FLAMES TEMPERATURE MEASUREMENT 2

[pyrometer]

I WOLD LIKE TO KNOW HOW I CAN MEASURE THE FLAMES TEMPERATURE USING A SUCCION PYROMETER, IS THERE A METHOD FOR IT? IS THERE A DETERMINATED ZONES TO PUT THE PYROMETER? THANK YOU I WAIT YOUR ANSWER, PLEASE IT IS URGENT!!!

 

[davefitz]

What is the specific application?

You can calculate the "adiabatic flame temperature" Tad knowing the fuel analysis and excess air. You can measure the fluegas temperature downstream of the flame Tfe using a suction pyrometer, and may need to add correction factors due to radiaton of heat from the shielded tip to the surrounding surfaces.

You can estimate the peak flame temperature Tmax either by a numerical model of the combustion chamber ( galerkin 3D cfd) or using simplified radiation zonal models, or by the use of the simplified "russian normative method" ( by a.g. blokh) , but these mthods presume you have avialable accurate values of some radiative properties, such as the complex index of refraction of the entrained flyash.

Ther may be other experimental techniques such as raman scattering or laser doppler methods.

 

[bonzoboy]

If the flame is visible (i.e. like a coal or oil flame), just use an optical pyrometer. It's quick and easy. Adiabatic flame temperatures are theoretical, and do not reflect the actual temperature that a reactor vessel may experience. Adiabatic would be the highest temperature possible, but not necessarily the correct temperature.

 

[athomas236]

I have come across methods that use the speed of sound as a way of calculating the average gas temperature along a line of sight.

athomas236

 

[davefitz]

athomas236:
Yes, the soundspeed would yield the average temperature across the furnace, but you would need to know the gas mixture molecular weight , and it does not yield the peak flame temp, only the avg temp.

bonzoboy;
The optical pyrometer may require an accurate input of gas or flame emmisivity. Also, most combusting gases behave as "participating media" and are partially opaque to infrared radiation and also tend to scatter radiation (if ash is entrained), so it is not clear if the temperature reading is of the flame or the temp of the gases in the boundary layer near the viewing wall.


As a check , the actual flame temp would need to be bracketed between adiabatic flame temp and the furnace exit gas temp, and modern numerical simulation programs should provide a reasonably accurate value .

 

[athomas236]

davefitz,

you are right of course, but what your answer to the question.

athomas236

 

[0707]

Hi PYROMETER
“When a bare thermocouple is introduced into a flame for the measurement of gas temperature, errors arise due to the irradiative exchange between the thermocouple and its surroundings. In the standard suction pyrometers a platinum-rhodium thermocouple, protected from chemical attack by a sintered alumina sheath, is surrounded by two concentric radiation shields. The gases are drawn between the shields and over the sheath with high velocity (min. 150 mls) so that the equilibrium thermocouple temperature is nearly that of the gases without the need for correction.
The gases are normally sucked in a dynamic position through a hole drilled at the side of the outer shield with the end of the shield closed with a cement plug.
However, when low dust concentrations are present in the flame, the hole can be placed in the wake of the shield to minimize blockage. Similarly, for highly solids laden jets, two holes may be drilled in the outer shield to allow large particles to flow directly through the shield without deposition.”

For better understanding of what is a suction pyrometer go to:

http://www.combustion-centre.ifrf.net/requipment/temperature-heat/suction_pyrometer.html

Regards
Luis Marques

 

[athomas236]

Luis

I tried the link, but it did not work. Is there another link?

athomas236