Case Studies in Thermal Engineering最新文献_第10页

Research on the dynamics of flame propagation and overpressure evolution in full-scale residential gas deflagration 全尺寸住宅气体爆燃中火焰传播和超压演变动力学研究

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105204

To determine the effect of ignition height on indoor flame spread behavior and overpressure development, a comprehensive full-scale deflagration testing facility was established. Extensive experimental research was conducted within this facility. The findings indicate that indoor flame reignition and the occurrence of secondary explosions are most pronounced with intermediate ignition. Furthermore, the explosion overpressure generated during the reverse turn of shock wave propagation is greater than that produced by the forward turn. In comparison to the peak overpressure P_ext in the master bedroom for top, middle, and bottom ignition, the peak overpressure P_ext in the second bedroom increased by approximately 14.48 %, 15.04 %, and 19.20 %, respectively. When comparing middle ignition to top ignition, the propagation speed of shock waves in the kitchen balcony, restroom, second bedroom, and master bedroom was enhanced by 34.21 %, 40.85 %, 40.70 %, and 34.65 %, respectively. Furthermore, when comparing middle ignition to bottom ignition, the propagation speed of shock waves in these areas experienced a significant increase of 126.32 %, 124.39 %, 123.26 %, and 113.86 %, respectively. These research findings provide a theoretical foundation and empirical data to support the investigation and analysis of the causes of indoor gas explosion incidents.

为了确定点火高度对室内火焰蔓延行为和超压发展的影响，建立了一个全面的全尺寸爆燃试验设施。在该设施内进行了广泛的实验研究。研究结果表明，在中间点火时，室内火焰复燃和二次爆炸的发生最为明显。此外，冲击波反向传播时产生的爆炸超压大于正向传播时产生的爆炸超压。与主卧室顶部、中间和底部点火时的峰值超压 Pext 相比，次卧室的峰值超压 Pext 分别增加了约 14.48 %、15.04 % 和 19.20 %。中间点火与顶部点火相比，厨房阳台、洗手间、次卧室和主卧室的冲击波传播速度分别提高了 34.21 %、40.85 %、40.70 % 和 34.65 %。此外，中间点火与底部点火相比，这些区域的冲击波传播速度分别显著增加了 126.32 %、124.39 %、123.26 % 和 113.86 %。这些研究结果为调查和分析室内气体爆炸事故的原因提供了理论基础和经验数据支持。

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引用次数: 0

Experimental study on internal heat transfer among adjacent rooms for building energy efficiency with housing vacancy consideration 考虑房屋空置率的建筑节能相邻房间内部传热实验研究

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105188

With the expansion of the real estate sector and the rise of tourist resorts, many individuals now own multiple properties, resulting in a substantial number of homes remaining vacant for extended periods or being used seasonally. Despite being unheated, rooms in these vacant properties continue to transfer heat to adjacent heated rooms. While previous research has explored the heat transfer between non-heated and heated rooms based on their relative positioning, few studies have considered the dynamic aspects of this process. To fill this gap, we developed a scaled-down model to replicate real-world conditions and conducted experiments to track the dynamic temperature changes between non-heated and heated rooms in different configurations. The heat transfer mechanism was analyzed, and a theoretical model was constructed to quantify the dynamic heat exchange. This model accounts for variations in both convective and radiative heat transfer between rooms. Initial findings suggest that heat transfer to a non-heated room below a heated space can reach 28 % of the total heat supplied, while heat transfer to an upper adjacent room can account for 16 %. The peak heat transfer is observed after 5–10 h of heating. These results provide valuable insights for optimizing space heating, promoting energy-saving practices, and improving indoor heating efficiency, alongside offering actionable recommendations for behavioral energy conservation.

