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环路热管作为一种高效的相变传热装置,其性能与位于蒸发器和储液槽之间的毛细芯结构密切相关。为了更深入研究双层毛细芯对环路热管传热性能的影响,利用不同颗粒直径铜粉制备双层毛细芯,在毛细芯总厚度为5 mm的条件下,通过调整大粒径和小粒径层的相对厚度来改变毛细芯厚度比,对平板型蒸发器环路热管启动和变工况运行进行实验测试。实验结果表明:在同一工况下,不同厚度比的双层毛细芯启动特性存在显著差异,启动过程中出现小粒径层蒸发效率低引起的温度过冲和环路热管中气液两相流变化导致的温度振荡;同时存在一个较优的双铜层毛细芯厚度比,大粒径(180~280μm)铜层厚度为3 mm可提高蒸发效率,小粒径(56~71μm)铜层厚度为2 mm可提供足够毛细抽吸力保证环路热管稳定运行。搭载该厚度毛细芯的环路热管不仅启动速度快(125 s),而且总热阻和蒸发器壁面温度均最低,最大加热功率达到120 W(21.10 W/cm~2),对应热阻为0.17 K/W。 相似文献
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井筒重力热管是利用热管将油藏自身能量即井底热量传递到井筒上部,在无需外加动力条件下实现对井筒近井口流体加热,改善井口流体温度分布,防止近井口结蜡和絮凝,从而降低采油成本。本文利用N-S方程,根据液膜内微元体的质量守恒、动量守恒和热平衡原理,模拟分析重力热管冷凝段冷却温度、加热段加热功率、冷凝段、绝热段长度以及热管内径等参数对热管运行的影响。研究变参数下热管内液膜厚度变化以及冷凝和蒸发换热系数的变化,进而分析得出变参数时重力热管传热特性,为优化重力热管参数和提高热管的换热性能提供了理论依据,从而使重力热管在最佳传热状态下运行,提高其换热效率。 相似文献
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为揭示多壁碳纳米管水基纳米流体应用在重力热管中的传热特性,基于多相流模型(VOF)建立其重力热管数值模型,并将数值结果与实验数据进行对比验证。以热阻作为性能评价指标,改变加热功率和充液率,讨论二者对热管换热性能的具体影响。通过添加传热传质源项来编写用户自定义函数(UDF)完成内部流体蒸发冷凝过程中的相变模拟。模拟结果表明:该数值模型能够较好模拟多壁碳纳米管水基纳米流体应用重力热管内部复杂的流动与传热过程;在选定的加热功率及充液率参数范围内,该重力热管的整体热阻随蒸发段加热功率的增大而减小,随充液率的增大而增大。 相似文献
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文中利用Fluent软件对流化床反应器内气液两相流进行数值模拟,通过改变进气速度、气泡直径来研究操作参数对流化床反应器内气液两相流速度场和气含率的影响。从模拟结果分析比较可以看出,增大进气速度能够增加液相循环速度和气含率;减小气泡直径能够增加反应器内气含率,但会降低液相循环速度。研究结果对流化床反应器的设计及应用具有一定的参考价值。 相似文献
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着重分析在重力热管内加内螺纹 ,研究它的冷凝段的传热及流动状况。在理论分析的基础上 ,得出在热流密度 q一定时 ,凝结液膜厚度δ沿壁面x变化的函数关系 ,并用计算机模拟求解 ,再进一步求出局部换热系数αx 和平均总换热系数α ,得出选择螺旋角在π/ 3与π/ 4之间时进行换热是较理想的和用内螺纹热管代替光滑内壁面热管是一种有效的强化传热的方法两个结论 相似文献
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Condensation heat transfer in a closed two‐phase thermosyphon is experimentally examined using two different types of test section. Test Section 1 is a straight‐pipe‐type thermosyphon, whereas Test Section 2 has a large‐diameter evaporator compared with a condenser to minimize entrainment at the evaporator. Condensation heat transfer in Test Section 1 shows much lower heat transfer coefficients than those estimated by a Nusselt theory. This low condensation heat transfer occurs due to a working fluid entrainment. It is confirmed from a result of Test Section 2 that the condensation heat transfer is similar to the values predicted by the Nusselt theory as far as the effect of the working fluid entrainment is negligible and flooding does not occur. A new correlation for the heat transfer coefficient considering the effect of entrainment is proposed. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(3): 212–225, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10030 相似文献
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探究两相闭式热虹吸管的传热混沌,以及操作参数对其混沌性和传热性能的影响,建立混沌特征参数与传热性能间的联系。通过搭建实验台测量两相闭式热虹吸管稳定运行过程中不同工况下的管壁温度信号,基于非线性分析的混沌理论研究处理测量的温度脉动信号,绘制吸引子轨迹图,建立最大Lyapunov指数与传热特征参数的联系,揭示传热性能与混沌特性的关系。结果表明:两相闭式热虹吸管具有确定性混沌行为,操作参数对混沌性和传热性能具有显著影响,混沌性与传热性能呈正相关关系。 相似文献
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An experimental study was performed on heat transfer of an open thermosyphon with constant wall heat flux. Water and aqueous glycerin were used as working fluids. The experimental range of modified Rayleigh number was 1 × 103 < Ram < 3 × 105. The average and local heat transfer coefficients, vertical temperature distributions of the tube wall and fluid at the centerline of the tube, and temperature fluctuations of the fluid were measured. Flow patterns were observed by adding tracer powder to the fluid. Fluid velocities were measured by laser Doppler velocimeter. Experimental results indicate that, for a water thermosyphon, there are three regimes where different heat transfer characteristics and flow patterns occur. For 1 × 103 < Ram < 3 × 103, the flow was laminar and