Heat Transfer Problem
Heat Transfer Problem
(OP)
Hello- I am new to the forum. I am an ME who specializes in hydraulic/pneumatic circuit design and special applications. I have recently been tasked with a heat transfer problem that, after review of my college text (25 years old), indicates that i may have to re-learn Laplace Transforms. Before i go back to University after dinner tonite, i figured i would ask around and maybe someone could help. Here is the problem:
How many Watts/square inch are required to maintain a temperature of 122 degrees F on the inside wall of a stainless steel cylinder 16 inches in diameter(wall thickness = .0625")when there is an air flow of 5730 standard cubic feet per minute of 77 degree F air?
We are building a heated blanket that wraps around the cylinder to heat it up. There will be a 1" air gap between the inner (heated) side of the blanket and the outer surface of the cylinder.
In case anybody wants to know, this is for a dilution tunnel used in automotive emissions testing. The tunnel is 50 feet long. I appreciate any input and will make myself available for hydro/pneumatic questions which i am much better qualified to answer. Thank you very much.
How many Watts/square inch are required to maintain a temperature of 122 degrees F on the inside wall of a stainless steel cylinder 16 inches in diameter(wall thickness = .0625")when there is an air flow of 5730 standard cubic feet per minute of 77 degree F air?
We are building a heated blanket that wraps around the cylinder to heat it up. There will be a 1" air gap between the inner (heated) side of the blanket and the outer surface of the cylinder.
In case anybody wants to know, this is for a dilution tunnel used in automotive emissions testing. The tunnel is 50 feet long. I appreciate any input and will make myself available for hydro/pneumatic questions which i am much better qualified to answer. Thank you very much.





RE: Heat Transfer Problem
2) Will the heated blanket remain on all the time or is this a transient problem?
3) Do you have a drawing of your setup that you can share?
4) There's a free heat transfer text that you can download:
http://web.mit.edu/lienhard/www/ahtt.html
Patricia Lougheed
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RE: Heat Transfer Problem
Some of these tests run for hours and hours. I have checked around various dyno labs for similar situations, and many indicators point to a value of around 1 watt/sq. in. A 50 foot long heated blanket that wraps around an 18 inch diameter cylinder will require 35kW. Thats alot of power (and money).
I must verify this number. I appreciate the help.
Mark Zeleney
RE: Heat Transfer Problem
corus
RE: Heat Transfer Problem
At 25 W/m^2-K, you'd need 0.4 W/in^2 just for the air. You must also account for heat loss outward away from the heater blanket, as well as the air gap inefficiency, so 1 W/in^2 doesn't sound that far out of bed.
The power you calculated should be for the 16 in diam, so, more like 31 kW.
TTFN
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RE: Heat Transfer Problem
Mark