16fin+and+tube+heatexchanger.pdfVIP

Determination of heat transfer correlations for plate-fin-and-tube heat exchangers Dawid Taler Abstract This paper presents a numerical method for determining heat transfer coefficients in cross-flow heat exchangers with extended heat exchange surfaces. Coeffi- cients in the correlations defining heat transfer on the li- quid- and air-side were determined using a non-linear regression method. Correlation coefficients were deter- mined from the condition that the sum of squared fluid temperature differences at the heat exchanger outlet, ob- tained by measurements and those calculated, achieved minimum. Minimum of the sum of the squares was found using the Levenberg-Marquardt method. The outlet tem- perature of the fluid leaving the heat exchanger was cal- culated using the mathematical model describing the heat transfer in the heat exchanger. Since the conditions at the liquid-side and those at the air-side are identified simul- taneously, the derived correlations are valid in a wide range of flow rate changes of the air and liquid. This is especially important for partial loads of the exchanger, when the heat transfer rate is lower than the nominal load. The correlation for the average heat transfer coefficient on the air-side based on the experimental data was compared with the correlation obtained from numerical simulation of 3D fluid and heat flow, performed by means of the commercially available CFD code. The numerical predic- tions are in good agreement with the experimental data. List of Symbols A area, m2 Af fin surface area, m 2 Ain, Aoval inside and outside cross section area of the oval tube, m2 Amf tube outside surface between fins, m 2 Amin minimum free flow frontal area on the air side, m2 Ars smooth tube outside surface area, m 2 c specific heat, J/kg K
c mean specific heat, J/kg K C covariance matrix dh hydraulic diameter of air flow passages, m dz hydraulic diameter on the liquid side, 4Ain/ Pin, m D diagonal matrix with positive diagonal elements f