Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of ca...Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of calcium carbonate （CaCO3）, which has inverse solubility characteristics. This investigation focused on the mechanism to control deposition and the morphology of crystalline deposits. A series of experiments were carried out at different surface and bulk temperatures, fluid velocities and salt ion concentrations. It is shown that the deposition rate is controlled by different mechanism in the range of experimental parameters, depending on salt ion concentration. At higher ion concentration, the fouling rate increases linearly with surface temperature and the effect of flow velocity on deposition rate is quite strong, suggesting that mass diffusion controls the fouling process. On the contrary, at lower ion concentration, the fouling rate increases exponentially with surface temperature and is independent of the velocity, illustrating that surface reaction controls the fouling process. By analysis of the morphology of scale, two types of crystal （calcite and aragonite） are formed. The lower the temperature and ion concentration, the longer the induction period and the higher the percentage of calcite nreciDitated.展开更多
Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat...Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.展开更多
Experiments on subcooled flow boiling have been conducted using water in a rectangular flow channel.Similar to the coolant channel in internal combustion engines(IC engines),the flow channel in this experiment was asy...Experiments on subcooled flow boiling have been conducted using water in a rectangular flow channel.Similar to the coolant channel in internal combustion engines(IC engines),the flow channel in this experiment was asymmetrically heated.Bubble images were captured using a high speed camera from the side view of the channel.The experimental conditions in terms of bulk temperature,bulk velocity,pressure and heat flux ranged from 65°C–75°C,0.25 m/s–0.75 m/s,1–1.7 bar and 490 kW/m2–700 kW/m2,respectively.On the basis of these tests,a statistical analysis of the bubble size has been conducted considering a population of 1400 samples.It has been found that the mean Sauter bubble diameter increases with the decrease of subcooling,bulk velocity,pressure and increased heat flux.A modified correlation has been finally proposed to predict the mean Sauter bubble diameter under subcooled flow boiling conditions upstream of the onset of significant void,which shows good accuracy with the experimental results.展开更多
A novel analytical model to determine the heat flux of subcooled pool boiling in fractal nanofluids is developed. The model considers the fractal character of nanofluids in terms of the fractal dimension of nanopartic...A novel analytical model to determine the heat flux of subcooled pool boiling in fractal nanofluids is developed. The model considers the fractal character of nanofluids in terms of the fractal dimension of nanoparticles and the fractal dimen- sion of active cavities on the heated surfaces; it also takes into account the effect of the Brownian motion of nanoparticles, which has no empirical constant but has parameters with physical meanings. The proposed model is expressed as a function of the subcooling of fluids and the wall superheat. The fractal analytical model is verified by a reasonable agreement with the experimental data and the results obtained from existing models.展开更多
The increasing demand of cooling in internal combustion engines(ICE)due to engine downsizing may require a shift in the heat removal method from the traditional single phase liquid convection to the application of new...The increasing demand of cooling in internal combustion engines(ICE)due to engine downsizing may require a shift in the heat removal method from the traditional single phase liquid convection to the application of new technologies based on subcooled fluid boiling.Accordingly,in the present study,experiments based on subcooled flow boiling of 50/50 by volume mixture of ethylene glycol and water coolant(EG/W)in a rectangular channel heated by a cast iron block are presented.Different degrees of subcooling,velocity and pressure conditions are examined.Comparison of three empirical reference models shows that noticeable deviations occur especially when low bulk subcooling and velocity conditions are considered.On the basis of the experimental data,a modified power-type wall heat flux model is developed and its ability to represent adequately reality is tested through numerical simulations against a reference rig case and a practical diesel engine.Computational results show that this modified model can effectively be used for practical engine cooling system design.展开更多
