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Flow boiling heat transfer Coefficient used for the Design of the Evaporator of a Refrigeration Machine using CO2 as Working Fluid 用于设计使用二氧化碳作为工作流体的制冷机蒸发器的流动沸腾传热系数
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-02-01 DOI: 10.1615/heattransres.2024048932
Rabah GOMRI, Nadim KAROUN
In this work, a comparative study of the flow boiling heat transfer coefficient of carbon dioxide (CO2) in evaporation is presented. The main objective of the this work is to analyze and evaluate 1886 experimental points of the CO2 heat transfer coefficient with the help of two evaporation correlations (Fang et al., 2013 and Fang et al., 2017); the correlation of Fang et al., 2017 gives the best results.
本研究对二氧化碳(CO2)在蒸发过程中的流动沸腾传热系数进行了比较研究。这项工作的主要目的是借助两个蒸发相关系数(Fang 等人,2013 年和 Fang 等人,2017 年)对二氧化碳传热系数的 1886 个实验点进行分析和评估;Fang 等人,2017 年的相关系数给出了最佳结果。
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引用次数: 0
Analyzing The Heat and Flow Characteristics In Spray Cooling By Using An Optimized Rectangular Finned Heat Sink 使用优化矩形鳍片散热器分析喷雾冷却中的热量和流动特性
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-02-01 DOI: 10.1615/heattransres.2024051370
Altug Karabey, Kenan Yakut
Rapid advancements in technology constantly keep the need for thermal systems, which have high performance, on the agenda and direct the attention of researcher-engineers to studies on improving heat transfer. The spray cooling process depends on many parameters including nozzle diameter, surface area, surface geometry, critical heat flux, mass flow, gravity, spraying angle, and surface slope. One would need results from many experiments to better analyze the spray structure. In the present study, by using the rectangular-finned heat sinks optimized for spray cooling and those called “general”, the heat and flow characteristics in spray cooling were analyzed. Water was used as the cooling fluid and the cooling fluid was atomized by using an air-supported atomized. The experiments were conducted with six air-liquid ratio (ALR) values, three different jet heights, three different spraying times, three different fin heights, and three different fin widths. The results are presented in Nusselt number-air liquid ratio (Nu-ALR) and jet thickness-jet velocity (tjet-Ujet) diagrams. It was determined that air-liquid ratio (ALR) value tended to decrease with increasing Nusselt numbers. For the determined air-liquid ratio (ALR) values, Nusselt numbers decreased as the fin height increased. It was concluded that Nusselt numbers tended to decrease in all fin widths as the air-liquid ratio (ALR) value increased. In addition, considering the parameters examined for the rectangular-finned heat sink, separate correlations were developed for Nusselt number, spray angle, and jet thickness.
技术的飞速发展不断将对高性能热系统的需求提上日程,并将研究人员和工程师的注意力引向了改进传热的研究。喷雾冷却过程取决于许多参数,包括喷嘴直径、表面积、表面几何形状、临界热通量、质量流、重力、喷雾角度和表面坡度。要更好地分析喷雾结构,需要许多实验结果。在本研究中,通过使用针对喷雾冷却进行了优化的矩形鳍片散热器和被称为 "一般 "的散热器,分析了喷雾冷却中的热量和流动特性。冷却液为水,冷却液通过空气支撑雾化器雾化。实验采用了六种气液比(ALR)值、三种不同的喷射高度、三种不同的喷射时间、三种不同的翅片高度和三种不同的翅片宽度。实验结果用努塞尔特数-气液比(Nu-ALR)和喷射厚度-喷射速度(tjet-Ujet)图表示。结果表明,随着努塞尔特数的增加,气液比(ALR)值呈下降趋势。对于确定的气液比 (ALR) 值,随着鳍片高度的增加,努塞尔特数也随之降低。结论是,随着气液比(ALR)值的增加,所有翅片宽度的努塞尔特数都呈下降趋势。此外,考虑到对矩形鳍片散热器进行的参数检查,还对努塞尔特数、喷射角和喷射厚度分别建立了相关关系。
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引用次数: 0
Molecular dynamics study of the thermal transport properties in the graphene/C3N multilayer in-plane heterostructures 石墨烯/C3N 多层平面异质结构热传输特性的分子动力学研究
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2023050345
Junjie Zhu, Jifen Wang, Xinyi Liu, Kuan Zhao
We investigated the interfacial thermal conductance of the graphene/C3N multilayer in-plane heterostructures by non-equilibrium molecular dynamics simulation. The results showed that the interfacial thermal conductance is 12.97 GW/(m2·K) and the thermal rectification ratio is 23.80% in the bilayer of the multilayer parallel stacked heterostructure. The interfacial thermal conductance and the thermal rectification ratio of the multilayer staggered stacked heterostructure decreased with number of the layers increasing and both convergent as the layers. The phonon participation ratio of two stacking types exhibits a similar trend with interfacial thermal conductance as the number of layers changes. The interfacial thermal conductance of both structures were raised substantially with the temperatures. The interfacial thermal conductance of multilayer heterostructures could be adjusted by altering the defect type, concentration, and distribution proportion and the changes in phonon activities were investigated through phonon density of states and overlap factor S. This work proves the reference for thermal management applications in microelectronic devices.
