With the rapid increase in heat flux from microelectronic devices, efficient thermal management solutions for high power applications are urgently required. Close-contact melting (CCM) has emerged as a promising strategy for high power density heat dissipation. However, the coupled effects of melt drainage and interfacial heat transfer induced by microscale heater surface geometries remain poorly understood. This study aims to develop an efficient thermal management strategy by elucidating the heat transfer and flow regulation mechanisms at the CCM interface induced by micro-fin array geometries. Here, micro-fin arrays (rectangular, triangular, and pin) are experimentally investigated, and the effects of fin geometry and height are systematically quantified. The introduction of micro-fins significantly enhances CCM heat transfer, with rectangular fins exhibiting the best overall performance. At a heat flux of 10 W/cm(2) and a pressure of 0.169 atm, the thermal resistance of the rectangular fin array decreases to 0.09 K & centerdot;cm(2)/W, representing an 83.0% reduction compared with the finless case (0.53 K & centerdot;cm(2)/W). Meanwhile, the steady-state temperature is reduced to 44.3 degrees C (superheat <7 degrees C), corresponding to a 72.4% decrease relative to the finless case superheat. Mechanistically, the enhancement of CCM is governed by a synergistic trade-off between liquid film thermal resistance and drainage resistance. For rectangular fins, heat transfer is dominated by the fin tip, where an ultra-thin liquid film governs the thermal resistance. Moreover, their straight, low-resistance drainage effectively suppresses the thickening of the liquid film. The proposed micro-fin array provides an effective pathway for achieving efficient thermal management in high power applications.

Current research on close-contact melting (CCM) primarily focuses on enhancing the thermal conductivity of composite phase change materials (CPCMs), while overlooking the accompanying increase in viscosity and the thermal–rheological trade-off. To address this challenge, a CCM model for CPCMs based on the Sisko non-Newtonian fluid model is developed. By capturing the microscale rheological characteristics of the pressure, velocity, and temperature fields within the liquid film, the model elucidates the heat transfer mechanisms driven by shear-thinning behavior. Experimental and simulation results demonstrate that CPCMs can achieve effective thermal management under a high heat flux of 10 W/cm2. Specifically, at a pressure of 0.169 atm, the loading of 5 wt.% graphene nanoplatelet (GNP) reduces the steady-state temperature superheat and thermal resistance by 8.3% and 5.7%, respectively, compared with pure PCM. The study reveals a synergistic mechanism between thermal conductivity enhancement and rheological regulation, identifying an optimal loading range for stable thermal performance. While the loading of 5 wt.% maintains an extremely thin liquid film (43 μm) through superior thermal conductivity and rapid radial drainage, the loading of 10 wt.% suffers from a synergistic imbalance. Despite its higher thermal conductivity, the sharp increase in viscosity at 10 wt.% leads to liquid film thickening and drainage resistance. These findings provide a clear design strategy for high-performance CPCMs: maximizing thermal conductivity by exploiting the shear-thinning rheology of non-Newtonian fluids to mitigate shear-induced liquid film thickening. The findings provide a theoretical basis for optimizing filler loading and designing high-performance CCM thermal management systems.

Close-contact melting governed by external pressure has emerged as a promising route for managing the increasingly severe thermal loads in high-power electronic systems. Although close-contact melting has been extensively investigated, the melting heat transfer mechanisms under high heat flux densities and the resulting elevated superheat conditions remain insufficient. Specifically, the flow characteristics within microscale liquid films under high superheat and their nonlinear response to pressure and high heat flux require further investigation. This study integrated a visualized close-contact melting experimental apparatus and a high-precision quasi-steady-state co-simulation model to systematically elucidate the flow and heat transfer characteristics of pressure-enhanced close-contact melting microfilms. Results demonstrate that the model can sustain a high heat flux of 10 W/cm2, maintain a steady-state temperature of 59.8 degrees C, and limit the superheat to within 22 degrees C under a pressure of 0.169 atm. The influence of pressure on steady-state temperature regulation shows a strong dependence on heat flux. As pressure increases, the steady-state temperature decreases by up to 27.5% at a high heat flux of 10 W/cm2, whereas the effect is negligible at a low heat flux of 2 W/cm2. The proposed model exhibits excellent predictive performance under high pressure, with a melting time prediction error of only 1.3%. Furthermore, the thermal resistance exhibits a significant monotonically nonlinear decreasing trend with increasing pressure, with the maximum reduction in thermal resistance reaching 53.3%. These findings may provide valuable insights into the thermal management design of compact high-power devices.

