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Assessment of a Simpler Friction Factor in an Algebraic Solution for Adiabatic Coiled Capillary Tubes 绝热毛细管的一个更简单的摩擦系数的代数解的评估
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-11-25 DOI: 10.1142/s2010132520500339
Thiago Torres Martins Rocha, S. I. D. M. Resende, Hélio Augusto Goulart Diniz, F. A. R. Filho, Raphael Nunes de Oliveira
In this work, the performance of an existing algebraic solution for adiabatic coiled capillary tubes, in subcritical cycles, is investigated. However, the C-M&N friction factor, commonly used, was replaced by Schmidt friction factor, which is less complex. Two existing dimensionless correlations were also evaluated for comparison. To assess the effect of altering the friction factor, experimental data collected in the literature were used as reference. Analyzing the present results and that with C-M&N friction factor, it was observed that adopting the Schmidt friction factor does not cause a relevant impact on the solution. The deviations of the predicted versus experimental mass flow rates were comprised in a range between –8% and 12%, with average deviation (AD), absolute average deviation (AAD) and root mean square (RMS) error of –0.1%, 2.7% and 3.4%, respectively. The empirical correlations presented unsatisfactory results, with maximum deviation around 40%. Therefore, it was concluded that using the Schmidt friction factor is adequate to reduce the complexity of the algebraic solution and to maintain the accuracy.
在这项工作中,研究了现有的绝热螺旋毛细管在亚临界循环中的代数解的性能。然而,常用的C-M&N摩擦因数被施密特摩擦因数所取代,其复杂性较低。还评估了两个现有的无量纲相关性以进行比较。为了评估改变摩擦系数的影响,我们参考了文献中收集的实验数据。分析目前的结果和C-M&N摩擦因数,可以看出,采用施密特摩擦因数不会对溶液产生相关影响。预测质量流量与实验质量流量的偏差在-8% ~ 12%之间,平均偏差(AD)、绝对平均偏差(AAD)和均方根误差(RMS)分别为-0.1%、2.7%和3.4%。经验相关性的结果不令人满意,最大偏差约为40%。因此,使用施密特摩擦因子足以降低代数解的复杂性并保持精度。
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引用次数: 1
The Effects of Hydrophobicity and Drainage Velocity on Water Retention Behaviour in Porous Media: A Computational Study 疏水性和排水速度对多孔介质保水行为影响的计算研究
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-11-23 DOI: 10.1142/s2010132520500340
K. W. Yong, P. Ganesan, E. Hamidi, S. Kazi, S. Ramesh
The present study investigates the water retention behavior in two different types of porous media, i.e., porous metal — a type of metallic foam and ideal geometry. The present study uses computational fluid dynamics (CFD) to model a decreasing water level in a reservoir consisting of a stationary porous medium beneath the water surface at initial stage. It mimics the setup of dynamics dip-testing which measures the amount of retained water for different types of fins-tubes heat exchangers. The study varies parameters like static contact angle ([Formula: see text]) and drainage velocity ([Formula: see text]). The literature review summarizes the unique water retention behaviors for different types of heat exchangers and the findings of the present study. Furthermore, the present study proposed new parameters for evaluating the structural variations in porous metal that explains the water saturation distribution in detail. The evaluation method could provide an insightful idea for performing the quality control check on metallic foam.
本研究研究了两种不同类型的多孔介质,即多孔金属-一种金属泡沫和理想几何介质中的保水行为。本研究采用计算流体力学(CFD)方法模拟了在初始阶段由水面下固定多孔介质组成的油藏中水位下降的过程。它模拟了动态浸渍测试的设置,该测试测量了不同类型的翅片-管换热器的保留水量。研究改变了静接触角([公式:见文])和排水速度([公式:见文])等参数。文献综述总结了不同类型换热器独特的保水行为以及本研究的发现。此外,本研究提出了评价多孔金属结构变化的新参数,详细解释了含水饱和度分布。该评价方法可为金属泡沫的质量控制提供有见地的思路。
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引用次数: 0
Optimized Refrigerant Flow Rate and Dimensions of the Ejector Employed in a Modified Ejector Vapor Compression System 改进的喷射器蒸汽压缩系统中喷射器的优化制冷剂流量和尺寸
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-11-20 DOI: 10.1142/s2010132520500388
Dishant Sharma, G. Sachdeva, D. K. Saini
This paper presents the analysis of a modified vapor compression cooling system which uses an ejector as an expansion device. Expanding refrigerant in an ejector enhances the refrigeration effect and reduces compressor work. Therefore, it yields a better coefficient of performance. Thermodynamic analysis of a constant area ejector model has been done to obtain primary dimensions of the ejector for given condenser and evaporator temperature and cooling capacity. The proposed model has been used to design the ejector for three refrigerants; R134a, R152a and R1234yf. The refrigerant flow rate and the diameters at various sections of the ejector have been obtained by doing numerical modeling in Engineering Equation Solver (EES). Refrigerant R1234yf demanded the highest diameter requirements at a fixed 5∘C evaporator temperature and 40∘C condenser temperature for a given range of cooling load. Both primary and secondary refrigerants flow rates are higher for R1234yf followed by R134a and then R152a.
