Study On Flow & Heat Transfer Characteristics Of Solar Salt In Solar Receiver Tube

Solar energy is both a source of renewable energy and the cleanest energy source in the world.The use of solar power technology can reduce dependence on fossil energy.The 13 th Five-Year Plan for Economic and Social Development of the People’s Republic of China claim that solar power generation capacity would achieve 5000 MW by the end of 2020.The thermal efficiency and light concentration of tower solar power stations are higher than the mature trench technology,but what restricts the development of tower solar power stations is the lack of verification of the existing technology maturity and high risks.One of the main ways to reduce risk is to improve the efficiency of the thermal cycle.The receiver is the core heat transfer unit in the thermodynamic cycle,and improving the efficiency of the receiver is an effective way to improve the efficiency of the thermal cycle.In order to obtain a more efficient heat transfer system,it is necessary to study and accurately grasp the flow and heat transfer characteristics of the working fluid in the absorber heat absorption tube.The heat transfer medium used in the receivers of tower solar power stations in the world is mainly solar salt and water.Solar salt has more potential because of its good thermal stability,large heat capacity,and wide operating temperature range.Therefore,in this paper,the numerical simulation method is used to explore the flow of binary molten salt(solar salt)mixed with 60% sodium nitrate and 40% potassium nitrate in the heated heat pipe.The Nu number of the convective heat transfer intensity between the solar salt and the solar salt and the resistance coefficient f of the solar salt in the heat absorption tube are analyzed to obtain the flow condition and heat transfer characteristics of the solar salt when flowing in the heat absorption tube.The main work contents and conclusions are as follows:Firstly,the numerical simulation of solar salt flow in a round tube was performed,and the distribution of the flow field and temperature field of the solar salt in the round tube was obtained.The resistance coefficients f of the solar salt flow and the Nu number of heat transfer were obtained.By comparing the Nu number calculated by the Fluent software with the Nu number calculated by the Sieder-Tate classic formula,the average error is 2%,which indicates that the results obtained by numerical simulation are credible.At the same time,it is proved that the classical formula can also be used to predict the convective heat transfer performance of solar salt in a round tube.The simulation results show that the velocity of the solar salt in the round tube is concentrically distributed,he changes of the Nu number and the Re number of the solar salt in the smooth circular tube are consistent,and the outlet temperature distribution is uneven.Secondly,Using Ansys software to simulate the flow and heat transfer characteristics of solar salt in the spirally fluted tubes with different geometric parameters to explore the feasibility of predicting the flow and heat transfer characteristics of solar salt in spirally fluted tubes with numerical simulation method.Under the conditions of half-cycle heating,the flow and heat transfer characteristics of the solar salt were investigated under different conditions of inlet temperature and heat flux.The flow velocity plot and vector diagram of solar salt in the spiral fluted tube are obtained through the numerical simulation.Also,the temperature distribution of the outlet of the tube was obtained.Finally,the Nu-Re curve of solar salt is obtained through the further calculation.The results show that there are still some secondary circulation flow phenomena in the tube and the flow velocity changes periodically.The changes of the Nu number and the Re number of the solar salt in the spiral fluted tube are consistent,and the unevenness of the outlet temperature distribution is small.With the increase of the depth of the spiral groove,the heat transfer ability of solar salt increases accordingly.In the comprehensive evaluation performance.The higher the solar salt inlet temperature is,the better the heat transfer ability of the solar salt in the spirally fluted tubes is.Finally,the heat transfer characteristics Nu and resistance coefficient f of the two types of heat absorption tubes are comprehensively considered,and the calculation results are compared by the comprehensive performance evaluation formula.The comprehensive performance evaluation of the spiral fluted tube is 1.3 to 1.35 times that of the round tube.This indicated that the heat transfer characteristics of the solar salt in the spiral fluted tube are higher than that of the smooth round tube,so the use of spiral fluted tube as the heat absorption tube can improve the efficiency of the receiver.