This method is called a Hot-wire manometer, more airflow equals less
heat transfer between a heat source and a thermal sensor (Thermocouple,
Thermistor..). A similar method is also commonly used in high vacuum
systems to determine the absence of atmosphere called a Hot-wire anemometer.
73,
K4GVT
On 4/15/2011 4:23 AM, Dr. David Kirkby wrote:
> On 04/13/11 07:24 PM, Jim Barber wrote:
>> I wonder if a hand-held anemometer would have significant back pressure?
> I would not think it be very significant myself.
>
>> It's fairly easy to convert flow rate to volume if the duct size is known.
>> Inexpensive units go for 20-30 USD on eBay.
>
> My ex-boss (Prof. D. T. Delpy) used a technique for measuring air *velocity*,
> which I don't think is particularly relevant here, but I'll describe it since
> it
> is quite interesting. Although it used platinum wires, I suspect you could use
> copper, though I do see platinum would have some advantages.
>
> It was used for measuring the speed babies breathed out air, so had to have
> negligible restriction on the airflow. Using a plastic bag would not have been
> very good for this purpose!
>
> Going left to right there is:
>
> Source of air ---> heater ----> thermometer
>
> 1) The source of air. This was the babies mouth.
>
> 2) Heater. This is a thin platinum wire through which a short pulse of high
> current is passed. I've no idea of the temperature the wire reached, but it's
> not important to know the temperature.
>
> 3) Thermometer. This is another thin platinum wire, forming part of a platinum
> resistance thermometer. This responds very rapidly to temperature changes.
>
> The time between heating the first platinum wire, and when the temperature
> increase was observed on the second is measured. Knowing the distance between
> the two wires and the time allows one to calculate the velocity.
>
>> The "Bagometer" method is straightforward as well; just curious about
>> alternatives.
> Well, above is a curious alternative, though not very useful in this
> application.
>
> I'd be surprised if this technique was not described in some medical journal
> by
> him, but a quick glance with Google Scholar was unable to unearth the paper.
>
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