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### Topic: Basic Heat Transfer  (Read 9559 times)

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#### gera19

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##### Basic Heat Transfer
« on: April 03, 2006, 09:39:21 AM »
1)if a surface emits 300W at a temp of T(K), how much will it emit at a temp 2T?

2)I think that in a heat exchanger, it is impossible for the exit temperature of the cold fluid to be greater than the exit temp of the hot fluid when both fluids are single phase fluids. But i'm not sure..am i right?

3)How is natural convection different from forced boiling?

Thanks pp....
« Last Edit: April 04, 2006, 11:35:33 PM by geodome »

#### Donaldson Tan

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##### Re:Some Qs
« Reply #1 on: April 04, 2006, 11:33:51 PM »
1)if a surface emits 300W at a temp of T(K), how much will it emit at a temp 2T?
Assuming radiation is the only mode of heat transfer, use Wien's Law

2)I think that in a heat exchanger, it is impossible for the exit temperature of the cold fluid to be greater than the exit temp of the hot fluid when both fluids are single phase fluids. But i'm not sure..am i right?
YES because you need a temperature gradient for heat transfer to occur. This holds true even if multiphase fluid is being used.

3)How is natural convection different from forced boiling?
think of density
« Last Edit: April 04, 2006, 11:39:14 PM by geodome »
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

#### HCaulfield

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##### Re:Basic Heat Transfer
« Reply #2 on: April 08, 2006, 01:16:55 PM »
Regarding the second question. If the fluids go counter current, the exit temperature of the cold fluid can be higher than that of the hot fluid.

#### Donaldson Tan

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##### Re:Basic Heat Transfer
« Reply #3 on: April 09, 2006, 02:34:38 PM »
Regarding the second question. If the fluids go counter current, the exit temperature of the cold fluid can be higher than that of the hot fluid.

for a counter-current heat exchanger, the maximum outlet temperature of the cold fluid is the inlet temperature of the hot fluid.

for a co-current heat exchanger, the maximum outlet temperature of the cold fluid is the outlet temperature of the hot fluid.
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

#### michal

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##### Re: Basic Heat Transfer
« Reply #4 on: June 15, 2006, 02:06:19 AM »
IT MEANS TEMPERATURE CROSS IS GOOD PRACTICE

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