The effect of operating conditions on the performance of a supersonic ejector for refrigeration

A previously developed one-dimensional model, based on a forward marching solution technique of the conservation equations has been used to study ejector operation and performance in a large range of refrigeration working conditions. Several important features of ejector operation characteristics were simulated. Global parameter values, their local distributions along the ejector including the temperature, the pressure and the Mach number were calculated for design and off design conditions. Operation parameters such as the entrainment ratio ω, compression ratios P_exit/P_ev, P_g/P_exit and the geometric ratio (D/D_c)² were found to significantly affect performance. The impact of the generator, the evaporator, the condenser and related thermodynamic parameters, which have been assessed in this study, are summarized as:

Fluid mixing conditions dictated by the fluid type, the mixing chamber geometry, the inlet and outlet constraints, may lead to off design operation with related stability and performance deterioration

Internal superheat generation, due to inefficient mixing and normal shock waves is very important in off design operation

Some degree of inlet superheat (around 5 °C) is necessary to prevent internal condensation but excess superheat is detrimental to the condenser efficiency at exit

Generator pressure conditions and the evaporator temperature significantly affect ejector performance.

Effects of bottom profile on the circulation and classification of particles in cylindrical hydrocyclones

The cylindrical hydrocyclone has been increasingly used in coarse classification due to its reduced fine particle entrainment, but the loss of coarse particles to overflow remains an intractable problem. Based on the notion that the strong circulation flow caused by the flat bottom structure bears primary responsibility for the problem, this study designs eight unique bottom profiles to regulate the particle circulating flow and attempts to correlate particle circulation flow with classification performance. The effects of the bottom profile on flow field characteristics, particle spatial distribution, circulation flow rates, and grade efficiency are explored in detail using validated models in a Φ200 mm cylindrical hydrocyclone. The findings suggest that bottom profiles have the greatest effect on the axial velocity near the bottom and the grade efficiency of intermediate and coarse particles, while all unique designs have the potential to lower turbulence intensity. An ascending segment near the wall or a descending segment near the axis can help to mitigate the misplacement of coarse particles by reducing particle circulation flow without affecting the entrainment of fines appreciably. Additionally, two circles are found on each side of the cut plane, which is conducive to releasing coarse particles from the circulation flow. Regulation of particle circulation flow by adjusting bottom profile parameters can improve separation performance.     

In press conditions and their effect on runnability and convertability in digital package printing

A major advantage of digital printing is that printing can be performed on demand, but like all printing techniques it suffers from specific runnability problems. This study reports on an investigation of problems during printing and how to improve the runnability, with the aim of pointing out the most critical factors. Test printing has been performed on three different paperboard types in digital print units, based on both dry and liquid toner electrophotographic technology. The results show that the three main problems during printing were feeding in sheet‐fed print units, cutting in web‐fed print units, and increasing curl after printing. Feeding problems in sheet‐fed print units were mainly explained by curl and varying format size of the paperboard, but also by exceeding thicknesses limits for the press. Curl after printing principally occurred due to high temperature loads caused by, for example, fusing and conditioning. Copyright © 2005 John Wiley & Sons, Ltd.     

Contributions of system components and operating conditions to the performance of desiccant cooling systems

This study systematically analyzes the effect of various kinds of design parameters on the performance of a desiccant cooling system under two different system configurations. The considered parameters include system components such as the sensible heat exchanger, regenerative evaporative cooler and desiccant wheel, as well as operating conditions of outdoor conditions, regenerative temperature and rate of outdoor influx. Numerical simulation has been conducted for these 11 design parameters with 3 levels. The orthogonal array L₂₇(3¹³) is adopted for the analysis of variance. In the range of the parameters considered, the regenerative temperature is found to be the most dominant parameter of contribution ratio of 31.9% and 23.9% for each system configuration. In the case of confined interest of the applications such as a district cooling system or a solar system using medium-temperature collectors, the cooling performance of the regenerative evaporative cooler is the most crucial for the system performance.     

自膨胀支架几何参数对服役影响的有限元分析

自膨胀式血管支架的成功服役主要受制作材料和支架几何参数的影响。大波段Z型支架由于其实验室制作工艺简单、便于测试、有好的临床适用性,广泛用于实验分析和有限元分析中。本文主要运用有限元法,分析了自膨式Z型支架几何参数对其力学服役的影响。通过参数化模拟对照,发现增加顶端圆弧半径、增加支撑体长度、增加圆周V型个数均会减小支架径向抗力。但是支架超出血管的尺寸对径向抗力影响不大。对支架脉动受载及易疲劳区位置进行分析表明,支架在服役时,舒张压和收缩压下平均应变和交变应变分布不一致,最先发生疲劳的位置是支架顶端圆弧内侧,受力状态是压缩。     

Experimental investigation of the performance of industrial evaporator coils operating under frosting conditions

This paper describes a field experimental investigation of the effects of frost formation on the performance of a low-temperature large-scale evaporator coil used in industrial refrigeration systems. A series of experiments were conducted to determine the in situ coil cooling capacity of the evaporator over time as frost builds on its surfaces. Field-measured quantities include inlet and outlet air temperatures, inlet and outlet air relative humidity, and air volume flow rate. These measurements provide a baseline set of experimental data that can be used to validate numerical models of industrial evaporators operating under frosting conditions.     

