Prediction of heat transfer correlations in a low-loaded plate-fin-and-tube heat exchanger based on flow-thermal tests

New theoretical and empirical relationships for the Nusselt number on the liquid-side in the transitional and turbulent range were derived, using various procedures for calculating the friction factor. The water-side friction factor in the transition flow range R-ew.trb <= Re-w <= Re-w.tre was calculated by linear interpolation between the values of the friction factor for R-ew.trb = 2100 or R-ew.trb = 2300 and It was assumed that the transitional flow ends at R-ew.trb = 3000. Other values of R-ew.trb and R-ew.trb determined experimentally can be adopted based on experimental data. Alternatively, the friction factor in the correlation for the Nusselt number on the liquid side was calculated using the Churchill formula valid for all fluid flow regimes in smooth and rough pipes. The paper presents new results of experimental testing of a new design two-pass car radiator with two rows of tubes. New empirical heat transfer relationships for the air and water-side were determined based on experimental data using the least squares method. Also, the empirical formulas for the water-side pressure loss coefficient and air side friction factor were developed. The temperature of the water at the outlet of the heat exchanger was calculated using P-NTU (Effectiveness-Number of Transfer Units) method. The theoretical and empirical correlations for the water-side Nusselt number agree very well. By using the P-NTU method, the procedure proposed in the paper can be used to determine the heat transfer correlations in heat exchangers with different constructions.