A series of Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al were solution treated in α+β phase field and air-cooled. The precipitation of a2 phase in cooling was investigated by transmission electron microsco...A series of Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al were solution treated in α+β phase field and air-cooled. The precipitation of a2 phase in cooling was investigated by transmission electron microscopic analysis The precipitation characteristic of α2 phase was discussed. The precipitation of α2 phase would proceed by the nucleation and growth of α2 phase dependent on the diffusion of Al atoms. And a comparison on the difference of precipitation of α2 phase was carried out under the conditions of air-cooling and quenching in water. The investigation showed that the air-cooling and even quenching could supply enough time for the precipitation and growth of α2 phase when Al content reached a certain value even though far away from the stoichiometric composition of Ti3Al.展开更多
The quantitative effects of chromium content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the c...The quantitative effects of chromium content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.展开更多
The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit ...The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.展开更多
Physical properties and geometrical morphologies of crushed air-cooled blast furnace slag (SCR) and crushed limestone (LCR) were comparatively investigated. The shape, angularity, surface texture and internal pore...Physical properties and geometrical morphologies of crushed air-cooled blast furnace slag (SCR) and crushed limestone (LCR) were comparatively investigated. The shape, angularity, surface texture and internal pore structure of aggregate particles for different size and gradation were numerically represented by sphericity (ψ) and shape index (SI), angularity number (AN), index of aggregate particle shape and texture (IAPST), porosity and pore size, respectively. The results show that SCR is a porous and rough aggregate. Apparent density, void, water absorption and smashing index of SCR are obviously higher than those of LCR with the same gradation, respectively. However, bulk density of SCR is lower than that of LCR with the same gradation. SI, AN, IAPST and porosity of SCR are obviously higher than those of LCR with the same gradation, respectively. The smaller particle size of SCR, the larger of its AN, IAPST and porosity.展开更多
The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregat...The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.展开更多
Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag(SCR) and crushed limestone(LCR) with 5-20 mm and 20-40 mm gradation were represented by numerical parameters including angula...Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag(SCR) and crushed limestone(LCR) with 5-20 mm and 20-40 mm gradation were represented by numerical parameters including angularity number(AN) and index of aggregate particle shape and texture(IAPST).The effect of mix aggregates containing SCR on compressive strength and splitting tensile strength of concrete was investigated.Fracture characteristics of concrete,interfacial structure between aggregates and matrix were analyzed.The experimental results show that porous and rough SCR increases contact area with matrix in concrete,concave holes and micro-pores on the surface of SCR are filled by mortar and hydrated cement paste,which may increase interlocking and mechanical bond between aggregate and matrix in concrete.SCR can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with LCR.The increase of AN and IAPST of aggregate may enhance mechanical properties of concrete.展开更多
The quantitative effect of Ni content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels was analyzed using artificial neural network models. The results showed that Ni may retard...The quantitative effect of Ni content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels was analyzed using artificial neural network models. The results showed that Ni may retard the high- and medium-temperature transformation and martensite transformation. The results conform to the materials science theories.展开更多
The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV...The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.展开更多
The natural wind plays disadvantageous roles in the operation of air-cooled steam condensers in power plant.It is of use to take various measures against the adverse effect of wind for the performance improvement of a...The natural wind plays disadvantageous roles in the operation of air-cooled steam condensers in power plant.It is of use to take various measures against the adverse effect of wind for the performance improvement of air-cooled condensers.Based on representative 2×600 MW direct air-cooled power plant,three ways that can arrange and optimize the flow field of cooling air thus enhance the heat transfer of air-cooled condensers were proposed.The physical and mathematical models of air-cooled condensers with various flow leading measures were presented and the flow and temperature fields of cooling air were obtained by CFD simulation.The back pressures of turbine were calculated for different measures on the basis of the heat transfer model of air-cooled condensers.The results show that the performance of air-cooled condensers is improved thus the back pressure of turbine is lowered to some extent by taking measures against the adverse impact of natural wind.展开更多
