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.     

The performance analysis of a hydrocarbon refrigerant R-600a in a household refrigerator/freezer

The performance of a hydrocarbon refrigerant, R-600a, as an alternative for R-12 has been evaluated in a 215 ℓ household auto-defrost refrigerator/freezer. A theoretical analysis was performed with NIST REFPROP, based on the ASHRAE refrigeration cycle and a series of tests with R-600a was conducted according to the Korea Standard (KS C 9305). All the tests were performed in the climate chamber of which the temperatures and relative humidities were maintained at 30±1°C and 75±5%, respectively. The test results showed that the energy efficiencies and the cooling speeds with R-600a were improved by 1–11% and 3–10%, respectively, compared to R-12.     

Effects of mesh size in a flat evaporator and condenser cooling capacity on the thermal performance of a capillary pumped loop

The thermal performance of a flat evaporator for capillary pumped loop (CPL) applications was investigated. Two to four layers of coarse wire screen wicks were placed onto the heated surface to provide irregular passages for vapor flow. The evaporator and condenser were separated by a distance of 1.2 m and connected by individual liquid and vapor lines. The wall material was copper and the working fluid was ethanol. The experimental facility utilized a combination of capillary and gravitational forces for liquid return, and distribution over the evaporator surface. The tubing used for vapor and liquid lines was 9.35 mm or less in diameter and heat was removed from the condenser by convection of air. A heat flux of up to 4.9×10⁴ W/m² was applied to a flat evaporator having dimensions of 100 mm by 200 mm, 20 mm thick. The thermal resistance of the system as well as the temperature characteristics of the system was investigated as the evaporator heat flux and the condenser cooling capacity varied. The performance of the evaporator and effect of condenser cooling capacity were analyzed and discussed.     

A study on performance analysis of the helically coiled evaporator with circular minichannels

In order to develop a compact evaporator, experiments that show characteristics of evaporating heat transfer and pressure drop in the helically coiled minichannel were performed in our previous research. This study was focused on the performance analysis of helically coiled heat exchangers with circular minichannels with an inner diameter=1.0 mm. The working fluid was R-22, and the properties of R-22 were estimated using the REFPROP program. Numerical simulation was performed to compare results with the experimental results of the helically coiled heat exchanger. As the heat transfer rate and pressure drop were calculated at the micro segment of the branch channels, the performance of the evaporator was evaluated. The following conclusions were obtained through the numerical simulations of the helically coiled heat exchanger. It showed good performance when the flow rate of each branch channels was suitable to heat load of air-side. The numerical simulation value agreed with experimental results within ± 15%. In this study, a numerical simulation program was developed to estimate the performance of a helically coiled evaporator. And, an optimum helically coiled minichannels evaporator was designed.     

Fractionation of oligomers of linear alphaolefins in a molecular evaporator

Oligomers of higher alphaolefins, mainly of 1-decene and 1-octene have important applications as synthetic lubricating oils or their components. The results of fractionation of polydecene, polyoctene, and polybutene oils in a wiped-film molecular evaporator, for the purpose of preparing narrow distillate cuts, are presented in the paper. Characteristics and properties of the fractions obtained are shown, and the possibilities for this distillation method in the fractionation of polyolefin oils discussed.     

Advances in compact manufacturing for shape and performance controllability of large-scale components-a review

Research on compact manufacturing technology for shape and performance controllability of metallic components can realize the simplification and high-reliability of manufacturing process on the premise of satisfying the requirement of macro/micro-structure. It is not only the key paths in improving performance, saving material and energy, and green manufacturing of components used in major equipments, but also the challenging subjects in frontiers of advanced plastic forming. To provide a novel horizon for the manufacturing in the critical components is significant. Focused on the high-performance large-scale components such as bearing rings, flanges, railway wheels, thick-walled pipes, etc, the conventional processes and their developing situations are summarized. The existing problems including multi-pass heating, wasting material and energy, high cost and high-emission are discussed, and the present study unable to meet the manufacturing in high-quality components is also pointed out. Thus, the new techniques related to casting-rolling compound precise forming of rings, compact manufacturing for duplex-metal composite rings, compact manufacturing for railway wheels, and casting-extruding continuous forming of thick-walled pipes are introduced in detail, respectively. The corresponding research contents, such as casting ring blank, hot ring rolling, near solid-state pressure forming, hot extruding, are elaborated. Some findings in through-thickness microstructure evolution and mechanical properties are also presented. The components produced by the new techniques are mainly characterized by fine and homogeneous grains. Moreover, the possible directions for further development of those techniques are suggested. Finally, the key scientific problems are first proposed. All of these results and conclusions have reference value and guiding significance for the integrated control of shape and performance in advanced compact manufacturing.     

