# Nusselt calculation

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 November 6, 2019, 10:57 Nusselt calculation #1 Member   ... Join Date: May 2018 Posts: 37 Rep Power: 7 hi every body i need to determine the local Nusselt number in vertical channel and then plot the nusselt versus length of the channel by openfoam but i dont know do it how can i preform it? (the wall of this channel under condition of constant heat flux and phase change occures) any help, comment and reply would be appreciated thanks in advance

 November 10, 2019, 14:35 #2 Member   ... Join Date: May 2018 Posts: 37 Rep Power: 7 any help, comment and reply would be very very appreciated

 November 15, 2019, 09:16 #3 New Member   Kevin Join Date: May 2018 Posts: 6 Rep Power: 7 I'm not sure I got it right, but that could be a solution. If it's ok with you, if you calculate it at the end. Choose your location where you want to determine the nusselt number. Add some lines in a sampleDict (you dont need the line data but the wall temperature is the first entry of the line). For example the nusselt number at location y=0.1 and 0.2. Code: ```type sets; interpolationScheme cellPoint; setFormat raw; writeControl runTime; writeInterval 1; fields ( TMean //or T ); TYPE lineUniform; sets ( s00 { type \$TYPE; axis distance; nPoints 3000; start (0.0 0.1 0.0); end (0.01 0.1 0.0); } s01 { type \$TYPE; axis distance; nPoints 3000; start (0.0 0.2 0.0); end (0.01 0.2 0.0); } )``` With the wall temperature at a certain location T_w,i, the mean temperature of the flow T_m and the given heat flux at the wall q_w you can determine your local heat transfer coefficient alpha_i alpha_i = q_w / (T_m - T_w,i) And your local nusselt number Nu_i = (alpha_i * D_h) / lambda If you need a time evaluation you can also include the sampleDict in the controlDict and write the wall temperature at certain times. But still, this is a simple post processing solution. You need to calculate it afterwards, which could be time consuming if you need your local nusselt number at many time steps. regard likes this.

 November 15, 2019, 10:10 #4 Member   ... Join Date: May 2018 Posts: 37 Rep Power: 7 very very thanks for your kind reply I use the swake for calculate the heat transfer coefficient in your idea this code can be corrected? thanks in advance code: (q=30000) h1 { type swakExpression; valueType surface; surfaceName X1; surface { type plane; basePoint (0 0.1 0); normalVector (0 1 0); interpolate true; } verbose true; variables ( "T_inf=sum(U.y*Sf().y*T)/sum(U.y*Sf().y);" "Ts{patch'heater}=sum(T*area())/sum(area());" ); expression "30000/(Ts-T_inf)"; accumulations ( average ); //writeSurfaceOnConstruction true; // autoWriteSurface true; //surfaceFormat vtk; outputControlMode timeStep;//outputTime;// outputInterval 10; //writeStartTime no; }

 Tags nusselt calculation, nusselt local