随着房地产行业的扩张和旅游胜地的兴起，许多人现在拥有多处房产，导致大量房屋长期空置或季节性使用。尽管没有暖气，但这些空置房中的房间仍会将热量传递到相邻的暖气房间。虽然之前的研究已经根据非供暖房间和供暖房间的相对位置探讨了它们之间的热量传递，但很少有研究考虑到这一过程的动态方面。为了填补这一空白，我们开发了一个按比例缩小的模型来复制真实世界的条件，并进行了实验来跟踪不同配置下非供暖房间和供暖房间之间的动态温度变化。我们分析了热传递机制，并构建了一个理论模型来量化动态热交换。该模型考虑了房间之间对流和辐射传热的变化。初步研究结果表明，向供暖空间下方的非供暖房间传热的热量可达总供热量的 28%，而向上方相邻房间传热的热量可达 16%。加热 5-10 小时后可观察到传热峰值。这些结果为优化空间供暖、促进节能实践和提高室内供暖效率提供了宝贵的见解，同时也为行为节能提供了可行的建议。

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引用次数: 0

Optimization of piezo pump and air impact cooling based on a synthetic jet 基于合成射流的压电泵和空气冲击冷却的优化

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105216

A synthetic jet piezo (PE) pump with an inlet channel structured akin to a diffuser/nozzle, featuring smoothed walls, was developed. The synthetic jet was characterized by analyzing the internal flow field of the PE pump. Furthermore, the flow performance of this novel PE pump was compared with that of a basic PE pump, thereby demonstrating the advantages of the proposed design. Utilizing regression equations and standardized effect plots derived from the response surface method, both the main and interaction effects of parameters on the flow rate were assessed. Subsequently, the flow performance of the optimized PE pump was evaluated through experimental testing. Additionally, air impact cooling experiments were conducted, focusing on the influence of the impact distance on cooling performance. The findings indicated that the PE pump's open cavity height, closed cavity height, outlet diameter, and orifice diameter were 1.3 mm, 0.5 mm, 1.5 mm, and 0.8 mm, respectively. The proposed synthetic jet PE pump achieved a flow rate of 1832.3 ml/min at 50 Vpp and 4.6 kHz. Furthermore, it was observed that the operation of the PE pump reduced the temperature of the heater by 63 % at an impact distance of 20 mm.

我们开发了一种合成射流压电（PE）泵，其入口通道结构类似于扩散器/喷嘴，具有平滑的内壁。通过分析 PE 泵的内部流场，对合成射流进行了表征。此外，还将这种新型 PE 泵的流动性能与基本 PE 泵的流动性能进行了比较，从而证明了拟议设计的优势。利用响应面法得出的回归方程和标准化效应图，评估了各参数对流量的主效应和交互效应。随后，通过实验测试评估了优化 PE 泵的流量性能。此外，还进行了空气冲击冷却实验，重点研究冲击距离对冷却性能的影响。结果表明，聚乙烯泵的开腔高度、闭腔高度、出口直径和孔径分别为 1.3 毫米、0.5 毫米、1.5 毫米和 0.8 毫米。在 50 Vpp 和 4.6 kHz 的条件下，拟议的合成喷射聚乙烯泵的流速达到了 1832.3 毫升/分钟。此外，据观察，在 20 毫米的冲击距离内，聚乙烯泵的运行使加热器的温度降低了 63%。

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引用次数: 0

Mechanism of initiation and propagation of surface cracks in gun bore under thermomechanical coupling impact 热机械耦合冲击下炮孔表面裂纹的产生和扩展机理

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105194

Surface cracks in gun bore may exacerbate rifling ablation and wear and in turn shorten barrel life. Thermomechanical coupling finite element (FE) models of bore are established and the dynamic responses of the bore under high-temperature and high-pressure are numerically simulated. The stress distribution characteristics on the inner surface are analyzed and the effects of autofrettage, number of firings and harden layer on the stress distribution are discussed. Based on the stress distribution characteristics, FE models with two initial cracks on the ledge of land surface are set up and the propagation, interaction and intersection of the cracks are numerically simulated, considering the effect of the distance between the two cracks. Based on simulation results, the initiation and propagation pattern and mechanism of the cracks on the inner surface are analyzed. An ablation test system was designed and produced, and used to experimentally verify the initiation and propagation mechanism of the cracks. The observed crack patterns on the inner surface of a real gun bore are also used to illustrate the mechanism obtained in this work. Understanding of the initiation and propagation mechanism of cracks in gun bore can be applied to improve and optimize the design of barrels.

