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Guru

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Compare Roll Bond Evaporator to Tube & Fin Evaporator in BTU

04/15/2017 10:15 AM

Hello all. I wish to compare a roll bond plate evaporator/condenser to a tube and fin condenser. Size is 900 mm x 650 mm. What I am asking is how do I compare one style to the other in heat exchange capacity. If I had a 900 x650 mm roll bond unit what size of tube and fin exchanger would I require to do same work? I have had no success in searching so far. Thanks.

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#1

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 1:55 PM

You could do a CFS analysis, or you might find one done already online, for your application....

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-58782010000400006

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Guru

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#2
In reply to #1

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 2:02 PM

Thanks Eagle I also have sent several inquiries asking the manufacturers to provide a comparison on this topic. I am not into the math part but I will try every resource to find an answer.

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Guru

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#3

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 2:57 PM

This may help.

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Guru

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#4

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 3:55 PM

Offhand and without looking at hard numbers, my gut tells me that the tube-and-fin exchanger would be more efficient because it offers more surface area per tube volume than does roll-bonded plate. Roll-bonded plate is a two dimensional affair whilst a comparably-sized tube-and-fin unit distributes its surface area throughout a volume and so can offer more total surface area (far more in fact depending on its depth and fin density) to the tube than roll-bonded plate.

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#9
In reply to #4

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/18/2017 11:27 AM

Also something to consider is the other side of the heat exchanger, how is the heat transferred, convection, conduction, forced fluid flow, gas, liquid, solid? Different physical configurations lend themselves to optimum transfer mechanisms, some are more resistant to fouling and other unwanted external influence.

On a macro level, as Andrew suggests, surface area should dictate capacity, all other factors being equal. Evaluating fluid thermodynamics at the higher pressure seems to be really what you're looking for, my guess is overall, it should be better, viscosity seems to hold at the higher pressure, see

https://www.nist.gov/sites/default/files/documents/srd/jpcrd535.pdf

Have no idea if heat transfer at high pressure is better, I had to look up roll bond heat exchanger first...:)

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#5

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 4:13 PM

No information on process fluids? One would use different equipment for the same heat duty between methanol and raspberry jam.

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#6
In reply to #5

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 4:16 PM

Not to mention the Reynolds number for raspberry jam is terrible. Laminar all the way.

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#7
In reply to #5

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 4:25 PM

I get your point I am using R744 CO2 but the roll bond units will not take the pressure unless I reduce the pressure using a cascade system. I tried the strawberry jam and raspberry jam along with honey but it was a sticky mess.

I also presume that the temperature in the heat exchanger may be a factor but if I can use or make a system similar to the roll bond principal then I may be progressing on this project. Possibly if I can get the ton or fraction of a ton from a stand up refrigerator and measure the roll bond condenser I may get a clue.

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#8
In reply to #7

Re: Compare Roll Bond evaporator to tube & fin evaporator in BTU

04/15/2017 4:59 PM

Sizing is on the basis of the log-mean temperature difference, the heat duty, and the overall heat transfer coefficient, which is a function of the process fluids and their properties. It sounds as though the problem is best discussed with equipment suppliers directly. Fortunately there are loads of telephone numbers in the public domain.

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