| Advances in energy technology require efficient heat transfer of organic working fluids during condensation,so the mechanism of condensation heat transfer of organic working fluids in conventional scale channels and the research and development of enhanced heat transfer technologies have been one of the key research topics in the field of energy technology.In this paper,a flow condensation test rig for organic working fluid R245fa was designed and built in order to improve the condensation heat transfer of organic working fluid R245fa in inclined tube.Based on the operation parameters of submarine hydrothermal organic Rankine cycle power generation system,the phase change heat transfer of R245fa flow condensation and header separated liquid condensation in inclined tube was studied experimentally and numerically.The experimental results of flow condensation show that the smooth laminar flow disappears and the region of laminar flow decreases with increasing bank angle.The total pressure drop of condensation increases nonlinearly with the increase of mass flow density.when the mass flow density is less than 200 kg/m~2·s,the total pressure drop of each inlet vapor quality condition approaches.The total pressure drop increases slowly when it is less than the critical vapor quality,and rapidly when it exceeds the critical vapor quality.The total pressure drop does not change significantly with increasing inclination.The average condensation heat transfer coefficient increases with mass flow density and increases faster at low mass flow density.The average coefficient of condensation heat transfer increases with inlet vapor quality,and the change rate of average coefficient of condensation heat transfer varies with inlet vapor quality;The average coefficient of condensation heat transfer first increases and then decreases with the increase of inclination.the average coefficient of condensation heat transfer has a maximum when inclination angle is 15.1°.A single hole header was used in the separation condensation experiment,which was divided into four structures according to the location and aperture of the separation holes.The results showed that the state of gas-liquid separation in the header under the same structure was affected by the inlet conditions,and there was a more stable leakage rate that could achieve effective separation when the inlet vapor quality was less than 0.5.The leakage rate fluctuated violently after the inlet vapor quality was further increased until gas phase breakdown.The separation efficiency increased first and then decreased with the inlet vapor quality,and the maximum separation efficiency was 97.0%when the inlet vapor quality was0.11.The height of buildup in the header depends on the size of the leak rate,which increases as the leak rate increases.The effect of structural changes on the separation characteristics is that the leakage rate increases when the separation hole is close to the exit branch,and decreases when it is close to the inlet branch.When the separation efficiency decreases,the average vapor quality inside the tube decreases,and the effect of header separation on enhancing the condensation heat transfer inside the tube also decreases.SST K-OMEGA turbulence model,VOF multiphase model and Lee condensation phase change mass transfer model are used in the numerical simulation of condensation in inclined tubes.The numerical simulation results of condensation heat transfer coefficient differ from the experimental values by 7.9%～13.5%.The numerical results show that the temperature gradient is larger near the wall,and the thickness of the liquid film decreases with the increase of mass flow density;The coefficient of condensation heat transfer increases with mass flow density,temperature difference and absolute value of inclination;The condensation heat transfer coefficient increases first and then decreases with 0°as the boundary when the inclination angle changes,and reaches a maximum at±15°. |
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