| Aluminum alloy is a kind of alloy with excellent performance,wide application and great demand.Its wide use can reduce the weight of traditional mechanical devices by more than 60%.In industry,AC induction heating is commonly used to heat aluminum alloy,but the efficiency of this way is lower than 50%,resulting in a large amount of energy consumption.The principle of DC induction heating is that the motor drives the aluminum alloy component to be heated to rotate in a uniform magnetic field,so as to generate Joule heat and realize heating.Compared with the AC induction,the heating efficiency is greatly improved,up to 80%-90%.In order to reduce the energy loss in the magnetic field coil,a kind of DC induction heating device based on superconducting magnet was proposed at the beginning of this century and has been initially industrialized.However,in the research of the heating efficiency and temperature distribution control of the device,it is found that there is always a big difference between the numerical simulation results and the experimental measurements.One of the reasons is that the flow field around the aluminum alloy component to be heated will change significantly during the rotation process,which has not been considered in the previous analysis and research.This master’s degree thesis mainly focuses on the heat flow field morphology around the horizontal rotating heating component and its influence on the convective heat transfer intensity of the component.The temperature field and velocity field are observed through the classic Mach-Zehnder interferometer and PIV velocimeter.The dominant factors in steady flow field and unsteady flow field are analyzed and compared,and the main results are as follows:1.For the steady flow field,with the gradual increase of the speed,the wake around the component deflects,and the temperature boundary layer in the circulation area thickens to a certain extent,but the isotherms and streamlines near the wall are concentric rings.Subsequently,the Fluent software is used to simulate this phenomenon numerically.At the same time,using the field coordination theory,it is found that the air velocity does not directly affect the convective heat transfer,which quantitatively explains the 1/4 power relation in the convective heat transfer scaling law,and qualitatively explains the experimental phenomenon that the overall convective heat transfer intensity decreases slightly with the increase of the rotational speed.2.In the field of unsteady flow,also known as medium speed region,the previous observed unstable wavy temperature fringes at the side view of component is reproduced,according to the principle of optical interference,the physical meaning of the fringes is given,combining with tracer particles in PIV experiments,the characteristic in the temperature field of unsteady flow boundary layer with periodic expansion-shrinkage behavior is verified.3.By comparing the time scales of the dominant forces in the governing equation,it is found that the dominant forces in the temperature boundary layer change from the original viscous force to the Coriolis force and the centrifugal buoyancy force with the increase of the rotational speed.Based on the rotational speed of the upper and lower side of the component with different diameters obtained by experiment,the corresponding time scales of Coriolis force is equivalent to the time scale of viscosity force.Therefore,when the Coriolis force is equivalent to the viscosity force,the temperature boundary layer appears unstable expansion and shrinkage.In addition,because the magnitude of centrifugal buoyancy and Coriolis force are also similar,it is considered that centrifugal buoyancy is also involved in the instability,which extends the traditional boundary layer control theory. |
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