Is this even possible? (heat exchanger problem)

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In summary, Eugene is trying to design a compact heat exchanger to produce 900 kW from the heat transfer of JP-8 Fuel Exhaust and water. There are size and input range restrictions, and he is hoping to use a plates-in-shell heat exchanger. He has not done a basic energy balance between the two streams, and is unsure of what process/cycle to use to produce the 900 kW.
  • #1
yujean
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I am currently dealing with a problem involving the heat transfer between two gases. Would it be possible to take JP-8 Fuel Exhaust (990C) and heat up water (starting at 140C, 9.8MPa) to produce 900 KW? The flow-rate of the water is 0.9kg/sec.

There is an extreme size-restriction on this heat exchanger, which is limited to 1.5m x 0.6m x 0.6m.

I read through this "Guide to Compact Heat Exchangers" (link below), and found that the Module 2.5 was the closest to the one I am trying to design, however the size-constraints and input-ranges specified are not within my range of desired inputs.


Thanks for all your help.

eugene


link to "Guide to Compact Heat Exchangers"
http://www.ept.ntnu.no/fag/tep32/Pensum/CompactHeatExchangers.pdf [Broken]
 
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  • #2
Two issues I see right off the bat:

1) Have you done a basic energy balance between the two streams? By that I mean a basic first law energy balance? Forget about losses and such. Can you even, theoretically get to where you need to go?

[tex]\Sigma \dot{m}h_{in} = \Sigma \dot{m}h_{out}[/tex]

2) What process/cycle will you be employing to produce the 900 kW?
 
  • #3
FredGarvin said:
Two issues I see right off the bat:

1) Have you done a basic energy balance between the two streams? By that I mean a basic first law energy balance? Forget about losses and such. Can you even, theoretically get to where you need to go?

[tex]\Sigma \dot{m}h_{in} = \Sigma \dot{m}h_{out}[/tex]

2) What process/cycle will you be employing to produce the 900 kW?

1) Yes. I calculated around 1500HP, or 1200 kW, using the values below.

2) I'm hoping to use a plates-in-shell heat exchanger, as described by "Module 2.5" in the provided link. This 900 kW (~1200HP) will be powering a turbine.

***

Perhaps I am approaching this problem from the wrong angle.

Here is the basic outline of the problem:

"H20, 1":

T= 272F
P= 1433 psia
h= 245.23 Btu/lbm

"JP-8 Diesel Fuel Exhaust":
T=1800F
P= TBD
h= TBD


"H20, 1" enters heat exchanger and is heated by the JP-8 Fuel Exhaust, it is now "H20, 2"

"H20, 2":
T = 1500F
P = 1040 psia
h = 1786.62 Btu/lbm


"H20, 2" enters turbine then becomes "H20, 3"

"H20, 3" (isentropic):
T = 160F
P = 4.72 psia
h = 1109.9 Btu/lbm

"H20, 3" (actual):
T = 483 F
P = 4.72 psia
1280.00 Btu/lbm

***

The problem is basically getting "H20, 1" into "H20, 2" within a 5' x 2' x 2' container. I believe that it would require a tremendous amount of surface area. I'm now wondering if the Module 2.5 is the best choice (as seen in the below link, page 58)


link to "Guide to Compact Heat Exchangers"
http://www.ept.ntnu.no/fag/tep32/Pensum/CompactHeatExchangers.pdf [Broken]
 
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  • #4
Not to sluff you off, but have you contacted a heat exchanger manufacturer? All of the ones I have ever dealt with could tell me exactly what I needed, in about two minutes, as far as overall HT coefficient as well as expected required HT area. You give them the two fluid streams and desired conditions and they can size you a heat exchanger very efficiently. Of course, if this is for a school project, then that changes things.

The other thing you need to be concerned with, that is very difficult for us lay people, is the structural aspects of the heat exchanger. This is especially true when you have a wide delta between conditions. The thermal stresses alone get to be very harsh.
 
  • #5
Doing just that. Thanks for your help & suggestions, Fred.
 

1. Can heat be transferred without any energy input?

No, according to the laws of thermodynamics, heat can only be transferred from a hotter object to a cooler object. This requires some form of energy input, such as a heat source or mechanical work.

2. How efficient can a heat exchanger be?

The efficiency of a heat exchanger depends on several factors, such as the design and materials used. Some heat exchangers can have efficiencies as high as 90%, but it ultimately depends on the specific application and conditions.

3. Can a heat exchanger work in both directions?

Yes, a heat exchanger can be designed to work in both directions, transferring heat from one fluid to another in either direction. This is known as a reversible heat exchanger.

4. What is the role of surface area in a heat exchanger?

The surface area of a heat exchanger plays a crucial role in its efficiency. A larger surface area allows for more heat transfer to occur, resulting in a more efficient heat exchanger. This is why many heat exchangers have fins or other structures to increase surface area.

5. Can a heat exchanger handle different types of fluids?

Yes, heat exchangers can be designed to handle a variety of fluids, including gases, liquids, and even solids. The materials and design of the heat exchanger may need to be adjusted depending on the specific fluids being used, but in general, heat exchangers are versatile and can be used for various applications.

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