OCT. 10, 1921 PARSONS AND HARPER: ENGINE RADIATORS 413 



The laboratory measurements of heat-dissipating power were made 

 with two sources of heat, steam and hot water. For superheated 

 steam, the effective temperature is computed by weighting properly 

 the heat derived in each stage (loss of superheat, condensation, cool- 

 ing of water) : 



T 



(^ + 1) 



CpS + T,L 



CS + L 



where T^ is mean effective temperature, T^ is temperature of con- 

 densation, 5 is superheat (in degrees), L is latent heat of condensa- 

 tion and Cp is specific heat of superheated steam. The condensate 

 was usually not cooled significantly below the temperature of conden- 

 sation and the formula above is in the simplified form resulting from 

 neglecting such cooling. An intercomparison of test data on ten cores, 

 using both superheated steam and hot water as sources of heat for 

 the calorimetric measurements, showed that no appreciable difi'erence 

 existed between the results obtained by the two methods. A series 

 of measurements using water as the source of heat were made with 

 the rate of water flow varying over a wide range. As might be ex- 

 pected, a wide range of variation of heat dissipation occurred with 

 change of rate of water flow when the rates were extremely low, 

 but at the rates of flow common in radiator use, the effect was not 

 significant. It seems safe to assume that heat dissipation for con- 

 ditions all constant except rate of water flow will attain a value within 

 5 per cent of the maximum which it will reach with any rate of flow, 

 if the rate be as much as 3 gallons per minute per inch depth of core 

 1 foot wide. This flow is well within the margin of circulation found 

 in most aircraft cooling systems. 



The effectiveness of indirect cooling surface, namety, cooling sur- 

 face not backed by flov^ring water, is considered in detail and the math- 

 ematical relations are developed which describe its behavior. The 

 eft'ectiveness of indirect surface is defined as the ratio of its heat- 

 dissipating power to that of an equal area of direct cooling surface 

 all at the temperature of the edge of the indirect surface which has 

 contact with the source of heat. For long narrow fins such as the in- 

 direct cooling surface found in a square cell or hexagonal cell con- 

 struction, the effectiveness is 



_, tanh U 



