The Experts below are selected from a list of 75 Experts worldwide ranked by ideXlab platform
B M Burnside - One of the best experts on this subject based on the ideXlab platform.
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two dimensional flow modelling of a thin slice Kettle Reboiler
International Journal of Heat and Mass Transfer, 2011Co-Authors: David Archibald Mcneil, Khalid Bamardouf, B M BurnsideAbstract:Abstract The two-fluid model is applied to a thin sliced Kettle Reboiler. The tube bundle is treated as a porous medium in which the drag coefficient and tube-wall force are deduced from the empirically-based, one-dimensional model. Methods available in the open literature are used in the two-phase pool surrounding the tube bundle. The predictions are verified by comparing them with experimental data and models available in the open literature. The boundary condition applied at the free surface of the pool is found to be crucial in determining the flow pattern within it. When only liquid re-enters through the boundary an all-liquid pool results. Comparison with the experimental evidence suggests that this boundary condition corresponds to bubbly flow within the tube bundle. Allowing a predominantly vapour re-entry produces a two-phase pool that is consistent with intermittent flow in the tube bundle. When the appropriate boundary condition is applied, the two-fluid model predictions are shown to reproduce the visual records and pressure drop measurements reasonably accurately.
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a one fluid two dimensional flow simulation model for a Kettle Reboiler
International Journal of Heat and Mass Transfer, 2010Co-Authors: David Archibald Mcneil, Khalid Bamardouf, B M BurnsideAbstract:Abstract A one-fluid, or algebraic slip, model has been developed to simulate two-dimensional, two-phase flow in a Kettle Reboiler. The model uses boundary conditions that allow for a change in flow pattern from bubbly to intermittent flow at a critical superficial gas velocity, as has been observed experimentally. The model is based on established correlations for void fraction and for the force on the fluid by the tubes. It is validated against pressure drop measurements taken over a range of heat fluxes from a Kettle Reboiler boiling R113 and n-pentane at atmospheric pressure. The model predicts that the flow pattern transition causes a reduction in vertical mass flux, and that the reduction is larger when the transition occurs at a lower level. Before transition, the frequently-used, one-dimensional model and the one-fluid model are shown to predict similar heat-transfer rates because similar magnitudes of mass flux are predicted. After transition, the one-dimensional model significantly over-predicts the mass fluxes. The average heat-transfer coefficient predicted by the one-fluid model is consequently about 10% lower. The one-fluid model shows that tube dryout can be expected at much lower heat fluxes than previously thought and that the fluid kinetic energy available to induce tube vibrations is significantly smaller.
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investigation of flow phenomena in a Kettle Reboiler
International Journal of Heat and Mass Transfer, 2010Co-Authors: David Archibald Mcneil, B M Burnside, Khalid Bamardouf, Mohammed AlmeshaalAbstract:Abstract Two-phase flow phenomena were investigated while boiling R113 and n -pentane in a 241-tube thin slice Kettle Reboiler. For heat fluxes between 10 and 40 kW/m 2 , row pressure drop measurements were made in three columns and visual observations of the flow patterns were recorded by a video camera. The height of the two-phase mixture above the tube bundle was also varied. The results revealed that the height of the mixture had little effect on the row pressure drop distribution in each column. At heat fluxes below 10 kW/m 2 , the pressure drops were reasonably constant. However, at heat fluxes greater than this, the row pressure drop continuously declined. Two one-point-five-dimensional models were developed, one to aid the investigation of static liquid driven lateral flow in the tube bundle, and another to aid the investigation of the cause of the change from reasonably constant to continually declining row pressure drop. The data and the analysis showed that the flow within the tube bundle was always two-dimensional and that the flow pattern was dominated by the static liquid at the tube bundle edge when the heat flux was less than 10 kW/m 2 . This corresponded to the bubbly flow regime. At larger heat fluxes, the flow pattern changed to intermittent flow. The change occurred when the Kutateladze number was 1.09. Declining row pressure drops occurred in this latter flow regime.
