Simulation of gas species and temperature separation in the counter-flow Ranque–Hilsch vortex tube using the large eddy simulation technique

A computational fluid dynamic model is used to predict the species and temperature separation within a counter flow Ranque–Hilsch vortex tube. The large eddy simulation (LES) technique was employed for predicting the gas flow and temperature fields and the species mass fractions (nitrogen and helium) in the vortex tube. A vortex tube with a circumferential inlet stream of nitrogen–helium mixture and an axial (cold) outlet stream and a circumferential (hot) outlet stream was considered. The temporal evolutions of the axial, radial and azimuthal components of the velocity along with the temperature, pressure and mass density and species concentration fields within the vortex tube are simulated. Even though a large temperature separation was observed, only a very minimal gas separation occurred due to diffusion effects. Correlations between the fluctuating components of velocity, temperature and species mass fraction were calculated to understand the separation mechanism. The inner core flow was found to have large values of eddy heat flux and Reynold’s stresses. Simulations were carried out for varying amounts of cold outlet mass flow rates. Performance curves (temperature separation/gas separation versus cold outlet mass fraction) were obtained for a specific vortex tube with a given inlet mass flow rate.     

Large eddy simulations of the flow field and temperature separation in the Ranque–Hilsch vortex tube

A computational fluid dynamic model is used to predict the flow fields and the associated temperature separation within a Ranque–Hilsch vortex tube. The large eddy simulation (LES) technique was employed for predicting the flow and temperature fields in the vortex tube. A vortex tube with a circumferential inlet stream and an axial (cold) outlet stream and a circumferential (hot) outlet stream was considered. The temporal evolutions of the axial, radial and azimuthal components of the velocity along with the temperature, pressure and density fields within the vortex tube are simulated. Performance curves (temperature separation versus cold outlet mass fraction) were obtained for a specific vortex tube with a given inlet mass flow rate. Simulations were carried out for varying amounts of cold outlet mass flow rates. Predictions from the present large eddy simulations compare favorably with available experimental measurements.     

An experimental investigation of the optimum geometry for the cold end orifice of a vortex tube

A vortex tube is a simple mechanical device, which splits a compressed gas stream into a cold and hot stream without any chemical reactions or external energy supply. This paper presents the results of a series of experiments focusing on various geometries of the “cold end side” for different inlet pressures and cold fractions. Specifically, the tests were conducted using different cold end orifice diameters.Energy separation and energy flux separation efficiencies are defined and used to recover characteristic properties of the vortex tube. These are used to show an appropriate scale to non-dimensionalize the energy separation effect. The experimental results indicate that there is an optimum diameter of cold end orifice for achieving maximum energy separation. The results also show that the maximum value of energy separation was always reachable at a 60% cold fraction irrespective of the orifice diameter and the inlet pressure. The results are compared with the previous studies on internal flow structure, and optimal operating parameters are shown to be consistent with a matching of orifice size with the secondary circulation being observed.     

Cycle parameter optimization of vortex tube expansion transcritical CO2 system

Optimization studies along with optimum parameter correlations are presented in this article for a vortex tube expansion transcritical CO₂ refrigeration cycle with two cycle layouts based on the Maurer model (1999) and the Keller model (1997). A simple thermodynamic model is proposed and used for vortex tube analysis. Finally, the COP improvement and effect on optimum discharge pressure by using vortex tube in transcritical CO₂ cycle instead of expansion valve are presented. The results show that the effect of cold mass fraction and inlet water temperature to desuperheater (used to cool hot gas from vortex tube) on the cycle optimization is negligible. The Maurer model is better than the Keller model in terms of moderately more COP improvement and lower cost due to less components. The use of a vortex tube is more effective for higher gas cooler exit temperature for both models. Results show that the vortex tube expansion transcritical CO₂ cycle for the Maurer model can give higher COP improvement for lower cooling temperature applications; however the trend is reverse for the Keller model.     