In order to realize safe and stable operation of a water-cooled W/Cu divertor under high heating condition,the exact knowledge of its subcooled boiling heat transfer characteristics under different design parameters i...In order to realize safe and stable operation of a water-cooled W/Cu divertor under high heating condition,the exact knowledge of its subcooled boiling heat transfer characteristics under different design parameters is crucial.In this paper,subcooled boiling heat transfer in a water-cooled W/Cu divertor was numerically investigated based on computational fluid dynamic（CFD）.The boiling heat transfer was simulated based on the Euler homogeneous phase model,and local differences of liquid physical properties were considered under one-sided high heating conditions.The calculated wall temperature was in good agreement with experimental results,with the maximum error of 5%only.On this basis,the void fraction distribution,flow field and heat transfer coefficient（HTC）distribution were obtained.The effects of heat flux,inlet velocity and inlet temperature on temperature distribution and pressure drop of a water-cooled W/Cu divertor were also investigated.These results provide a valuable reference for the thermal-hydraulic design of a water-cooled W/Cu divertor.展开更多
Subcooled liquid solubility is the water solubility for a hypothetical state of liquid. It is an important parameter for multicomponent nonaqueous phase liquids （NAPLs） containing polycyclic aromatic hydrocarbons （...Subcooled liquid solubility is the water solubility for a hypothetical state of liquid. It is an important parameter for multicomponent nonaqueous phase liquids （NAPLs） containing polycyclic aromatic hydrocarbons （PAHs）, which can exist as liquids even though most of the solutes are solid in their pure form at ambient temperature. So far, subcooled liquid solubilities were estimated from the solid water solubility and fugacity ratio of the solid and （subcooled） liquid phase, but rarely derived from experi- mental data. In our study, partitioning batch experiments were performed to determine the subcooled liquid solubility of PAHs in NAPL-water system. For selected PAH, a series of batch experiments were carried out at increased mole fractions of the target component in the NAPL and at a constant NAPL/ water volume ratio. The equilibrium aqueous PAH concentrations were measured with HPLC and/or GC- MS. The suhcooled liquid solubility was derived by extrapolation of the experimental equilibrium aqueous concentration to a mole fraction of unity. With the derived subcooled liquid solubility, the fugacity ratio and enthalpy of fusion of the solute were also estimated. Our results show a good agreement between the experimentally determined and published data.展开更多
Based on acquisition of sound pressure in subcooled boiling twophase system and through dynamic data processing methods, the dynamical behavior of the system is discussed. With the introduction of fractal concept, an ...Based on acquisition of sound pressure in subcooled boiling twophase system and through dynamic data processing methods, the dynamical behavior of the system is discussed. With the introduction of fractal concept, an analysis to the fractal feature of sound pressure signal is carried out. Moreover, the pseudo phase diagrams of typical time series of sound pressure are given. Finally, through dynamic clustering and on the basis of calculating correlation dimension and Hurst exponent of sound time series on different subcooling conditions, the recognition of developing regime of the twophase system is delivered, which provides a new practical approach of recognition and diagnosis for vaporliquid boiling system.展开更多
In order to realize steady-state operation of the neutral beam injection（NBI） system with high beam energy,an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside hig...In order to realize steady-state operation of the neutral beam injection（NBI） system with high beam energy,an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside high-heat-flux（HHF） components in the system are key issues.In this paper,taking the HHF ion dump with swirl tubes in NBI system as an example,an accurate thermal dynamic simulation method based on computational fluid dynamics（CFD） and the finite volume method is presented to predict performance of the HHF component.In this simulation method,the Eulerian multiphase method together with some empirical corrections about the inter-phase transfer model and the wall heat flux partitioning model are considered to describe the subcooled boiling.The reliability of the proposed method is validated by an experimental example with subcooled boiling inside swirl tube.The proposed method provides an important tool for the refined thermal and flow dynamic analysis of HHF components,and can be extended to study the thermal design of other complex HHF engineering structures in a straightforward way.The simulation results also verify that the swirl tube is a promising heat removing structure for the HHF components of the NBI system.展开更多
During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the in...During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.展开更多
