Cold Mass Fraction Research Articles

Computational investigation of precessing vortex breakdown and energy separation in a Ranque–Hilsch vortex tube

The flow structure and energy separation considering the effect of cold mass fraction in a Ranque–Hilsch vortex tube were investigated computationally based on the vortex breakdown theory. The velocity distributions and pressure fields for nine different cold mass fractions were considered. A quasi-cylindrical approximation was adopted to predict the size of the vortex core size by considering the pressure gradient. Further, a novel analysis was conducted on the energy separation mechanism, in which the large-scale vortex structure plays an important role; for example, increasing the cold mass fraction within a certain range can result in bigger vortex cores, yielding better energy separation performance. Finally, the type of vortex breakdown was also discussed for further understanding the vortex structure. This paper offers a new idea on the manner in which the external conditions (here, cold mass fraction) affect the large-scale vortex structure and on the subsequent energy separation performance.

Performance Analysis on CO2 Heat Pump Cycle with a Vortex Tube

This study presents a CO2 heat pump cycle with a vortex tube in which a vortex tube is applied to replace the throttle valve used in the conventional CO2 heat pump cycle. The COPh and total heating capacity of this cycle are theoretically investigated and compared with that of conventional CO2 heat pump cycle for the ranges of evaporating temperature (−15 to 3 ℃ ) and gas-cooler pressure (8 to 9.8 MPa). The COPh of this cycle increases with the increasing of nozzle efficiency, the evaporating temperature and the heating effect of vortex tube; moreover, the COPh of this cycle increases with the decreasing of the temperature of gas cooler outlet and the cold mass fraction. Under the same operating conditions, the COPh of this cycle can be improved by up to 3.9 ～ 16.8% over the conventional CO2 heat pump cycle.

Experimental investigation for thermal performance of series and parallel Ranque-Hilsch vortex tube systems

The present study investigated experimentally the cooling and heating performance of two identical counter flow vortex tubes arranged in-series (VTS) and parallel (VTP). The vortex tube used has general specifications of: aspect ratio AR=1.6, hot tube length L=112.5mm, hot tube inner diameter D=7.5mm, cold end diameter dc=5mm, and generator of three nozzles, N=3. Dry air is used as a working fluid with different inlet air pressures adjusted from 2 to 6bars. The experimental results revealed that the maximum cold temperature difference occurred at the inlet air pressure of 6bars and cold mass fraction of 0.4 for both VTS and VTP systems. The conducted results demonstrated that the values of COPref for VTS system were higher than the values of VTP system. However, the VTP yielded higher values of COPHP over the range of investigation. The VTS system improved the COPref by 22.5% and 31.5% compared with the VTP and the single vortex tube system (VTO), respectively. For the case of VTP system, the COPHP is enhanced by 18.2% and 27.3% than VTS and VTO, respectively.

Experimental investigation & CFD analysis of Ranque–Hilsch vortex tube

A vortex tube (VT) is a very simple, yet effective device to generate instantaneous spot cooling effect, using compressed air as input. Present work is experimental analysis of effect of insulation on temperature separation performance of VT. Firstly, reliability of experimental setup and experimentation procedure is established through observation of transitional characteristics & energy balance. Then, interactive effect of inlet pressure (2–5 bar), cold mass fraction (0.1–0.9) and insulation on the performance of VT is investigated. In the second stage, essential parameters such as temperature and pressure values from experimentation were used to develop computational model of VT and results of experimentation were compared with CFD results. More importantly, utilization of flow physics derived from CFD model has been made to put forth the hypothesis about improvement in performance of VT due to insulation.For both insulated and non-insulated condition, temperature separation increases with increase in inlet pressure. Performance of insulated VT is better than non-insulated VT. It is proposed that significant heat leakage from atmosphere to VT is responsible for performance degradation of non insulated VT. Results of present experimental as well as CFD study in non-dimensional form are observed to be in good agreement with those of other works. Also, it is concluded that cooling power separation seems more realistic performance parameter of VT than cold end temperature alone.

