Numerical investigation of supercritical heat transfer of water flowing in vertical and horizontal tube with emphasis of gravity effect

Abstract

Over a decade, coal-based thermal power plants are upgraded to operate at supercritical pressure conditions due to its high efficiency and low emissions. Water wall panels of a typical supercritical boiler are structured spirally in the lower furnace and vertically placed in the upper furnace. The spiral tubes are inclined at 19 to 22 degrees in which fluid behaves as in horizontal tubes. The design of water wall panels plays the key role in designing a supercritical boiler. The present work aims to numerically investigate the heat transfer behavior of both vertical and horizontal tubes at the supercritical conditions. Since the temperature distribution across the cross-section of vertical tube is uniform, a 2D axis symmetry tube has been considered for analyzing the vertical tube. Unlike vertical tube, the heat transfer characteristics is different for horizontal tubes. Therefore, a 3D tube has been modelled for the computation of horizontal tubes. In order to gain confidence, the present simulations are validated with experiments results available in the literature. Ansys-Fluent has been used in the present simulation. SST k-ω turbulence model is used in this analysis. In the present work, 10 mm diameter of 4m length of vertical tube has been chosen and simulated at low heat flux to mass flux ratio 0.27 and high heat flux to mass flux ratio 0.67 with pressure 241 bar. The effect of heat flux (q) to mass flux (G) ratio which is responsible for heat transfer enhancement and heat transfer deterioration has been studied for both vertical and horizontal tubes. The wall temperature has been plotted along the length of the tube for both top and bottom portion of horizontal tube and compared with wall temperature of vertical tube. The effect of buoyancy plays a vital role in the heat transfer behavior of horizontal tube compared to vertical tube. Heat transfer deterioration occurs due to buoyancy which has a direct linkage with gravity. Three cases were studied, one with full gravity (factor 1), half gravity (factor 0.5) and zero gravity (factor 0). It has been observed that, sudden rise in wall temperature occurs for the case gravity factor 1.0, i.e, considering the gravity effect. For the case of zero gravity, no sudden peak of local wall temperature is observed due to the absence of buoyancy term in the Navier-Stokes equations. Some of the thermo-physical properties like velocity, turbulent kinetic energy, density, wall temperature and turbulent viscosity are analyzed for three cases.

Keywords

• Supercritical heat transfer
• Horizontal tube
• Buoyancy
• Heat transfer deterioration
• Turbulence model

References

1. [1] Lei X, Li H, Zhang, W, Dinh T, Guo Y, Yu S. Experimental study on the difference of heat transfer characteristics between vertical and horizontal flows of supercritical pressure water. Applied Thermal Engineering 2017;113:609–620. [CrossRef]
2. [2] Rowinski M, Zhao J, White T, Soh Y. Numerical investigation of supercritical water flow in a vertical pipe under axially non-uniform heat flux. Progress in Nuclear Energy 2017;97:11–25. [CrossRef]
3. [3] Bazargan M, Fraser D, Chatoorgan V. Effect of buoyancy on heat transfer in super critical water flow in a horizontal round tube. Journal of Heat Transfer 2005;127:897–902. [CrossRef]
4. [4] Belyakov II, Krasyakova LY, Zhukovskii AV, Fefelova ND. Heat transfer in vertical risers and horizontal tubes at supercritical pressure. Teploenergetika (Thermal Engineering) 1971;18:39–43.
5. [5] Yamagata K, Nishikawa K, Hasegawa S, Fujii T, Yoshida S. Forced convective heat transfer to supercritical water flowing in tubes. Int J Heat Mass Transfer 1972;15:2575–2593. [CrossRef]
6. [6] Adebiyi GA, Hall WB. Experimental investigation of heat transfer to supercritical pressure carbon dioxide in a horizontal pipe. Int J Heat Mass Transfer 1976;19:715–720. [CrossRef]
7. [7] Shang Z, Yao Y, Chen S. Numerical investigation of system pressure effect on heat transfer of supercritical water flows in a horizontal round tube. Chemical Engineering Science 2008;63:4150–4158. [CrossRef]
8. [8] Shang Z, Chen S. Numerical investigation of diameter effect on heat transfer of supercritical water flows in horizontal round tubes. Applied Thermal Engineering 2010;31:5732. [CrossRef]

9. [9] Koshizuka SN, Takano N, Oka Y. Numerical analysis of deterioration phenomenon in heat transfer to supercritical water. Int J Heat Mass Transfer 1995:38:3077–3084. [CrossRef]
10. [10] Jaromin M, Anglart H. A numerical study of heat transfers to supercritical water flowing upward in vertical tubes under normal and deteriorated conditions. Nuclear Engineering and Design 2013;264:61–70. [CrossRef]
11. [11] Wen QL, Gu HY. Numerical simulation of heat transfer deterioration phenomenon in supercritical water through vertical tube. Annals of Nuclear Energy 2010;37:1272–1280. [CrossRef]
12. [12] Cai C, Wang X, Mao S, Kang Y, Lu Y, Han X, et al. Heat transfer characteristics and prediction modelof supercritical carbon dioxide (SC-CO2) in a vertical tube. Energies 2017;10:1–21. [CrossRef]
13. [13] Mokry S, Pioro I, Farah A, King K, Gupta S, Peimana WP, et al. Development of super critical water heat-transfer correlation for vertical bare tubes. Nuclear Engineering and Design 2010;241:1126–1136. [CrossRef]
14. [14] Mokry S, Pioroa I, Kirillov P, Gospodinov Y. Supercritical-water heat transfer in a vertical bare tube, Nuclear Engineering and Design 2019;240:568–576. [CrossRef]
15. [15] Yıldız S. Investigation of natural convection heat transfer at constant heat flux along a vertical and inclined plate. Journal of Thermal Engineering 2018;4:2432–2444.
16. [16] Shang Z, Yao Y, Chen S. Numerical investigation of system pressure effect on heat transfer of supercritical water flows in a horizontal round tube. Chemical Engineering Science 2008;63:4150–4158. [CrossRef]