Research On Optical And Thermal Properties Of Cavity Heat Pipe Central Receiver

Traditional cavity receiver suffers from deterioration of the heat transfer performance and receiver structural instability due to the uneven heat flux density distribution.In this thesis,a new solar cavity heat pipe central receiver is presented,in order to improve the reliability without reducing the thermal performance of the receiver.And its optical and steady-state,transient thermal properties are studied.The main contents and conclusions are as follows:(1)The expressions of solar angle,receiver optical and thermal efficiency are given,and the heat transfer limit model of high temperature sodium heat pipe is established and analyzed.The results show that the viscous limit and sonic velocity limit are much higher than the capillary limit and entrainment limit when the temperature is higher than 870℃,the capillary limit and entrainment limit play the main role at this time.In the temperature range,the capillary limit changes more smoothly,and the boiling limit is much higher than the other limits and it may not be considered.(2)Three schemes for heat pipe arrangement are given,an optical simulation model of the cavity heat pipe central receiver is established,and the heat flux density distribution and optical efficiency are studied.The results show:for scheme three,the heat pipes are arranged loosely,the maximum value on the fifth row of heat pipes is 39.11 k W,and the heat flux distribution is relatively uniform.Among the three schemes,scheme three is adopted,which has the highest optical efficiency of 0.901 with 78 heat pipes in total.(3)Using the micro-element analysis method and the equivalent thermal resistance method,a steady-state thermal simulation model of the receiver is established,in order to study the temperature distribution characteristics of the heat-absorbing surface of the receiver and the temperature rise of the molten salt fluid and thermal efficiency characteristics.The results show: along the whole process of molten salt fluid,the temperature rise rate in the heat pipe absorption surface area is the largest,44.92%.The overall thermal efficiency of the receiver is 0.861,which is close to the thermal efficiency of traditional receiver in the Sandia National Laboratories’ molten salt electric experiment(MSEE).The radiation loss is 6.30%,which accounts for the highest proportion of heat loss.(4)By writing the System Function(S function)and based on the Simulink platform,a transient thermal simulation model of the receiver is established,in order to study the transient thermal performance of the molten salt outlet temperature and the step response characteristics of the receiver outlet parameters.The results show: under the condition of constant input parameters,the molten salt outlet temperature increases to 525℃with time,and reaches a stable state in about 550 s.Under the step change of the solar radiation intensity,molten salt inlet flow rate and molten salt inlet temperature,the temperature and thermal efficiency of the molten salt outlet both reached a new stable state after about 230 s.