我们通过非平衡分子动力学模拟研究了石墨烯/C3N多层平面异质结构的界面热导率。结果表明,多层平行堆叠异质结构双层的界面热导率为 12.97 GW/(m2-K),热整流比为 23.80%。多层交错堆叠异质结构的界面热导率和热整流比随着层数的增加而减小,并随着层数的增加而收敛。随着层数的变化,两种堆叠类型的声子参与比也呈现出与界面热导类似的趋势。两种结构的界面热导率都随着温度的升高而大幅提高。多层异质结构的界面热导率可通过改变缺陷类型、浓度和分布比例来调节,声子活动的变化则通过声子态密度和重叠因子 S 来研究。
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引用次数: 0
Convective heat transfer inside a rotating helical pipe filled with saturated porous media 充满饱和多孔介质的旋转螺旋管内的对流传热
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2024051673
Krishan Sharma, Deepu P, Subrata Kumar
In this paper, we study the hydrothermal characteristics of flow inside a rotating helical pipe filled with a saturated homogenous porous medium. The analysis is being carried out for the case of small curvature and torsion. Using perturbation approach, velocity and temperature fields are solved for both uniform wall heat-flux and uniform wall temperature boundary conditions. Perturbation expansion up to third-order is carried out to investigate the effect of rotation on the flow. The influence of rotation on velocity is noticed as early as the first order, and on temperature solution, it has an effect in the third order. The influence of rotation on Nusselt number does not appear till third order, and it is discovered that Nusselt number grows as dimensionless curvature increases.
本文研究了充满饱和均质多孔介质的旋转螺旋管内流动的水热特性。分析针对的是小曲率和小扭转情况。采用扰动方法,求解了均匀壁面热流和均匀壁面温度边界条件下的速度场和温度场。为了研究旋转对流动的影响,进行了高达三阶的扰动扩展。旋转对速度的影响最早出现在一阶,而对温度求解的影响则出现在三阶。旋转对努塞尔特数的影响直到三阶才出现,并且发现努塞尔特数随着无量纲曲率的增加而增加。
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引用次数: 0
Flow boiling critical heat flux in a small tube for FC-72 FC-72 小管中的流动沸腾临界热通量
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2023051482
Yuki Otsuki, Makoto Shibahara, Qiusheng Liu, Sutopo Fitri
Flow boiling of FC-72 in a small tube was investigated experimentally. The material of the tube was SUS304 stainless steel with an inner diameter of 1.8 mm and a length of 129 mm. The effect of flow velocity and subcooling on critical heat flux (CHF) was measured in this experiment. The flow velocity, u, was varied from 0.33 to 4.26 m/s, and the inlet subcooling degree was varied from 25 to 36 K. The heat transfer coefficients from the non-boiling to boiling region were then measured. Experimental results showed that CHF increased as flow velocity was raised, but it sharply declined above u = 3.0 m/s because of premature CHF. On the basis of the experimental data, the empirical correlation between the boiling number and Weber number was obtained. The predicted value of this correlation was in agreement with the measured data within 17%.
