Pub Date : 2011-06-06DOI: 10.2174/1877729501103010017
Z. Razlan, H. Goshima, M. Hirota, Ryota Isobe, Y. Mizuno, N. Maruyama, A. Nishimura
The gas-liquid flow distributions in multi-pass channels that simulate a compact evaporator used for an automobile air-conditioning system was examined experimentally. The test channel had a horizontal header with a square cross section of 20mm × 20mm and a length of 255mm, and ten upward branches with a length of 200mm were connected to it. Experiments were conducted in an isothermal air-water flow system. Special attention was directed to influences of (i) flow-inlet condition at the header entrance (stratified-flow inlet and mist-flow inlet), (ii) pressure condition at the branch outlets (uniform backpressure and non-uniform backpressure) and (iii) pressure-loss characteristics of branches (flat tubes and multi-port tubes) on the gas-liquid distribution characteristics. In addition to the gas-liquid distributions to branches, the pressure distributions in the headers were measured to make clear the pressure condition in a real evaporator. It was found that the outlet pressure condition of branches exerts great influence on the gas-liquid distributions to branches in the channel with flat tube branches, but it has only minor influence in the channel with multi- port tube branches. The flow-inlet condition at the header entrance has significant influence on the gas-liquid distribution, and the uniformity of the liquid distribution to branches is improved under the mist-flow inlet condition. The pressure in the headers showed uniform distributions in the longitudinal direction, suggesting that the uniform backpressure condition at the branch outlets is appropriate for reproducing the flow in a real compact evaporator with multi-pass channels.
{"title":"Gas-liquid flow distributions in multipass channels with vertical upward branches","authors":"Z. Razlan, H. Goshima, M. Hirota, Ryota Isobe, Y. Mizuno, N. Maruyama, A. Nishimura","doi":"10.2174/1877729501103010017","DOIUrl":"https://doi.org/10.2174/1877729501103010017","url":null,"abstract":"The gas-liquid flow distributions in multi-pass channels that simulate a compact evaporator used for an automobile air-conditioning system was examined experimentally. The test channel had a horizontal header with a square cross section of 20mm × 20mm and a length of 255mm, and ten upward branches with a length of 200mm were connected to it. Experiments were conducted in an isothermal air-water flow system. Special attention was directed to influences of (i) flow-inlet condition at the header entrance (stratified-flow inlet and mist-flow inlet), (ii) pressure condition at the branch outlets (uniform backpressure and non-uniform backpressure) and (iii) pressure-loss characteristics of branches (flat tubes and multi-port tubes) on the gas-liquid distribution characteristics. In addition to the gas-liquid distributions to branches, the pressure distributions in the headers were measured to make clear the pressure condition in a real evaporator. It was found that the outlet pressure condition of branches exerts great influence on the gas-liquid distributions to branches in the channel with flat tube branches, but it has only minor influence in the channel with multi- port tube branches. The flow-inlet condition at the header entrance has significant influence on the gas-liquid distribution, and the uniformity of the liquid distribution to branches is improved under the mist-flow inlet condition. The pressure in the headers showed uniform distributions in the longitudinal direction, suggesting that the uniform backpressure condition at the branch outlets is appropriate for reproducing the flow in a real compact evaporator with multi-pass channels.","PeriodicalId":373830,"journal":{"name":"The Open Transport Phenomena Journal","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115183620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2011-03-29DOI: 10.2174/1877729501103010009
A. Kanamori, M. Hiwada, K. Oyakawa, I. Senaha
Impingement jets are widely used in industries because they provide a high heat transfer coefficient near the stagnation region. However, few methods exist for controlling impingement heat transfer. Recently, a peculiar diffusion process called "axis switching" for three-dimensional free jet has begun to attract attention, and there is a novel possibility of control diffusion and mixture process using this phenomenon. In this paper, we report on the effect of non-circular polygonal orifice shapes on impingement heat transfer. In addition, we demonstrate axis-switching phenomenon by using flow visualization with hydrogen bubbles. Orifice configurations are the regular polygons with 3 to 6 sides. Heat transfer experiments covered the distance between the orifice-to-target plate is 4 to 8 and Reynolds number is 5 × 10 4 and the heat flux is 600 W/m 2 . The flow was visualized in Reynolds number 1,500. For a free jet emerging from a regular polygonal orifice, the location of axis-switching phenomenon shifts toward the orifice exit as the number of sides on the orifice is increased. The iso-Nusselt number profile tends to take the shape of a concentric circle farther upstream. However, with a decrease in the number of sides of the orifice, the iso-Nusselt number profile after axis switching remains downstream. ing the flow using hydrogen bubbles. We also investigated the heat transfer characteristics of an impinging air jet from a non-circular orifice shapes including triangle, square, penta- gon, and hexagon. Moreover, we examined the possibility of controlling impinging heat transfer by changing the orifice configuration.
