Parametric study on flow and heat transfer characteristics of porous wick evaporator based on AMTEC

By establishing an axial symmetric invariable temperature phase change interface model of porous wick evaporator based on alkali metal thermal-to-electric converter (AMTEC), a parametric study has been implemented to explore the impact of effective thermal conductivity model, working fluid, wick material, porosity and particle size of porous wick on the flow and heat transfer characteristics. The results indicate that the inner surface temperature profile of wick is closely dependent on effective thermal conductivity models; it is the minimum for series model while the highest for parallel model. The inner surface temperature of wick with Na-K alloy as working fluid is obviously lower than that with sodium or potassium as working fluid. The wick made of refractory ceramics makes the minimum of inner surface temperature, while the one with nickel appears the highest temperature. Increasing the porosity can reduce the pressure drop in the wick, but also increases the temperature of evaporator.     

微沟槽热管传热性能实验研究

为研究充液率、真空度和长度对热管传热性能的影响作用,利用基于虚拟仪器技术的热管传热性能测试平台对直径6mm的微梯形沟槽热管在不同充液率、不同真空度以及不同长度等条件下进行实验测试.实验表明:微沟槽热管的最佳充液率在(75～100)%之间.热管内必须具备足够低的真空度,且充液率需根据真空度的不同适当调整.热管长度缩短可以提高其传热性能,但长度较短时,需适当提高充液率.     

An experimental investigation on heat transfer performance of pulsating heat pipe

Journal of Mechanical Science and Technology - Heat input and inclination angle are essential factors influencing heat transfer performance of a pulsating heat pipe (PHP). The heat transfer...     

A numerical study on heat transfer characteristics in a spray column direct contact heat exchanger

A reliable computational heat transfer model has been investigated to define the heat transfer characteristics of a spray column direct contact heat exchanger, which is often utilized in the process involving counterflows for heat and mass transfer operations. Most of the previous studies investigated are one-dimensional unsteady solutions based on rather fragmentary experimental data. Development of a multidimensional numerical model and a computational algorithm are essential to analyze the inherent multidimensional characteristics of a direct contact heat exchanger. The present study has been carried out numerically and establishes a solid simulation algorithm for the operation of a direct contact heat exchanger. Operational and system parameters such as the speed and direction of working fluid droplets at the injection point, and the effects of aspect ratio and void fraction of continuous fluid are examined thoroughly as well to assess their influence on the performance of a spray column.     

Effects of saturation temperature variation due to pressure drop of working fluid in heat exchanger on heat transfer performance

The effect of the saturation temperature drop on the heat transfer performance of a heat exchanger was analyzed under air-conditioner condensing condition, air-conditioner evaporating condition, and refrigerator evaporating condition. The thermodynamic analysis results show that the heat transfer capacity due to the pressure drop of the saturated refrigerant was at least 2.3 % and at most 91.1 % compared to the evaluated heat transfer capacity assuming no pressure loss. The rate of change of heat transfer capacity was the largest in the order of R600a, R1234yf, R134a, R410A, and R32. Heat exchanger performance simulation under practical air-conditioner operating conditions showed that the heat transfer capacity was reduced by 0.72 % due to refrigerant pressure drop under the condensing condition. On the other hand, the heat transfer capacity was increased by 26.55 % under the evaporating condition.

     

大功率LED相变热沉的传热性能研究

研制了一种利用相变传热原理进行传热的大功率LED相变热沉.实验结果表明与传统实体热沉相比,相变热沉具有更快的启动性能,随着加热功率的增加,其热阻逐渐减小,并低于传统实体热沉,同时在高加热功率条件下,仍能保持良好的均热性能与轴向导热性能.     

不同工质沟槽式微热管传热性能实验研究

为了研究工质对沟槽式微热管传热性能的影响,通过试验对不同充液率下,不同工质对沟槽式微热管的温差、热阻与极限功率等性能的影响进行研究.结果表明:充液率对丙酮热管的温差变化影响较大,在相同情况下,丙酮热管需要更高的充液率.乙醇热管的温差性能较差,但充液率小的乙醇热管其热阻较小.水热管的极限功率最高,且在100%的充液率时,有着最为良好的传热性能,较另两种工质更适合用于高功率场合.该研究对实际生产和应用中的工质选择有着重要的参考意义.     

