Onset of Nucleate Boiling in Research Reactors with Thin Rectangular Channels Under Low-Velocity Upward-Flow Conditions

Riverine fish are subjected to heterogeneous flow velocities and turbulence and may use this to their advantage by selecting regions that balance energy expenditure for station holding while maximizing energy gain through feeding opportunities. This study investigated microhabitat selection by guppies Poecilia reticulata in terms of flow characteristics generated by hemisphere boulders in an open channel flume. Velocity and turbulence influenced the variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the areas of high-velocity and low-turbulence regions beside the boulders, whereas smaller guppies frequented the low-velocity and high-turbulence regions directly behind the boulders. Male guppies selected the regions of low velocity, indicating possible reduced swimming ability owing to hydrodynamic drag imposed by their fins. With increasing Gyrodactylus turnbulli burden, fish spent more time in regions with moderate velocity and lowest turbulent kinetic energy which were the most spatially and temporally homogeneous in terms of velocity and turbulence. These findings highlight the importance of heterogeneous flow conditions in river channel design owing to the behavioural variability within a species in response to velocity and turbulence.

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Roughness Effects on Flow and Heat Transfer for Additively Manufactured Channels

Journal of Turbomachinery ◽

10.1115/1.4032167 ◽

2016 ◽

Vol 138 (5) ◽

Cited By ~ 39

Author(s):

Curtis K. Stimpson ◽

Jacob C. Snyder ◽

Karen A. Thole ◽

Dominic Mongillo

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Friction Factor ◽

Flow Conditions ◽

Roughness Effects ◽

Flow And Heat Transfer ◽

Technological Advances ◽

Rectangular Channels ◽

Significant Augmentation ◽

Flow Through

Recent technological advances in the field of additive manufacturing (AM), particularly with direct metal laser sintering (DMLS), have increased the potential for building gas turbine components with AM. Using the DMLS for turbine components broadens the design space and allows for increasingly small and complex geometries to be fabricated with little increase in time or cost. Challenges arise when attempting to evaluate the advantages of the DMLS for specific applications, particularly because of how little is known regarding the effects of surface roughness. This paper presents pressure drop and heat transfer results of flow through small, as produced channels that have been manufactured using the DMLS in an effort to better understand roughness. Ten different coupons made with the DMLS all having multiple rectangular channels were evaluated in this study. Measurements were collected at various flow conditions and reduced to a friction factor and a Nusselt number. Results showed significant augmentation of these parameters compared to smooth channels, particularly with the friction factor for minichannels with small hydraulic diameters. However, augmentation of Nusselt number did not increase proportionally with the augmentation of the friction factor.

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Metal/Metal Exothermic Reactions Induced by Low Velocity Impact*

MRS Proceedings ◽

10.1557/proc-418-445 ◽

1995 ◽

Vol 418 ◽

Cited By ~ 3

Author(s):

Diana L. Woody ◽

Jeffery J. Davis ◽

Philip J. Miller

Keyword(s):

Plastic Flow ◽

Porous Metal ◽

Basic Mechanism ◽

Low Velocity Impact ◽

Small Scale ◽

Flow Conditions ◽

Low Velocity ◽

Metal Mixtures ◽

Exothermic Reactions ◽

Metal Metal

AbstractThis paper discusses experimental results from an effort conducted to discern the basic mechanism of reactions in porous metal/metal compositions under rapid plastic flow conditions. Small-scale impact tests were performed on various intermetallic mixtures: 3CuO + 2AI, Fe2O3 + 2AI, Ni + Al, and 5Ti + 3Si. The addition of polytetrafluoroethylene (Teflon) to the metal/metal mixtures has been demonstrated to affect the extent of the reactions. Real-time emissivity and species evolution measurements of the reacting materials were used to discern the chemical reactions occurring under rapid plastic flow conditions.

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Crevice Boiling in Steam Generators

Journal of Heat Transfer ◽

10.1115/1.3248155 ◽

1987 ◽

Vol 109 (3) ◽

pp. 761-767 ◽

Cited By ~ 7

Author(s):

S. Tieszen ◽

H. Merte ◽

V. S. Arpaci ◽

S. Selamoglu

Keyword(s):

Power Plants ◽

Heated Surface ◽

Nucleate Boiling ◽

Forced Flow ◽

High Speed Photography ◽

Flow Conditions ◽

Steam Generators ◽

Pressurized Water ◽

Support Plate ◽

Primary Fluid

Experimental results are presented on the influence of confinement (normal to heated surface) on nucleate boiling in forced flow. The forced flow conditions and confinement geometry studied are similar to those found for boiling between a primary-fluid tube and a tube-support plate in steam generators of pressurized-water-reactor nuclear power plants. Visual observations of the boiling process within the confined region (crevice) between the tube and its support plate, obtained by high-speed photography, are related to simultaneous two-dimensional temperature maps of the hot primary-fluid-tube surface. The results demonstrate the existence of three confinement-dependent boiling regimes in forced flow conditions that are similar to those found in pool boiling conditions. These regimes are shown to be associated with the Weber number.