枪膛表面裂纹可能加剧膛线烧蚀和磨损，进而缩短枪管寿命。本文建立了枪膛的热力学耦合有限元（FE）模型，并对枪膛在高温高压下的动态响应进行了数值模拟。分析了内表面的应力分布特征，并讨论了自动修整、发射次数和硬化层对应力分布的影响。根据应力分布特征，建立了陆地表面台阶上有两个初始裂纹的 FE 模型，并考虑了两个裂纹之间距离的影响，对裂纹的传播、相互作用和交叉进行了数值模拟。根据模拟结果，分析了内表面裂纹的起始、扩展模式和机理。设计并制作了一个烧蚀测试系统，用于实验验证裂纹的产生和扩展机制。此外，还利用在真实炮膛内表面观察到的裂纹形态来说明本研究中获得的机理。了解枪膛裂纹的产生和扩展机理可用于改进和优化枪管设计。

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引用次数: 0

Comparison analysis of three CO2-based binary mixtures performing in the supercritical Brayton cycle for molten salt energy storage 在超临界布雷顿循环中用于熔盐储能的三种二氧化碳二元混合物的比较分析

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105200

It is generally acknowledged that using CO₂-based binary mixtures as working fluids in supercritical recompression Brayton cycle for waste heat recovery is a promising technique. This study examines the performance of CO₂-Kr (0.76/0.24) and CO₂-Xe (0.56/0.44) mixtures, comparing them with pure CO₂. Both thermodynamic and thermo-economic considerations are taken into account to establish optimal parameter settings. The findings suggest that the minimum system temperature should be around but not below the critical temperature of the working fluid. The system performs badly at lower pressures and shows nearly the same at higher pressures, with 25 MPa being the recommended value for the main compressor. When the system split ratio and the low temperature recuperator temperature difference are well matched, the heat exchangers exhibit an optimal temperature distribution. The exergy loss distributions of the exchangers in the CO₂-Kr and CO₂-Xe systems are likewise rather uniform when the input pressure of the main compressor is above the critical pressure of the fluid, typically between 0.2 MPa and 0.4 MPa, enhancing system efficiency. The corresponding temperature difference of the LTR should be within 5 °C above or below the critical temperature of the fluid. This advantageous feature is not immediately apparent in the pure SCO₂ cycle.

人们普遍认为，在超临界再压缩布雷顿循环中使用二氧化碳二元混合物作为工作流体进行余热回收是一项很有前景的技术。本研究考察了 CO2-Kr（0.76/0.24）和 CO2-Xe（0.56/0.44）混合物的性能，并将其与纯 CO2 进行了比较。在确定最佳参数设置时，既考虑了热力学因素，也考虑了热经济因素。研究结果表明，系统最低温度应在工作流体临界温度附近，但不应低于临界温度。系统在较低压力下表现不佳，而在较高压力下表现几乎相同，主压缩机的推荐值为 25 兆帕。当系统分流比和低温换热器温差匹配良好时，热交换器显示出最佳温度分布。当主压缩机的输入压力高于流体的临界压力（通常在 0.2 兆帕和 0.4 兆帕之间）时，CO2-Kr 和 CO2-Xe 系统中热交换器的能量损失分布同样相当均匀，从而提高了系统效率。LTR 的相应温差应在流体临界温度上下 5 °C 的范围内。这一优势在纯 SCO2 循环中并不明显。

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引用次数: 0

Kinetic analysis of coal oxidative pyrolysis before and after immersion effect 浸泡效应前后煤氧化热解的动力学分析