Indoor environmental quality (IEQ), influenced by ventilation and acoustic conditions, directly affects human health and comfort. Existing studies often concern either ventilation or sound insulation alone, neglecting the impact of the trickle ventilator's internal structure and its combination with windows on overall performance. This study introduced a double-chamber model to quantify the ventilation performance of three trickle ventilators using tracer-gas-decay and pressure-difference methods. We calculated the flow coefficient (Cd) and flow exponent (n) to reveal differences in pressure sensitivity, with trickle ventilator TV2 showing the highest-pressure sensitivity (Cd = 1.34, n = 0.89). The weighted sound reduction index (RW) and weighted sound insulation index for traffic-noise correction (RW + Ctr) were measured, showing trickle ventilators TV1-1 and TV1-2, and TV2 were 29 dB, 30 dB, and 34 dB, respectively. And the sound insulation and ventilation performance of window-trickle ventilator combinations were analyzed. Trickle ventilators could enhance acoustic performance for low-insulation windows but reduce it for high-insulation windows. The study also quantitatively balanced ventilation and acoustics. This research provides data support and theoretical guidance for the synergistic optimization of ventilation and sound insulation in building environments and provides guidance on ventilation and noise control strategies suited to different floor levels and outdoor noise environments.

The utilization of underground working space in the rapidly developing global economy has broadened the scope of human activities. However, it has also brought new challenges to existing environmental construction strategies. The comfort and performance of the people inside a building are influenced by multiple factors. This study investigates the main factors affecting personnel perception and work performance, such as humidity, heat, and light, to guide the construction of underground working environments. Therefore, an experiment was designed and carried out in an artificial climate chamber to explore the differences in subjective evaluation, physiological parameters, and working performance of personnel under different thermal and lighting environments. The results show that air temperature has a significant effect on most subjective and objective parameters, while lighting has a weak effect. Air temperature and illumination are the two main environmental factors that affect comfort. Regression analysis shows that the recommended air temperature and illumination ranges are 22.0-27.3 °C and 545-1000 lx, respectively. This study also found that the interaction between color temperature and air temperature had significant effects on several evaluation parameters.

建立了1000 MW超超临界火电机组燃烧系统虚拟仿真实验系统,根据实际电站设计资料,应用虚拟现实技术模拟电厂环境和燃烧系统操作过程;以机理动态教学模型为基础,实现了"三维虚拟电站+DCS中控室"二位一体的全面仿真系统.在实验中借助三维效果、图表等直观地展示燃烧器摆角、空气量、吹灰等操控对燃烧效率和污染物控制的影响.

本文采用设计串联式复叠系统的方法,研究了水产冷库在8种不同天然工质组合下的系统性能优劣,分析了不同工质组合与水产冷库温度需求的吻合程度,结果表明:利用系统性能优良(性能系数COP为0.85)的C3H6/NH3组合与安全性高的CO2/NH3组合,作为循环设计的工质再次组合设计出的串联式复叠系统,能够获得与分立系统相同的性能系数(COP),均为1.08,同时节约循环部件的使用,降低系统成本.

医用大型灭菌器承担着医疗器械的消毒灭菌工作,关系到患者的生命安全.医疗器械灭菌过程内部的温度,尤其是局部的"冷点"温度的监测对灭菌质量有着决定性的影响.本文采用实验和数值模拟方法对医用大型灭菌器内内部冷点分布情况进行研究,为医用大型蒸汽灭菌器的计量校准和溯源提供技术依据.研究发现高温灭菌室内温度并非全部均匀分布,以点盖全的监测手段在医院灭菌监控中存在不足,单靠某一测点温度来维持除菌时间并不可靠.灭菌过程中蒸汽的流速对灭菌室内"冷点"分布极其重要,随着入口蒸汽速度的增加,温度的最大值与最小值之差逐渐减小,局部低温区域将逐渐消失;对于非满载工况,室内温度变化相差较大,传统冷点测试方法不适用.

The tip leakage flow passed over the tip clearance makes the flow very complicated near the tip gap, and the interaction of the tip leakage vortex and endwall vortex enhances the instability of the flow. Accurately capturing detailed flow structures and investigating the relationship between the flow structures and loss are beneficial for understanding the flow physics and providing guidance on reducing the loss. Due to the conventional Reynolds Averaged Navier-Stokes (RANS) methods is limited to predict the complex turbulence structures of the tip clearance flow, high fidelity simulation approaches are needed. In this work, the hybrid RANS/Large Eddy Simulation (LES) is adopted to simulate the tip leakage flow in linear cascade and demonstrates its ability to capture the small-scale flow structures. With the POD method, the time-averaged flow field and the dominating modes are obtained. Based on the analysis of the POD modes, it is found that the induced vortex generated by the interaction between the leakage vortex and the endwall vortex has strong turbulence characteristics. Based on the entropy generation rates, viscous loss mechanism is further analyzed. It is found that the shear strain rates dominate the viscous dissipation losses, and the fluctuation dissipation has a strong local enhancement effect.

