Heat transfer to air flowing through heated tubes: Part I: Effect of entry and exit conditions Part II: Effect of length to diameter ratio

Abstract

Part I—A preliminary study has been made of the effect of various end conditions on surface conductances to air flowing through a heated tube. The effects of thermometric errors and flow disturbances lead to characteristic forms for the variation of surface conductance with flow characteristics. The inlet disturbance produced large changes from the accepted correlation forms for nominally streamline flow for values of GRAETZ number between 5 and 300 in tubes with lengths 12 to 48 times their diameters. Part II—Surface conductances have been measured in the transfer of heat from the wall of a steam heated tube to air flowing through the tube of 1 in. diameter, the flow being disturbed at the inlet by a perforated plate and gauze. A range of L/D t of 4:1 has been tested. Three regions of flow have been observed in the range of Re from (a) 100 to 250 ( L/D t ) 0.16 to 2200, (c) 2200 to 4000. The surface conductances for region (b) agree with the equation. ▪ In the flow range wherein D t G/μ<2200 the following equations apply: ▪