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105235

The oxidative pyrolysis kinetics of coal before and after immersion effect was studied by thermogravimetric experiments. Non-isothermal thermogravimetric analysis data were analyzed at four heating rates of 5, 10, 20 and 30 K/min. Furthermore, temperature-programmed experiments and Fourier-transform infrared (FTIR) spectroscopy were employed to understand the oxidation activity and chemical structure of raw coal and soaked coal. After coal immersion effect, the increase in the content of active functional groups, the increase in the concentration of gaseous products, and the decrease in crossing point temperature during oxidation process all indicate that soaked coal is easier to oxidize and spontaneously combust. Lastly, four model-free methods such as Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Friedman and Kissinger methods are employed to calculate the activation energy (E_α). Kinetic analysis reveals that E_α value obtained by the former three methods significantly depends on the conversion of coal oxidative pyrolysis process, and the average E_α value of soaked coal obtained by four methods is lower than that of raw coal. For the kinetic analysis of coal oxygen adsorption and combustion stages, it is more reliable to adopt the FWO and KAS methods in turn. This research helps to better understand the mechanism of enhanced oxidation activity of soaked coal and optimizes the calculation method of kinetic parameters in different oxidation stages of coal.

通过热重实验研究了煤在浸泡效应前后的氧化热解动力学。分析了 5、10、20 和 30 K/min 四种加热速率下的非等温热重分析数据。此外，还采用了温度编程实验和傅立叶变换红外光谱（FTIR）来了解原煤和浸泡煤的氧化活性和化学结构。经过煤的浸泡作用后，活性官能团含量的增加、气态产物浓度的增加以及氧化过程中交叉点温度的降低都表明浸泡煤更容易氧化和自燃。最后，四种无模型方法，如 Flynn-Wall-Ozawa (FWO)、Kissinger-Akahira-Sunose (KAS)、Friedman 和 Kissinger 方法被用来计算活化能（Eα）。动力学分析表明，前三种方法得到的 Eα 值明显取决于煤氧化热解过程的转化率，四种方法得到的浸水煤平均 Eα 值低于原煤。对于煤炭吸氧和燃烧阶段的动力学分析，依次采用FWO和KAS方法更为可靠。该研究有助于更好地理解浸泡煤氧化活性增强的机理，优化煤不同氧化阶段动力学参数的计算方法。

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引用次数: 0

Asymmetrical distribution of buoyancy flux and its effect on smoke propagation velocity and backlayering length in inclined tunnel fires 倾斜隧道火灾中浮力通量的非对称分布及其对烟雾传播速度和背层长度的影响

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105205

Inclined tunnels are commonly seen in modern society. Compared with horizontal tunnel fires, smoke movement in inclined tunnel fires exhibits noticeable asymmetry. In this study, a series of numerical simulations are conducted to investigate the asymmetrical distribution of source buoyancy flux and its impact on smoke movement in inclined tunnel fires. Because of buoyancy and the stack effect, the proportion of the buoyancy flux of the smoke advancing towards the upper portal,

η

, varies with time. When the fire plume impinges the tunnel ceiling, there is an initial distribution of buoyancy flux and the value of

η

is determined by tunnel inclination angle

α

. Subsequently,

η

gradually increases until the steady state is achieved. The growth trajectory of

η

with time is also controlled by

α

, but the steady-state value is dependent on both

α

and the fire location. Models are established to calculate

η

in different stages. The value of

η

influences smoke flow characteristics. Smoke propagation velocity scales with the cubic root of buoyancy flux per unit width, which can be derived based on

η

. Additionally, the backlayering length increases with the steady-state value of

η

. The findings contribute to a better understanding of the mechanisms governing the smoke flow in inclined tunnel fires.