Cooling and dehumidification using vortex tube

The Ranque-Hilsch vortex tube (RHVT) is a small interesting extraordinary mechanical device used as refrigeration machine. An experimental setup has been developed for the study of both temperature and relative humidity separation in vortex tube for the two important cases: (a) with insulation and (b) without insulation on vortex tube. Two influential configurations are examined: (1) variations of cold mass fraction (by varying the mass flow at hot outlet) at different pressures and (2) variations of inlet pressures when the hot outlet is fully opened. Over the whole pressure range covered, the cold end temperature drop increases with the cold mass fraction and then decreases for both non-insulated and insulated cases. However, hot end temperature drop increases for whole range of the cold mass fraction for the non-insulated case, whereas it increases to some optimum value, then decreases with the cold mass fraction for the insulated case. Over the range of pressure the relative humidity increases to some optimum value, and then decreases with the cold mass fraction for both non-insulated and insulated cases. The maximum optimum value of relative humidity is found 65% and 67% at 4bar inlet pressure with and without insulation respectively. Moreover, the correlations for cold end temperature drop, hot end temperature drop, relative humidity and isentropic efficiency have been developed and explained in this paper for the better understanding of the inside behavior of the RHVT. The variation of optimum non-dimensional cold/hot temperature drop with the cold mass fraction at different pressures obeys approximately single cubic equation and also it is true for the case of non-dimensional relative humidity.

CFD Analysis of Temperature Separation in a Convergent Vortex Tube

The purpose of this paper is to investigate the effect of using a convergent hot tube on the vortex tube refrigeration capacity. The computational fluid dynamics (CFD) model used is a three-dimensional steady compressible model that utilizes the k-?turbulence model. In this numerical research, different convergence angles of the hot tube (β=0?, 0.5?, 0.88?, 1?, 1.5?, and 2?) have been considered to analyze the vortex tube performance. The results showed that as the angle converges from the cylindrical model (β=0?), the cold temperature separation improves at the cold mass fractions greater than about 0.3, but increasing the angle more than 2?impairs the cold temperature separations compared to the cylindrical model, because of the secondary circulation development inside the vortex tube. Also, a successful validation has been carried out between some available experimental results and the present numerical model (for cylindrical vortex tube) Table 1.

An experimental study of nozzle number on Ranque Hilsch counter-flow vortex tube

The present study investigates the effects of the orifice nozzle number and the inlet pressure experimentally on the cooling performance of the counter flow type vortex tube. The energy generation has been conducted using a generator of type stream–tek generator model GNMD-KIT with the number of nozzles (2, 3, and 6), and aspect ratio 1.6 and, an inner diameter of 7.5mm. In the experiments, for each of the orifices, inlet pressures have been adjusted from 200kPa to 600kPa. The energy separation to be investigated here focuses on the cold temperature difference and coefficient of performance for cooling. The experimental results concluded in this paper proved that the higher effect of nozzle number is for nozzle number three and hence that nozzle number could affect the energy separation efficiently. A comparison of the present experiments with other published works has been conducted. An analytical study of the characteristics equation has been carried out to evaluate the best correlation of the ratio of cold temperature difference to the inlet temperature as a function of pressure, cold mass fraction and nozzle numbers. The goodness of fit of the regression model is inspected using the analysis of variance and t-test. The values of R2 are adjusted close to 97% which show a very good agreement between the experimental and predicted values.

Experimental investigation of the effect of nozzle numbers on Ranque–Hilsch vortex tube performance

The present study investigates the effects of the orifice nozzle number and the inlet pressure experimentally on the cooling performance of the counter flow-type vortex tube. The energy generation has been conducted using a stream-tek generator (model GNMD-KIT) with different numbers of nozzles (2, 3, and 6), an aspect ratio of 1:6, and an inner diameter of 7.5 mm. In the experiments, for each of the orifices, inlet pressures have been adjusted from 200–600 kPa. The energy separation investigated here focuses on the cold temperature difference and coefficient of performance for cooling. The experimental results concluded in this article prove that the greatest effect of nozzle number is for three nozzles, and hence, that nozzle number could affect the energy separation efficiently. A comparison of the present experiments with other published works has been conducted. An analytical study of the characteristics equation has been carried out to evaluate the best correlation of the ratio of cold temperature difference to the inlet temperature as a function of pressure, cold mass fraction, and nozzle number.

