Experimental study of local air-side heat transfer coefficient on real-scale heat exchanger fins by employing an absorption-based mass transfer method

Local air-side heat transfer coefficients (HTCs) of real-scale heat exchanger fins have been experimentally investigated in the current study. A recently developed absorption-based mass transfer method has been employed to visualize and obtain two-dimensional HTC distributions on different fins at a high resolution (8.6 µm). The process involves a mass transfer from airflow to a color change thin film coating. The local mass transfer is obtained through observing and quantifying the color change. Thus, local HTCs can be determined by applying the analogy between heat and mass transfer. The accuracy of this absorption-based experimental method has been validated on external flow across a flat plate which shows good agreement compared to the analytical solution. Moreover, the averaged HTCs and pressure drops of the three fin-and-tube arrays in the current study agree well with data from other researchers who have measured entire heat exchangers with similar fin geometries. To the authors’ best knowledge, this is the first time that local HTCs for real-scale heat exchanger fins with complex surface geometries have been experimentally obtained and published in the open literature. Moreover, the degradation of the HTCs with increasing row numbers of the three fin types has been quantified. The data shows the plain fin with inline tube arrangement has the largest HTC degradation in the second row compared to the wavy fin and louver fin with staggered tube arrangement. The method of the current study has provided a way to obtain a local and reliable comparison of heat transfer on different fin shapes. It can be utilized to generate better HTC correlations for heat exchangers and to recognize opportunities for improvement.