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在详细地分析了电弧传热和废钢熔化过程的基础上,建立了完整的废钢熔化过程数学模型。该模型可以适应不同电弧炉的不同装料制度,模拟电弧炉的穿井和塌料过程,并能在自电弧炉熔化起始直至废钢完全熔清的全阶段上进行数值模拟。模型计算结果可以反映实际生产情况,完善后的数学模型为工艺优化及过程控制等奠定了坚实的理论基础。 相似文献
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对以水为热载体,方形槽内水平圆管外石蜡的相变蓄热过程进行了数值模拟.通过合理的分析与假设,建立数学模型及其定解条件,并利用实验数据进行验证.引入无量纲管壁温度Ste数和无量纲相变材料初温G数,分析了Ste和G数对相变材料熔化、凝固过程的影响,给出了不同Ste教的熔化过程固液相图,结果表明:Ste数对熔化和凝固过程有显著影响,与S=0.098时的熔化时间相比,Ste =0.1875时熔化时间将会缩短将近1/2,而Ste =0.277时比Ste=0.1875时熔化时间缩短了1/3.与Ste=0.0804时的熔化时间相比,Ste =0.170时凝固时间缩短1/2,而Ste =0.259时比Ste =0.170时凝固时间缩短了1/3.G数对相变过程的影响比较小,凝固时甚至可以忽略不计. 相似文献
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对螺旋盘管相变蓄热装置性能和相变材料 (PCM)的传热特性开展理论和试验研究,建立相变蓄热装置物理和数学模型,对蓄热温度场进行了数值模拟和实验测试。结果表明 :自然对流换热对PCM的熔化过程影响很大,当考虑自然对流时,相变蓄热速率加快,相变分层现象明显;实验实测温度与模拟温度相近,说明所建立的模型适用于相变装置内部温度场的模拟。 相似文献
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矩形腔内相变材料接触熔化的分析 总被引:9,自引:1,他引:8
对矩形腔内相变材料紧密接触熔化过程进行了理论分析。应用努谢尔特液体边界层理论,求得了便于工程计算用的接触熔化传热过程的理论解。分析结果与实验数据进行了比较,吻合程度良好。 相似文献
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“烟管式”电加热锅炉采用烟火管锅炉的筒体结构,电热棒与锅水间接式传热,承压性能好,且电热棒易更换。若考虑运行成本,可将“烟管式”电加热锅炉与承压蓄热成一体式。 相似文献
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ABSTRACTA detailed experimental study has been carried out to evaluate the heat transfer performance of a solid/liquid phase-change thermal energy storage system. The phase-change material, 99% pure eicosane with a melting temperature of 36.5°C, was contained in a vertically oriented test cylinder that was cooled or heated at its outside boundary, resulting in radially inward freezing or melting, respectively. Detailed quantitative time-dependent temperature distributions and melt-front motion and shape data were obtained. In the freezing case study, a mathematical model was developed based on a one-dimensional analysis, which considered heat conduction as the only mode of heat transfer. In the melting case study, a heat transfer scale analysis was used to help interpret the data and development of heat transfer correlations. In the melting scale analysis, conduction heat transfer in the solid and natural convection heat transfer in liquid were considered. Comparison of experimental data with scale analysis predictions of the solid-liquid interface position and temperature distribution was performed. The analytical results agreed, in the worst case, within 10% of the experimental results in both melting and freezing cases. In the case of melting, scale analysis results agreed within 5% (after initial superheat disappeared in 50 minutes) with experimental results, and experimental results confirm the existence of four melting regions. 相似文献
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Experimental study on melting in a rectangular enclosure heated below with discrete heat sources 总被引:1,自引:0,他引:1
Zhou Jianhua Chen Zhongqi Liu Dengying Li Ji . Institute of Engineering Thermophysics Chinese Academy of Sciences Beijng China . Energy Power Engineering School Xi''''an Jiaotong University Xi''''an China 《热科学学报(英文版)》2001,10(3):254-259
lntroductionSolid-liquid phase change hed transfer involvingmelhng and solidification has received considerableattenhon for many years because of its wide-rangingaPplicationsI']. Generall speaking, there are tWo kindsof melting phenomena: fixed melting"l and contactmelhng[',]. In the case of fixed mehng, the solid phasechange material is forced to rehan stahonary and themelted liquid takes up the space betWeen the solid-liquldinteiface and the hea source schce. In the case ofcontaCt melhng,… 相似文献
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M.J. Hosseini A.A. RanjbarK. Sedighi M. Rahimi 《International Communications in Heat and Mass Transfer》2012
A combined experimental and numerical study is performed aiming to understand the role of buoyancy-driven convection during constrained melting of phase change materials (PCMs) inside a shell and tube heat exchanger. A series of experiments is conducted to investigate the effect of increasing the inlet temperature of the heat transfer fluid (HTF) on the charging process (melting) of the PCM. The computations are based on an iterative, finite-volume numerical procedure that incorporates a single-domain enthalpy formulation for simulation of the phase change phenomenon. It was observed from experimental results that the melting front appeared at different times at positions close to the HTF tube and progressing at different rates outwards towards the shell. The computational results show that by increasing the inlet water temperature to 80 °C, the total melting time is decreased to 37%. 相似文献