The performance of film cooling is influenced by many parameters, and the nonuniform flow caused by the internal cooling system is found to largely affect the film cooling, which further complicates the in-hole flow and draws new difficulties in predicting the cooling performance. In this study, we find a very interesting phenomenon that there always exists an in-hole interface, on which distributions of many parameters, including the velocity and kinetic energy, are seldom affected by the mainstream. The existence of this specific interface can be observed for both cylindrical and shaped film cooling holes under most operating conditions. The theoretical analysis of this interface is conducted in this study based on the characteristic decomposition of the Navier–Stokes equation, and this interface is named as the characteristic interface. Theoretical analysis and numerical observations suggest the film cooling system can be simplified to two weakly coupled regions separated by this interface. It also explains why existing source term models for film cooling may fail. Based on these findings, a new prediction model is developed, which uses the convolutional neural networks (CNN) model to predict the boundary conditions on the characteristic interface. The new model outperforms existing source term models and yields similar accuracy as full-mesh computational fluid dynamics (CFD), while reducing the computational cost by one order of magnitude. This model is further evaluated in large eddy simulation (LES), showing moderate success. To sum up, the current work reports the characteristic interface phenomenon in the film cooling hole, based on which a new and efficient prediction model is developed and verified.

以水平壳管式相变蓄能单元为研究对象,建立了考虑相变的流动传热耦合数学模型,对蓄能单元熔化/凝固过程的传热机理进行了研究.结果表明:熔化过程传热机理为从以导热主导到以自然对流主导再恢复到以导热主导;而凝固过程,传热机理为全程以导热主导;自然对流对熔化过程影响较大,可以强化传热,减少总的熔化时间,而对凝固过程影响很小;由于自然对流的强化传热效果,熔化过程蓄热速率会在快速下降后经历一个先上升再缓慢下降直至熔化结束的过程;凝固过程释热速率呈现快速下降后再缓慢下降直至凝固结束;熔化和凝固过程热量的吸收与释放均以潜热为主.

Strong secondary flow results in substantial aerodynamic loss for highly-loaded turbine. Accurate prediction of the complicated flow structures proposes challenges to the widely used Reynolds Average Navier-Stokes (RANS) approach. This work employs the hybrid RANS/Large Eddy Simulation (LES) method to study the unsteady flows for a highly-loaded turbine blade, with both flat endwall and optimized contoured endwall. Evolution of the unsteady flows in the endwall region is analyzed, with emphasis on the loss generation mechanism. Results show that for the flat endwall, the horseshoe vortex system is highly unsteady and is a significant source of unsteadiness in both the passage and the wake region. It contributes to the unsteady passage vortex, also the earlier breakdown of the trailing edge shedding vortex. The Probability Density Function (PDF) histogram of velocity in the wake region is bimodal, implying the perturbations from two mechanisms. For the contoured endwall, the unsteady evolution of the horseshoe vortex is blocked, which results in significantly reduced unsteadiness, also the merge between the horseshoe vortex with the passage vortex is prevented. Effect of the flow unsteadiness on the loss generation is assessed based on the entropy generation rates contributed by the time-averaged flow and the fluctuations. The effect of unsteadiness is two-fold: unsteady perturbations trigger the vortex breakdown into small-scale structures and thus weakened wake velocity deficit and loss generation; however, in both the passage and the wake region the entropy generation by the fluctuations are remarkable. For the contoured endwall, due to the reduced flow unsteadiness, loss generation contributed by the fluctuations are much smaller compared to the flat endwall. The results highlight the importance of including the loss generation by the fluctuations, also a possible mechanism to reduce the secondary loss by attenuating the flow unsteadiness with the contoured endwall.

The development and utilization of underground spaces can ease the shortage of urban land resources, ensure urban safety, and improve the urban ecological environment. Human overall comfort and work efficiency in underground spaces are affected by several environmental factors, such as thermal, acoustic, and lighting. Owing to the particularities of an underground space at any given location, the guarantee of a comfortable indoor environment is different from that in aboveground buildings. Based on the thermal, acoustic, and illumination characteristics of an underground space, the main differences between underground spaces and aboveground buildings, limitations of current standards/codes, and imperfections of internal environmental evaluation indicators are summarized and analyzed, and human comfort and work efficiency in terms of one-way and three-way interactions are discussed based on the literature published since 2000. The findings reveal that the current standards/codes for underground spaces mainly refer to aboveground buildings. Where the parameter index is single, there exists a large difference between the underground environment and the design standard, and there is no evaluation index for human comfort in underground spaces. In the existing research, two methods have been adopted: field surveys and climate room experiments. These have mainly focused on the effects of thermal, acoustic, and lighting environment unidirectional control on personnel comfort, while only a few studies have been conducted on work efficiency. Research on the three-directional interactions involving thermal, acoustic, and lighting environments in underground spaces is lacking. The creation of a microenvironment based on local cooling and heating, and the technologies generated under the concepts of imitating the ground environment, imitating the natural environments, and thermal–acoustic–light coordinated control are expected to play important roles in the construction of underground space environments in the future, and lay the foundation for the construction of an ecological environment system in underground spaces.