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flow velocities in an experimental Kettle Reboiler determined by particle image velocimetry
International Journal of Heat and Mass Transfer, 2005Co-Authors: B M Burnside, David Archibald Mcneil, K M Miller, Tom BruceAbstract:Abstract A particle image velocimetry (PIV) autocorrelation technique was applied to produce whole field vector maps of flow beneath and to the side of a 17 row × l7 column Kettle Reboiler thin slice rig, boiling pentane at atmospheric pressure. The flow proved to be time dependent. The average values of the mass flowrates of the recirculating liquid were evaluated at various positions and compared to predictions of models of the flow which reproduced the measured pressure drops [B.M. Burnside, K.M. Miller, D.A. McNeil T. Bruce, Heat transfer coefficient distributions in an experimental Kettle Reboiler thin slice, Trans. IChemE 79A (2001) 445–452]. The use of the results as a platform for 2D numerical modelling of the flow is emphasised.
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a comparison between highflux and plain tubes boiling pentane in a horizontal Kettle Reboiler
Applied Thermal Engineering, 2002Co-Authors: David Archibald Mcneil, B M Burnside, K M Miller, Ali Hussain TarradAbstract:Abstract An experimental study has been undertaken into the enhancement obtained in the heat-transfer coefficients when HIGHFLUX tubes are used in preference to plain tubes while boiling pentane. The study involved two experimental facilities, a single-tube pool boiler and a 241 tube, 17 row by 17 column, thin slice Kettle Reboiler. The pool boiling results show that the HIGHFLUX tubes produce heat-transfer coefficients that are up to five times larger than their plain tube counterparts. In flow boiling the enhancement is 3–6 times. In both cases, HIGHFLUX tube performance is shown to deteriorate when small degrees of subcooling are present in the liquid. The deterioration still leaves the HIGHFLUX tubes with a significantly higher heat-transfer coefficient than the plain tubes. Existing flow boiling design methodologies are shown to produce performance characteristics that HIGHFLUX tubes do not follow.
David Archibald Mcneil - One of the best experts on this subject based on the ideXlab platform.
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two dimensional flow modelling of a thin slice Kettle Reboiler
International Journal of Heat and Mass Transfer, 2011Co-Authors: David Archibald Mcneil, Khalid Bamardouf, B M BurnsideAbstract:Abstract The two-fluid model is applied to a thin sliced Kettle Reboiler. The tube bundle is treated as a porous medium in which the drag coefficient and tube-wall force are deduced from the empirically-based, one-dimensional model. Methods available in the open literature are used in the two-phase pool surrounding the tube bundle. The predictions are verified by comparing them with experimental data and models available in the open literature. The boundary condition applied at the free surface of the pool is found to be crucial in determining the flow pattern within it. When only liquid re-enters through the boundary an all-liquid pool results. Comparison with the experimental evidence suggests that this boundary condition corresponds to bubbly flow within the tube bundle. Allowing a predominantly vapour re-entry produces a two-phase pool that is consistent with intermittent flow in the tube bundle. When the appropriate boundary condition is applied, the two-fluid model predictions are shown to reproduce the visual records and pressure drop measurements reasonably accurately.
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a one fluid two dimensional flow simulation model for a Kettle Reboiler
International Journal of Heat and Mass Transfer, 2010Co-Authors: David Archibald Mcneil, Khalid Bamardouf, B M BurnsideAbstract:Abstract A one-fluid, or algebraic slip, model has been developed to simulate two-dimensional, two-phase flow in a Kettle Reboiler. The model uses boundary conditions that allow for a change in flow pattern from bubbly to intermittent flow at a critical superficial gas velocity, as has been observed experimentally. The model is based on established correlations for void fraction and for the force on the fluid by the tubes. It is validated against pressure drop measurements taken over a range of heat fluxes from a Kettle Reboiler boiling R113 and n-pentane at atmospheric pressure. The model predicts that the flow pattern transition causes a reduction in vertical mass flux, and that the reduction is larger when the transition occurs at a lower level. Before transition, the frequently-used, one-dimensional model and the one-fluid model are shown to predict similar heat-transfer rates because similar magnitudes of mass flux are predicted. After transition, the one-dimensional model significantly over-predicts the mass fluxes. The average heat-transfer coefficient predicted by the one-fluid model is consequently about 10% lower. The one-fluid model shows that tube dryout can be expected at much lower heat fluxes than previously thought and that the fluid kinetic energy available to induce tube vibrations is significantly smaller.
