Energy Separation Process Research Articles

Investigation of cold tube structure on flow characteristics and energy separation in vortex tube based on numerical and thermodynamic analyses

A combined approach of computational fluid dynamics modelling, experimental validation and thermodynamic analysis is used to investigate the effect of cold end tube geometry (namely, straight tube, divergent tube, convergent tube, and convergent-divergent tube) on flow characteristics and energy separation, which to improve the energy efficiency and sustainability of the vortex tube in industrial applications. The analyses indicate that the highest axial velocity (212 m/s) and swirl velocity (193 m/s) at different axial locations in the cold tube are demonstrated in the divergent and convergent-divergent structures, respectively. The divergent tube shows better energy separation at lower cold mass fraction, while the convergent-divergent tube is dominant at higher cold mass fraction. The highest coefficient of performance is found at μc = 0.6, with maximum cooling and heating energy transfer efficiencies of 0.112 and 0.103, respectively. By innovatively incorporating the work-heat transfer theory into structural investigation of cold tubes, it is found that tangential viscous shear effect is the dominant factor in energy separation process. It is noteworthy that the highest net energy transfer of 973 W is achieved by convergent-divergent tube at a cold mass fraction of 0.7.

RATIONAL CONTROL BY TEMPERATURE IN VORTEX ENERGY SEPARATOR UNDER DESTABILIZING EFFECTS

The focus of this study is the arrangement of a rational control technique used to maintain the airflow temperature in a vortex energy separator (VES) under destabilizing effects. The objectives include the development of tools for the rational control of temperature in the cold and hot air flows of a VES. Methods used: Discrete state space, production rule statement, resolution of two-valued predicate equations, dichotomous trees, diagnosis, and recovery of dynamic objects. Problems settled: the studied features of the vortex energy separation process, architecture, and operation links of the rational control system were considered, mathematical models were deduced, and tools for diagnosing and recovering the efficiency of the vortex energy separator as a rational control object were developed. The scientific novelty of the study lies in the formation of instrumental tools to provide rational control of the airflow condition in the VES, where the control object is subjected to the substantial influence of various destabilizing effects.

Using an optimized venturi instead of cold orifice in Vortex tube: Thermodynamic and experimental approach

A vortex tube (VT) is a separator system (for energy, fluids and particles) that is often used in the industries to provide cooling and heating services. Its exceptional features including; “simplicity of the structure” and “high temperature difference between the outlets” have made it widely used in the thermal applications. The cold outlet structure located in the vortex chamber significantly can change the thermodynamic performance of the VT due to its position at the beginning of the energy separation process. This experimental research focuses on increasing the thermal efficiency of the VT by designing an optimized venturi instead of the cold orifice. The effects of the venturi structural parameters including the middle part diameter (Ø = 12, 13 and 14 mm), the convergence angle (β = 0, 1, 2, 3 and 4°) and the divergence angle (θ = 0, 1, 2, 3 and 4°) are considered on the VT efficiency criteria like; the temperature separations (ΔTc,h,t), the isentropic efficiency (η), the power separations (Q̇c,h,t) and the coefficient of performance (COP). The results show that there are optimum values (Ø = 13 mm, β = 3° and θ = 1°) for obtaining the maximum thermal improvements: ΔTc: 61.68%, ΔTh: 58.74%, ΔTt: 53.39%, η: 61.70%, Q̇c: 47.16%, Q̇h: 61.71%, Q̇t: 55.44%, COPCM: 50% and COPHP: 65%.

Influence of flow parameters in the dual nozzle CO2-based vortex tube cooling system during turning of Ti-6Al-4V

Dual nozzle vortex tube cooling system (VTCS) is developed to improve the machinability of Ti-6Al-4V where cold-compressed CO2 gas is used as a coolant. The cooling effect is produced by the process of energy separation in the vortex tube and the coolant is supplied into the machining zone to remove the generated heat in machining. In this study, the responses such as cutting force (Fz), cutting temperature (Tm), and surface roughness (Ra) are analyzed by considering coolant inlet pressure, cold fraction, and nozzle diameter as input variables. Further optimization is performed for the input variables using the genetic algorithm technique, and the results at optimum conditions are compared with those of dry cutting. From the results, lower cutting force is observed at lower coolant pressure and cold fraction and higher nozzle diameter. The cutting temperature is minimized by increasing coolant pressure and cold fraction and by decreasing nozzle diameter. A better surface finish is observed at high coolant pressure and cold fraction and lower nozzle diameters. It is observed from the response surface method (RSM) that the coolant pressure is most significantly affecting all the responses. At optimum conditions, the cutting temperature and surface roughness are 35.6% and 66.14%, respectively, lower than dry cutting due to the effective cooling and lubricating action of the CO2 gas, whereas cutting force observed under the VTCS is 18.6% higher than that of dry cutting because of the impulse force of the coolant VTCS and thermal softening of the workpiece in dry cutting.

