I would like to measure the air pressure in our furnace at temperature above 800C. Any equipment and method are suitable? Thank you for advance for your advice
I would like to measure the air pressure in our furnace at temperature above 800C. Any equipment and method are suitable? Thank you for advance for your advice
Hi Simon.
Thank you for your answer.
Our furnace is not totally environmentally sealed, but I wonder if the pressure inside the furnace equals ambient room pressure, because the difference in temperature and also the movement of air from the bottom to the top in the furnace. Is any method to measure the pressure inside the furnace directly? Thank you.
Hi Baoliang,
You can use the ideal gas laws for estimating the pressure difference between the hot and cold zones of the furnace by:
1. first measuring the temperature difference
2. calculating the pressure nRT/V for the volume of the furnace.
As you see, all other things being equal, i.e. the volume is fixed, and 'n' is fixed, the ratio of the pressures will equal that of the absolute temperatures. So, if your furnace is at 800 C, then a 10 deg C difference in hot and cold regions will only result in a 0.93 % difference in pressure, in other words, a small difference.
If you want to really measure the pressure difference, you can buy inexpensive manometers (analog or digital) and feed the head into the furnace through using a feedthrough. You just have to make sure that they are sensitive enough to pick up the small pressure differences that you are looking for.
Yes, Simon, I was just suggesting to Baoliang, that the pressure difference can be estimated using the approximation of a sealed vessel, just to demonstrate to him that the pressure difference he should be expecting is small even if the vessel was sealed. For his case, the pressure difference should be even less. Just trying to help him think this through before he gets too invested in an issue that may be unimportant.
Hi Baoliang, if you do want to measure the pressure within your furnace enclosure there are several companies that can supply you with devices capable of doing this even at 800C as many industrial facilities that have boilers, heaters, and furnaces, which have their heating enclosoures/housings operating at or even above this temperature, have draft sensors installed on the housing of the heater assembly to measure the internal pressure (which can actually vary quite alot and something that can affect the performance of gas fired/flame burners but these pressures are still rather low like at several inH2O at the most, this is even for vacuum or positive pressure depending on the type of heating system [i.e., natural, induced, or forced draft] and location within the heating enclosure this measurement is being taken).
You can just search for manometers or magnahelics for heaters, boilers, or furnaces on the web and you will probably find several companies to buy such an instrument from. Dwyer is a company that I have used in the past to buy such magnahelic devices from which seem quite reliable although these might be kind of expensive for installing on natural and induced draft gas fired furnaces. They can be found on the web at: http://www.dwyer-inst.com/
You might even consider trying to make your own manometer a simple design can proabably be found on the web also where you can use a non-volatile alcohol or other liquid as the sensing media for determining the pressures. You would have to setup a sight gauge type apparatus with this and then calibrate it yourself but not impossible. Also, you will need to have a port location on the heating enclosure to set the meter of the instrument (regardless of the type you go with, i.e. your own homemade one or a commercial one you purchase) on the outside so this is not exposed to the heating conditions and then have a sensing element the will feel/see the heating conditions and report back to the meter installed outside of the heater. Typically this consists of simply using gas sensing lines but care needs to be taken in both their design and installation to make sure that the measurement you are making is reliable.
Hope this helps,
Jacob H. Prosser
It is very easy if you have a connection with your working zone by a tube (quartz glass, inox or anything else which is not destoyed by temperature) with the room temperature zone. You can use any manometer (Bourdon, U tube, piezo...) you want since the pressure is transmitted (is the same that inside your working zone).
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