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Somchai Wongwises - One of the best experts on this subject based on the ideXlab platform.
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A comparison of flow characteristics of refrigerants flowing through adiabatic straight and helical Capillary Tubes
International Communications in Heat and Mass Transfer, 2011Co-Authors: Sukkarin Chingulpitak, Somchai WongwisesAbstract:This paper presents a numerical investigation of the flow characteristics of helical Capillary Tubes compared with straight Capillary Tubes. The homogenous two-phase flow model developed is based on the conservation of mass, energy, and momentum of the fluids in the Capillary tube. This model is validated by comparing it with the experimental data of both straight and helical Capillary Tubes. Comparisons of the predicted results between the straight and helical Capillary Tubes are presented, together with the experimental results for straight Capillary Tubes obtained by previous researchers. The results show that the refrigerant flowing through the straight Capillary tube provides a slightly lower pressure drop than that in the helical Capillary tube, which resulted in a total tube length that was longer by about 20%. In addition, for the same tube length, the mass flow rate in the helical Capillary tube with a coil diameter of 40 mm is 9% less than that in the straight tube. Finally, the results obtained from the present model show reasonable agreement with the experimental data of helical Capillary Tubes and can also be applied to predict the flow characteristics of straight Capillary Tubes by changing to straight tube friction factors, for which Churchill's equation was used in the present study.
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Effects of coil diameter and pitch on the flow characteristics of alternative refrigerants flowing through adiabatic helical Capillary Tubes
International Communications in Heat and Mass Transfer, 2010Co-Authors: Sukkarin Chingulpitak, Somchai WongwisesAbstract:Abstract This paper presents the effects of various geometries of helical Capillary Tubes on the flow characteristics of alternative refrigerants flowing through adiabatic helical Capillary Tubes. The theoretical model is based on the conservation of mass, energy and momentum of fluids in the Capillary tube. The two-phase flow model developed was based on a homogenous flow assumption. The model was validated by comparing it with the experimental data of published in literature for R-22, particularly various pairs of refrigerants. It was found conventional refrigerants had lower Capillary lengths than alternative refrigerants. For all pairs, the numerical results showed that the traditional refrigerants consistently gave lower pressure drops for both single-phase and two-phase flows, which resulted in longer tube lengths. The results show that coil diameter variation (less than 300 mm) for helical Capillary tube geometries affected the length of helical Capillary Tubes. However, pitch variation (more than 300 mm) had no significant effect on the length of helical Capillary Tubes. This adiabatic helical Capillary tube model can be used to integrate system models working with alternative refrigerants for design and optimisation.
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two phase flow model of refrigerants flowing through helically coiled Capillary Tubes
Applied Thermal Engineering, 2010Co-Authors: Sukkarin Chingulpitak, Somchai WongwisesAbstract:This paper presents a numerical study of the flow characteristics of refrigerants flowing through adiabatic helically coiled Capillary Tubes. The theoretical model is based on conservation of mass, energy and momentum of the fluids in the Capillary tube. The two-phase flow model developed was based on the homogeneous flow assumption. The viscosity model was also based on recommendations from the literature. The developed model can be considered as an effective tool for designing and optimizing Capillary Tubes working with newer alternative refrigerants. The model is validated by comparison with the experimental data of Kim et al. (2002) for R-22, R-407C and R-410A, and Zhou and Zhang (2006) for R-22. The results obtained from the present model show reasonable agreement with the experimental data. The proposed model can be used to design helical Capillary Tubes working with various refrigerants.
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Correlations for sizing adiabatic Capillary Tubes
International Journal of Energy Research, 2003Co-Authors: Visinee Trisaksri, Somchai WongwisesAbstract:This paper presents new correlations for the practical sizing of adiabatic Capillary Tubes used as an expansion device in small refrigerating and air-conditioning systems. The governing equation based on conservation of mass, energy and momentum is modelled. The developed model is used as an effective tool for studying the effects of relevant parameters on Capillary tube length and developing the correlation. In this model, Colebrook's equation is used to determine the friction factor. The two-phase viscosity models are varied depending on the type of refrigerant and are based on the recommendations from past research. By varying the model input parameters, it is possible to show that for all refrigerants, the length decreases as the mass flow rate increases, increases as subcooling increases, increases as tube diameter increases, decreases as tube roughness increases and increases as condensing temperature increases. After the developed model is validated by comparing with existing experimental data, correlations for sizing Capillary Tubes, which contains the relevant parameters, namely condensing temperature, degree of subcooling, refrigerant mass flow rate, Capillary tube inner diameter and roughness, are presented. Different from previous studies, correlations are presented for an extensive number of refrigerants and a wide range of operations. The developed correlations are validated with previous studies and found to agree well with the experimental data. The correlations can be used to integrate with system models working with alternative refrigerants for practical design and optimization. Copyright © 2003 John Wiley & Sons, Ltd.