This paper aims to model a subcooled flow boiling in a vertical stainless-steel micro-channel with an upward flow in 1 mm diameter, 40 mm length and 0.325 mm thickness tube. Water has been considered as a working flui...This paper aims to model a subcooled flow boiling in a vertical stainless-steel micro-channel with an upward flow in 1 mm diameter, 40 mm length and 0.325 mm thickness tube. Water has been considered as a working fluid. The heat flux varies from 600 - 750 kW·m-2, input velocity from 1 - 2 m·s-1, and the subcooled temperature varies from 59.6 - 79.6 K. The working pressure and saturation temperature are 1 atm and 372.75 K, respectively. The results show that, the flow boiling keeps the temperature of the channel wall lower and more uniform than a single-phase flow, as long as the flow boiling does not reach the dry-out point. The onset point of dry-out depends on three factors, heat flux, inlet velocity, and subcooled temperature. In addition, the dry-out occurs at a point near the channel inlet with increased heat flux and subcooled temperature. Decreasing the inlet velocity would also cause the dry-out point to shift closer to the inlet of the channel.展开更多
The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow ann...The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow annular channels under the working condition of pressure ranging from 0.1 to 0.3 MPa and low mass flow rate from 6 to 60 kgm^-2 s^-1. Experimental test channels were annular and heated bilaterally with the channel gap of lmm and 1.5mm, and heated length of 1500mm.The location of the dryout was observed and measured by experiment with investigating the various system parameter effects on dryout point, and the results show that the location of dryout point is basically stable and repeating and the heat transfer coefficient increased with heat flux, mass flux and pressure, however, decreases with the gap size. Next, new correlations of CHF and critical vapor quality for narrow annular channels was proposed and calculation results shown a good agreement with the experimental data.展开更多
The dynamical behavior of the subcooled boiling two-phase system was introduced and discussed. With the introduction of fractal concept, an analysis of the fractal feature of pressure wave signals from nonlinear dynam...The dynamical behavior of the subcooled boiling two-phase system was introduced and discussed. With the introduction of fractal concept, an analysis of the fractal feature of pressure wave signals from nonlinear dynamics point of view, was carried out. Meanwhile, the pseudo phase diagrams of typical time series of sound pressure were given. Finally, through dynamic clustering and on the basis of calculating correlation dimension and Hurst exponent of pressure wave time series on different subcooling conditions, the recognition of developing regime of the two-phase system was delivered, which might provide a promising approach of recognition and diagnosis of a boiling system.展开更多
The two-stage transcritical CO_(2) refrigeration cycle with dedicated dual-subcooling and mechanical recooling is proposed.The inter-stage pressure is critical for such cycle performances;however,it has not been studi...The two-stage transcritical CO_(2) refrigeration cycle with dedicated dual-subcooling and mechanical recooling is proposed.The inter-stage pressure is critical for such cycle performances;however,it has not been studied exactly.Therefore,the research aim is to disclose the effect of inter-stage pressure on performances of the proposed cycle.The main work consists of four aspects.Firstly,the comparative study is performed to display advantages of the proposed cycle.Secondly,the key temperatures,heat and power consumptions as well as performance indicators for different inter-stage pressures are analyzed in detail,based on the parametric model.Thirdly,the optimal inter-stage pressure for different conditions is obtained by the nonlinear direct search method.Finally,the economic performance is assessed.It is found that the compressor power of the proposed cycle drops by 12%,and the working temperature lower limit is reduced by 11℃.Furthermore,it is considered that the optimal inter-stage pressure is insensitive to the heat source temperature.The novelty lies in illustrating the effect of inter-stage pressure,obtaining trends of the optimal value,and pointing out the system feasibility.The paper is favorable for design and operation optimization of the proposed system.展开更多
Energy storage devices are the hub of a multi-energy complementary distributed energy system.Hydrated salts are the most suitable phase change material for energy storage devices,but subcooling is the main obstacle to...Energy storage devices are the hub of a multi-energy complementary distributed energy system.Hydrated salts are the most suitable phase change material for energy storage devices,but subcooling is the main obstacle to their application.Nucleation requires a driving force so the use of nucleating agents alone does not reduce subcooling to a very low level.To address this issue,this paper first screened nucleating agents and then further reduced the subcooling of sodium acetate trihydrate in conjunction with stirring or direct current.The effects of rotor mass,rotational speed,direct current voltage,and electrode material on nucleation were analyzed.Finally,the stability of the composite phase change material in the presence of simultaneous stirring and energization was analyzed.The results showed that the addition of 1.5%in weight of disodium hydrogen phosphate dodecahydrate to sodium acetate trihydrate can