Thermodynamic Analysis of Buoyancy-Induced Flow in Rotating Cavities

2007 ◽  
Author(s):  
J. Michael Owen
Keyword(s):  
Entropy Production ◽  
Open System ◽  
Closed System ◽  
Outer Part ◽  
Compressor Rotor ◽  
Circulation Form ◽  
Induced Flow ◽  
Gas Turbine Compressor ◽  
Cooling Air ◽  
Buoyancy Induced Flow

Buoyancy-induced flow occurs in the rotating cavities between the adjacent discs of a gas-turbine compressor rotor. In some cases, the cavity is sealed, creating a closed system; in others, there is an axial through-flow of cooling air at the centre of the cavity, creating an open system. For the closed system, Rayleigh-Be´nard (R-B) flow can occur in which a series of counter-rotating vortices, with cyclonic and anti-cyclonic circulation, form in the r-φ plane of the cavity. For the open system, R-B flow can occur in the outer part of the cavity, and the core of fluid containing the vortices rotates at a slower speed than the discs: that is, the rotating core ‘slips’ relative to the discs. These flows are examples of self-organizing systems, which are found in the world of far-from-equilibrium thermodynamics and which are associated with the maximum entropy production (MEP) principle. In this paper, these thermodynamic concepts are used to explain the phenomena that have been observed in rotating cavities, and expressions for the entropy production have been derived for both open and closed systems. For the closed system, MEP corresponds to the maximisation of the heat transfer to the cavity; for the open system, it corresponds to the maximisation of the sum of the rates of heat and work transfer. Some suggestions, as yet untested, are made to show how the MEP principle could be used to simplify the computation of buoyancy-induced flows.

Thermodynamic Analysis of Buoyancy-Induced Flow in Rotating Cavities

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
J. Michael Owen
Keyword(s):  
Entropy Production ◽  
Open System ◽  
Closed System ◽  
Outer Part ◽  
Compressor Rotor ◽  
Circulation Form ◽  
Induced Flow ◽  
Gas Turbine Compressor ◽  
Cooling Air ◽  
Buoyancy Induced Flow

Buoyancy-induced flow occurs in the rotating cavities between the adjacent disks of a gas-turbine compressor rotor. In some cases, the cavity is sealed, creating a closed system; in others, there is an axial throughflow of cooling air at the center of the cavity, creating an open system. For the closed system, Rayleigh–Bénard (RB) flow can occur in which a series of counter-rotating vortices, with cyclonic and anticyclonic circulation, form in the r-ϕ plane of the cavity. For the open system, the RB flow can occur in the outer part of the cavity, and the core of the fluid containing the vortices rotates at a slower speed than the disks: that is, the rotating core “slips” relative to the disks. These flows are examples of self-organizing systems, which are found in the world of far-from-equilibrium thermodynamics and which are associated with the maximum entropy production (MEP) principle. In this paper, these thermodynamic concepts are used to explain the phenomena that were observed in rotating cavities, and expressions for the entropy production were derived for both open and closed systems. For the closed system, MEP corresponds to the maximization of the heat transfer to the cavity; for the open system, it corresponds to the maximization of the sum of the rates of heat and work transfer. Some suggestions, as yet untested, are made to show how the MEP principle could be used to simplify the computation of buoyancy-induced flows.

Buoyancy-Induced Flow in Open Rotating Cavities

2007 ◽  
Vol 129 (4) ◽  
pp. 893-900 ◽  
Author(s):  
J. Michael Owen ◽  
Hans Abrahamsson ◽  
Klas Lindblad
Keyword(s):  
Tangential Velocity ◽  
Axial Flow ◽  
Quantitative Agreement ◽  
Turbine Engines ◽  
The Third ◽  
Commercial Code ◽  
Heated Disk ◽  
Induced Flow ◽  
Cooling Air ◽  
Buoyancy Induced Flow

