查看更多>>摘要：Frosting is an inevitable adverse phenomenon in many fields such as industrial refrigeration,cryo-genics,and heat pump air conditioning,which may influence the efficiency of the equipment and increase the energy consumption of the system.The complicated louvered-fin structure and fluid-channels arrangements of the microchannel heat exchanger(HEX)will affect the heat transfer performance and frosting characteristics.First,this article analyzes different factors such as refrigerant distribution,refrigerant flow pattern,and HEX surface temperature distribution.Further,combined with the features of the microchannel HEX,the existing anti-frosting technologies and various methods of surface treatment for anti-frosting are summarized.The review focuses on the preparation of superhydrophobic surfaces and their superior properties.Furthermore,the internal mechanism is analyzed in conjunction with the relevant research of our group.Superhydrophobic character has excellent anti-frosting performance and heat transfer performance,which is of great significance for improving energy-saving and system performance.Finally,the future development of superhydrophobic surface technology is analyzed and prospected.
查看更多>>摘要：A new type of microchannel condenser applied in the air source heat pump water heater(ASHPWH)with cyclic heating was proposed in this study.The operating performance of the ASHPWH was first tested.Then,the structure of the microchannel condenser was optimized with the implement of vortex generators.Finally,a numerical model of the ASHPWH was established and the optimized microchannel condenser was studied.The experimental results showed that the average coefficient of performance(COP)of the 1 HP(735 W)ASHPWH reached 3.48.In addition,the optimized microchannel condenser could be matched with a 3 HP(2430W)ASHPWH with an average heating capacity of 10.30 kW,and achieving an average COP of 4.24,14.6％higher than the limit value in the national standard.
查看更多>>摘要：Charge-based studies,in particular investigations of mass distribution,are still almost absent,although the efficiency of the organic Rankine cycle(ORC)has attracted a great deal of scholarly attention.This paper aims to provide a new perspective on the intrinsic relationship among the mass distribution,phase-zone distribution in the heat exchanger(HEX),charge of working fluid(WF),rotation speed of the pump(RSP),and system performance.A comprehensive ORC simulation model is presented by linking each component's sub-models,including the independent models for HEX,pump,and expander in an object-oriented fashion.The visualization study of mass distribution of the WF in the system is investigated under different working conditions.Furthermore,the volume and mass of the gas phase,two-phase and liquid phase of WF in the HEX and their variation rules are analyzed in-depth.Finally,the strategies of charge reduction considering HEX areas and pipe sizes are investigated.The results show that the model based on the interior-point method provides high levels of accuracy and robustness.The mass ratio of the WF is concentrated in the liquid receiver,especially in the regenerator,which is 32.9％and 21.9％of the total mass,respectively.Furthermore,2.4 kg(6.9％)WF in the system gradually migrates to the high-temperature side as the RSP increases while 6.1 kg(17.4％)WF migrates to the low-temperature side,especially to the condenser,as the charge in the system increases.Output power and efficiency both decrease gradually after the peak due to changes in RSP and charge.Last,reducing heat transfer areas of the condenser and regenerator is the most effective way to reduce WF charge.
查看更多>>摘要：The dynamics of negative surface discharges in c-C4F8/CF3I/CO2 gas mixture is investigated here with a 2D fluid model.The distributions of ion concentration,electric field strength and photon flux during the propagation of the streamer are obtained by solving the drift-diffusion equations of particles and Poisson's equation,and the photon flux variation function during the propagation is also fitted.It is found that the streamer branches occur when the streamer transitions from the upper surface of the insulator to the side surface,and then when the streamer approaches the plane electrode,the photon flux will increase significantly.On this basis,the positive and negative surface discharge models are compared in terms of streamer characteristics,particle characteristics and streamer branches.It is found that the streamer has a higher electron concentration and electric field in the positive model.The streamer develops"floating"in the positive surface discharge,while it is close to the surface of the insulator in the negative model.In addition,the negative streamer branch has a wider width and develops further.
查看更多>>摘要：The reduction of oxygen consumption is a key factor to improve the energy density of underwater Stirling engine.A series of fundamental experiments are carried out to elucidate the spray characteristics of soybean oil/2,5-dimethylfuran(DMF)blended fuel in an underwater Stirling engine.Spray characteristics such as spray penetration,spray angle,spray area,and light intensity level under low injection and ambient pressures are obtained using image post-processing method.The results show that the effects of injection pressure,ambient pressure,and nozzle diameter on the transient spray characteristics of underwater Stirling engine are similar to those of diesel engine.However,in the steady spray process,the injection pressure has little effect on spray near angle,and the spray far angle increases with the increase of the injection pressure.Compared with the spray far angle at injection pressure of 3 MPa,the spray far angle at 5 MPa and 7 MPa increased by 11.38％and 18.14％respectively.The addition of DMF can obviously improve the atomization of soybean oil/DMF blended fuel.The spray angle of blended fuel in transient process increases with the increase of the DMF concentration.The spray near angle has exceeded that of diesel(46.21°)when the DMF volume fraction exceeds 25％.The spray far angle is equivalent to that of diesel when the DMF volume fraction reaches 75％.Moreover,the spray with gas ejection no longer keeps conical,the droplet diameter distribution is more dispersed,and the droplet diameter is smaller.