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Min Chan Kim Chang Kyun Choi Do-Young Yoon 《International Journal of Heat and Mass Transfer》2008,51(21-22):5097-5101
When an ice layer is melting from below, buoyancy-driven convection often appears in a thermally-unstable water layer. In this study, the onset of convection during time-dependent melting is investigated by using similarly transformed disturbance equations under the propagation theory. The critical Rayleigh numbers based on the water layer thickness are obtained for various conditions and compared with previous experimental and theoretical results. For a slowly melting system, the present prediction is quite close to that under the quasi-static assumption. However, for a rapidly melting system the critical condition deviates from the quasi-static one. With increasing the ratio of the depth of the unstable layer to the whole depth of the liquid layer the system becomes more unstable. But with increasing the phase change rate the system becomes more stable. With decreasing the phase change rate the present results approach the available critical conditions from the quasi-static model. The double cell pattern is predicted at the critical condition and the present results agree reasonably well with existing experimental data. 相似文献
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Induction melting process using segmented graphite crucible was investigated to melt silicon feedstock for solar cells. Induction melting is the key technology used in silicon melting process, such as ingot-growing, metallurgical refining and ribbon production. However, contamination of silicon from the crucible in induction melting is the main source of degrading the silicon. In this paper, new structure of crucible was suggested to minimize the contamination from the crucible wall. It was the segmentation of graphite crucible wall that introduced the non-contact between melt and inner wall of crucible. Numerical and experimental studies of induction melting process of silicon using the suggested crucible were conducted. For numerical analysis, 3D models of crucible, induction coil and silicon were constructed and electromagnetic force and temperature distribution in silicon and crucible were calculated. To evaluate a process with the suggested crucible, induction melting system was built up based on the simulated results and experiments of silicon melting were carried out. 相似文献
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《Renewable Energy》2006,31(13):2025-2041
This paper is aimed at analyzing the melting behavior of paraffin wax as a phase change material (PCM) encapsulated in a cylindrical capsule, used in a latent heat thermal energy storage system with a solar water heating collector. The heat for melting of PCM in the capsule is provided by hot water surrounding it. Since it is observed experimentally that the phase change occurs in a range of temperature, the present analysis considers this range instead of constant phase change temperature and the deviation between the results of these two is presented. The numerical analysis has been carried out by using enthalpy method and the results are verified with the experimental data. The experiments have been done by visualization technique without disturbing the actual process of melting. Three distinct stages of melting process have been identified as revealed by visualization studies. Results indicate that the melting process is chiefly governed by the magnitude of the Stefan number, Ste, phase change temperature range and the capsule radius. The analysis shows that the agreement between analytical and experimental results is significantly improved when the results are obtained considering phase change temperature range and the natural convection in the liquid phase instead of considering the process to be conduction dominated only. 相似文献
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The present paper investigates the effect of ultrasonic vibrations on the melting process of a phase-change material (PCM). Furthermore, the present study considers constant heat-flux boundary conditions, whereas much of the previous research had adopted constant wall-temperature conditions. The experimental results revealed that ultrasonic vibrations accompanied the effects like agitation, acoustic streaming, cavitation, and oscillating fluid motion, accelerating the melting process as much as 2.5 times, compared to the rate of natural melting (i.e., the case without ultrasonic vibration). In addition, temperature and Nusselt numbers over time provided conclusive evidence of the important role of the ultrasonic vibrations on the melting phenomena of the PCM. 相似文献
