For combined sensible-latent heat storage system(CSLHS)(termed as the hybrid configuration),macro encapsulation can effectively solve the leakage problem of PCMs.However,due to the poor thermal conductivity of PCMs,th...For combined sensible-latent heat storage system(CSLHS)(termed as the hybrid configuration),macro encapsulation can effectively solve the leakage problem of PCMs.However,due to the poor thermal conductivity of PCMs,the charging performance of the hybrid configuration slightly increases compared to the solid structure(with only sensible materials).Meanwhile,the natural convection in the PCMs zone could improve the charging performance.So,how to improve natural convection intensity is a key issue for the CSLHS by macro encapsulating.It is found that adding fins can significantly enhance natural convection and accelerate the melting of PCM.In this paper,we proposed the hybrid configuration with fins built-in by macro encapsulation,and analyzed its charging performance with different fin structural parameters in the PCM zone by CFD simulation.In the case,the sensible heat storage material is high-temperature concrete and the PCM is a low-melting-point mixed molten salt.We analyzed the effects of fin number,fin length and fin thickness on the charging performance of the hybrid configuration respectively.From the result,the charging performance increases with the fin number,but the increase rate gradually decreases.When the fin number is 6,the charging performance increases by 20.18%compared to the situation without fin.The charging performance increases gradually with the fin length.Compared with the hybrid configuration without fin,for each 10 mm increase in fin length,its charging performances increase by 4.09%,5.26%,7.02%,8.77%,11.70%,and 15.79%,respectively.Different from number and length of fins,the effect of thickness on the charging performance is very small.When the fin thickness increased from 1 mm to 4 mm,the charging performance only increased by 2.3%.It indicates that the main reason for the improving the charging performance is to increase the natural convection intensity by dividing the PCM zone through fins.These results show that the charging performance of the CSLHS with macro encapsulation can be improved by optimizing fin structural parameters.展开更多
In recent years,heat storage system combining sensible and latent heat materials has received more and more attentions.In this paper,we proposed the hybrid configuration with a macro-encapsulation,and analyzed its cha...In recent years,heat storage system combining sensible and latent heat materials has received more and more attentions.In this paper,we proposed the hybrid configuration with a macro-encapsulation,and analyzed its charging performance with different influencing factors by CFD simulation.In the case,the sensible heat storage materials are magnesia brick or HT concrete and the phase change materials(PCMs)are mixed molten salts.Firstly,we analyzed the heat transfer characteristics of the hybrid configuration in charging process.Then,we analyzed the effect of heating power on charging performance.The maximum temperature of the heating surface shall not exceed 500℃as the constraint condition,the heat storage capacity increases at first and then decreases with the heating power.Then,we compared the charging performance of different solid structure and the hybrid configurations.Whether magnesia brick or HT concrete,the charging performance of the solid structure is better than that of the hybrid configuration,because the thermal conductivity of the molten salt is significantly lower than that of the two sensible heat storage materials.Then,we compared the charging performance of different molten salts.The hybrid configuration with lower melting point molten salt has better performance because of more intensity natural convection.Finally,we analyzed the charging performance of the hybrid configuration used the composite phase change material(CPCM)with high thermal conductivity and specific heat.From the result,the charging performance increases by 22.5%compared with the solid structure.These results indicate that the hybrid configuration with the macro-encapsulation method is a potential form of thermal energy storage,but it needs to be further optimized.展开更多
Static and dynamic experiments were carried out to validate scale inhibition performance of a green scale inhibitor-polyaspartic acid (PASP). From the static experiment, it was shown that below 60°C, polyaspartic...Static and dynamic experiments were carried out to validate scale inhibition performance of a green scale inhibitor-polyaspartic acid (PASP). From the static experiment, it was shown that below 60°C, polyaspartic acid is very effective in scale inhibition, with the scale inhibition ratio exceeding 90% with only 3 mg/L PASP for the 600 mg/L hardness solution. For a higher hardness solution of 800 mg/L, the scale inhibition ratio can also reach 90% with 6 and 12 mg/L PASP at 30 and 60°C respectively. The SEM photographs of CaCO3 crystals indicate that the crystal structure transforms from a compact stick-shape to a loose shape so that the scale can be washed away easily instead of being deposited on the heat transfer surface. The dynamic experimental results show that almost no scales formed on the heat transfer surface and the fouling thermal resistance decreases extraordinarily if PASP is added in the solution.展开更多