A new hot rolled low-carbon air-cooled bainitic steel containing Nb of 0.02% has been developed based on alloying design of the grain boundary allotriomorphic ferrite (FGBA)/granular bainite (BG) duplex steel. The...A new hot rolled low-carbon air-cooled bainitic steel containing Nb of 0.02% has been developed based on alloying design of the grain boundary allotriomorphic ferrite (FGBA)/granular bainite (BG) duplex steel. The as-rolled microstructure and mechanical properties of bainitie steel containing Nb of 0. 02% were investigated by tensile test, optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that adding 0.02 % of Nb obviously improves the strength without sacrificing toughness of the FGBA/BG steel. Adding 0.02% of Nb not only refines the grain boundary allotriomorphic ferrite grains but also promotes the refinement of granular bainite including its bainitic ferrite and M/A island. Any Nb(C,N) has been hardly observed in the steel containing Nb of 0.02%. It is suggested that the strengthening mechanism of Nb of 0.02% can be mainly attributed to the effect of Nb in solution (solute drag-like effect) on the phase transformation rather than the precipitation strengthening of Nb(C, N) particles.展开更多
The cooling performance of air-cooled condenser(ACC)is susceptible to adverse impacts of ambient winds.In this work,three kinds of lateral double-layered deflectors installed under the ACC platform are proposed to wea...The cooling performance of air-cooled condenser(ACC)is susceptible to adverse impacts of ambient winds.In this work,three kinds of lateral double-layered deflectors installed under the ACC platform are proposed to weaken the unfavorable effects of cross winds.Through CFD simulation methods,the main parameters of thermo-flow performances of a 2×660 MW direct dry cooling system are obtained,by which it can be concluded that the deflectors can effectively reduce the inlet air temperatures while enhance the mass flow rates of upwind fans due to the guiding effect,especially at high wind speeds,while the improvement of cooling capacity of ACCs in the 0°wind direction is weak.The inclined-vertical deflectors are superior to others in performance improvement of ACCs for all cases,which can reduce the turbine back pressure by 12.15%when the wind speed is 12 m/s,so they can be applied to the performance enhancement of ACCs under windy conditions in practical engineering.展开更多
Ambient wind has an unfavourable impact on air-cooled steam condenser(ACSC) performance. A new measure to improve ACSC performance is proposed by setting a diffusion type guide vane cascade beneath the ACSC platform. ...Ambient wind has an unfavourable impact on air-cooled steam condenser(ACSC) performance. A new measure to improve ACSC performance is proposed by setting a diffusion type guide vane cascade beneath the ACSC platform. The numerical models are developed to illustrate the effects of diffusion type guide vane cascade on ACSC performance. The simulation results show that this vane cascade can cause the increases in coolant flows across almost all fans due to its diffusion function and lower flow resistance. Meanwhile, the guide vane cascade also decreases the fan inlet temperatures because of the uniform flow field around the condenser cells. Comparing with the case without guide device, the overall heat transfer efficiency is increased by 11.2% for guide vane cascade case under the condition of 9 m/s. The heat transfer efficiency firstly enhances and then decreases with decreasing stagger angle of guide vane under a certain wind speed. The optimum stagger angle corresponding to the maximum heat transfer efficiency is about 65.5°. The heat transfer efficiency always enhances as increasing vane cascade height, and a vane cascade with 20 m to 30 m height may be suitable to the ACSC as considering the cost.展开更多
Buildings worldwide account for nearly 40%of global energy consumption.The biggest energy consumer in buildings is the heating,ventilation and air conditioning(HVAC)systems.In HVAC systems,chillers account for a major...Buildings worldwide account for nearly 40%of global energy consumption.The biggest energy consumer in buildings is the heating,ventilation and air conditioning(HVAC)systems.In HVAC systems,chillers account for a major portion of the energy consumption.Maintaining chillers in good conditions through early fault detection and diagnosis is thus a critical issue.In this paper,the fault detection and diagnosis for an air-cooled chiller with air coming from outside in variable flow rates is studied.The problem is difficult since the air-cooled chiller is operating under major uncertainties including the cooling load,and the air temperature and flow rate.A potential method to overcome the difficulty caused by the uncertainties is to perform fault detection and diagnosis based on a gray-box model with parameters regarded as constants.The method is developed and verified by us in another paper for a water-cooled chiller with the uncertainty of cooling load.The verification used a Kalman filter to predict parameters of a gray-box model and statistical process control(SPC)for measuring and analyzing their variations for fault detection and diagnosis.The gray-box model in the method,however,requires that the air temperature and flow rate be nearly constant.By introducing two new parameters and deleting data points with low air flow rate,the requirement can be satisfied and the method can then be applicable for an air-cooled chiller.The simulation results show that the method with the revised model and some data points dropped improved the fault detection and diagnosis(FDD)performance greatly.It can detect both sudden and gradual air-cooled chiller capacity degradation and sensor faults as well as their recoveries.展开更多
