THE INFLUENCE OF ATMOSPHERIC PRESSURE UPON 



THE FORCED THERMAL CONVECTION FROM 



SMALL ELECTRICALLY HEATED 



PLATINUM WIRES. 



By a. E. KENNELLY and H. S. SANBORN. 



(Read April 24, 1914.) 



Object of Enquiry. 



This paper describes the process and resuks of a research made 

 at Harvard University in 191 1, to determine the effect of change in 

 atmospheric pressure on forced thermal convection from thin plati- 

 num wires. By forced thermal convection is meant the carrying 

 away of heat from the surface of a wire by wind-motion, i. e., by a 

 rapid transverse movement of the wire through the surrounding air. 

 This wind motion through the air dissipates the heat from the wire 

 convectively. The rate of thermal convection depends upon the 

 length and diameter of the wire, its surface condition, the tem- 

 perature elevation of the wire above the air, the velocity of the 

 motion, and the pressure of the air. The object of the enquiry was 

 to determine the efifect of the last-named variable — variation of 

 atmospheric pressure — upon the thermal dissipation, the other quanti- 

 ties being kept constant. 



History of the Enquiry. 



The research here described was the outcome of an earlier inves- 

 tigation on " The Convection of Heat from Small Copper Wires," 

 by Messrs. A. E. Kennelly, C. A. Wright and J. S. Van Bylevelt, 

 presented at the Frontenac Convention of the American Institute of 

 Electrical Engineers, June 28, 1909, and published at p. 363, Vol. 

 XXVIII. , part I., of the Transactions for that year. In that research, 

 the forced convection of heat from a thin copper wire, electrically 

 heated to a constant temperature, i. e., maintained at a constant 



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