本文分析了一种采用喷射器作为膨胀装置的改进蒸汽压缩冷却系统。在喷射器中膨胀制冷剂可以提高制冷效果,减少压缩机的工作量。因此,它产生了更好的性能系数。对定面积喷射器模型进行了热力学分析,得到了给定冷凝器和蒸发器温度和制冷量时喷射器的基本尺寸。应用该模型对三种制冷剂的喷射器进行了设计;R134a, R152a和R1234yf。在工程方程求解器(EES)中进行了数值模拟,得到了喷射器各截面上制冷剂的流量和直径。制冷剂R1234yf要求在给定的冷负荷范围内,在固定的5°C蒸发器温度和40°C冷凝器温度下,最大直径要求。R1234yf、R134a、R152a的一次、二次制冷剂流量均较大。
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引用次数: 2
Rotary Compressor Performance at Low Ambient Temperatures 旋转压缩机在低温环境下的性能
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-11-18 DOI: 10.1142/s2010132520500376
S. Lowrey, G. Reboux
Small rotary compressors are used in domestic heat pump appliances, for example, in domestic dehumidifiers and heat pump clothes dryers. Compressor performance curves provided by the manufacturer can be based on testing at relatively high ambient temperatures, in some cases as high as 35∘C. This can be much higher compared with the ambient temperature in which the compressor operates when, for example, it is installed in a domestic dehumidifier which can operate in ambient temperatures as low as 10∘C. We have developed a compressor calorimeter to test a small R134a rotary compressor extracted from a commercial domestic dehumidifier and use this to measure compressor performance parameters including the isentropic and volumetric efficiencies and the compressor heat loss fraction. The performance testing has been carried out at ambient temperatures 10∘C, 15∘C, 20∘C and 25∘C for a fixed relative humidity of 70% to compare how the compressor performance varies with the ambient temperature, and to determine how well the compressor performs outside of the performance envelope provided by the manufacturer. The results show that isentropic and volumetric efficiency of these small compressors is relatively insensitive to variation in ambient temperature, even outside of the performance envelope provided by the manufacturer. However, the compressor heat loss fraction can, on average, double from 15% to 30%, between operation at ambient 25∘C and ambient 10∘C. The data obtained in this work is used to construct compressor sub-models for certain ambient temperatures. We show how these sub-models can be used to improve a domestic dehumidifier model for operation at low ambient conditions within the evaporator frosting regime and good agreement is obtained between experimental and simulated data. The authors are not aware of a domestic dehumidifier model designed to work at ambient temperatures within the frosting regime.