An in-situ visualization of two-phase flow inside anode flow bed of a small liquid fed direct methanol fuel cells in normal and reduced gravity has been conducted in a drop tower.The anode flow bed con-sists of 11 par...An in-situ visualization of two-phase flow inside anode flow bed of a small liquid fed direct methanol fuel cells in normal and reduced gravity has been conducted in a drop tower.The anode flow bed con-sists of 11 parallel straight channels.The length,width and depth of single channel,which had rec-tangular cross section,are 48.0,2.5 and 2.0mm,respectively.The rib width was 2.0mm.The experi-mental results indicated that when the fuel cell orientation is vertical,two-phase flow pattern in anode channels can evolve from bubbly flow in normal gravity into slug flow in microgravity.The size of bub-bles in the reduced gravity is also bigger.In microgravity,the bubbles rising speed in vertical channels is obviously slower than that in normal gravity.When the fuel cell orientation is horizontal,the slug flow in the reduced gravity has almost the same characteristic with that in normal gravity.It implies that the effect of gravity on two-phase flow is small and the bubbles removal is governed by viscous drag.When the gas slugs or gas columns occupy channels,the performance of liquid fed direct methanol fuel cells is failing rapidly.It infers that in long-term microgravity,flow bed and operating condition should be optimized to avoid concentration polarization of fuel cells.展开更多
A new heat mass transfer model was developed to predict the fouling process of calcium carbonate on heat transfer surface. The model took into account not only the crystallization fouling but also the particle fouling...A new heat mass transfer model was developed to predict the fouling process of calcium carbonate on heat transfer surface. The model took into account not only the crystallization fouling but also the particle fouling which was formed on the heat transfer surface by the suspension particles of calcium carbonate in the su- persaturated solution. Based on experimental results of the fouling process, the deposition and removal rates of the mixing fouling were expressed. Furthermore, the coupling effect of temperature with the fouling process was considered in the physics model. As a result the fouling resistance varying with time was obtained to describe the fouling process and the prediction was compared with experimental data under same conditions. The results showed that the present model could give a good prediction of fouling process, and the deviation was less than 15% of the experimental data in most cases. The new model is credible to predict the fouling process.展开更多
The single screw compressor(SSC)is widely used in air compression and refrigeration systems due to its many advantages.The meshing clearance between the screw groove and gate rotor teeth flank has a significant influe...The single screw compressor(SSC)is widely used in air compression and refrigeration systems due to its many advantages.The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance.In this paper,mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights.The refrigerating capacity,volume efficiency and adiabatic efficiency of the SSC are calculated and discussed.Three prototypes,with different meshing clearance heights,were manufactured to study the internal influence mechanisms.The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results.Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%-7.98%and 5.92%-9.4%,respectively.Based on the models,analysis under varying meshing clearance heights and working conditions was performed.Taking into account working performance,actual manufacturing conditions and manufacturing cost limitations,a meshing clearance height range from 0.01 mm to 0.08 mm is suggested.This study can provide important theoretical data and experimental support for the design,manufacturing and optimization of single screw compressors.展开更多
In order to get the natural convection heat transfer mechanism of molten salt, the experimental investigation of natural convective heat transfer of LiNO3was studied after it was simulated by numerical calculation. Ex...In order to get the natural convection heat transfer mechanism of molten salt, the experimental investigation of natural convective heat transfer of LiNO3was studied after it was simulated by numerical calculation. Experiment was carried out on the nat-ural convection heat transfer of air and water around the fine wire using the method of Joule heating. The results showed that the natural convection heat transfer of air and water around the fine wire agreed well with Fand's correlation. Based on the aforementioned experiment, the natural convection heat transfer of molten salt LiNO3was studied by experiment and the same results were got. Therefore, the natural convection heat transfer of molten salt can be calculated by Fand's correlation, which takes into consideration the effect of viscosity dissipation.展开更多
