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The Characteristic Investigation of Evacuated Tube Transport System on Thermodynamics

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Tutor: LiQingLing
School: Qingdao University of Science and Technology
Course: Chemical Process Equipment
Keywords: thermal-pressure coupling effect,evacuated tube transport,blockingratio,boundary
CLC: U171
Type: PhD thesis
Year:  2013
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Abstract:
Heavy train load and high plane velocity are two advantages in the evacuated tube transport system. It is the only way probably to achieve the higher economic speed in the future. The train travels in the closed space of long-narrow pipelines. The thermodynamics problems in the system can not be ignored increasingly while seeking for the higher economic speed.In this paper, with combining the theoretical analysis, numerical simulation is used as main research method. Three important parameters including the blocking ratio, the train speed and the system pressure are taken into account. Physical and mathematical models of objects with high speed linear motion are built under the thermal-pressure coupling effect. For safe operation, comfort of passengers, operating efficiency, economic construction and operating cost, using the method of computational fluid thermal dynamics including mobile grid technology, the problems of air thermodynamics are studied in the evacuated tube transport system. It could provide proof for the efficient economic safe operation in evacuated tube transport system. The main works are as follows:1. Based on hydromechanics and heat transfer theory, the unsteady model of three-dimensional compressible and viscidity is built. The high speed train in evacuated tube is analysed on three-dimensional air thermal dynamics by using FVM. It labors three-dimensional flow field, pressure field and temperature field in the system under different blocking ratio (0.23¡¢0.32¡¢0.46¡¢0.57), different system pressure (1atm¡¢0.5atm¡¢0.1atm¡¢0.01atm) and different train speed (150m/s¡¢200m/¡¢300m/s¡¢360m/s¡¢400m/s). And the formation mechanism is studied. The pressure drag between headstock and tailstock is calculated as well. Heat accumulation phenomenon is analyzed when the train moves at high speed by overcoming resistance. We get parameters under economic operation in the system.The results show that the blocking ratio has the greatest influence on differential pressure between front and back during temperature field changing. The values present exponential growth along with the increasing of blocking ratio. And they are direct ratio relationship between square of train speed. And there is linear relation between system pressure. It also shows that the variation of temperature field is much more active in the first1000s. But it will be gentle later.2. In the supersonic speed status, considering formation mechanism and characteristic of thin shock layers and on the basis of Crocco theory of compressible flow and entropy layer, thermal-pressure coupling phenomenon and characteristic of evacuated tube transportation system. are analyzed along direction of train axis. As a result, the value of entropy is maximum in the apex nose of front and back. It shows that energy distribution is uniformity. Outside the layer along the flow front position entropy from car body streamline form of thin shock layer ring distribution, with the air flow to the body, boundary layer stability gradually, the temperature and velocity boundary layer near the body of the entropy layer in turn into a ring body contour distribution; They run to the second half of the car body, at the bottom of the car body area there is a small range of low entropy layer; Around the shoulder cross-section in the car, car body entropy "cap" shaped distribution, this is because the air came to the end of the upper annular space, so start along the rear of the streamline diffusion, the diffusion process, formed in the rear of the streamline contours of bonnet entropy layer, layer in this part of the entropy flow rate change is great, quick heat transfer, thus the stability of the original is destroyed, the entropy value is around to reduce.3. Thermal boundary layer effect and flow resistance properties are analysed by changing the block ratio and speed tube. Under the condition of invariable pressure and speed of train, as the block ratio increasing, the thickness of the temperature boundary layer on the train surface increases as well. At the same cross-section of the train, the thickness of the boundary increases as the temperature increasing. The temperature change at the axis of the rear vehicle is relatively flat. The temperature difference between the front and rear is increased. The temperature of the front shoulder increases more significantly than the rear shoulder in the annulus centre. The body is the same too. So with blocking ratio increasement, the thermal boundary layer effect in vacuum pipeline transportation system is increased.Pressure in the tube and blocking ratio are constant, change the train speed only, the variation of temperature in the center of a cross section curve is basically the same. Front stagnation point has the minimum temperature, the rear shoulder has the maximum temperature, the thermal boundary layer in the high temperature significantly increased with the velocity increasing. When the train speed is200m/s, the rear of the car at the top of the highest temperature is343k, as the speed increases to360m/s, the rear of the car at the top of the highest temperature is up to425k, the temperatures around the shoulder and body also have certain amplitude increasement. According to temperature changes along the axis, we know that the temperature changes at the rear is relatively smoothly, the difference temperature of the front to the rear increases with the speed; Compared to the low speed status, the temperature in the center of the ring gap front shoulder increases more significantly than the rear shoulder, the body section of the train shows the same law too. It is shown that the thermal boundary layer effect in upper and lower boundaries of train and inner wall of tube is increased with speed raising.
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