Performance of Air-Cooled Heat Exchanger with Laminar, Transitional, and Turbulent Tube Flow

Cracow University of Technology, Faculty of Environmental Engineering, Department of Thermal Processes, Air Protection and Waste Utilization, 31-155 Cracow, Poland

^* Corresponding author: dtaler@pk.edu.pl

Abstract

Some air-cooled heat exchangers, especially in air conditioning and heating installations, heat pumps, as well as car radiators, work in a wide range of loads when the liquid flow in the tubes can be laminar, transitional or turbulent. In this paper, a semi-empirical and empirical relationship for the Nusselt number on the liquid-side in the transitional and turbulent range was derived. The friction factor in the transition flow range Re_w,trb ≤ Re_w ≤ Re_w,tre was calculated by linear interpolation between the values of the friction factor for Re_w,trb =2,100 and Re_w,tre =3,000. Based on experimental data for a car radiator, empirical heat transfer relationships for the air and water-side were found by using the least squares method. The water temperature at the outlet of the heat exchanger was calculated using P-NTU (effectiveness-number of transfer units) method. The heat flow rate from water to air was calculated as a function of the water flow rate to compare it with the experimental results. The theoretical and empirical correlation for the water-side Nusselt number developed in the paper were used when determining the heat flow rate. The calculation results agree very well with the results of the measurements.