Analysis And Optimization Design Of The Defroster System In Bus

For the buses running in the north cold areas, the ice/mist layer often forms on thefront and side windshield interior surface, which influences the driver’s field of visionand becomes the insecurity factor on the road. Based on the theory of jet impingementheat transfer and the structure parameters of a Zhongtong bus, this thesis uses thenumerical calculation to analyze the function of its defroster system and puts forwardsome local optimization design on it.Considering of the complex geometry of windshield, dashboard and relatedaccessories, which may cause the mesh distortion and cost more computer time, thisthesis first simplifies the geometry of the bus model while adopting the simple variablemethod to analyze the impact of different geometry factors to the defrosting process.Providing that other conditions are invariant, increasing the velocity and temperature ofthe air flow into the defroster duct may enhance the defrosting efficiency and also wastemore energy which may get lower economy. It is efficient to shorten the distancebetween defrost nozzles and the edge of front windshield and also decreasing theimpinging angle can get the same effect if the dashboard geometry is available.This thesis also builds the real model included the dashboard and complicateddefroster system. The hot flow field, temperature distribution covering windshield, frostthickness and heat transfer characteristics are also simulated during the defrostingprocess. It is found that the distribution of hot flow covering the windshield is equal tothe working range of windscreen wiper, but the local sharp corners of the nozzlesproduce some velocity loss. The isothermals on the windshield interior surface have twopeaks at the early period of defrosting and spread higher and wider with the time goingon. The average frost thickness of the windshield and monitor points has the samechanging rule with the temperature distribution. Affected by the deflection of velocity,the defrost efficiency varies in non-monotonic way both in width and length, but theaverage frost thickness of the whole windshield diminishes in logistic curve. This thesisalso plots the curve of the area averaged non-dimensional heat transfer coefficientNu with time, which has the variation tendency of a parabola going downwards.In addition, based on the original bus model, some location and structureparameters are redesigned to get the better models A-D, such as shortening the distancebetween defrost nozzles and windshield lower edge, enlarging the windshield angle,removing the flute upon nozzles and changing the nozzle shape to ellipse, and adopts the same operation condition to simulate the defrosting process of them. The calculatedresult shows that the defrost efficiency is raised from model A to model D in turn, whichproves the optimization design is effective.