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R. N. N. Koury - One of the best experts on this subject based on the ideXlab platform.
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Adiabatic Capillary Tube Model for a Carbon Dioxide Transcritical Cycle
International Journal of Air-Conditioning and Refrigeration, 2015Co-Authors: R. O. Nunes, R. N. Faria, N. Bouzidi, L. Machado, R. N. N. KouryAbstract:This paper presents a mathematical model for a Capillary Tube using CO 2 as fluid in steady flow transcritical cycle. The Capillary Tube is divided into N volumes controls and the model is based on applying the equations of conservation of energy, mass and momentum in the fluid in each of these volumes controls. The model calculates the mass flow of the CO 2 in the Capillary Tube as a function of CO 2 pressures at the inlet and outlet of the Capillary and the temperature of CO 2 at the input of this device. The Capillary Tube is considered to be adiabatic, and the limit of operation due to blocked flow condition is also considered in the model. The validation of the model was performed with experimental data and the results showed that the model is capable of predicting the mass flow in the Capillary Tube with errors less than 10%. The model was also used to determine the minimum diameter of the Capillary Tube for various conditions of CO 2 transcritical cycle.
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potential use of Capillary Tube thermal mass flow meters to measure residential natural gas consumption
Journal of Natural Gas Science and Engineering, 2015Co-Authors: Mahmood Farzanehgord, Ahmad Arabkoohsar, S Parvizi, Luiz Machado, R. N. N. KouryAbstract:Accurate natural gas measurement is an important issue especially in domestic usage level in which the lack of accurate measurement is well sensed. On the other hand, thermal mass flow meters are widely used in industries such as semiconductor manufacturing and chemical processes. Capillary Tube thermal mass flow meter is one of the most common types of thermal mass flow meters which are mostly used for low mass flow rates. In this work, the use of Capillary Tube mass flow meters for measuring residential natural gas consumption, where the flow rate is extremely low, was proposed. A Capillary Tube flow meter was simulated, two-dimensional steady state heat transfer in its sensor Tube was numerically analyzed and the sensitivity of this type of flow meter to Methane, as natural gas is mainly constituted by Methane, was investigated. In order to validate the simulation approach and conditions taken in this study, the simulation was also accomplished for Nitrogen, for which experimental data was available in the literature, leading to satisfactory results. Considering all the possible effective parameters, the uncertainty of the flow meter was also calculated to be 1.56%. Finally, the simulation was accomplished for a sample natural gas composition with 94.38% methane, resulting to an uncertainty equal to 1.83%.
Akhilesh Gupta - One of the best experts on this subject based on the ideXlab platform.
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An experimental study of the flow of R-407C in an adiabatic helical Capillary Tube
International Journal of Refrigeration, 2010Co-Authors: M K Mittal, Ravi Kumar, Akhilesh GuptaAbstract:Abstract This paper presents an experimental investigation of coiling effect on the flow of R-407C in an adiabatic helical Capillary Tube. It has been observed that the coiling of Capillary Tube significantly influences the mass flow rate of R-407C through the adiabatic helical Capillary Tube. For the sake of comparison, the experiments have also been conducted for straight Capillary Tube and it has been observed that the mass flow rates in coiled Capillary Tube are 5–10 percent less than those in a straight one. The data obtained from the experiments have been analyzed and non-dimensional correlations for the prediction of mass flow rate of R-407C in straight and helical Capillary Tube have been developed. The proposed correlations predict our experimental data in an error band of ±10 percent. The predictions by developed correlations are also in good agreement with the data of other investigators.
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numerical analysis of adiabatic flow of refrigerant through a spiral Capillary Tube
International Journal of Thermal Sciences, 2009Co-Authors: M K Mittal, Ravi Kumar, Akhilesh GuptaAbstract:In the present work, a homogenous model including the metastable liquid region has been developed for the adiabatic flow of refrigerant through the spiral Capillary Tube. In order to develop the model, both liquid region and two phase region have been discretized into infinitesimal segments to take into account the effect of varying radius of curvature of spiral Tube on the friction factor. The effect of the pitch of spiral on the mass flow rate of refrigerant and Capillary Tube length has been investigated. A comparison of flow characteristics of refrigerant R22 and its alternatives, i.e., R407C and R410A has been made at different operating conditions at the inlet of the Capillary Tube and it has been found that the flow characteristics of R22 and R407C are almost similar for a given condenser pressure and degree of subcooling at the inlet of Capillary Tube.