Experimental investigation of vortex tube using natural substances

An experimental investigation is carried out on Ranque–Hilsch vortex tube (RHVT). Influential parameters such as L/D ratio, cold mass fraction, inlet pressure etc. are investigated. Further, three different working media (air, nitrogen and carbon dioxide) are also tested. An in-house facility is developed to test the vortex tubes. A value of cold mass fraction is observed at which vortex tube performs optimally at the given pressure and L/D ratio. It is found that vortex tube performs better with carbon dioxide as working fluid.     

Flow visualization of annular and delta winlet vortex generators in fin-and-tube heat exchanger application

This study presents flow visualization and frictional results of enlarged fin-and-tube heat exchangers with and without the presence of vortex generators. Two types of vortex generators and a plain fin geometry were examined in this study. For plain fin geometry at Re=500, the horseshoe vortex generated by the tube row is not so pronounced, and the horseshoe vortex separates into two streams as it flows across the second row and consequently loses its vortical strength. This phenomenon may supports the “maximum phenomenon” in low Reynolds number region reported by previous studies. With the presence of annular vortex generator, the presence of a pair of longitudinal vortices formed behind the tube is seen. The strength of the counter-rotating vortices increases with the annular height and the strength of the longitudinal vortices is so strong that may swirl with the horseshoe vortices and other flow stream. For the same winlet height, the delta winlet shows more intensely vortical motion and flow unsteadiness than those of annular winlet. This eventually leads to a better mixing phenomenon. However, it is interesting to know that the corresponding pressure drops of the delta winlet are lower than those of annular winlet. Compared to the plain fin geometry, the penalty of additional pressure drops of the proposed vortex generators is relatively insensitive to change of Reynolds number.     

天然气压力能回收装置热力学分析

高压天然气调压过程中存在着巨大的可供回收的压力能,节流阀、透平膨胀机、气波制冷机、涡流管是典型的能量回收设备。在对上述四种能量回收装置进行简要介绍之后,以[火用]概念为基础,以[火用]平衡为工具,对其进行了全面的热力学分析。结果表明：透平膨胀机的火用效率最高,其次是气波制冷机、涡流管、节流阀,且当膨胀比变化时,透平膨胀机的性能较稳定。涡流管、气波制冷机具有分离效果,可用于天然气脱水预冷。研究结果对于压力能回收装置的选用和调压流程的优化具有一定的指导意义。     

涡流室结构特性实验研究

涡流管是一种新型的冷热气流分离装置。涡流室是涡流管的核心部件,其结构对涡流管的性能有很大的影响。本文以压缩空气为工质,对不同流道结构、喷嘴数和内径的涡流管的制冷制热效应进行实验研究,获得了不同结构下随冷气流率变化的制冷制热效应曲线。研究结果表明:渐缩型流道的性能优于直流型和渐扩型;六流道数涡流室能够较好地满足性能要求;较大的涡流室内径表现出更好的制冷制热效应。     

An Extended Pinch Analysis and Design procedure utilizing pressure based exergy for subambient cooling

A new methodology for process synthesis extending traditional Pinch Analysis with exergy calculations is described. The methodology shows great potential for minimizing energy requirements (total shaft work) in subambient processes. This is achieved by optimizing compression and expansion work for the process streams together with the work needed to create necessary cooling utilities. The procedure, referred to as Extended Pinch Analysis and Design (ExPAnD), is illustrated by two examples, first in a simple example on how to utilize pressure based exergy in a cold stream for subambient cooling of a hot stream, then in the main example describing the use of the design methodology to develop a novel process for liquefaction of natural gas to LNG.     

Issues and prospects of energy separation in vortex tubes: Review

A vortex tube is a device that separates entering compressed fluid into hot and cold fluid streams simultaneously. This energy separation phenomenon inside the tube is a mystery and the mechanism that causes heat transfer needs attention. Since the invention of the vortex tube, the scientific community has taken efforts to search for energy separation mechanisms. Performance augmentation and the physics of energy separation was the objective of many experimental studies. The performance of the vortex tube varies with changes in geometric and operational parameters. Most of the theoretical studies addressed the issue of energy separation. Prospects and issues of energy separation in a vortex tube in view of the literature is the core of this paper. The main objective is to discuss efforts made in order to justify the physics and to identify new areas for research.     

