Effect of radiation on thermocouple
Effect of radiation on thermocouple
(OP)
Hello
How can i find the effect of radiation on temperature measurement in high temperature stream with thrmocouple for example if i want to measure the high temperature of gas stream in a furnace with thermocouple without shield how much error arise due to the radiation
thx
How can i find the effect of radiation on temperature measurement in high temperature stream with thrmocouple for example if i want to measure the high temperature of gas stream in a furnace with thermocouple without shield how much error arise due to the radiation
thx





RE: Effect of radiation on thermocouple
TTFN
RE: Effect of radiation on thermocouple
RE: Effect of radiation on thermocouple
At those temperatures, radiation is just about all you measure.
RE: Effect of radiation on thermocouple
TTFN
RE: Effect of radiation on thermocouple
A combustion furnace is quite a complex environment from the heat transfer viewpoint. The combustion mass contains radiating solids and gases, as well as diathermic (infrared radiation-transparent) gases.
As for the temperature reading error, it all depends on the radiating enclosure; for example, whether the measuring thermowell "sees" a radiating flame or just cooler walls and tubes.
If we call temperatures
T1: the true gas temperature
T2: the temperature reading
T3: the enclosure temperature
T1-T2 = ΔT: the error
I think we could say that in the radiant section, where radiating flames are "seen" by the thermowell, T3>T2 ≥ or ≤T1, while in the convection section, T1>T2>T3.
As hacksaw says the convection heat transfer coefficient, hc, would be small in comparison with the radiant one, hr, at ~ 1100oC. Thus hT = hr + hc ≈ hr.
Have a look at Holman's Heat Transfer example 8-11 for an illustration. The exercise refers to air and a bulb thermometer, but it could also be applied to a thermocouple in a ceramic thermowell. The example refers better to the case of gases in the convection section.
RE: Effect of radiation on thermocouple
thx
RE: Effect of radiation on thermocouple
It all depends on the details of the thermal environment offered by your process.
There plenty of general responses to your question, but I think you are looking for those that can be substantiated. That requires more detail than is generally suited for this forum.
RE: Effect of radiation on thermocouple
>> The workpieces also see the thermal radiation, so the question is whether your measurement of the gas temperature alone is meaningful in the context of the process.
>> A decent thermal baffle is non-trivial. You need to allow access to the gas, but not the radiation. This generally requires a multilayer shield, with no direct line of sight of the furnace walls.
TTFN