小型旋转压缩机用于家用热泵电器,例如家用除湿机和热泵干衣机。制造商提供的压缩机性能曲线是基于在较高环境温度下的测试,有些情况下可高达35°C。这比压缩机工作的环境温度要高得多,例如,当压缩机安装在家用除湿机上时,它可以在低至10°C的环境温度下工作。我们开发了一种压缩机量热计,用于测试从商用家用除湿机中提取的小型R134a旋转压缩机,并使用它来测量压缩机性能参数,包括等熵和容积效率以及压缩机热损失分数。在10°C、15°C、20°C和25°C的固定相对湿度为70%的环境温度下进行了性能测试,以比较压缩机性能随环境温度的变化情况,并确定压缩机在制造商提供的性能范围之外的性能表现。结果表明,这些小型压缩机的等熵和容积效率对环境温度的变化相对不敏感,即使超出了制造商提供的性能范围。然而,在25°C环境和10°C环境下运行时,压缩机的热损失分数平均可从15%增加到30%。利用所得数据建立了一定环境温度下的压缩机子模型。我们展示了如何使用这些子模型来改进家用除湿机模型,使其在蒸发器结霜状态下在低环境条件下运行,并且在实验和模拟数据之间获得了良好的一致性。作者不知道国内除湿机模型设计在环境温度下工作在结霜制度。
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引用次数: 2
Multi-Objective Optimization of Cascade Refrigeration System Using the Concept of Modified and Advanced Exergy, Risk Level and Thermal Inventory 基于改进和先进火用、风险水平和热库存概念的梯级制冷系统多目标优化
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-11-11 DOI: 10.1142/s2010132520500364
V. Jain, Rajiv Rawat, G. Sachdeva, V. Kumar
This work conceives the performance of vapor compression cascaded refrigeration system (CRS) from the exergy, safety and thermal inventory points of view employing the theory of effective temperature ([Formula: see text] than environment temperature ([Formula: see text] in Gouy–Stodola equation. Comparative results show that the actual irreversible loss in CRS is 8.1% higher. Further, advanced exergy analysis results showed that 17.985[Formula: see text]kW irreversible loss (out of 33.737[Formula: see text]kW irreversible loss) in the system is evadable with improvement in the system design. Besides, the vulnerability of toxic fluid R717 is reported in terms of the total risk level. Moreover, the economy matter is expressed in terms of its total thermal inventory. At the base case, total risk level and total thermal inventory are determined to be 454.3 US$ and 48.86[Formula: see text]kW/K, respectively. First, sensitivity analysis is carried out to evaluate the variation in irreversible loss, total risk level and thermal inventory at different evaporator and condenser temperatures with different degrees of overlap (decision variables). A total of nine simulations are designed using the Taguchi technique. Later, multi-objective optimization is employed. The optimization process reduced the total irreversibility and annual risk level of CRS by 10.2% and 8.9%, respectively, with 6.8% increase in thermal inventory.
本文采用Gouy-Stodola方程中的有效温度([公式:见文])比环境温度([公式:见文])理论,从火用、安全和热库存的角度对蒸汽压缩级联制冷系统(CRS)的性能进行了设想。对比结果表明,CRS的实际不可逆损失高出8.1%。进一步,先进的火用分析结果表明,随着系统设计的改进,系统中17.985[公式:见文]kW不可逆损失(其中33.737[公式:见文]kW不可逆损失)是可以避免的。此外,报告了R717有毒流体的总风险等级脆弱性。此外,经济问题是用其总热库存来表示的。在基本情况下,确定总风险水平和总热库存分别为454.3美元和48.86千瓦/千瓦。首先,进行敏感性分析,评价不同重叠程度蒸发器和冷凝器温度下的不可逆损失、总风险水平和热库存(决策变量)的变化。采用田口法设计了9个仿真。然后采用多目标优化。优化后的CRS总不可逆性和年风险水平分别降低了10.2%和8.9%,热库存增加了6.8%。
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引用次数: 3
Experimental Evaluation of Window-Type Air-Conditioning Unit with New Expansion Device and R404A Alternative Refrigerant 新型膨胀装置和R404A替代制冷剂的开窗空调机组试验评价
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-10-27 DOI: 10.1142/s2010132520500315
A. Al-Sayyab
In this study, the performance of a window-type air-conditioning unit with an alternative, ozone-friendly refrigerant was enhanced by incorporating a nozzle instead of a capillary tube as an expansion device. An experimental evaluation was adopted on a 1.5 RT window-type air-conditioning unit with a controlled environmental zone. According to operating conditions, an ANSYS-Fluent program was used to predict an appropriate nozzle size for a lower pressure ratio. The refrigeration cycle model was simulated using the Engineering Equation Solver (EES).27 The results showed that using a nozzle of 30[Formula: see text]mm length and inner and outer diameters of 9 and 2[Formula: see text]mm, respectively instead of the capillary tube with R404A reduces compressor power consumption by 7.7% and increases the coefficient of performance (COP) by 7.4%.
在本研究中,采用替代臭氧友好型制冷剂的开窗式空调机组的性能通过将喷嘴代替毛细管作为膨胀装置而得到增强。采用环境控制区1.5 RT开窗式空调机组进行试验评价。根据实际工况,利用ANSYS-Fluent软件对较低压力比下的喷嘴尺寸进行预测。利用工程方程求解器(EES)对制冷循环模型进行了仿真结果表明,采用长度为30 mm、内径为9 mm、外径为2 mm的喷嘴代替R404A的毛细管,可使压缩机功耗降低7.7%,性能系数(COP)提高7.4%。
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引用次数: 2
Analysis of Additive Alignment in a 90∘ Elbow Channel 90°肘形通道的加性对齐分析
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-10-21 DOI: 10.1142/S2010132520500327
H. Nguyen, D. Oh
Short-fiber reinforced polymer composites have been widely used in industrial applications due to high strength-to-weight ratio, versatile manufacturing process, and etc. The alignment of fiber type additives plays an important role in the mechanical properties of a composite material. In this paper, an injection molding process was imitated with a liquid polymer composite flow inside a [Formula: see text] elbow channel. We performed a flow visualization experiment and analyzed the additive alignment of carbon fiber flowing in the polydimethylsiloxane (PDMS) medium. By analyzing the flow visualization images, the angle changes at the corner region of the elbow channel were calculated. At the corner region, the change of passage direction leads to the change of fiber orientation. It was observed that near to the convex region, fibers have angle change values larger than the fibers traveling near to the concave region.
