heat transfer

摘要： In this research,a numerical study of mixed convection of non-Newtonian fluid and magnetic field effect along a vertical wavy surface was investigated.A simple coordinate transformation to transform wavy surface to a flat surface is employed.A cubic spline collocation numerical method is employed to analyze transformed equations.The effect of various parameters such as Reynolds number,volume fraction 0-,Hartmann number,and amplitude of wave length was evaluated in improving the performance of a wavy microchannel.According to the presented results,the sinusoidal shape of the microchannel has a direct impact on heat transfer.By increasing the microchannel wave amplitude,the Nusselt number has risen.On the other hand,increasing the heat transfer in the higher wavelength ratio corrugated channel is seen as an effective method of increasing the heat transfer,especially at higher Reynolds numbers.The results showed that with increasing Hartmann numbers,the flow line near thewall becomesmore regular and,according to the temperature gradient created,theNusselt number growth.

摘要： The utilization of vortex generators to increase heat transfer from cylinders installed inside a duct is investigated.In particular,a channel containing eight cylinders with volumetric heat sources is considered for different values of the Reynolds number.The effective possibility to use vortex generators with different sizes to increase heat transfer and,consequently,reduce the surface temperature of the cylinders is examined.Also,the amount of pressure drop inside the channel due to the presence of vortex generators is considered and compared with the cases without vortex generators.The results show that although the addition of generators increases the pressure drop,it strongly contributes to increase the heat transfer coefficient inside the duct(up to 80–90%).

摘要： The utilization of solar energy is essential to all living things since the beginning of time.In addition to being a constant source of energy,solar energy(SE)can also be used to generate heat and electricity.Recent technology enables to convert the solar energy into electricity by using thermal solar heat.Solar energy is perhaps the most easily accessible and plentiful source of sustainable energy.Copper-based nanofluid has been considered as a method to improve solar collector performance by absorbing incoming solar energy directly.The goal of this research is to explore theoretically the Agrawal axisymmetric flow induced by Cu-water nanofluid over a moving permeable disk caused by solar energy.Moreover,the impacts of Maxwell velocity and Smoluchowski temperature slip are incorporated to discuss the fine points of nanofluid flow and characteristics of heat transfer.The primary partial differential equations are transformed to similarity equations by employing similarity variables and then utilizing bvp4c to resolve the set of equations numerically.The current numerical approach can produce double solutions by providing suitable initial guesses.In addition,the results revealed that the impact of solar collector efficiency enhances significantly due to nanoparticle volume fraction.The suction parameter delays the boundary layer separation.Moreover,stability analysis is performed and is found that the upper solution is stable and physically trustworthy while the lower one is unstable.

摘要： Numerous intersected rock fractures constitute the fracture network in enhanced geothermal systems.The complicated convective heat transfer behavior in intersected fractures is critical to the heat recovery in fractured geothermal reservoirs.A series of three-dimensional intersected fracture models is constructed to perform the flow-through heat transfer simulations.The geometry effects of dead-end fractures(DEFs)on the heat transfer are evaluated in terms of intersected angles,apertures,lengths,and the connectivity.The results indicate that annular streamlines appear in the rough DEF and cause an ellipse distribution of the cold front.Compared to plate DEFs,the fluid flow in the rough DEF enhances the heat transfer.Both the increment of outlet water temperatureΔToutand the ratio of heat production Qrpresent the largest at the intersected angle of 90°while decline with the decrease of the intersected angle between the main flow fracture(MFF)and the DEFs.The extension of the length of intersected DEFs is beneficial to heat production while enhancing its aperture is not needed.Solely increasing the number of intersected DEFs induces a little increase of heat extraction,and more significant heat production can be obtained through connecting these DEFs with the MFF forming the flow network.

摘要： A numerical study of partial slip boundary condition is investigated. The stagnation-point flow problem involving some physio-chemical parameters has been elucidated. The process involves developing a multivariate mathematical model for the flow and transforming it into a coupled univariate equation. Key parameters of interest in the study are the buoyancy force, the surface stretching, the unsteadiness, the radiation, the dissipation effects, the slip effects, the species reaction and the magnetic field parameters. It is concluded that the impact of physio-chemical factors significantly alters the kinematics of the flow in order to optimally achieve desired product characteristics.

摘要： The two-phase zone continuous casting(TZCC)technique was used to continuously cast high-strength aluminum alloy hollow billets,and a verified 3D model of TZCC was used to simulate the flow and temperature fields at casting speeds of 2-6 mm·min^(-1).Hollow billets under the same conditions were prepared,and their macro/microstructures were analyzed by an optical microscope and a scanning electron microscope.During the TZCC process,a circular fluid flow appears in front of the mushy zone,and the induction heated stepped mold and convective heat transfer result in a curved solidification front with depressed region near the inner wall and a vertical temperature gradient.The deflection of the solidification front decreases and the average cooling rate in the mushy zone increases with increasing casting speed.Experimental results for a 2D12 alloy show that hot tearing periodically appears in the hollow billet accompanied by macrosegregation near the inner wall at casting speeds of 2 and 4 mm·min^(-1),while macroscopic defects of hot tearing and macrosegregation weaken and the average size of columnar crystals in the hollow billets decreases with further increasing casting speed.2D12 aluminum alloy hollow billets with no macroscopic defects,the finest columnar crystals,and excellent mechanical properties were prepared by TZCC at a casting speed of 6 mm·min^(-1),which is beneficial for the further plastic forming process.