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flow characteristics of pure refrigerants and refrigerant mixtures in adiabatic Capillary Tubes
Applied Thermal Engineering, 2001Co-Authors: Somchai Wongwises, Worachet PirompakAbstract:Abstract This paper provides the results of simulations using an adiabatic Capillary tube model which is developed to study the flow characteristics in adiabatic Capillary Tubes used as a refrigerant control device in refrigerating systems. The developed model can be considered as an effective tool of Capillary Tubes' design and optimization for systems using newer alternative refrigerants. The model is validated by comparing with the experimental data of Li et al. and Mikol for R12 and Melo et al. for R134a. In particular, it has been possible to compare various pairs of refrigerants. It is found that the conventional refrigerants consistently give longer Capillary lengths than the alternative refrigerants. For all pairs, the conventional refrigerant consistently give lower pressure drops for both single-phase and two-phase flow which resulted in longer tube lengths. In addition, an example of Capillary tube selection chart developed from the present numerical simulation is shown. The chart can be practically used to select the Capillary tube size from the flow rate and flow condition or to determine mass flow rate directly from a given Capillary tube size and flow condition. The results of this study are of technological importance for the efficient design when systems are assigned to utilize various alternative refrigerants.
Cláudio Melo - One of the best experts on this subject based on the ideXlab platform.
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A two-fluid model for refrigerant flow through adiabatic Capillary Tubes
Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2014Co-Authors: André Luiz Seixlack, Alvaro T. Prata, Cláudio MeloAbstract:This work presents a numerical model to simulate refrigerant flow through Capillary Tubes, commonly used as expansion devices in refrigeration systems. The flow is divided in a single-phase region, where the refrigerant is in the subcooled liquid state, and a region of two-phase flow. The Capillary tube is considered straight and horizontal. The flow is taken as one-dimensional and adiabatic. Steady-state condition is also assumed and the metastable flow phenomena are neglected. The two-fluid model, considering the hydrodynamic and thermal non-equilibrium between the liquid and vapor phases, is applied to the two-phase flow region. Comparisons are made with experimental measurements of the mass flow rate and pressure distribution along two Capillary Tubes working with refrigerant R-134a in different operating conditions. The results indicate that the present model provides a better estimation than the commonly employed homogeneous model. Some computational results referring to the quality, void fraction, velocities, and temperatures of each phase are presented and discussed.
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a study of transcritical carbon dioxide flow through adiabatic Capillary Tubes
International Journal of Refrigeration-revue Internationale Du Froid, 2009Co-Authors: Diogo Londero Da Silva, Cláudio Melo, J. M. Goncalves, Christian J L Hermes, Gustavo C WeberAbstract:This paper advances a study of the transcritical expansion of carbon dioxide (R-744, CO2) through adiabatic Capillary Tubes. The influence of both operating conditions (inlet and exit pressures, inlet temperature) and tube geometry (Capillary diameter and tube length) on the CO2 mass flow rate was experimentally evaluated using a purpose-built testing facility with a strict control of the measured variables. A dimensionless correlation to predict the refrigerant mass flow rate as a function of tube geometry and operating conditions was developed. In addition, a theoretical model was put forward based on the mass, energy and momentum conservation principles. The model results were compared with experimental data, when it was found that the model predicts 95% of the measured refrigerant mass flow rate within an error band of ±10%. The model was also employed to advance the knowledge about the transcritical carbon dioxide flow through adiabatic Capillary Tubes.
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An experimental analysis of adiabatic Capillary Tubes
Applied Thermal Engineering, 1999Co-Authors: Cláudio Melo, R. T. S. Ferreira, C.boabaid Neto, J. M. Goncalves, M.m. MezavilaAbstract:Abstract This paper presents an experimental study on Capillary Tubes commonly used as expansion devices in household refrigerators and freezers. The paper discusses the details of the experimental facility that has been developed and used to generate reliable experimental data within an acceptable level of uncertainty. The investigations include the effect of Capillary length, Capillary diameter, refrigerant subcooling, condensing pressure and type of refrigerant on the mass flow-rates through the capillaries. The experiments were performed with three refrigerants, namely CFC-12, HFC-134a and HC-600a, and at different condensing pressures and levels of subcooling under choked flow conditions. Eight capillaries with different combinations of lengths, diameters and tube roughnesses were used, and extensive data (exceeding 1000 sets) were collected. A conventional, dimensional analysis was performed to derive correlations to predict the mass flow rates for different refrigerants. The predictions from the developed correlations are found to be in good agreement with the measured data and other studies in the literature. The correlations would be very valuable in the design exercise of Capillary Tubes for alternative refrigerants in future.