The regulation of the cold neutral gas mass fraction by turbulent motions

We present results from hydrodynamic simulations with forced turbulence at a scale of 50 pc and cooling functions adapted to describe the thermal conditions at four different Galactocentric distances: 8.5, 11, 15, and 18 kpc. These experiments are aimed to study the effects of varying the turbulent velocity vrms on the cold gas mass fraction. With realistic vrms we obtain average one-dimensional cold gas mass fractions which are comparable with the observed values. Our simulations can also lead to an approximately constant cold gas mass fraction for distances ≥11 kpc when considering subsonic perturbations for 15 and 18 kpc. We also find that the average one dimensional cold gas mass fraction and the volumetric cold gas mass fraction do not follow the same radial trends.

The effects of orifice nozzle number and nozzle made of polyamide plastic and aluminum with different inlet pressures on heating and cooling performance of counter flow Ranque–Hılsch vortex tubes: An experimental investigation

In this paper, the effects of the orifice nozzle number and the inlet pressure on heating and cooling performance of a counter flow Ranque–Hilsch type vortex tube (RHVT) (L/D ration is 10) are investigated by using air and oxygen as a fluid via an experimental method. Five orifices with two, three, four, five and six nozzles are made from the polyamide plastic and aluminum. The object of this research is to observe thermal behavior of air and oxygen, which are passing through an RHVT. Using two different fluids for each one of the orifices (nozzle numbers), inlet pressure is varied between 150 kPa and 700 kPa by increasing 50 kPa for each step and comparison is made between these two fluids by holding the cold mass fraction constant at 0.36. We show that the temperature gradient between the cold and hot fluid decreases whenever the orifice nozzle number increases.

Three-Dimensional CFD Simulation of Fluid Flow inside a Vortex Tube on Basis of an Experimental Model- The Optimization of Vortex Chamber Radius

Vortex-chamber is a main part of vortex tube which the pressured gas is injected into this part tangentially. An appropriate design of vortex-chamber geometry leads to better efficiency and good vortex tube performance. In this study, the computational fluid dynamics (CFD) model is created on basis of an experimental model and is a three-dimensional (3D) steady compressible model that utilizes the k-e turbulent model. In this paper the effect of changing radius of vortex-chamber (R*) on vortex tube performance has been studied for different value of R* and the optimized radius of vortex-chamber has been determined. According to numerical results the cold temperature difference has increased when we take into account the effect of the radius of vortex-chamber in range of 5.7-11 mm and when the radius of vortex chamber has located in range of 11-13 mm, the cold temperature difference has decreased. The highest ΔTc is 46.77 K for R*=11 mm at a cold mass fraction of 0.3, higher than basic model around 6.3% at the same cold flow fraction. Finally, the results obtained, particularly the temperature values, are compared with some available experimental data, which show good agreement.

Effect of Mach number, valve angle and length to diameter ratio on thermal performance in flow of air through Ranque Hilsch vortex tube

Ranque Hilsch vortex tube is a device that can produce cold and hot air streams simultaneously from pressurized air. Performance of vortex tube is influenced by a number of geometrical and operational parameters. In this study parametric analysis of vortex tube is carried out. Air is used as the working fluid and geometrical parameters like length to diameter ratio (15, 16, 17, 18), exit valve angles (30°–90°), orifice diameters (5, 6 and 7 mm), 2 entry nozzles and tube divergence angle 4° is used for experimentation. Operational parameters like pressure (200–600 kPa), cold mass fraction (0–1) is varied and effect of Mach number at the inlet of the tube is investigated. The vortex tube is tested at sub sonic (0 < Ma < 1), sonic (Ma = 1) and supersonic (1 < Ma < 2) Mach number, and its effect on thermal performance is analysed. As a result it is observed that, higher COP and low cold end temperature is obtained at subsonic Ma. As CMF increases, COP rises and cold and temperature drops. Optimum performance of the tube is observed for CMF up to 0.5. Experimental correlations are proposed for optimum COP. Parametric correlation is developed for geometrical and operational parameters.