短纤维增强聚合物复合材料因其高强度比、制造工艺通用等优点在工业上得到了广泛的应用。纤维型添加剂的排列对复合材料的力学性能起着重要的作用。本文模拟了液体聚合物复合材料在[公式:见文]弯头通道内的注射成型过程。我们进行了流动可视化实验,分析了碳纤维在聚二甲基硅氧烷(PDMS)介质中流动的添加剂排列。通过对流动可视化图像的分析,计算了弯头通道转角区域的角度变化。在角区,通道方向的改变导致纤维取向的改变。观察到,在靠近凸区时,纤维的角度变化值比靠近凹区时大。
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引用次数: 1
Potential Alternative Materials used in Evaporative Coolers for Sustainable Energy Applications: A Review 可持续能源蒸发冷却器中潜在替代材料的研究进展
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-10-21 DOI: 10.1142/S2010132520300062
Shiva Kumar, J. Singh, Jogendra Siyag, S. Rambhatla
In hot climatic conditions, increased energy consumption toward cooling has led to the development of evaporative coolers. The performance of evaporative cooler depends on the various material and operating parameters. Type of material selected for cooling pad is the most important factor among them. In this study, various types of cooling pad materials have been discussed based on their potential benefits, influence on the cooling performance like characteristics wettability, porosity, water holding capacity and cost. It is seen that organic- and fiber-based materials have been extensively used, whereas the studies related to materials based on plastics and metals are limited. Ideal material properties to be possessed by a good pad material have been discussed. Prospects and future scope for further research have been identified. Hence, this review paper certainly throws some light on the selection criteria for a potential alternative evaporative cooling pad material that shows the maximum cooling performance and helps achieve sustainable cooling in buildings.
在炎热的气候条件下,对冷却的能源消耗增加导致了蒸发冷却器的发展。蒸发冷却器的性能取决于各种材料和操作参数。冷却垫选用的材料类型是其中最重要的因素。在本研究中,讨论了各种类型的冷却垫材料的潜在效益,对冷却性能的影响,如特性润湿性,孔隙率,保水能力和成本。可见,有机基材料和纤维基材料得到了广泛的应用,而塑料基材料和金属基材料的相关研究却很有限。讨论了一种好的衬垫材料应具有的理想材料性能。确定了进一步研究的前景和范围。因此,这篇综述论文无疑为潜在的替代蒸发冷却垫材料的选择标准提供了一些启示,这种材料可以显示出最大的冷却性能,并有助于实现建筑物的可持续冷却。
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引用次数: 6
Effects of Nanostructure Additives on Supercooling and Freezing of Distilled Water 纳米结构添加剂对蒸馏水过冷和过冻的影响
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-10-21 DOI: 10.1142/s2010132520500297
Donggyu Lee, Donghyun Kim, Chaedong Kang
The phenomenon of supercooling, which prevents freezing of water below the freezing point, is an obstacle to the production of inexpensive ice. In the case of ice heat storage systems using bio-preservation, low-temperature refrigeration of food and ice capsules in the HVAC industry, the supercooled water in capsules that indirectly come into contact with the outside is one of the problems that must be solved to maintain energy costs and the quality of food or organs. To improve this, experimental evaluation of additives that serve as crude nuclear agents is needed. However, research on this area needs to be supported because the types of additives are limited and their physical properties are unstable. In this paper, the effect of distilled water containing an additive of average diameter nanometer size on solution (frozen) supercooled below the freezing point was investigated. The supercooling time and supercooling level of each specimen were analyzed after addition of kaolin, strontium hydroxide, oxidizing mineral and nano-sized single-wall carbon nanotubes (SWCNT) as mineral fine particles in the distilled water. As a result, it has been confirmed that kaolin and SWCNT can be used as nuclear materials to release supercooling of water. In addition, when kaolin, a mineral fine particle, is used as a nuclear material, its size affects the performance of nuclearization. This confirmed the impact of nuclear material particle size and structure on overcooled emissions.
