rate in a macro is used to calculate the coolant temperature change which is provided as the inlet coolant temperature of the next macro. The present model has been applied to radiators of 120～365 kW capacity and the results showed reasonable agreement with available test data, although the difference can be attributed to the uncertainty in the j-factor model as well as to imperfectness in brazing the radiators tested.

Air-side pressure drop in louvered fin heat exchanger is affected by many design parameters such as louver pitch, louver angle, fin pitch, tube pitch, etc. In the present study, a model heat exchanger of 200×150 in frontal area was tested in a circulation wind tunnel. Pressure drop was measured at various air velocity and the friction factors were reduced from the pressure drop data. The measured friction factor was compared with four available correlations and a sizable difference was observed between the data and the predictions.