Buoyancy-induced flow can occur in the cavity between the co-rotating compressor disks in gas-turbine engines, where the Rayleigh numbers can be in excess of 1012. In most cases the cavity is open at the center, and an axial throughflow of cooling air can interact with the buoyancy-induced flow between the disks. Such flows can be modeled, computationally and experimentally, by a simple rotating cavity with an axial flow of air. This paper describes work conducted as part of ICAS-GT, a major European research project. Experimental measurements of velocity, temperature, and heat transfer were obtained on a purpose-built experimental rig, and these results have been reported in an earlier paper. In addition, 3D unsteady CFD computations were carried out using a commercial code (Fluent) and a RNG k‐ε turbulence model. The computed velocity vectors and contours of temperature reveal a flow structure in which, as seen by previous experimenters, “radial arms” transport cold air from the center to the periphery of the cavity, and regions of cyclonic and anticyclonic circulation are formed on either side of each arm. The computed radial distribution of the tangential velocity agrees reasonably well with the measurements in two of the three cases considered here. In the third case, the computations significantly overpredict the measurements; the reason for this is not understood. The computed and measured values of Nu for the heated disk show qualitatively similar radial distributions, with high values near the center and the periphery. In two of the cases, the quantitative agreement is reasonably good; in the third case, the computations significantly underpredict the measured values.

Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors

2017 ◽  
Author(s):  
Hui Tang ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Gravitational Acceleration ◽  
Centripetal Acceleration ◽  
Closed Cavity ◽  
Nusselt Numbers ◽  
Industrial Gas Turbines ◽  
Induced Flow ◽  
Cooling Air ◽  
Buoyancy Induced Flow

The cavities between the rotating compressor discs in aeroengines are open, and there is an axial throughflow of cooling air in the annular space between the centre of the discs and the central rotating compressor shaft. Buoyancy-induced flow occurs inside these open rotating cavities, with an exchange of heat and momentum between the axial throughflow and the air inside the cavity. However, even where there is no opening at the centre of the compressor discs — as is the case in some industrial gas turbines — buoyancy-induced flow can still occur inside the closed rotating cavities. The closed cavity also provides a limiting case for an open cavity when the axial clearance between the cobs — the bulbous hubs at the centre of compressor discs — is reduced to zero. Bohn and his co-workers at the University of Aachen have studied three different closed-cavity geometries, and they have published experimental data for the case where the outer cylindrical surface is heated and the inner surface is cooled. In this paper, a buoyancy model is developed in which it is assumed that the heat transfer from the cylindrical surfaces is analogous to laminar free convection from horizontal plates, with the gravitational acceleration replaced by the centripetal acceleration. The resulting equations, which have been solved analytically, show how the Nusselt numbers depend on both the geometry of the cavity and its rotational speed. The theoretical solutions show that compressibility effects in the core attenuate the Nusselt numbers, and there is a critical Reynolds number at which the Nusselt number will be a maximum. For the three cavities tested, the predicted Nusselt numbers are in generally good agreement with the measured values of Bohn et al. over a large range of Raleigh numbers up to values approaching 1012. The fact that the flow remains laminar even at these high Rayleigh numbers is attributed to the Coriolis accelerations suppressing turbulence in the cavity, which is consistent with recently-published results for open rotating cavities.

Buoyancy-Induced Flow in Open Rotating Cavities

2006 ◽  
Author(s):  
J. Michael Owen ◽  
Hans Abrahamsson ◽  
Klas Lindblad
Keyword(s):  
Tangential Velocity ◽  
Axial Flow ◽  
Quantitative Agreement ◽  
Turbine Engines ◽  
The Third ◽  
Commercial Code ◽  
Heated Disc ◽  
Induced Flow ◽  
Cooling Air ◽  
Buoyancy Induced Flow

Buoyancy-induced flow can occur in the cavity between the co-rotating compressor discs in gas-turbine engines, where the Rayleigh numbers can be in excess of 1012. In most cases the cavity is open at the centre, and an axial throughflow of cooling air can interact with the buoyancy-induced flow between the discs. Such flows can be modeled, computationally and experimentally, by a simple rotating cavity with an axial flow of air. This paper describes work conducted as part of ICAS-GT, a major European research project. Experimental measurements of velocity, temperature and heat transfer were obtained on a purpose-built experimental rig, and these results have been reported in an earlier paper. In addition, 3D unsteady CFD computations were carried out using a commercial code (Fluent) and an RNG k-ε turbulence model. The computed velocity vectors and contours of temperature reveal a flow structure in which, as seen by previous experimenters, ‘radial arms’ transport cold air from the centre to the periphery of the cavity, and regions of cyclonic and anti-cyclonic circulation are formed on either side of each arm. The computed radial distribution of the tangential velocity agrees reasonably well with the measurements in two of the three cases considered here. In the third case, the computations significantly over-predict the measurements; the reason for this is not understood. The computed and measured values of Nu for the heated disc show qualitatively similar radial distributions, with high values near the centre and the periphery. In two of the cases, the quantitative agreement is reasonably good; in the third case, the computations significantly under-predict the measured values.

