# Energy balance in conjugative/ porous simulation; Domain Energy is greater than Input

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 November 29, 2017, 18:18 Energy balance in conjugative/ porous simulation; Domain Energy is greater than Input #1 Member   VB Join Date: Jul 2016 Posts: 35 Rep Power: 9 Hello people, As a result from another thread I use massFlowInt(Total Enthalpy)@Inlet and massFlowInt(Total Enthalpy)@outlet in order to measure Total Energy passing through Inlet and outlet surface areas. I have a fluid-- Porous--fluid, domain in the sequental order with squrare cross section. I performed a transient simulation of Total time = 5hr. I used volumeInt(density*Static Enthaly)@domain to calculate the Energy after simulation. I found the energy(in J) in porous is greater than the accumulated sum of Energy through inlet face considering losses. So, I tried the same setup and checked the values after Iteration 1 and the energy in Porous is greater than the Energy at Inlet. Is it over predicts? The conditions were 1 kg/s @ Inlet at 500 deg C; "0" Pa releative pressure @ outlet. Transient simulation with time step = 20sec, Total time = 5 hr(900 Iterations in total), I stopped at Iteration 1 and checked the Energy values at Porous using volumeInt(density*Enthalpy) which was higher than the Energy through the Inlet face. The values are given below: massFlowInt(Total Enthalpy)@Inlet = 266166 W. so, (time step)20sec*massFlowInt(Total Enthalpy)@Inlet = 31933920 J; volumeInt(density*Static Enthalpy)@Porous = 94102500 J. Am I using wrong formulas? I even tried subtracting the Energy that might be present at the Initialization temp 25 C but even then Porous Energy was way higher than Energy supplied through Inlet. Any setup tweaks necessary? I tried with both fluid and solid densities in the expression volumeInt(density*Static Enthalpy)@domain but still it is way higher.. Suggestions are highly appreciated?

 December 4, 2017, 17:25 #2 Senior Member   Join Date: Jun 2009 Posts: 1,770 Rep Power: 31 How are you accounting for the porosity in your formulas? I would check the case for Volume Porosity = 1 first and see if the problem persists. If it does not, then you know you are missing the porosity contribution to the integrals somewhere.

June 27, 2018, 11:08
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Gioacchino La Rochelle
Join Date: Jul 2016
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Quote:
 Originally Posted by Vishnu_bharathi Hello people, As a result from another thread I use massFlowInt(Total Enthalpy)@Inlet and massFlowInt(Total Enthalpy)@outlet in order to measure Total Energy passing through Inlet and outlet surface areas. I have a fluid-- Porous--fluid, domain in the sequental order with squrare cross section. I performed a transient simulation of Total time = 5hr. I used volumeInt(density*Static Enthaly)@domain to calculate the Energy after simulation. I found the energy(in J) in porous is greater than the accumulated sum of Energy through inlet face considering losses. So, I tried the same setup and checked the values after Iteration 1 and the energy in Porous is greater than the Energy at Inlet. Is it over predicts? The conditions were 1 kg/s @ Inlet at 500 deg C; "0" Pa releative pressure @ outlet. Transient simulation with time step = 20sec, Total time = 5 hr(900 Iterations in total), I stopped at Iteration 1 and checked the Energy values at Porous using volumeInt(density*Enthalpy) which was higher than the Energy through the Inlet face. The values are given below: massFlowInt(Total Enthalpy)@Inlet = 266166 W. so, (time step)20sec*massFlowInt(Total Enthalpy)@Inlet = 31933920 J; volumeInt(density*Static Enthalpy)@Porous = 94102500 J. Am I using wrong formulas? I even tried subtracting the Energy that might be present at the Initialization temp 25 C but even then Porous Energy was way higher than Energy supplied through Inlet. Any setup tweaks necessary? I tried with both fluid and solid densities in the expression volumeInt(density*Static Enthalpy)@domain but still it is way higher.. Suggestions are highly appreciated?

Hello,
I've have a very different problem but trying to use the same formulation you type to figure the energy balances out.
Have you tried to check the differences between the 'Hybrid' and 'Conservative' scheme while evaluate such quantities? (referring to the Calculators tool of CFX-post).

 Tags cfx, energy balance, porous heat transfer, thermal energy