Heat transfer Calculation
Heat transfer Calculation
(OP)
Is it possible to calculate the cold face temperature of insulation panel knowing :
k (W/m.K) thermal conductivity
A (m2) Area
Th (K) Hot Face Temperature
x (m) wall thickness
I don't know:
Q (W) Heat Transfer
Tc (K) Cold Face Temperature
Guess I need to use Fourier's equation:
Q=k.A(Th-Tc)/x
BUT I NEED SOMETHING MORE...
another equation?
Thanks
k (W/m.K) thermal conductivity
A (m2) Area
Th (K) Hot Face Temperature
x (m) wall thickness
I don't know:
Q (W) Heat Transfer
Tc (K) Cold Face Temperature
Guess I need to use Fourier's equation:
Q=k.A(Th-Tc)/x
BUT I NEED SOMETHING MORE...
another equation?
Thanks





RE: Heat transfer Calculation
Tobalcane
"If you avoid failure, you also avoid success."
RE: Heat transfer Calculation
TTFN
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RE: Heat transfer Calculation
Twoballcane, thanks for the reply.
So ignoring radiation I need to calculate the composite Heat transfer (cond+conv) & from this get the cold face temp.
CONDUCTION CONVECTION
k,W/mK h,W/m2K
x,m A,m2
A,m2
|/////////|
|/////////|
|/////////|
Thot,K |/////////| Tcold,K ========> Tamb,K
|/////////|
|/////////|
k.A.(Thot-Tcold)
Qcond=--------------- Qconv=A.h.(Tcold-Tamb)
x
REScond=x/(k.A) RESconv=1/(h.A)
Thot-Tamb Thot-Tcold
Qcomposite= ------------------- = ------------
REScond+RESconv REScond
A.k.Thot-x.Qcomposite
Tcold=----------------------
k.A
RE: Heat transfer Calculation
Right now you've got two many unknowns to solve your problem. As a first approximation, just worry about the conduction through the insulation and set Tcold equal to Tambient and calculate Q.
I'd also point out that in the equation at the bottom of your second post, the terms "A.k" and "k.A" would cancel.
However, assuming that this is a work problem, the easiest way to solve the problem would be by direct measure.
If it's not a work problem, and you're more a car enthusiast, I'd recommend that you think about why car manufacturers wouldn't add insulation to their car exhaust.
Patricia Lougheed
******
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RE: Heat transfer Calculation
Your algebra at the bottom seems wonky. It should be:
stuff1*(Thot-Tcold)=stuff2(Tcold-Tamb), solve for Tcold:
Tcold = (stuff1*Thot+stuff2*Tamb)/(stuff1+stuff2)
TTFN
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RE: Heat transfer Calculation
KKolev, I think one of your Ak is suppose to be Ah, but in any case, you have to find q for the system. Thus this will equal the sum of the resistance (conduction plus convection) times the internal wall temp mines ambient temp. Once you find q, you can recalculate either the conduction or convection alone and get the external wall temp. Your biggest challenge will be to calculate h.
Tobalcane
"If you avoid failure, you also avoid success."
RE: Heat transfer Calculation
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Heat transfer Calculation
Tobalcane
"If you avoid failure, you also avoid success."
RE: Heat transfer Calculation
But, once you have the temperatures, the Q can be calculated and compared against any other data or experience you might have.
TTFN
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RE: Heat transfer Calculation
The cold wall temperature will depend on the data you have (except for the surface area, which is not relevant), plus the mechanism for removing heat from the cold wall.
For example, if the cold wall is connected to ordinary air, and temperatures are moderate, then the cold wall temp will have one solution, somewhat higher than the ambient air temperature. Qdot = Hcair * (Tcoldwall - Tair ambient), Hcair is generally small.
If the cold wall is connected to a highly turbulent flow of cooling water, then the cold wall temperature would usually be very close to the water temperature. Qdot = Hcwater * (Tcoldwall - Twater ambient), Hcwater is generally large.
If the cold wall is connected to ordinary air, and temperatures are high, then the cold wall temp will again have one solution, somewhat higher than the ambient air temperature, but with both convective and radiation heat transfer mechanisms. Qdot = Hcair * (Tcoldwall - Tair ambient) + Emissivity * (Tcoldwall^4 - Tambient^4)
For any of these cases, the fundamental equations dictate that the specific heat transfer via conduction through the insulation will be set equal to the heat removal from the cold surface via its various mechanisms. A unique Tcoldwall exists for each condition.