Professor A.P. Merkulov’ role in the process of research and development of the vortex effect

The article is prepared for the centenary of the birth of Alexander Petrovich Merkulov. The stages of creating the theoretical basis of the vortex effect of energy separation of gases (the hypothesis of vortex interaction), and the creation and implementation of vortex devices based on the use of the vortex effect for aviation and medicine are considered. The role of Professor A.P. Merkulov in the study of characteristic features of the energy separation process in vortex tubes and practical application of the vortex effect in the USSR is shown. The works of ONIL-9 (KuAI-SGAU) headed by Alexander Petrovich Merkulov ensured the leading position of the Soviet school of thought in the field of vortex effect. These works contributed to the formation of modern understanding of the vortex effect and the successful beginning of industrial application of vortex apparatuses.

Experimental study of energy separation in a Ranque-Hilsch tube with a screw vortex generator

The paper considers the process of energy separation in a vortex tube with an original screw-type vortex generator, which was not previously used for this purpose. The effects of inlet pressure, pressure at hot and cold outlets of the tube, and mass fraction of the cold stream in the total flow on the temperature separation and process efficiency have been investigated. It is shown that increasing inlet pressure, the effect of the flow temperature separation increases, and an increase in the outlet pressure leads to a decrease in the effect. To determine the region of energy separation, the vortex gas flow in a screw swirl placed in a round tube and designed to swirl the flow in a Ranque-Hilsch vortex tube was experimentally studied. It has been experimentally shown that the temperature of the swirling gas flow leaving the screw swirl at the periphery increases with respect to the inlet gas temperature, and the temperature of the swirling gas flow in the axial region decreases. This indicates that energy separation occurs in the screw vortex generator.

Analysis on the patterns of precessing frequency characteristics and energy separation processes in a Ranque–Hilsch vortex tube

Recently, the particular energy separation of the vortex tube was thought to be caused by the energy transferred from the inner core stream to the outer periphery stream through the precessing vortex core, and the precessing frequency is a remarkable signal released by the vortex core. To study the basic distribution of the precessing frequency and the relationship between the frequency and energy separation, precessing frequency characteristics were analysed in a vortex tube with a diameter of 30 mm in this paper. To achieve this, axial velocity time series were obtained by LDV measurements. It is demonstrated that the impact of the precessing vortex core on the flow field is consistent under different radial positions at the same axial position. However, the impact gradually weakens downstream. In addition, the precessing characteristics vanish within the swirl decay zone, which results in the deterioration of the energy separation performance. An enhancement in the inlet pressure results in an improvement in the performance and a significant increase in the magnitude of the peak frequency. In addition, the energy separation process and performance under increasing inlet pressure were analysed. It was observed that the growth of the precessing frequency imparts a higher energy transfer capability, which results in higher performance. The patterns of large-scale vortices and energy separation of the vortex tube were determined based on these observations. In addition, the enhancement in the precessing frequency may offer a novel concept based on which the performance of the vortex tube can be enhanced. Finally, a large eddy simulation was recommended to obtain more detailed information on large-scale precessing vortices.

