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# measure flow rate

Member Posts: 1,790
If you know the flow and delta-T on one side of the heat exchanger, you know how much heat is being transferred. Then if you have the delta-T on the other side of the heat exchanger, you can calculate the flow rate from the heat transfer on the other side and delta-T on that side using GPM=(heat transferred)/(500*dT) For glycol solution, apply a coefficient (given by the manufacturer) to the "500" to account for reduced heat capacity. It would be somewhat approximate, but probably pretty accurate. It just saves the cost of installing two flow meters, but if the cost of the extra meter is not a concern, two would be nice. Also verify the accuracy of the rotameter design for the viscosity of the glycol solution. The Pentair meters should be ok for up to 50% glycol solution above 70°F or so.

• Member Posts: 16
measure flow rate

is there a gauge to measure the flow rate into a heat exchanger? I ordered one which will just meet my requirements if I can keep my flow rates at or below 2 gpm
• Member Posts: 1,320
Without the special fittings...

that have gage taps across the fitting, it is hard; but not impossible.

What tool did you order?

• Member Posts: 16

I meant I ordered a flat plate heat exchanger that just met my requirements. That' why I want to measure the flow rate. It had to be 2-2.5 gpm on either side to get the output I need.
• Member Posts: 236
Flow

Would a higher flow rate not work with a smaller delta-T? Are you trying to maintain a particular outlet temperature?

Pentair makes good rotometers to measure flow rates accurately. The nice part is, with four thermometers and one flow meter, you can tell the flow rates on each side (by backing out the flow from the delta-T on the flowmeter-less side) and heat transfer at any moment.
• Member Posts: 16

the Flat Plate exchanger I bought doesn't leave me any wiggle room with flow rates. I've entered many different variables in the design conditions but it only seems to work with 2-2.5 gpm. I like your idea of 4 temp gauges and a flow meter. I'll check that link you sent. Thanks
• Member Posts: 16

Andrew, could you elaborate a bit more on how to set up the flow meter and temp gauges so as to measure flow on either side? I'm not sure what you mean by "backing out the flow from the delta T"
• Member Posts: 16

I understand now. thanks for taking the time to explain.
Peace, Tom
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