difference betwen theory based solutions and numeric for heat tansfer

gokhanS · December 15, 2013, 18:29

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, 05:54

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.

December 15, 2013, 18:29	difference betwen theory based solutions and numeric for heat tansfer	#1
gokhanS New Member Gökhan Join Date: Dec 2012 Posts: 5 Rep Power: 13	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

December 24, 2013, 05:54		#2
Ahmed Senior Member Ahmed Join Date: Mar 2009 Location: NY Posts: 251 Rep Power: 18	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.