不同排尘结构旋风分离器的分离特性

在欧拉-拉格朗日坐标系中对常规旋风分离器和两个不同直管长度旋风分离器内气固流动特性进行了数值模拟．模拟时气相场采用雷诺应力输运模型,应用随机轨道模型模拟湍流流场中颗粒的运动轨迹,并考虑气固两相之间的双向耦合．给出了不同排尘结构旋风分离器的速度、湍动能分布．对不同排尘结构旋风分离器的分离性能进行了实验研究．结果表明,底部加延长的直管可以使灰斗中气流的速度和湍动能得到较大衰减,能有效防止已分离颗粒的二次扬尘．直管内仍具有一定的分离能力,分级效率实验表明,加直管后旋风分离器分级效率有一定的提高．对于给定的旋风分离器,直管长度应有一最优值．     

The extraction of power from a hot stream

The solution to the problem of maximizing the extraction of exergy from a stream of hot gas showed that the hot stream must be cooled in a counterflow heat exchanger with optimal imbalance of capacity rates, i.e. with an optimal capacity rate on the cold side. This paper outlines the first few steps toward making this solution practical, by combining the optimized counterflow with conventional components for compressing and expanding the cold stream. In the first part of the paper, the cold stream is compressed in an isothermal compressor, expanded in an adiabatic turbine, and discharged into the ambient. In the second part, the cold stream is compressed in an adiabatic compressor. Both designs are optimized with respect to two degrees of freedom, the capacity‐rate imbalance of the counterflow, and the pressure ratio maintained by the compressor. The effect of other constraints is documented, e.g. heat transfer area size, hot gas initial temperature and compressor and turbine efficiencies. This study shows the tradeoff between simplicity and increased performance, and outlines the path for further conceptual work on the extraction of exergy from a hot stream that is being cooled gradually. Copyright © 2001 John Wiley & Sons, Ltd.     

CFD analysis and experimental investigations towards optimizing the parameters of Ranque-Hilsch vortex tube

Computational fluid dynamics (CFD) and experimental studies are conducted towards the optimization of the Ranque-Hilsch vortex tubes. Different types of nozzle profiles and number of nozzles are evaluated by CFD analysis. The swirl velocity, axial velocity and radial velocity components as well as the flow patterns including secondary circulation flow have been evaluated. The optimum cold end diameter (d_c) and the length to diameter (L/D) ratios and optimum parameters for obtaining the maximum hot gas temperature and minimum cold gas temperature are obtained through CFD analysis and validated through experiments. The coefficient of performance (COP) of the vortex tube as a heat engine and as a refrigerator has been calculated.     

进口压力对涡流管冷却特性影响的实验研究

为了解决燃气轮机高温部件热防护问题,采用实验研究涡流管在不同进口压力（0.20~0.65 MPa）和冷气流率（0.17~0.89）下的冷却特性。实验结果表明：实际温降,在不同进口压力下随着冷气流率的增加先增大后减小,在相同冷气流率下随着进口压力的增大而增大;温度〖JP2〗效率,在不同进口压力下随着冷气流率的增大先增大后减小,在冷气流率等于0.5时达到最大值;绝热效率,在进口压力等于0.20 MPa时最小,在大于0.30 MPa时随着进口压力的增加变化不大;制冷效率,随冷气流率的增加会先增加后减小,进口压力等于0.30和0.40 MPa时制冷效率最高。     

管壳式换热器壳侧气液两相流路分析法的研究

以Tinker壳侧流动模型为基础，提出了适宜于单相和气液两相流路分析法的壳侧单元流动模型。以主流、旁路流和泄漏流等各分流路的气液流量分布在稳态下应使壳侧流动的能量损耗达到最小的原则为基础，建立了壳侧气液两相流路分析法，给出了各流路的气液流量比例及错流区、窗口区压降的预测步骤，也给出了壳侧总压降计算式。建立的两相流路分析法预测结果与试验结果符合较好。     

