Thermal Performance Analysis Of Solar Power Tower Plants Based On Supercritical CO₂ Brayton Cycle

Solar energy is an inexhaustible renewable energy source,and the application of the solar thermal power technology can avoid the dependence on primary energy.The capacities of the solar energy power station installed in China will reach to 5GW by2020.The cycle efficiency of solar thermal power station used in Rankine cycle is35%⁴5%,whilst that of recompressed Brayton cycle?700??is more than50%.Presently,the main factor of resticting the large-scale development of solar thermal power generation is its high cost of power generation,and improving the system efficiency is one of the main ways to reduce the cost of power generation.This paper both analyses the energy and exergy efficiency of the solar thermal power plants based on the supercritical CO₂ Brayton cycle,and discuss the main parameters and systems affecting the energy and exergy efficiency.For the system with maximum exergy loss,the reserch on heat transfer charasteristics and heat transfer enhancement will also be down.The main contents are as follows:Firstly,takng the 1MW solar experimental station in Beijing,China as an example,the energy and exergy efficiency of solar thermal based on supercritical CO₂brayton cycle was carried out by using the MATLAB programming software.With the aim of getting the optimum parameters and the relation between them,this study reports the performance assement of the cycle in different DNI,concentration ratio,maximum pressure,minimun pressure,component efficiency and split ratio.Secondly,each subsystem has been analysed with reference to both energy and exergy efficiency through the self-programming software.Then we find that the higher exergy loss was,the lower exergy efficiency was.onsequently,the higher power efficiency can be achieved by enhancing the heat transfer of the receiver.Thirdly,the research object has been considered in this study is the areas in transverse tube and smooth circular tube,the CFD software is used to simulate the heat transfer of receiver tube which are used standard k-?model and unstructured gird.The characteristics of heat transfer and flow of the receiver tubes are studied with reference to different flow velocity,heat flux and physical properties,and the simulation results of two different heating pipes are compared.Comparing with the smooth circular tube,the lateral-cut can reduce the temperature inhomogeneity of the fluid in the tube,and there is vortex both in front of and behind the grooves of the lateral-cut,which increases the flow resistance and Nu number.For lateral-cut tube,the temperature of molten salt in heating side is lower than that of the smooth pipe,avoiding the decomposition of fluid,blasting of the tube and so on.Finally,using the transverse tube as the receiver tube can effectively reduce the energy loss of heat transfer and radiation.The synergy theory and criterion of?Nu/Nu₀?/?f/f₀?^1/3are used to compare the performance of different structural parameters.It is found that the average synergy angle of the transverse tube is less than that of the smooth tube,and increasing the groove depth and selecting the appropriate pitch are benefical to the heat transfer.Increasing the Re number only increases the turbulence intensity in the absorbed tube,not improving the synergy of the velocity and temperature field.