An Experimental Investigation on the Effects of Heat and Mass Flux on Vapor Bubble Growth Characteristics in a Microchannel

2009 ◽  
Author(s):  
Zachary Edel ◽  
Abhijit Mukherjee
Keyword(s):  
Flow Rate ◽  
Heat Exchangers ◽  
Bubble Growth ◽  
High Speed ◽  
Flow Boiling ◽  
Bubble Formation ◽  
Flow Characteristics ◽  
Vapor Bubbles ◽  
Constant Flow Rate ◽  
Temperature Liquid

Micro heat exchangers are emerging as one of the most effective cooling technologies for high power-density applications. The design of micro heat exchangers is complicated by the presence of alternating flow regimes, which give way to flow boiling instability. Bubble formation inside microchannels can be correlated directly to flow boiling instability and can regulate flow characteristics and wall heat transfer when the bubbles grow to reach the microchannel hydraulic diameter. In this study, the growth of vapor bubbles in a single microchannel was examined using an experimental setup capable of measuring coolant flow rate, inlet and outlet liquid temperatures, and channel wall surface temperature. Liquid flow rate and wall heat flux were systematically varied while a high-speed camera was used to capture images of vapor bubbles forming in the channel. These images were used to compare bubble growth rates for a constant flow rate. The results provide fundamental understanding of the bubble growth process.

Study of Subcooled Film Boiling on a Horizontal Disc:1 Part 2—Experiments

2000 ◽  
Vol 123 (2) ◽  
pp. 285-293 ◽  
Author(s):  
D. Banerjee ◽  
V. K. Dhir
Keyword(s):  
Liquid Phase ◽  
Particle Tracking ◽  
Bubble Growth ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Digital Camera ◽  
Film Boiling ◽  
Convection Flow ◽  
Vapor Bubbles ◽  
Natural Convection Flow

Experiments were performed to study subcooled film boiling of performance liquid PF-5060 (made by 3-M Company) on a horizontal copper disc. The experiments were performed for two regimes of film boiling involving departing vapor bubbles (low subcooling) and nondeparting vapor bubbles (high subcooling). By employing high speed digital camera, data were obtained for temporal variation of bubble height, bubble shape and bubble growth rate over one cycle. Heat flux data were deduced from temperatures measured with thermocouples embedded in the solid. The results from the numerical model are compared with experimental data and are found to be in general agreement. Particle Tracking Velocimetry (PTV) experiments were performed for a configuration of non-departing vapor bubbles to study the flow field in the liquid phase. The PTV experiments point to the existence of natural convection flow in the liquid phase and is in qualitative agreement with the predictions available in the literature.

Dynamics of Vapor Bubble Growth and Detachment in a Channel Flow

2006 ◽  
Author(s):  
G. Duhar ◽  
C. Colin
Keyword(s):  
Channel Flow ◽  
Bubble Growth ◽  
High Speed ◽  
Dominant Role ◽  
Bubble Radius ◽  
Video Camera ◽  
Vapor Bubbles ◽  
Equivalent Radius ◽  
Multiple Bubbles ◽  
Hot Film

The aim of this study is to improve the knowledge of the dynamics of vapor bubbles growing on a wall in a shear flow. Vapor bubbles are created on a hot film probe flushed mounted in the lower wall of a horizontal channel. The film overheat temperature controlled by an anemometer is limited to 20°C to avoid the growth of multiple bubbles. The liquid flow in the channel measured by Particle Image Velocimetry is laminar or turbulent. Bubble growth and detachment in the channel flow are filmed with a high-speed video camera at 2000 frame/second. Image processing allows obtaining the temporal evolutions of the bubble kinematics characteristics: the equivalent radius and the position of the centre of gravity. These data are then used to calculate the bubble growth rate and the forces acting on the bubbles during their growth and after their detachment. After detachment, drag, buoyancy and added mass forces play a dominant role. From the investigation of the bubble trajectories after detachment, the drag coefficient can be determined. When the bubble is attached to the wall capillary forces are dominant. A predictive model for bubble radius at detachment is provided depending on the wall overheat.