THE GAS MASS OF STAR-FORMING GALAXIES AT z ≈ 1.3

ABSTRACT We report a Giant Metrewave Radio Telescope search for H i 21 cm emission from a large sample of massive star-forming galaxies at z ≈ 1.18–1.34, lying in sub-fields of the DEEP2 Redshift Survey. The search was carried out by co-adding (“stacking”) the H i 21 cm emission spectra of 857 galaxies, after shifting each galaxy’s H i 21 cm spectrum to its rest frame. We obtain the 3σ upper limit S H i &lt; 2.5 μJy on the average H i 21 cm flux density of the 857 galaxies, at a velocity resolution of ≈315 km s−1. This yields the 3σ constraint M H I &lt; 2.1 &times; 10 10 &times; [ &Delta; V / 315 km s &minus; 1 ] 1 / 2 M &CircleDot; ?> on the average H i mass of the 857 stacked galaxies, the first direct constraint on the atomic gas mass of galaxies at z &gt; 1. The implied limit on the average atomic gas mass fraction (relative to stars) is M GAS/M * &lt; 0.5, comparable to the cold molecular gas mass fraction in similar star-forming galaxies at these redshifts. We find that the cosmological mass density of neutral atomic gas in massive star-forming galaxies at z ≈ 1.3 is ΩGAS &lt; 3.7 × 10−4, significantly lower than ΩGAS estimates in both galaxies in the local universe and damped Lyα absorbers at z ≥ 2.2. Massive blue star-forming galaxies thus do not appear to dominate the neutral atomic gas content of the universe at z ≈ 1.3.

Numerical Analysis of a Vortex Tube: A Review

Ranque–Hilsch vortex tube is a simple devise with no moving parts which could generate cold and hot air/gas streams simultaneously with compressed air/gas as a working fluid. The energy and flow separation in a vortex tube is highly depends on factors like nozzle shape, nozzle number, diameter and length of the vortex tube, inlet pressure, control valve, diaphragm hole size and cold mass fraction. As the energy separation and flow patterns in a vortex tube are highly complex and were not explained successfully by any researcher, a computational study of vortex tube flow and energy separation will give a better understanding about the physics and mechanism involved. Many researchers conducted computational fluid dynamic analysis of the vortex to have a deep insight about the process of flow separation. In this paper computational analysis of vortex by many researchers were presented along with the results obtained and suggestions to improve the performance of the vortex tube. Researchers considered Turbulence models which predict the performance precisely were discussed in the present paper. Researchers considered turbulence models like LES, k–e, k–ω and RMS to predict the energy separation in vortex tube. Some researchers considered artificial neural networks (ANN) and Taguchi methods for their analysis. Comparison of the predictions with simulation results were also presented to give a clear idea for the reader about the CFD models prediction capabilities.

Modeling the cooling performance of vortex tube using a genetic algorithm-based artificial neural network

In this study, artificial neural networks (ANNs) have been used to model the effects of four important parameters consist of the ratio of the length to diameter(L/D), the ratio of the cold outlet diameter to the tube diameter(d/D), inlet pressure(P), and cold mass fraction (Y) on the cooling performance of counter flow vortex tube. In this approach, experimental data have been used to train and validate the neural network model with MATLAB software. Also, genetic algorithm (GA) has been used to find the optimal network architecture. In this model, temperature drop at the cold outlet has been considered as the cooling performance of the vortex tube. Based on experimental data, cooling performance of the vortex tube has been predicted by four inlet parameters (L/D, d/D, P, Y). The results of this study indicate that the genetic algorithm-based artificial neural network model is capable of predicting the cooling performance of vortex tube in a wide operating range and with satisfactory precision.

