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-   -   difference betwen theory based solutions and numeric for heat tansfer (http://www.cfd-online.com/Forums/main/127607-difference-betwen-theory-based-solutions-numeric-heat-tansfer.html)

gokhanS December 15, 2013 19:29

difference betwen theory based solutions and numeric for heat tansfer
 
hi guys i have a problem with my basic analysis

my case is a simple recalculation of 2d puiseulle flow with numerical. i have surface domain 1m x 40m and i made laminar flow inside with changing velocity inlet. i added constant heat flux at top and bottom wall with same value, for example 10w/m2.

i expected that average outlet temperature have same value with calculated from theoritical equation. but it was not same.

M^dot(mass flow inlet) x Cp x (Toutlet - Tinlet) =Qdot(heat flux) x A (area)

in this equation with known mass flow inlet, Cp, heat flux and Tinlet, Toutlet can be calculated. But, calculating outlet temperature in cfd-post with drawing line at outlet and using calculator for average temp. at this line is not give same value with theory above.

so, what i still have missed, it is a very basic convection relation and it has to be give same results with any simple numerical case

Ahmed December 24, 2013 06:54

it is spelled
Poiseuille

How did you calculate the outlet average temperature?

Just to give you a tip, the left hand side of your energy balance is a thermodynamic relation, i.e. the temperatures there are Equilibrium Temperatures.


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