reduce the subcooling to about 2.3℃.Continued addition of stirring or electricity can reduce the subcooling of sodium acetate trihydrate to within 0.5℃ or even eliminate it.The higher the momentum of the stirring,the better the improvement in subcooling,phase separation,and thermal conductivity.The higher the direct current voltage,the better the nucleation effect,but the electrode life will be lower.The silver electrode has the best nucleation effect.No new material was produced in the solution after 100 cycles in the presence of both stirring and direct current.The melting point of the phase change material was increased by 0.2℃ and the latent heat value decreased by 1.8%,still with good stability.The trace of deionized water should be added to the phase change material in subsequent studies to compensate for the consumption ofwaterby theanodicelution.展开更多
An experimental investigation was conducted on subcooled nucleate boiling on ultra-small wires having diameters of 25―100 μm. High-speed photography and laser PIV (Particle Image Velocimetry) technology were used to...An experimental investigation was conducted on subcooled nucleate boiling on ultra-small wires having diameters of 25―100 μm. High-speed photography and laser PIV (Particle Image Velocimetry) technology were used to visually observe the bubble dynamics. For highly subcooled boiling at moderate heat fluxes, the bubbles generally remained attached to the micro heating wires and bubble-top jet flows were clearly observed. Smaller bubbles usually had stronger bubble-top jet flows, while larger bubbles seemed to produce multi-jet flows. The structures of the bubble-top jet flows, as well as multi-jet flows, were proposed from the experimental observation. A model was developed to describe jet flow phenomena from bubbles on micro wires. Numerical simulations for bubbles having diameter of 0.03 and 0.06 mm showed that both the bubble-top and multi-jet flows were induced by a strong Marangoni effect due to high temperature gradients near the wire. The predicted velocity magnitudes and flow structures agreed very well with experimental measurements. The bubble size relative to the wire is an important factor affecting the jet flow structure. For a 0.03 mm bubble on a 0.1 mm wire, only a bubble-top jet flow forms, while a complex multi-jet flow pattern forms around the bubble with a weak bubble-top jet and two side jet flows for a 0.06 mm bubble.展开更多
基金Supported by the Special Funds for Major State Basic Research Projects of China (G2000026304)
文摘Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of calcium carbonate （CaCO3）, which has inverse solubility characteristics. This investigation focused on the mechanism to control deposition and the morphology of crystalline deposits. A series of experiments were carried out at different surface and bulk temperatures, fluid velocities and salt ion concentrations. It is shown that the deposition rate is controlled by different mechanism in the range of experimental parameters, depending on salt ion concentration. At higher ion concentration, the fouling rate increases linearly with surface temperature and the effect of flow velocity on deposition rate is quite strong, suggesting that mass diffusion controls the fouling process. On the contrary, at lower ion concentration, the fouling rate increases exponentially with surface temperature and is independent of the velocity, illustrating that surface reaction controls the fouling process. By analysis of the morphology of scale, two types of crystal （calcite and aragonite） are formed. The lower the temperature and ion concentration, the longer the induction period and the higher the percentage of calcite nreciDitated.
基金Supported by the National Natural Science Foundation of China （51106119, 81100707）, the Fundamental Research Funds for the Central University of China, Doctoral Fund of Ministry of Education （20110201120052） and the National Science and Technology Sur0orting Item （2012BAA08B03）.
文摘Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.
基金the National Natural Science Foundation of China(Grant No.51576116)the National Natural Science Foundation of Shandong Province(Grant No.ZR2019MEE041)。
文摘Experiments on subcooled flow boiling have been conducted using water in a rectangular flow channel.Similar to the coolant channel in internal combustion engines(IC engines),the flow channel in this experiment was asymmetrically heated.Bubble images were captured using a high speed camera from the side view of the channel.The experimental conditions in terms of bulk temperature,bulk velocity,pressure and heat flux ranged from 65°C–75°C,0.25 m/s–0.75 m/s,1–1.7 bar and 490 kW/m2–700 kW/m2,respectively.On the basis of these tests,a statistical analysis of the bubble size has been conducted considering a population of 1400 samples.It has been found that the mean Sauter bubble diameter increases with the decrease of subcooling,bulk velocity,pressure and increased heat flux.A modified correlation has been finally proposed to predict the mean Sauter bubble diameter under subcooled flow boiling conditions upstream of the onset of significant void,which shows good accuracy with the experimental results.
