scholarly journals The second law analysis of natural gas behavior within a vortex tube

2013 ◽  
Vol 17 (4) ◽  
pp. 1079-1092 ◽  
Author(s):  
Mahyar Kargaran ◽  
A. Arabkoohsar ◽  
S.J. Hagighat-Hosini ◽  
V. Farzaneh-Kord ◽  
Mahmood Farzaneh-Gord
Keyword(s):  
Natural Gas ◽  
Entropy Generation ◽  
Vortex Tube ◽  
Tube Length ◽  
Orifice Diameter ◽  
Working Fluid ◽  
Energy Separation ◽  
Second Law ◽  
Gas Streams ◽  
Mass Fractions

Vortex tube is a simple device without a moving part which is capable of separating hot and cold gas streams from a higher pressure inlet gas stream. The mechanism of energy separation has been investigated by several scientists and second law approach has emerged as an important tool for optimizing the vortex tube performance. Here, a thermodynamic model has been used to investigate vortex tube energy separation. Further, a method has been proposed for optimizing the vortex tube based on the rate of entropy generation obtained from experiments. Also, an experimental study has been carried out to investigate the effects of the hot tube length and cold orifice diameter on entropy generation within a vortex tube with natural gas as working fluid. A comparison has been made between air and natural gas as working fluids. The results show that the longest tube generates lowest entropy for NG. For air, it is middle tube which generates lowest entropy. Integration of entropy generation for all available cold mass fractions unveiled that an optimized value for hot tube length and cold orifice diameter is exist.

scholarly journals An Investigation of a Micro-Scale Ranque-Hilsch Vortex Tube

2006 ◽  
Author(s):  
Amar F. Hamoudi ◽  
Amir Fartaj ◽  
Gary W. Rankin
Keyword(s):  
Reynolds Number ◽  
Vortex Tube ◽  
Operating Conditions ◽  
Tube Length ◽  
Orifice Diameter ◽  
Working Fluid ◽  
Dimensionless Temperature ◽  
Separation Performance ◽  
Micro Scale ◽  
Cold Mass

The results of an experimental investigation of the energy separation performance of a micro-scale Ranque-Hilsch vortex tube are presented in this paper. The micro-scale vortex tube is 2 mm in diameter and constructed using a layered technique from multiple pieces of Plexiglas and aluminum. Four inlet slots, symmetrically located around the tube, form the vortex. The hydraulic diameter of each inlet slot and the orifice diameter for the cold exit are 229 and 800 microns respectively. The working fluid is low pressure, non-dehumidified compressed air at room temperature. The rate of the hot gas flow is varied by means of a control valve to achieve different values of cold mass fraction. The mass flow rates, temperatures and pressures of the supply and outlet flows are measured and the performance of the device presented. The supply channel Reynolds number is varied over a considerable range which extends into the laminar regime in order to determine the operating conditions for cooling. An increase in dimensionless temperature is found in both the cold and hot outlets as supply nozzle Reynolds number increases from zero. Maximum values occur at a Reynolds number of approximately 500 and the cold flow dimensionless temperature becomes negative at about 2500. Although the optimum cold mass ratio is higher than the conventional tubes, the effect on performance of tube length and cold exit diameter is similar to the conventional devices.

Experimental and Numerical Investigation on Effect of Convergent Angle and Cold Orifice Diameter on Thermal Performance of Convergent Vortex Tube

2015 ◽  
Vol 7 (4) ◽  
Author(s):  
Seyed Ehsan Rafiee ◽  
M. M. Sadeghiazad ◽  
Nasser Mostafavinia
Keyword(s):  
Numerical Investigation ◽  
Cfd Simulation ◽  
Vortex Tube ◽  
Orifice Diameter ◽  
Energy Separation ◽  
Separation Procedure ◽  
Laboratory Setup ◽  
Air Temperatures ◽  
Invaluable Tool ◽  
Air Separator

