The Experts below are selected from a list of 46461 Experts worldwide ranked by ideXlab platform
Narsing K Jha - One of the best experts on this subject based on the ideXlab platform.
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contaminant transport by human passage through an air curtain separating two sections of a corridor part ii two zones at different temperatures
Energy and Buildings, 2021Co-Authors: Narsing K Jha, Daria Frank, L Darracq, P F LindenAbstract:Abstract Air curtains are installed in open doorways of a building to reduce buoyancy-driven exchange flows across the doorway. Although an air curtain allows an unhampered passage of humans and vehicles, the interaction of this traffic with an air curtain is not well understood. In this study, we investigate the problem of the simultaneous interaction between the air curtain, the wake of a moving person and the buoyancy-driven flow arising due to the density difference across the doorway. To this end, we conduct small-scale waterbath experiments with fresh water and salt water solutions to achieve different Fluid densities. As a model of human passage, a vertical cylinder is pulled through a planar jet representing an air curtain and separating two zones at different densities. For a fixed travel distance of the cylinder before and after the air curtain, the average infiltration flux of dense Fluid into the light Fluid Side increases with increasing cylinder velocity. Remarkably, we find that the infiltration flux is independent of the density difference across the doorway and is mainly due to the interaction between the air curtain and the cylinder wake with negligible effects from the buoyancy-driven flow. Furthermore, the infiltration flux is also independent of the travel direction of the cylinder. As a consequence, the sealing effectiveness of an air curtain reduces with an increasing cylinder speed and this reduction is independent of the direction of the buoyancy-driven flow. We provide a theoretical explanation for the observed changes in the effectiveness curve of the air curtain as the function of the deflection modulus. Dye visualisations of the air curtain and the cylinder wake are used to examine the re-establishment process of the air curtain after its disruption by the cylinder. We observe that the re-establishment time of the air curtain and the infiltration in the cylinder wake increases with an increasing cylinder speed.
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contaminant transport by human passage through an air curtain separating two sections of a corridor part ii two zones at different temperatures
arXiv: Fluid Dynamics, 2020Co-Authors: Narsing K Jha, Daria Frank, L Darracq, P F LindenAbstract:Air curtains are installed in open doorways of a building to reduce buoyancy-driven exchange flows across the doorway. Although an air curtain allows an unhampered passage of humans and vehicles, the interaction of this traffic with an air curtain is not well understood. We study this problem by conducting small-scale waterbath experiments with fresh water and salt water solutions. As a model of human passage, a vertical cylinder is pulled through a planar jet representing an air curtain and separating two zones at different densities. For a fixed travel distance of the cylinder before and after the air curtain, the average infiltration flux of dense Fluid in light Fluid Side increases with increasing cylinder velocity. However, we find that the infiltration flux is independent of density difference across the doorway and the travel direction of the cylinder. As a consequence, the sealing effectiveness of an air curtain reduces with an increasing cylinder speed and this reduction is independent of the direction of the buoyancy-driven flow. Dye visualisations of the air curtain and the cylinder wake are used to examine the re-establishment process of the air curtain after its disruption by the cylinder. We observe that the re-establishment time of the air curtain and the infiltration in the cylinder wake increases with an increasing cylinder speed.
Nigel H Brookes - One of the best experts on this subject based on the ideXlab platform.
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riding the cell jamming boundary geometry topology and phase of human corneal endothelium
Experimental Eye Research, 2018Co-Authors: Nigel H BrookesAbstract:Abstract It is important to assess the viability of eye-banked corneas prior to transplantation due to inherent senescence and known loss of endothelial cells during surgical manipulation. Corneal endothelial cells have a complex basal and paracellular shape making them challenging to accurately measure, particularly in oedematous ex vivo tissue. This study used calibrated centroidal Voronoi Diagrams to segment cells in images of these human corneas, in order to characterize endothelial geometry, topology, and phase. Hexagonal cells dominated the endothelia, with most comprised of five different pleomorphs exhibiting self-similar topological coarsening through most of the endothelial cell density range. There was a linear relationship between cell size and shape, though cells with greater than six Sides were present in larger proportions than cells with less. Hexagonal cell regularity was stable and largely independent of density. Cell and tissue phase was also examined, using the cell shape index relative to the recently discovered ‘cell jamming’ phase transition boundary. Images showed Fluid endothelia with a range of shape indices spanning the boundary, independent of density but dependent on hexagonal regularity. The cells showed a bimodal distribution centred at the boundary, with the largest proportion of cells on the Fluid Side. A shoulder at the boundary suggested phase switching via shape transformation across the energy barrier, with cells either Side having distinctly different size and shape characteristics. Regular hexagonal cells were closest to the boundary. This study showed the corneal endothelium acts as a glassy viscous foam characterized by well-established physical laws. Endothelial cell death transiently and locally increases cell Fluidity, which is subsequently arrested by jamming of the pleomorphically diverse cell collective, via rearrangement and shape change of a small proportion of cells, which become locked in place by their neighbours thereby maintaining structural equilibrium with little energy expenditure.