A S Rupasinghe - One of the best experts on this subject based on the ideXlab platform.
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an homogeneous model for adiabatic Capillary Tubes
Applied Thermal Engineering, 1998Co-Authors: Pradeep Bansal, A S RupasingheAbstract:Abstract This paper presents a homogeneous two-phase flow model, CAPIL, which is designed to study the performance of adiabatic Capillary Tubes in small vapour compression refrigeration systems, in particular household refrigerators and freezers. The model is based on the fundamental equations of conservation of mass, energy and momentum that are solved simultaneously through iterative procedure and Simpson's rule. The model uses empirical correlations for single-phase and two-phase friction factors and also accounts for the entrance effects. The model uses the REFPROP data base where the Carnahan-Starling-DeSantis equation of state is used to calculate the refrigerant properties. The model includes the effect of various design parameters, namely the tube diameter, tube relative roughness, tube length, level of subcooling and the refrigerant flow rate. The model is validated with earlier models over a range of operating conditions and is found to agree reasonably well with the available experimental data for HFC-134a.
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An empirical model for sizing Capillary Tubes
International Journal of Refrigeration, 1996Co-Authors: Pradeep Bansal, A S RupasingheAbstract:Abstract This paper presents an empirical model that has been developed to size adiabatic and non-adiabatic Capillary Tubes for small vapour compression refrigeration systems, in particular, household refrigerators and freezers. The model is based on the assumption that the length of a Capillary tube is dependent on five primary variables, namely the Capillary tube inner diameter, the mass flow rate of the refrigerant in the Capillary tube, the pressure difference between highside and lowside, the refrigerant subcooling at Capillary inlet and the relative roughness of the Capillary tube material. The model is validated with previous studies over a range of operating conditions and is found to agree reasonably well with the experimental data for HFC134a.
Yongchan Kim - One of the best experts on this subject based on the ideXlab platform.
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Experimentation and modeling of refrigerant flow through coiled Capillary Tubes
International Journal of Refrigeration, 2007Co-Authors: Cha-sik Park, Sunil Lee, Hoon Kang, Yongchan KimAbstract:Abstract Air-conditioners use spirally coiled Capillary Tubes as an expansion device to enhance compactness of the unit. However, most empirical correlations for predicting refrigerant flow rate through Capillary Tubes were developed for straight Capillary Tubes without consideration of coiled effects. The objectives of this study are to investigate the flow characteristics of the coiled Capillary Tubes and to develop a generalized correlation for the mass flow rate through the coiled Capillary Tubes. The mass flow rate of R22 through the coiled Capillary Tubes and straight Capillary Tubes was measured for various operating conditions and tube geometries. The mass flow rates of the coiled Capillary Tubes decreased by 5–16% more than those of the straight Capillary Tubes at the same operating conditions. A generalized correlation for predicting refrigerant mass flow rate through coiled Capillary Tubes was developed by introducing the parameter of Capillary equivalent length. The present correlation showed good predictions with the present database for R22, R407C and R410A in the straight and coiled Capillary Tubes, yielding average and standard deviations of 0.24% and 4.4%, respectively.
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an empirical correlation and rating charts for the performance of adiabatic Capillary Tubes with alternative refrigerants
Applied Thermal Engineering, 2004Co-Authors: Jongmin Choi, Yongchan Kim, Jin Taek ChungAbstract:With the phaseout of conventional refrigerants, refrigeration and air conditioning systems must be redesigned to improve system performance and reliability with alternative refrigerants. In this study, a generalized correlation for the prediction of refrigerant flow rate through adiabatic Capillary Tubes is developed by generating dimensionless parameters for operating conditions, Capillary tube geometry, and refrigerant properties using the Buckingham Pi theorem. The database for the present correlation includes extensive experimental data for R12, R22, R134a, R152a, R407C, and R410A obtained from the open literature. The present correlation, which has a relatively simpler form to employ, yields a mean deviation of 5.4% and a standard deviation of 6.5% from the database. In addition, rating charts for predicting refrigerant flow rate through adiabatic Capillary Tubes are generated for R12, R22, R134a, R152a, R407C, and R410A.