倾斜隧道在现代社会中十分常见。与水平隧道火灾相比，倾斜隧道火灾中的烟雾运动表现出明显的不对称性。本研究进行了一系列数值模拟，以研究源浮力通量的非对称分布及其对倾斜隧道火灾中烟雾移动的影响。由于浮力和烟囱效应，向上部入口推进的烟气浮力通量比例 η 随时间变化。当火灾烟流撞击隧道顶板时，浮力通量出现初始分布，η 值由隧道倾角 α 决定。η随时间的增长轨迹也受α控制，但稳态值取决于α和着火位置。我们建立了模型来计算不同阶段的 η。η值会影响烟流特性。烟雾传播速度与单位宽度浮力通量的立方根成比例，而浮力通量可根据 η 得出。此外，背层长度随 η 的稳态值增加而增加。这些发现有助于更好地理解倾斜隧道火灾中的烟流机制。

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引用次数: 0

Performance assessment and multi-objective optimization of a novel transcritical CO2 Rankine cycle for engine waste heat recovery 用于发动机余热回收的新型跨临界二氧化碳郎肯循环的性能评估和多目标优化

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105223

In this study, a novel self-condensing transcritical CO₂ Rankine cycle, which integrates the three-stage expansion process with an ejector cycle, is proposed to recover engine waste heat deeply and overcome the condensation issue caused by the relatively low critical temperature of CO₂. Thermodynamic and economic mathematical models are developed, and the detailed parametric analysis is carried out to investigate the effect of main parameters on both thermodynamic and economic performances of the system. Thereafter, a multi-objective optimization is conducted to trade off the two different performances. Results show that the proposed system could operate under higher temperature cold source conditions with desirable performance. The increases of turbine1 inlet pressure and LT gas heater outlet temperature, the decreases of LT gas heater outlet pressure and turbine3 back pressure are beneficial to achieve better thermodynamic and economic performances. On the basis of multi-objective optimization, the maximum net power output is 70.04 kW, which is a 10.20 % improvement compared to the reference cycle. Meanwhile, the engine power output could be increased by 7.03 % through adopting the novel system. Furthermore, the optimal exergy efficiency and unit net power cost are 37.02 % and 0.1567$/kWh, respectively.

本研究提出了一种新型自冷凝跨临界二氧化碳郎肯循环，该循环将三级膨胀过程与喷射器循环集成在一起，可深度回收发动机余热，并克服二氧化碳临界温度相对较低造成的冷凝问题。建立了热力学和经济数学模型，并进行了详细的参数分析，研究了主要参数对系统热力学和经济性能的影响。随后，进行了多目标优化，以权衡两种不同的性能。结果表明，提议的系统可以在温度较高的冷源条件下运行，并且性能理想。提高涡轮机 1 入口压力和低温燃气加热器出口温度，降低低温燃气加热器出口压力和涡轮机 3 背压，有利于获得更好的热力学性能和经济性能。在多目标优化的基础上，最大净输出功率为 70.04 kW，与参考循环相比提高了 10.20%。同时，通过采用新系统，发动机输出功率可提高 7.03%。此外，最佳能效和单位净功率成本分别为 37.02 % 和 0.1567 美元/千瓦时。

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引用次数: 0

Influence of space conjugate temperature varying non-uniform heat sink/source on hydromagnetic slip water-EG (50:50) nanofluid 空间共轭温度变化的非均匀散热器/热源对水磁滑移水-EG（50:50）纳米流体的影响

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105220

Significant cooling is an essential requirement in the field of aeronautical and bio-medical engineering, nuclear reactor system, solar collectors, and in development of electronic chips etc. Involving rotating conical geometries. In view of this, flow and heat transfer over conical geometries subject to different constraints of motion are highly needed. Implementation of magnetic field subject to flow pattern controls the fluid motion thereby imparting better cooling. Consideration of nanofluid instead of regular fluid yields prominent cooling of the associated surface. Such relevance has motivated the authors to work on magnetohydrodynamics and heat transfer investigation of water-EG (50:50) mixture based

A l_{2} O_{3}

and

F e_{3} O_{4}

past heated and rotating down-pointing upright cone subject to impact of space and temperature varying non-uniform heat source or sink. Numerical solution of dimensionless governing equations is accomplished by implementing Runge-Kutta method. The findings indicate that swirl and axial velocities peter out with rise in magnetic parameter while both exhibit opposite impact in response to slip parameter. Temperature profiles upgrade due to amplification of space and temperature dependent parameters. Skin friction and heat transportation upsurge with growth of solid volume fraction of nanoparticle.