LES study on the working mechanism of large-scale precessing vortices and energy separation process of Ranque-Hilsch vortex tube

In this paper, a large eddy simulation model (LES) was adopted to analyse the large-scale precessing vortices and energy separation in a Ranque–Hilsch vortex tube. By comparing the time-averaged axial velocity field between the Laser Doppler velocimetry data and the numerical results, the feasibility of the LES model was confirmed. The 2D instant flow field presents two vortex structures of secondary circulation flow at the cold end, and precessing vortices inside the tube. It also reveals two opposite flows in the axial and radial directions, and the precessing vortices formed by the reverse flow turn towards the main flow. Then, the 3D coherent structure inside the vortex tube was obtained by the vortex identification method for the first time. The basic vortex structure inside the vortex tube consists of the vortex body, detached vortex, and fragmentised detached vortex. Through the evolution of the 3D vortex structure, it was found that the detached vortices experienced a life cycle of growth, shedding, fragmenting, and vanishing. Benefitting from the vortex shedding processes, the precessing vortices overcame the adverse radial pressure gradient and drove part of the reverse flow towards the main flow from the low-pressure zone to the high-pressure zone. Through these processes, the vortex core precession that drives the reciprocating motion of the gas parcels near the reverse flow boundary was established, and energy could be transferred from the inner layer to the outer layer through a heat pump cycle.

Microporous Materials in Scalable Shapes: Fiber Sorbents

Microporous materials have the potential to enable new low energy separation processes due to their superb textural properties and structural diversity, yet these materials are facing practical cha...

Computational Fluid Dynamic Simulation of Single and Two-Phase Vortex Flow—A Comparison of Flow Field and Energy Separation

In the present work, a computational fluid dynamic (CFD) simulation has been performed to investigate single and two-phase vortex tube. Air in compressed form and partially condensed phase are used as working fluid, respectively. Simulation has been carried out using commercial CFD software package fluent 6.3.26. A detailed study has been performed to generate the profiles of velocity, pressure, and pathlines. These profiles provide an insight on how the process of energy separation as well as the flow field in the vortex tube gets affected on introduction of a liquid phase. The result shows that in case of cryogenic vortex tube, the flow reversal takes place closer to wall due to presence of a very thin wall adhering liquid film, while, in single-phase flow vortex tube, flow reversal is observed at the central portion. The model also predicts that presence of recirculation zone near warm end diminishes the refrigeration effect of vortex tube for two-phase flow.

Experimental research of the possibility of heat transfer enhancement in gas dynamic energy separation process

Analysis of the mechanism of heat transfer enhancement in a device of machineless energy separation of flows (Leontiev tube) is presented in the paper. The main parameters that define the device's efficiency are the temperature recovery factor and heat transfer in the supersonic channel of the device. Changes in the shape and relief of the flow surface, the use of working fluids with a low Prandtl number, low-intensity shock waves and local separation areas in the supersonic channel are among the methods of heat transfer enhancement in an energy separation device. The results of experimental investigation of the influence of a supersonic separation flow on the adiabatic wall temperature and the temperature recovery factor are presented. The range of the Mach numbers analyzed is between 2 and 3.5. The Reynolds criterion along the length of the dynamic boundary layer amounts to at least 6106. Field distributions of the adiabatic wall temperature and temperature recovery factors along the plate are presented for different Mach numbers. The results indicate that local separation boundary layer regions will probably intensify heat transfer in the supersonic channel of a gas dynamic energy separation device. The research has been conducted using the experimental facilities of the Institute of Mechanics of Lomonosov Moscow State University.

Energy separation of gases with low and high Prandtl numbers

The process of energy separation of a gas with the Prandtl number which is not equal to unity is investigated. The gas flows through a heat exchanger consisting of two coaxial axisymmetric pipes with sub- and supersonic velocities. Heat exchange between the gas streams takes place as a result of the fact that the recovery factor is not equal to unity. The flow is described by one-dimensional gas dynamic equations for averaged quantities.

Low energy ballasted flotation

A novel process which involves the replacement or supplementation of bubbles in the dissolved air flotation process with low density beads is presented. The work comprised a series of bench-scale flotation trials treating three commonly encountered algal species ( Microcystis, Melosira and Chlorella) that were removed in a flotation cell configured as either: conventional dissolved air flotation (DAF); ballasted flotation using low density 70 μm glass beads with a density of 100 kg m −3; or a hybrid process of ballasted flotation combined with conventional DAF. Results indicated that the bead only system was capable of achieving better residual turbidity than standard DAF at bead concentrations of 500 mg L −1. Addition of beads in combination with standard DAF reduced turbidity further to even lower residual turbidity levels. Algae removal was improved when glass beads were dosed, but removal was dependent on algal species. Microcystis was removed by 97% for bead only systems and this removal did not change significantly with the addition of air bubbles. Melosira was the next best removed algae with bead only dosed systems giving similar removals to that achieved by standard DAF using a 10% air recycle ratio (81 and 76% removal respectively). Chlorella was the least well removed algae by bead only systems (63% removal). However, removal was rapidly improved to 86% by the addition of air bubbles using only a 2% recycle ratio. Energy estimations suggested that at least a 50% energy reduction could be achieved using the process offering a potential route for future development of low energy separation processes for algae removal.