the thermal boundary layer reached the center of the tube. Heat was exchanged between the wall and descending flow. Wall temperature increased in the downward direction. For 4 × 103 < Ram < 3 × 104, no turbulence was observed in the flow and the thermal boundary layer was localized in the vicinity of the wall. The wall temperature increased upward. For 3 × 104 < Ram < 3 × 105, flow was considerably disturbed by the mixing of upward and downward flow in the upper part of the tube. However, the flow was laminar in the lower part of the tube. Reduction of the flow rate induced by the flow mixing at high Ram can be one of the major causes of the deterioration of heat transfer from Lighthill's theory. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 301–312, 2001 相似文献
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Investigation on the effect of filling ratio on the steady-state heat transfer performance of a vertical two-phase closed thermosyphon 总被引:3,自引:0,他引:3
Filling ratio of the working fluid has a predominant effect on the heat transfer characteristics of a two-phase closed thermosyphon (TPCT). A comprehensive model is developed to investigate the effect of filling ratio on the steady-state heat transfer performance of a vertical TPCT. Three types of flow pattern and two types of transition, according to the distribution of liquid film and liquid pool, are considered in this model, while other models generally focus on only one or two types of them. The total heat transfer rate of liquid pool, including those of natural convection and nucleate boiling, is calculated by combination of their effective areas and heat transfer coefficients. New correlations of the effective area are proposed based on the experimental results from other study. Two different geometries of the TPCT with nitrogen as working fluid are performed experimentally, and the evaporator temperatures accord well with the theoretical calculation. And the calculated results are compared with those by other empirical heat transfer correlations for liquid pool. The range of filling ratio, which can keep a TPCT steady and effective, is proposed based on analysis and comparison. The effects of heat input, operating pressure and geometries of the TPCT on the range are also discussed. 相似文献
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An energy storage system that stores energy in the form of liquid air was studied. In this system, the cool storage unit was the most important unit. From the viewpoint of safety and economy, it was most promising to store the cold energy as the sensitive heat of a solid such as pebbles or concrete. A simulator was developed to predict temperature variations of the solid cool storage unit. The simulator calculated unsteady heat transfer between a supercritical gas flow and the solid material. Comparison of calculated and experimental results showed that the temperature variation of the metal cool storage medium was accurate within 11%. The calculated results showed for the concrete cool storage unit that a smaller quantity of medium was required with a smaller pitch of the tube. The minimum quantity of concrete calculated at the smallest pitch was three times that of concrete, which was simply estimated from the heat capacity of concrete and air. The volume required for concrete cool storage was less than 1/100 that of reservoirs for a pumped‐hydro power station having a vertical drop of 500 m. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 284–296, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10035 相似文献
