Investigation of Geyser Boiling Phenomenon in a Two-Phase Closed Thermosyphon

In this paper, geyser boiling phenomenon (GBP) in a two-phase closed thermosyphon has been investigated experimentally. Here, the effects of the inclination angle, filling ratio, input heat rate, mass flowrate of coolant, and inside diameter of the tube on the GBP have been discussed. Three copper thermosyphons with inside diameters of 14 mm, 20 mm, and 24 mm and a length of 1000 mm were employed. Distilled water was used as the working fluid. A series of experiments was carried out to investigate the effect of the inclination angle range of 5° to 90°, the input heat rate range of 50 to 312.4 W, the coolant mass flow rate range of 0.00389 to 0.0164 kg/s, and the filling ratio range of 15 to 45%. The GBP has been investigated by analyzing the time variations of the evaporator and adiabatic wall temperature and outlet water temperature from condenser jacket. The results show that the period of GBP was longer for higher inclination angles and filling ratios. Furthermore, it was discovered that the GBP did not take place for inclination angles of less than 15°.     

两相闭式热虹吸管换热特性的数值模拟

本文建立数学模型对两相闭式热虹吸管换热特性进行数值模拟。考察了几何尺寸、工质及加热条件对液膜流态、液膜厚度等的影响,从而提示了这三个部因素影响冷凝段换热特性的内在机理。     

Thermal Performance Prediction of Two-Phase Closed Thermosyphon Using Adaptive Neuro-Fuzzy Inference System

In this paper the Adaptive Neuro-Fuzzy Inference System (ANFIS) is used for the prediction of thermal efficiency and thermal resistance of a two-phase closed thermosyphon (TPCT). Aqueous suspensions of pristine multiwalled carbon nanotubes (CNTs) and functionalized CNTs with ethylene diamine were used as nanofluid in the TPCT. The experimental results regarding the TPCT performance including thermal efficiency and thermal resistance were modeled by the ANFIS technique. The ANFIS network was initiated by 70% of experimental data, and 30% of primary data were considered for testing and checking the suitability of the ANFIS model. The modeling results were compared with five arithmetical criteria. The arithmetical criteria suggested that the obtained modeling by ANFIS is valid and it could be expanded for other conditions. Also, to determine optimal ranges of experimental conditions, three-dimensional diagrams were traced by the modeling data. The proposed method of ANFIS modeling may be applied for optimization of other TPCTs with different configurations.     

闭式空气干燥循环研究

提出了一种采用空气做工作介质的闭式空气干燥循环,对循环过程和工况参数的影响进行了计算分析,结果表明,该闭式空气干燥循环具有除湿量大,节能,运行安全等特点。     

Optimization of the Thermal Efficiency of a Two-Phase Closed Thermosyphon using Active Learning on the Human Algorithm Interaction

Here, pristine and functionalized multi-walled carbon nanotubes with silver/water nanofluids were first synthesized. To investigate thermal performance of two-phase closed thermosyphon, thermal efficiency was experimentally obtained as a key parameter. To obtain optimal points in operational condition, the active learning method was employed in concentration ranges of 0–1 wt% as well as input power of 30–150 W which cannot be accessed. The active learning method is based on the fuzzy logic rules; here query synthesis and the measure human algorithm interaction (HAI) were used for learning. As the primary data obtained from experiments is small, this method was used to suggest the most optimal conditions. First, primary data obtained from experiments are given to the algorithm and then algorithm proposed some suggestions based on the maximum uncertainty. Subsequently, thermal efficiency is estimated based on fuzzy inference. Here, two mechanisms are employed as combined ones. The mentioned suggestions will be tested in the offered operational conditions. If the accuracy of the suggestions was confirmed by the obtained data, these data would be added to the primary ones. In fact, the used method can be considered in the area of HAI performing with the aid of experienced human simultaneously with intelligent algorithms. Meanwhile, the best working concentration to obtain the most optimum thermal efficiency obtained in the range 0.90 to 0.95 for both nanofluids.     

