VDI Heat Atlas eReference

eReference Springer Verlag

ϑ_wi= ϑ_wa

Liquids

For liquids the effect of temperature dependent property variations on the heat transfer is considered by the factor

with

Pr = Prandtl number at mean liquid temperature T

Pr_W = Prandtl number at wall temperature T_W

Gases

For gases the effect of temperature dependent property variations on the heat transfer is considered by the factor

with

T = mean temperature of the gas in Kelvin

T_W = wall temperature in Kelvin

When cooling a gas

for all gases the exponent n = 0

When heating a gas

the exponent n is depending on the type of gas.

For CO₂ the exponent n = 0.12 in the range 1 > T/T_W > 0.5

For superheated steam (H₂O) the exponent n = - 0.18 in the range 1 > T/T_W > 0.67 and 21 bar < p < 100 bar.

For all other gases the exponent n = 0.45 in the range 1 > T/T_W > 0.5

Literature: VDI-Wärmeatlas, 11. edition, 2013