A data-driven surrogate model is proposed for a 64-cell air-cooled condenser system at a power plant.The surro-gate model was developed using thermofluid simulation data from an existing detailed 1-D thermofluid netwo...A data-driven surrogate model is proposed for a 64-cell air-cooled condenser system at a power plant.The surro-gate model was developed using thermofluid simulation data from an existing detailed 1-D thermofluid network simulation model.The thermofluid network model requires a minimum of 20 min to solve for a single set of in-puts.With operating conditions fluctuating constantly,performance predictions are required in shorter intervals,leading to the development of a surrogate model.Simulation data covered three operating scopes across a range of ambient air temperatures,inlet steam mass flow rates,number of operating cells,and wind speeds.The surrogate model uses multi-layer perceptron deep neural networks in the form of a binary classifier network to avoid ex-trapolation from the simulation dataset,and a regression network to provide performance predictions,including the steady-state backpressure,heat rejections,air mass flowrates,and fan motor powers on a system level.The integrated surrogate model had an average relative error of 0.3%on the test set,while the binary classifier had a 99.85%classification accuracy,indicating sufficient generalisation.The surrogate model was validated using site-data covering 10 days of operation for the case-study ACC system,providing backpressure predictions for all 1967 input samples within a few seconds of compute time.Approximately 93.5%of backpressure predictions were within±6%of the recorded backpressures,indicating sufficient accuracy of the surrogate model with a significant decrease in compute time.展开更多
The Self-adaptive control of the temperature can achieve the start of fuel cell at different operating temperatures, which is very important for the successful cold-start of the air-cooled PEMFC. The temperature distr...The Self-adaptive control of the temperature can achieve the start of fuel cell at different operating temperatures, which is very important for the successful cold-start of the air-cooled PEMFC. The temperature distribution characteristics during the cold-start process were analyzed based on adaptive temperature recognition control in this paper. Preheating model and cold-start model were established and the optimal balance between the hot air flow rate and the temperature required to promote a uniform temperature distribution in the stack was explored in the preheating stage. Finally, the non-equilibrium mass transfer, as well as the temperature rise in the catalyst layer and gas diffusion layer with different current densities, were analyzed in the start-up stage. The results indicate that the air-cooled PEMFC stack can be successfully started up at -40 ◦C within 10 min by means of external gas heating. The current density and air velocity have significant impacts on the temperature of aircooled PEMFC stack. Dynamic analysis of air-cooled PEMFCs and real-time monitoring are suitable for machine learning and self-adaptive control to set the operation parameters to achieve successful cold start. Optimize the matching of load current and cathode inlet speed to achieve thermal management in low temperature environment.展开更多
Lithium-ion battery packs are made by many batteries, and the difficulty in heat transfer can cause many safety issues. It is important to evaluate thermal performance of a battery pack in designing process. Here, a m...Lithium-ion battery packs are made by many batteries, and the difficulty in heat transfer can cause many safety issues. It is important to evaluate thermal performance of a battery pack in designing process. Here, a multiscale method combining a pseudo-two-dimensional model of individual battery and three-dimensional computational fluid dynamics is employed to describe heat generation and transfer in a battery pack. The effect of battery arrangement on the thermal performance of battery packs is investigated. We discuss the air-cooling effect of the pack with four battery arrangements which include one square arrangement, one stagger arrangement and two trapezoid arrangements. In addition, the air-cooling strategy is studied by observing temperature distribution of the battery pack. It is found that the square arrangement is the structure with the best air-cooling effect, and the cooling effect is best when the cold air inlet is at the top of the battery pack. We hope that this work can provide theoretical guidance for thermal management of lithium-ion battery packs.展开更多
This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different appro...This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different approaches and the results showed that the simplified calculations would give approximated cooling values with an 11.6% maximum error. The mass flow rate, upstream pressure and cooling capacity of the gaseous CO2 decreased with time. A maximum 48.5 watts of cooling was recorded at minute 4 and a minimum value of 10.4 watts at the end of the test. The drop in cooling capacity is due to the evaporation of the liquid CO2 inside the small cylinder which cools the two-phase CO2 mixture and causes a pressure drop (from 6 MPa to 2.97 MPa), which also affects the mass flow rate of gaseous CO2 exiting the orifice (from 0.56 g/s to 0.24 g/s). If this cooling technique is to be considered in portable compact-cooling systems, the mass, pressure and cooling capacity drop with time must be solved. One of the solutions could be to cover the cylinder with a heating coat to compensate for the heat absorbed by the evaporation of the liquid CO2.展开更多
Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant t...Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant to independently research and develop air-cooling technologies. Through experimental research, simulative calculation, process and equipment development, field tests and a demonstration project, the design and operation technologies for air-cooling system are grasped and relevant key equipment is developed. The results of the demonstration project show that the technical indicators for the air-cooling system have met or exceeded the design requirements. Part of the research results have been incorporated into the relevant national design standards. The technologies developed have been applied to more than 23 sets of thermal power units of or above 600 MW in China.展开更多
Designing a good energy storage system represents the most important chall</span><span style="font-family:Verdana;">enge for spreading over a large scale of electric mobility. Proper thermal</...Designing a good energy storage system represents the most important chall</span><span style="font-family:Verdana;">enge for spreading over a large scale of electric mobility. Proper thermal</span> <span style="font-family:Verdana;">management is critical and guarantees optimum working temperature in a</span><span style="font-family:Verdana;"> battery pack. In the various battery thermal management technologies, air cooling is one of the most used solutions. The following work analyzes the cooling performance of the air-cooling thermal management system by choosing appropriate system parameters and analyzes using CFD simulations for accurate thermal modeling. These parameters include the influence of airflow rate </span><span style="font-family:Verdana;">and cell spacing on the configuration. The outcome of the simulations is</span><span style="font-family:Verdana;"> compared using parameters like maximum temperature, and temperature distribution in the battery module to obtain optimum results for further applications. Finally, the simulations of the optimal solution will be compared to experimental results for validation.展开更多
Base on Prof. Maa Dah-You’s general theory of the microperforated-panel (MPP) absorber, We designed a noise reduction structure-sound attenuating cabinet (SAC). It can be applied to air-cooled communication products ...Base on Prof. Maa Dah-You’s general theory of the microperforated-panel (MPP) absorber, We designed a noise reduction structure-sound attenuating cabinet (SAC). It can be applied to air-cooled communication products to reduce system noise. This article introduces engineering design method of SAC and laboratory test noise reduction results of application of SAC.展开更多
文摘A series of Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al were solution treated in α+β phase field and air-cooled. The precipitation of a2 phase in cooling was investigated by transmission electron microscopic analysis The precipitation characteristic of α2 phase was discussed. The precipitation of α2 phase would proceed by the nucleation and growth of α2 phase dependent on the diffusion of Al atoms. And a comparison on the difference of precipitation of α2 phase was carried out under the conditions of air-cooling and quenching in water. The investigation showed that the air-cooling and even quenching could supply enough time for the precipitation and growth of α2 phase when Al content reached a certain value even though far away from the stoichiometric composition of Ti3Al.
文摘The quantitative effects of chromium content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.
文摘The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.
基金Funded by the National Basic Research Program of China(No.2009CB623105)the Natural Science Foundation of Education Agency of Anhui Province(No.KJ2012A052)+1 种基金the Anhui Provincial Natural Science Foundation(No.1208085ME82)the Doctor Fund of Anhui University of Architecture(No.20123302)
文摘Physical properties and geometrical morphologies of crushed air-cooled blast furnace slag (SCR) and crushed limestone (LCR) were comparatively investigated. The shape, angularity, surface texture and internal pore structure of aggregate particles for different size and gradation were numerically represented by sphericity (ψ) and shape index (SI), angularity number (AN), index of aggregate particle shape and texture (IAPST), porosity and pore size, respectively. The results show that SCR is a porous and rough aggregate. Apparent density, void, water absorption and smashing index of SCR are obviously higher than those of LCR with the same gradation, respectively. However, bulk density of SCR is lower than that of LCR with the same gradation. SI, AN, IAPST and porosity of SCR are obviously higher than those of LCR with the same gradation, respectively. The smaller particle size of SCR, the larger of its AN, IAPST and porosity.
基金Funded by the National Natural Science Foundation of China(Nos.51778003 and 51308004)the Project of Anhui Provincial Education Department for Sending Visiting Scholars to Research Abroad(No.gxfx ZD2016134)+1 种基金the Anhui Province Higher Education Revitalization Program Talent Project([2014]No.11)the National Key Research and Development Plan(No.2017YFB0310001)
文摘The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.