Effect of Inclination Angle and Filling Ratio on Thermal Performance of a Two-Phase Closed Thermosyphon under Normal Operating Conditions

In this paper, the effect of the inclination angle on the thermal performance of a two-phase closed thermosyphon with different filling ratios has been investigated experimentally under normal operating conditions. A series of experiments were carried out for inclination angle range of 5°–90° and filling ratios of 15%, 22%, and 30%. A copper thermosyphon with an outside diameter of 16 mm, an inside diameter of 14.5 mm, and a length of 1000 mm was employed. Distilled water was used as the working fluid. The results show that the two-phase closed thermosyphon has the highest thermal performance in the inclination angle range of 15°–60°. A good agreement was observed between the experimental results of this study and those available in the open literature. The interesting phenomenon of geyser boiling occurred in our experiments for filling ratios equal or greater than 30%. The geyser boiling puts no limitation on thermal performance of thermosyphon, but it should be avoided because it damages the condenser end cap due to the slug striking.     

闭式布雷顿循环变工况试验研究与仿真分析

依托MW级多功能闭式布雷顿循环试验平台,开展了容积法和旁通法试验研究,详细分析了相应的系统各设备节点压力、温度和流量等参数的动态关联响应。依据AspenHYSYS对试验平台建立了仿真模型,并分别对容积法和旁通法进行了仿真分析。结果表明:旁通法和容积法2种调控手段能够有效调节系统设备的工作状态,使之达到新的匹配点,进而改变整个系统的工作特性;采用容积法时,受充气条件的影响,系统响应缓慢,但压气机效率和压比基本不变;采用旁通法时,系统响应较快,但压气机效率和压比发生变化;仿真结果与试验结果一致,证明了仿真模型的可靠性,为制定闭式布雷顿循环发电系统的控制策略奠定了基础。     

两相闭式热虹吸管传热特性研究

本文通过实验研究在不同热流密度下,两相闭式热虹吸管传热特性,并通过计算比较了三个较为常用的换热准则系统,同时提出了改进意见,为热管换热器的设计提供了较为可靠的依据。     

基于He-N2混合工质的闭式Brayton循环系统及设备的优化设计

对以He-N_2混合气体为工质的闭式Brayton循环系统进行了优化分析,获得循环最高效率下系统各组成设备的性能参数。以此优化结果为目标,设计了轮机和换热器的初步方案。以纯氦气工质时轮机和换热器的成本为基准,利用设备成本与几何参数之间的近似关系,获得不同氦气摩尔分数下轮机和换热器的相对成本。通过Brayton循环中轮机与换热器的成本权重分配,得到不同氦气摩尔分数下Brayton循环的相对总成本。结果表明:当氦气摩尔分数为50%～60%时,存在一个相对总成本的最小值,与纯氦气时相比,其相对总成本降低了12%左右,这对于闭式Brayton循环系统工质的选择具有一定的指导意义。     

A Study of the Heat Transfer Characteristics of an FC-72(C6F14) Two-Phase Closed Thermosyphon with Helical Grooves on the Inner Surface

This study is a fundamental work performed to obtain basic information about designing two-phase closed thermosyphons with a working fluid of FC-72 (C₆F₁₄). FC-72 is a kind of alternative refrigerant designed to be chemically safe and more environmentally friendly than any other conventional CFC refrigerants.

To obtain experimental data on operational performances of a FC-72 two-phase closed thermosyphon, an experimental model was designed and manufactured with a micro fin groove copper tube with an outside diameter of 22.2 mm for its container, on which a series of operational performance tests were conducted. Its maximum capacity of heat transport rate was designed to be about 300–400 W. The focus was given to investigate the effects of such parameters as micro fin grooves and fill charge ratios on operational performances of the FC-72 two-phase closed thermosyphon. The experimental data on phase change heat transfer coefficients and heat transport limitations were compared with some corresponding correlations, and a couple of measures that would help to predict operational performances were suggested with some physical explanations.     