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a generalized correlation for refrigerant mass flow rate through adiabatic Capillary Tubes
International Journal of Refrigeration-revue Internationale Du Froid, 2003Co-Authors: Jongmin Choi, Yongchan Kim, Ho Young KimAbstract:Abstract A Capillary tube is a common expansion device used in small sized refrigeration and air-conditioning systems. A generalized correlation for refrigerant flow rate in adiabatic Capillary Tubes is developed by implementing dimensionless parameters based on extensive experimental data for R-22, R-290, and R-407C measured in this study. Dimensionless parameters are derived from the Buckingham Pi theorem, considering the effects of tube inlet conditions, Capillary tube geometry, and refrigerant properties on mass flow rate. The generalized correlation yields good agreement with the present data for R-22, R-290, and R-407C with average and standard deviations of 0.9 and 5.0%, respectively. Approximately 97% of the present data are correlated within a relative deviation of ±10%. Further assessments of the correlation are made by comparing the predictions with measured data for R-12, R-134a, R-152a, R-410A, and R-600a in the open literature. The correlation predicts the data for those five refrigerants with average and standard deviations of −0.73 and 6.16%, respectively.
B. Cros - One of the best experts on this subject based on the ideXlab platform.
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reproducibility of electron beams from laser wakefield acceleration in Capillary Tubes
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2014Co-Authors: F.g. Desforges, Olle Lundh, Anders Persson, M. Hansson, L. Senje, T.l. Audet, J Ju, S Doboszdufrenoy, Claesgoran Wahlstrom, B. CrosAbstract:The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside Capillary Tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter Capillary Tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.
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Reproducibility of electron beams from laser wakefield acceleration in Capillary Tubes
Nuclear Instruments and Methods in Physics Research Section A: Accelerators Spectrometers Detectors and Associated Equipment, 2014Co-Authors: F.g. Desforges, M. Hansson, L. Senje, T.l. Audet, S. Dobosz-dufrénoy, A. Persson, O. Lundh, C.-g. Wahlström, B. CrosAbstract:The stability of accelerated electron beams produced by self-injection of plasma electrons into the wakefield driven by a laser pulse guided inside Capillary Tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC ±11%, a FWHM beam divergence of 9 mrad ±14%, a maximum energy of 120 MeV ±10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178µm diameter Capillary Tubes at an electron density of (10.0±1.5)×1018 cm-3. Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability.
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Enhanced stability of laser wakefield acceleration using dielectric Capillary Tubes
PRST AB, 2014Co-Authors: B. Cros, M. Hansson, S. Dobosz-dufrénoy, O. Lundh, P. Monot, A. Senje M. Persson, F.g. WahlströmAbstract:The stability of beams of laser wakefield accelerated electrons in dielectric Capillary Tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.
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modelling of laser plasma electron acceleration in Capillary Tubes
Plasma Physics and Controlled Fusion, 2011Co-Authors: H E Ferrari, A Lifschitz, B. CrosAbstract:Modelling of electron acceleration driven by laser wakefield in centimetre-long Capillary Tubes was performed and compared with experimental results. Simulations using the WAKE code (Mora and Antonsen 1997 Phys. Plasma 4 217) were compared with the results of the 3D particle-in-cell CALDER-CIRC code (Lifschitz et al 2009 J. Comput. Phys. 228 1803). The results give some insight into the role of guiding to achieve electron energies of the order of 250 MeV with modest input laser intensities (~0.77 × 1018 W cm−2) and low plasma densities (n = 5 × 1018 cm−3).
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analysis of laser wakefield dynamics in Capillary Tubes
New Journal of Physics, 2010Co-Authors: F. Wojda, Kevin Cassou, Guillaume Genoud, Matthias Burza, Olle Lundh, Anders Persson, B. Cros, N E Andreev, V E FortovAbstract:A general approach to the modifications of the spectrum of a laser pulse interacting with matter is elaborated and used for spectral diagnostics of laser wakefield generation in guiding structures. Analytical predictions of the laser frequency red shift due to the wakefield excited in a Capillary waveguide are confirmed by self-consistent modeling results. The role of ionization blue shift, and nonlinear laser pulse and wakefield dynamics on the spectrum modification, is analyzed for recent experiments on plasma wave excitation by an intense laser pulse guided in hydrogen-filled glass Capillary Tubes up to 8?cm long. The dependence of the spectral frequency shift, measured as a function of filling pressure, Capillary tube length and incident laser energy, is in excellent agreement with the simulation results, and the associated longitudinal accelerating field is in the range 1?10?GV?m?1.