基金Funded by the National Basic Research Program of China(2009CB623105)the Natural Science Foundation of Education Agency of Anhui Province (KJ2012A052)+1 种基金the Anhui Provincial Natural ScienceFoundation(1208085ME82)the Doctor Fund of Anhui University of Architecture(20123302)
文摘Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag(SCR) and crushed limestone(LCR) with 5-20 mm and 20-40 mm gradation were represented by numerical parameters including angularity number(AN) and index of aggregate particle shape and texture(IAPST).The effect of mix aggregates containing SCR on compressive strength and splitting tensile strength of concrete was investigated.Fracture characteristics of concrete,interfacial structure between aggregates and matrix were analyzed.The experimental results show that porous and rough SCR increases contact area with matrix in concrete,concave holes and micro-pores on the surface of SCR are filled by mortar and hydrated cement paste,which may increase interlocking and mechanical bond between aggregate and matrix in concrete.SCR can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with LCR.The increase of AN and IAPST of aggregate may enhance mechanical properties of concrete.
文摘The quantitative effect of Ni content on continuous cooling transformation (CCT) diagrams of novel air-cooled bainite steels was analyzed using artificial neural network models. The results showed that Ni may retard the high- and medium-temperature transformation and martensite transformation. The results conform to the materials science theories.
文摘The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No.2009CB219804)
文摘The natural wind plays disadvantageous roles in the operation of air-cooled steam condensers in power plant.It is of use to take various measures against the adverse effect of wind for the performance improvement of air-cooled condensers.Based on representative 2×600 MW direct air-cooled power plant,three ways that can arrange and optimize the flow field of cooling air thus enhance the heat transfer of air-cooled condensers were proposed.The physical and mathematical models of air-cooled condensers with various flow leading measures were presented and the flow and temperature fields of cooling air were obtained by CFD simulation.The back pressures of turbine were calculated for different measures on the basis of the heat transfer model of air-cooled condensers.The results show that the performance of air-cooled condensers is improved thus the back pressure of turbine is lowered to some extent by taking measures against the adverse impact of natural wind.
基金Item Sponsored by National Hi-Tech Research and Development Program of China(2007AA03Z511)
文摘A new hot rolled low-carbon air-cooled bainitic steel containing Nb of 0.02% has been developed based on alloying design of the grain boundary allotriomorphic ferrite (FGBA)/granular bainite (BG) duplex steel. The as-rolled microstructure and mechanical properties of bainitie steel containing Nb of 0. 02% were investigated by tensile test, optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that adding 0.02 % of Nb obviously improves the strength without sacrificing toughness of the FGBA/BG steel. Adding 0.02% of Nb not only refines the grain boundary allotriomorphic ferrite grains but also promotes the refinement of granular bainite including its bainitic ferrite and M/A island. Any Nb(C,N) has been hardly observed in the steel containing Nb of 0.02%. It is suggested that the strengthening mechanism of Nb of 0.02% can be mainly attributed to the effect of Nb in solution (solute drag-like effect) on the phase transformation rather than the precipitation strengthening of Nb(C, N) particles.
基金The National Natural Science Foundation of China(Grant No.51476055,51821004)the National Basic Research Program of China(Grant No.2015CB251503)the Fundamental Research Funds for the Central Universities(Grant No.2018QN036)are gratefully acknowledged for supporting this research.
文摘The cooling performance of air-cooled condenser(ACC)is susceptible to adverse impacts of ambient winds.In this work,three kinds of lateral double-layered deflectors installed under the ACC platform are proposed to weaken the unfavorable effects of cross winds.Through CFD simulation methods,the main parameters of thermo-flow performances of a 2×660 MW direct dry cooling system are obtained,by which it can be concluded that the deflectors can effectively reduce the inlet air temperatures while enhance the mass flow rates of upwind fans due to the guiding effect,especially at high wind speeds,while the improvement of cooling capacity of ACCs in the 0°wind direction is weak.The inclined-vertical deflectors are superior to others in performance improvement of ACCs for all cases,which can reduce the turbine back pressure by 12.15%when the wind speed is 12 m/s,so they can be applied to the performance enhancement of ACCs under windy conditions in practical engineering.
