热管式真空管太阳能聚光集热系统传热特性分析
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摘要
该文设计了一套最高可提供473 K高温热水的热管式真空管太阳能聚光集热系统,为研究该系统的传热特性并为系统设计提供理论依据,建立了热管式真空管太阳能聚光集热系统传热过程的一维数学模型,计算并分析了该系统的传热性能。计算结果表明,该文设计的热管式真空管太阳能聚光集热系统的瞬时热效率均高于70%,且随太阳直射辐照强度和环境温度的升高逐渐升高,随传热流体温度和风速的升高逐渐降低。热管式真空管接收器内工质的工作温度和压力也随太阳直射辐照强度、传热流体温度、环境温度及风速的变化而变化。在该文计算条件下,热管的工作温度在327.6~503.2 K,工作压力在0.016~2.8 MPa,符合以水作为热管工质的最佳工作范围(293~523 K)。环形区域压力和渗入气体种类对集热系统传热性能也有明显影响。当环形区域压力P<10~(–3) Pa时,接收器热损失较小且随压力变化基本保持不变;当P>10~(–3) Pa时,随着环形区域压力升高,接收器热损失逐渐增大。另外,环形区域渗入气体的导热系数越大,接收器热损失越大。该研究对了解热管式真空管太阳能聚光集热系统传热特性、优化集热系统结构、指导系统设计具有一定的实用价值。
Heat pipe is an efficient heat transfer component. If the heat pipe and the trough concentrator with higher concentration ratio can be effectively combined, the operating temperature of working fluid can be increased obviously, thus achieving higher system thermal efficiency. Parabolic trough solar collector system with heat-pipe evacuated tube is designed in this paper to provide enough heat input to raise the temperature of an heat transfer fluid to around 200 ℃. The system consists of parabolic trough solar concentrator, heat-pipe evacuated tube(a heat collector element) and support structure. The heat-pipe evacuated tube with material of stainless steel consists of evaporator and condenser sections, and water is used as the working liquid. The evaporator section inside a glass envelope is about 45 mm in diameter with a special coating(selective coating) on the outside surface to provide the required optical properties. The selective coating has a high absorptance for radiation in the solar energy spectrum, and has low emittance in the long wave energy spectrum to reduce thermal radiation losses. The annulus space between the evaporator section and the glass envelope is under vacuum to reduce thermal losses. The condenser section of the heat pipe is inserted into the jacketed vessel and rejects heat to the heat transfer fluid. In order to analyze thermal efficiency and provide theoretical basis for collector system design, a one-dimensional heat transfer mathematical model was established. Using this model, heat transfer characteristics of the system were calculated and analyzed. The results indicate that the transient thermal efficiency of the parabolic trough solar collector system with heat-pipe evacuated tube is higher than 70%, and increases with the increase of the ambient temperature and direct normal solar insolation, and decreases with the increase of the heat transfer fluid temperature and wind speed. Working liquid in heat pipe is at saturated state when the system is running, and the temperature is affected mainly by temperature of absorber tube inner wall. The working liquid temperature in heat pipe increases with the increase of direct normal solar insolation, heat transfer fluid temperature and ambient temperature, and decreases with the increase of wind speed. The working liquid temperature in heat pipe is about 327.6-503.2 K under the given calculation condition. Operating pressure of heat-pipe evacuated tube is obtained by the operating temperature of working liquid, and is about 0.016-2.8 MPa in this paper. The working liquid temperature in this paper is within the optimal range with water as the working liquid in the heat pipe. The heat transfer characteristics of the system are influenced obviously by annulus pressure. Annulus pressures below 0.001 Pa have slight influence on the system performance. But under the annulus pressure above 0.001 Pa, the heat loss of the collector increases significantly with the increase of annulus pressure. The system performance is also influenced by the type of gases in the annulus space. Heat loss of the collector is changed with the gases(air, hydrogen and argon) in the annulus space and heat transfer fluid temperature. An inert gas with a high thermal condition coefficient, such as hydrogen, results in the higher heat loss of the collector. The encouraging results in this paper will provide a fundamental reference for researching heat-transfer characteristics and optimization design and performance of parabolic trough solar collector system with heat-pipe evacuated tube.
