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Heat transfer between a hollow cylinder(flowing water inside) and a c?

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Askara
#1
Mar20-13, 10:17 AM
P: 21
let say i have a piece of metal cylinder (say 3cm dia) and heat it to 500 c, and put it inside a hollow cylinder with inside diameter 3cm (so they are touching) and outside diameter of say 8 cm), the hollow cylinder is empty inside so water pass through. is there anyway to calculate the heat conduction rate? meaning how much heat energy absorb per second by the water flow.

in other word, i have a cylinder heat it at 500 c and put it inside a water jacket. and want to find out heat dissipation rate of the water jacket
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sci-phy
#2
Mar23-13, 05:25 AM
P: 17
I didn't understand your question properly. You are putting a heated cylinder inside a hollow one of the same internal diameter. How can the water pass through the hollow one? Isn't it sealed using the smaller solid cylinder??
sci-phy
#3
Mar23-13, 05:36 AM
P: 17
For the question asked in the end... Yes it is possible. Again, it depends on whether the pipe is running full of water, or half or any other level.. The heat transfer rate is given by :
Q = h.A.ΔT where
h= heat transfer coefficient of water which depends on whether the water is still or flowing. If the water is stagnant in pipe, h≈ 20 to 100 W/[itex]m^{2}[/itex]K. If water is flowing, h usually lies between 300 and 10,000.
A is the area wetted by water. If the pipe is running full, A = ∏.d.L where d is the inner dia of pipe, L is the length of pipe
ΔT is the temp diff btw water and heated pipe. If the water is stationary, this value keeps on decreasing till the heat transfer is very small as both the temperatures become nearly equal..

Hope it's good enough

Askara
#4
Mar23-13, 05:37 AM
P: 21
Heat transfer between a hollow cylinder(flowing water inside) and a c?

soory, the hollow cylinder is a water jacket, basically what you see here http://www.olerc.com/electronics/bru...8wcj-30mm.html


i know thats how you calculater heat transfer rate but how do you determin h? 300-10000 is too different
sci-phy
#5
Mar23-13, 06:41 AM
P: 17
Quote Quote by Askara View Post
i know thats how you calculater heat transfer rate but how do you determin h? 300-10000 is too different
Ah! Now I understand your question!

Finding h would be difficult indeed. But it can be done experimentally using heat exchangers.
It's better to use Q= [itex]m^{.}[/itex] [itex]c_{p}[/itex] ΔT find heat transfer rate. Mind you, ΔT is the change in temperature over time of the cold water and NOT the difference in temperature between cylinder and water. This has to be done experimentally.

And if u want to find h, it can be done by equating Q= [itex]m^{.}[/itex] [itex]c_{p}[/itex] ΔT and Q = h A Δt where Δt is the log mean temp difference for the heat exchanger. If you want further info this site gives an idea: http://www.merusonline.com/heat-transfer


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