The vortex tube (VT) air separator is an invaluable tool which has the ability to separate a high-pressure fluid into the cold and hot fluid streams. The hot tube is a main part of the air separator VT which the energy separation procedure happens along this part. This research has been done to analyze the effect of the convergent angle and cold orifice diameter on the thermal efficiency of a convergent vortex tube (CVT). The CVT is linked to an air pipeline with the fixed pressure of 6.5 bar. The convergent hot tube angle is varied over the range of 1 deg to 9 deg. The consideration of the main angle effect denotes that the highest thermal ability could be achieved at β = 5 deg. The laboratory setup results show this subject that the optimization of the hot tube convergent angle elevates the cooling and heating effectiveness around 32.03% and 26.21%, respectively. Experiments denoted that both cooling capability and heating effectiveness reach the highest magnitudes when the DCold is around 9 mm. After these two stages, the optimized CVT was capable of decreasing and rising air temperatures at the cold and the hot sides up to 9.05 K (42.89%) and 10.48 K (44.74%), respectively. A computational fluid dynamics (CFD) model was employed to predict the performance of the air flow inside the CVT. The numerical investigation was done by full 3D steady-state CFD-simulation using fluent6.3.26. The results show that the agreement between computation predictions and laboratory measurements is fairly good.

scholarly journals CFD Analysis of Energy Separation in Ranque-Hilsch Vortex Tube at Cryogenic Temperature

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
T. Dutta ◽  
K. P. Sinhamahapatra ◽  
S. S. Bandyopadhyay
Keyword(s):  
Cryogenic Temperature ◽  
Vortex Tube ◽  
Atmospheric Temperature ◽  
Working Fluid ◽  
Energy Separation ◽  
Cfd Analysis ◽  
Sensible Heat ◽  
Cfd Model ◽  
Parametric Sensitivity ◽  
Fluid Layers

Study of the energy separation phenomenon in vortex tube (VT) at cryogenic temperature (temperature range below 123 K) has become important because of the potential application of VT as in-flight air separator in air breathing propulsion. In the present study, a CFD model is used to simulate the energy separation phenomenon in VT with gaseous air at cryogenic temperature as working fluid. Energy separation at cryogenic temperature is found to be considerably less than that obtained at normal atmospheric temperature due to lower values of inlet enthalpy and velocity. Transfer of tangential shear work from inner to outer fluid layers is found to be the cause of energy separation. A parametric sensitivity analysis is carried out in order to optimize the energy separation at cryogenic temperature. Also, rates of energy transfer in the form of sensible heat and shear work in radial and axial directions are calculated to investigate the possible explanation of the variation of the hot and cold outlet temperatures with respect to various geometric and physical input parameters.

Investigations of Energy Separation Effect in Vortex Tube for Real Gases

2013 ◽  
Vol 724-725 ◽  
pp. 1293-1300
Author(s):  
Jing Tang ◽  
Wen Chuan Wang ◽  
Xiang Jun Fang ◽  
Shi Long Liu ◽  
Wen Long Sun
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Vortex Tube ◽  
Ideal Gas ◽  
Energy Separation ◽  
Separation Effect ◽  
Real Gas ◽  
Real Gas Effect ◽  
Effect Difference ◽  
Gas Effect

This paper aims to investigate real gases energy separation effect such as real natural gas, CH4 and C2H4 in vortex tube. Energy separation phenomena of real natural gas (RNG) were investigated by means of three-dimensional Computational Fluid Dynamics (CFD) method. Flow fields of ideal natural gas (ING), or RNG in low and high pressure were simulated. The results main factors were found that affect the separation effect. At the same time, this paper has illustrated the effect and tendency of energy separation with real gas in the tube under the same cold mass fraction and pressure ratio. The results show low pressure ideal gas and real gas energy separation effect difference about 3-4°C, the real gas effect is not obvious; High pressure real natural gas (HPRNG) and ideal gas (HPING) effect difference is 13-14°C, the real gas effect is obvious; CH4 (LRCH4) and C2H4 (HRC2H4) energy separation effect is obvious and effect of real gas is generated.

