Prediction of turbulent convective heat transfer to a fluid at supercritical pressure in square and triangular channels

Abstract

The paper presents results obtained on the prediction of three-dimensional turbulent heat transfer to CO 2 at supercritical pressure, flowing upward through heated vertical passages of non-circular cross-section. The problem is relevant to certain technical applications, including the cooling of fuel bundles in supercritical water nuclear reactors. Several k– ε turbulence models, implemented in the FLUENT code, are used; they include low-Reynolds number formulations and an RNG k– ε model with a two-layer near wall treatment. The reference experimental data are from a recent published study in which CO 2 at supercritical pressure was used to cool uniformly heated channels of triangular and square cross sections. In keeping with previous work on circular ducts, the results obtained using the low-Reynolds number models were able to reproduce the trend of heat transfer deterioration due to buoyancy influence, but with a relatively large overestimation of measured wall temperatures. On the other hand, the RNG model with the two-layer approach was unable to capture even the expected qualitative trends. The results obtained in the current study are useful in confirming the mechanisms of heat transfer deterioration and also highlight interesting three-dimensional features related to flow redistribution under strong buoyancy forces.