Transient response of a plate-fin-and-tube heat exchanger considering different heat transfer coefficients in individual tube rows

Abstract

Experimental studies of multi-row plate-fin heat exchangers show that the highest average heat transfer coefficient on the air side occurs in the first row of tubes. In the next rows of tubes up to about the sixth row the heat transfer coefficient decreases.It is necessary to find the relationships for the air-side Nusselt number on each tube row to design a plate-fin and tube heat exchanger (PFTHE) with the optimum number of tube rows. The air-side Nusselt number correlations can be determined experimentally or by CFD modeling (Computational Fluid Dynamics). The paper presents a new method of modeling the transient operation of PFTHE, considering that the Nusselt numbers on the air side of individual tube rows are calculated from different empirical relationships. CFD modeling of the PFTHE was used to establish the heat transfer coefficients on individual tube rows. A transient model of a double-row, two-pass PFTHE was developed, considering different heat transfer coefficients in the first and second row of tubes. The influence of the adoption of different coefficients on the heat flow rate exchanged between water and air in the first and second row of tubes in two passes of the heat exchanger was shown.