基金Project supported by the National Natural Science Foundation of China (Grant No.11102100)the Natural Science Foundation of Fujian Province,China (Grant No.2012J01017)the Scientific Research Special Foundation for Provincial University of Education Department of Fujian Province,China (Grant No.JK2011056)
文摘A novel analytical model to determine the heat flux of subcooled pool boiling in fractal nanofluids is developed. The model considers the fractal character of nanofluids in terms of the fractal dimension of nanoparticles and the fractal dimen- sion of active cavities on the heated surfaces; it also takes into account the effect of the Brownian motion of nanoparticles, which has no empirical constant but has parameters with physical meanings. The proposed model is expressed as a function of the subcooling of fluids and the wall superheat. The fractal analytical model is verified by a reasonable agreement with the experimental data and the results obtained from existing models.
基金This work was supported by the National Key Research and Development Project of China(Grant No.2017YFB0103504)National Natural Science Foundation of China(Grant No.51576116).
文摘The increasing demand of cooling in internal combustion engines(ICE)due to engine downsizing may require a shift in the heat removal method from the traditional single phase liquid convection to the application of new technologies based on subcooled fluid boiling.Accordingly,in the present study,experiments based on subcooled flow boiling of 50/50 by volume mixture of ethylene glycol and water coolant(EG/W)in a rectangular channel heated by a cast iron block are presented.Different degrees of subcooling,velocity and pressure conditions are examined.Comparison of three empirical reference models shows that noticeable deviations occur especially when low bulk subcooling and velocity conditions are considered.On the basis of the experimental data,a modified power-type wall heat flux model is developed and its ability to represent adequately reality is tested through numerical simulations against a reference rig case and a practical diesel engine.Computational results show that this modified model can effectively be used for practical engine cooling system design.
基金supported by the National Magnetic Confinement Fusion Science Program of China(No.2010GB104005)Funding of Jiangsu Innovation Program for Graduate Education(CXLX12.0170)the Fundamental Research Funds for the Central Universities of China
文摘In order to realize safe and stable operation of a water-cooled W/Cu divertor under high heating condition,the exact knowledge of its subcooled boiling heat transfer characteristics under different design parameters is crucial.In this paper,subcooled boiling heat transfer in a water-cooled W/Cu divertor was numerically investigated based on computational fluid dynamic（CFD）.The boiling heat transfer was simulated based on the Euler homogeneous phase model,and local differences of liquid physical properties were considered under one-sided high heating conditions.The calculated wall temperature was in good agreement with experimental results,with the maximum error of 5%only.On this basis,the void fraction distribution,flow field and heat transfer coefficient（HTC）distribution were obtained.The effects of heat flux,inlet velocity and inlet temperature on temperature distribution and pressure drop of a water-cooled W/Cu divertor were also investigated.These results provide a valuable reference for the thermal-hydraulic design of a water-cooled W/Cu divertor.
基金financial support by the Deutsche Forschungsgemeinschaft as part of the research unit"Transport and Reactions in Porous Media"(HA 3453/6-2)
文摘Subcooled liquid solubility is the water solubility for a hypothetical state of liquid. It is an important parameter for multicomponent nonaqueous phase liquids （NAPLs） containing polycyclic aromatic hydrocarbons （PAHs）, which can exist as liquids even though most of the solutes are solid in their pure form at ambient temperature. So far, subcooled liquid solubilities were estimated from the solid water solubility and fugacity ratio of the solid and （subcooled） liquid phase, but rarely derived from experi- mental data. In our study, partitioning batch experiments were performed to determine the subcooled liquid solubility of PAHs in NAPL-water system. For selected PAH, a series of batch experiments were carried out at increased mole fractions of the target component in the NAPL and at a constant NAPL/ water volume ratio. The equilibrium aqueous PAH concentrations were measured with HPLC and/or GC- MS. The suhcooled liquid solubility was derived by extrapolation of the experimental equilibrium aqueous concentration to a mole fraction of unity. With the derived subcooled liquid solubility, the fugacity ratio and enthalpy of fusion of the solute were also estimated. Our results show a good agreement between the experimentally determined and published data.