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Low-Velocity Subcooled Nucleate Flow Boiling at Various Orientations

Journal of Heat Transfer ◽

10.1115/1.2822533 ◽

1995 ◽

Vol 117 (2) ◽

pp. 380-386 ◽

Cited By ~ 10

Author(s):

K. M. Kirk ◽

H. Merte ◽

R. Keller

Keyword(s):

Thin Film ◽

Heat Transfer ◽

Liquid Velocity ◽

Flow Boiling ◽

Copper Substrate ◽

Nucleate Boiling ◽

Bulk Liquid ◽

Heater Surface ◽

Low Velocity ◽

Buoyant Force

Subcooled forced convection nucleate boiling experiments with R-113 were conducted at low velocities using both thin film semitransparent gold-on-quartz and gold-coated copper substrate flat heaters at various orientations. The experiments demonstrate that if buoyancy is significant relative to bulk liquid momentum, then a decrease in the buoyant force normal to and away from the heater surface enhances the heat transfer, with the effect being greatest at low values of heat flux. Furthermore, the effect of the bulk liquid velocity is shown to be dependent on the surface orientation.

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Gas-Liquid Bubbly Flow in Vertical Pipes

Journal of Fluids Engineering ◽

10.1115/1.2817389 ◽

1996 ◽

Vol 118 (2) ◽

pp. 377-382 ◽

Cited By ~ 44

Author(s):

V. E. Nakoryakov ◽

O. N. Kashinsky ◽

V. V. Randin ◽

L. S. Timkin

Keyword(s):

Shear Stress ◽

Single Phase ◽

Liquid Velocity ◽

Bubbly Flow ◽

Upward Flow ◽

Flow Conditions ◽

Downward Flow ◽

Velocity Fluctuations ◽

Turbulent Fluctuations ◽

Diameter Pipe

Gas-liquid bubbly flow was investigated in vertical pipes for different flow conditions: fully developed turbulent downward flow in a 42.3 mm diameter pipe and upward flow in a 14.8 mm diameter pipe with liquid of elevated viscosity. Wall shear stress, local void fraction, and liquid velocity profiles, shear stress, and velocity fluctuations were measured using an electrodiffusional method. Results obtained demonstrate the existence of “universal” near-wall velocity distribution in a downward bubbly flow. The reduction of turbulent fluctuations is observed in downward flow as compared to a single-phase turbulent flow. The development of bubble-induced liquid velocity fluctuations in a “laminar” bubbly flow was studied.

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Submergence coefficient of full-width sharp-edged broad-crested rectangular weirs

Journal of Hydrology and Hydromechanics ◽

10.2478/johh-2019-0022 ◽

2019 ◽

Vol 67 (4) ◽

pp. 329-338

Author(s):

Zbyněk Zachoval ◽

Jakub Major ◽

Ladislav Roušar ◽

Ján Rumann ◽

Jan Šulc ◽

...

Keyword(s):

Experimental Research ◽

Full Range ◽

Limited Range ◽

Measured Data ◽

System Of Equations ◽

Full Width ◽

Flow Conditions ◽

Principle Of Superposition ◽

Rectangular Channels ◽

New System

Abstract Full-width sharp-edged broad-crested rectangular weirs in the range 0.1 < h/L ≤ 0.3 situated in rectangular channels are frequently used in submerged flow conditions. To determine the discharge for the submerged flow, submergence coefficient and modular limit shall be known. This article deals with their determination upon a theoretic derivation and experimental research. The equation for modular limit has been determined from energy balance with simplifications. To validate it, extensive experimental research was carried out. However, the derived equation is too complicated for practical use which is why it was approximated by a simple equation applicable for the limited range. The equation for submergence coefficient was derived by modifying Villemonte’s application of the principle of superposition and its coefficients were determined using the data from experimental research of many authors. The new system of equations computes the discharge more accurately than other authors’ equations, with the error of approximately ±10% in full range of the measured data.

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A Numerical Simulation of a Bypass Conduit With Steady and Pulsatile Flow

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45300 ◽

2003 ◽

Author(s):

Leok Poh Chua ◽

Junmei Zhang ◽

Simon Ching Man Yu ◽

Tongming Zhou

Keyword(s):

Pulsatile Flow ◽

Vascular Graft ◽

Flow Rate Ratio ◽

Stress Distributions ◽

Flow Conditions ◽

Low Velocity ◽

Piv Measurements ◽

Deceleration Phase ◽

Flow Phase ◽

Good Agreement

Intimal hyperplasia (IH) has been cited as a major cause of vascular graft failure, which is associated with the hemodynamic conditions [1, 2]. Most of the earlier studies were concentrated at the distal anastomosis, therefore in this study computational methods were used to describe the blood motion in the proximal anastomosis models. Both steady and pulsatile flow conditions have been investigated. For steady flow cases, low velocity regions were found to appear on both the heels and the toes of the junction. The spatial extent of these low velocity regions was dependent on the graft Reynolds number as well as on the grafting angle and the flow rate ratio of the graft and aorta. For the pulsatile flow, a low velocity recirculating region was formed during the peak flow phase and the flow was reverted from the graft back to the aorta during the deceleration phase of the cycle. Wall shear stress distributions for various cases were also computed. A reasonable good agreement was found between the present results and the previous PIV measurements.

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