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.     

双金属复合翅片管振动特性的研究

双金属复合翅片管是一种高效传热元件,容易发生流体诱导振动破坏,对其进行振动模态理论分析具有重要的工程指导意义。针对双金属复合翅片管的结构特征,将其简化为串、并联刚度系统,采用组合截面等效弯曲刚度、等效扭转刚度和等效抗拉压刚度,并结合等效质量和等效转动惯量的方法,对其弯曲、扭转和轴向振动模态进行理论解析。为了验证理论分析方法的准确性,对双金属复合翅片管的振动模态进行了实验测试和有限元分析。研究了翅片几何参数对双金属复合翅片管振动频率的影响规律。结果表明,对于矩形翅片形式的钢铝双金属翅片管,其弯曲、扭转和轴向振动频率均随翅片高度和翅片厚度的增大而减小,随翅片间距的增大而增大。     

Numerical investigations of laminar flow characteristics in helically finned pipes

The laminar flow in a helically finned pipe has been considered. The steady solutions have been obtained by numerical integration of the Navier-Stokes equations formulated in a cylindrical coordinate system. Three-dimensional fins have been embedded in the structured mesh as immersed boundaries. A helical fin generates a swirling flow which exhibits a helical symmetry. In the presence of a single fin, the circumferential velocity turned out to increase both with fin height and fin angle. The core region with high axial velocity is shifted away from the pipe axis. High levels of axial vorticity caused by the fin-induced swirl are observed in the vicinity of the tip of the fin whereas substantial vorticity of opposite sign is produced in the wall-layer near the suction side of the fin. In the presence of two fins with the same pitch, i.e., a double helix, the symmetry about a diametrical plane gave rise to a keyhole-shaped axial velocity distribution. The drag coefficient was increased by all the fin configurations considered when compared to regular pipe flow at the same Reynolds number.     

Investigation on separation performance and structural optimization of a two-stage series cyclone using CPFD and RSM

Cyclones are generally operated in series when the efficiency of a single cyclone is not sufficient for the process. This study firstly used computational particle fluid dynamics (CPFD) to simulate the gas-solid two-phase flow characteristics in a two-stage series cyclone separator. The separation efficiency and distribution of energy consumption was interpreted by analyzing particle distribution characteristics. Secondly, the structure of the two-stage cyclone separator was optimized via response surface methodology (RSM) to make up for the disadvantage that the distribution of the separation load was non-uniform. The results showed that the grade efficiency for 3 μm of the first-stage cyclone separator was increased from 45.408% to 59.932% compared to the original model. The pressure drop of the first-stage cyclone separator is about 2.147 kPa while the second-stage cyclone separator is about 2.774 kPa. It can be seen that the overall optimized two-stage cyclone separator has the advantages of high efficiency, low energy consumption and load-balanced separation performance.     

Modification of the cyclone separator geometry for improving the performance using Taguchi and CFD approach

ABSTRACT

The cyclone separator performance has been affected by its high-pressure drop. The main geometric ratios such as outlet diameter, inlet width and inlet height and total height have been preferred to reduce the pressure drop and improve the performance of cyclone separator. These standard geometric values have been altered with the aid of design of experiment technique by Taguchi method for reducing the pressure drop. This changed new design produce low-pressure drop compared with the standard cyclone separator. Moreover, the collection efficiency of the new design is high when compared with standard cyclone separator. The pressure drop, Euler number, cut-off diameter and efficiency of the standard and new cyclone separator have been compared with the results of mathematical and computational fluid dynamics technique (CFD). The Reynolds stress turbulence model and discrete phase model have been used for simulating the cyclone separator in CFD. An acceptable agreement has been obtained between these results.     

水平管外二氧化碳膜状凝结传热分析

综述了水平低翅片管外凝结传热的基本模型,阐述了二氧化碳制冷剂的物性特点,讨论了表面张力与凝液滞留角及二氧化碳管外凝结换热系数的关系,分析了翅片密度、环形翅片管尺寸对翅片效率、滞留角、凝结换热系数以及传热增强比的影响,优化了外翅片管的齿高与齿距,并求得相应的强化传热增强比.结果表明,对于根径为20mm的低翅片管,最佳翅片密度为每米435个翅片,最佳齿高为5.1mm,最佳齿距2.3mm.     