在航空和生物医学工程、核反应堆系统、太阳能集热器以及电子芯片开发等领域，大量冷却是一项基本要求。这涉及到旋转的锥形几何体。有鉴于此，亟需研究受不同运动限制的锥形几何体上的流动和传热问题。根据流动模式实施磁场控制流体运动，从而提供更好的冷却效果。考虑用纳米流体代替普通流体，可以显著冷却相关表面。这种相关性促使作者着手研究基于 Al2O3 和 Fe3O4 的水-EG（50:50）混合物的磁流体力学和传热学，该混合物经过受空间和温度变化影响的非均匀热源或散热器加热和旋转的向下直立锥体。采用 Runge-Kutta 方法对无量纲控制方程进行了数值求解。研究结果表明，漩涡速度和轴向速度随着磁性参数的增加而减弱，而两者对滑移参数的影响则相反。由于空间和温度相关参数的放大作用，温度曲线上升。随着纳米粒子固体体积分数的增加，表面摩擦和热传导也随之增加。

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引用次数: 0

Transient behavior of ablation and swelling for C/C composite and HfC-coated C/C composite in an arc-heated wind tunnel 电弧加热风洞中 C/C 复合材料和 HfC 涂层 C/C 复合材料的烧蚀和膨胀瞬态行为

IF 6.4 2区工程技术 Q1 THERMODYNAMICS

Case Studies in Thermal Engineering

Pub Date : 2024-10-01 DOI: 10.1016/j.csite.2024.105213

This study investigated and modeled the transient behavior of surface recession, defined as the difference between ablative length and swelling length, for thermal protection materials within a high-enthalpy flow. Needle punch carbon-carbon (NPCC) and hafnium carbide coated carbon-carbon (HfC-coated NPCC) were exposed to high-enthalpy flow with a heat flux of 7.67 MW/m² generated by an arc-heated facility. The NPCC and the HfC-coated NPCC represent an ablative surface and a non-ablative surface, respectively. Surface recession histories were estimated through an image analysis and visualizations monitored by a high-speed camera. Moreover, measured data including surface temperature histories, mass loss, and total length were presented. We proposed the models for the transient recession on the ablative surface and the non-ablative surface considering the ablation and the swelling. The ablative length was calculated using non-dimensional parameter B′, which computes ablation rates under equilibrium air conditions. While B’ modeling accurately predicted the ablation rates, it could not reflect the swelling phenomenon during an initial heating phase. The swelling was modeled with consideration of the thermal expansion. Specifically, the effect of increased porosity near the ablative surface was incorporated into the thermal expansion coefficient. The model developed in this study well agreed with the experimental data.

本研究对高焓流中热保护材料的表面后退（定义为烧蚀长度与膨胀长度之差）的瞬态行为进行了研究和建模。针刺碳碳（NPCC）和碳化铪涂层碳碳（HfC 涂层 NPCC）暴露在电弧加热设施产生的 7.67 MW/m2 热通量的高焓流中。NPCC 和 HfC 涂层 NPCC 分别代表烧蚀表面和非烧蚀表面。表面衰退历史是通过高速摄像机监控的图像分析和可视化来估算的。此外，还提供了包括表面温度历史、质量损失和总长度在内的测量数据。考虑到烧蚀和膨胀，我们提出了烧蚀表面和非烧蚀表面的瞬时衰退模型。烧蚀长度是通过计算平衡空气条件下的烧蚀率的非尺寸参数 B′计算得出的。虽然 B′模型能准确预测烧蚀率，但不能反映初始加热阶段的膨胀现象。在建立膨胀模型时考虑了热膨胀。具体来说，烧蚀表面附近孔隙率增加的影响被纳入了热膨胀系数。该研究建立的模型与实验数据十分吻合。

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引用次数: 0