Heat transfer in molten salt in a cylinder tank is studied via simulation and experiment to obtain its natural convection heat transfer in a single energy storage tank. Simulation and experimental results show that th...Heat transfer in molten salt in a cylinder tank is studied via simulation and experiment to obtain its natural convection heat transfer in a single energy storage tank. Simulation and experimental results show that the natural convection heat transfer of water in a cylinder tank fits well with Garon＇s correlation. However, significant deviations occur when Garon＇s correlation is used to predict the natural convection heat transfer of molten salt because of its high viscosity and low thermal conductivity. However, the simulated data of the natural convection heat transfer of molten salt fit well with those of the experimental results Thus, a correlation that considers the effect of variable physical properties is proposed in this study to predict the natural con- vection heat transfer of molten salt. The deviation of the present data from the proposed correlation is less than ＋20%. The re- sults of this study can serve as a basis for the design of single energy storage tanks.展开更多
A miniature vapor compression refrigeration equipment prototype was developed for a range of microclimate control applications, including man portable cooling and distributed space conditioning. The miniature refriger...A miniature vapor compression refrigeration equipment prototype was developed for a range of microclimate control applications, including man portable cooling and distributed space conditioning. The miniature refrigeration equipment has dimensions of 260 mm × 250 mm × 120 mm, and weighs approximately 2.85 kg. The optimal motor and its transmission ratio, the optimal dimension of capillary tube and the optimal quantity of refrigerant charge were obtained by matching and operating performance experimental study. Experimental results show that the miniature refrigeration equipment can provide 300 W cooling, and its COPc is above 2.0.展开更多
In this paper several kinds of high temperature molten salts were investigated experimentally on viscosity-temperature characteristics with high-temperature viscometer.The viscosities of the molten salts were measured...In this paper several kinds of high temperature molten salts were investigated experimentally on viscosity-temperature characteristics with high-temperature viscometer.The viscosities of the molten salts were measured and compared with those from references to verify the reliability of the viscometer and measuring methods,and a good agreement was observed from the comparisons.Then,two new high-temperature molten salts were made from the HITEC salt by some additives and the viscosity-temperature profiles of them were obtained by experiments.The results show that the new molten salts have much lower viscosities,thus suitable for reducing the flow resistance in transportation system of high-temperature solar thermal power generation.展开更多
Single-phase and gas-liquid two-phase pressure drops caused by a sudden con-traction in microtubes were experimentally investigated at room temperature and atmospheric pressure,using nitrogen and water. The experiment...Single-phase and gas-liquid two-phase pressure drops caused by a sudden con-traction in microtubes were experimentally investigated at room temperature and atmospheric pressure,using nitrogen and water. The experimental results on pressure drop with a novel measurement method,the tiny gaps on the tubes,were used to characterize the sudden contraction pressure drop for tube diameters from 850 to 330 μm. The ranges of the gas and liquid superficial velocity were 2.55―322.08 and 0.98―9.78 m/s in the smaller tube respectively. In single-phase flow experiments,the contraction loss coefficients were larger than the experimental results from conventional tubes in the laminar flow. While in the turbulent flow,the contraction loss coefficients were slightly smaller than those from conventional tubes and predicted well by Kc=0.5×(1-σ2)0.75. In two-phase flow experiments,the slip flow model with a velocity slip ratio S=(ρL/ρG)1/3 showed a good prediction that reveals the occurrence of velocity slip. An empirical correlation for two-phase flow pressure drops caused by the sudden contraction was developed based on the proposed contraction loss coefficients correlation for single-phase flow and Mar-tinelli factor.展开更多
In this study, a novel generator for the single-effect LiBr-H2O absorption chiller using solar energy was investigated. A dual-chamber vortex generator (DCVG) consisted of a lower chamber and an upper chamber. The hot...In this study, a novel generator for the single-effect LiBr-H2O absorption chiller using solar energy was investigated. A dual-chamber vortex generator (DCVG) consisted of a lower chamber and an upper chamber. The hot weak LiBr-H2O liquid entered the lower chamber tangentially through a small nozzle to create a strong vortex flow. Due to the rotating flow, the pressure was reduced toward the central portion of the lower chamber. Experiments were conducted under different solution flow rates and temperatures. The experimental results showed that the lower pressure developed in the lower chamber could reduce the saturated temperature and help the evaporation in the generator that is more heat could be utilized to generate more refrigerant vapor. When the inlet temperature was 90°C, the COP of a solar absorption chiller using the DCVG could reach 0.83, which was higher than of the conventional absorption chiller by 22%.展开更多
