Heat Exchanger Sizing Question
Heat Exchanger Sizing Question
(OP)
Im looking to purchase a heat exchanger to cool oil in circulating lube oil system.
This will be cooled by the shop water line.
I had initially suggested these types.
https://www.mcmaster.com/heat-exchangers/heat-exch...
https://www.mcmaster.com/heat-exchangers/heat-exch...
Heat Capacity = 70HP/170,000 BTU
Oil Flow Rate = 21 GPM
Shop Water Flow Rate = 15 GPM
Water In = (60F - 90F)
Water Out = N/A (Water Will be Dumped out)
Oil In = 150F
Oil Out = 100F (Going Back into the system)
What is a good-sized heat exchanger for this application?
This will be cooled by the shop water line.
I had initially suggested these types.
https://www.mcmaster.com/heat-exchangers/heat-exch...
https://www.mcmaster.com/heat-exchangers/heat-exch...
Heat Capacity = 70HP/170,000 BTU
Oil Flow Rate = 21 GPM
Shop Water Flow Rate = 15 GPM
Water In = (60F - 90F)
Water Out = N/A (Water Will be Dumped out)
Oil In = 150F
Oil Out = 100F (Going Back into the system)
What is a good-sized heat exchanger for this application?
RE: Heat Exchanger Sizing Question
RE: Heat Exchanger Sizing Question
RE: Heat Exchanger Sizing Question
Heat capacity of your oil?
Look closely on how they've calculated the heating and look at your flows and temperatures which seem to be higher or lower than mentioned in the website listing.
For off the shelf HXs, you need to be within their stated limits or it won't work.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Heat Exchanger Sizing Question
If you work 6 days a week x 3 shifts it is more like 200,000gal/yr
Even when I worked places with private wells we used cooling towers and recirculated the water.
There are plenty of helps out there to size the HX.
The biggest issue is the variation in cooling water temperature.
Whether this is morning to afternoon or season to season it is a big factor.
There are different ways to deal with this, from multi-speed or variable speed pumps to multiple HX in parallel.
You need to hire someone that know how to do this.
There are skid mounted pre-engineered packages available with cooling tower and HX bundled.
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P.E. Metallurgy, consulting work welcomed
RE: Heat Exchanger Sizing Question
Ideally my boss would like to use water for oil cooling.
What additional information is needed to help narrow down some options?
RE: Heat Exchanger Sizing Question
Converting energy to motion for more than half a century
RE: Heat Exchanger Sizing Question
You need a small cooling tower.
These are usually fiberglass (or some other non-metalic) and they have a fan and a circulation pump.
Some of them have a two speed pump motor so that you have high and low cooling options.
This circ pump would run water through the HX to cool the oil.
You need to calculate the heat load to size the cooling tower and then you can size the HX.
Yes, it is more complex. And the cooling tower will require some ongoing makeup water and chemical treatment.
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P.E. Metallurgy, consulting work welcomed
RE: Heat Exchanger Sizing Question
Option A - 2(or more) tube side pass TEMA U HX
Water in / out : 90 / 100
Oil in / out: 150 / 110
Option B: - Full countercurrent shell and tube HX
Water in / out : 90 /100
Oil in / out : 150 / 100
Option C : Full countercurrent compact wide plate HX - clean non fouling service only on both sides.
Water in / out : 90 / 100
Oil in / out : 150 / 95 to 100
For option C, a compact spiral HX could handle a more fouling service, and can be cleaned also. Allow some 5psi dp minimum for water side and same for oil side.
RE: Heat Exchanger Sizing Question
RE: Heat Exchanger Sizing Question
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Heat Exchanger Sizing Question
RE: Heat Exchanger Sizing Question
Just eyeballing this it looks like you need pure countercurrent flow so a small fixed-tubesheet shell and tube heat exchanger might work but you'd probably need somewhere around 200-300 sq. ft. of surface area.
-Christine
RE: Heat Exchanger Sizing Question
Having the water max temperature be 95°F and a situation where the cooling water is anywhere near 90°F is going to be challenging, as others have mentioned. I'm surprised your boss doesn't want to investigate air cooling and I think it may be necessary to show why it should be considered given that it may be a more cost effective solution to your problem. Did your boss give a reason for discounting air cooling?
I'm assuming you're confident that your drain pipe can't handle 95°F with no problems in their current state because someone did a routine borescope inspection within the last 5-ish years (forgive me, it's a recent sore subject).
RE: Heat Exchanger Sizing Question
Your temperature demands are modest ....
It sounds like the junkyards would be full of HXs in the size and materials you desire
MJCronin
Sr. Process Engineer
RE: Heat Exchanger Sizing Question
Thank you for the feedback.
In doing the basic heat exchanger equation, i came up with the following.
Using my original temperature values and having a max runoff water temp of 95F (Also replacing inlet water temp with 85 F max)
Q (Heat Transfer Rate) = 175,000 BTU/Hr
U (Heat Transfer Coeff) = (25 - 250) BTU/Hr*F*Ft^2 (Common measurements I found online for my situation)
A (Heat Transfer Area) = Unknown
dTm (Log Mean Temp Diff) = 30.79 F
∴ A = Q/U*dTm
A(Umax) = 28.41 ft^2
A(Umin) = 227.34 ft^2
Looks like Christine74 was fairly spot on.
Am i on the right track?
Best Regards,
Sam M
RE: Heat Exchanger Sizing Question
Oil Cp = 2.5kJ/kg/degC, assumed
Oil dt = 27.8degC
Duty = 4050 x 2.5 x 27.8 = 281 600 kJ/hr = 267 000 Btu/hr
RE: Heat Exchanger Sizing Question
What happens now or is this a new installation?
What is cooling the rest of the machine?
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Heat Exchanger Sizing Question
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
RE: Heat Exchanger Sizing Question
During low load or cool weather the F-F was plenty of cooling (in cool weather even with the fan off).
When the outlet temp was too high the water flow valve opened to get us additional cooling.
This kept both units small and it minimized water use.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
RE: Heat Exchanger Sizing Question
Consider this resource about air cooler.
Pierre
RE: Heat Exchanger Sizing Question
I would have liked to see some closure on this one.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.