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## #1 2019-11-06 08:30:21

maxmss
Member
Registered: 2019-09-03
Posts: 25

### what are the correct units for COEF_H of ECHANGE_PAROI?

Hello everyone,
I want to add a heat exchange between two surfaces in my heat transfer analysis. Im using ECHANGE_PAROI and I must give three data, two meshes that correspond to the thermal contact surface and a heat exchange coefficient (COEF_H).

The value of COEF_H can be obtained with the formula:
H = W/A,
where W is the thermal contact conductance (watt/ kelvin) and A is the thermal contact surface (m^2).

The question is, for code_aster the area is implicit?, that is, only give to aster the value of W (thermal contact conductance w/k) and aster  automatically recognize the area of heat exchange given the two meshes (case 1 ) or give the value of H calculated with the above formula (case 2)?

example:
if  Area =  3.97e-3 m^2  and  W = 0.0017 (w/k)

case 1
H = W = 0.0017 (w/k)

case 2
H = W / A =(0.0017/3.97e-3)  = 0.434 (w/m^2 k)

the reason of this question is because code aster defines the radiation by rad = sigma*epsilon*(Text^4 - T∞^4)
and not by  rad = sigma*epsilon*Area*(Text^4 - T∞^4)

what is the correct way to apply heat exchange between two surfaces?

best regards,
Max

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