Heat transfer from plain and finned cylinders to air in crossflow

• Main Author: Franklin, Raymond Eric
• Published: University of Surrey 1954
• Subjects: 620
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.751472

Part One describes experiments carried out on an electrically heated single cylinder mounted normal to the airstream in a closed jet wind tunnel with a square working section. Comparison of the results with previous work reveals serious discrepancies, (+20%, -40%), and these could not be accounted for by turbulence in the airstream. It is suggested that the dispersion of the results is due to the effects of the flow boundaries. After supporting this hypothesis with flow measurements the existing results are critically examined and a new correlation presented which includes the geometry of the set-up. An equation is given which correlates several workers results to within +/- 10%. Part Two describes experiments on finned cylinders. The first of these is a cylinder of diameter 2 in, to which are soldered concentric fins 4 in. diameter, 3/16 in. thick, 1/2 in. pitch. It is shown that provided the results are evaluated in a particular way, the theoretical equation for the conduction through the fins agrees closely. After a dimensional analysis of the problem, the results of the research are correlated with those of previous researches on nine different finned cylinders. Experiments in which the shape of the fins was changed are then described. It is shown that by removing material from the rear of the fins, their performance can be improved. Tests are reported which were carried out on a cylinder with eccentric fins. These fail to support the idea that such a cylinder would give better heat transfer than one with concentric fins. Further tests on the cylinder whose fins were modified reveal that two states of flow can exist over the fins. One of these results in an increase of 12% in the heat transfer. The effect is examined experimentally and suggestions to account for it are submitted.