# energy equation in terms of entropy

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 September 18, 2008, 06:37 energy equation in terms of entropy #1 kiran Guest   Posts: n/a Hi is it possible to have energy equation in in terms of entropy. thanx.

 September 18, 2008, 10:09 Re: energy equation in terms of entropy #2 mettler Guest   Posts: n/a just as a quick thought: I know you can get it in terms of enthalpy and enthalpy has Q, which is in the entropy integral. I have never seen it or derived, so I am not sure if there would be any snares when trying to derive it.

 September 19, 2008, 04:56 Re: energy equation in terms of entropy #3 Paolo Lampitella Guest   Posts: n/a Of course, it is. It should be (for a Newtonian - Fourier fluid): rho * T * DS/Dt = div(Kh * grad(T)) + k * div(u)^2 + 2 * mu * (Sij - 1/3 * div(u) * dij) * (Sij - 1/3 * div(u) * dij) + rho * E where: rho = density mu = dynamic viscosity u = velocity vector S = entropy E = source term DS/DT = dS/dt + div(uS) = material (or substantial) derivative Kh * grad(T) = thermal flux (following fourier) k = lambda + 2/3 * mu = bulk viscosity (usually set to zero following Stoke's Hypotesis) dij = i,j component of the Kronecker's delta tensor Sij = 1/2 * (dui/dxj + duj/dxi) = i,j component of the symmetric part of grad(u) (Sij - 1/3 * div(u) * dij) * (Sij - 1/3 * div(u) * dij) = Aij * Aij = trace of the tensor A*A (A squared) It is difficult to distinguish the different operators but should be clear

 September 20, 2008, 05:49 Re: energy equation in terms of entropy #4 Ahmed Guest   Posts: n/a The Energy equation, is a statement of the first law of thermodynamics,i.e. the principle of conservation of energy, on the contrary, entropy, is a property of matter that is always increasing as long as there is a change of state. You can write a transport equation for the entropy (Check the book bt Vedat Arpaci Convection Heat Transfer)but not a conservation principle. I hope you get the picture and see the difference. Good luck

 September 20, 2008, 06:11 Re: energy equation in terms of entropy #5 Paolo Lampitella Guest   Posts: n/a Of course, i was not clear about this. This is a second law of thermodynamics statement, nothing to do with first law. In fact, the equation writed is not a conservation principle.

 September 22, 2008, 10:52 Re: energy equation in terms of entropy #6 Kiran Guest   Posts: n/a Hi, Thanks a lot !!!