{"title":"Effect of Orifice Shape on Flow Behavior and Impingement Heat Transfer","authors":"A. Kanamori, M. Hiwada, K. Oyakawa, I. Senaha","doi":"10.2174/1877729501103010009","DOIUrl":"https://doi.org/10.2174/1877729501103010009","url":null,"abstract":"Impingement jets are widely used in industries because they provide a high heat transfer coefficient near the stagnation region. However, few methods exist for controlling impingement heat transfer. Recently, a peculiar diffusion process called \"axis switching\" for three-dimensional free jet has begun to attract attention, and there is a novel possibility of control diffusion and mixture process using this phenomenon. In this paper, we report on the effect of non-circular polygonal orifice shapes on impingement heat transfer. In addition, we demonstrate axis-switching phenomenon by using flow visualization with hydrogen bubbles. Orifice configurations are the regular polygons with 3 to 6 sides. Heat transfer experiments covered the distance between the orifice-to-target plate is 4 to 8 and Reynolds number is 5 × 10 4 and the heat flux is 600 W/m 2 . The flow was visualized in Reynolds number 1,500. For a free jet emerging from a regular polygonal orifice, the location of axis-switching phenomenon shifts toward the orifice exit as the number of sides on the orifice is increased. The iso-Nusselt number profile tends to take the shape of a concentric circle farther upstream. However, with a decrease in the number of sides of the orifice, the iso-Nusselt number profile after axis switching remains downstream. ing the flow using hydrogen bubbles. We also investigated the heat transfer characteristics of an impinging air jet from a non-circular orifice shapes including triangle, square, penta- gon, and hexagon. Moreover, we examined the possibility of controlling impinging heat transfer by changing the orifice configuration.","PeriodicalId":373830,"journal":{"name":"The Open Transport Phenomena Journal","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131232059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-05-18DOI: 10.2174/1877729501002010069
Y. Yonemoto, T. Kunugi
A gas-liquid interface involves complex physics along with unknown phenomena related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. Each phenomenon has various characteristic time and space scales, which makes detailed understanding of the interfacial phenomena very complex. Therefore, modeling the gas- liquid interface is a key issue for numerical research on multiphase flow. Currently, the continuum surface force (CSF) model is popular in modeling the gas-liquid interface in multiphase flow. However, the CSF model cannot treat the vari- ous chemical and physical phenomena at the gas-liquid interface because it is derived based only on mechanical energy balance and it assumes that the interface has no thickness. From certain experimental observations, bubble coales- cence/repulsion was found to be related to a contamination at the interface. The present study developed a new gas-liquid interfacial model based on thermodynamics via a mathematical approach, assuming that the interface has a finite thickness like a thin fluid membrane. In particular, free energy, including an elec- trostatic potential due to the contamination at the interface, is derived based on a lattice gas model. Free energy is incorpo- rated into the conventional Navier-Stokes equation as new terms using Chapman-Enskog expansion based on the multi- scale concept. Using the Navier-Stokes equation with the free energy terms, we derived a new governing equation of fluid motion that characterizes mesoscopic scale phenomena. Finally, the new governing equation was qualitatively evaluated by simulating an interaction between two microbubbles in two dimensions while also accounting for electrostatic force.