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investigation of flow phenomena in a Kettle Reboiler
International Journal of Heat and Mass Transfer, 2010Co-Authors: David Archibald Mcneil, B M Burnside, Khalid Bamardouf, Mohammed AlmeshaalAbstract:Abstract Two-phase flow phenomena were investigated while boiling R113 and n -pentane in a 241-tube thin slice Kettle Reboiler. For heat fluxes between 10 and 40 kW/m 2 , row pressure drop measurements were made in three columns and visual observations of the flow patterns were recorded by a video camera. The height of the two-phase mixture above the tube bundle was also varied. The results revealed that the height of the mixture had little effect on the row pressure drop distribution in each column. At heat fluxes below 10 kW/m 2 , the pressure drops were reasonably constant. However, at heat fluxes greater than this, the row pressure drop continuously declined. Two one-point-five-dimensional models were developed, one to aid the investigation of static liquid driven lateral flow in the tube bundle, and another to aid the investigation of the cause of the change from reasonably constant to continually declining row pressure drop. The data and the analysis showed that the flow within the tube bundle was always two-dimensional and that the flow pattern was dominated by the static liquid at the tube bundle edge when the heat flux was less than 10 kW/m 2 . This corresponded to the bubbly flow regime. At larger heat fluxes, the flow pattern changed to intermittent flow. The change occurred when the Kutateladze number was 1.09. Declining row pressure drops occurred in this latter flow regime.
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Experimental and numerical investigation of two-phase pressure drop in vertical cross-flow over a horizontal tube bundle
Applied Thermal Engineering, 2009Co-Authors: Khalid Bamardouf, David Archibald McneilAbstract:Abstract Experimental pressure drop data for vertical two-phase air–water flow across horizontal tubes is presented for gas mass fractions in the range 0.0005–0.6 and mass fluxes in the range 25–700 kg/m2 s. The square in-line tube bundle had one column containing ten tubes and two columns of half tubes attached to the walls. The tubes had a diameter of 38 mm and a pitch to diameter ratio of 1.32. This data and air–water and R113 vapour–liquid data available in the literature are compared with the predictions from two Kettle Reboiler models, the one-dimensional model and a one-dimensional formulation of the two-fluid model. The one-dimensional model was implemented with three separate void fraction correlations and one two-phase friction multiplier correlation. The results show that the two-fluid model predicts air–water void fraction data well but R113 data poorly with pressure drop predictions for both being unsatisfactory. The one-dimensional model is shown to predict pressure drop and void fraction data reasonably well, provided a careful choice is made for the void fraction correlation.
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flow velocities in an experimental Kettle Reboiler determined by particle image velocimetry
International Journal of Heat and Mass Transfer, 2005Co-Authors: B M Burnside, David Archibald Mcneil, K M Miller, Tom BruceAbstract:Abstract A particle image velocimetry (PIV) autocorrelation technique was applied to produce whole field vector maps of flow beneath and to the side of a 17 row × l7 column Kettle Reboiler thin slice rig, boiling pentane at atmospheric pressure. The flow proved to be time dependent. The average values of the mass flowrates of the recirculating liquid were evaluated at various positions and compared to predictions of models of the flow which reproduced the measured pressure drops [B.M. Burnside, K.M. Miller, D.A. McNeil T. Bruce, Heat transfer coefficient distributions in an experimental Kettle Reboiler thin slice, Trans. IChemE 79A (2001) 445–452]. The use of the results as a platform for 2D numerical modelling of the flow is emphasised.
