[tjushang]

Hi everyone,

Recently I carried out a numerical simulation using Star-CCM+ which can be described as following:

A cube is put on a cooling plate with rectangular channels. A total heat source of Q1 is set on the cube. The fluid inside rectangular has an inlet mass flow rate of m, inlet temperature of Tin, outlet temperature of Tout. The specific heat of fluid is represented as Cp. Thus the heat taken away by fluid can be calculated by Q2 = Cp * m * (Tout - Tin) in steady state. Other boundaries other than inlet and outlet are all set as adiabatic.

If the described case reaches steady state, then Q1 = Q2 in theory.

However, The calculated result shows that Q1 is smaller than Q2. As mass flow rate grows smaller, the gap between Q1 and Q2 become greater. Even if I refined the mesh and set boundary layer of fluid, the gap still remains and becomes even larger.

I also check the heat from cooling plate internal surface to fluid Q3, which matches perfectly with Q1. So I guess there has to be issue of calculation of Q2.

I wonder if this is caused by numerical errors or by inappropriate models. The models I chose are:
segregated flow
k-epsilon turbulence model
segregated fluid temperature
conjugate heat transfer
I use surface average temperature of outlet boundary as Tout.

Can someone enlighten me why the gap exists? I'd be quite grateful.