换热器各流路对壳侧气液两相流动特性的影响

针对工业中广泛应用的管壳式换热器，应用空气-水两相混合物实验研究了壳侧旁路，泄漏流对气液两相流体流动特性的影响，以Ishihara两相流动模型为基础，建立了以横掠管束的主流路为基础的错流区通用两相压降计算关联式，通过错流区，泄漏流的分相流动模型，分析计算了主流路，旁路，泄漏流中气液分布，也分析了泄漏流对壳侧单相，两相总流量在各个分流路的流量分配影响，研究表明，主流路和旁路中气液各自占相应总流量的比例在不同的流型下明显不同，且比例值的波动范围较大，气液流量的分布在壳侧是不均匀的，折流板/换热管之间的泄漏流对壳侧的两相流动特性影响较小，而折流板/壳体之间的泄漏流影响较大。     

Simultaneous optimization of heat-integrated water networks involving process-to-process streams for heat integration

This paper presents an extension of our recent work, in which we addressed the simultaneous synthesis of heat-integrated water networks. The novelty and goal of this work is the development of an extended superstructure and simultaneous optimization model of heat-integrated water networks now involving process-to-process streams, and other streams within the overall network, for heat integration. Those heat-integration opportunities have not yet been fully taken into account in most existing models of heat-integrated water networks. In this study, we presented two strategies for heat integration of process-to-process streams. The first one includes the placement of heat exchangers on each hot and cold process-to-process stream. The second allows for the cooling and splitting of hot streams, and heating and splitting of cold streams. This extended model was formulated as a non-convex mixed-integer non-linear programming (MINLP) problem. The objective was to minimize the total annual network cost. Two examples with single and multiple contaminants are used in order to demonstrate that involving process-to-process streams for heat integration, novel and improved solutions can be obtained compared to those reported in the literature.     

The effects of nozzle aspect ratio and nozzle number on the performance of the Ranque–Hilsch vortex tube

An experimental study is carried out to investigate the effects of nozzle aspect ratio and nozzle number on the performance of a vortex tube. Two sets of vortex generator (a single nozzle set with aspect ratio of AR = 0.25, 0.44 and 0.69 and a multiple nozzle set with 2 and 3 nozzle number having the same total flow area) are tested under different inlet pressures. Dry air is used as the working fluid. The experimental results reveal that the nozzle aspect ratio has a great effect on the energy/temperature separation mechanism. The increase in the nozzle aspect ratio leads to the larger mixing zones, which, in turn, decreases the temperature difference between the cold and hot stream, the heating and the cooling performance. The results also showed that the vortex tube with a single nozzle yields better performance than the vortex tube with 2 and 3 nozzles.     

Effects of geometric parameters on the separated air flow temperature of a vortex tube for design optimization

Vortex tubes are used in many industrial fields as parts for refrigerating machines due to their many intrinsic benefits. Although the use of these types of tubes has become common, the characteristics of energy separation associated with these tubes have yet to be vigorously researched. In this study, a counter-flow type of vortex tube is employed to investigate the energy separation characteristics with various geometric configurations. As a preliminary step, the effect of the nozzle area ratio and the inlet pressure were studied given a selected tube length (L = 14 D). The temperature distribution inside the vortex tube was measured to understand the physics of the energy separation phenomena. The measurement showed that the temperature distribution on the hot air side recovers to the inlet temperature at a cold air mass fraction of 0.5 (y_c) with two types of nozzle area ratios. A parametric study was conducted to evaluate the performance of the vortex tube with various geometric structures and operating inlet pressures. The results show that variation of the cold exit orifice hole diameter significantly influences the energy separation between two exits.     

蚁群算法在换热网络优化中的应用

提出将蚁群算法应用于换热网络优化中,按照相等的能量份额将各股热流体分解成能量集合,热流体能量通过换热器在与冷流体换热的过程中得到分配,换热器单元面积得到相应地调整．能量分配过程中换热网络得到优化,从而使年综合费用减少的换热器面积不断积累,最终形成了一个最优的换热网络结构．通过具体算例验证了该方法的可行性和有效性,最终优化的结果证明该方法具有较强的全局搜索能力,能够应用于复杂换热网络的优化问题中．