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This study investigated the effects of cross-sectional geometries, filling ratio and aspect ratio on thermal performance of thermosyphon at different rates of heat input. Two cross-sectional geometries of thermosyphon (circular and flat) were used. Each cross-sectional geometry was charged with distilled water with different filling ratios, aspect ratios and heat input. The results indicated that the FTPCT had a higher average wall temperature in the evaporator section than that of the CTPCT. The maximum heat input had a significant influence on the heat fluxes for each filling ratio and evaporator length. Heat fluxes were increased with an increase of aspect ratio and heat input and decreased slightly at the maximum aspect ratios. 相似文献
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A high‐efficiency coupled device, with a high‐temperature phase‐change medium used to store the heat energy, and a two‐phase closed thermosyphon used as the transfer part, could be widely used in the future. Based on a series of experiments, a combined heat transfer model considering natural convection with phase‐change heat transfer and two‐phase closed heat transfer is proposed. The position and shape of the freezing interface were numerically calculated. Good agreement between the numerical and experimental results shows that the model and numerical investigations are feasible. © 2000 Scripta Technica, Heat Trans Asian Res, 30(1): 54–62, 2001 相似文献
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Linjiang Zou 《Numerical Heat Transfer, Part B: Fundamentals》2017,72(1):55-70
By establishing a mathematical model in the thermosyphon system, the numerical simulation method is used for the temperature field, flow field distribution in heat pipe simulated calculation in recent years. In this article, we combine the thermosyphon engineering actuality, build up the Nusselt model, write the visual program with the VB code, and make use of the computer to carry on imitating the calculation. Meanwhile, the calculation predicted temperature profile in the thermosyphon was compared with experimental measurements and a good agreement was observed. Through the research, it can provide theoretical basis for the optimization of heat pipe model in the future. 相似文献
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Simulation modeling and analysis of a high temperature phase change heat storage and exchange device 下载免费PDF全文
相变储热因单位体积储热量大,储热和放热过程温度基本恒定等优点而成为目前研究的热点。相变过程中涉及固液两相间融化和凝固的传热问题,其储放热过程是一个复杂的非稳态相变过程。本文对高温相变储热换热装置进行换热特性研究,通过研究储热单元的换热特性,基于FLUENT软件,结合装置的设计参数和相变复合材料的物性参数,对相变储热系统储/放热过程中内部的温度分布、传热速率和储放热效率进行了数学建模及模拟分析,重点研究了不同传热流体速度对单元储/放热性能的影响规律。根据仿真结果,在相变储热装置的设计中,可选择合适的空气流速,以实现不同的散热功率及储放热时间,满足不同用户的用热需求。物理实验表明仿真结果偏差较小,可为高温相变储换热装置设计、优化等工作提供依据。 相似文献
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MicroChannel heat sinks with two-phase flow can satisfy the increasing heat removal requirements of modern micro electronic devices. One of the important aspects associated with two- phase flows in microchannels is to study the bubble behavior. However, in the literature most of the reports present data of only a single channel. This does not account for flow mixing and hydrodynamic instability that occurs in parallel microchannels, connected by common inlet and outlet collectors. In the present study, experiments were performed for air- water and steam- water flow in parallel triangular microchannels with a base of 200-300μ m. The experimental study is based on systematic measurements of temperature and flow pattern by infrared radiometry and high-speed digital video imaging. In air-water flow, different flow patterns were observed simultaneously in the various microchannels at a fixed values of water and gas flow rates. In steam-water flow, instability in uniformly heated microchannels was observed. 相似文献