Experiments on High-Speed Liquid Films Over Downward-Facing Wetting and Nonwetting Surfaces

2003 ◽  
Vol 44 (1) ◽  
pp. 132-137 ◽  
Author(s):  
J. K. Anderson ◽  
M. Yoda ◽  
S. I. Abdel-Khalik ◽  
D. L. Sadowski ◽  
Keyword(s):  
High Speed ◽  
Liquid Films

Study of the Fluid Dynamics of Thin Liquid Films Flowing Down a Vertical String With Counterflow of Gas

2015 ◽  
Author(s):  
Zezhi Zeng ◽  
Gopinath Warrier ◽  
Y. Sungtaek Ju
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Film Thickness ◽  
Liquid Film ◽  
Direct Contact ◽  
High Speed ◽  
Small Diameter ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Liquid Coolant

Direct-contact heat transfer between a falling liquid film and a gas stream yield high heat transfer rates and as such it is routinely used in several industrial applications. This concept has been incorporated by us into the proposed design of a novel heat exchanger for indirect cooling of steam in power plants. The DILSHE (Direct-contact Liquid-on-String Heat Exchangers) module consists of an array of small diameter (∼ 1 mm) vertical strings with hot liquid coolant flowing down them due to gravity. A low- or near-zero vapor pressure liquid coolant is essential to minimize/eliminate coolant loss. Consequently, liquids such as Ionic Liquids and Silicone oils are ideal candidates for the coolant. The liquid film thickness is of the order of 1 mm. Gas (ambient air) flowing upwards cools the hot liquid coolant. Onset of fluid instabilities (Rayleigh-Plateau and/or Kapitza instabilities) result in the formation of a liquid beads, which enhance heat transfer due to additional mixing. The key to successfully designing and operating DILSHE is understanding the fundamentals of the liquid film fluid dynamics and heat transfer and developing an operational performance map. As a first step towards achieving these goals, we have undertaken a parametric experimental and numerical study to investigate the fluid dynamics of thin liquid films flowing down small diameter strings. Silicone oil and air are the working fluids in the experiments. The experiments were performed with a single nylon sting (fishing line) of diameter = 0.61 mm and height = 1.6 m. The inlet temperature of both liquid and air were constant (∼ 20 °C). In the present set of experiments the variables that were parametrically varied were: (i) liquid mass flow rate (0.05 to 0.23 g/s) and (ii) average air velocity (0 to 2.7 m/s). Visualization of the liquid flow was performed using a high-speed camera. Parameters such as base liquid film thickness, liquid bead shape and size, velocity (and hence frequency) of beads were measured from the high-speed video recordings. The effect of gas velocity on the dynamics of the liquid beads was compared to data available in the open literature. Within the range of gas velocities used in the experiments, the occurrence of liquid hold up and/or liquid blow over, if any, were also identified. Numerical simulations of the two-phase flow are currently being performed. The experimental results will be invaluable in validation/refinement of the numerical simulations and development of the operational map.

A comparative study on the breakup of Newtonian and viscoelastic liquid films

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840032
Author(s):  
Lijuan Qian ◽  
Shaobo Song ◽  
Lisha Jiang ◽  
Xiaolu Li ◽  
Jianzhong Lin
Keyword(s):  
Liquid Film ◽  
High Speed ◽  
Liquid Films ◽  
Viscoelastic Liquid ◽  
Ligament Length ◽  
Time Resolved ◽  
Liquid Bubble ◽  
Mean Size ◽  
The Difference ◽  
The Stability

The breakup of viscoelastic liquid films are investigated experimentally and analytically. The breakup phenomena of viscoelastic liquid film are recorded by the time resolved high speed camera. Video images reveal the difference behavior of liquid bubble breakup for Newtonian and viscoelastic liquid. For the Newtonian liquid, cylindrical ligaments are stretched into droplets with large distributions of drop size. For the viscoelastic liquid, the pinch-off point is located on the liquid connections to the nozzle and finally the main part of the ligament no longer elongates. Furthermore, a dispersion relation based on the stability analysis is involved to predict the ligament length and drop mean size after breakup for liquid film. The calculated ligament length is validated by the measured drop mean size at higher air-to-liquid mass flow ratio.

