Direct numerical simulation of supercritcal flows in developing pipes

Turbulent heat transfer characteristics of supercritical pressure fluids are quite different from those of subcritical pressure fluids. Experimental studies showed that heat transfer to supercritical fluids can exhibit dramatic heat transfer deterioration or enhancement. These phenomena lead to the presence of local minima/maxima in heat transfer coefficients or wall temperatures along a heated surface. In nuclear reactors the prediction of wall temperature is of paramount importance to improve the safety and performance of the nuclear power plants. We perform Direct Numerical Simulation (DNS) of a heated pipe flow to study in detail the occurring mechanisms leading to the heat transfer deterioration. The simulation is such, that the temperature within the flow domain incorporates the thermodynamic region where large thermophysical property variations occur (figure1). Figure 2 shows an instantaneous enthaply distribution within a heated pipe flow simulation. 

 

 
Fig. 1: Normalized thermophysical properties of CO2 at 80 bar as a function of temperature. (b) Temperature-entropy diagram of CO2 indicating the liquid and vapor saturation lines and an isobar at 80 bar. The critical conditions for CO2 are 31.1 C and 73.9 bar.
 
 
Fig. 2: Result showing the enthalpy (top and middle) and axial velocity (bottom) of a heated pipe flow of CO2 at supercritical pressure (Re*=360)