. Transactions - American Society of Heating, Refrigerating and Air-Conditioning Engineers. over the two foot center square is , while that observed at the center is deg. above the averageand maximum variation from the average is deg. The averagetemperature over the same area of the cold surface of the corkboard deg. fahr., which differs by deg. from the center couple. Themaximum variation from the average is deg. fahr. Since thesecouples were placed under a thin shaving of the corkboard, which, thoughvery thin, probably varied considerable in thickness,
. Transactions - American Society of Heating, Refrigerating and Air-Conditioning Engineers. over the two foot center square is , while that observed at the center is deg. above the averageand maximum variation from the average is deg. The averagetemperature over the same area of the cold surface of the corkboard deg. fahr., which differs by deg. from the center couple. Themaximum variation from the average is deg. fahr. Since thesecouples were placed under a thin shaving of the corkboard, which, thoughvery thin, probably varied considerable in thickness, this variation mightbe expected. Further, the variation between the center cou])le and theaverage is not sufficient to influence the conductivity constant by anamount greater than its homogeneity. It is, however, enougli to affectthe surface transmission constant by a considerable amount, for the New Thermal Testing Plate, F. C. Houghten 391 reason that the error is a much greater per cent of the total temperaturedifference between surface of the corkboard and the temperature ofthe FIG. 6. MAIN HEATING ELEMENT AND EDGE HEATER, SHOWING METHOD OFAPPLYING THE RESISTANCE RIBBON METHODS OF CALCULATION After a condition of equilibrium has been reached the heat passingthrough the specimen during any period of time is: dt (1) H — cA dS where, //=heat passing through the area A of the r= temperature gradient through the specimen. dSc = thermal conductivity of the material. 392 Transactions of Am. Soc. of Engineers If ti is the temperature of the hot side of the specimen, fj the tem-perature of the cold side and S the thickness of the specimen, the tem- dtperature gradient through the material, may be expressed by, dS ti — h . (^ —^2) , and equation (1) becomes : H = c A c, the thermal conductivity of the material, then becomes: HS A(t, — t,) (3) (3)
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