Heat pipe is an efficient heat transfer component. If the heat pipe and the trough concentrator with higher concentration ratio can be effectively combined, the operating temperature of working fluid can be increased obviously, thus achieving higher system thermal efficiency. Parabolic trough solar collector system with heat-pipe evacuated tube is designed in this paper to provide enough heat input to raise the temperature of an heat transfer fluid to around 200 ℃. The system consists of parabolic trough solar concentrator, heat-pipe evacuated tube(a heat collector element) and support structure. The heat-pipe evacuated tube with material of stainless steel consists of evaporator and condenser sections, and water is used as the working liquid. The evaporator section inside a glass envelope is about 45 mm in diameter with a special coating(selective coating) on the outside surface to provide the required optical properties. The selective coating has a high absorptance for radiation in the solar energy spectrum, and has low emittance in the long wave energy spectrum to reduce thermal radiation losses. The annulus space between the evaporator section and the glass envelope is under vacuum to reduce thermal losses. The condenser section of the heat pipe is inserted into the jacketed vessel and rejects heat to the heat transfer fluid. In order to analyze thermal efficiency and provide theoretical basis for collector system design, a one-dimensional heat transfer mathematical model was established. Using this model, heat transfer characteristics of the system were calculated and analyzed. The results indicate that the transient thermal efficiency of the parabolic trough solar collector system with heat-pipe evacuated tube is higher than 70%, and increases with the increase of the ambient temperature and direct normal solar insolation, and decreases with the increase of the heat transfer fluid temperature and wind speed. Working liquid in heat pipe is at saturated state when the system is running, and the temperature is affected mainly by temperature of absorber tube inner wall. The working liquid temperature in heat pipe increases with the increase of direct normal solar insolation, heat transfer fluid temperature and ambient temperature, and decreases with the increase of wind speed. The working liquid temperature in heat pipe is about 327.6-503.2 K under the given calculation condition. Operating pressure of heat-pipe evacuated tube is obtained by the operating temperature of working liquid, and is about 0.016-2.8 MPa in this paper. The working liquid temperature in this paper is within the optimal range with water as the working liquid in the heat pipe. The heat transfer characteristics of the system are influenced obviously by annulus pressure. Annulus pressures below 0.001 Pa have slight influence on the system performance. But under the annulus pressure above 0.001 Pa, the heat loss of the collector increases significantly with the increase of annulus pressure. The system performance is also influenced by the type of gases in the annulus space. Heat loss of the collector is changed with the gases(air, hydrogen and argon) in the annulus space and heat transfer fluid temperature. An inert gas with a high thermal condition coefficient, such as hydrogen, results in the higher heat loss of the collector. The encouraging results in this paper will provide a fundamental reference for researching heat-transfer characteristics and optimization design and performance of parabolic trough solar collector system with heat-pipe evacuated tube.
引文
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[15]Behnam P,Shafii M B.Examination of a solar desalination system equipped with an air bubble column humidifier,evacuated tube collectors and thermosyphon heat pipes[J].Desalination,2016,397(1):30-37.
[16]Daghigh R,Shafieian A.Theoretical and experimental analysis of thermal performance of a solar water heating system with evacuated tube heat pipe collector[J].Applied Thermal Engineering,2016,103(25):1219-1227.
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[20]王银峰,陈海军,张鑫,等.跟踪式CPC热管真空管集热器聚光及集热特性[J].太阳能学报,2015,36(11):2643-2650.Wang Yinfeng,Chen Haijun,Zhang Xin,et al.Optical and thermal performance of sun-tracking CPC heat pipe evacuated tubular collector[J].Acta Energiae Solaris Sinica,2015,36(11):2643-2650.(in Chinese with English abstract)
[21]张维薇,朱跃钊,蒋金柱,等.新型CPC热管式集热器的设计与模拟分析[J].热能动力工程,2009,24(3):395-399.Zhang Weiwei,Zhu Yuezhao,Jiang Jinzhu,et al.Design and simulation analysis of a novel CPC heat-pipe heat collector[J].Journal of Engineering for Thermal Energy and Power,2009,24(3):395-399.(in Chinese with English abstract)
[22]刘赟,张红,战栋栋,等.用于槽式太阳能热发电系统的热管式集热器开发[J].华东电力,2008,36(3):78-80.Liu Yun,Zhang Hong,Zhan Dongdong,et al.Development of heat pipe evacuated tubular collectors in solar parabolic through power generation systems[J].East China Electric Power,2008,36(3):78-80.(in Chinese with English abstract)
[23]战栋栋,张红,刘赟,等.中温太阳能热管接收器的开发与传热分析[J].太阳能学报,2009,30(5):602-606.Zhan Dongdong,Zhang Hong,Liu Yun,et al.Development and thermal analysis of the medium temperature heat pipe solar receiver[J].Acta Energiae Solaris Sinica,2009,30(5):602-606.(in Chinese with English abstract)
[24]战栋栋,张红,刘赟,等.太阳能中温接收器的开发与研究[J].南京工业大学学报,2009,31(5):63-67.Zhan Dongdong,Zhang Hong,Liu Yun,et al.Development and research of medium temperature heat pipe solar power receiver[J].Journal of Nan Jing University of Technology:Natural Science Edition,2009,31(5):63-67.(in Chinese with English abstract)
[25]Forristall R.Heat transfer analysis and modeling of aparabolic trough solar receiver implemented in engineering equation solver[R].Golden,USA:National Renewable Energy Laboratory,2003.