scholarly journals CFD simulation of length to diameter ratio effects on the energy separation in a vortex tube

2011 ◽  
Vol 15 (3) ◽  
pp. 833-848 ◽  
Author(s):  
Reza Bramo ◽  
Nader Pourmahmoud
Keyword(s):  
Stagnation Point ◽  
Cfd Simulation ◽  
Vortex Tube ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Diameter Ratio ◽  
Tube Length ◽  
Energy Separation ◽  
Computational Fluid Dynamics Analysis ◽  
Length To Diameter Ratio

The objective of the present computational fluid dynamics analysis is an attempt to investigate the effect of length to diameter ratio on the fluid flow characteristics and energy separation phenomenon inside the Ranque-Hilsch vortex tube. In this numerical study, performance of Ranque-Hilsch vortex tubes (RHVT), with length to diameter ratios (L/D) of 8, 9.3, 10.5, 20.2, 30.7 and 35 with six straight nozzles was investigated. It includes generating better understanding of the effects of the stagnation point location on the performance of RHVT. It was found that the best performance was obtained when the ratio of vortex tube length to the diameter was 9.3 and also fort this case the stagnation point was found to be the farthest from the inlet. The results show that the closer distance to the hot end is produced the larger magnitude of the temperature difference. Computed results show good agreement with published experimental results.

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

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Gaurav Sharma ◽  
Sumana Ghosh ◽  
Srinibas Karmakar
Keyword(s):  
Flow Field ◽  
Computational Fluid Dynamic ◽  
Vortex Tube ◽  
Fluid Dynamic ◽  
Flow Reversal ◽  
Working Fluid ◽  
Energy Separation ◽  
Phase Flow ◽  
Thin Wall ◽  
Two Phase

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.

SEN Analysis of Stratified Hot Water Heat Stores With Respect to Axial Position and Number of Charging-Discharging Equipments

2008 ◽  
Author(s):  
Varghese Panthalookaran
Keyword(s):  
Entropy Generation ◽  
Fluid Dynamic ◽  
Second Law Of Thermodynamics ◽  
Efficiency Index ◽  
Hot Water ◽  
Dead Volume ◽  
Axial Position ◽  
Working Fluid ◽  
Second Law ◽  
Definition Of

SEN analysis [Solar Energy, 2007, Vol. 81, pp. 1043–1054] is a robust characterization method for stratified thermal energy stores (TES). It integrates the concerns of the First and Second Law of Thermodynamics into single efficiency index. The First Law concern is incorporated into the definition of SEN efficiency index through energy response factor (ER) and the Second Law concern through entropy generation ratio (REG). SEN analysis thus estimates the ability of a TES to store energy and exergy. In the current paper SEN analysis is utilized to characterize hot water heat stores (HWHS) with respect to the axial position and number of charging/discharging equipments they possess. Diffusers or flow-guides are used as charging-discharging equipments in view of reducing turbulent mixing within the HWHS, especially in the entrance and exit ports. For HWHS charging-discharging equipments are commonly positioned in the top-most and bottom-most regions of the HWHS in order to avoid development of dead volume, i.e., volume that does not take part in the charging-discharging process. Axially placed conical diffusers are observed to circumvent the issue of dead volumes. However, the effect of their axial position on the entropy generation is not yet studied. Further, one may use intermediate charging-discharging equipment in association with the original pair in order to feed or withdraw the working fluid into/from the HWHS at different heights. This paper provides a detailed analysis of the position and number of axially placed conical diffusers with zero diffuser angles inside a cylindrical HWHS. The thermal field information obtained from a computational fluid dynamic (CFD) analysis is subjected to the SEN analysis to achieve required design insights.