面向月球基地的有机工质透平/泵一体化

以蒸发与冷凝温差为30℃的20 kW月球基地能量系统为例,采用R600a为工质研究了有机工质透平/泵一体化一维设计和三维建模,使用CFD模拟计算了蒸发温度对透平和工质泵效率、流量和功率的影响规律,及透平/泵在转速、质量流量和压比相等的强耦合约束条件下的变工况运行特性。研究表明：透平/泵最佳设计转速为23 610 r/min,透平进口直径为156 mm时效率为79%,泵出口直径为29 mm时效率为71%;随着蒸发温度的增加,透平/泵的转速呈线性增加,效率先上升后下降,保持在70%以上,输出功呈线性增加趋势;当考虑蒸发器、冷凝器和管路压损时,同转速下蒸发温度比理想情况低2.16℃、输出功率低3.13 kW、效率略微下降;透平/泵一体化技术结构紧凑,在变工况时拥有良好的运行性能,非常适用于对体积重量要求较高的航空航天领域。     

Effect of Surface Tension Variation of the Working Fluid on the Performance of a Closed Loop Pulsating Heat Pipe

In this article, the effect of surface tension variation of the working fluid on the thermal performance of a pulsating heat pipe (PHP) is presented. A two-turn closed loop PHP is fabricated with a combination of copper and quartz tubes having 2 mm inner diameter. Three filling ratios are considered in the present study. A common surfactant namely sodium dodecyl sulfate is used to vary the surface tension of the distilled water which is the base working fluid tested in the PHP. Visualization as well as heat transfer studies is performed in the PHP. Thermal resistances of working fluids with different surface tension are estimated for each filling ratio. Further, the effect of surfactant concentration on the hydrodynamics of the PHP is also discussed. Addition of surfactant induces formation of foam after the filling process and in some phase of PHP operation. It changes the flow regime boundaries and lowers the evaporator temperature under specific operating conditions. A flow regime map is also constructed for the present PHP. The working fluid with a lower surface tension gives a minimum evaporator temperature in the vertical orientation and thus, lowest thermal resistance has been obtained. However, surface tension does not influence the performance in the horizontal position appreciably.     

Effects of a Nanofluid and Magnetic Field on the Thermal Efficiency of a Two‐Phase Closed Thermosyphon

Heat transfer of a CuO/water nanofluid in a two‐phase closed thermosyphon (TPCT) that is thermally enhanced by a magnetic field has been predicted by an optimized artificial neural network (ANN). The magnetic field strength, volume fraction of nanoparticles in water, and inlet power were used as input parameters and the thermal efficiency was used as the output parameters. The correlation coefficient (R² = 0.924), mean square error (MSE = 0.000340231), mean absolute error (MAE = 0.012410941), and normalized mean‐squared error (NMSE = 0.112417498) between the measured and predicted thermal efficiency by the ANN model were developed. The results were compared with experimental data and it was found that the thermal efficiency estimated by the multi‐layer perception neural network is accurate. In this study, a new approach for the auto‐design of neural networks, based on a genetic algorithm, has been used to predict collection output of a TPCT. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(7): 630–650, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21043     

Performance Improvement of Thermosyphon Heat Exchangers by Using Two Kinds of Working Fluids

In this study, the concept of introducing two-fluid thermosyphons is examined. Calculations were performed for both low and high temperature ranges with parallel and counter-flow arrangements. For lower-temperature application, 125°C > T _hi > 75°C, use of ammonia in some rows and water in the rest of the thermosyphon can slightly improve the associated heat transfer performance for balanced counter-flow arrangement. However, for balanced parallel-flow arrangement in both lowand high-temperature applications, the concept of using two-fluid thermosyphons may not be feasible. The use of two-fluid thermosyphons is especially advantageous for high-temperature applications. For instance, in the range of 375°C > T _hi > 350°C, the two-fluid thermosyphons (Dowtherm A-water) shows a 15-99% increase of heat transfer performance relative to Dowtherm A alone.     

Analysis and Application of Variable Conductance Heat Pipe Air Preheater

The heat transfer analysis of variable conductance heat pipe air preheater was carried out. The temperature trans-fer matrix was obtained for the air preheater that comprises several discrete heat transfer units with same or different heat transfer surface area in a parallel or counter flow mode. By using the temperature transfer matrix, the outlet fluid temperatures could be easily calculated for a given air preheater and inlet fluid temperatures. The active length of condenser in a variable conductance he...     