实验研究了 FC-72 在小管内的流动沸腾。管子材料为 SUS304 不锈钢,内径为 1.8 毫米,长度为 129 毫米。实验测量了流速和过冷度对临界热通量(CHF)的影响。流速 u 在 0.33 至 4.26 m/s 之间变化,入口过冷度在 25 至 36 K 之间变化。实验结果表明,CHF 随流速的增加而增加,但在 u = 3.0 m/s 以上,由于过早出现 CHF,CHF 急剧下降。在实验数据的基础上,得到了沸腾数和韦伯数之间的经验相关性。该相关性的预测值与测量数据的一致性在 17% 以内。
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引用次数: 0
A NOVEL MACHINE LEARNING STUDY: MAXIMIZING THE EFFICIENCY OF PARABOLIC TROUGH SOLAR COLLECTORS WITH ENGINE OIL-BASED COPPER AND SILVER NANOFLUIDS 一项新颖的机器学习研究:利用基于机油的铜银纳米流体最大化抛物槽太阳能集热器的效率
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2024053037
Andaç Batur Çolak, Mustafa Bayrak
Estimating the heat transfer parameters of parabolic trough solar collectors with machine learning is crucial forimproving the efficiency and performance of these renewable energy systems, optimizing their design and operation,and reducing costs while increasing the use of solar energy as a sustainable power source. In this study, the heat transfer characteristics of two different nanofluids flowing through the porous media in a straight plane underneath thermal jump conditions were investigated by machine learning methods. For the flow in the parabolic trough solar collector,two different nanofluids obtained from silver- and copper-based motor oil are considered. Flow characteristics wereobtained by nonlinear surface tension, thermal radiation, and Cattaneo–Christov heat flow, which was used to calculatethe heat flow in the thermal boundary layer. A neural network structure was established to estimate the skin frictionand Nusselt number determined for the analysis of the flow characteristic. The data used in the multilayer neuralnetwork, which was developed using a total of 30 data sets, were divided into three groups as training, validation, andtesting. In the input layer of the network model with 15 neurons in the hidden layer, 10 parameters were defined andfour different results were obtained for two different nanofluids in the output layer. The prediction performance of the established neural network model has been comprehensively studied by means of several performance parameters. The study findings presented that the established artificial neural network can predict the heat transfer characteristics of two different nanofluids obtained from silver- and copper-based motor oil with deviation rates less than 0.06%.
利用机器学习估算抛物面槽式太阳能集热器的传热参数对于提高这些可再生能源系统的效率和性能、优化其设计和运行、降低成本以及增加太阳能作为可持续能源的使用至关重要。本研究利用机器学习方法研究了两种不同的纳米流体在热跃迁条件下流经直面多孔介质的传热特性。对于抛物面槽式太阳能集热器中的流动,考虑了从银基和铜基机油中获得的两种不同的纳米流体。通过非线性表面张力、热辐射和卡塔尼奥-克里斯托夫热流获得了流动特性,并利用这些特性计算了热边界层中的热流。建立了一个神经网络结构来估算为分析流动特性而确定的表皮摩擦力和努塞尔特数。多层神经网络共使用了 30 组数据,分为训练、验证和测试三组。网络模型的输入层有 15 个隐层神经元,定义了 10 个参数,在输出层对两种不同的纳米流体得出了四种不同的结果。通过几个性能参数对所建立的神经网络模型的预测性能进行了全面研究。研究结果表明,所建立的人工神经网络可以预测从银基和铜基机油中获得的两种不同纳米流体的传热特性,偏差率小于 0.06%。
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引用次数: 0
Investigation of the Effect of Using Different Nanofluids on the Performance of the Organic Rankine Cycle 研究使用不同纳米流体对有机郎肯循环性能的影响
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2024051490
Meltem ARISU, Tayfun MENLİK
Energy consumption worldwide continues to increase due to factors such as population growth, rural-to-urban migration, technological advancements, and the rising use of technological products that make life easier. As a result, there is a growing demand for renewable energy sources in energy supply, and technological research is conducted to address energy losses and improve existing systems for more efficient energy use. The Organic Rankine Cycle (ORC) is a thermodynamic cycle used for converting heat energy, similar to the Clausius-Rankine cycle. With evolving technology and increasing energy needs, studies related to the Organic Rankine Cycle are of great interest to researchers. This study examines the impact of adding nano-particles to the working fluids used in the ORC system on its performance. Seven different working fluids were selected, including R141b, R123, R142b (isentropic), R22, and R32 (wet), as well as R114 and R600 (dry). Performance was calculated for 14 different nano-fluids created by adding Al2O3 and TiO2 nano-particles to the working fluids. The EES software was used in the analyses. Among the types of working fluids, it was observed that isentropic working fluids were more suitable for the ORC system, particularly R141b and R123. When considering the working fluid type for the ORC system, it was found that isentropic working fluids achieved higher efficiency, followed by dry-type working fluids. The lowest efficiency values were obtained for R22 and R32 working fluids.
