【作者】 鹿院卫； 吴玉庭； 马重芳；

【Author】 LU Yuanwei;WU Yuting;MA Chongfang;Key Laboratory of Enhanced Heat Transfer and Energy Conservation,Ministry of Education of China,College of Environmental and Energy Engineering,Beijing University of Technology;

【机构】 北京工业大学环境与能源工程学院,传热强化与过程节能教育部重点实验室暨传热与能源利用北京市重点实验室；

【摘要】 储热可以解决太阳能高温热发电的间歇性问题,实现太阳能的连续热发电,也是太阳能高温热发电不同于其它可再生能源发电(风电、光伏发电)的优越性所在。目前较为成熟、且被大规模应用的太阳能储热方式是双罐储热,熔盐是通过熔盐泵驱动流动来完成储热和释热过程,故强迫对流是其流动与传热的基本规律,故在高温熔盐的受迫对流传热与强化研究方面,北京工业大学、中国科学院、西安交通大学,中山大学等科研单位,完成了许多有意义的研究工作。但双罐储热储热成本过高,这正是目前太阳能高温热发电技术与风电、光伏发电难以竞争的关键所在。为了降低储热成本,人们寻求单罐的储热方法,如单罐斜温层、相变胶囊储热,中山大学、中科院等单位在这方面做了很多创新性的研究工作。寻求多样化的单罐蓄热方法,仍是人们追求的目标。如果将盘管换热器布置在熔盐储热罐内,通过传热和释热介质流过罐内换热器,实现熔盐的储热和释热过程,也是熔盐单罐蓄热的一种方式,那么在罐内熔盐侧,熔盐完成的就是相变及自然对流传热过程。北京工业大学一直尝试研究熔盐的相变及自然对流传热的规律。为了研究熔盐的自然对流传热规律,采用焦耳加热法,加热微细金属丝,分析微细圆柱表面熔盐的自然对流传热规律。结果表明,小雷利数(R_a)条件下熔盐的自然对流传热规律可以考虑采用黏性耗散的Fand关联式来预测,数值计算得到了相同的结果。在R_a<108的层流范围内,数值计算结果同样表明,圆柱表面熔盐自然对流传热规律可以用Fand关联式预测。但Fand关联式使用较为复杂,且没有考虑熔盐的变物性传热影响。根据数值计算及实验结果,同时考虑熔盐的变物性影响,研究拟合得到了可以简单预测熔盐层流自然对流传热规律的关联式,该关联式能够预测瑞利数小于108的层流自然对流传热。图1展示了努歇尔特数随瑞利数和普朗特数的变化规律。更多还原

【Abstract】 Thermal energy storage(TES) can solve the intermittent problem of the higher temperature solar thermal power generation,and make it necessary to produce uninterruptable power.Solar thermal power generation with TES has more superiority than other renewable energy power,such as wind and photovoltaic power.Currently,the double TES tank has been successfully used in the commercial solar power plant,in which molten salt was pumped out or in to charging and discharging heat,so the forced convection heat transfer of molten salt was the key issue to be determined.Therefore,the forced convective heat transfer of molten salt and heat transfer enhancement were studied comprehensively by many research groups,such as that from Beijing University of technology,Chinese academy of sciences,Xi’an Jiaotong University and Sun yat-sen University,etc.However,the cost of TES by two tanks is too higher,which result in the power production cost is difficult to compete with that of wind and photovoltaic power at present.In order to reduce the cost of TES for solar thermal power,other different TES methods was proposed,such as thermocline tank and capsule phase change materials.In this filed,many meaningful research has been done by the researchers from Sun yat-sen university,Chinese academy of sciences and other units.At presently,it is still a research direction pursued by many researchers for TES by one tank.To complete the charging and discharging process in a single TES tank,one try to make the heat transfer medium flow through a heat exchanger immersed in a molten salt tank,during which the natural convective heat transfer of molten salt outside the heat exchanger occurred.To study the natural convection heat transfer mechanism of molten salt,the Joule heating method was used to heat a platinum wire by experiment and simulation.The results show that the natural convection heat transfer of molten salt around a horizontal cylinder at the lower Rayleigh number(R_a) can be predicted by Fand’s correlation for it take the viscous dissipation into account.The simulation results also confirmed it when Ra<108.However,Fand’s correlation is complicated and can’t be used easily to predict the natural convection heat transfer in actual application.Also,the correlation has not considers the effect of variable physical properties on heat transfer.According to the numerical and experimental results along with the effect of the variable physical properties of molten salt,a similar and simple correlation was proposed,as shown in Eq.(l),which can predict the laminar natural convective heat transfer of molten salt when R_a<108.Fig.l shows Nuseselt number(Nu) varies with Ra and Prandtl number(Pr).更多还原