{"title":"Multi-scale modeling of the gas-liquid interface based on mathematical and thermodynamic approaches","authors":"Y. Yonemoto, T. Kunugi","doi":"10.2174/1877729501002010069","DOIUrl":"https://doi.org/10.2174/1877729501002010069","url":null,"abstract":"A gas-liquid interface involves complex physics along with unknown phenomena related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. Each phenomenon has various characteristic time and space scales, which makes detailed understanding of the interfacial phenomena very complex. Therefore, modeling the gas- liquid interface is a key issue for numerical research on multiphase flow. Currently, the continuum surface force (CSF) model is popular in modeling the gas-liquid interface in multiphase flow. However, the CSF model cannot treat the vari- ous chemical and physical phenomena at the gas-liquid interface because it is derived based only on mechanical energy balance and it assumes that the interface has no thickness. From certain experimental observations, bubble coales- cence/repulsion was found to be related to a contamination at the interface. The present study developed a new gas-liquid interfacial model based on thermodynamics via a mathematical approach, assuming that the interface has a finite thickness like a thin fluid membrane. In particular, free energy, including an elec- trostatic potential due to the contamination at the interface, is derived based on a lattice gas model. Free energy is incorpo- rated into the conventional Navier-Stokes equation as new terms using Chapman-Enskog expansion based on the multi- scale concept. Using the Navier-Stokes equation with the free energy terms, we derived a new governing equation of fluid motion that characterizes mesoscopic scale phenomena. Finally, the new governing equation was qualitatively evaluated by simulating an interaction between two microbubbles in two dimensions while also accounting for electrostatic force.","PeriodicalId":373830,"journal":{"name":"The Open Transport Phenomena Journal","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123208670","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-05-18DOI: 10.2174/1877729501002010055
S. Shaw, P. Murthy, S. C. Pradhan
Two dimensional flow of a non-Newtonian fluid through an asymmetric stenosed artery is analysed under the influence of body acceleration with an external magnetic field on the flow field. The Casson fluid model is considered to characterize the non-Newtonian behaviour of the blood. The flow is assumed to be unsteady, laminar, two-dimensional, asymmetric and of pulsatile nature. The artery wall has been treated as an elastic (moving wall) cylindrical tube. The un- steady flow mechanics is influenced by externally imposed periodic body acceleration. An explicit finite difference scheme is applied to obtain the flow field. The effect of body acceleration, magnetic field on the flowing blood is ana- lyzed and these results are presented through graphs for the axial and radial velocities, flow rate and wall shear stress.
{"title":"The effect of body acceleration on two dimensional flow of casson fluid through an artery with asymmetric stenosis","authors":"S. Shaw, P. Murthy, S. C. Pradhan","doi":"10.2174/1877729501002010055","DOIUrl":"https://doi.org/10.2174/1877729501002010055","url":null,"abstract":"Two dimensional flow of a non-Newtonian fluid through an asymmetric stenosed artery is analysed under the influence of body acceleration with an external magnetic field on the flow field. The Casson fluid model is considered to characterize the non-Newtonian behaviour of the blood. The flow is assumed to be unsteady, laminar, two-dimensional, asymmetric and of pulsatile nature. The artery wall has been treated as an elastic (moving wall) cylindrical tube. The un- steady flow mechanics is influenced by externally imposed periodic body acceleration. An explicit finite difference scheme is applied to obtain the flow field. The effect of body acceleration, magnetic field on the flowing blood is ana- lyzed and these results are presented through graphs for the axial and radial velocities, flow rate and wall shear stress.","PeriodicalId":373830,"journal":{"name":"The Open Transport Phenomena Journal","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132753112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-04-16DOI: 10.2174/1877729501002010016
Menghuai Wu, A. Vakhrushev, G. Nummer, C. Pfeiler, A. Kharicha, A. Ludwig
A mixture solidification model is employed to study the interaction between the melt flow and the growing mushy zone. The goal is to address the importance of considering the melt flow and flow pattern (laminar or turbulent) in the growing mushy zone. A simple 2D benchmark with parallel flow passing by/through a vertically growing mushy zone is considered. Parameter studies with different velocities and flow patterns are performed. It is found that the flow velocity and flow pattern in and near the mushy zone plays an extremely important role in the formation of the mushy zone. The mushy zone thickness is dramatically reduced with the increasing melt velocity. Simulations with/without considering turbulence show significantly different results. The turbulence in the mushy zone is currently modeled with a simple assumption that the turbulence kinetic energy is linearly reduced with the mush permeability.
