Experimentelle untersuchung des wärmeübergangs in parallel durchströmten rohrbündeln bei konstanter wärmestromdichte im bereich mittlerer Prandtl-Zahlen

Abstract

The heat-transfer parameters were determined experimentally in electrically heated tube bundles for turbulent flow parallel to the axis. The tubes were arranged in a pattern of equilateral triangles. The ratios of the distance between the axes of the tubes to their external diameter were 1,60 and 1,25 in the two test sections studied. The bundles contained 31 heated tubes of the same diameter and were surrounded in each case by a cylindrical shell which was also equipped with electric heating. The heat flux at the surface of the tubes was about 10 W/cm 2. The wall temperatures in the bundle were measured directly with thermocouples which were embedded in the surfaces. The points of temperature measurements were chosen at numerous positions in the lateral cross-section and permitted measurement of the mean and local heat transfer coefficients in the tube bundle. The experiments were carried out with distilled water and with a mixture of 60% ethylene glycol and 40% water. The values obtained for the Prandtl numbers in this way fell within the range from 2,3 to 18. The Reynolds numbers were varied between 10 4 and 2.10 5. The relation between the mean heat-transfer coefficients and the friction factor in the tube bundles was found from the experiments as: 1446-1 The experimentally determined mean Nusselt numbers were also given by the following function: Nu = [00122 + 0.00245 ( p/ d)] Re 0.86 Pr 0.4 with a maximum deviation of ± 4 per cent For certain local Nusseh numbers, deviations of up to 20 per cent with respect to the relations given were observed.