| Because Type 50 wheel loader is applicable to the departments of construction, mine, railway, road, harbor, hydroelectric power and other national economic departments, it develops fast in its output and variety at home and abroad and becomes a major model in engineering machinery. Nowadays, as the international engineering machinery is confronted with fiercer competition, the national faces both challenges and opportunities. For a long time in the future, the Type 50 wheel loader is still about to be one of the major models in engineering machinery and its annual quantity demand will remain at a relatively high level. Facing fierce competition, in order to survive in the challenges, all factories have to develop new products and improve their property.The coolant (water or oil) of Type 50 wheel loader will be overheated in summer, which influences the operation and harms the wheel loader, reducing the economic and social benefit. To solve this problem, we can improve the speed of ventilator to increase the flow of air coolant ,preventing hydraulicfluid from heating up.However, in this way, it is certain to increase fuel consumption and cause much more noise.Therefore, in this paper we have adopted the way of optimizing the structure of engine cover.In order to find the reason of overheating and the solution to the problem, this paper establishes the simulation calculation on the air flow in the cooled units (inside engine cover) and thermal transmission based on the temperature test of heat source in Type 50 wheel loader and combines with the FEA (Finite Element Analysis) numerical simulation and other modern methods. Basically, it has the following points1. To introduce the heat transfer theory, computational fluid dynamics (CFD), numerical heat transfer (NHT), Vehicle-Engine-Cooling system (VEC) theories. They are the basic theories of Software simulation, which provide theoretical support for using the finite element software to analyze the air flow in the engine cover and temperature distribution.2. To bring forth the reduced physical model, paying more attention to studying the properties of air coolant in the heat source system,including air velocity, air temperature,air-pressure, turbulent kinetic energy and so on. During the experiment, basing on relevant boundary conditions,we can get the characteristics of heat exchange of radiator modules.3. To introduce turbulence model and wall-function method, togther with the boundary conditions,we can do the meshing and present the relevant choices of solver. Meanwhile,based on the ANSYS/FLOTRAN, the excavation effect of finite element simulation is analyzed and the calculation has been done.4. Presented by the result of the numerical simulation, the original structure has the problem of heat air recirculation in the cooled units. From the Newton's law of cooling introduced in Chapter 2, we learn that the temperature contrast between the heat source and the air coolant influences greatly the effect of the cooling of the heat source. With the factor unchanged, the less the temperature difference is, the smaller the heat dissipating capacity is, and the effect will be weakened. The backflow of the heat air will warm the cooling air that flows into the cooled units, which leads to the danger of coolant being overheated by degrading the performance of radiator. In the experiment, the heat air that flowing through the cooled unit is up to more than 80 Celsius degrees,and the backflow will cause the coolant to be heated again after flowing into the radiator.5. Under three operating modes of bulldozing, high-speed working and spading, it turns out that the concerned air temperature (the temperature between the engine and the ventilator) in front of the ventilator is close to the tests of the experiment, which proves the methods mentioned in this paper are effective and feasible.6. In connection with the issues of heat air backflow and overheated of the air in front of the ventilator, after making a contrastive analysis, six improvement proposals have been put forward. The first proposal is to enlarge engine outlet. The second and the third, expand inlet from the different position. Installing a thermal baffle in front of water tank is the fourth one,and synthesizing the advantages of the foregoing, the fifth and the sixth proposals come at last.7. Finally, it is proposed that the fifth one is the best. In this way, the air coolant can be cut down by more than 10 Celsius degrees, improving heating ability. Thus, in the aspects of increasing radiating effectiveness, preventing hydraulic fluid from heating up, saving materials, conservation of energy, it has the very practical significance. |
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