纳米悬浮液热虹吸管的传热性能试验研究

在相同的试验条件下,对比研究了纳米CuO-去离子水(DW)悬浮液重力热管与普通DW重力热管的启动性和等温性,研究了纳米工质热管的充液率和颗粒浓度对热管工作特性的影响,对纳米工质热管的强化传热机理进行了初步探讨。研究表明:纳米工质热管比普通热管启动快;纳米工质热管蒸发段外壁温的高低与充液率、纳米浓度和加热条件有关;纳米颗粒浓度和充液率对热管的传热性能影响较大,且存在最佳浓度(本研究为5%)和最佳充液率(本研究为44.3%);高浓度纳米工质热管比普通DW重力热管易于达到传热极限;试验中纳米悬浮液重力热管的传热强化率为16.19%～146.27%。     

200MW直接空冷机组变工况特性研究

以200MW直接空冷机组为例,考虑排汽管道的压损,排汽口和凝汽器入口间水蒸汽柱高度压差及排汽管道对环境散热量,建立直接空冷机组冷端系统变工况数学模型,编程计算做出直接空冷机组冷端系统特性曲线,同时分析了凝汽器入口压力及管道压损的变工况特性,对于空冷机组的运行具有一定的指导价值。     

空间流体回路的动态特性建模与闭环控制仿真

某航天器在轨运行面临外热流的频繁波动和载荷热耗的时变性扰动,热控分系统需要利用流体回路的自适应调节能力,维持被控对象在稳定的温度范围内。首先通过Sinda/Fluint模型对流体回路的动态特性进行了分析,验证了集总参数法的可行性,为Matlab的建模提供了依据,并对Sinda/Fluint模型的PI控温算法进行了初步探索,阐述了Matlab深入细化建模的必要性。最后基于理论分析,对流体回路系统的传热和流动过程进行了分析和简化,搭建了Matlab的动态特性仿真平台。结果表明,模型和算法满足系统控温需求。     

超临界工质布雷顿循环热力学分析

  [目的]  N₂O、C₂H₆、SF₆用于制冷剂或朗肯循环的工质,这些工质的临界点和物性特征使其具有作为超临界布雷顿循环工质的潜力。  [方法]  采用自行开发的MATLAB程序并调用美国国家标准与技术研究所(NIST)发布的REFPROP物性数据库,对超临界N₂O(S-N₂O)、超临界C₂H₆(S-C₂H₆)、超临界SF₆(S-SF₆)布雷顿循环进行热力学分析,并与超临界CO₂(S-CO₂)布雷顿循环进行对比。选择再压缩循环方式,分别计算得到了透平入口温度为300～550 ℃、压力为15～25 MPa,预冷器出口温度为32 ℃和47 ℃的各种工况。  [结果]  热效率计算表明:S-N₂O、S-C₂H₆、S-SF₆再压缩循环均表现较高的热效率,且比相对应的S-CO₂再压缩循环的热效率高,再压缩循环热效率总是随着透平入口温度的提高而提高,但提高压力不一定总是提高循环热效率,提高预冷器出口温度导致循环热效率显著下降。流量计算表明,S-N₂O、S-C₂H₆、S-SF₆、S-CO₂循环的总质量流量和透平入口体积流量均远高于同等参数条件的蒸汽朗肯循环,但这四种超临界工质循环的透平出口体积流量相近。  [结论]  S-N₂O、S-C₂H₆、S-SF₆、S-CO₂循环均有潜在应用价值。     

碳钢_水热虹隙管内部强化传热机理研究

在微层蒸发模型的理论基础上,对热虹吸管内部设置分流管结构强化沸腾传热者机理分析。建立分流管强化热哐吸管内部沸腾传热模型,同时选择七种不同的分流管开孔结构,与光滑管进行了对比实验研究,寻得最佳分流管结构,并综合大量实验数据建立强化沸腾传热准数方程式。