翅片结构对翅片管换热器积灰与压降影响的实验研究

积灰对具有不同翅片结构的翅片管换热器均会造成长效性能的衰减。本文搭建了换热器积灰可视化实验台,研究了翅片结构对积灰量及积灰后空气侧压降的影响。测试样件的翅片类型包括平直翅片、波纹翅片和开窗翅片;翅片间距范围为1.3~1.8 mm。实验结果表明:开窗翅片管换热器表面最容易沉积粉尘并增大积灰后压降,与平直翅片相比,波纹翅片和开窗翅片表面粉尘沉积量分别提高了25.6%和52.8%、积灰后压降增量分别提高了44.4%和165.6%;对于开窗翅片,小翅片间距有利于积灰并增大积灰后压降,与翅片间距1.8 mm的样件相比,翅片间距1.5 mm和1.3 mm的样件表面粉尘沉积量分别提高了26.2%和43.2%、积灰后压降增量分别提高了24.1%和49.4%;在积灰过程中,随着粉尘沉积量的增加,翅片管换热器空气侧压降先增大后保持稳定。     

Experimental study on the separation performance of a novel gas–liquid separator

A novel two-stage dynamic separator called high-gravity cyclone separator (HGCS) has been designed for gas–liquid separation. It is mainly composed of a cyclone chamber and rotary drum. In this study, its performance, including the separation efficiency and pressure drop, is experimentally investigated, and the effects of the operating conditions and drum parameters are evaluated. For droplets with a mean diameter of 7 μm, the results indicate that the optimal gas inlet velocity and high-gravity factor are 12 m/s and 59.4, respectively, and the separation efficiency reaches 98 %. The effect of liquid concentration is sensitive to the high-gravity factor. At a liquid concentration of 57 g/m³, the maximum efficiency will be 98.75 % when increasing the high-gravity factor to 85.6. Furthermore, a smaller radial height is preferable when the gas inlet velocity is greater than 12 m/s, and a better separation efficiency can be obtained by increasing the drum length to 190 mm. However, when the length is 235 mm, the efficiency will be poor because of the Kelvin–Helmholtz and Rayleigh–Taylor instabilities. Compared with the predominant roles of gas inlet velocity, drum length and radial height in pressure drop, the effects of liquid concentration and high-gravity factor are small.     

Impact of fin spacing on temperature distribution in adsorption cooling system for vehicle A/C applications

Effects of fin spacing on the temperature distribution in a finned tube adsorber bed are studied to decrease the temperature gradient inside the adsorber bed and minimize the adsorber bed to adsorbent mass ratio (AAMR) for vehicle air conditioning applications. Finned tube adsorber beds have shown higher specific cooling power and coefficient of performance, and low AAMR among the existing adsorber beds. A single-adsorber bed ACS with interchangeable heat exchangers is built and equipped with hermetic type T thermocouples. Two copper heat exchangers with 6.35 mm (1/4″) and 9.5 mm (3/8″) fin spacing are custom-built and packed with 2–4 mm silica gel beads. The experimental results show that by decreasing the fin spacing from 9.5 mm to 6.35 mm, the temperature difference between the fin and adsorbent reduces by 4.6 °C under the cycle time of 600 s and an adsorption to desorption time ratio (ADTR) of one. A greater reduction in the temperature gradient inside the adsorber bed with smaller fin spacing is observed for short cycle time operation, e.g. 600 s, compared to long cycle time operation, e.g. 1400 s. Finally, simultaneous comparison of the temperature gradient between the fins and AAMR against fin spacing indicates that the optimum fin spacing for a finned tube heat exchanger packed with 2–4 mm silica gel beads is about 6 mm.     

Development of a miniature cyclone separator operating at low Reynolds numbers as a pre-separator for portable black carbon monitors

In this study, a cyclone separator that can be used as a sampling inlet for portable black carbon (BC) monitors operating at a flow rate of less than 200 mL/min was developed. A prototype was fabricated to evaluate its performance by experiments, and the cut-off size of the cyclone separator was predicted through numerical analysis by applying various turbulence models. The RNG k–ε model was found to be suitable for the analysis of the cyclone separator operating at Reynolds numbers of less than 1000. Cyclone separators were designed through simulation and fabricated for each operating flow rate (50, 100, 150, and 200 mL/min) of a BC monitor, and their performances were experimentally verified. Meanwhile, when the non-dimensional analysis method of the previous study conducted at Reynolds numbers of 1000 or higher was used, the cyclone separator operating at Reynolds numbers of less than 1000 also exhibited a similar linear tendency.     