文摘Based on acquisition of sound pressure in subcooled boiling twophase system and through dynamic data processing methods, the dynamical behavior of the system is discussed. With the introduction of fractal concept, an analysis to the fractal feature of sound pressure signal is carried out. Moreover, the pseudo phase diagrams of typical time series of sound pressure are given. Finally, through dynamic clustering and on the basis of calculating correlation dimension and Hurst exponent of sound time series on different subcooling conditions, the recognition of developing regime of the twophase system is delivered, which provides a new practical approach of recognition and diagnosis for vaporliquid boiling system.
基金supported by the Special Program of ITER(International Thermonuclear Experimental Reactor)in China(No.2013GB101002)
文摘In order to realize steady-state operation of the neutral beam injection（NBI） system with high beam energy,an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside high-heat-flux（HHF） components in the system are key issues.In this paper,taking the HHF ion dump with swirl tubes in NBI system as an example,an accurate thermal dynamic simulation method based on computational fluid dynamics（CFD） and the finite volume method is presented to predict performance of the HHF component.In this simulation method,the Eulerian multiphase method together with some empirical corrections about the inter-phase transfer model and the wall heat flux partitioning model are considered to describe the subcooled boiling.The reliability of the proposed method is validated by an experimental example with subcooled boiling inside swirl tube.The proposed method provides an important tool for the refined thermal and flow dynamic analysis of HHF components,and can be extended to study the thermal design of other complex HHF engineering structures in a straightforward way.The simulation results also verify that the swirl tube is a promising heat removing structure for the HHF components of the NBI system.
文摘During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.
文摘This paper aims to model a subcooled flow boiling in a vertical stainless-steel micro-channel with an upward flow in 1 mm diameter, 40 mm length and 0.325 mm thickness tube. Water has been considered as a working fluid. The heat flux varies from 600 - 750 kW·m-2, input velocity from 1 - 2 m·s-1, and the subcooled temperature varies from 59.6 - 79.6 K. The working pressure and saturation temperature are 1 atm and 372.75 K, respectively. The results show that, the flow boiling keeps the temperature of the channel wall lower and more uniform than a single-phase flow, as long as the flow boiling does not reach the dry-out point. The onset point of dry-out depends on three factors, heat flux, inlet velocity, and subcooled temperature. In addition, the dry-out occurs at a point near the channel inlet with increased heat flux and subcooled temperature. Decreasing the inlet velocity would also cause the dry-out point to shift closer to the inlet of the channel.
基金This work is supported by the Project of National Natural Science Foundation of China （No. 50076014） and the Project of Major State Basic Research Program （No. G2000026303）.
文摘The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow annular channels under the working condition of pressure ranging from 0.1 to 0.3 MPa and low mass flow rate from 6 to 60 kgm^-2 s^-1. Experimental test channels were annular and heated bilaterally with the channel gap of lmm and 1.5mm, and heated length of 1500mm.The location of the dryout was observed and measured by experiment with investigating the various system parameter effects on dryout point, and the results show that the location of dryout point is basically stable and repeating and the heat transfer coefficient increased with heat flux, mass flux and pressure, however, decreases with the gap size. Next, new correlations of CHF and critical vapor quality for narrow annular channels was proposed and calculation results shown a good agreement with the experimental data.
文摘The dynamical behavior of the subcooled boiling two-phase system was introduced and discussed. With the introduction of fractal concept, an analysis of the fractal feature of pressure wave signals from nonlinear dynamics point of view, was carried out. Meanwhile, the pseudo phase diagrams of typical time series of sound pressure were given. Finally, through dynamic clustering and on the basis of calculating correlation dimension and Hurst exponent of pressure wave time series on different subcooling conditions, the recognition of developing regime of the two-phase system was delivered, which might provide a promising approach of recognition and diagnosis of a boiling system.
基金supported by National Foreign Expert Projectunderthecontract No.G2022163009LGuangdong Basic and Applied Basic Research Foundation under the contract No.2023A1515011337+1 种基金Zhuhai Industry-University-Research Cooperation Project under the contract No.ZH22017001210017PWCKey Laboratory of Efficient and Clean Energy Utilization of Guangdong Higher Education Institutes underthecontract No.KLB10004.
