Mathematical modeling of unsteady response of plate and fin heat exchanger to sudden change in liquid flow rate

¹ Cracow University of Technology, Faculty of Mechanical Engineering, Institute of Thermal Power Engineering, Al. Jana Pawła II 37, 31-864 Cracow, Poland
² Cracow University of Technology, Faculty of Environmental Engineering, Institute of Thermal Engineering and Air Protection, Ul. Warszawska 24, 31-155 Cracow, Poland

^* Corresponding author: korzen@mech.pk.edu.pl

Abstract

A mathematical simulation of plate fin and tube heat exchanger will be presented. The transient operation of the heat exchanger was carried out using general numerical model developed in [1]. Reynolds number of the water flowing inside the tubes varied in the range from 4000 to 12000. A detailed analysis of transient response was modeled for growth in the water volume flow in time.

At first, heat transfer correlations for air and water were determined based on the experimental data. Unknown parameters appearing in the relationships for the Nusselt numbers on the air and water-sides were estimated using the least squares method. The power-type form of the relationship for the air-side Nusselt number was used while two correlations of different form were chosen for the water-side Nusselt number. The first is the exponential correlation, and the second form is similar to the relationships of Petukhov-Kirillov and Gnielinski. These correlations were used in the mathematical model of the heat exchanger for the simulation of its transient operation.

The results of the numerical simulations of a heat exchanger using experimentally determined air and water-side heat transfer formulas for calculation of heat transfer coefficient were compared with the experimental data. Very good agreement of computation results (i.e. air and water temperature at the outlet of the heat exchanger) with the experimental data was obtained.