heat transfer differences between superheated steam and saturated
heat transfer differences between superheated steam and saturated
(OP)
Im trying to calculate the difference in heat transfer between a pipe carrying saturated steam and a pipe carrying superheated steam. I know there is a difference in heat transfer due to the properties and because saturated steam has a wetted perimeter, but im at a loss as to the particular calculation. Could anyone point me in the right direction?





RE: heat transfer differences between superheated steam and saturated
Perhaps you can share your reasons for trying to quantify the amount of inefficiency involved. Is this an academic pondering? Or is it a serious industrial project need?
Kern discusses this in page 281 of his "Process Heat Transfer" and cites one of the obvious reasons for not giving superheat any importance in heat transfer: the desuperheat in atmospheric pressure steam with 100 of of superheat represents only 5% of the total heat load. I've never known anyone to take credit for the superheat transfer in steam heaters/condensers. Maybe you have a better system or method.
RE: heat transfer differences between superheated steam and saturated
RE: heat transfer differences between superheated steam and saturated
The assumption doesn't introduce major errors, not greater, anyway, than those in estimating the convective and radiative HTC from the outer surface, and at the same time simplifies the analysis.
RE: heat transfer differences between superheated steam and saturated
RE: heat transfer differences between superheated steam and saturated
I wonder... If the "conservative" assumption of taking the pipe wall temperature equal that of superheated steam renders a result of a temperature drop of, say, 0.5oF per 100 ft of pipe length, what purpose would have producing more sophisticated estimations ?
RE: heat transfer differences between superheated steam and saturated
Second, if you did your heat loss calculations based on a saturated condition, which infers the benefit of latent heat transfer on the steam side (and produces moisture I am sure you don't want in the piping) then you would be safer for the superheated portion of the piping, and would have to only deal with the driving force of the delta T of the superheated steam.
Sounds like the best of both worlds to me, unless, of course, there is a real possibility of getting into saturation.
rmw
RE: heat transfer differences between superheated steam and saturated
Treat the superheated flow as a non condensible gas. From Reynolds number, etc Determine a heat transf coef and the resulting heat flux thru that region of pipe metal and insulation.
With the known heat flux and inside film coef determine the pipe wall inside temp. If the temp is above saturation, the original calc is fine. If temp of inside wall is sat or less, then condensation will occur and heat trans coef should be that of wet steam.