Sanja Milivojevic - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of two dimensional Kettle Reboiler shell side thermal hydraulics with swell level and liquid mass inventory prediction
International Journal of Heat and Mass Transfer, 2014Co-Authors: Blazenka Maslovaric, Vladimir Stevanović, Sanja MilivojevicAbstract:Abstract Simulation and analyses of two-phase flows across tube bundles is important for design and safety analyses of various types of steam generators and Kettle Reboilers. The information about the shell side thermal–hydraulics in this thermal equipment should include the liquid and vapour two-phase flow velocity fields, the void fraction distribution, as well as the swell level position and the liquid mass inventory. The two-fluid model of boiling two-phase flow around tubes in the bundle is applied for the simulation of the Kettle Reboiler shell side thermal–hydraulics. The tube bundle is modelled as a porous medium. Transfer processes at the vapour–liquid interfaces and on the tube walls are predicted with closure laws. The model is numerically solved by the “in-house” CFD code. The applied modelling method is validated against measured data of pressure drops in refrigerant R113 and n-pentane two-phase flows across tube rows in the bundle of a thin slice Kettle Reboiler, which are available in the open literature. The swell level position on the shell side is calculated solely by solving of the two-phase flow governing equations and with the application of an appropriate closure law for the vapour–liquid drag force, which enables the prediction of the liquid separation due to gravity from the upward flowing two-phase mixture. This is an improvement on the thermal–hydraulic modelling and numerical simulation of the Kettle Reboiler since the previous numerical simulations from the open literature have been performed with a priori specified swell level position and arbitrary boundary conditions for the velocity (or pressure) and void fraction boundary conditions at the swell level. The prediction of the swell level position also enables the calculation of the liquid mass inventory on the shell side, which gives insight into the Kettle Reboiler operating conditions and is crucial for the reliable prediction of the tube bundle dry-out during incidents of liquid feeding stoppage. There is a one-to-one correspondence between the liquid mass inventory and the swell level position. The presented simulation method enables iterative prediction of the liquid mass inventory for the specified swell level position and vice versa. In addition, the correlations for the liquid–vapour interfacial drag coefficient, which have shown previously fairly good predictions in cases of water–steam and water–air two-phase flows, are extended for the general application to other fluids.
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Numerical simulation of two-dimensional Kettle Reboiler shell side thermal–hydraulics with swell level and liquid mass inventory prediction
International Journal of Heat and Mass Transfer, 2014Co-Authors: Blazenka Maslovaric, Vladimir Stevanović, Sanja MilivojevicAbstract:Abstract Simulation and analyses of two-phase flows across tube bundles is important for design and safety analyses of various types of steam generators and Kettle Reboilers. The information about the shell side thermal–hydraulics in this thermal equipment should include the liquid and vapour two-phase flow velocity fields, the void fraction distribution, as well as the swell level position and the liquid mass inventory. The two-fluid model of boiling two-phase flow around tubes in the bundle is applied for the simulation of the Kettle Reboiler shell side thermal–hydraulics. The tube bundle is modelled as a porous medium. Transfer processes at the vapour–liquid interfaces and on the tube walls are predicted with closure laws. The model is numerically solved by the “in-house” CFD code. The applied modelling method is validated against measured data of pressure drops in refrigerant R113 and n-pentane two-phase flows across tube rows in the bundle of a thin slice Kettle Reboiler, which are available in the open literature. The swell level position on the shell side is calculated solely by solving of the two-phase flow governing equations and with the application of an appropriate closure law for the vapour–liquid drag force, which enables the prediction of the liquid separation due to gravity from the upward flowing two-phase mixture. This is an improvement on the thermal–hydraulic modelling and numerical simulation of the Kettle Reboiler since the previous numerical simulations from the open literature have been performed with a priori specified swell level position and arbitrary boundary conditions for the velocity (or pressure) and void fraction boundary conditions at the swell level. The prediction of the swell level position also enables the calculation of the liquid mass inventory on the shell side, which gives insight into the Kettle Reboiler operating conditions and is crucial for the reliable prediction of the tube bundle dry-out during incidents of liquid feeding stoppage. There is a one-to-one correspondence between the liquid mass inventory and the swell level position. The presented simulation method enables iterative prediction of the liquid mass inventory for the specified swell level position and vice versa. In addition, the correlations for the liquid–vapour interfacial drag coefficient, which have shown previously fairly good predictions in cases of water–steam and water–air two-phase flows, are extended for the general application to other fluids.
Vladimir Stevanović - One of the best experts on this subject based on the ideXlab platform.