Numerical study on the operational performance of spray column direct contact heat exchangers

Spray columns have received considerable attention as direct contact heat exchangers due to their potential high throughput, as well as their near perfect counterflow operations if one-dimensional flow is obtainable. In practice, the degree of success in obtaining one-dimensional flow has depended on the design of the injectors for the disperse and continuous phases. In the past, the design of the injectors have been a trial and error procedure not sufficiently backed up by analyses. In this paper, theoretical analyses are carried out and several designs are evaluated. The influence of proper inlet conditions for the continuous phase to assure near one-dimensional flow is illustrated.     

管内流体换热性能测试系统

设计了一种测试流体(煤油)管内换热性能的实验系统.该实验系统包括了循环系统、加热系统、冷却系统、增压系统、测量系统(流量测量、压力测量、温度测量)和数据采集系统,各部分做了详细的说明,对其测试原理也作了说明.流体进、出口温度以及预热段流体进口温度都用铠装热偶测量.预热段和实验段都采用电加热方法加热(采用低电压、大电流加热).预热段和实验段都均匀布置20个热电偶测量管外壁温度,电加热管内壁温可通过龙格一库塔方法由外壁温和加热功率求得.该系统也可以用来测量其它流体管内换热性能,还可以用来测量流体的比热;还可以测量流动压降和摩擦阻力系数.     

Performance of a shell-and-tube heat exchanger with spiral baffle plates

School of Mechanical and Industrial System Engineering, Dong-Eui University, Busan 614-714, Korea In a conventional shell-and-tube heat exchanger, fluid contacts with tubes flowing up and down in a shell, therefore there is a defect in the heat transfer with tubes due to the stagnation portions. Fins are attached to the tubes in order to increase heat transfer efficiency, but there exists a limit. Therefore, it is necessary to improve heat exchanger performance by changing the fluid flow in the shell. In this study, a highly efficient shell-and-tube heat exchanger with spiral baffle plates is simulated three-dimensionally using a commercial thermal-fluid analysis code, CFX4.2. In this type of heat exchanger, fluid contacts with tubes flowing rotationally in the shell. It could improve heat exchanger performance considerably because stagnation portions in the shell could be removed. It is proved that the shell-and-tube heat exchanger with spiral baffle plates is superior to the conventional heat exchanger in terms of heat transfer.     

Numerical simulation of fluid flow and heat transfer in a plasma spray gun

A computational fluid dynamics (CFD) simulation for analyzing fluid flow patterns in a plasma spray gun is presented in this study. It is coupled with a heat transfer simulation of the plasma spray gun. Based on CFD and heat transfer theory, the numerical model of the nozzle in the plasma spray gun is developed, and the coupled simulation of the flow fluid and heat transfer is carried out with the semi-implicit method for pressure-linked equations (SIMPLE) method. Local turbulence, which will lead to appearance of a static-water region, is found at the front corner of the cooling channel in the nozzle. The locations insufficiently cooled are found in the wall near the heat source and in the gasket in the rear of the nozzle. Then, cooling processes with different parameters of cooling water are analyzed. The optimal velocity and direction of cooling water, which efficiently cool the nozzle and improve the service life of the plasma jet, are obtained .     