Neeraj Agrawal - One of the best experts on this subject based on the ideXlab platform.
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Flow behavior of spiral Capillary Tube for CO_2 transcritical cycle
Journal of Thermal Analysis and Calorimetry, 2020Co-Authors: Pravin Jadhav, Neeraj AgrawalAbstract:A numerical study has been carried out on the spiral Capillary Tube for the CO_2 transcritical cycle. The model is based on the basic principles of conservation of mass, momentum, and energy. The results of this model are validated with earlier published test results. The effect of various geometric parameters like Tube diameter, length, roughness, and pitch on the mass flow rate, cooling capacity, and COP has been calculated. The mass flow rate of the Tube is mostly influenced by the internal Tube diameter, as the diameter increases by 28%, the mass flow increases by 88%. A minor change in mass is observed with a change in pitch and surface roughness, as the pitch increases from 300 to 700 mm, and surface roughness increases by 14%, the mass flow rate and cooling capacity increase only by 2% and 1%, respectively. Similarly, the influence of various operating factors like gas cooler pressure, evaporator temperature, and gas cooler temperature is evaluated. A significant change in mass is observed with the change in gas cooler temperature, as the gas cooler temperature increases by 5%, the mass flow rate, cooling capacity, and COP decrease by 19%, 40%, and 33%, respectively. Relatively less variation in mass flow rate is observed with the change in evaporator temperature. As the evaporator temperature increases by 12%, the mass flow rate decreases by nearly 5.5%, and cooling capacity decreases by 18%. Energy and exergy analyses of a CO_2 transcritical system are carried out.
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flow characteristics of Capillary Tube with co2 transcritical refrigerant using new viscosity models for homogeneous two phase flow
International Journal of Low-carbon Technologies, 2011Co-Authors: Neeraj Agrawal, Souvik Bhattacharyya, Prasant NandaAbstract:New definitions of two-phase viscosity, based on its analogy with thermal conductivity of porous media, are investigated for transcritical Capillary Tube flow, with CO 2 as the refrigerant. Friction factor and pressure gradient quantifies are computed based on the proposed two-phase viscosity model using homogeneous modelling approach. The Proposed new models are assessed based on test results in the form of temperature profile and mass flow rate in a chosen Capillary Tube. It is shown that all the proposed models of two-phase viscosity models show a good agreement with the existing models such as McAdams et al., Cicchitti et al., etc. The influence of the viscosity model is found to be insignificant unlike to other conventional refrigerants in Capillary Tube flow. Copyright , Oxford University Press.
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flow rate prediction for an adiabatic Capillary Tube in a transcritical co2 system an analytic approach
International Journal of Low-carbon Technologies, 2010Co-Authors: Souvik Bhattacharyya, Neeraj Agrawal, Shashikant BurnwalAbstract:Transcritical nature of the CO 2 refrigeration cycle makes the Capillary Tube behavior distinctly different compared with a conventional subcritical system. A novel closed-form analytical solution is proposed to simulate the flow characteristics of an adiabatic Capillary Tube. Such an analytical solution is being proposed, for the first time, for the transcritical--superheated--two phase region in a CO 2 -based transcritical heating--cooling system. Improved K value relations based on Gaussian function for CO 2 are obtained employing MATLAB-based tools. Predictions by the proposed analytical model have been validated against carefully obtained test data and the observed agreement is fairly good. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.
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parametric study of a Capillary Tube suction line heat exchanger in a transcritical co2 heat pump cycle
Energy Conversion and Management, 2008Co-Authors: Neeraj Agrawal, Souvik BhattacharyyaAbstract:Abstract The Capillary Tube in a transcritical CO 2 system behaves differently as temperature and pressure are two independent parameters unlike those in a sub-critical cycle. A Capillary Tube-suction line heat exchanger (CL-SLHX) in a transcritical vapour compression cycle considering homogeneous two-phase flow is modelled in this study based on mass, energy and momentum equations. Effects of gas cooler temperature, evaporator temperature and internal diameter of Capillary Tube are investigated. Heat transfer rate is observed to be influenced by refrigerant quality, mass flow rate and the prevailing temperature difference. Heat transfer rate variation with gas cooler temperature is unique, recording an initial increase followed by a decrease. Frictional pressure drop influences the heat transfer; consequently, chances of re-condensation of refrigerant vapour are very marginal. Larger diameter of Capillary Tube leads to increase in refrigerant mass flow rate and increase in heat transfer rate as well. Shorter inlet adiabatic Capillary length with larger heat exchanger length is better for heat transfer. This study is an attempt to dispel the scepticism prevailing in transcritical CO 2 system community overemphasising the need for a throttle valve to control the optimum discharge pressure.