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Numerical simulation of two-dimensional Kettle Reboiler shell side thermal–hydraulics with swell level and liquid mass inventory prediction
International Journal of Heat and Mass Transfer, 2014Co-Authors: Blazenka Maslovaric, Vladimir Stevanović, Sanja MilivojevicAbstract:Abstract Simulation and analyses of two-phase flows across tube bundles is important for design and safety analyses of various types of steam generators and Kettle Reboilers. The information about the shell side thermal–hydraulics in this thermal equipment should include the liquid and vapour two-phase flow velocity fields, the void fraction distribution, as well as the swell level position and the liquid mass inventory. The two-fluid model of boiling two-phase flow around tubes in the bundle is applied for the simulation of the Kettle Reboiler shell side thermal–hydraulics. The tube bundle is modelled as a porous medium. Transfer processes at the vapour–liquid interfaces and on the tube walls are predicted with closure laws. The model is numerically solved by the “in-house” CFD code. The applied modelling method is validated against measured data of pressure drops in refrigerant R113 and n-pentane two-phase flows across tube rows in the bundle of a thin slice Kettle Reboiler, which are available in the open literature. The swell level position on the shell side is calculated solely by solving of the two-phase flow governing equations and with the application of an appropriate closure law for the vapour–liquid drag force, which enables the prediction of the liquid separation due to gravity from the upward flowing two-phase mixture. This is an improvement on the thermal–hydraulic modelling and numerical simulation of the Kettle Reboiler since the previous numerical simulations from the open literature have been performed with a priori specified swell level position and arbitrary boundary conditions for the velocity (or pressure) and void fraction boundary conditions at the swell level. The prediction of the swell level position also enables the calculation of the liquid mass inventory on the shell side, which gives insight into the Kettle Reboiler operating conditions and is crucial for the reliable prediction of the tube bundle dry-out during incidents of liquid feeding stoppage. There is a one-to-one correspondence between the liquid mass inventory and the swell level position. The presented simulation method enables iterative prediction of the liquid mass inventory for the specified swell level position and vice versa. In addition, the correlations for the liquid–vapour interfacial drag coefficient, which have shown previously fairly good predictions in cases of water–steam and water–air two-phase flows, are extended for the general application to other fluids.
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numerical simulation of two dimensional Kettle Reboiler shell side thermal hydraulics with swell level and liquid mass inventory prediction
International Journal of Heat and Mass Transfer, 2014Co-Authors: Blazenka Maslovaric, Vladimir Stevanović, Sanja MilivojevicAbstract:Abstract Simulation and analyses of two-phase flows across tube bundles is important for design and safety analyses of various types of steam generators and Kettle Reboilers. The information about the shell side thermal–hydraulics in this thermal equipment should include the liquid and vapour two-phase flow velocity fields, the void fraction distribution, as well as the swell level position and the liquid mass inventory. The two-fluid model of boiling two-phase flow around tubes in the bundle is applied for the simulation of the Kettle Reboiler shell side thermal–hydraulics. The tube bundle is modelled as a porous medium. Transfer processes at the vapour–liquid interfaces and on the tube walls are predicted with closure laws. The model is numerically solved by the “in-house” CFD code. The applied modelling method is validated against measured data of pressure drops in refrigerant R113 and n-pentane two-phase flows across tube rows in the bundle of a thin slice Kettle Reboiler, which are available in the open literature. The swell level position on the shell side is calculated solely by solving of the two-phase flow governing equations and with the application of an appropriate closure law for the vapour–liquid drag force, which enables the prediction of the liquid separation due to gravity from the upward flowing two-phase mixture. This is an improvement on the thermal–hydraulic modelling and numerical simulation of the Kettle Reboiler since the previous numerical simulations from the open literature have been performed with a priori specified swell level position and arbitrary boundary conditions for the velocity (or pressure) and void fraction boundary conditions at the swell level. The prediction of the swell level position also enables the calculation of the liquid mass inventory on the shell side, which gives insight into the Kettle Reboiler operating conditions and is crucial for the reliable prediction of the tube bundle dry-out during incidents of liquid feeding stoppage. There is a one-to-one correspondence between the liquid mass inventory and the swell level position. The presented simulation method enables iterative prediction of the liquid mass inventory for the specified swell level position and vice versa. In addition, the correlations for the liquid–vapour interfacial drag coefficient, which have shown previously fairly good predictions in cases of water–steam and water–air two-phase flows, are extended for the general application to other fluids.