基金supported by the National Key Research and Development Program of China (2018YFB0604302-02)the National Natural Science Foundation of China (No.51606066)
文摘Ambient wind has an unfavourable impact on air-cooled steam condenser(ACSC) performance. A new measure to improve ACSC performance is proposed by setting a diffusion type guide vane cascade beneath the ACSC platform. The numerical models are developed to illustrate the effects of diffusion type guide vane cascade on ACSC performance. The simulation results show that this vane cascade can cause the increases in coolant flows across almost all fans due to its diffusion function and lower flow resistance. Meanwhile, the guide vane cascade also decreases the fan inlet temperatures because of the uniform flow field around the condenser cells. Comparing with the case without guide device, the overall heat transfer efficiency is increased by 11.2% for guide vane cascade case under the condition of 9 m/s. The heat transfer efficiency firstly enhances and then decreases with decreasing stagger angle of guide vane under a certain wind speed. The optimum stagger angle corresponding to the maximum heat transfer efficiency is about 65.5°. The heat transfer efficiency always enhances as increasing vane cascade height, and a vane cascade with 20 m to 30 m height may be suitable to the ACSC as considering the cost.
文摘Buildings worldwide account for nearly 40%of global energy consumption.The biggest energy consumer in buildings is the heating,ventilation and air conditioning(HVAC)systems.In HVAC systems,chillers account for a major portion of the energy consumption.Maintaining chillers in good conditions through early fault detection and diagnosis is thus a critical issue.In this paper,the fault detection and diagnosis for an air-cooled chiller with air coming from outside in variable flow rates is studied.The problem is difficult since the air-cooled chiller is operating under major uncertainties including the cooling load,and the air temperature and flow rate.A potential method to overcome the difficulty caused by the uncertainties is to perform fault detection and diagnosis based on a gray-box model with parameters regarded as constants.The method is developed and verified by us in another paper for a water-cooled chiller with the uncertainty of cooling load.The verification used a Kalman filter to predict parameters of a gray-box model and statistical process control(SPC)for measuring and analyzing their variations for fault detection and diagnosis.The gray-box model in the method,however,requires that the air temperature and flow rate be nearly constant.By introducing two new parameters and deleting data points with low air flow rate,the requirement can be satisfied and the method can then be applicable for an air-cooled chiller.The simulation results show that the method with the revised model and some data points dropped improved the fault detection and diagnosis(FDD)performance greatly.It can detect both sudden and gradual air-cooled chiller capacity degradation and sensor faults as well as their recoveries.
基金The authors would like to thank the National Research Foundation(NRF)[Grant Number 122957]the University of Cape Town,and the Eskom EPPEI program for funding this research.
文摘A data-driven surrogate model is proposed for a 64-cell air-cooled condenser system at a power plant.The surro-gate model was developed using thermofluid simulation data from an existing detailed 1-D thermofluid network simulation model.The thermofluid network model requires a minimum of 20 min to solve for a single set of in-puts.With operating conditions fluctuating constantly,performance predictions are required in shorter intervals,leading to the development of a surrogate model.Simulation data covered three operating scopes across a range of ambient air temperatures,inlet steam mass flow rates,number of operating cells,and wind speeds.The surrogate model uses multi-layer perceptron deep neural networks in the form of a binary classifier network to avoid ex-trapolation from the simulation dataset,and a regression network to provide performance predictions,including the steady-state backpressure,heat rejections,air mass flowrates,and fan motor powers on a system level.The integrated surrogate model had an average relative error of 0.3%on the test set,while the binary classifier had a 99.85%classification accuracy,indicating sufficient generalisation.The surrogate model was validated using site-data covering 10 days of operation for the case-study ACC system,providing backpressure predictions for all 1967 input samples within a few seconds of compute time.Approximately 93.5%of backpressure predictions were within±6%of the recorded backpressures,indicating sufficient accuracy of the surrogate model with a significant decrease in compute time.
基金supported by the National Key Research and Development Program of China(No.2020YFB1506300)the National Natural Science Foundation of China(No.51806071)+1 种基金the Natural Science Foundation of Hubei Province(No.2020CFA040)Wuhan Applied Foundational Frontier Project(No.2020010601012205).