[26]杨世铭,陶文铨.传热学[M].北京:高等教育出版社,2015.
[27]Ratzel A C,Hickox C E,Gartling D K.Techniques for reducing thermal conduction and natural convection heat losses in annular receiver geometries[J].Journal of Heat Transfer,1979,101:108-113.
[28]Bejan A.Convection Heat Transfer[M].New York,NY:John Wiley&Sons,2013.
[29]Vernon E Dudley,Gregory J Kolb,et al.Test Results-SEGSLS2 Solar Collector[R].USA:Report of Sandia National Laboratories,SANDIA94-1884,1994.
[30]周小雯,董光军,朱秀珍,等.真空太阳集热管在应用不同吸气剂时的残气分析[J].太阳能学报,2009,30(1):27-31.Zhou Xiaowen,Doug Guangjun,Zhu Xiuzhen,et al.Study on the residual gas in glass evacuated collector tubes with various getters[J].Acta Energiae Solaris Sinica,2009,30(1):27-31.(in Chinese with English abstract)
[31]崔映红,卑振华.抛物面槽式太阳能集热器热力性能研究[J].华北电力大学学报:自然科学版,2010,37(3):49-54,63.Cui Yinhong,Bei Zhenhua.Research on the thermal performance of the solar parabolic trough collectors[J].Journal of North China Electric Power University,2010,37(3):49-54,63.(in Chinese with English abstract)
[2]Jouhara H,Ezzuddin H.Thermal performance characteristics of a wraparound loop heat pipe(WLHP)charged with R134A[J].Energy,2013,61(1):128-138.
[3]Jadhav T S,Lele M M.Theoretical energy saving analysis of air conditioning system using heat pipe heat exchanger for Indian climatic zones[J].Engineering Science and Technology,an International Journal,2015,18(4):669-673.
[4]Ong K S,Haider-E-Alalhi M.Experimental investigation on the hysteresis effect in vertical two-phase closed thermosyphons[J].Applied Thermal Engineering,1999,19(4):399-408.
[5]Mahajan G,Thompson S M,Cho H.Energy and cost savings potential of oscillating heat pipes for waste heat recovery ventilation[J].Energy Reports,2017,3:46-53.
[6]Ahmadzadehtalatapeh M.An air-conditioning system performance enhancement by using heat pipe based heat recovery technology[J].Scientia Iranica,2013,20(2):329-336.
[7]苏向辉.航空电子设备冷却用环路热管冷凝器热沉分析[J].航空动力学报,2010,25(9):1942-1947.Su Xianghui.Analysis of heat sink for rejected condenser heat of loop heat pipes for cooling avionics[J].Journal of Aerospace Power,2010,25(9):1942-1947.(in Chinese with English abstract)
[8]Tsai T E,Wu H H,Chang C C,et al.Two-phase closed thermosyphon vapor-chamber system for electronic cooling[J].International Communications in Heat and Mass Transfer,2010,37(5):484-489.
[9]Khodabandeh R,Furberg R.Instability,heat transfer and flow regime in a two-phase flow thermosyphon loop at different diameter evaporator channel[J].Applied Thermal Engineering,2010,30(10):1107-1114.
[10]Mathioulakis E,Belessiotis V.A new heat-pipe type solar domestic hot water system[J].Solar Energy,2002,72(1):13-20.
[11]Lin M C,Chun L J,Lee W S,et al.Thermal performance of a two-phase thermosyphon energy storage system[J].Solar Energy,2003,75(4):295-306.
[12]Li J,Lin F,Niu G.An insert-type two-phase closed loop thermosyphon for split-type solar water heaters[J].Applied Thermal Engineering,2014,70(1):441-450.
[13]Hussein H M S,Mohamad M A,El-Asfouri A S.Optimization of a wickless heat pipe flat plate solar collector[J].Energy Conversion&Management,1999,10(18):1949-1961.
[14]朱婷婷,刁彦华,赵耀华,等.微热管阵列式太阳能平板空气集热器集热性能[J].农业工程学报,2016,32(11):250-257.Zhu Tingting,Diao Yanhua,Zhao Yaohua,et al.Thermal performance of new flat plate solar air heater based on micro-heat pipe arrays(MHPA)[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2016,32(11):250-257.(in Chinese with English abstract)
[15]Behnam P,Shafii M B.Examination of a solar desalination system equipped with an air bubble column humidifier,evacuated tube collectors and thermosyphon heat pipes[J].Desalination,2016,397(1):30-37.