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a two dimensional model of the Kettle Reboiler shell side thermal hydraulics
International Journal of Heat and Mass Transfer, 2006Co-Authors: Milada Pezo, Vladimir Stevanović, Zarko StevanovicAbstract:Abstract A two-dimensional two-fluid numerical model is developed for the prediction of two-phase flow thermal-hydraulics on the shell side of the Kettle Reboiler. The two-phase flow around tubes in the bundle is modeled with the porous media approach. A closure law for the vapour–liquid interfacial friction is based on modified pipe two-phase flow correlations. The tube bundle flow resistance is calculated by applying to each phase stream the correlations for the pressure drop in a single phase flow across tube bundles and by taking into account the separate contribution of each phase to the total pressure drop. Physically based boundary conditions for the velocity field at the two-phase mixture swell level are stated. The system of governing equations is solved numerically with the finite volume approach for two-phase flow built in the commercial computer program. Simulations are performed for available conditions of performed physical experiments. In comparison to the previous Kettle Reboiler two-dimensional modeling approaches, here presented model is original regarding the applied closure laws for the interfacial friction and bundle flow resistance, as well as applied boundary conditions for the modeling of two-phase mixture free surface. Also, regarding the previous published results, here obtained numerical results are compared with the available measured data of void fraction within the tube bundle and acceptable agreement is shown.
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simulations of the Kettle Reboiler shell side thermal hydraulics with different two phase flow models
Thermal Science, 2006Co-Authors: Milada Pezo, Vladimir Stevanović, Zarko StevanovicAbstract:A computational fluid dynamics approach is presented for the simulation and analyses of the Kettle Reboiler shell side thermal-hydraulics with two different models of two-phase flow – the mixture and two fluid model. The mixture model is based on solving one momentum equation for two-phase mixture flow and a closure law for the calculation of the slip between gas and liquid phase velocities. In the two fluid modeling approach the momentum balance is formed for each phase, while the gas-liquid interaction due to momentum exchange at the interface surface is predicted with an empirical correlation for the interface friction coefficient. In both approaches the two-phase flow is observed as two inter-penetrating continua. The models are solved for the two-dimensional geometry of the Kettle Reboiler shell side vertical cross section. The computational fluid dynamics numerical method based on the SIMPLE type algorithm is applied. The results of both liquid and vapor velocity fields and void fraction are presented for each modeling approach. The calculated void fraction distributions are compared with available experimental data. The differences in the modeling approaches and obtained results are discussed. The main finding is that the void fraction distribution and two-phase flow field strongly depends on the modeling of the slip between liquid and gas phase velocity in mixture model or on the interface friction model in two fluid model. The better agreement of the numerically predicted void fraction with the experimental data is obtained with the two fluid model and an interfacial friction model developed for the conditions of two-phase flows in large volumes of Kettle Reboilers or different designs of steam generators.
Khalid Bamardouf - One of the best experts on this subject based on the ideXlab platform.
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two dimensional flow modelling of a thin slice Kettle Reboiler
International Journal of Heat and Mass Transfer, 2011Co-Authors: David Archibald Mcneil, Khalid Bamardouf, B M BurnsideAbstract:Abstract The two-fluid model is applied to a thin sliced Kettle Reboiler. The tube bundle is treated as a porous medium in which the drag coefficient and tube-wall force are deduced from the empirically-based, one-dimensional model. Methods available in the open literature are used in the two-phase pool surrounding the tube bundle. The predictions are verified by comparing them with experimental data and models available in the open literature. The boundary condition applied at the free surface of the pool is found to be crucial in determining the flow pattern within it. When only liquid re-enters through the boundary an all-liquid pool results. Comparison with the experimental evidence suggests that this boundary condition corresponds to bubbly flow within the tube bundle. Allowing a predominantly vapour re-entry produces a two-phase pool that is consistent with intermittent flow in the tube bundle. When the appropriate boundary condition is applied, the two-fluid model predictions are shown to reproduce the visual records and pressure drop measurements reasonably accurately.
