Structure Optimization For The Solar Tower Receiver Absorber With Non-uniform Flux

Tower solar receiver is the core of tower solar thermal generation plant,which performance will affect the safety and economy of unit operation directly.This contribution introduces the characteristics and operation principle of tower solar thermal power generation technology and the key technologies of tower solar receivers such as working fluids and suitable structures.Meanwhile,we classify the tower solar receivers according to the types of working fluids and analyze the advantages and disadvantages of the current type of receivers.When the liquid sodium was proposed,the liquid metal receiver becomes the new promising receiver.Water/water-stream receivers and air receivers are the earliest and widely types of tower solar receivers,but the thermal efficiency is limited.The molten salt cavity receiver has the higher thermal efficiency,however,the molten salt will decompose when the operation temperature is over 600°C.The dual receiver applies the two kinds of working fluids in order to improve the thermal efficiency,whereas the structure is too complex to be practical application.What's more,the particle receiver is the new receiver,which can improve the operating temperature and solar-to-electric efficiency.The structure of the particle receiver is very complex,so the particle receiver is not widely used in the tower solar system at present.To sum up,the effects of the working-fluid and the structure of receiver are highlighted,the main research direction of the tower solar receiver is to select the appropriate working-fluid and optimize the receiver structure.At present,the cavity tubular solar receive is the most widely used,and its research point is optimizing the structure of the absorbers to improve its reliability.Taking the cavity tubular solar receiver absorber as the research object and the super-heated steam as the medium,the flow field in the absorber during the endothermic absorption was simulated by using FLUENT software and HFCAL heat flux density method.The role of spoiler is to disturb the flow field in the absorber then reduce the circumferential temperature difference of the absorber.Select four spoiler pieces,such as spiral fin,twisted-tape,spiral line and double-dogleg tube,to compare their spoiler effect.Analyze its velocity distribution and temperature distribution,we can find that the longitudinal vortex diameter of the twisted-tape is the largest,the temperature difference at the outlet of the absorber is the smallest andthe pressure loss is small.Furthermore,we analyze of the influence of the number of warped pieces,cross-section parameters,pitch and location on the temperature difference of absorbr.The result is that the change of twist-tape cross section and pitch have little effect on the temperature difference,the twisted-tape disposed on the backlight side of the absorber and the number 2 is better.Although it is possible to reduce the circumferential temperature difference of the absorber by inserting the spoiler in the pipe,it will increase the pressure loss of the absorber.In addition to the spoiler inserts,but the absorber structure changes is proposed to homogenize the circumferential temperature distribution of absorber and improve the thermal efficiency and reliability of receiver.We establish three dimensional models to simulate the convective flow and heat transfer analyze the cylinder pipe,tapered conduit and diffuser tube respectively.We can found that the circumferential temperature difference of the tapered conduit is smallest.Then,we changed the expansion ratio of the tapered conduit to optimize the circumferential temperature difference.The circumferential temperature difference decreases with the increase of the expansion ratio.When the expansion ratio is 20/16,the excellent performance will obtain and the temperature difference is reduced by 5.7%,the pressure loss is 0.21 Pa.Compared to the tapered conduit,inserting twisted-tapes in the absorber can further reduce the circumferential temperature difference,and improve the reliability of receiver.