Transport Characteristic And Its Enhancement Mechanism For Transverse Ridged Tubes With Molten Salts Materials In Receiver

Solar thermal power as a very promising and inexpensive clean energy technology has become a supporting sustainable development of China's national economy forward, and it is a key development direction and priorities in the national long-term development plan for science and technology which was promulgated in 2006. The key problem which commercializes the solar thermal power system is coupled heat transfer processes with conduction, radiation and convection under unsteady and non-uniform conditions and its associated mechanisms and ways of enhancement in receiverThe characteristic of heat transfer and flow in receiver with molten salts materials have been investigated experimentally and theoretically. The characteristics of the heat transfer process for the receiver are high temperature,high heat flux, half circumference heating and half circumference adiabatic. Mathematical model which describes the heat transfer and flow processes with molten nitrate salts in transversely ridged tube has been set up. The heat transfer process in transversely ridged tube and smooth tube have been simulated respectively by use of the unstructured grid and standardκ?εturbulence model. The effects of temperature, velocity and thermal properties of molten salts, heat flux, and geometry parameters of receiver tube on the characteristic of heat transfer and flow in transversely ridged tube have been investigated. The effect of evaluation criteria has also been discussed. The results showed that the flow distribution and temperature distribution in the transversely ridged tube developed periodically along the direction of axis. And there is high-speed flowing region of molten salts in the ridge, the wall temperature decreased notably with the decrease of the boundary layer. Since the ridge damaged the flow boundary layer, the flow resistance coefficient and heat transfer coefficient for the transversely ridged tube were both higher than that of smooth tube. The variation of viscosity and heat conductivity can affect the flow and heat transfer performances, while the variation of density and heat capicity can be ignored. The ridge structure can also affect greatly the performance of flow and heat transfer. When the ridge shape of tube is triangle,, the flow boundary was damaged by the ridge, so the flow resistance coefficient and heat transfer coefficient were both higher. When the ridge shape of tube is parabolic, the flow and temperature gradually varied, so the flow resistance coefficient was lower, and the heat transfer coefficient was not very higher. When the ridge shape of tube is quadratic,, the flow will collide with the ridge, so the flow resistance coefficient was higher, and the heat transfer coefficient was near to that in parabolic ridge structure tube. The evaluation criteria for enhancing heat transfer also affected greatly the choosing of different ridge structure. When the criteria of Nu/Nus was considered, the triangle ridge structure tube will have the best performance of heat transfer. When the criteria of were considered, the parabolic ridge structure tube will have better performance under the condition of higher Reynolds number, and the triangle ridge structure will have better performance under the condition of lower Reynolds number.The heat transfer performances of Nitrate salts in transversely ridged tube have been investigated experimentally. The results show that the heat transfer of molten nitrate salts in transversely ridged tube was obviously better than that in smooth tube, and that the heat transfer coefficient of Nitrate salts in transversely ridged tube is higher than that in smooth tube for about 30%-100%. The heat transfer coefficient increased notably with the increase of the Re number in transversely ridged tube, Its associated empirical formula was derived by experimental results. The simulated results from hard sphere model have a good agreement with the experimental results. The simulated results from hard sphere model have a good agreement with the experimental results, its uncertainty is 5-30%. And the correlation relationship of flow resistance can be obtained by analogy for the experimental results.The heat absorption theoretical efficiency and heat-resistant performance of the solar absorb coating has been investigated quantificationally under the different concentration ratios. The apparent morphology, reflectivity and emissivity of high-temperature coating, were measured. The results show that the solar selective coating with higher absorptance should be used under the receiver with lower concentration ratio,. the solar absorb coating with high absorptivity and high temperature should be used under the receiver with higher concentration ratio.