在煤的发热量测定教学实验中,越来越多地使用自动氧弹量热仪进行测定,实验内容简单空洞.尝试从煤在氧化性气氛下燃烧以后,硫氧化物和氮氧化物的生成机理以及它们最终生成硫酸和硝酸带来的热效应的计算作为切入点设计实验教学内容,使学生更深入地理解氧弹量热仪的工作原理,推导出仪器测定的弹筒发热量与高位发热量的关系,弹筒发热量与酸校正的关系,酸校正经验公式与燃烧过程之间的关系以及为什么需要进行冷却校正.这种尝试丰富了实验课内容,可以更好地解释实验数据,进而更好地理解课程内容,具有很好的教学效果.

风/光/储微电网实验平台面向分布式发电、微电网等专业课程展开相关设计,集成了模拟风力发电系统、光伏发电系统、蓄电池储能系统、可控负荷等装备.该实验平台可开展模拟风力发电系统并网、光伏系统跟踪等实验,通过实验设计与实现增强学生对光伏、风机等分布式电源以及微电网系统的理解与认识,从而激发学生学习兴趣,提高实验教学效果.

设计了一套竖直管内气液两相流流量的测量教学实验系统.该系统采用双参数测量法,即测量竖直管上方孔板流量计压差和测压管压差,将气液两相流视为物理性质均匀的单相混合物,则可推算出气液两相流总体积流量QM和空泡率αA,并最终获得液相体积流量QL和气相体积流量QG.实验原理和实验数据表明,该方法适用于竖直管内泡状流的流量测量,低液体流速时,获得的气体体积流量精度高;高液体流速时,获得的液体体积流量精度高.

创建填料与盘管间隔布置的新型横流闭式冷却塔,在冷却塔进风中引入部分排风,设计了可控制冷却塔空气进口湿球温度的简易实验室,并在设计工况下对该实验室内横流闭式冷却塔进行实验.通过分析换热温差和进口湿球温度与冷却塔换热能力的关系,提出在非标准工况下测试冷却塔的冷却能力评价折算方法,并根据实验结果对比验证了该评价方法的可行性.结果 表明:采用该折算方法评价所测冷却塔的冷却能力为71冷吨,与冷却能力计算软件的结果接近.

Intermittent heating and cooling are energy efficient measures for building indoor thermal environment, and improvements to the thermal response speed of the indoor terminal are particularly important for thermal comfort. In this study, a novel integrated flat-heat-pipe radiant heating and cooling terminal was proposed. The flat-heat-pipe is used as the radiant panel in this terminal, providing a quick thermal response speed and high thermal uniformity. Moreover, the proposed radiant terminal could also be operated in both winter and summer owing to its integrated flat structure. In this study, an experimental rig was built for studying the thermal performance of the flat heat pipe terminal, including the heat response speed, heating/cooling capacity, heating/cooling temperature, and heat transfer coefficient. The experimental results show that the heating/cooling response speed ranges from 550 s to 1810 s and the vertical temperature difference is less than 1.4 degrees C/m. In addition, the heat transfer capacity showed a significant increase of 36.1% to 42.6% when the emissivity of the surface of the flat heat pipe increased from 0.1 to 0.9. The heating/cooling temperature is significantly influenced by the heat source temperature and heat transfer ability on the source side and is less influenced by the flow rate. Overall, this novel terminal has good thermal performance and is worthy of further optimization. (C) 2019 Elsevier B.V. All rights reserved.

非稳态平面热源法导热系数和热扩散率虚实结合实验教学平台,包括实体装置和虚拟仿真系统两部分.实体装置利用非稳态平面热源法测定导热系数和热扩散率,采用触摸屏系统进行控制、数据采集和人机交互,可使学生认识客观现象,提高动手能力,强化实验技能.虚拟仿真实验系统与实体装置互补,并增加了试样空间温度场动态分布云图,可实现学生在线自主性实验研究.该虚实结合实验教学平台极大地提高了实验教学的质量和效率.