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riding the cell jamming boundary geometry topology and phase of human corneal endothelium
bioRxiv, 2018Co-Authors: Nigel H BrookesAbstract:It is important to assess the viability of eye-banked corneas prior to transplantation due to inherent senescence and known loss of endothelial cells during surgical manipulation. In oedematous ex vivo tissue, corneal endothelial cells have a complex basal and paracellular shape making them challenging to accurately measure. This study used calibrated centroidal Voronoi Diagrams to segment cells in images of ex vivo human corneas, in order to characterize endothelial geometry, topology, and phase. Hexagonal cells dominated the endothelia, with most comprised of five different pleomorphs exhibiting self-similar topological coarsening through most of the endothelial cell density range. There was a linear relationship between cell size and shape, though cells with greater than six Sides were present in larger proportions than cells with less. Hexagonal cell regularity was stable and largely independent of density. Cell and tissue phase was also examined, using the cell shape index relative to the recently discovered cell jamming phase transition boundary. Images showed Fluid endothelia with a range of shape indices spanning the boundary, independent of density but dependent on hexagonal regularity. The cells showed a bimodal distribution centred at the boundary, with the largest proportion of cells on the Fluid Side. A shoulder at the boundary suggested phase switching via shape transformation across the energy barrier, with cells either Side having distinctly different size and shape characteristics. Regular hexagonal cells were closest to the boundary. This study showed the corneal endothelium acts as a glassy viscous foam characterized by well-established physical laws. Endothelial cell death transiently and locally increases cell Fluidity, which is subsequently arrested by jamming of the pleomorphically diverse cell collective, via rearrangement and shape change of a small proportion of cells, which become locked in place by their neighbours and maintain endothelial function with little energy expenditure.
Fatih Aksoy - One of the best experts on this subject based on the ideXlab platform.
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an experimental study on the development of a β type stirling engine for low and moderate temperature heat sources
Applied Energy, 2009Co-Authors: Halit Karabulut, Can Cinar, Huseyin Serdar Yucesu, Fatih AksoyAbstract:In this study, a [beta]-type Stirling engine was designed and manufactured which works at relatively lower temperatures. To increase the heat transfer area, the inner surface of the displacer cylinder was augmented by means of growing spanwise slots. To perform a better approach to the theoretical Stirling cycle, the motion of displacer was governed by a lever. The engine block was used as pressurized working Fluid reservoir. The escape of working Fluid, through the end-pin bearing of crankshaft, was prevented by means of adapting an oil pool around the end-pin. Experimental results presented in this paper were obtained by testing the engine with air as working Fluid. The hot end of the displacer cylinder was heated with a LPG flame and kept about 200 °C constant temperature throughout the testing period. The other end of the displacer cylinder was cooled with a water circulation having 27 °C temperature. Starting from ambient pressure, the engine was tested at several charge pressures up to 4.6 bars. Maximum power output was obtained at 2.8 bars charge pressure as 51.93 W at 453 rpm engine speed. The maximum torque was obtained as 1.17 Nm at 2.8 bars charge pressure. By comparing experimental work with theoretical work calculated by nodal analysis, the convective heat transfer coefficient at working Fluid Side of the displacer cylinder was predicted as 447 W/m2 K for air. At maximum shaft power, the internal thermal efficiency of the engine was predicted as 15%.
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an experimental study on the development of a β type stirling engine for low and moderate temperature heat sources
Applied Energy, 2009Co-Authors: Halit Karabulut, Can Cinar, Huseyin Serdar Yucesu, Fatih AksoyAbstract:Abstract In this study, a β-type Stirling engine was designed and manufactured which works at relatively lower temperatures. To increase the heat transfer area, the inner surface of the displacer cylinder was augmented by means of growing spanwise slots. To perform a better approach to the theoretical Stirling cycle, the motion of displacer was governed by a lever. The engine block was used as pressurized working Fluid reservoir. The escape of working Fluid, through the end-pin bearing of crankshaft, was prevented by means of adapting an oil pool around the end-pin. Experimental results presented in this paper were obtained by testing the engine with air as working Fluid. The hot end of the displacer cylinder was heated with a LPG flame and kept about 200 °C constant temperature throughout the testing period. The other end of the displacer cylinder was cooled with a water circulation having 27 °C temperature. Starting from ambient pressure, the engine was tested at several charge pressures up to 4.6 bars. Maximum power output was obtained at 2.8 bars charge pressure as 51.93 W at 453 rpm engine speed. The maximum torque was obtained as 1.17 Nm at 2.8 bars charge pressure. By comparing experimental work with theoretical work calculated by nodal analysis, the convective heat transfer coefficient at working Fluid Side of the displacer cylinder was predicted as 447 W/m 2 K for air. At maximum shaft power, the internal thermal efficiency of the engine was predicted as 15%.