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The melting of a vertical ice cylinder into a homogeneous calcium chloride aqueous solution inside a rotating cylindrical cavity with several rotating speeds is considered experimentally. The melting mass and temperature are measured on four initial conditions of the solution and four rotating speeds of the cavity. The temperature of the liquid layer becomes uniform by the mixing effect resulting from cavity rotation and it enhances the melting rate of the ice cylinder. As the cavity‐rotating speed increases, the melting rate increases. The dimensionless melting mass is related to the Fourier number and the rotating Reynolds number in each initial condition, therefore an experimental equation that is able to quantitatively calculate the dimensionless melting mass is presented. It is seen that the melting Nusselt numbers increase again in the middle of the melting process. The ice cylinder continues to melt in spite of the small temperature difference between the ice cylinder and the solution. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(6): 359–373, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20211 相似文献
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Mingyu ChenShaopeng Wu Hong WangJizhe Zhang 《Solar Energy Materials & Solar Cells》2011,95(12):3241-3250
This paper investigates the snow melting process on asphalt pavements as solar collector by experiments and numerical simulation. A numerical simulation method was used to predict the general design requirements for snow melting system of asphalt pavements, and a type of experimental asphalt snow melting system has been built using the design parameters obtained from the preceding simulation. Graphite powders were used to improve the thermal conductivity of asphalt concrete and thus resulting in an improved efficiency of asphalt collector. A laboratory snow melting test was performed after real snowstorm events. The effects of thermal conductive asphalt concrete (CAC) on snow melting performance and asphalt pavement temperature distribution were evaluated. The heat transfer in the asphalt slabs and the heat requirement for the snow melting were analyzed. The results that are obtained show that asphalt solar collector (ASC) provides us a better alternative method for snow melting. The higher fluid temperature is a positive way to improve the performance of snow melting system. However, it is unnecessary to keep a too high fluid temperature so as to reduce the waste of energy. The non-uniform temperatures in the asphalt slabs are noticeable. Furthermore, the heat-transmission and the snow melting performance can be enhanced using CAC. 相似文献
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Thermal performance of PCM thermal storage unit for a roof integrated solar heating system 总被引:2,自引:0,他引:2
The thermal performance of a phase change thermal storage unit is analysed and discussed. The storage unit is a component of a roof integrated solar heating system being developed for space heating of a home. The unit consists of several layers of phase change material (PCM) slabs with a melting temperature of 29 °C. Warm air delivered by a roof integrated collector is passed through the spaces between the PCM layers to charge the storage unit. The stored heat is utilised to heat ambient air before being admitted to a living space. The study is based on both experimental results and a theoretical two dimensional mathematical model of the PCM employed to analyse the transient thermal behaviour of the storage unit during the charge and discharge periods. The analysis takes into account the effects of sensible heat which exists when the initial temperature of the PCM is well below or above the melting point during melting or freezing. The significance of natural convection occurring inside the PCM on the heat transfer rate during melting which was previously suspected as the cause of faster melting process in one of the experiments is discussed. The results are compared with a previous analysis based on a one dimensional model which neglected the effect of sensible heat. A comparison with experimental results for a specific geometry is also made. 相似文献