过冷现象阻碍水在冰点以下结冰,这是生产廉价冰的一个障碍。在暖通空调行业中使用生物保鲜、食品低温制冷和冰囊的冰蓄热系统中,为了保持能源成本和食品或器官的质量,胶囊中间接与外界接触的过冷水是必须解决的问题之一。为了改善这一点,需要对作为粗核剂的添加剂进行实验评价。然而,由于添加剂种类有限且物理性质不稳定,这一领域的研究需要得到支持。本文研究了加入纳米级添加剂的蒸馏水对过冷溶液(冷冻)在冰点以下的影响。在蒸馏水中分别加入高岭土、氢氧化锶、氧化性矿物和纳米单壁碳纳米管(SWCNT)作为矿物细颗粒,分析各试样的过冷时间和过冷程度。结果证实了高岭土和swcnts可以作为核材料释放过冷却水。此外,高岭土是一种矿物细颗粒,当用作核材料时,其大小影响着成核性能。这证实了核材料粒度和结构对过冷排放的影响。
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引用次数: 1
Energy, Exergy, and Exergoeconomic Analysis of Solar Thermal Power Plant Hybrid with Designed PCM Storage 设计PCM储能的太阳能热电厂的能量、火用和耗力经济分析
IF 1 Q4 THERMODYNAMICS Pub Date : 2020-10-19 DOI: 10.1142/s2010132520500303
M. Fani, N. Norouzi, Molood Ramezani
The tendency of renewable energies is one of the consequences of changing attitudes towards global energy issues. As a result, solar energy, which is the leader among renewable energies based on availability and potential, plays a crucial role in thoroughly filing global needs. Significant problems with the solar thermal power plants (STPP) are the operation time, which is limited by daylight and is approximately half of the power plants with fossil fuels, and the capital cost. In the present study, a new suggested sketch of adding latent heat storage (LHS) filled with commercial phase change material (PCM) to a 500-kW STPP case study has been investigated. Solar system details and irradiation amounts for a case study, including total and beam radiation have been determined. Also, the theoretical energetic and exergetic analysis of adding PCM storage to STTP is conducted, which showed a 19% improvement in the exergetic efficiency of the power plant to reach 30%. Besides, an optimized storage tank and appropriate PCM material have been investigated and selected concerning the practical limitations of the case study. By designing a new cycle, the LHS will be charged during daylight and will be discharged at night, doubling power plant operation time up to 2500[Formula: see text]h. Finally, exergoeconomic survey of STPP hybrid with PCM storage was carried out using Engineering Equation Solver (EES) program with genetic algorithm (GA) for three different scenarios, based on eight decision variables, which led us to decrease final product cost (electricity) in optimized scenario up to 30% compared to base case scenario from 28.99 to 20.27 $/kWh for the case study. Also, a comparison is made to demonstrate the effectiveness of the proposed new cycle on 250, 500, 1000, and 2000 kW STTPs.
可再生能源的发展趋势是人们对全球能源问题态度转变的结果之一。因此,太阳能作为可再生能源中可用性和潜力最大的能源,在彻底满足全球需求方面发挥着至关重要的作用。太阳能热电厂(STPP)的主要问题是运行时间,它受到日光的限制,大约是化石燃料发电厂的一半,以及资本成本。在本研究中,研究了一种新的建议草图,即在500千瓦STPP案例研究中加入商业相变材料(PCM)填充的潜热储存(LHS)。已经确定了一个案例研究的太阳系细节和辐照量,包括总辐射和光束辐射。同时,对STTP增加PCM储能系统进行了理论能量和火用分析,结果表明电厂的火用效率提高了19%,达到30%。此外,考虑到案例研究的实际局限性,对优化的储罐和合适的PCM材料进行了研究和选择。通过设计一个新的循环,LHS白天充电,晚上放电,使电厂运行时间增加一倍,达到2500小时。最后,基于8个决策变量,利用工程方程求解器(EES)程序和遗传算法(GA)对三种不同方案进行了STPP与PCM混合储能的努力经济性调查,结果表明,与基本方案相比,优化方案的最终产品成本(电力)从28.99美元/千瓦时降低到20.27美元/千瓦时,降低了30%。此外,还对250kw、500kw、1000kw和2000kw的sttp进行了比较,以证明所提出的新循环的有效性。
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引用次数: 10
期刊
International Journal of Air-conditioning and Refrigeration
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