Computational analysis of energy separation in counter—flow vortex tube

Present paper is aimed towards reporting CFD study carried out on counter—flow vortex tube using different gases at various values of cold mass fraction and using different turbulence models. In CFD analysis of counter flow vortex tube, various working gases have been seldom used and their energy separation effect studied relative to cold mass fraction. Also, computational efforts to compare results of one equation Spalart Allmaras model used for analysis of counter—flow vortex tube with other two equation turbulence models, that is, Standard k-ε and Standard k-ω model as well as RSM (Reynolds Stress Model) have been seldom reported.All turbulence models are observed to predict similar flow physics inside vortex tube, however, with different magnitude. Spalart Allmaras model over predicts while RSM under predicts temperature separation magnitude. Nitrogen as working fluid of vortex tube produces highest temperature separation, while it is least for CO2 among the working fluids studied. Cold mass fraction is an important parameter which directly affects the temperature separation. Cooling power separation should also be considered as an important performance parameter of vortex tube, instead of cold end temperature alone.Results of present CFD study are in better agreement with experimental results than previous CFD results.

Computational investigation of different effects on the performance of the Ranque–Hilsch vortex tube

The Ranque–Hilsch vortex tube is a simple device with no moving parts and no mechanical operations. This device separates the inlet air into two distinctive regions; an outward high temperature region and an inner low temperature one.A computational study of the tube is presented in this article using an axisymmetric model using the ANSYS Fluent® software whose results showed good agreement with the experimental measurements. The effects of the tube length to diameter ratio and the cold orifice size on the performance of the tube were investigated.The results showed that length to tube diameter ratio (L/D) affects the performance of the tube, and that this effect changes when operating the tube at different cold mass fractions.The results showed also that the maximum cooling occurs at the lowest cold orifice to tube diameter ratio (dc/D) at the lowest cold mass fraction (μc) possible while the maximum heating occurs at the highest dc/D at the highest μc possible. Secondary circulations were investigated when operating at low dc/D values.In order to enhance the cooling capabilities of the tube fins were added to the tube to enhance the natural convection on the wall of the tube.

Experimental study of the energy separation in a vortex tube

A vortex tube is a simple-structure device which can separate a compressed stream into a hot and a cold stream. The accurate flow pattern inside the vortex tube remains elusive and no satisfactory explanation of its energy separation mechanism has been put forward yet. In this work, the influences of inlet pressure and cold mass fraction on the performance of the vortex tube were explored.The experimental results show that the static temperature in the center of vortex tube is higher than that of the peripheral part. Besides, the stagnation point inside the vortex tube moves to the cold end with the decrease of the inlet pressure or the increase of the cold mass fraction. This paper also tries to present an explanation for the maximum cooling effect and the maximum heating effect when the cold mass fraction is about 0.3 and 0.8, respectively.

Numerical Investigation of Flow Characteristics in Counter Flow Vortex Tube

Despite of simplicity in construction and operation, determination of nature of flow physics parameters inside vortex tube is highly difficult due to presence of highly swirling and turbulent flow inside very small dimensional domain of vortex tube. At this point of difficulty, the methodology of Computational Fluid Dynamics can significantly help the researchers. Present paper is intended to discuss the outcomes of CFD study carried out on counter flow vortex tube. Standard k-ɛ turbulence model has been used to replicate the turbulence inside vortex tube. This model is found to be very well capable of predicting flow features inside vortex tube. Results indicate that cold mass fraction is an important parameter affecting the temperature separation magnitude in vortex tube. Cooling power separation is also an important parameter to evaluate performance of counter flow vortex tube, instead of cold end temperature only. A recirculating secondary flow has also been identified near the inlet region of vortex tube, which is accompanied by backflow at cold end for smaller values of cold mass fraction. Results of present CFD study are in good agreement with experimental results.

A parametric study on the performance of a Ranque-Hilsch vortex tube using a CFD-based approach

In this paper, a numerical investigation is carried out to realize the behavior of a fabricated vortex tube. A computational fluid dynamics model is used to simulate the flow field structure in the tube in order to study the effects of various parameters on the performance and temperature separation. Numerical results such as temperature separation versus cold outlet mass fraction are obtained for a specific vortex tube with given inlet thermo physical properties. The numerical results are obtained for various amounts of cold outlet mass fractions. The calculated temperature distributions inside the Ranque-Hilsch Vortex Tube (RHVT) are simultaneously compared with available experimental results and a good agreement between them is noticed. It is found that increasing the inlet nozzle height improves the performance of the RHVT. The results also indicated that small values of cold mass fraction give best result in cold exit temperature difference.