文摘The Self-adaptive control of the temperature can achieve the start of fuel cell at different operating temperatures, which is very important for the successful cold-start of the air-cooled PEMFC. The temperature distribution characteristics during the cold-start process were analyzed based on adaptive temperature recognition control in this paper. Preheating model and cold-start model were established and the optimal balance between the hot air flow rate and the temperature required to promote a uniform temperature distribution in the stack was explored in the preheating stage. Finally, the non-equilibrium mass transfer, as well as the temperature rise in the catalyst layer and gas diffusion layer with different current densities, were analyzed in the start-up stage. The results indicate that the air-cooled PEMFC stack can be successfully started up at -40 ◦C within 10 min by means of external gas heating. The current density and air velocity have significant impacts on the temperature of aircooled PEMFC stack. Dynamic analysis of air-cooled PEMFCs and real-time monitoring are suitable for machine learning and self-adaptive control to set the operation parameters to achieve successful cold start. Optimize the matching of load current and cathode inlet speed to achieve thermal management in low temperature environment.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 91834301 and 22078088)the National Natural Science Foundation of China for Innovative Research Groups (Grant No. 51621002)the Shanghai Rising-Star Program (Grant No. 21QA1401900)。
文摘Lithium-ion battery packs are made by many batteries, and the difficulty in heat transfer can cause many safety issues. It is important to evaluate thermal performance of a battery pack in designing process. Here, a multiscale method combining a pseudo-two-dimensional model of individual battery and three-dimensional computational fluid dynamics is employed to describe heat generation and transfer in a battery pack. The effect of battery arrangement on the thermal performance of battery packs is investigated. We discuss the air-cooling effect of the pack with four battery arrangements which include one square arrangement, one stagger arrangement and two trapezoid arrangements. In addition, the air-cooling strategy is studied by observing temperature distribution of the battery pack. It is found that the square arrangement is the structure with the best air-cooling effect, and the cooling effect is best when the cold air inlet is at the top of the battery pack. We hope that this work can provide theoretical guidance for thermal management of lithium-ion battery packs.
文摘This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different approaches and the results showed that the simplified calculations would give approximated cooling values with an 11.6% maximum error. The mass flow rate, upstream pressure and cooling capacity of the gaseous CO2 decreased with time. A maximum 48.5 watts of cooling was recorded at minute 4 and a minimum value of 10.4 watts at the end of the test. The drop in cooling capacity is due to the evaporation of the liquid CO2 inside the small cylinder which cools the two-phase CO2 mixture and causes a pressure drop (from 6 MPa to 2.97 MPa), which also affects the mass flow rate of gaseous CO2 exiting the orifice (from 0.56 g/s to 0.24 g/s). If this cooling technique is to be considered in portable compact-cooling systems, the mass, pressure and cooling capacity drop with time must be solved. One of the solutions could be to cover the cylinder with a heating coat to compensate for the heat absorbed by the evaporation of the liquid CO2.
文摘Given the distribution feature of resources such as coal and water, the requirements for the development of Chinese power industry, and the fact of monopoly by foreign companies, it is very necessary and significant to independently research and develop air-cooling technologies. Through experimental research, simulative calculation, process and equipment development, field tests and a demonstration project, the design and operation technologies for air-cooling system are grasped and relevant key equipment is developed. The results of the demonstration project show that the technical indicators for the air-cooling system have met or exceeded the design requirements. Part of the research results have been incorporated into the relevant national design standards. The technologies developed have been applied to more than 23 sets of thermal power units of or above 600 MW in China.
文摘Designing a good energy storage system represents the most important chall</span><span style="font-family:Verdana;">enge for spreading over a large scale of electric mobility. Proper thermal</span> <span style="font-family:Verdana;">management is critical and guarantees optimum working temperature in a</span><span style="font-family:Verdana;"> battery pack. In the various battery thermal management technologies, air cooling is one of the most used solutions. The following work analyzes the cooling performance of the air-cooling thermal management system by choosing appropriate system parameters and analyzes using CFD simulations for accurate thermal modeling. These parameters include the influence of airflow rate </span><span style="font-family:Verdana;">and cell spacing on the configuration. The outcome of the simulations is</span><span style="font-family:Verdana;"> compared using parameters like maximum temperature, and temperature distribution in the battery module to obtain optimum results for further applications. Finally, the simulations of the optimal solution will be compared to experimental results for validation.
文摘Base on Prof. Maa Dah-You’s general theory of the microperforated-panel (MPP) absorber, We designed a noise reduction structure-sound attenuating cabinet (SAC). It can be applied to air-cooled communication products to reduce system noise. This article introduces engineering design method of SAC and laboratory test noise reduction results of application of SAC.