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Simulation of Temperature-field During Rail Air-cooling Quenching Process [Sensors & Transducers (Canada)](Sensors & Transducers (Canada) Via Acquire Media NewsEdge) Abstract: Temperature is a vital parameter in quenching process. When cooling style was changing to air cooling, it was necessary to simulate the temperature-field of air cooling quenching. Temperature-field at each time was accomplished. Through numerical expression of experimental heat transfer coefficient curves as well as least squares technique, the heat transfer coefficient at different temperature were calculated to specify the heat transfer coefficient of heavy rail. In this way, the temperature field of heavy rail in air cooling process was obtained simultaneously. It is significantly valuable for parameters' selection in heavy rail's technical operation. Copyright© 2013 IFSA. Keywords: Temperature field, Air-cooling, Heavy rail. (ProQuest: ... denotes formulae omitted.) 1. Introduction Quenching is a key technology of the heavy rail heat treatment, also is one of the main factors influencing quality of heavy rail quenching [1-2]. It not only influences the operating economical efficiency of the heavy rail, but also influences the reliability of the heavy rail [7]. Through the simulation of temperature field of the process of heavy rail quenching can get the temperature distribution in the process of the quenching cooling at any time, even can be specific to any heavy rail internal surface, the temperature of a point, can accurately reflect the distribution of temperature of heavy rail [3]. Temperature simulation process can intuitively reflect that whether a certain place at a certain moment temperature is appropriate, and more importantly, the heavy rail internal temperature distribution can be predicted and validated that whether the scene of the production situation is in line with the requirements, and through hardening parameter adjustment to achieve the goal of control cooling process [5]. Therefore, it is necessary to study spray thunder to simulate the transient temperature field in the process of air cooling [6]. Obtaining the air-cooled heavy rail surface heat transfer coefficient through the experiment as the inlet pressure was 0.4 MPa, temperature field of heavy rail was simulated [4]. Carry on the finite element modeling through simplified geometric model, mesh division, material attribute set, such as steps for heavy rail [8]. The modeling of finite element models, the selection of material parameters, the condition of environment, the condition of border, the meshing of the model are introduced in detail [9]. 2. The Establishment of Numerical Model Air-jet device was a symmetric structure, as shown in Fig. 1. 5 Air inlets with 10 mm diameter, the diameter of inner hole was 0.5 mm, distance was 3 mm between two adjacent holes. Use the Gambit that the pre-processing software of Fluent to create model. Make numerical simulation and the simulation analysis combined with fluent software [10]. Numerical simulation, as an efficient method of studying the temperature field of heavy rail, promises to be widely applied in this field [11]. Because the model was a structure of the axial symmetry, in modeling only took 1/4 model to research. As shown in Fig. 1, lower model of air-jet was heavy rail, the heavy rail was surrounded by external flow-field, air inlet took one circle and one quarter, the air outlet was three walls. In order to analyze the performance of heat exchange, make an overall division for the overall model [12]. Take the an unstructured tetrahedral to mesh generation, the grid number was 2,070,000, because the diameter of small hole was too litter, the area which close to the porous panel will be block processing, in order to reduce the grid number. The wall condition of the nozzle entrance was pressure entrance, the values was pressure of gas supply, took 0.4 MPa in calculate, entrance temperature was 320 K, the export interface was pressure outlet, the pressure value was zero, and the temperature was 320 K; the interface of heavy rail and the flow field with the wall type, which use the way of convection, the heat transfer coefficient was 780 W/(m2K). The reference pressure was 101325 Pa, temperature was 320 K. The researched model of this paper was 3D model, selected pressure solver, used the steady-state solver to calculate fluid, used the unsteady solver to calculate the temperature field, turbulence model took the standard ks turbulence model. Considering the calculation of temperature field relates to surface heat transfer, so the flow of gas to the ideal gas. U71Mn steel material density was 7800 kg/m3, which Thermal conductivity of steel and the mean specific heat at constant pressure were set in the material properties with linear way respectively, the coefficient as shown in Table 2 and Table 1, the surface heat transfer coefficient of air-cooling was 