G • COOLING BY PROTECTIVE FLUID FILMS 



results indicate that the fluid leaves a porous surface in the form of a 

 number of small jets which coalesce almost immediately to form a uni- 

 form outward-moving layer. On the other hand, there is another type of 

 flow pattern in which the fluid leaves the porous surface in the form of 

 isolated jets which maintain their identity and create a very turbulent 



10-^ 



1 0-3 1 0-2 



Air flow (G), Ib/in^ sec 



10-' 



Fig. G,2b. Relation between strength, flow rate, relative density and pressure 

 for Poroloy with 35° crossing angle. (From [2].) 



boundary layer. However, the uniformity of the flow pattern can be con- 

 trolled to a satisfactory degree by mechanical means during the fabri- 

 cating process of a sintered-wire porous metal. 



G,3. Physical Nature of Transpiration-Cooling Process. In 



discussing the problem of heat transfer inside transpiration-cooled porous 

 walls, it is desirable to consider the simplest possible case. Since the 

 pattern of the porous passages is a very complicated three-dimensional 

 network, the assumption of a network consisting of identical cylindrical 

 channels running from one end of the specimen to the other is made. 

 Fig. G,3 shows the variation of the temperature throughout the porous 



(434 > 