Effects of spray axis incident angle on heat transfer performance of rhombus-pitch shell-and-tube interior spray evaporator

An interior spray method is proposed for enhancing the heat transfer performance of a compact rhombus-pitch shell-and-tube spray evaporator. The experimental results show that the shell-side heat transfer coefficient obtained using the proposed spray method is significantly higher than that achieved in a conventional flooded-type evaporator. Four different spray axis incident angles (0°, 45°, 60° and 75°) are tested in order to investigate the effect of the spray inclination angle on the heat transfer performance of the spray evaporator system. It is shown that the optimal heat transfer performance is obtained using a spray axis incident angle of 60°.     

基于Rogowski线圈动态性能的结构、电磁参数研究

本文研究了Rogowski线圈的测量原理、等效电路,以及自积分和外积分两种测量电流的方法,并分析了其适用场所。研究了截面形状(圆形截面和矩形截面)、截面直径、匝数等结构参数对其动态性能的影响,通过建立传递函数,利用Matlab仿真软件进行仿真,分析阶跃响应、幅频特性曲线并得出结论。针对不同的分布电容、取样电阻、线圈内阻等电磁参数建立传递函数,利用Matlab软件进行仿真分析得出结论。通过分析比较提出了优选罗氏线圈结构和电磁参数的方法,对于设计动态特性良好的罗氏线圈具有理论指导作用。     

Dynamic analysis of evaporator characteristics

An analysis of the dynamic characteristics in an evaporator was numerically performed for control and design of the refrigeration and air conditioning systems. The important factors, such as refrigerant flow rate, inlet enthalpy, inlet air velocity and air temperature, are incorporated with this analysis. An evaporator is modeled for the dynamic characteristics analysis separated into three regions which are the two-phase region, the saturated vapor region and the superheated vapor region. The basic equations of each region were derived in the continuity, heat energy equilibrium and heat transfer equations. The transfer functions of the dynamic characteristics were obtained by the linearization and Laplace transformation. The dynamic response characteristics were evaluated on the Bode diagram with the frequecy response method. These results may be used for the analysis of the dynamic characteristics and design in the total system.     

Reduction of flow-induced noise in a household air purifier

Journal of Mechanical Science and Technology - In this study, we propose a design for a household air purifier that reduces the flow-induced noise caused by the impeller of the fan system. The...     

Development of a compact tomography camera system using a multianode photomultiplier tube for compact torus experiments

A compact tomography camera system consisting of a photomultiplier tube, a multislit optical system, and a band-pass interference filter has been developed. The viewing area and spatial resolution can be configured by the arrangement of the slit system. The camera system has been specially designed for self-organized compact torus experiments having strong magnetohydrodynamics events with a submicrosecond time-scale. The developed system has been tested on a field-reversed configuration formed by the field-reversed theta-pinch. Performance evaluation of the system has been performed by comparison to the former optical system.     

Thermal performance of a spirally coiled finned tube heat exchanger under wet-Surface conditions

This paper is a continuation of the authors’ previous work on spiral coil heat exchangers. In the present study, the heat transfer characteristics and the performance of a spirally coiled finned tube heat exchanger under wet-surface conditions are theoretically and experimentally investigated. The test section is a spiral-coil heat exchanger which consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled finned tubes. Each tube is fabricated by bending a 9.6 mm diameter straight copper tube into a spiral-coil of four turns. The innermost and outermost diameters of each spiral-coil are 145.0 and 350.4 mm, respectively. Aluminium crimped spiral fins with thickness of 0.6 mm and outer diameter of 28.4 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Air and water are used as working fluids in shell side and tube side, respectively. The experiments are done under dehumidifying conditions. A mathematical model based on the conservation of mass and energy is developed to simulate the flow and heat transfer characteristics of working fluids flowing through the heat exchanger. The results obtained from the present model show reasonable agreement with the experimental data.     

