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# Calorimetry Under flow

07/22/2016 4:50 PM

I am planning a small thermal experiment where I will need to undertake some calorimetry of flowing air around a reactor that is being driven electrically at a known power input, although pulsed DC, and auxiliary pulsed negative DC on a secondary electrode will be used. That part seems pretty straightforward (until I actually capture the V and I waveforms, most likely).

I need to measure the heat being transferred to a current of air flowing around the reactor enclosure. Probably will use a computer fan, and may as first order approximation use the rated flow (cfm) of this fan to determine the heat removal from temperature in and out.

Question: Calibrate thermal mass flow by inserting a test load (with known applied DC power) into a flow tube in series with the fan's output. Temperature rise will give me the product of mass flow with heat capacity instantaneous (air + humidity) is the hypothesis. Will this work to periodically calibrate the device?

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#1

### Re: Calorimetry under flow

07/22/2016 6:43 PM

It will surely give you a baseline. Of course I have no clue in the world what you're trying to do? Is it bigger than a breadbox?

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#5

### Re: Calorimetry under flow

07/25/2016 10:32 AM

Yes, it is slightly larger than a breadbox. about 2.5 ft x 1.5 ft x 2 ft ht., with flow ports same size in and out, whether suction drafted or forced draft, I do not expect much difference, as the edges to reactor platform are to be sealed with weatherstrip. Probably will be slightly more accurate to use suction draft of the enclosure, although there is a slight heat contribution from the fan motor. That heat can be measured, and subtracted off the results.

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#2

### Re: Calorimetry under flow

07/22/2016 10:36 PM

I would use the highest temperature reading with a thermo-anemometer positioned in the air flow to set the base line for temperature and air speed.....possibly using a ducted flow...

https://pacer-instruments-usa.com/multi-function-instruments/da420-thermo-anemometer?gclid=CjwKEAjwiMe8BRD0ts3Vtv-ohWgSJAAZurk1P6NyNpxbMZZVLenFQAhN-U0HK3nGmyrc8dFnhcfhsRoCibfw_wcB

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#6

### Re: Calorimetry under flow

07/25/2016 10:35 AM

\$850 is just a tad more than I want to spend (at least at first) on this aspect of the project. The product of mass flow with incident heat capacity (includes whatever humidity or excess moisture gets into the flow), should be useful to me. However, any changes in moisture content of the air flowing through the calorimeter box does affect final reading in heat removed from reactor. I guess I need to ensure leak tight reactor, huh.

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#3

### Re: Calorimetry under flow

07/23/2016 2:32 AM

My biggest concern is how well you are able to accurately capture the variables. As I'm sure you know, quantifying how much heat is transferred to the air flowing past is not trivial.

I would suggest getting a totalized mass air flow over the duration of the experiment and have several temperature measurement points. Setting up the geometry and parameters as a simulation in a FEA-based software package would really give you an idea of where to place the sensors too.

Best wishes for success!

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#7

### Re: Calorimetry under flow

07/25/2016 10:39 AM

Thank Mikerho, the new digital 1 wire probes for Arduino make it possible to add as many temperatures to the profile as are deemed necessary. For now, the plan is KISS method, until we (I and me mouse) find issues that must be addressed.

If the COP (heat out total / energy in total) is greater than 1.5 it should not be that hard to find it. If COP is something like 0.95 then I have measurement issues, clearly. If COP is around 1.05 then the "myth" is busted, or no energy is being produced other than typical chemical and heat inefficiencies.

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#4

### Re: Calorimetry under flow

07/23/2016 7:47 AM

You might like to look at somehting like these from automotive.

http://www.autozone.com/engine-management/mass-air-flow-sensor

They are used to monitor inlet air temps for IC engines and installed into feedback loop to pre-heater elements.

I suggest that for your application that you would want one with the smallest mass element possible. Note that it would have to have an operating temperature above the maximum or your airflow so that it can operate.

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#8

### Re: Calorimetry under flow

07/25/2016 10:42 AM

Interesting. I noticed they come in various shapes, sizes, and prices, too. Obviously, the least expensive one is an automatic fit to my experiment.

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#9

### Re: Calorimetry under flow

07/26/2016 12:47 PM

James,

Let us know how this project proceeds. It would be great to see photos of the eventual setup.

Mike

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#10

### Re: Calorimetry under flow

07/26/2016 1:33 PM

As with most of my home projects, they end up on YouTube. I will make a short documentary before firing this thing up (so it will still be in one piece at the time).

I don' plan for the unit reactor to fail destructively, but it might, since alkaline attack of the polycarbonate vessel halves is likely. I might be able to incorporate some CR39 blanks into the upper vessel half for act as radiation track detector for Beta, Alpha emitted if any. Gas output line with incorporate a flash arrester to prevent ignition inside reactor volume.

Quick calculation of test heater:

1. 12 V supply

2. 50 Ohms test load (1% precision resistor), if found at correct wattage.

Power added = V2/R = 2.88 W

I think that could heat up the air from a smaller computer fan of say 50mm diameter, so the temperature difference will be significant.

If that does not work, there are always hair dryer elements, although I would not expect these to heat up fast enough, since the power will need to be in the form of a pulse lasting only a fraction of a minute.

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