In this paper,we carried out a series of experiments on fouling characteristics of 6 kinds of spiral-grooved tubes to investigate the impact of hardness,temperature and structure parameters of cold water on fouling ch...In this paper,we carried out a series of experiments on fouling characteristics of 6 kinds of spiral-grooved tubes to investigate the impact of hardness,temperature and structure parameters of cold water on fouling characteristics of spiral-grooved tube.Experimental results showed that when cold-water temperature decreased,fouling resistance of spiral-grooved tube also decreased.Asymptotic fouling resistance increased accompanied with increase of cold-water hardness.However,the asymptotic fouling resistance appeared to reduce when hardness increased to some extent.Geometric parameters of spiral-grooved tubes had remarkable effect on fouling resistance,which showed a tendency of decrease with increase of groove depth and decrease of pitch.In this study,the minimum asymptotic fouling resistance was observed in the spiral-grooved tube with small pitch and large groove depth.展开更多
Organic Rankine Cycle(ORC)is a promising technology for converting low or medium temperature heat into power.In order to improve the thermodynamic efficiency of ORC systems,adding a regenerator to the system has been ...Organic Rankine Cycle(ORC)is a promising technology for converting low or medium temperature heat into power.In order to improve the thermodynamic efficiency of ORC systems,adding a regenerator to the system has been widely discussed.However,this needs additional pipes and devices and they will produce additional pressure drop.Considering both the contributions of the regenerator and the power losses caused by additional pressure drop,a theoretical criterion for evaluating the thermodynamic effectiveness of adding a regenerator was proposed by means of mathematic and thermodynamic equations.The core of the criterion is a new concept named Critical Pressure Drop produced by the Regenerator(CPDR).A negative value of CPDR indicates that adding a regenerator will not contribute to the thermodynamic efficiency of ORC systems in any case.An effective regenerator needs a positive value of CPDR,and requires that the value of additional pressure drop produced by introducing the regenerator should be smaller than CPDR.The influences of evaporation temperature,condensation temperature,expander efficiency,regenerator effectiveness and working fluids on CPDR were also examined.It was found that lower evaporation temperature or using working fluids with higher critical temperature tends to reduce the value of CPDR.展开更多
基金supported by National Key R&D Program of China(Grant numbers 2022YFB2405202)。
文摘For combined sensible-latent heat storage system(CSLHS)(termed as the hybrid configuration),macro encapsulation can effectively solve the leakage problem of PCMs.However,due to the poor thermal conductivity of PCMs,the charging performance of the hybrid configuration slightly increases compared to the solid structure(with only sensible materials).Meanwhile,the natural convection in the PCMs zone could improve the charging performance.So,how to improve natural convection intensity is a key issue for the CSLHS by macro encapsulating.It is found that adding fins can significantly enhance natural convection and accelerate the melting of PCM.In this paper,we proposed the hybrid configuration with fins built-in by macro encapsulation,and analyzed its charging performance with different fin structural parameters in the PCM zone by CFD simulation.In the case,the sensible heat storage material is high-temperature concrete and the PCM is a low-melting-point mixed molten salt.We analyzed the effects of fin number,fin length and fin thickness on the charging performance of the hybrid configuration respectively.From the result,the charging performance increases with the fin number,but the increase rate gradually decreases.When the fin number is 6,the charging performance increases by 20.18%compared to the situation without fin.The charging performance increases gradually with the fin length.Compared with the hybrid configuration without fin,for each 10 mm increase in fin length,its charging performances increase by 4.09%,5.26%,7.02%,8.77%,11.70%,and 15.79%,respectively.Different from number and length of fins,the effect of thickness on the charging performance is very small.When the fin thickness increased from 1 mm to 4 mm,the charging performance only increased by 2.3%.It indicates that the main reason for the improving the charging performance is to increase the natural convection intensity by dividing the PCM zone through fins.These results show that the charging performance of the CSLHS with macro encapsulation can be improved by optimizing fin structural parameters.
基金supported by Science and technology plan of Inner Mongolia Autonomous Region of China(Grant numbers 2019ZD014).