查看更多>>摘要：The increasingly stringent emission regulations and fuel consumption requirements have elevated the demands of internal combustion engines with higher fuel efficiency and lower emissions.It has been widely demonstrated that flash boiling spray can generate shorter and wider spray with improved atomization and evaporation to promote a better air-fuel mixing process.In this study,macroscopic(far-field)spray morphologies and primary breakup(near-field)characteristics of a two-hole gasoline direct injection injector are investigated under non-flash boiling and flash boiling conditions.High speed macroscopic and microscopic imaging was used to capture the overall spray structure and near-field characteristics,respectively.N-Hexane is used as the test fuel with the injection pressure ranging from 10 MPa up to 40 MPa.For sub-cooled liquid fuel sprays,increasing fuel pressure contributes to enhanced fuel atomization and evaporation.Evident collapses occurred under flare flash boiling conditions,and higher injection pressure weakened this phenomenon since the spray cone angle decreased due to a higher injection velocity.
查看更多>>摘要：Fluid-structure interaction(FSI)of gas-liquid two-phase flow in the horizontal pipe is investigated numerically in the present study.The volume of fluid model and standard k-e turbulence model are integrated to simulate the typical gas-liquid two-phase flow patterns.First,validation of the numerical model is conducted and the typical flow patterns are consistent with the Baker chart.Then,the FSI framework is established to investigate the dynamic responses of the interaction between the horizontal pipe and gas-liquid two-phase flow.The results show that the dynamic response under stratified flow condition is relatively flat and the maximum pipe deformation and equivalent stress are 1.8 mm and 7.5 MPa respectively.Meanwhile,the dynamic responses induced by slug flow,wave flow and annular flow show obvious periodic fluctuations.Furthermore,the dynamic response characteristics under slug flow condition are maximum;the maximum pipe deformation and equivalent stress can reach 4 mm and 17.5 MPa,respectively.The principal direction of total deformation is different under various flow patterns.Therefore,the periodic equivalent stress will form the cyclic impact on the pipe wall and affect the fatigue life of the horizontal pipe.The present study may serve as a reference for FSI simulation under gas-liquid two-phase transport conditions.
查看更多>>摘要：The airflow field in the condensing zone is crucial as it affects the fiber condensing,additional twists,and consequently yarn properties.Parameters of spinning and suction slot geometric were found to be key factors influencing the airflow characteristics.To develop a better understanding of the complex airflow field within the pneumatic compact spinning system with lattice apron,a 3D numerical simulation model was built and the influence of negative pressure and geometric of suction slot was investigated.The results reveal that the accelerating air from the top of the suction slot generates transverse condensing force and downward pressure on the fiber strand.The inclination angle has a small effect on airflow velocity.The absolute z-velocity and x-velocity in the positive x-ax is were both increased with increasing the slot width from 1.0 mm to 1.5 mm.An arc suction slot increased the absolute z-velocity and x-velocity compared with a linear one,thus benefiting fiber condensing.By decreasing the outlet negative pressure to-3 kPa,the airflow velocity increased significantly.
查看更多>>摘要：This paper presents a quantitative risk analysis of liquefied petroleum gas(LPG)transportation.An accident that happened on June 13,2020,on the highway near Wenling,China is studied as a case.In this accident,LPG carried by a tank truck on the highway leaked and caused a large explosion,which led to 20 deaths.Different methods are combined to calculate the consequence of the accident.Multi-energy model and rupture of vessel model are employed to calculate the overpressure;the simulation result of the multi-energy model is closer to the damage caused by the accident.The safety distances in accidents of LPG transport storage tanks of different capacities are calculated in this study;the results show that the damage of explosion will increase with the filling degree of the tank.Even though the filling degree is 90％(value required by law),the 99％fatality rate range will reach 42 m,which is higher than regulated distance between road and building.The social risk of the tank truck has also been calculated and the results show that the risk is not acceptable.The calculating method used in this study could evaluate the risk of LPG tanker more accurately,which may contribute to the establishment of transportation regulation so that losses from similar accidents in the future could be reduced.
查看更多>>摘要：Identification of steady state and transient state plays an important role in modeling,control,optimiza-tion,and fault detection of industrial processes.Many existing methods for state identification are not satisfactory in practical applications due to problems of ideal hypothesis,too many parameters,and poor robustness.In this paper,a novel state identification approach is proposed.The problem of state identification is transformed into finding the noise band of differential signal.For practical application,automatic selection of noise band amplitude is proposed to make the method convenient to be used.Problems of gross errors,low signal-to-noise ratio and online identification are considered.And comparison with other two methods shows that the proposed method has better identification performance.Simulations and experiments also prove the effectiveness and practicability of the proposed method.
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