780 W/(m2K), and set the initial temperature of solid materials was 900 °C. Afterward determined the parameters of the heavy rail, did the finite element analysis of the heavy rail with Fluent [13]. Thermal conductivity of U71Mn with the change of temperature was shown in Table 1. Mean specific heat at constant pressure Cp, unit is J/(kg-°C). Mean specific heat at constant pressure of U71Mn steel as shown in Table 2. When solved the surface heat transfer coefficient of gas cooling, usually use the temperature data of work-piece that measured by experiment, and then through the finite volume difference method, nonlinear estimation method to solve. The nonlinear relationship between the surface heat transfer coefficient and surface temperature was shown in Fig. 2. The heat transfer coefficient was in the range of 200-1500 W/(m2-K). Coefficient in 270-720 °C range basically unchanged. Heat convection transfer was the main way in air-cooled. As can be seen from Fig. 2, temperature from 300 °C to 750 °C, heat transfer coefficient was basically stable at around 800 W/(m2-K), so in this temperature range, select 800 W/(m2-K) for heat transfer coefficient, while at 760-810 °C temperature, heat transfer coefficient as a curve, selected of 4 key points numerical in the curve, in turn (745, 800), (760, 750), (800, 500), (810, 450), then, took four coordinates into the MATLAB use the method of least squares to calculate the expression of the curve. This expression was as follows: ... And as far as data of blow 300 °C, the software does not involve the calculation to 300 °C, therefore not be considered. The heat transfer coefficient remains numerical value at 810 °C for the 810-900 °C just took 450 W/(m2-K), which the heat transfer coefficient data only test to 810 °C in experiment. So the expressions of heat transfer coefficient changed to this: ... 3. The Simulation Analysis and Results of Temperature Field The figure of temperature field about heavy rail was shown on the air-cooled 50 s moment as below (Fig. 3). The following rules can be drawn: The part of highest temperature was located in the central of the rail head, temperature approach to 890 K that was 617 °C. The temperature of rail head decreases gradually from outside to inside, and the lowest temperature was 540 K, namely 267 °C; At the part of rail waist, the temperature reduces gradually from top to bottom, and the top temperature was 500 K, the equivalent of 227 °C; The foot part, the temperature was basically 300 K, temperature of 27 °C. The cooling rate of some key points of heavy rail end was analyzed for statistics, and these key points should be selected according to Fig. 4, setting greater distance >10 mm between two points on the tread surface and greater distance > 6 mm between two points in the part of the maxilla. The selected points are marked in Fig. 4. The temperature falling curve of 8 nodes was shown in the Fig. 5. 4. Conclusions In this paper, making models of the heavy rail quenching process under the spray limelight aircooled models, using least squares method to determine the heat transfer coefficient expression for the data obtained from experiments, getting the heat transfer coefficient under different temperature, and then use Fluent software for heavy rail in the process of air cooling temperature field to simulate, use transient solver to get heavy rail distribution of temperature field in the 50 s time, fitting out the eight key nodes temperature drop curve of the heavy rail cross-section, as a tool of simulating the heavy rail quenching air cooling experiment provide certain reference value for the influence of the spray limelight parameter adjustment for air cooling effect. Acknowledgements This research reported in the paper is supported by Research Center of Green manufacturing and Energy-Saving &Emission Reduction Technology in Wuhan University of Science and Technology (B1004), Education Department Fund of Hubei (T201102) and National Natural Science Foundation of China (51205295). References [1]. Jintang Yang, Hairui Qu, Gongfa Li, Numerical Simulation of U71Mn Heavy Rail Quenching Organization Field Based on ANSYS, Hot Working Processes, 6,2010, pp. 151-154. [2] . Jintang Yang, Hairui Qu, Gongfa Li, Numerical Simulation of U71Mn Heavy Rail Quenching Induction Heating Temperature Field Based on ANSYS, Hot Working Processes, 3,2010, pp. 88-90. [3] . Hua Long, Jintang Yang, Gong Fa Li, Temperature Field Simulation In the Process of Heavy Rail Quenching, Hot Working Processes, 22, 2008, pp. 77-79. [4] . 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Fuwei Cheng, Gongfa Li, Guozhang Jiang, Jianyi Kong, Jia Liu, Shao Yang Shi, Yikun Zhang, Wentao Xiao College of Machinery and Automation, Wuhan University of Science and Technology, China, 430081 Tel: 15671565179 E-mail: [email protected] Received: 21 October 2013 /Accepted: 22 November 2013 /Published: 30 December 2013 (c) 2013 International Frequency Sensor Association |