Measuring Airflow

roasting & roastery operations

Measuring Airflow

Postby Phil Robertson on Sat Oct 17, 2009 10:57 pm

Is anyone measuring airflow on their roasting machines to ensure consistency from roast-to-roast? (i.e. as creosote builds up in the ducting, or if airflow is being changed between batches). If so, are you using a hand-held anemometer? Or something installed in the ducting? Where in the system are you taking measurements? What brands / models do people like...

Whichever airflow measurement tool we use would be measuring airflow on our UG15 and our 1-lb San Franciscan.

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Re: Measuring Airflow

Postby JackieBillings on Wed Oct 21, 2009 10:09 am

Yes! We measure the airflow on our UG-22. We have a gauge installed just before the fan casing. It's pretty sweet... it's a really great indicator of what is going on inside your machine in a way that your other controls are not. Our gauge is pretty standard... just a Magnehelic. But you should definitely do it. It's not an expensive modification and it will change the way that you roast.
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Re: Measuring Airflow

Postby Andre Vornbrock on Wed Oct 21, 2009 9:43 pm

Magnahelics are a great tool, and often used in the HVAC industry. They are known to be accurate and reliable, but as with any sensor it's a good idea to have a calibration plan to ensure it's reliability. Just be sure you get one that is scaled properly for your fan.
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Re: Measuring Airflow

Postby Phil Robertson on Thu Oct 22, 2009 8:17 am

Thanks for the responses Jackie and Andre. I had been looking at various anemometers and hadn't really consider just measuring pressure. They're certainly more cost-effective than the $600 hot-wire anemometers I've found.

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Re: Measuring Airflow

Postby calebnicholes on Thu Oct 29, 2009 7:02 pm

Great topic everyone! I have been thinking about how to do this for some time and have been considering using a Pitot tube to measure differential pressure.

It is important to note that Magnehelic's are not able to work effectively with air temperatures exceeding 150 degrees. It is therefore important to have enough tubing and enough distance from the hot roaster, to allow the air to cool off before it is measured by the magnehelic sensor.

Has anyone out there used the Pitot tube? I am wondering if Chaff will clog it up and whether it has any clear advantages over just the magnehelic. I'll have to call Dwyer about this.

For those who have used the magnehelics, does it not have to measure both a high and a low pressure, so you would need to place a tube both before and after the drum fan?

Any input on this is very much appreciated. We are getting ready to retrofit our Probat UG30 very soon.

Cheers,
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Re: Measuring Airflow

Postby jdavidwaldman on Sat Oct 31, 2009 12:52 pm

i spoke to their tech support guy last week for a good while, and he was very informed and helpful. he recommended, in the case of a roaster (mine a UG-15), to find a run ideally 6 or 8 feet (horizontal or vertical, presumably preferably vertical?), because temp is critical as you say. he recommended using metal tubing for the run from the pitot tube to the readout, thereby acting as a heat sink to lower the temp. their site is pretty useful [don't waste your time on the product selector, they admit it sucks] - i would be interested in which part numbers you choose to install. i have been playing with adjusting the airflow vent (by intuition and feel) at different times during each cycle (with good results), and i suspect the magnehelics will give me better understanding of measurable increases/decreases in flow when i make certain adjustments. exciting stuff.
... but how does it taste?
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Re: Measuring Airflow

Postby Andre Vornbrock on Mon Nov 02, 2009 1:30 am

Pitot tubes can be used to measure air velocity. It's basically just a tube that points directly at your flow, and another that gives you a static pressure at non flow. With the two you can calculate velocity.

If you want flow rate from there, just multiply by your area. Of course this gives you only a rough estimate of the actual amount of air going, because flow is not linear through a duct, you could be measuring the velocity at a high or low point. They make more complex flow stations and meters which average a number of these pitot tubes across the area of a duct.

Magnahelics should come with scaling for either static pressure, or velocity...but I'm not sure if any come with flow rates for typical duct sizes. In this case, I don't think static pressure really gives you much useful information.

As mentioned earlier, chaff might be a problem with this setup. If it completely blocks your pitot tube, it would be better as at least you'd know...but if small pieces get lodged in, you might have a hard time keeping it clean. I'd try some different sizes and go from there, hopefully you can find something to work.
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Re: Measuring Airflow

Postby Jimmy Oneschuk on Fri Dec 10, 2010 11:38 pm

Sorry to revive a long-dead thread, but out of curiousity, what sort of numbers did you guys end up figuring out for airflow?

I'd be curious to see how the different manufacturers stack up with their measurements, and measuring in different locations, such as where the exhaust terminates from the roaster into the chimney, through the trier, etc. Of course, numbers are likely to vary when you measure smaller roasters against larger, if you're measuring with varying amounts of coffee in the drum...

Thanks for the thread - it has been highly illuminating!
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Re: Measuring Airflow

Postby Jimmy Oneschuk on Tue Jun 28, 2011 8:45 am

An addendum to this thread for others in my newb position, after getting my hands a little more dirty, I've discovered indeed, airflow can be too much of a good thing. That is, high airflow can mean heat is being sucked out of the drum faster than it can be charged, in certain instances.
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