scholarly journals Quasi 3D Nacelle Design to Simulate Crosswind Flows: Merits and Challenges

2019 ◽  
Vol 4 (3) ◽  
pp. 25 ◽  
Author(s):  
Alex Yeung ◽  
Nagabhushana Rao Vadlamani ◽  
Tom Hynes ◽  
Sumit Sarvankar
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
High Speed ◽  
Computational Modelling ◽  
Flow Characteristics ◽  
Attached Flow ◽  
Set Up ◽  
Engine Nacelle ◽  
Shape Changes

This paper studies the computational modelling of the flow separation over the engine nacelle lips under the off-design condition of significant crosswind. A numerical framework is set up to reproduce the general flow characteristics under crosswinds with increasing engine mass flow rate, which include: low-speed separation, attached flow and high speed shock-induced separation. A quasi-3D (Q3D) duct extraction method from the full 3D (F3D) simulations has been developed. Results obtained from the Q3D simulations are shown to largely reproduce the trends observed (isentropic Mach number variations and high-speed separation behaviour) in the 3D intake, substantially reducing the simulation time by a factor of 50. The agreement between the F3D and Q3D simulations is encouraging when the flow either fully attached or with modest levels of separation but degrades when the flow fully detaches. Results are shown to deviate beyond this limit since the captured streamtube shape (and hence the corresponding Q3D duct shape) changes with the mass flow rate. Interestingly, the drooped intake investigated in the current study is prone to earlier separation under crosswinds when compared to an axisymmetric intake. Implications of these results on the industrial nacelle lip design are also discussed.

Effects of the Gas Feed on Bubble Formation in a Microfluidic T-Junction: Constant-Pressure versus Constant-Flow-Rate Injection

2019 ◽  
Vol 58 (23) ◽  
pp. 10092-10105 ◽  
Author(s):  
Sheng Mi ◽  
Netsanet Tesfaye Weldetsadik ◽  
Zafar Hayat ◽  
Taotao Fu ◽  
Chunying Zhu ◽  
...  
Keyword(s):  
Flow Rate ◽  
Constant Pressure ◽  
Bubble Formation ◽  
Constant Flow ◽  
Constant Flow Rate

Motion of a deformable capsule through a hyperbolic constriction

1994 ◽  
Vol 279 ◽  
pp. 135-163 ◽  
Author(s):  
Anne Leyrat-Maurin ◽  
Dominique Barthes-Biesel
Keyword(s):  
Pressure Drop ◽  
Flow Rate ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Quantitative Information ◽  
Maximum Energy ◽  
Centre Of Mass ◽  
Intrinsic Properties ◽  
Constant Flow Rate ◽  
Reynolds Number Flow

A model for the low-Reynolds-number flow of a capsule through a constriction is developed for either constant-flow-rate or constant-pressure-drop conditions. Such a model is necessary to infer quantitative information on the intrinsic properties of capsules from filtration experiments conducted on a dilute suspension of such particles. A spherical capsule, surrounded by an infinitely thin Mooney-Rivlin membrane, is suspended on the axis of a hyperbolic constriction. This configuration is fully axisymmetric and allows the entry and exit phenomena through the pore to be modelled. An integral formulation of the Stokes equations describing the flow in the internal and external domains is developed. It provides a representation of the velocity at any location in the flow as a function of the unknown forces exerted by the boundaries on the fluids. The problem is solved by a collocation technique in the case where the internal and external viscosities are equal. Microscopic quantities (instantaneous geometry, centre of mass velocity, elastic tensions in the membrane) as well as macroscopic quantities (entry time, additional pressure drop or flow rate reduction) are predicted as a function of the capsule intrinsic properties and flow characteristics. The results obtained for a capsule whose initial diameter is larger than that of the constriction throat show that the maximum energy expenditure occurs when the particle centre of mass is still upstream of the throat (typically 1 diameter away), and is thus due to the entry process. For large enough or rigid enough capsules, the model predicts entrance or exit plugging, in agreement with experimental observations. It is then possible to correlate the variation of the pore hydraulic resistance to the flow capillary number (ratio of viscous to elastic forces) and to the size ratio between the pore and the capsule.