文摘In recent years,heat storage system combining sensible and latent heat materials has received more and more attentions.In this paper,we proposed the hybrid configuration with a macro-encapsulation,and analyzed its charging performance with different influencing factors by CFD simulation.In the case,the sensible heat storage materials are magnesia brick or HT concrete and the phase change materials(PCMs)are mixed molten salts.Firstly,we analyzed the heat transfer characteristics of the hybrid configuration in charging process.Then,we analyzed the effect of heating power on charging performance.The maximum temperature of the heating surface shall not exceed 500℃as the constraint condition,the heat storage capacity increases at first and then decreases with the heating power.Then,we compared the charging performance of different solid structure and the hybrid configurations.Whether magnesia brick or HT concrete,the charging performance of the solid structure is better than that of the hybrid configuration,because the thermal conductivity of the molten salt is significantly lower than that of the two sensible heat storage materials.Then,we compared the charging performance of different molten salts.The hybrid configuration with lower melting point molten salt has better performance because of more intensity natural convection.Finally,we analyzed the charging performance of the hybrid configuration used the composite phase change material(CPCM)with high thermal conductivity and specific heat.From the result,the charging performance increases by 22.5%compared with the solid structure.These results indicate that the hybrid configuration with the macro-encapsulation method is a potential form of thermal energy storage,but it needs to be further optimized.
基金Supported by the Special Funds for Major State Basic Research Projects of China (Grant No. 2007CB206904)the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (Grant No. 00084)
文摘Static and dynamic experiments were carried out to validate scale inhibition performance of a green scale inhibitor-polyaspartic acid (PASP). From the static experiment, it was shown that below 60°C, polyaspartic acid is very effective in scale inhibition, with the scale inhibition ratio exceeding 90% with only 3 mg/L PASP for the 600 mg/L hardness solution. For a higher hardness solution of 800 mg/L, the scale inhibition ratio can also reach 90% with 6 and 12 mg/L PASP at 30 and 60°C respectively. The SEM photographs of CaCO3 crystals indicate that the crystal structure transforms from a compact stick-shape to a loose shape so that the scale can be washed away easily instead of being deposited on the heat transfer surface. The dynamic experimental results show that almost no scales formed on the heat transfer surface and the fouling thermal resistance decreases extraordinarily if PASP is added in the solution.
基金Supported by the National Natural Science Foundation of China(Grant No. 50406010)Excellent Talents Programme of Beijing Municipality(Grant No. 20081D0501500167)
文摘An in-situ visualization of two-phase flow inside anode flow bed of a small liquid fed direct methanol fuel cells in normal and reduced gravity has been conducted in a drop tower.The anode flow bed con-sists of 11 parallel straight channels.The length,width and depth of single channel,which had rec-tangular cross section,are 48.0,2.5 and 2.0mm,respectively.The rib width was 2.0mm.The experi-mental results indicated that when the fuel cell orientation is vertical,two-phase flow pattern in anode channels can evolve from bubbly flow in normal gravity into slug flow in microgravity.The size of bub-bles in the reduced gravity is also bigger.In microgravity,the bubbles rising speed in vertical channels is obviously slower than that in normal gravity.When the fuel cell orientation is horizontal,the slug flow in the reduced gravity has almost the same characteristic with that in normal gravity.It implies that the effect of gravity on two-phase flow is small and the bubbles removal is governed by viscous drag.When the gas slugs or gas columns occupy channels,the performance of liquid fed direct methanol fuel cells is failing rapidly.It infers that in long-term microgravity,flow bed and operating condition should be optimized to avoid concentration polarization of fuel cells.
基金the National Basic Research Program of China ("973" Project) (Grant No. G2000026304)the Beijing Municipal Elitist Cultivation Project (Grant No. 20061D0501500186)
文摘A new heat mass transfer model was developed to predict the fouling process of calcium carbonate on heat transfer surface. The model took into account not only the crystallization fouling but also the particle fouling which was formed on the heat transfer surface by the suspension particles of calcium carbonate in the su- persaturated solution. Based on experimental results of the fouling process, the deposition and removal rates of the mixing fouling were expressed. Furthermore, the coupling effect of temperature with the fouling process was considered in the physics model. As a result the fouling resistance varying with time was obtained to describe the fouling process and the prediction was compared with experimental data under same conditions. The results showed that the present model could give a good prediction of fouling process, and the deviation was less than 15% of the experimental data in most cases. The new model is credible to predict the fouling process.