运行条件对家用型净水机中反渗透膜性能的影响

研究了进水pH值、原水回收率、膜前压力、进水盐浓度、进水水温、进水余氯浓度等运行条件对家用净水机中反渗透膜性能的影响.家用净水机适宜的运行条件为:pH值在6～8,原水回收率为15%～50%,膜前压力维持在0.4～0.6 MPa,进水温度保持在15～30℃.     

Effect of operating conditions on the hydrophobisation of silica-based porous particles in a fluidised-bed reactor: Temperature effect

This study concerns the modification of silica surface wettability by silanisation reaction which consists in the transformation of hydrophilic silanol groups into hydrophobic groups. The chemical modification of silica surface is carried out using n-Octadecyltrichlorosilane (ODTCS). It is a reagent with three chlorines as functional group and with one long alkyl chain containing 18 carbon atoms, responsible for the hydrophobic behavior. The reaction is performed at dry phase [1], [2] by mixing two classes of particles during the fluidisation: target particles to be treated (MP Silica 63–200 Active 6 Å) and ODTCS-carrier particles consisting of coarser porous alumina beads (300–800 μm) containing an adequate amount of reagent.The aim of this work was to study the effect of the temperature (from 30 to 110 °C) at dry condition on the silanisation reaction rate and the silica surface characteristics. The hydrophobisation treatment is characterized by IR/ATR, Washburn method, elementary analyses and RMN.The experimental results show that the reaction rate increases with temperature in dry environment but this effect seems to be more significant at lower temperatures. Also, the quantity of reagents can be estimated by measuring the amount of HCl generated by the reaction using a pH sensor. The RMN spectra showed an increased extent of disordering of the grafted chains at lower operating temperatures.     

焙烧条件对CaTiO3光催化性能的影响

为了制得性能良好的CaTiO3催化剂,探讨了焙烧条件对CaTiO3光催化性能的影响.考察了以Ca(NO3)2和TiO(OH)2为原料,NaOH为矿化剂,固态反应合成CaTiO3时,焙烧前驱物升温速率、焙烧温度、焙烧时间及焙烧产物降温速率对CaTiO3光催化活性的影响,并对不同焙烧条件制得的CaTiO3样品进行了XRD和SEM分析.结果表明,CaTiO3的光催化活性随着焙烧前驱物升温速率的增大先升高,后降低;焙烧产物的快速降温将显著降低CaTiO3的活性;焙烧时间及焙烧温度因对固态反应的完全性和CaTiO3粒度的双重影响而存在适宜值.适宜的焙烧条件制得的CaTiO3再负载0.2%(质量分数)的CoO后得到活性较高的光催化剂.     

Development of low temperature approaches to device quality CdS: A modified geometry for solution growth of thin films and their characterisation

Cadmium sulphide thin films have been grown using a modified chemical bath deposition method with four innovative features: i) ethylenediamine was used as the complexing agent, enabling the use of low cadmium concentrations, ii) a rectangular bath geometry with heated glass plate walls was employed, iii) a low deposition temperature (30 °C) was used and iv) nitrogen gas was flowed over the substrate surface during growth. The latter two features eliminate the formation and adherence of gas bubbles on the substrate during growth, hence reducing pinhole formation. On inspection, films were found to be specularly reflective and homogeneous with no visible pinholes. Characterisation was performed by atomic force microscopy, grazing incidence X-ray diffraction, optical transmittance and photoluminescence spectroscopy. It was shown that films possessed a low surface roughness value of 5.2 nm, were highly crystalline, textured, had a grain size of 15 nm and a bandgap of 2.42 eV. Preliminary results from CdTe/CdS thin film photovoltaic devices demonstrate a notable efficiency of 9.8%.     

Microwave curing of carbon–epoxy composites: Penetration depth and material characterisation

Microwave heating has several major advantages over conventional conductive heating when used to cure carbon–epoxy composites, especially in speed of processing. Despite this and many other well-known advantages, microwave heating of carbon–epoxy composites has not taken off in industry, or even academia, due to the problems associated with microwave energy distribution, arcing, tool design and (ultimately) part quality and consistency, thus leading to a large scepticism regarding the technique/technology for heating such type of materials. This paper presents some evidence which suggests that with the correct hardware and operating procedure/methodology, consistent and high quality carbon–epoxy laminates can be produced, with the possibility of scaling up the process, as demonstrated by the micro- and macro-scale mechanical test results. Additionally, the author proposes a methodology to practically measure the maximum microwave penetration depth of a carbon–epoxy composite material.     

Drying conditions and their effect on ceramic shell investment casting process

Abstract

The ceramic shell investment casting process has gained an important position in the family of precision casting techniques owing to the scientific advances in many of its aspects, such as binder solutions, refractory materials, pattern materials, and in the manufacturing process. In this endeavour an effort was made to investigate the effect of drying conditions on the performance of ceramic shell moulds. The binder used in this work was an acetone based polysilicic acid, which had been considered as an alternative to the conventionally used binders (namely, ethyl silicate, colloidal silica aquasols etc.). The effects of drying conditions were observed on ceramic wafers, prepared from the slurry, made of fused silica and the binder. The wafers were dried at different temperatures and relative humidity conditions. The effect of drying conditions was observed through the measurement of compressive strength of the ceramic shell wafers. The binder was also subjected to various drying conditions and the characteristic changes of the binder solutions were investigated.     

