Numerical study of the heat transfer to carbon dioxide in horizontal helically coiled tubes under supercritical pressure

- Centrifugal Richardson number increases with increase of fluid temperature.
- The Nusselt number correlations are presented with a high accuracy.
- Pressure is affected by fluid temperature after pseudo-critical temperature.
- Pressure difference has the minimum values in pseudo-critical temperature region.
- The wall temperature and h close to inner region are lower than other regions.

The cooling heat transfer and pressure drop characteristics of supercritical CO2 in the horizontal helically coiled tube are numerically simulated using RNG k-ε turbulent model. The results show that the heat transfer coefficient and pressure drop in the helically coiled tube are larger than that in the straight tube because of the secondary flow. The heat transfer coefficient and pressure drop increase with the increase of mass flux and the peak value of heat transfer coefficient is shifted to high temperature region with the increase of pressure. The gravitational Richardson number decreases with the increase of the mass flux and the centrifugal Richardson number increases with the fluid temperature and mass flux increasing. The Nusselt number correlations are presented by using the numerical simulation values. The pressure distribution in helically coiled tube fluctuates from top to bottom like a wave because of the gravitational buoyancy force. When the fluid temperature is higher than the pseudo-critical temperature, the pressure is mainly affected by the fluid pressure and when the fluid temperature is lower than the pseudo-critical temperature, the pressure is mainly affected by the fluid temperature. The static pressure difference has the minimum values in the pseudo-critical temperature region. The wall temperature and the heat transfer coefficient close to the inner region are lower than the other regions.