[16]Daghigh R,Shafieian A.Theoretical and experimental analysis of thermal performance of a solar water heating system with evacuated tube heat pipe collector[J].Applied Thermal Engineering,2016,103(25):1219-1227.
[17]Nkwetta D N,Smyth M,Zacharopoulos A,et al.Optical evaluation and analysis of an internal low-concentrated evacuated tube heat pipe solar collector for powering solar air-conditioning systems[J].Renewable Energy,2012,39(1):65-70.
[18]Nkwetta D N,Smyth M,Haghighat F,et al.Experimental performance evaluation and comparative analyses of heat pipe and direct flow augmented solar collectors[J].Applied Thermal Engineering,2013,60(1/2):225-233.
[19]Wang Y F,Zhu Y Z,H J,et al.Performance analysis of a novel sun-tracking CPC heat pipe evacuated tubular collector[J].Applied Thermal Engineering,2015,87:381-388.
[20]王银峰,陈海军,张鑫,等.跟踪式CPC热管真空管集热器聚光及集热特性[J].太阳能学报,2015,36(11):2643-2650.Wang Yinfeng,Chen Haijun,Zhang Xin,et al.Optical and thermal performance of sun-tracking CPC heat pipe evacuated tubular collector[J].Acta Energiae Solaris Sinica,2015,36(11):2643-2650.(in Chinese with English abstract)
[21]张维薇,朱跃钊,蒋金柱,等.新型CPC热管式集热器的设计与模拟分析[J].热能动力工程,2009,24(3):395-399.Zhang Weiwei,Zhu Yuezhao,Jiang Jinzhu,et al.Design and simulation analysis of a novel CPC heat-pipe heat collector[J].Journal of Engineering for Thermal Energy and Power,2009,24(3):395-399.(in Chinese with English abstract)
[22]刘赟,张红,战栋栋,等.用于槽式太阳能热发电系统的热管式集热器开发[J].华东电力,2008,36(3):78-80.Liu Yun,Zhang Hong,Zhan Dongdong,et al.Development of heat pipe evacuated tubular collectors in solar parabolic through power generation systems[J].East China Electric Power,2008,36(3):78-80.(in Chinese with English abstract)
[23]战栋栋,张红,刘赟,等.中温太阳能热管接收器的开发与传热分析[J].太阳能学报,2009,30(5):602-606.Zhan Dongdong,Zhang Hong,Liu Yun,et al.Development and thermal analysis of the medium temperature heat pipe solar receiver[J].Acta Energiae Solaris Sinica,2009,30(5):602-606.(in Chinese with English abstract)
[24]战栋栋,张红,刘赟,等.太阳能中温接收器的开发与研究[J].南京工业大学学报,2009,31(5):63-67.Zhan Dongdong,Zhang Hong,Liu Yun,et al.Development and research of medium temperature heat pipe solar power receiver[J].Journal of Nan Jing University of Technology:Natural Science Edition,2009,31(5):63-67.(in Chinese with English abstract)
[25]Forristall R.Heat transfer analysis and modeling of aparabolic trough solar receiver implemented in engineering equation solver[R].Golden,USA:National Renewable Energy Laboratory,2003.
[26]杨世铭,陶文铨.传热学[M].北京:高等教育出版社,2015.
[27]Ratzel A C,Hickox C E,Gartling D K.Techniques for reducing thermal conduction and natural convection heat losses in annular receiver geometries[J].Journal of Heat Transfer,1979,101:108-113.
[28]Bejan A.Convection Heat Transfer[M].New York,NY:John Wiley&Sons,2013.
[29]Vernon E Dudley,Gregory J Kolb,et al.Test Results-SEGSLS2 Solar Collector[R].USA:Report of Sandia National Laboratories,SANDIA94-1884,1994.
[30]周小雯,董光军,朱秀珍,等.真空太阳集热管在应用不同吸气剂时的残气分析[J].太阳能学报,2009,30(1):27-31.Zhou Xiaowen,Doug Guangjun,Zhu Xiuzhen,et al.Study on the residual gas in glass evacuated collector tubes with various getters[J].Acta Energiae Solaris Sinica,2009,30(1):27-31.(in Chinese with English abstract)
[31]崔映红,卑振华.抛物面槽式太阳能集热器热力性能研究[J].华北电力大学学报:自然科学版,2010,37(3):49-54,63.Cui Yinhong,Bei Zhenhua.Research on the thermal performance of the solar parabolic trough collectors[J].Journal of North China Electric Power University,2010,37(3):49-54,63.(in Chinese with English abstract)