原位聚合增密次数对C/C复合材料性能的影响

以萘为基体碳源,Lewis酸为催化剂,通过对芳烃小分子的催化缩聚建立了一种新型原位聚合C/C复合材料的增密方法。分别对两种不同密度的炭纤维增强C/C复合材料预制体进行致密化处理,研究了原位增密次数对材料体积密度、电阻率、弯曲强度和断面形貌的影响。结果表明:经过五次致密化循环,样品密度分别由原来的1.05 g/cm3和1.68g/cm3提高到1.52g/cm3和1.83g/cm3,电阻率由4.44mΩ.cm和0.84mΩ.cm降至1.09mΩ.cm和0.28mΩ.cm,弯曲强度由26MPa和86MPa增至95MPa和211MPa,说明原位聚合增密方法非常有利于快速提高复合材料的密度和其他物理性能,是一种有前途的增密新途径。     

Structural geometry effect on the size-scaling of strength

The sensitivity of the empirical exponent of Bazant's size-effect scaling law on structural geometry is clarified through numerical experiments. For large centre- cracked tension panels, made of a linearly softening material, the best-fitting exponent is 0.90, whereas for large edge-cracked panels it is 0.75. For edge-cracked panels, the value of the exponent increases as a function of increasing crack-length-to-width-ratio. The results indicate that with structures of brittleness numbers below unity, reliable predictions of strength require the size-effect scaling law to be fitted for any particular structural geometry.     

几何参数对线性压缩机板弹簧性能的影响

在设计了11款不同基圆半径、厚度及涡旋槽偏心距的圆渐开线型板弹簧的基础上,利用ANSYS有限元分析软件,对上述板弹簧的刚度及应力特性进行了分析与比较,总结出了主要几何参数对板弹簧性能的影响.     

Numerical study on the performance of swirl tube based on orthogonal design

Here, an axial flow cyclone separator is design is proposed. The effects of varying the structural parameters and operating conditions on pressure drops and separation efficiency were investigated via a numerical simulation approach. The results show that of the three structural parameters considered, the distance between the diffuser and blade is the most significant factor impacting separation performance compared to the blade pitch and blade shaft diameter. Increasing the distance between conical outlet and blade can decrease its pressure drops and increase separation efficiency; while increasing the shaft diameter can increase pressure drops, and the increasing blade pitch can decrease both the pressure drop and the separation efficiency. The pressure drop of the optimized swirl tube was 102.1 Pa, with a corresponding separation efficiency of 95.04% for 100 μm particles at an extraction ratio of 10%. Further, the cut-off particle size can reach 3 μm, demonstrating that the swirl tube offers good separation performance and has the potential to be widely applied in industrial gas–solid separation applications.     

Monitoring and analysis of the operating conditions of heat sources

Data-analysis systems for monitoring and analyzing the operating conditions of heat sources are described. The functional capabilities of systems are considered as part of a retrospective analysis of measurement results. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 51–55, November, 2008.     

Study of the conditions affecting dye adsorption on titania films and of their effect on dye photodegradation rates

Nanocrystalline titania films have been deposited on glass slides by the sol-gel technique in the presence of surfactant, which plays the role of template of the nanostructure. Several different dyes, both anionic and cationic, have been adsorbed on these films from aqueous solutions. Some of these dyes were adsorbed at large quantities some at lower quantities. Some of them were adsorbed in monomeric form and others formed aggregates. Aggregates are easily distinguished by absorption spectrophotometry, since absorption of light is observed at a different wavelength than monomer absorption in a dilute solution. In all cases, aggregation demonstrated a hypsochromic shift, indicating repulsive interactions, which are justified in view of the fact that titania surface is charged and that adsorbed molecules are aligned in parallel. The above titania films are hydroxylated. Therefore, cationic dyes were readily adsorbed. Anionic dyes could be adsorbed only from aqueous solutions brought at low pH. Photodegradation rates of adsorbed dyes were generally fast since these films are efficient photocatalysts. Nevertheless, photodegradation of an adsorbed dye was faster when the quantity of the dye was smaller. When the adsorbed dyes formed aggregates, aggregation had adverse effect on photodegradation rates.     

Connecting hose’s operating characteristics and its effect on the cooling performance of an 80 K Oxford split-Stirling-cycle cryocooler

In this paper, a mathematical model on the connecting hose of a one-stage Oxford split-Stirling cryocooler has been made to simulate its dynamic performance. A set of governing equations has been discretized by method of characteristics and dissolved by a numerical method. The present paper emphasizes the validation of this model against experimental results of pressure phase lag and amplitude attenuation through connecting hose, and cooler performance vs. connecting hose in different dimensions. The comparison shows acceptable agreement between the simulation and experimental results.