Buoyancy-Induced Flow in a Heated Rotating Cavity

2004 ◽  
Vol 128 (1) ◽  
pp. 128-134 ◽  
Author(s):  
J. Michael Owen ◽  
Jonathan Powell
Keyword(s):  
Laser Doppler Anemometry ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Velocity Measurements ◽  
Turbine Engine ◽  
Rotating Cavity ◽  
Heated Disk ◽  
Induced Flow ◽  
Cooling Air ◽  
Buoyancy Induced Flow

Experimental measurements were made in a rotating-cavity rig with an axial throughflow of cooling air at the center of the cavity, simulating the conditions that occur between corotating compressor disks of a gas-turbine engine. One of the disks in the rig was heated, and the other rotating surfaces were quasi-adiabatic; the temperature difference between the heated disk and the cooling air was between 40 and 100°C. Tests were conducted for axial Reynolds numbers, Rez, of the cooling air between 1.4×103 and 5×104, and for rotational Reynolds numbers, Reϕ, between 4×105 and 3.2×106. Velocity measurements inside the rotating cavity were made using laser Doppler anemometry, and temperatures and heat flux measurements on the heated disk were made using thermocouples and fluxmeters. The velocity measurements were consistent with a three-dimensional, unsteady, buoyancy-induced flow in which there was a multicell structure comprising one, two, or three pairs of cyclonic and anticyclonic vortices. The core of fluid between the boundary layers on the disks rotated at a slower speed than the disks, as found by other experimenters. At the smaller values of Rez, the radial distribution and magnitude of the local Nusselt numbers, Nu, were consistent with buoyancy-induced flow. At the larger values of Rez, the distribution of Nu changed, and its magnitude increased, suggesting the dominance of the axial throughflow.

Buoyancy-Induced Flow in a Heated Rotating Cavity

2004 ◽  
Author(s):  
J. Michael Owen ◽  
Jonathan Powell
Keyword(s):  
Reynolds Numbers ◽  
Velocity Measurements ◽  
Turbine Engine ◽  
Nusselt Numbers ◽  
Rotating Cavity ◽  
Heated Disc ◽  
Flux Measurements ◽  
Induced Flow ◽  
Cooling Air ◽  
Buoyancy Induced Flow

Experimental measurements were made in a rotating-cavity rig with an axial throughflow of cooling air at the centre of the cavity, simulating the conditions that occur between corotating compressor discs of a gas-turbine engine. One of the discs in the rig was heated, and the other rotating surfaces were quasi-adiabatic; the temperature difference, between the heated disc and the cooling air was between 40 and 100 °C. Tests were conducted for axial Reynolds numbers, Rez, of the cooling air between 1.4 × 103 and 5 × 104, and for rotational Reynolds numbers, Reφ, between 4 × 105 and 3.2 × 106. Velocity measurements inside the rotating cavity were made using LDA, and temperatures and heat flux measurements on the heated disc were made using thermocouples and fluxmeters. The velocity measurements were consistent with a 3D, unsteady, buoyancy-induced flow in which there was a multicell structure comprising one, two or three pairs of cyclonic and anti-cyclonic vortices. The core of fluid between the boundary layers on the discs rotated at a slower speed than the discs, as found by other experimenters. At the smaller values of Rez, the radial distribution and magnitude of the local Nusselt numbers, Nu, were consistent with buoyancy-induced flow. At the larger values of Rez, the distribution of Nu changed, and its magnitude increased, suggesting the dominance of the axial throughflow.