scholarly journals Microlayer dynamics during the growth process of a single vapour bubble under subcooled flow boiling conditions

2021 ◽  
Vol 931 ◽  
Author(s):  
Gulshan Kumar Sinha ◽  
Surya Narayan ◽  
Atul Srivastava
Keyword(s):  
Bubble Growth ◽  
High Speed ◽  
Growth Process ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Working Fluid ◽  
Vapour Bubble ◽  
Subcooled Flow Boiling ◽  
High Speed Cinematography ◽  
Fringe Patterns

The phenomena of microlayer formation and its dynamic characteristics during the nucleate pool boiling regime have been widely investigated in the past. However, experimental works on real-time microlayer dynamics during nucleate flow boiling conditions are highly scarce. The present work is an attempt to address this lacuna and is concerned with developing a fundamental understanding of microlayer dynamics during the growth process of a single vapour bubble under nucleate flow boiling conditions. Boiling experiments have been conducted under subcooled conditions in a vertical rectangular channel with water as the working fluid. Thin-film interferometry combined with high-speed cinematography have been adopted to simultaneously capture the dynamic behaviour of the microlayer along with the bubble growth process. Transients associated with the microlayer have been recorded in the form of interferometric fringe patterns, which clearly reveal the evolution of the microlayer beneath the growing vapour bubble, the movement of the triple contact line and the growth of the dryspot region during the bubble growth process. While symmetric growth of the microlayer was confirmed in the early growth phase, the bulk flow-induced bubble deformation rendered asymmetry to its profile during the later stages of the bubble growth process. The recorded fringe patterns have been quantitatively analysed to obtain microlayer thickness profiles at different stages of the bubble growth process. For Re = 3600, the maximum thickness of the almost wedge-shaped microlayer was obtained as δ ~ 3.5 μm for a vapour bubble of diameter 1.6 mm. Similarly, for Re = 6000, a maximum microlayer thickness of δ ~ 2.5 μm was obtained for a bubble of diameter 1.1 mm.

Unsaturated flow characteristics in dual-scale fibre fabrics at one-dimensional constant flow rate

2016 ◽  
Vol 23 (6) ◽  
pp. 617-624
Author(s):  
Yan Shilin ◽  
Yan Fei ◽  
Li Dequan ◽  
Li Yongjing
Keyword(s):  
Flow Rate ◽  
Unsaturated Flow ◽  
Flow Characteristics ◽  
Constant Flow ◽  
One Dimensional ◽  
Constant Flow Rate ◽  
Liquid Composite Moulding ◽  
Mould Filling ◽  
Set Up ◽  
Dual Scale

AbstractFibre fabrics in liquid composite moulding can be considered as dual-scale porous media. In different gap scales, an unsaturated flow is produced during the mould filling process. This particular flow behaviour deviates from the traditional Darcy’s law, which is used to calculate the filling pressure and will cause errors. To prove the mechanism of this unsaturated flow, an experimental device was set up with a one-dimensional constant flow rate. The influencing factors, such as injected media, flow velocity and fibre fabric, were investigated in this study. Based on the experimental data, several useful conclusions were drawn, providing good references for optimising the process parameters and controlling the product quality.

Wetting and Capillarity Effects On Bubble Formation From Orifice Plates Submerged in Pools of Water

2021 ◽  
Author(s):  
Sanjivan Manoharan ◽  
Raj M. Manglik ◽  
Milind A. Jog
Keyword(s):  
Contact Angle ◽  
Bubble Growth ◽  
High Speed ◽  
Bubble Formation ◽  
Minimum Energy ◽  
Hydrophobic Surface ◽  
Contact Angles ◽  
Orifice Diameter ◽  
Capillary Length ◽  
Critical Contact

