| Solar thermal power generation is an important part of the clean energy field and plays an important role in the sustainable development of China's energy green.In solar thermal power stations,fluid heat transfer technology is one of the key technologies in the optical-thermal energy transmission and conversion process,directly affecting the efficiency and safety of the entire energy system.Among many heat transfer fluids,high-temperature molten salt has many advantages such as wide temperature range,good thermal stability,large heat capacity,low viscosity and low price,and has broad application prospects in solar thermal power stations.In order to design and optimize the high-temperature molten salt energy transmission system,it is necessary to first accurately grasp the flow and heat transfer characteristics.In this paper,a molten salt(a binary molten salt of 60%sodium nitrate and 40%potassium nitrate)is used as a heat transfer fluid.The numerical calculation method is used to study the convective heat transfer characteristics in the tube,and the technical measure to strengthen high-temperature molten salt transmission is explored.The main work and conclusions are as follows:(1)The numerical study on the heat transfer characteristics of high temperature molten salt in smooth round tube was carried out.The flow field and temperature field distribution of molten salt in the tube were analyzed.The flow resistance coefficient and Nusselt number of high temperature molten salt were obtained and compared with the classical correlation.The results show that in the transitional flow region,the Nusselt number simulation value agrees well with the calculated value of the Gnielinski formula,and the average error is 5.1%,which indicates that the Gnielinski formula can be used to predict the heat transfer performance of the high temperature molten salt in the smooth round tube.(2)The convective heat transfer characteristics of high temperature molten salt in the horizontal tube were studied.The effects of flow rate,temperature,wall heat flux density and transverse tube geometry on the heat transfer of high temperature molten salt in the tube were studied and evaluated by comprehensive performance parameters PEC.The horizontal tube enhances heat transfer performance.Since the groove of the horizontal tube breaks the boundary layer and reduces the flow cross section,the disturbance and resistance of the fluid increase,and the resistance coefficient and the Nusselt number of the fluid in the tube are higher than that of the smooth tube,and the PEC parameter is 1.63-1.8,indicating that the horizontal tube can effectively enhance the high temperature molten salt heat transfer.(3)In order to simulate the heat transfer process of high temperature molten salt in the heat absorption tube under actual operating conditions,a physical model of circumferential non-uniform heating heat absorption tube was established.The standard k-? turbulence model was used to solve the three-dimensional flow NS momentum equation and energy equation,and the circumferential non-uniform heat flow was obtained.The distribution of molten salt in the endothermic tube under the density condition,the distribution of the wall temperature and the heat transfer characteristics of the molten salt in the tube.The results show that when the heat absorbing tube is unevenly heated in the circumferential direction,the temperature distribution of the molten salt in the heat absorbing tube at the same section is not uniform.Due to the cosine effect of the heat flux density,the heat flux density of the heat absorbing tube reaches the maximum at ? ? 0°,the corresponding Nusselt number also increases to the maximum value,and the lower the molten salt inlet temperature at the same Reynolds number,the heat exchange the better the effect. |
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