Impact of flavours, device, nicotine levels and price on adult e-cigarette users’ tobacco and nicotine product choices

2021 ◽  
pp. tobaccocontrol-2021-056599
Author(s):  
Yong Yang ◽  
Eric N. Lindblom ◽  
Ramzi G. Salloum ◽  
Kenneth D. Ward
Keyword(s):  
Open System ◽  
Closed System ◽  
Smoking Status ◽  
Discrete Choice Experiments ◽  
User Characteristics ◽  
Product Attributes ◽  
Product Choices ◽  
Nicotine Level ◽  
The Difference ◽  
The Impact

IntroductionTo understand the impact of e-cigarette devices, flavours, nicotine levels and prices on adult e-cigarette users’ choices among closed-system and open-system e-cigarettes, cigarettes and heated tobacco products (HTPs).MethodsOnline discrete choice experiments were conducted among adult (≥18 years) e-cigarette users (n=2642) in August 2020. Conditional logit regressions were used to assess the relative impact of product attributes and the interactions between product attributes and user characteristics, with stratified analyses to examine differences by smoking status and primarily used e-cigarette device and flavour.ResultsOn average, participants preferred non-tobacco and non-menthol flavours most, preferred open-system over closed-system e-cigarettes and preferred regular nicotine level over low nicotine level. However, the preference varied by demographics, smoking status and the primarily used e-cigarette device and flavour. The differences in preference among products/devices were larger than the difference among flavours or nicotine levels. Participants who primarily used closed-system e-cigarettes exhibited similar preferences for closed-system and open-system e-cigarettes, but those who primarily used open-system e-cigarettes preferred much more open-system over closed-system e-cigarettes. HTP was the least preferred product, much lower than cigarettes in general, but participants living in states where IQOS is being sold had similar preferences to cigarettes and HTPs.ConclusionsPeople are unlikely to switch to another product/device because of the restriction of flavour or nicotine level. If non-tobacco and non-menthol flavours were banned from open-system e-cigarettes, users may switch to menthol flavour e-cigarettes. Intervention strategies should be tailored to specific groups.

Buoyancy-induced flow, heat, and mass transfer in a porous annulus

2017 ◽  
Vol 72 (2) ◽  
pp. 107-125 ◽  
Author(s):  
F. Moukalled ◽  
J. Kasamani ◽  
M. Darwish ◽  
A. Hammoud ◽  
M. Khamis Mansour
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Flow Heat ◽  
Induced Flow ◽  
Buoyancy Induced Flow

scholarly journals Water and fertilizers use efficiency in two hydroponic systems for tomato production

2020 ◽  
Vol 38 (1) ◽  
pp. 47-52 ◽  
Author(s):  
Rodolfo De la Rosa-Rodríguez ◽  
Alfredo Lara-Herrera ◽  
Libia Iris Trejo-Téllez ◽  
Luz Evelia Padilla-Bernal ◽  
Luis Octavio Solis-Sánchez ◽  
...  
Keyword(s):  
Nutrient Solution ◽  
Open System ◽  
Closed System ◽  
Good Alternative ◽  
Fruit Production ◽  
Tomato Production ◽  
Hydroponic System ◽  
Production Water ◽  
Use Efficiency ◽  
Hydroponic Systems

ABSTRACT The amount of water and fertilizers used in the production of vegetables, specifically tomatoes, is high. This study was carried out to determine water and fertilizers use efficiency in closed and open hydroponic systems for tomato production under greenhouse conditions. Two treatments with eight replications were assessed; each replication consisted of 67 pots with two plants each. One treatment was a closed hydroponic system (with nutrient solution recirculation), and the other was an open hydroponic system (with non-recirculating nutrient solution). We quantified the amounts of water and fertilizers applied, as well as the losses (drained nutrient solution), in the two treatments during the entire cycle of tomato. In the nutrient solution (NS) we also measured electric conductivity (EC), pH, volume applied, and volume drained, and total weight of fruits (25 pickings). There were no significant differences between the two treatments on fruit production. Water use efficiency was 59.53 kg/fruit/m3 for the closed system and 46.03 kg/fruit/m3 in the open system. In comparison to the open system, the closed system produced 13.50 kg more fruit per cubic meter of water, while 10.31 grams less fertilizers per kilogram of fruit produced were only applied. Water and fertilizers use efficiency were higher in the closed system, by 22.68% and 22.69%, respectively. More efficiency was obtained in the closed system, regarding the open system. We concluded that the closed system is a good alternative to produce tomato and preserve the resources involved in the process (like water and fertilizers), thus reducing pollution.

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