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a one fluid two dimensional flow simulation model for a Kettle Reboiler
International Journal of Heat and Mass Transfer, 2010Co-Authors: David Archibald Mcneil, Khalid Bamardouf, B M BurnsideAbstract:Abstract A one-fluid, or algebraic slip, model has been developed to simulate two-dimensional, two-phase flow in a Kettle Reboiler. The model uses boundary conditions that allow for a change in flow pattern from bubbly to intermittent flow at a critical superficial gas velocity, as has been observed experimentally. The model is based on established correlations for void fraction and for the force on the fluid by the tubes. It is validated against pressure drop measurements taken over a range of heat fluxes from a Kettle Reboiler boiling R113 and n-pentane at atmospheric pressure. The model predicts that the flow pattern transition causes a reduction in vertical mass flux, and that the reduction is larger when the transition occurs at a lower level. Before transition, the frequently-used, one-dimensional model and the one-fluid model are shown to predict similar heat-transfer rates because similar magnitudes of mass flux are predicted. After transition, the one-dimensional model significantly over-predicts the mass fluxes. The average heat-transfer coefficient predicted by the one-fluid model is consequently about 10% lower. The one-fluid model shows that tube dryout can be expected at much lower heat fluxes than previously thought and that the fluid kinetic energy available to induce tube vibrations is significantly smaller.
-
investigation of flow phenomena in a Kettle Reboiler
International Journal of Heat and Mass Transfer, 2010Co-Authors: David Archibald Mcneil, B M Burnside, Khalid Bamardouf, Mohammed AlmeshaalAbstract:Abstract Two-phase flow phenomena were investigated while boiling R113 and n -pentane in a 241-tube thin slice Kettle Reboiler. For heat fluxes between 10 and 40 kW/m 2 , row pressure drop measurements were made in three columns and visual observations of the flow patterns were recorded by a video camera. The height of the two-phase mixture above the tube bundle was also varied. The results revealed that the height of the mixture had little effect on the row pressure drop distribution in each column. At heat fluxes below 10 kW/m 2 , the pressure drops were reasonably constant. However, at heat fluxes greater than this, the row pressure drop continuously declined. Two one-point-five-dimensional models were developed, one to aid the investigation of static liquid driven lateral flow in the tube bundle, and another to aid the investigation of the cause of the change from reasonably constant to continually declining row pressure drop. The data and the analysis showed that the flow within the tube bundle was always two-dimensional and that the flow pattern was dominated by the static liquid at the tube bundle edge when the heat flux was less than 10 kW/m 2 . This corresponded to the bubbly flow regime. At larger heat fluxes, the flow pattern changed to intermittent flow. The change occurred when the Kutateladze number was 1.09. Declining row pressure drops occurred in this latter flow regime.
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Experimental and numerical investigation of two-phase pressure drop in vertical cross-flow over a horizontal tube bundle
Applied Thermal Engineering, 2009Co-Authors: Khalid Bamardouf, David Archibald McneilAbstract:Abstract Experimental pressure drop data for vertical two-phase air–water flow across horizontal tubes is presented for gas mass fractions in the range 0.0005–0.6 and mass fluxes in the range 25–700 kg/m2 s. The square in-line tube bundle had one column containing ten tubes and two columns of half tubes attached to the walls. The tubes had a diameter of 38 mm and a pitch to diameter ratio of 1.32. This data and air–water and R113 vapour–liquid data available in the literature are compared with the predictions from two Kettle Reboiler models, the one-dimensional model and a one-dimensional formulation of the two-fluid model. The one-dimensional model was implemented with three separate void fraction correlations and one two-phase friction multiplier correlation. The results show that the two-fluid model predicts air–water void fraction data well but R113 data poorly with pressure drop predictions for both being unsatisfactory. The one-dimensional model is shown to predict pressure drop and void fraction data reasonably well, provided a careful choice is made for the void fraction correlation.