多效旋风分离器压降的实验研究

为了有效提高新型多效旋风分离器对粒径为0.1~3μm颗粒的分离效率,获取该设备的阻力性能,采用实验方法研究该新型多效旋风分离器压降与进口气速的关系,并与Lapple型旋风分离器进行比较。结果表明:进口风速为5~30m/s时,主体直径为0.25m的多效旋风分离器总阻力系数为7.29,其中,一级和二级预分离螺旋管的阻力系数分别为1.04和1.73;主体的阻力系数为4.52。直径为0.25m的Lapple型旋风分离器的阻力系数为7.21。     

Heat transfer from a cylindrical,heavily finned surface

The transfer of heat from a strongly heated, heavily finned surface is examined. The material of the surface and of the fins has high thermal conductivity (copper), while the heat transfer fluid has comparatively low thermal conductivity (oil). Under these conditions, increase in the number of fins and reduction of the distance between them makes possible a high value of the coefficient of heat transfer from the heated surface to the fluid.Notation R₂ and r₁ radii of cylindrical surface at tip and base of fins, respectively - r, z coordinate axes - angle between planes of adjacent slots - x slot width - b anda coordinates of tip and base of fin - thermal conductivity of fin material - t fin temperature - u mean fluid temperature over slot width - coefficient of heat transfer from fin surface to fluid - c specific heat of fluid - v fluid velocity (since the viscosity is considered constant over the flow, v is also constant) - q density of heat flux through base of fin - specific weight of fluid - ¯t, ¯u Laplace transforms - p Laplace transform parameter, s-auxiliary quantity determined from equation (13) - I, K, J, Y Bessel functions - u⁰ mean fluid temperature over height of slot     

锯齿与打孔翅片表面性能数值模拟

以两种翅片表面(锯齿翅片、打孔翅片)为研究对象,采用 FLUENT 软件模拟和分析不同结构参数和数对翅片表面传热与流动阻力的影响,得出不同结构参数和操作参数下两种翅片的表面性能曲线;分别分析了锯齿翅片的翅片高度、翅片间距、翅片厚度和切开长度以及打孔翅片开孔率对翅片表面流动与传热性能影响;分析比较了两种翅片的性能.     

板翅式换热器翅片性能的比较和选择

通过理论分析和实际计算,讨论了翅片节距对翅片性能的影响,并对不同种类、不同规格翅片的性能进行了比较,得出结论:在同样翅片高度的情况下,翅片节距变小、性能有提高的趋势,所以所有翅片应向节距小的方向发展;适当高度和节距的多孔形翅片,性能不亚于锯齿形翅片;同一种翅片在不同的场合使用,会表现出不同的特性。     

Effects of biofouling on air-side heat transfer and pressure drop for finned tube heat exchangers

Experimental investigations on the effects of biofouling on air-side heat transfer and pressure drop for three biofouled finned tube heat exchangers and one clean finned tube heat exchanger were performed. Artificial accelerated method of microorganism growth on the fin surface was used for simulating the biofouled finned tube heat exchangers. Experimental results indicate that the effects of biofouling on the air-side heat transfer coefficient decreases 7.2% at 2.0 m/s when the biofouled area ratio is 10%, while it decreases 15.9% at 2.0 m/s when the biofouled area ratio is 60%, and biofouling causes a 21.8% ～ 41.3% increase in pressure drop when the air velocity is between 0.5 and 2.0 m/s. The increase of inlet air velocity is helpful to improve the long-term performance of finned tube heat exchanger. Biofouling makes the hydrophilic coating failure, and the condensation water easily converges on the fin surface where biofouling grows.     

