Experimental quantification of air-side row-by-row heat transfer coefficients on fin-and-tube heat exchangers

Abstract

• Mass transfer experimental method to visualize and quantify local air-side HTCs. • Local and averaged HTCs on real-scale HX aluminum fin surfaces. • HTC comparison between fin-and-tube HXs with inline and staggered tube arrangement. • Row-by-row HTC degradation of plain fin-and-tube HXs at various Re. • Correlations of averaged HTC and pressure drop on measured HX fin geometry. An absorption-based mass transfer method has been employed in the current study to obtain two-dimensional HTC distributions on two different 8-row fin-and-tube heat exchangers. The method utilizes a color change coating material and a tracer gas to quantify local mass transfer on the fin surfaces and then employs the heat and mass transfer analogy to calculate local air-side HTCs. The accuracy and robustness of the method were validated in previous studies. The current study focuses on investigating the row-by-row HTC degradation by increasing the number of tube rows. The local HTC measurements of the current study ranged from 0.5-4.8 ms −1 face airflow velocity using dry fin surfaces. The two 8-row fin-and-tube heat exchangers have the same tube diameter, tube pitch, fin pitch, and fin shape. The only difference is the staggered vs. inline arrangement of the tube bundle. Averaged HTCs of each row are quantified and compared. The results show HTC degradation is related to the tube arrangement, airflow velocity, and row number. The heat exchanger with inline tube arrangement shows a more substantial HTC degradation than the heat exchanger with the staggered tube arrangement. The maximum HTC decline is observed on the second row with 40% compared to the first row while flow velocity is below 1 ms −1 . The row-by-row HTC degradation becomes less significant for higher flow velocities. HTC degradation appears to be negligible past the 5 th row. The current study provides a method that can be used to predict air-side HTCs of fin-and-tube heat exchangers with multiple rows.