The Defrosting Performance Control And Analysis Of Automobile Windshield

With the rapid development of the economy and the auto industry of China, the popularity of the automobile has been improved greatly. Automotive air conditioning is not only the symbol of the improvement of people's living standards, but also one of the symbols of the enhancement of automotive competitive ability. The defrost function of the automotive air conditioning not only effects the comfort of the automobile directly, but also influences the safe function of the automobile.In the past few decades,with the development of the calculation technique and the advance of the computer, computational fluid dynamics (CFD) has become more and more as a modern alternative for reducing the use of wind tunnels in automotive engineering. Now CFD is widely applied to various stages of aerodynamic design of automobiles. By contrast to the tunnel test, CFD is cheaper and takes less time to complete. However,the present CFD technology has still many problems to be solved for turbulence ,and it seems to be difficult to find an appropriate turbulence model to universal situations.Firstly,this paper investigates the status in study and the developing trends of automotive defrosting, and the international research actualities, matters, ways, the advantages, problems and technical nodus of experiment and simulate method is included. It points out the possibility that use computational fluid dynamics (CFD) software to analysis the defrost system of automotive. By comparing a few different CFD soft wares, I use FLUENT as the computational software to do the simulation.Secondly, this paper also carries on an academic analysis into the defrosting process, and investigates the impinging jet and solidification/melting problem. The impinging jet has an important influence on the heat transfer between fluid and surface, so it can be used for automotive windshield defrost/demist. By carrying on imitation, it can improve the heat transfer on the windshield; optimize the formation of the fluid and the defrosting function. The automotive defrosting simulation is a typical solidification/melting problem. Not only the shapes are complicated, but also it has the mutual influence between heat conduction and heat convection .The CFD software FLUENT uses solidification/melting module to solving this problem.Lastly, considering the impact of frost layer and glass layer, the defrosting model is set up with the software-GAMBIT, which is using to do the meshing and optimizing. It adopts FLUENT to do the imitation and uses the models of both standard k ?εdouble-equation turbulent stream and solidification and melting to carry on analysis. The influence on the temperature field and flow field of the vehicle compartment model compared and analyzed about different wind parameters, such as temperature, velocity, and distribution angle and opening number. It provides the reference for the optimization design of the defrosting system by comparing different parameters.The main conclusions are as follows:1. The impact of the wind velocity: aiming at different wind velocity of 5m/s,10m/s,20m/s,30m/s, this paper studies its influence on windshield defrosting. Relatively, the more the wind velocity is, the better the defrosting performance is. However, if the wind velocity is much too big, it not only impacts the comfort of the vehicle compartment, but also wastes energy. So the basic work condition i.e. the wind velocity 10m/s is the ideal condition.2. The impact of the wind temperature: this paper studies the wind temperature for four different conditions of 273K,278K,288K,and 298K.The higher the wind temperature is, the bigger the heat which the hot air current flow to the windshield is. The energy which transfer to the frost layer by thermal conduction and convection is more, so the temperature of the windshield outer surface is also higher and the frost layer melt more quickly. But it also wastes lots of energy. If we consider from economical of energy, the temperature of the wind should not too high. Comparing the above four different work conditions, the defrosting performance of wind temperature of 288K is the best.3. The impact of the initial wind temperature: this paper studies the initial wind temperature for three different conditions of 245K,255K,and 265K. From the calculation, we can see that the higher the initial wind temperature is, the better the defrosting performance is.4. The impact of the wind angle: In order to do research on wind angle, this paper studies impact on the jet angle in the XY plane (φ) and the jet angle in the YZ plane (β). This paper studies the jet angle in the XY plane for four different conditions of 45°,60°,75°,90°.Different jet angle in the XY plane (φ) has different impact on impinging jet and heat transfer. The conclusions are: the defrosting performance ofφ= 60°is the best, however, the defrosting performance ofφ= 45°is the worst. The jet angle in the YZ plane (β) influences the area that the jet sweeps on the windshield. This paper mainly discusses the jet angle in the YZ plane for four different conditions of 0°,10°,20°,30°.With the increasing inβ, the jet disperses in the left and right side, left the middle side of the windshield not to be blown. By comparing, the defrosting performance of the condition ofβ=10°is the best.5. The impact of the opening number: aiming at different opening numbers-one and two, this paper studies its influence on vehicle interior flow field, temperature field and windshield defrosting. It makes a conclusion that the condition of two opening numbers is the better one.To make a comprehensive view of the research work, the author advices the next work should do research on the real vehicle model and the defrosting duct .To make a further study on the distribution of the flow flux, the flow field and the temperature field of the defrosting duct exit. Another worthy study direction is to do research on guiding plate. The position and shape of guiding plate not only influences the distribution of the flow flux, but also impacts jet velocity and angle indirectly. What's more, it also influences the flow field in the defrosting duct. So it's another important study point.Moreover, in the process of imitation with the software FLUENT, the author also led into lots of artificial assumption, such as: it doesn't consider the heat loss condition of the people in the vehicle, the heat loss of the system, the fluxion effect of the outside air, the drop effect of the melted frost and the temperature delaminating of the defrosting nozzle exit. All of these should be studied further in the future.The meshing in the imitation has an influence on the reliability of the result. Usually, the denser the mesh is, the more reliable the result is. But if the mesh is too dense, it has a higher request for the computer capability. So we should use the least time to do the meshing, this problem needed to be studied further.The defrosting performance of the vehicle defrosting system influences the comfort and safety of the car directly. The software of FLUENT which is using for design stage has lots of superiority. It not only has a clear understanding of the defrosting system internal structure and the air flow condition, but also improves the efficiency of the defrosting system effectively.