Experimental Study of Heat Transfer Enhancement in Solar Tower Receiver Using Internal Fins

The receiver is an important element in solar energy plants. The principal receiver’s tubes in power plants are devised to work under extremely severe conditions, including excessive heat fluxes. Half of the tube’s circumference is heated whilst the other half is insulated. This study aims to improve the heat transfer process and reinforce the tubes’ structure by designing a new receiver; by including longitudinal fins of triangular, circular and square shapes. The research is conducted experimentally using Reynolds numbers ranging from 28,000 to 78,000. Triangular fins have demonstrated the best improvement for heat transfer. For Reynolds number value near 43,000 Nusselt number (Nu) is higher by 3.5% and 7.5%, sequentially, compared to circular and square tube fins, but varies up to 6.5% near Re = 61000. The lowest friction factor is seen in a triangular fin receiver; where it deviates from circular fins by 4.6%, and square fin tubes by 3.2%. Adding fins makes the temperature decrease gradually, and in the case of no fins, the temperature gradient between the hot tube and water drops sharply in the planed tube by 7%.     

Heat transfer characteristics of flat plate finned-tube heat exchangers with large fin pitch

The objective of this study is to provide experimental data that can be used in the optimal design of flat plate finned-tube heat exchangers with large fin pitch. In this study, 22 heat exchangers were tested with a variation of fin pitch, number of tube row, and tube alignment. The air-side heat transfer coefficient decreased with a reduction of the fin pitch and an increase of the number of tube row. The reduction in the heat transfer coefficient of the four-row heat exchanger coil was approximately 10% as the fin pitch decreased from 15.0 to 7.5 mm over the Reynolds number range of 500–900 that was calculated based on the tube diameter. For all fin pitches, the heat transfer coefficient decreased as the number of tube row increased from 1 to 4. The staggered tube alignment improved heat transfer performance more than 10% compared to the inline tube alignment. A heat transfer correlation was developed from the measured data for flat plate finned-tubes with large fin pitch. The correlation yielded good predictions of the measured data with mean deviations of 3.8 and 6.2% for the inline and staggered tube alignment, respectively.     

Pool boiling heat transfer at finned tubes: influence of surface roughness and shape of the fins

Pool boiling heat transfer from finned tubes with different shapes of fins (trapezoid-shaped, T-shaped, or Y-shaped) to various hydrocarbons and partly fluorinated hydrocarbons has been investigated at the Laboratorium für Wärme- und Kältetechnik, Universität-GH Paderborn during the recent past. Compared to corresponding measurements on plain tubes, heat transfer on traditionally finned tubes with trapezoid-shaped fins is considerably improved, and even better results are achieved with T-shaped or Y-shaped fins. The influences of the macrostructure (i.e. fin geometry) or microstructure (i.e. surface roughness) on the heat transfer coefficient have been studied separately, in order to evaluate the improvement of heat transfer by either influence.     

Experimental investigation of processes in acoustic cyclone separator

This paper presents air flow velocity profiles obtained in conventional and acoustic cyclone separators. It is shown that vortex air flow is created in acoustical cyclone separator in presence of secondary countercurrent air flow. It is obtained that in acoustic cyclone separator air pressure pulses occur at frequency of 8 kHz and pressure amplitude reaches a value of 170 dB. Separation efficiency of acoustic cyclone separator was established experimentally.     

Parametric analysis and optimization of gas-particle flow through axial cyclone separator: A numerical study

The separation of particles through an axial swirl tube cyclone separator is numerically investigated using Eulerian-Lagrangian approach by solving Reynolds Averaged Navier-Stokes equations with RNG K-epsilon model as turbulence closure and Discrete phase modeling (DPM) of particles. The four significant geometric parameters in an axial swirl tube cyclone separator for improving the performance are identified to be blade angle, blade length, blade-tube distance and number of blades. The impact of these parameters on the output parameters of a cyclone separator, is studied through numerical analysis with the open source CFD solver OpenFOAM. A one factor analysis is performed to understand the individual contributions of the parameters and a multiobjective optimisation is done using the Design of Experiments (DoE) approach. The blade length was found to be the most sensitive parameter whereas the blade tube distance had the least effect. Using statistical methods such as Analysis of Variance (ANOVA) and Multi Objective Genetic algorithm (MOGA), a set of Pareto optimum solutions are generated, with an effective trade off between the pressure drop and filtration efficiency. The configurations obtained after optimisation are validated with CFD simulations and found to be having a better overall performance as compared to the conventional configuration.