基金the financial support provided by the National Key R&D Program of China(NO.2016YFC0700403)Beijing Municipal Natural Science Foundation(NO.3181001)Project supported by Beijing Chaoyang District Postdoctoral Research Foundation(NO.2018ZZ-01-28)。
文摘The single screw compressor(SSC)is widely used in air compression and refrigeration systems due to its many advantages.The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance.In this paper,mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights.The refrigerating capacity,volume efficiency and adiabatic efficiency of the SSC are calculated and discussed.Three prototypes,with different meshing clearance heights,were manufactured to study the internal influence mechanisms.The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results.Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%-7.98%and 5.92%-9.4%,respectively.Based on the models,analysis under varying meshing clearance heights and working conditions was performed.Taking into account working performance,actual manufacturing conditions and manufacturing cost limitations,a meshing clearance height range from 0.01 mm to 0.08 mm is suggested.This study can provide important theoretical data and experimental support for the design,manufacturing and optimization of single screw compressors.
基金supported by the Beijing Natural Science Foundation(Grant No. 3132012)the National Basic Research Program of China("973" Program) (Grant No. 2010CB227103)Beijing Municipal Science and Technology Commission of Science and Technology Plan(Grant No. D121100001012002)
文摘In order to get the natural convection heat transfer mechanism of molten salt, the experimental investigation of natural convective heat transfer of LiNO3was studied after it was simulated by numerical calculation. Experiment was carried out on the nat-ural convection heat transfer of air and water around the fine wire using the method of Joule heating. The results showed that the natural convection heat transfer of air and water around the fine wire agreed well with Fand's correlation. Based on the aforementioned experiment, the natural convection heat transfer of molten salt LiNO3was studied by experiment and the same results were got. Therefore, the natural convection heat transfer of molten salt can be calculated by Fand's correlation, which takes into consideration the effect of viscosity dissipation.
基金supported by Beijing Natural Science Foundation(Grant No.3132012)the National Natural Science Foundation of China(Grant No.51756006)by the Project of the International Cooperation and Exchange of the National Natural Science Foundation of China(Grant No.5136113570)
文摘Heat transfer in molten salt in a cylinder tank is studied via simulation and experiment to obtain its natural convection heat transfer in a single energy storage tank. Simulation and experimental results show that the natural convection heat transfer of water in a cylinder tank fits well with Garon＇s correlation. However, significant deviations occur when Garon＇s correlation is used to predict the natural convection heat transfer of molten salt because of its high viscosity and low thermal conductivity. However, the simulated data of the natural convection heat transfer of molten salt fit well with those of the experimental results Thus, a correlation that considers the effect of variable physical properties is proposed in this study to predict the natural con- vection heat transfer of molten salt. The deviation of the present data from the proposed correlation is less than ＋20%. The re- sults of this study can serve as a basis for the design of single energy storage tanks.
基金the National Basic Research Program of China (Grant No. G2000026304)
文摘A miniature vapor compression refrigeration equipment prototype was developed for a range of microclimate control applications, including man portable cooling and distributed space conditioning. The miniature refrigeration equipment has dimensions of 260 mm × 250 mm × 120 mm, and weighs approximately 2.85 kg. The optimal motor and its transmission ratio, the optimal dimension of capillary tube and the optimal quantity of refrigerant charge were obtained by matching and operating performance experimental study. Experimental results show that the miniature refrigeration equipment can provide 300 W cooling, and its COPc is above 2.0.
基金supported by the National Natural Science Foundation Key Project of China (Grant No. 50736005)the National Basic Research Program of China ("973" Program) (Grant No. 2010CB227103)
文摘In this paper several kinds of high temperature molten salts were investigated experimentally on viscosity-temperature characteristics with high-temperature viscometer.The viscosities of the molten salts were measured and compared with those from references to verify the reliability of the viscometer and measuring methods,and a good agreement was observed from the comparisons.Then,two new high-temperature molten salts were made from the HITEC salt by some additives and the viscosity-temperature profiles of them were obtained by experiments.The results show that the new molten salts have much lower viscosities,thus suitable for reducing the flow resistance in transportation system of high-temperature solar thermal power generation.
