E • CONVECTIVE HEAT TRANSFER AND FRICTION 



Friction. There is one other phenomenon applying to boihng heat 

 transfer with forced convection which should be pointed out. As the heat 

 transfer improves, the frictional pressure drop increases. Typical results 

 are shown in Fig. E,9j. The increase in friction is certainly an important 

 consideration in the design of heat transfer equipment. 



With the purpose of studying the inter-relation between friction and 

 heat transfer, some experiments have been performed [83] in which water 



0.2 0.4 0.6 0.8 1.0 1.2 



Heat transfer, (BTU/ft^ hr) X 10^^ 



Fig. E,9j. Frictional pressure drop with boiling heat transfer. Distilled degassed 

 water. SS347 tube, 0.226 I.D., 25 inches long. Data taken at constant subcooling of 

 100°F and constant mass flow of 3.81 X lO^ Ib/hr-ft^ [78]. 



was forced through an electrically heated tube of about |-in. diameter. 

 Sufficient measurements were taken so that the local Stanton number St, 

 as well as the local friction coefficient Cj, could be computed. The two 

 coefficients are defined by the equations 



St = -^- 



and 



pVc^{T 

 dp 



Cf 



dx 

 2pV 



d 



T.) 



{ 332 > 



