Researches on New Heat Transmitting Tubes : 1st Report

Abstract

We have been studying experimentally the heat transmission characteristic of our of new type as the case of air flowing normal to a bank of staggered tubes, and have already reported a portion of the results twice. Now we will report about the characteristic of the bundles of No.I (each has two fins 10 mm height, stretching in axial direction on its front surface of circular tube holding the angle 2θ=40°between the two fins), of No.III (each has two fins of 14 mm height, on the front (θ=0°) and the back (θ=180°) of the circular tube respetively) and of the ordinary circular named as circular tubes to make a distinction from the two above. Here all the have the same outer diameter of 38 mm. The main results of our researches are as follows : (1) No.I as bundle have the characteristic of higher coefficient of heat transfer (as for the total area of its outer surface) and less pressure loss, comparing with the case of simple circular tubes. Especially this characteristic is most striking when the are arranged in staggered type holding the same spacings of 80 mm to the transverse and longitudinal directions respectively. (2) We know that No.III tube has inferior characteristic when it is used as single tube (1st reprot). Now we see that the bundle of No.III in staggered arrangement with equal spacings of 80 mm has in appearance the characteristic approximate to that of the case of No.I tubes, if we do not consider the increase of tube weight. But according to the order of magnitude of coefficients of heat transfer, we can say that the largest is No.I tubes', the second is the simple circular tubes' and the third is No.III tubes'.