State‐of‐the‐Art Adsorption and Membrane Separation Processes for Hydrogen Production in the Chemical and Petrochemical Industries

This review on the use of adsorption and membrane technologies in H2 production is directed toward the chemical and petrochemical industries. The growing requirements for H2 in chemical manufacturing, petroleum refining, and the newly emerging clean energy concepts will place greater demands on sourcing, production capacity and supplies of H2. Currently, about 41 MM tons/yr of H2 is produced worldwide, with 80% of it being produced from natural gas by steam reforming, partial oxidation and autothermal reforming. H2 is used commercially to produce CO, syngas, ammonia, methanol, and higher alcohols, urea and hydrochloric acid. It is also used in Fischer Tropsch reactions, as a reducing agent (metallurgy), and to upgrade petroleum products and oils (hydrogenation). It has been estimated that the reforming of natural gas to produce H2 consumes about 31,800 Btu/lb of H2 produced at 331 psig based on 35.5 MM tons/yr production. It is further estimated that 450 trillion Btu/yr could be saved with a 20% improvement in just the H2 separation and purification train after the H2 reformer. Clearly, with the judicious and further use of adsorption or membrane technology, which are both classified as low energy separation processes, energy savings could be readily achieved in a reasonable time frame. To assist in this endeavor of fostering the development of new adsorption and membrane technologies suitable for H2, CO and syngas production, the current industrial practice is summarized in terms of the key reforming and shift reactions and reactor conditions, along with the four most widely used separation techniques, i.e., absorption, adsorption, membrane, and cryogenic, to expose the typical conditions and unit processes involved in the reforming of methane. Since all of the reactions are reversible, the H2 or CO productivity in each one of them is limited by equilibrium, which certainly provides for process improvement. Hence, the goal of this review is to foster the development of adsorption and membrane technologies that will economically augment in the near term and completely revamp in the far term a typical H2, CO or syngas production plant that produces these gases from natural gas and hydrocarbon feedstocks. A review of the emerging literature concepts on evolving adsorption and membrane separations applicable to H2 production is provided, with an emphasis placed on where the state‐of‐the‐art is and where it needs to go. Recommendations for future research and development needs in adsorbent and membrane materials are discussed, and detailed performance requirements are provided. An emphasis is also placed on flow sheet design modification with adsorption or membrane units being added to existing plants for near term impact, and on new designs with complete flow sheet modification for new adsorption or membrane reactor/separators replacing current reactor and separator units in an existing plant for a longer term sustainable impact.

Similarity of the energy-separation process in vortex Ranque tubes

Criteria for estimating the effect of energy separation in a vortex tube have been developed on the basis of the similarity theory and the theory of dimension. The most reliable available experimental data on the process considered have been generalized in the form of criteria equation relating the main characteristics of the energy-separation process in tubes with determined parameters.

Temperature separation and friction losses in vortex tube

The process of energy separation and friction losses in a vortex tube is studied in detail. The hot and cold exit air temperatures were measured. Experiments have been conducted at inlet pressure of 3.5, 5, 7.5 and 9 bar, at inlet temperature of 292.15 and 298.15 K and at cold air mass ratio from 0 to1. The results demonstrate that the hot air temperature reaches its maximum value at a cold air mass ratio of nearly 0.82, while the minimum value of cold air temperature is found at a cold air mass ratio of 0.3. Based on energy and mass balances as well as on the definition of internal energy and on experimental results a new model for the determination of hot and cold exit gas temperature has been developed. The model includes the relevant primary parameters and predicts the experimental results as well as the data published in the literature sufficiently accurate for engineering purposes.