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non adiabatic Capillary Tube flow of carbon dioxide in a transcritical heat pump cycle
Energy Conversion and Management, 2007Co-Authors: Neeraj Agrawal, Souvik BhattacharyyaAbstract:Abstract Flow characteristics of a non-adiabatic Capillary Tube in a transcritical CO 2 heat pump cycle have been investigated employing homogeneous flow model. The model is based on fundamental equations of mass, energy and momentum which are solved simultaneously through an iterative process. Chosen empirical correlations are used for calculating viscosity and friction factor. Single and two phase heat transfer coefficients are estimated through appropriate empirical correlations. Sub-critical and super-critical thermodynamic and transport properties of CO 2 are calculated employing precision property subroutines. Three different cases are considered to optimise location of the heat exchange process: only single phase flow region, only two phase flow region, and both single and two phase flow regions. Heat transfer is more prominent in single phase region due to larger temperature difference between suction line fluid and Capillary Tube fluid. Relatively superior performance is obtained when the heat exchanger is placed in the single phase region. Chances of condensation are lower as refrigerant quality is relatively higher at the time of inception of vaporisation. Design and simulation are employed to investigate the refrigerant flow behaviour inside the non-adiabatic Capillary Tube.
Ravi Kumar - One of the best experts on this subject based on the ideXlab platform.
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Adiabatic flow characteristics of R-600a inside a helically coiled Capillary Tube
Applied Thermal Engineering, 2018Co-Authors: Santhosh Kumar Dubba, Ravi KumarAbstract:Abstract This paper presents an experimental investigation of a helically coiled Capillary Tube with an adiabatic flow of R-600a. The details of experimental facility for testing a Capillary Tube with different inlet sub-cooling degree and varying pressure are discussed. The effect of coil diameter, Capillary length, Capillary Tube diameter, sub-cooling degree and inlet pressure on mass flow rate are described. The degree of sub-cooling at the inlet of both straight and helical Capillary Tube is varied from 3 to 15 °C. The experimental results confirm that, the mass flow rate in the straight Capillary Tube is 1.5–16 percent higher than the coiled Capillary Tube. A non-dimensional correlation to predict the mass flow rate through a straight and helical coiled Capillary Tube has been developed with a good agreement of ±20 percent of measured mass flow rate.
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An experimental study of the flow of R-407C in an adiabatic helical Capillary Tube
International Journal of Refrigeration, 2010Co-Authors: M K Mittal, Ravi Kumar, Akhilesh GuptaAbstract:Abstract This paper presents an experimental investigation of coiling effect on the flow of R-407C in an adiabatic helical Capillary Tube. It has been observed that the coiling of Capillary Tube significantly influences the mass flow rate of R-407C through the adiabatic helical Capillary Tube. For the sake of comparison, the experiments have also been conducted for straight Capillary Tube and it has been observed that the mass flow rates in coiled Capillary Tube are 5–10 percent less than those in a straight one. The data obtained from the experiments have been analyzed and non-dimensional correlations for the prediction of mass flow rate of R-407C in straight and helical Capillary Tube have been developed. The proposed correlations predict our experimental data in an error band of ±10 percent. The predictions by developed correlations are also in good agreement with the data of other investigators.