管壳式换热器管束与管板连接问题的探讨

就管壳式换热器在使用过程中，管束经常出现的几个问题进行了分析，提出了在设计、制造管束的过程中，易出现的问题并采取应对措施加以防范，避免换热器在使用中出现泄漏，以满足生产装置安、稳、长、满、优运行的需要。     

Numerical simulation of fluid flow and heat transfer in a plasma spray gun

A computational fluid dynamics (CFD) simulation for analyzing fluid flow patterns in a plasma spray gun is presented in this study. It is coupled with a heat transfer simulation of the plasma spray gun. Based on CFD and heat transfer theory, the numerical model of the nozzle in the plasma spray gun is developed, and the coupled simulation of the flow fluid and heat transfer is carried out with the semi-implicit method for pressure-linked equations (SIMPLE) method. Local turbulence, which will lead to appearance of a static-water region, is found at the front corner of the cooling channel in the nozzle. The locations insufficiently cooled are found in the wall near the heat source and in the gasket in the rear of the nozzle. Then, cooling processes with different parameters of cooling water are analyzed. The optimal velocity and direction of cooling water, which efficiently cool the nozzle and improve the service life of the plasma jet, are obtained .     

多区域开窗翅片的热力性能实验研究

在汽车空调综合性能测试台上对7种不同结构参数的百叶窗翅片进行了传热和流动阻力的性能实验.分析比较了百叶窗翅片表面开窗区域对其传热和阻力性能的影响,总结出了表面开窗区域多,对无量纲传热j因子和摩擦阻力f因子影响较大的特点;同时,采用(j/f)1/3因子综合评价了多区域开窗翅片的强化传热效果.研究结果表明,翅片表面多区域开窗对强化传热的影响非常显著.     

Study of the heat transfer performance of gravity heat pipes based on lattice Boltzmann surface modification

Journal of Mechanical Science and Technology - Surface modification is an important means to improve boiling heat transfer. Based on the research of surface wettability, this paper briefly...     

薄膜蒸发器转子动力学性能的有限元分析

转子是薄膜蒸发器的核心部件.系统中的不平衡力易导致转子振幅加大,从而加剧刮板磨损,导致刮板失效.利用Solidworks软件建立转子的3D模型,实现了Solidworks到ANSYS的无缝连接,应用ANSYS Workbench对薄膜蒸发器转子进行模态分析,从而求得转子结构的模态参数,对转子某些位置上的不平衡量进行不平衡响应分析,进一步实现薄膜蒸发器转子系统的动力学分析,从而对薄膜蒸发器安全运行进行实时监测,具有重要的工程应用价值.     

Effects of nozzle arrangement angle on the performance of partially admitted turbines

Journal of Mechanical Science and Technology - This paper presents the experimental and numerical evaluations of the effects of a supersonic Nozzle arrangement angle (NAA) on the performance of an...     

入射角度变化对角锥棱镜测量精度的影响

为了掌握角锥棱镜用在激光跟踪仪中光束入射角度变化对其测量精度的影响规律。详细分析了角锥棱镜的工作原理和反射特性。计算出了角锥棱镜在不同入射角下的实际有效反射面积,并建立了角锥棱镜有效反射面积随光束入射角度变化的理论公式,进而得到角锥棱镜测量精度随光束入射角度变化的规律。实验结果表明：角锥棱镜测量精度随入射角增大而减小,在最大允许入射角处发生突变。在最大允许入射角±35.26°时其测量误差达到0.050mm;而在±20°范围内时其测量精度优于0.010mm,且入射角度在±15°范围内其测量精度最高,稳定性最好。所得结论证明了当角锥棱镜在入射角度为±20°范围内工作时能满足了激光跟踪仪的测量精度要求,这对角锥棱镜设计和实际测量工作具有指导意义。     

百叶窗角度对管带式中冷器传热与阻力特性影响研究

根据影响中冷器综合性能的因素,建立了四组不同开窗角度的百叶窗翅片计算模型,采用Fluent软件,SIMPLE算法和标准k-ε模型对传热特性和阻力特性进行了仿真分析,得到不同开窗角度下中冷器空气侧的温度、压力和换热系数,及中冷器综合性能评价因子。研究发现换热主要集中在百叶窗前端,阻力损失主要集中在翅片区域;压降随着开窗角度的增大而增大;在相同的工况条件下,开窗角度为27°时,翅片表面传热系数最大,具有更好的综合性能。计算结果为中冷器散热带结构设计提供了参考。