Energy Separation of Incompressible Fluid Using Vortex Tube

The vortex tube is a simple device which separates fluid stream into a cold stream and a hot stream without any chemical reaction. The process of energy separation in the vortex tube has caused a great deal of interest. Although many studies on energy separation in the vortex tube using air as the working fluid have been made so far, few experimental studies treated energy separation for incompressible fluid. So, an experimental study for the energy separation in the vortex tube using the water which is essentially an incompressible fluid is presented. When working fluid is the water, the best geometric values of nozzle area ratio and number of nozzle holes are 0.155, 6 respectively. These geometric values are showed by the similar values which are presented by compressible fluid as working fluid. But hot side mass fraction of which maximum temperature drop is happened are different from compressible fluid.

Measurement and Computation of Energy Separation in the Vortical Wake Flow of a Turbine Nozzle Cascade

This paper describes the observation, measurement, and computation of vortex shedding behind a cascade of turbine nozzle guide vanes that have a blunt trailing edge. At subsonic discharge speeds, periodic wake vortex shedding was observed at all times at a shedding frequency in the range 7–11 kHz. At high subsonic speeds the wake was susceptible to strong energy redistribution. The effect was greatest around an exit Mach number of 0.95 and results are presented for that condition. An unusually cold flow on the wake centerline and hot spots at the edges of the wake were measured. These were found to be a manifestation of Eckert–Weise effect energy separation in the shed vortex street. Experimental identification of these phenomena was achieved using a new stagnation temperature probe of bandwidth approaching 100 kHz. Using phase-averaging techniques, it was possible to plot contours of time-resolved entropy increase at the downstream traverse plane. Computational work has been undertaken that gives qualitative confirmation of the experimental results and provides a more detailed explanation of the fine scale structure of the vortex wake. The topology of the wake vortical structures behind blunt trailing-edged turbine blades is becoming clearer. These measurements are the first instantaneous observations of the energy separation process occurring in turbine blade wake flows. This was also the first demonstration of the use of the probe in the frequency, Mach number, and temperature ranges typical of operation behind the rotors of high-performance turbomachines such as transonic fans.

GENERALIZED CORRELATIONS FOR THE PROCESS OF ENERGY SEPARATION IN VORTEX TUBES

The Ranque-Hilsch vortex tube is a simple device which splits a compressed gas stream into a cold stream and a hot stream. The process of energy separation taking place in the vortex tube has been investigated theoretically and experimentally. The analysis of the dimensional groups that govern the tube performance as a cooling device have shown that; for geometrically similar tubes, the inside diameter of the tube is a parameter. This conclusion was verified experimentally. The experimental results have also indicated that there is an optimum tube diameter for best coolingperformance. It was also shown that the ratio between the temperature drop of the cold stream achieved at a certain pressure ratio to its maximum value (To - Tc)/(TO - Tc)max can be expressed by a sole function of the cold mass fraction U (U: kg. cold air per kg. supply air to the tube), and does not depened on other conditions of operation. On the other hand, the correlation between the analytical and experimental results have shown that the overall performance of the vortex tube can be expressed by a generalized formula which is valid for all conditions of operation. Stith formula can predict the cooling performance of the vortex tube from knowledge of its inside diameter, type of the working medium (expressed by the specific heat ratio Cp/Cv), its inlet condition (temperature 'To and pressure Po), the required cold stream pressure (Pc) and cold mass fraction (U).

PERFORMANCE CHARACTERISTICS OF ENERGY SEPARATION IN DOUBLE STAGE VORTEX TUBES

The performance characteristics of double stage vortex tubes have been investigated and compared with that for a single stage tube operating at the same inlet conditions. The effect of the diameter ratio of the second stage to the first stage tube (D2/D1) together with the operating pressure ratios for each stage were investigated. The analytical study of the process of energy separation taking place in the double stage tube have shown that the performance of the first stage isalways higher than that of the second stage tube. This conclusion was also verified experimentally. On the other hand, the experimental data have shown that the maximum temperature drop produced by the double stage vortex tube improves at higher inlet pressures (Po) and excels that of conventional single stage tubes when that pressure exceeds 3 bar. Best cooling performance for the double stage tube is achieved when the diameter ratio D2/D1 approaches unity. Also, the optimum value for the intermediate pressure (Pc1) for the double stage tube is expressed by: 0.45, Pct = Po. Experimental results have also indicated that; under all conditions of operation, the refrigerating effect produced by the double stage operation is always less that for the single stage operation.