Electrical Heating
Electrical Heating
(OP)
I'm looking for an equation that will give me the temperature of a heating element if I know the following:
- resistivity (in ohms mm^2/m)
- length (in meters)
- cross-sectional area (in meters or mm)
- power applied (in watts)
Do I need anything else? I'm trying to build a computer model. Thanks.
- resistivity (in ohms mm^2/m)
- length (in meters)
- cross-sectional area (in meters or mm)
- power applied (in watts)
Do I need anything else? I'm trying to build a computer model. Thanks.





RE: Electrical Heating
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Electrical Heating
RE: Electrical Heating
Emissivity of the element.
Emissivity of surfaces in direct view of the element.
Geometry and distances from element to surfaces in view.
Convective heat transfer coefficient between element and airstream.
RE: Electrical Heating
RE: Electrical Heating
Perhaps you need to download a textbook? http://web.mit.edu/lienhard/www/ahtt.html is free, as is OpenCourseWare: h
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Electrical Heating
Use Q(kW)*T(sec) = m(kg)Cp(kJ/kgC)(T1-T2)(C) to get the maximum temperature (if you have to get actual temperature, you should consider convective and radiation losses)
RE: Electrical Heating
quark: I don't have the specific heat, I have a resistivity. I'm basically building an electric heater and I need to know, based on the resistivity of the material, how hot it will get when power is applied.
RE: Electrical Heating
RE: Electrical Heating
What exactly is your academic status? For someone supposedly doing a Master's program, you seem to not know conservation of energy. I repeat my suggestion that you review the fundamentals of heat transfer.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Electrical Heating
RE: Electrical Heating
Energy in = Energy out + Energy stored
Energy stored is temperature on specific heat capacity.
For energy out you'll need the parameters that I listed above.
RE: Electrical Heating
RE: Electrical Heating
RE: Electrical Heating
and convection:
htt
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Electrical Heating
RE: Electrical Heating
As Quark correctly noted, you need to consider convection and radiation.
RE: Electrical Heating
h-bar = q/delta-T
where:
q = power/area
Can I use:
input power/area of element
in the calculation of h-bar? So say I have 4000 W going into an element of 4.7124E-3 m^2, so q = 8.4882E5 W/m^2, and delta-T = some theoretical maximum (say 1850-dec C) - some theoretical starting value (say 20-dec C), so delta-T = 1830-deg, giving an h-bar of 463.8361. I then calculate T = 1404.6K (using the calculations in Example 2.8), which I plug back into my delta-T and iterate to get a final T = 1271.4K = 998.4-deg C.
Does this make sense? Am I doing this correctly? The example iterates a temperature in calculating h-rad (again, I use the same theoretical maximum of 1850-deg C and a minimum of 20-deg C to do this and iterate with the 1404.6K), so that's how I came up with the idea to use theoretical values for the h-bar calculation and iterate. Thanks for the help with this.
RE: Electrical Heating
You really need to discuss this with your professor. This site is not intended for tutorials at this level.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Electrical Heating
RE: Electrical Heating
RE: Electrical Heating
RE: Electrical Heating
RE: Electrical Heating
"It should be a relatively easy problem if you took heat transfer, however, you have defined the problem well. For instance your OP did not state that it was ceramics you were heating; secondly you have not defined the size and position (horizontal, vertical,slanted, curved) of the ceramics; thirdly is the ceramic emitting on both sides or only one and what about the heated space or objects,what are they and how foar are they. Then you can start applyings the principles particularly those involving ratiation and convective heat transfer as aluded in the above replies."
RE: Electrical Heating
I am heating a ceramic element that is a tube folded in half. It will be emitting on both sides, but one side will be close to a wall. I know the emissivity, the thermal conductivity, and the specific heat capacity. What additional information do I need to solve this problem? Thank you.
RE: Electrical Heating
What comprises the wall surface (standard wallboard, or is it a metallic component?)
Cloa also mentioned other factors that need to be considered.
Is it possible to provide a sketch so we're all speaking to the same problem?
Otherwise, is this something where you can build a prototype and test? Being able to input real data into a program should make it easier to model the component's behavior under other conditions.
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.