{"title":"Importance of Melt Flow in Solidifying Mushy Zone","authors":"Menghuai Wu, A. Vakhrushev, G. Nummer, C. Pfeiler, A. Kharicha, A. Ludwig","doi":"10.2174/1877729501002010016","DOIUrl":"https://doi.org/10.2174/1877729501002010016","url":null,"abstract":"A mixture solidification model is employed to study the interaction between the melt flow and the growing mushy zone. The goal is to address the importance of considering the melt flow and flow pattern (laminar or turbulent) in the growing mushy zone. A simple 2D benchmark with parallel flow passing by/through a vertically growing mushy zone is considered. Parameter studies with different velocities and flow patterns are performed. It is found that the flow velocity and flow pattern in and near the mushy zone plays an extremely important role in the formation of the mushy zone. The mushy zone thickness is dramatically reduced with the increasing melt velocity. Simulations with/without considering turbulence show significantly different results. The turbulence in the mushy zone is currently modeled with a simple assumption that the turbulence kinetic energy is linearly reduced with the mush permeability.","PeriodicalId":373830,"journal":{"name":"The Open Transport Phenomena Journal","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130489758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2010-04-02DOI: 10.2174/1877729501002010001
K. Koyama, Y. Asako
Heat transfer characteristics of a gas-to-gas parallel flow microchannel heat exchanger have been experimen- tally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger are measured to obtain heat transfer rates and pressure drops. The heat transfer and pressure drop characteristics are discussed. The results show that experimental pressure drop is approximately ten times as large as theoretically estimated pressure drop. Geometric con- figuration of the heat exchanger dominates pressure drop characteristics. The conventional log-mean temperature differ- ence method and the constant wall temperature model proposed in our earlier work are applied to predict heat transfer rate of the parallel flow microchannel heat exchanger. Prediction accuracy of the log-mean temperature difference method is superior to that of the constant wall temperature model. Applicability of the log-mean temperature difference method de- pends on direction of fluid flow.
{"title":"Experimental investigation of heat transfer characteristics on a gas-to-gas parallel flow microchannel heat exchanger","authors":"K. Koyama, Y. Asako","doi":"10.2174/1877729501002010001","DOIUrl":"https://doi.org/10.2174/1877729501002010001","url":null,"abstract":"Heat transfer characteristics of a gas-to-gas parallel flow microchannel heat exchanger have been experimen- tally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger are measured to obtain heat transfer rates and pressure drops. The heat transfer and pressure drop characteristics are discussed. The results show that experimental pressure drop is approximately ten times as large as theoretically estimated pressure drop. Geometric con- figuration of the heat exchanger dominates pressure drop characteristics. The conventional log-mean temperature differ- ence method and the constant wall temperature model proposed in our earlier work are applied to predict heat transfer rate of the parallel flow microchannel heat exchanger. Prediction accuracy of the log-mean temperature difference method is superior to that of the constant wall temperature model. Applicability of the log-mean temperature difference method de- pends on direction of fluid flow.","PeriodicalId":373830,"journal":{"name":"The Open Transport Phenomena Journal","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114831088","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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