文摘The two-stage transcritical CO_(2) refrigeration cycle with dedicated dual-subcooling and mechanical recooling is proposed.The inter-stage pressure is critical for such cycle performances;however,it has not been studied exactly.Therefore,the research aim is to disclose the effect of inter-stage pressure on performances of the proposed cycle.The main work consists of four aspects.Firstly,the comparative study is performed to display advantages of the proposed cycle.Secondly,the key temperatures,heat and power consumptions as well as performance indicators for different inter-stage pressures are analyzed in detail,based on the parametric model.Thirdly,the optimal inter-stage pressure for different conditions is obtained by the nonlinear direct search method.Finally,the economic performance is assessed.It is found that the compressor power of the proposed cycle drops by 12%,and the working temperature lower limit is reduced by 11℃.Furthermore,it is considered that the optimal inter-stage pressure is insensitive to the heat source temperature.The novelty lies in illustrating the effect of inter-stage pressure,obtaining trends of the optimal value,and pointing out the system feasibility.The paper is favorable for design and operation optimization of the proposed system.
基金the Shandong Province Natural Science Foundation (NO.ZR2020ME190)Cyrus Chung Ying Tang Foundation for the financial support
文摘Energy storage devices are the hub of a multi-energy complementary distributed energy system.Hydrated salts are the most suitable phase change material for energy storage devices,but subcooling is the main obstacle to their application.Nucleation requires a driving force so the use of nucleating agents alone does not reduce subcooling to a very low level.To address this issue,this paper first screened nucleating agents and then further reduced the subcooling of sodium acetate trihydrate in conjunction with stirring or direct current.The effects of rotor mass,rotational speed,direct current voltage,and electrode material on nucleation were analyzed.Finally,the stability of the composite phase change material in the presence of simultaneous stirring and energization was analyzed.The results showed that the addition of 1.5%in weight of disodium hydrogen phosphate dodecahydrate to sodium acetate trihydrate can reduce the subcooling to about 2.3℃.Continued addition of stirring or electricity can reduce the subcooling of sodium acetate trihydrate to within 0.5℃ or even eliminate it.The higher the momentum of the stirring,the better the improvement in subcooling,phase separation,and thermal conductivity.The higher the direct current voltage,the better the nucleation effect,but the electrode life will be lower.The silver electrode has the best nucleation effect.No new material was produced in the solution after 100 cycles in the presence of both stirring and direct current.The melting point of the phase change material was increased by 0.2℃ and the latent heat value decreased by 1.8%,still with good stability.The trace of deionized water should be added to the phase change material in subsequent studies to compensate for the consumption ofwaterby theanodicelution.
基金This work was supported by the National Natural Science Foundation of China(Grant No,5997601 6)the Graduate Foundation of Tsinghua University.
文摘An experimental investigation was conducted on subcooled nucleate boiling on ultra-small wires having diameters of 25―100 μm. High-speed photography and laser PIV (Particle Image Velocimetry) technology were used to visually observe the bubble dynamics. For highly subcooled boiling at moderate heat fluxes, the bubbles generally remained attached to the micro heating wires and bubble-top jet flows were clearly observed. Smaller bubbles usually had stronger bubble-top jet flows, while larger bubbles seemed to produce multi-jet flows. The structures of the bubble-top jet flows, as well as multi-jet flows, were proposed from the experimental observation. A model was developed to describe jet flow phenomena from bubbles on micro wires. Numerical simulations for bubbles having diameter of 0.03 and 0.06 mm showed that both the bubble-top and multi-jet flows were induced by a strong Marangoni effect due to high temperature gradients near the wire. The predicted velocity magnitudes and flow structures agreed very well with experimental measurements. The bubble size relative to the wire is an important factor affecting the jet flow structure. For a 0.03 mm bubble on a 0.1 mm wire, only a bubble-top jet flow forms, while a complex multi-jet flow pattern forms around the bubble with a weak bubble-top jet and two side jet flows for a 0.06 mm bubble.