Abstract An experimental study of bubble growth from submerged orifice plates in pools of water is carried out to scale and correlate the effects of surface wettability and orifice diameter D0 on ebullience. Measurements of bubble growth on surfaces with nine different contact angles (38° ≤ θ ≤ 128°) with varying air flow rates (1 to 300 ml/min) were made using high speed videography and image processing. In the static or constant-volume regime, below a critical contact angle θc, the bubble base remains attached to the orifice and the equivalent departure diameter Db is independent of contact angle θ. On the other hand, above the critical contact angle, the bubble base spreads on the surface resulting in larger Db. For θ > θc, Db is strongly dependent on θ and increases with it. Using minimum energy method, it is shown that the wettability effects can be scaled and correlated by a modified capillary length, defined as a function of the Laplace length and contact angle. The proposed correlation provides predictions of Db that agree with experimental data of this study as well as those available in the literature to within ±15 %. Moreover, for a hydrophobic surface when D0 > twice the modified capillary length, the bubble grows inside the orifice; for a hydrophilic surface this scales with twice the capillary length and effect of θ is not seen.

Effect of Dual Frequency Ultrasound on the Bubble Formation in a Capillary Tube

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Benwei Fu ◽  
Nannan Zhao ◽  
Guoyou Wang ◽  
Hongbin Ma
Keyword(s):  
Bubble Growth ◽  
High Speed ◽  
Capillary Tube ◽  
Bubble Formation ◽  
Single Frequency ◽  
Quartz Tube ◽  
Outer Diameter ◽  
Dual Frequency ◽  
Heating Section ◽  
Frequency Ultrasound

A visual experimental investigation was conducted to determine the effect of dual frequency ultrasound on the bubble formation and growth in a capillary quartz tube. Two piezoelectric ceramics were used in this experiment. They were made of Pb-based lanthanum-doped zirconate titanates (PLZTs). The PLZTs were placed on a quartz tube with an inner diameter of 2 mm and an outer diameter of 3 mm. The capillary tube was vacuumed first and then charged with water using a filling ratio of 70%. The ultrasonic sound was applied to the heating section of a capillary tube. The bubble formation and growth were recorded by a high speed camera. As shown in figures, when the ultrasound with a single frequency of either 154 kHz or 474 kHz was applied, only one bubble was generated. When the dual frequencies of 154 kHz and 474 kHz were applied, more bubbles were generated. The speed of the bubble growth with dual frequency ultrasound was much higher than that with a single frequency. When a dual frequency ultrasound (154 kHz and 474 kHz) was used, the nucleation sites for bubble formation were significantly increased and the bubble growth rate enhanced.

A Novel Injection System for Hypovolemic Patients

2006 ◽  
Author(s):  
Simone P. Ercolani ◽  
Paolo Conti ◽  
Lucio Banetta
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Heart Valves ◽  
Venous Pressure ◽  
Vena Cava ◽  
Maximum Flow ◽  
Injection System ◽  
Constant Flow Rate ◽  
Experimental Apparatus

The aim of this paper is to test a new infusion system prototype which is intended to recover the normal venous return and lost blood quantity in hypovolemic patients. For this purpose a bolus of fluid is injected at a high speed in the vena cava, accelerating and dragging the stagnating flow upstream the catheter. In order to improve the effects of the injection and to avoid damage to heart valves, the injection is synchronized with the heart cycle and should be controlled by the electrocardiogram track of the patient in such a way that the maximum flow rate injected occurs when the tricuspid valve is open. An in-vitro experimental apparatus — simulating the vena cava and its environment — has been built and used to measure velocity and pressure fields in the vena cava during the high velocity injection. In a first embodiment, the experimental apparatus consists of two reservoirs arranged, respectively, upstream and downstream a Starling Resistor, but at different heights. A constant flow rate inside the vena cava is maintained, thus simulating the diastolic phase of the heart. In a second embodiment of the experimental apparatus, two electrical valves, arranged downstream the Starling Resistor, generate an oscillating pressure wave along the vena cava, thus simulating the human central venous pressure. By varying the flow rate inside the vena cava and the opening rate of the valves, it has been possible to evaluate the dragging effect of the new injection system and the mechanical behavior of the vena cava during both continuous and pulsating infusion.

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