CFD Study on Supersonic Ejectors Used for Suction of Two Different Gases

2015 ◽  
Author(s):  
Mohsen Tavakol ◽  
Maziar Shafaee
Keyword(s):  
Numerical Simulation ◽  
Water Vapor ◽  
Mass Fraction ◽  
Pure Water ◽  
Variable Mass ◽  
Working Fluid ◽  
Gas Streams ◽  
Mass Fractions ◽  
Suction Flow ◽  
Different Gases

In ejector refrigeration cycles, ejector working fluids include various refrigerants with different properties. In some cases, ejector works with mixture of two different refrigerants; that each refrigerant have distinct properties. The purpose of this paper is to evaluate the performance of an ejector used for suction of a mixture of air and water vapor. In this regard, the ejector performance was numerically studied under the operating condition that a mixture of air and steam with variable mass fractions, were sucked into the ejector. With the help of numerical simulation, various conditions for two perfect gas streams of air and water vapor were investigated. Initially, the numerical simulation was carried out for the case that pure water vapor was considered as the working fluid of ejector. After validation of initial case with experimental data, numerical method was expanded for a specific case that, water vapor was considered as the working fluid of motive flow and a mixture of air and water vapor was considered for suction flow. Numerical simulations were done for different mass fraction of air and water vapor for suction flow mixture. Results indicated that, variations of the mass fraction of air in suction flow, leads to obvious changes in ejector performance. Also, it was observed that the increment of suction flow pressure, leads to increment of the ejector performance sensitivity to variations of suction flow mass fraction.

Second Law Analysis of Evaporator for Organic Rankine Cycle System

2008 ◽  
Author(s):  
Wei Gu ◽  
Yiwu Weng
Keyword(s):  
Entropy Generation ◽  
Temperature Difference ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Second Law ◽  
Fluid Temperature ◽  
Working Fluids ◽  
Second Law Analysis

The evaporator is a key component for Organic Rankine Cycle (ORC) system. Second law analysis of the evaporator was carried out in this work. Three processes were included and studied: pre-heating, boiling and super-heating. Firstly, ε–NTU method was applied to study the heat transfer area of evaporator. Then, internal entropy generation for three processes of evaporator was studied by entropy generation number. Thirdly, entropy generation distribution (ds/dA) was predicted by analyzing the temperature difference between the two sides of single stage counter-flow evaporator, for both pure and mixed working fluids. The results show that increase of waste heat fluid temperature increases internal irreversibility, and higher evaporator pressure decreases this irreversibility. The results also show that temperature difference at the end part of boiling process is larger for pure working fluids; and for mixed fluids, because of its’ increasing boiling temperature, this irreversibility decreases remarkably. In conclusion, second law analysis shows that the evaporating pressure plays a key role in evaporator design for ORC system; and both evaporator and working fluid should be well designed to minimize the second law loss.

Research of Vortex Tube Energy Separation

2013 ◽  
Author(s):  
Wen-long Sun ◽  
Xiang-jun Fang ◽  
Qi-tai Eri ◽  
Wen-chuan Wang
Keyword(s):  
Numerical Simulations ◽  
Vortex Tube ◽  
Energy Separation ◽  
Gas Flows ◽  
Complex Flows ◽  
Mass Fractions ◽  
Key Factor ◽  
Calculation Results ◽  
Cold Mass ◽  
Made In

Since the vortex tube was invented, a variety of theoretical explanations were proposed to reveal the process and mechanism of energy separation in it. With simple structure but complex flows, it was hard to solve the two problems. Comparisons of the numerical simulations and experiments under different cold mass fractions (μc) in the vortex tube were made in this paper. The trend of numerical simulations was convinced by analyzing the experimental data. The radial and axial distributions of three types of gas flows and the contours of temperature and pressure were obtained from the calculation results under different μc. The key factor affecting the energy separation in the vortex tube was found and the explanation of energy separation process in the vortex tube was proposed by analyzing the results. The analysis showed that the energy separation was deeply related to the exchange of velocity. At last, the explanation was validated by the simulations with the change of throat area in the nozzles.

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