Suneet Singh - One of the best experts on this subject based on the ideXlab platform.
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evaluation of transient characteristics of medium temperature solar thermal systems utilizing thermal stratification
Applied Energy, 2018Co-Authors: Rudrodip Majumdar, Sandip K Saha, Suneet SinghAbstract:Abstract System level transient moving boundary models are interesting in the context of advanced control of the solar thermal systems. However, development of control-oriented heat exchanger models faces the key challenges that these models should remain both reasonably accurate and mathematically tractable. In this paper, dynamic moving boundary model is developed for the medium temperature (∼200 °C) solar thermal power plant using a novel concept based on auxiliary pressurized water storage tank to enhance overall thermal efficiency, where the time varying pressure on the subcooled organic Rankine cycle working Fluid (refrigerant) at the two-phase heat exchanger inlet is conSidered as the sole independent variable and all other thermodynamic variables are assumed to be dependent on the specified pressure. Modified idealized stratification model is adopted to analysis the thermal stratification in the storage tank. Small sinusoidal variation about the steady-state pressure level is conSidered to investigate its effect on the heat exchanger tube wall temperature and the length of different flow regimes. Additionally, the model incorporates a provision to capture the effect of transient changes in the bulk temperature of the heat transfer Fluid (commercial thermic oil) on the moving phase change boundaries in the working Fluid Side of the heat exchanger. At an indicative solar radiation level of 450 W/m2, the primary energy transfer at the solar collector is found to be enhanced by about 11% by using an auxiliary pressurized water storage tank, compared to the case where commercial thermic oil is used in the collector loop. The overall thermal efficiency of the solar thermal system for a peak power level of 840 kWt is estimated as 20.75%.
P F Linden - One of the best experts on this subject based on the ideXlab platform.
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contaminant transport by human passage through an air curtain separating two sections of a corridor part ii two zones at different temperatures
Energy and Buildings, 2021Co-Authors: Narsing K Jha, Daria Frank, L Darracq, P F LindenAbstract:Abstract Air curtains are installed in open doorways of a building to reduce buoyancy-driven exchange flows across the doorway. Although an air curtain allows an unhampered passage of humans and vehicles, the interaction of this traffic with an air curtain is not well understood. In this study, we investigate the problem of the simultaneous interaction between the air curtain, the wake of a moving person and the buoyancy-driven flow arising due to the density difference across the doorway. To this end, we conduct small-scale waterbath experiments with fresh water and salt water solutions to achieve different Fluid densities. As a model of human passage, a vertical cylinder is pulled through a planar jet representing an air curtain and separating two zones at different densities. For a fixed travel distance of the cylinder before and after the air curtain, the average infiltration flux of dense Fluid into the light Fluid Side increases with increasing cylinder velocity. Remarkably, we find that the infiltration flux is independent of the density difference across the doorway and is mainly due to the interaction between the air curtain and the cylinder wake with negligible effects from the buoyancy-driven flow. Furthermore, the infiltration flux is also independent of the travel direction of the cylinder. As a consequence, the sealing effectiveness of an air curtain reduces with an increasing cylinder speed and this reduction is independent of the direction of the buoyancy-driven flow. We provide a theoretical explanation for the observed changes in the effectiveness curve of the air curtain as the function of the deflection modulus. Dye visualisations of the air curtain and the cylinder wake are used to examine the re-establishment process of the air curtain after its disruption by the cylinder. We observe that the re-establishment time of the air curtain and the infiltration in the cylinder wake increases with an increasing cylinder speed.
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contaminant transport by human passage through an air curtain separating two sections of a corridor part ii two zones at different temperatures
arXiv: Fluid Dynamics, 2020Co-Authors: Narsing K Jha, Daria Frank, L Darracq, P F LindenAbstract:Air curtains are installed in open doorways of a building to reduce buoyancy-driven exchange flows across the doorway. Although an air curtain allows an unhampered passage of humans and vehicles, the interaction of this traffic with an air curtain is not well understood. We study this problem by conducting small-scale waterbath experiments with fresh water and salt water solutions. As a model of human passage, a vertical cylinder is pulled through a planar jet representing an air curtain and separating two zones at different densities. For a fixed travel distance of the cylinder before and after the air curtain, the average infiltration flux of dense Fluid in light Fluid Side increases with increasing cylinder velocity. However, we find that the infiltration flux is independent of density difference across the doorway and the travel direction of the cylinder. As a consequence, the sealing effectiveness of an air curtain reduces with an increasing cylinder speed and this reduction is independent of the direction of the buoyancy-driven flow. Dye visualisations of the air curtain and the cylinder wake are used to examine the re-establishment process of the air curtain after its disruption by the cylinder. We observe that the re-establishment time of the air curtain and the infiltration in the cylinder wake increases with an increasing cylinder speed.