摘要： Heat exchangers are integral parts of important industrial units such as petrochemicals,medicine and power plants.Due to the importance of systems energy consumption,different modifications have been applied on heat exchangers in terms of size and structure.In this study,a novel heat exchanger with helically grooved annulus shell and helically coiled tube was investigated by numerical simulation.Helically grooves with the same pitch of the helical coil tube and different depth are created on the inner and outer wall of annulus shell to improve the thermal performance of heat exchanger.In the first section,thermal performance of the shell and coil heat exchanger with the helical grooves on its outer shell wall was compared with same but without helical grooves.At the second section,helically grooves created on both outer and inner wall of the annulus shell with different groove depths.The results showed that the heat exchanger with grooves on both inner and outer shell wall has better thermal performance up to 20%compared to the heat exchanger with grooves on only outer shell wall.The highest thermal performance achieves at lower flow rates and higher groove depths whereas the pressure drop did not increase significantly.

摘要： Non-equilibrium thermodynamics theory is used to analyze the transmembrane heat and moisture transfer process,which can be observed in a membrane-type total heat exchanger(THX).A theoretical model is developed to simulate the coupled heat and mass transfer across a membrane,total coupling equations and the expressions for the four characteristic parameters including the heat transfer coefficient,molardriven heat transfer coefficient,thermal-driven mass transfer coefficient,and mass transfer coefficient are derived and provided,with the Onsager’s reciprocal relation being confirmed to verify the rationality of the model.Calculations are conducted to investigate the effects of the membrane property and air state on the coupling transport process.The results show that the four characteristic parameters directly affect the transmembrane heat and mass fluxes:the heat and mass transfer coefficients are both positive,meaning that the temperature difference has a positive contribution to the heat transfer and the humidity ratio difference has a positive contribution to the mass transfer.The molar-driven heat transfer and thermal-driven mass transfer coefficients are both negative,implying that the humidity ratio difference acts to reduce the heat transfer and the temperature difference works to diminish the mass transfer.The mass transfer affects the heat transfer by 1%–2%while the heat transfer influences the mass transfer by7%–14%.The entropy generation caused by the temperature difference-induced heat transfer is much larger than that by the humidity difference-induced mass transfer.

摘要： Based on multi-physical field coupling numerical simulation method,magnetic field distribution,melt flow,and heat transfer behavior of aΦ300 mm AZ80 alloy billet during differential phase electromagnetic DC casting(DP-EMC)with different electromagnetic parameters were studied.The results demonstrate that the increase in current intensity only changes the magnitude but does not change the Lorentz force's distribution characteristics.The maximum value of the Lorentz force increases linearly followed by an increase in current intensity.As the frequency increases,the Lorentz force's r component remains constant,and the z component decreases slightly.The change in current intensity correlates with the melt oscillation and convection intensity positively,as well as the liquid sump temperature uniformity.It does not mean that the higher the electric current,the better the metallurgical quality of the billet.A lower frequency is beneficial to generate a more significant melt flow and velocity fluctuation,which is helpful to create a more uniform temperature field.Appropriate DP-EMC parameters for aΦ300 mm AZ80 Mg alloy are 10-20 Hz frequency and 80-100 A current intensity.

摘要： The research paper tends to review the effectiveness of helical coil in heat exchangers (HCHE). Heat exchanger is a device used in transferring thermal energy between two or more fluids or solid interfaces and a fluid, in solid particulates and a fluid at different temperatures and thermal contact. The author has concisely discussed the helical coil in heat exchanger at different shapes and conditions and compared the HCHE with straight tubes heat exchangers, and the factors affecting the performance and effectiveness of the helical coil heat exchanger such as the curvature ratio, and other heat exchangers. The author demonstrated that the HCHE provided more excellent heat transfer performance and effectiveness than straight tubes and other heat exchangers because of secondary flow development inside the helical tube, and heat transfer coefficient increased with an increase in the curvature ratio of HCHE for the same flow rates. The secondary flow and mass flow rates, advantages and disadvantages have also been reviewed. The authors back their findings with available theories. Suitable fluid should be searched for high efficiency in the helical coil.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.

摘要： The fluid flow, heat transfer and the motion of particles (bubbles and solid inclusions)in the molten steel of steel refining ladles, continuous casting tundish, continuous casting mold and strand, and steel ingot casting process are investigated. The k-ε two-equation model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated by the Lagrangian-Eulerian approach, Eularian-Eulerian approach and Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface wave etc., which can be used to optimize the metallurgical operations.