Nomograph for Selecting Electrical Heaters JOHN J. SERRELL The Sharples Corporation, Philadelphia, Penna.
HEN selecting electrical heaters for installation in a
less than one per cent on standard heaters installed in a continuous system in which the amount of radiating surface is kept at a minimum. The formula from which this chart was constructed is based on that for variable specific heat':
continuous system with various petroleum products, one is confronted not only with various temperature rises and rates of flow but with the problem of variable specific heat of the material being heated. The nomograph specifies the heat capacity required under specific conditions easily and accurately. It is particularly useful in cases where the heater has already been installed and where one desires to determine the rise in temperature available at varying rates of flow. The losses due to radiation and convection will be
c=-
I
Cragoe,
1 dF (0.388$- 0.00045 t ) B.t. u./lb./'
c. s.,
F.
Bur. Standards, MisoeZlonsous Pub. 97 (1929).
I 50
45
150
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ELFICTRICAL HEATER DESIGN G. P. H. d e [3.235 0.001875 (ti $211 (12 - ti) K. W. = 3600 X 0.9486 Given: What K. mi. required to heat 200 gallons per hour of oil of d = 0.85 from 100' to 160" F.? To use chart: Connect 100' on tl with 160' on ta, connect intersection of this line with A t o 0.85 on d, connect intersection of thie line with B to 200 G. P.H.; read 12.1 on K.W. Note: Valid for petroleum products of specific gravity 0.72 to 0.96. Losses due to radiation and convection will be approximately 1 per cent on standard heaters.
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961
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