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Re: [Phys-l] Heat transfer lab



Realizing this (verticality of demo.) I needn't have asked my question, as it'll work w/ any orientation of the rod. Vertical is best. (The liquid drips down displacing the vapour?)

bc

p.s. A thumb rule I heard (read?) was the transfer of energy by a steam radiator was ~ 1/2 by convention and 1/2 by radiation. Using my handy dandy GE Rad. Calculator, I find at 212 F. and emissivity of one, ~ 350 BTU/hr - square foot.

Our floor furnace input is 30k BTU/hr. I estimate 20% is flu loss and the heat exchanger is 14 square feet. Or ~ 1.7 k BTU/hr-ft^2 Nope it's nearly all convection. The temp for equality is ~ 550 F.

p.p.s. Can one of you explain why metering a furnace increases efficiency, i.e. throttling the input so it cycles less frequently. Both a web page I just read and the consumers' reports claim this. I've done this to our water heater and floor furnaces. I estimate about 1/3 of max. On very cold days the front furnace (sit. and din. rooms) doesn't cycle.


On 2010, Nov 17, , at 05:54, Michael Edmiston wrote:

Also, the expansion from
liquid to gas at the hot end, and the contraction from gas back to liquid at
the cold end acts as the "pump" that moves the vapor from the hot to cold
end.