由于人口增长、农村人口向城市迁移、技术进步以及越来越多地使用使生活更便捷的技术产品等因素,全球能源消耗持续增长。因此,能源供应中对可再生能源的需求日益增长,人们也在进行技术研究,以解决能源损耗问题,改进现有系统,提高能源利用效率。有机郎肯循环(ORC)是一种用于转换热能的热力学循环,类似于克劳修斯-郎肯循环。随着技术的发展和能源需求的增加,与有机郎肯循环相关的研究引起了研究人员的极大兴趣。本研究探讨了在有机郎肯循环系统所用工作流体中添加纳米颗粒对其性能的影响。选择了七种不同的工作流体,包括 R141b、R123、R142b(等熵)、R22 和 R32(湿)以及 R114 和 R600(干)。通过在工作流体中添加 Al2O3 和 TiO2 纳米颗粒,计算了 14 种不同纳米流体的性能。分析中使用了 EES 软件。在各种工作流体中,等熵工作流体更适合 ORC 系统,特别是 R141b 和 R123。在考虑 ORC 系统的工作流体类型时,发现等熵工作流体的效率更高,其次是干式工作流体。R22 和 R32 工作流体的效率值最低。
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引用次数: 0
Entropy generation and heat transfer performance of cylindrical tube heat exchanger with perforated conical rings: a numerical study 带穿孔锥环的圆柱管式热交换器的熵产生和传热性能:数值研究
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2024051252
Anitha Sakthivel, Tiju Thomas
Here we report a numerical analysis of a cylindrical tube heat exchanger equipped with perforated conical rings. This study reports entropy generation, energy consumption and thermal evaluation of heat exchanger by using ternary hybrid nanofluid (as a coolant). The nanomaterials such as Al2O3, Cu, MWCNT (multi walled carbon nanotubes) with various volume fraction (φ=0-0.5%) are used. The mean diameter of the nanoparticles is 42 nm. The geometrical effects of perforated conical rings on the heat transfer rate, effectiveness, performance index, entropy generation and energy consumption are discussed. Mass flow rate is varied from 0.2 kg/s to 1 kg/s. The optimum performance is highlighted with 0.5% of volume fraction along with 0.4 kg/s mass flow rate. It is noted that the entropy generation is 50% lower by using ternary hybrid nanofluid. This study enables to understand the choice and volume fraction of particles, base fluid and flow rate of the fluid motion.
在此,我们报告了对装有穿孔锥形环的圆柱管热交换器的数值分析。本研究报告了使用三元混合纳米流体(作为冷却剂)进行热交换器的熵生成、能耗和热评估。使用了不同体积分数(φ=0-0.5%)的纳米材料,如 Al2O3、Cu、MWCNT(多壁碳纳米管)。纳米粒子的平均直径为 42 纳米。讨论了穿孔锥形环对传热速率、效率、性能指标、熵产生和能耗的几何影响。质量流量在 0.2 kg/s 至 1 kg/s 之间变化。当体积分数为 0.5%、质量流量为 0.4 kg/s 时,性能最佳。通过使用三元混合纳米流体,熵的产生降低了 50%。这项研究有助于了解颗粒的选择和体积分数、基础流体和流体运动的流速。
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引用次数: 0
Influence of Temperature Gradients and Fluid Vibrations on the Thermocapillary Droplet Behavior in a Rotating Cylinder 温度梯度和流体振动对旋转圆筒中热毛细管液滴行为的影响
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2024051366
Yousuf Alhendal
When a fluid moves from lower to higher surface tension regions, its bubble or droplet moves in the direction of the temperature gradient (∇T), a process known as Marangoni flow occurs. In this paper, the drop movement in both stagnant and vibrated liquid in a rotating cylinder is analyzed and numerically presented using a computational fluid dynamics (CFD) approach. For two-phase flow, the governing continuum conservation equations are solved using the commercial program Ansys-Fluent. The Volume of Fluid (VOF) method has been found to be a useful research tool for studying multiphase interaction. It tracks the liquid/liquid interface in 2D and 3D domains. As the Marangoni number increases, the inherent velocity of drops decreases, which is consistent with earlier space onboard experimental findings that have been documented in the literature. This work revealed the complex behavior of droplets in zero gravity, where some neglected forces, such as rotational motion and host fluid vibration, that vanish in the presence of gravity, are the main source of the observed behavior. It was discovered that the thermocapillary droplet migration, which was insignificant in the presence of gravity, was significantly influenced by the small frequency amplitude (Am), which decreases with an increase in it. The study also showed that, in a static liquid inside a rotating cylinder, the velocity of thermocapillary droplet migration decreased. Up until this effect vanishes with increasing temperature gradient, increasing the temperature gradient (∇T) also increases the migration speed of the droplet inside the vibrating fluid and a rotating cylinder of different number of Marangoni (Ma