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numerical analysis of adiabatic flow of refrigerant through a spiral Capillary Tube
International Journal of Thermal Sciences, 2009Co-Authors: M K Mittal, Ravi Kumar, Akhilesh GuptaAbstract:In the present work, a homogenous model including the metastable liquid region has been developed for the adiabatic flow of refrigerant through the spiral Capillary Tube. In order to develop the model, both liquid region and two phase region have been discretized into infinitesimal segments to take into account the effect of varying radius of curvature of spiral Tube on the friction factor. The effect of the pitch of spiral on the mass flow rate of refrigerant and Capillary Tube length has been investigated. A comparison of flow characteristics of refrigerant R22 and its alternatives, i.e., R407C and R410A has been made at different operating conditions at the inlet of the Capillary Tube and it has been found that the flow characteristics of R22 and R407C are almost similar for a given condenser pressure and degree of subcooling at the inlet of Capillary Tube.
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Experimental Study of the Flow of R-134a Through an Adiabatic Helically Coiled Capillary Tube
HVAC&R Research, 2008Co-Authors: Mohd. Kaleem Khan, Ravi Kumar, P.k. SahooAbstract:An experimental investigation was carried out to evaluate the flow characteristics of refrigerant R-134a through an adiabatic helically coiled Capillary Tube. The effect of various physical parameters like diameter and length of Capillary Tube, coil pitch, and inlet subcooling on the mass flow rate of R-134a was investigated. Moreover, the refrigerant mass flow rate through an instrumented Capillary Tube was also compared to that through a noninstrumented Capillary Tube. It was found that the provision of taps for pressure measurement on the Capillary Tube surface has a negligible effect on the mass flow rate of R-134a. Further, the coil pitch had a significant effect on the performance of the adiabatic helically coiled Capillary Tube. It was established that the coil pitch significantly influenced the mass flow rate through the adiabatic helically coiled Capillary Tube. It was concluded that the effect of coiling of the Capillary Tube reduces the mass flow rate by 5% to 15%, as compared to those of the s...
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An experimental study of the flow of R-134a inside an adiabatic spirally coiled Capillary Tube
International Journal of Refrigeration, 2008Co-Authors: Mohd. Kaleem Khan, Ravi Kumar, P.k. SahooAbstract:Abstract This paper presents an experimental investigation for the flow of R-134a inside an adiabatic spirally coiled Capillary Tube. The effect of various geometric parameters like Capillary Tube diameter, length and coil pitch for different Capillary Tube inlet subcoolings on the mass flow rate of R-134a through the spiral Capillary Tube geometry has been investigated. It has been established that the coil pitch significantly influences the mass flow rate of R-134a through the adiabatic spiral Capillary Tube. The effect of providing pressure taps on the Capillary Tube surface has a negligible effect on the mass flow rate through the Capillary Tube. It has been concluded that the effect of coiling of Capillary Tube reduces the mass flow rate by 5–15% as compared to those of the straight Capillary Tube operating under similar conditions. The data obtained from the experiments are analyzed and a semi-empirical correlation has been developed. The proposed correlation predicts more than 91% of the mass flow rate which is in agreement with measured data in an error band of ±10%.
Souvik Bhattacharyya - One of the best experts on this subject based on the ideXlab platform.
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flow characteristics of Capillary Tube with co2 transcritical refrigerant using new viscosity models for homogeneous two phase flow
International Journal of Low-carbon Technologies, 2011Co-Authors: Neeraj Agrawal, Souvik Bhattacharyya, Prasant NandaAbstract:New definitions of two-phase viscosity, based on its analogy with thermal conductivity of porous media, are investigated for transcritical Capillary Tube flow, with CO 2 as the refrigerant. Friction factor and pressure gradient quantifies are computed based on the proposed two-phase viscosity model using homogeneous modelling approach. The Proposed new models are assessed based on test results in the form of temperature profile and mass flow rate in a chosen Capillary Tube. It is shown that all the proposed models of two-phase viscosity models show a good agreement with the existing models such as McAdams et al., Cicchitti et al., etc. The influence of the viscosity model is found to be insignificant unlike to other conventional refrigerants in Capillary Tube flow. Copyright , Oxford University Press.
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flow rate prediction for an adiabatic Capillary Tube in a transcritical co2 system an analytic approach
International Journal of Low-carbon Technologies, 2010Co-Authors: Souvik Bhattacharyya, Neeraj Agrawal, Shashikant BurnwalAbstract:Transcritical nature of the CO 2 refrigeration cycle makes the Capillary Tube behavior distinctly different compared with a conventional subcritical system. A novel closed-form analytical solution is proposed to simulate the flow characteristics of an adiabatic Capillary Tube. Such an analytical solution is being proposed, for the first time, for the transcritical--superheated--two phase region in a CO 2 -based transcritical heating--cooling system. Improved K value relations based on Gaussian function for CO 2 are obtained employing MATLAB-based tools. Predictions by the proposed analytical model have been validated against carefully obtained test data and the observed agreement is fairly good. Copyright The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.