基金the National Key Basic Research Program (Grant No. G2000026300)Beijing Open Fund
文摘Single-phase and gas-liquid two-phase pressure drops caused by a sudden con-traction in microtubes were experimentally investigated at room temperature and atmospheric pressure,using nitrogen and water. The experimental results on pressure drop with a novel measurement method,the tiny gaps on the tubes,were used to characterize the sudden contraction pressure drop for tube diameters from 850 to 330 μm. The ranges of the gas and liquid superficial velocity were 2.55―322.08 and 0.98―9.78 m/s in the smaller tube respectively. In single-phase flow experiments,the contraction loss coefficients were larger than the experimental results from conventional tubes in the laminar flow. While in the turbulent flow,the contraction loss coefficients were slightly smaller than those from conventional tubes and predicted well by Kc=0.5×(1-σ2)0.75. In two-phase flow experiments,the slip flow model with a velocity slip ratio S=(ρL/ρG)1/3 showed a good prediction that reveals the occurrence of velocity slip. An empirical correlation for two-phase flow pressure drops caused by the sudden contraction was developed based on the proposed contraction loss coefficients correlation for single-phase flow and Mar-tinelli factor.
基金Supported by the Opening Foundation of Beijing Municipality
文摘In this study, a novel generator for the single-effect LiBr-H2O absorption chiller using solar energy was investigated. A dual-chamber vortex generator (DCVG) consisted of a lower chamber and an upper chamber. The hot weak LiBr-H2O liquid entered the lower chamber tangentially through a small nozzle to create a strong vortex flow. Due to the rotating flow, the pressure was reduced toward the central portion of the lower chamber. Experiments were conducted under different solution flow rates and temperatures. The experimental results showed that the lower pressure developed in the lower chamber could reduce the saturated temperature and help the evaporation in the generator that is more heat could be utilized to generate more refrigerant vapor. When the inlet temperature was 90°C, the COP of a solar absorption chiller using the DCVG could reach 0.83, which was higher than of the conventional absorption chiller by 22%.
基金supported by the Special Funds for Major State Basic Research Projects of China ("973" Program) (Grant No. 2007CB206904)
文摘In this paper,we carried out a series of experiments on fouling characteristics of 6 kinds of spiral-grooved tubes to investigate the impact of hardness,temperature and structure parameters of cold water on fouling characteristics of spiral-grooved tube.Experimental results showed that when cold-water temperature decreased,fouling resistance of spiral-grooved tube also decreased.Asymptotic fouling resistance increased accompanied with increase of cold-water hardness.However,the asymptotic fouling resistance appeared to reduce when hardness increased to some extent.Geometric parameters of spiral-grooved tubes had remarkable effect on fouling resistance,which showed a tendency of decrease with increase of groove depth and decrease of pitch.In this study,the minimum asymptotic fouling resistance was observed in the spiral-grooved tube with small pitch and large groove depth.
基金supported by Beijing Municipal Natural Science Foundation(NO.3202006).
文摘Organic Rankine Cycle(ORC)is a promising technology for converting low or medium temperature heat into power.In order to improve the thermodynamic efficiency of ORC systems,adding a regenerator to the system has been widely discussed.However,this needs additional pipes and devices and they will produce additional pressure drop.Considering both the contributions of the regenerator and the power losses caused by additional pressure drop,a theoretical criterion for evaluating the thermodynamic effectiveness of adding a regenerator was proposed by means of mathematic and thermodynamic equations.The core of the criterion is a new concept named Critical Pressure Drop produced by the Regenerator(CPDR).A negative value of CPDR indicates that adding a regenerator will not contribute to the thermodynamic efficiency of ORC systems in any case.An effective regenerator needs a positive value of CPDR,and requires that the value of additional pressure drop produced by introducing the regenerator should be smaller than CPDR.The influences of evaporation temperature,condensation temperature,expander efficiency,regenerator effectiveness and working fluids on CPDR were also examined.It was found that lower evaporation temperature or using working fluids with higher critical temperature tends to reduce the value of CPDR.