当流体从表面张力较低的区域流向表面张力较高的区域时,其气泡或液滴会沿着温度梯度(∇T)的方向移动,这一过程被称为马兰戈尼流。本文采用计算流体动力学(CFD)方法,对旋转圆筒中停滞和振动液体的液滴运动进行了分析和数值计算。对于两相流,使用商业程序 Ansys-Fluent 对支配连续守恒方程进行求解。流体体积 (VOF) 方法被认为是研究多相相互作用的有用研究工具。它在二维和三维域中跟踪液体/液体界面。随着马兰戈尼数的增加,液滴的固有速度降低,这与文献中记载的早期太空搭载实验结果一致。这项工作揭示了液滴在零重力下的复杂行为,其中一些被忽视的力,如旋转运动和主流体振动,在重力存在时消失,是观察到的行为的主要来源。研究发现,热毛细管液滴迁移在重力作用下并不明显,但受到小频率振幅(Am)的显著影响,随着振幅的增大而减小。研究还表明,在旋转圆筒内的静态液体中,热毛细管液滴迁移速度降低。温度梯度(∇T)的增加也会增加液滴在振动流体和不同马兰戈尼数(Ma)的旋转圆筒内的迁移速度。
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引用次数: 0
HORIZONTAL SINUSOIDAL WAVY FORM PLATE-FIN HEAT SINKS FOR NATURAL CONVECTION HEAT DISSIPATION 用于自然对流散热的水平正弦波浪形板翅式散热器
IF 1.7 4区 工程技术 Q3 THERMODYNAMICS Pub Date : 2024-01-01 DOI: 10.1615/heattransres.2024052307
Muhammed Musab Gavgali, Aziz Hakan Altun, Eyub Canli
The plate-fin heat sink geometry was modified to have the fin form sinusoidal wave shape in the horizontal direction with twelve variations by amplitude and period changes. Three different wave periods and four different wave amplitudes were used. The purpose was to alter natural convection motion in favor of heat transfer effectiveness. The main performance indicator was the base-plate average temperature. The independent geometric parameters were experimentally examined in terms of the effectiveness of natural convection heat transfer by the measured average temperature values. Heat transfer by radiation was calculated by an analytical algebraic approach in order to obtain the Nusselt number solely based on convective heat transfer. Eight different heat inputs were used for each tested geometry to change the Grashof and Rayleigh numbers in a laminar flow interval. As reference geometries, a flat plate and a heat sink with straight/flat-plate fins were utilized. The heat sinks were also oriented to three different angles by a test stand. Accordingly, thirty six unique experimental cases were examined as a result of 327 trials and 1100 hours of testing. It was realized that the wavy fin geometry enhances natural convection heat transfer compared to the base-plate and flat-plate-fin heat sinks. However, increasing period and amplitude of the wave form more than initial values deteriorated the gains by the modifications on the fins. Since a single-period, 2-mm-amplitude heat sink resulted in the highest Nusselt number for all orientations, an optimum may be sought about this setting. As a general evaluation, computational simulations for spatial resolution of the event physics and dimensional optimization are standing as future study targets.
对板翅式散热器的几何形状进行了修改,使翅片在水平方向上形成正弦波形,并通过振幅和周期变化产生十二种变化。使用了三种不同的波周期和四种不同的波幅。目的是改变自然对流运动,以提高传热效果。主要性能指标是底板平均温度。通过测量平均温度值,实验检验了独立几何参数对自然对流传热效果的影响。通过分析代数方法计算了辐射传热,以获得仅基于对流传热的努塞尔特数。对每个测试几何体使用了八种不同的热输入,以改变层流区间的格拉肖夫数和瑞利数。作为参考几何形状,使用了平板和带有直/平板鳍片的散热器。散热器还通过试验台进行了三个不同角度的定向。因此,经过 327 次试验和 1100 个小时的测试,对 36 个独特的实验案例进行了检验。结果表明,与底板和平板-鳍片散热器相比,波浪形鳍片几何形状增强了自然对流传热。然而,波形的周期和振幅比初始值增加,会使鳍片上的改性增益效果变差。由于单周期、2 毫米振幅的散热片在所有方向上都能获得最高的努塞尔特数,因此可以对这一设置进行优化。作为总体评估,未来的研究目标是对事件物理的空间分辨率和尺寸优化进行计算模拟。
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Heat Transfer Research
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