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parametric study of a Capillary Tube suction line heat exchanger in a transcritical co2 heat pump cycle
Energy Conversion and Management, 2008Co-Authors: Neeraj Agrawal, Souvik BhattacharyyaAbstract:Abstract The Capillary Tube in a transcritical CO 2 system behaves differently as temperature and pressure are two independent parameters unlike those in a sub-critical cycle. A Capillary Tube-suction line heat exchanger (CL-SLHX) in a transcritical vapour compression cycle considering homogeneous two-phase flow is modelled in this study based on mass, energy and momentum equations. Effects of gas cooler temperature, evaporator temperature and internal diameter of Capillary Tube are investigated. Heat transfer rate is observed to be influenced by refrigerant quality, mass flow rate and the prevailing temperature difference. Heat transfer rate variation with gas cooler temperature is unique, recording an initial increase followed by a decrease. Frictional pressure drop influences the heat transfer; consequently, chances of re-condensation of refrigerant vapour are very marginal. Larger diameter of Capillary Tube leads to increase in refrigerant mass flow rate and increase in heat transfer rate as well. Shorter inlet adiabatic Capillary length with larger heat exchanger length is better for heat transfer. This study is an attempt to dispel the scepticism prevailing in transcritical CO 2 system community overemphasising the need for a throttle valve to control the optimum discharge pressure.
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non adiabatic Capillary Tube flow of carbon dioxide in a transcritical heat pump cycle
Energy Conversion and Management, 2007Co-Authors: Neeraj Agrawal, Souvik BhattacharyyaAbstract:Abstract Flow characteristics of a non-adiabatic Capillary Tube in a transcritical CO 2 heat pump cycle have been investigated employing homogeneous flow model. The model is based on fundamental equations of mass, energy and momentum which are solved simultaneously through an iterative process. Chosen empirical correlations are used for calculating viscosity and friction factor. Single and two phase heat transfer coefficients are estimated through appropriate empirical correlations. Sub-critical and super-critical thermodynamic and transport properties of CO 2 are calculated employing precision property subroutines. Three different cases are considered to optimise location of the heat exchange process: only single phase flow region, only two phase flow region, and both single and two phase flow regions. Heat transfer is more prominent in single phase region due to larger temperature difference between suction line fluid and Capillary Tube fluid. Relatively superior performance is obtained when the heat exchanger is placed in the single phase region. Chances of condensation are lower as refrigerant quality is relatively higher at the time of inception of vaporisation. Design and simulation are employed to investigate the refrigerant flow behaviour inside the non-adiabatic Capillary Tube.
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adiabatic Capillary Tube flow of carbon dioxide in a transcritical heat pump cycle
International Journal of Energy Research, 2007Co-Authors: Neeraj Agrawal, Souvik BhattacharyyaAbstract:Flow characteristics of an adiabatic Capillary Tube in a transcritical CO2 heat pump system have been investigated employing the homogeneous model. The model is based on fundamental equations of mass, energy and momentum which are solved simultaneously. Two friction factor empirical correlations (Churchill, Lin et al., Int. J. Multiphase Flow 1991; 17(1):95–102) and four viscosity models (Mcadams, Cicchitti, Dukler and Lin) are comparatively used to investigate the flow characteristics. Choked condition at the outlet is also investigated for maximum mass flow rate. Subcritical and supercritical thermodynamic and transport properties of CO2 are calculated employing a precision property code. Choice of viscosity model causes minor variation in results unlike in chlorofluorocarbons (CFCs) refrigerants. Relationships between cooling capacity with Capillary Tube diameter, length and maximum mass flow rate are presented. A lower evaporating temperature yields a larger cooling capacity due to the unique thermodynamic properties of CO2. It is also observed that an optimum cooling capacity exists for a specified Capillary Tube. Copyright © 2006 John Wiley & Sons, Ltd.
