Heat Transfer from a hollow sphere to air
Heat Transfer from a hollow sphere to air
(OP)
I am looking for heat transfer from a heated hollow sphere to air by convection. say sphere temperature is 40 deg air temperature is 30. what would be convective heat transfer coeffeicent for sphere? how much heat will removed from the air if sphere diameter is .15 meter?





RE: Heat Transfer from a hollow sphere to air
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RE: Heat Transfer from a hollow sphere to air
I estimate that if the sphere is constantly kept at 40oC, and no radiation effects considered, the free convection htc to air would be in the range of 3-4 W/(m2K).
If it is becoming cooled with time (unsteady state heat transfer) the heat lost to air would be m×C×10,
where m is the mass of the sphere, C its heat capacity, and 10 the original difference in temperature.
In this case, the htc comes progressively down as the sphere cools and approaches the air temperature.
RE: Heat Transfer from a hollow sphere to air
RE: Heat Transfer from a hollow sphere to air
The formula you mentioned expresses the heat transferred per unit time. It is applicable when the ΔT is fixed.
But if the sphere is cooling down to ambient conditions, ie, an unsteady state heat transfer condition, the total heat (no time reference) transferred to the air stream equals the heat lost by the sphere: m.C.ΔT.
There is practically no way to calculate analytically the htc due to the air flow (boundary layer) separation processes around the sphere.
An estimate for the htc -based on a correlation from experimental data by Hilpert- is lower than yours, around 25 W/(m2K).
RE: Heat Transfer from a hollow sphere to air
corus
RE: Heat Transfer from a hollow sphere to air
RE: Heat Transfer from a hollow sphere to air
Can you provide more info on the application?
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: Heat Transfer from a hollow sphere to air
RE: Heat Transfer from a hollow sphere to air
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?