小型蒸发器蒸发量偏大的原因

每年汛期当遇到强降水时,在小型蒸发器蒸发量的观测过程中,就常常会出现蒸发量偏大的问题,影响了气象资料的准确性。本文就对蒸发量偏大的原因进行分析并寻找解决办法。     

Bypass line assisted start-up of a loop heat pipe with a flat evaporator

Loop heat pipes often experience start-up problems especially under low thermal loads. A bypass line was installed between the evaporator and the liquid reservoir to alleviate the difficulties associated with start-up of a loop heat pipe with flat evaporator. The evaporator and condenser had dimensions of 40 mm (W) by 50 mm (L). The wall and tube materials were stainless steel and the working fluid was methanol. Axial grooves were provided in the flat evaporator to serve as vapor passages. The inner diameters of liquid and vapor transport lines were 2 mm and 4 mm, respectively, and the length of the two lines was 0.5 m each. The thermal load range was up to 130 W for horizontal alignment with the condenser temperature of 10°C. The experimental results showed that the minimum thermal load for start-up was lowered by 37% when the bypass line was employed. This paper was recommended for publication in revised form by Associate Editor Dae Hee Lee Joon Hong Boo received his B.S. degree in Mechanical Engineering from Seoul National University in 1978. He then received his M.S.M.E. and Ph.D. degrees from Georgia Institute of Technology in 1984 and 1989, respectively. Dr. Boo is currently a Professor in the School of Aerospace and Mechanical Engineering at Korea Aerospace University, where he joined in 1989. His research interests include heat transfer, heat pipes, and energy systems. He conducted joint research with Texas A&M University and Waseda University in 1994 and 2008, respectively, as Visiting Professor. Dr. Boo is an active member of the International Heat Pipe Conference Committee. Eui Guk Jung received his B.S. and M.S. degrees in Aerospace and Mechanical Engineering from Korea Aerospace University, in 2002 and 2004, respectively. He is currently a Ph.D. candidate in the Graduate School at Korea Aerospace University. His research interests include applications of heat pipes and loop heat pipes.     

Thermal performance of mechanical seals with textured side-wall

Experimental measurements and numerical simulations are presented to show the effectiveness of cooling of a mechanical seal's active surface by means of cylindrically shaped dimples engraved circumferentially on the outside diameter of the mating ring. The working fluid is propylene glycol solution (70% in water by volume) and the flush rate is 107 cm³/s. A commercially available CFD code (FLUENT) is employed to numerically confirm the experimental measurements, and the numerical and experimental results are in agreement. Results of this study demonstrate the heat augmentation effectiveness of surface texture techniques on the mechanical seals.     

Refrigerant distribution in an evaporator having a horizontal header and horizontal mini-channel tubes

Journal of Mechanical Science and Technology - In this study, we investigated the R-1234yf distribution from a header into mini-channel tubes located in a horizontal plane, which may be of...     

Development of low-noise axial cooling fans in a household refrigerator

Experimental and numerical investigation on the aerodynamic noise of axial fans is carried out to develop a low-noise fan, which is used to cool a compressor and a condenser in the mechanical room in a household refrigerator. First, the noise performance of the target fan is experimentally investigated and, then, computational aeroacoustic techniques based on the hybrid method are applied to predict the radiated sound pressure levels. The validity of the computational aeroacoustic techniques is confirmed by comparing the predictions with the measurements. To develop a low-noise fan, we came up with two design concepts: one is that the uneven grooves are made on the surface of the suction side of blade along the rotational direction, and the other is that two different blades are combined into one blade. We have set systematic numerical analysis to evaluate the effects of these design factors on the noise generation of axial cooling fans. On the basis of the prediction results showing the possible reduction of noise levels by applying the proposed design factors to the existing fan, experiments using a full refrigerator with two prototype fans are made, which show that the sound power levels from the newly developed fans are less than those of noise from existing fans. Finally, an additional experiment performed by using a grooved/double-bladed fan installed in a household refrigerator shows that the overall noise from the new fan is reduced by approximately 1 dB to 2.2 dB in comparison with that from the existing fan in the refrigerator over the rotating speeds from 1090 rpm to 1210 rpm.     

原料库内翻卷机的设计改进

这里通过翻卷机的设计实践，简述了某冷轧厂原料卷库内翻卷机的用途和布置方式，着重介绍了该翻卷机的性能和结构特点以及动作程序。     

Effect of geometrical parameters on high frequency performance of Rogowski coil for partial discharge measurements

Partial discharges (PD) in a power system component is a sever threat, indicating a high likelihood of the imminent and complete failure of the insulation. The reliability of partial discharge diagnostics depends upon the design and accuracy of the measuring sensors. In this paper the Rogowski coil is employed as a PD measuring sensor. The selection of suitable geometrical parameters has been identified as an important aspect regarding the proper operation and installation of the coil around the under test power component. These parameters significantly affect the measuring performance of the coil in terms of its sensitivity and bandwidth. The measurement performance of different geometrical designs for the high frequency Rogowski coils is evaluated. The variation in parameters such as core and coil diameter, diameter of the copper wire used for winding and number of turns, has been experimentally investigated. In addition the return winding, as a non-conventional method of creating a return loop for the Rogowski coil, is compared with a return wire (loop) to analyze sensor performance. The comparative study of variation in mechanical design features provides a brief guideline to select the optimal design of the coil.