Breakdown of a Locally Heated Liquid Film Shear-Driven in a Minichannel

2006 ◽  
Author(s):  
D. V. Zaitsev ◽  
O. A. Kabov
Keyword(s):  
Heat Flux ◽  
Liquid Film ◽  
High Speed ◽  
Cooling System ◽  
Flow Regimes ◽  
High Heat ◽  
Liquid Films ◽  
High Heat Flux ◽  
Film Breakdown ◽  
High Heat Transfer

The paper focuses upon shear-driven liquid film evaporative cooling of high-speed computer chips. Thin liquid films may provide very high heat transfer rates, however development of cooling system based on thin film technology requires significant advances in fundamental research. The paper presents new experimental data on flow and breakdown of a liquid film driven by the action of a forced gas flow in a horizontal minichannel (2 mm high), heated from a 22×6.55 mm heater. A map of isothermal flow regimes is plotted and the lengths of smooth region and region of 2D/3D wave occurrence are measured. The scenario of liquid film breakdown under heating is found to differ widely for different flow regimes. It is revealed that the critical heat flux at which film breakdown occurs for a shear-driven liquid film can be several times higher than that for a gravitationally-driven liquid film. This fact makes shear-driven liquid films very promising in high heat flux cooling applications.

scholarly journals Formation and rupture of gas film of antibubble

2020 ◽  
Vol 23 (1) ◽  
pp. 91-104
Author(s):  
Lichun Bai ◽  
Jinguang Sun ◽  
Zhijie Zeng ◽  
Yuhang Ma ◽  
Lixin Bai
Keyword(s):  
Liquid Film ◽  
High Speed ◽  
Liquid Surface ◽  
Single Layer ◽  
Liquid Films ◽  
Droplet Impact ◽  
Liquid Interface ◽  
High Speed Photography ◽  
Merging Process ◽  
The Impact

The formation and rupture of gas film in the process of formation, rupture and coalescence of antibubbles were investigated by high-speed photography. It was found that a gas film will appear and wrap a droplet when the droplet hit a layer of liquid film or foam before impacting the gas-liquid interface. The gas film may survive the impact on the gas-liquid interface and act as the gas film of an antibubble. A multilayer droplet will be formed when the droplet hits through several layer of liquid films, and a multilayer antibubble will be formed when the multilayer droplet impact a gas-liquid interface or a single layer of foam on the liquid surface. The way to generate antibubbles by liquid films will undergo the formation and rupture of gas films. The coalescence of two antibubbles, which shows a similar merging process of soap bubbles, also undergo the rupture and formation of gas films. The rupture of gas film of antibubble caused by aging and impact is also discussed.

Cavity generation by accelerated relative motions between solid walls contacting in liquid

2008 ◽  
Vol 222 (9) ◽  
pp. 1695-1705 ◽  
Author(s):  
S Washio ◽  
S Takahashi ◽  
K Murakami ◽  
T Tada ◽  
S Deguchi
Keyword(s):  
Liquid Film ◽  
High Speed ◽  
Initial Pressure ◽  
Liquid Films ◽  
Constant Acceleration ◽  
Video Cameras ◽  
Initial Clearance ◽  
Solid Walls ◽  
Tangential Directions ◽  
Relative Motions

A contact motion between two solids in a liquid can give rise to a cavity. To investigate this phenomenon, processes of cavity generation in a liquid between two walls making accelerated relative motions in their normal and tangential directions have been observed in detail, using microscopes and high-speed video cameras. The results are as follows: generation and subsequent expansion of a cavity are influenced by factors such as the initial clearance between the walls, the acceleration of motion, the initial pressure, the liquid viscosity, and the contact area. In contrast, air solubility in oil does not affect generation, but the size of a bubble remaining in the liquid. The pressure in a liquid film between two parallel walls normally moving away with a constant acceleration has also been theoretically analysed, providing the basis for the generation of tensile stresses in liquid films. Finally, the following idea of mechanism has been proposed: a tensile stress occurring in a liquid film breaks the liquid—solid interface, producing a rift, which develops into a visible cavity. Considering that liquid machines have many parts of contacting solids making relative motions, it is presumed that cavitation in them can start from this phenomenon.

High-speed oblique drop impact on thin liquid films

2017 ◽  
Vol 29 (8) ◽  
pp. 082108 ◽  
Author(s):  
Yisen Guo ◽  
Yongsheng Lian
Keyword(s):  
High Speed ◽  
Liquid Films ◽  
Drop Impact ◽  
Thin Liquid Films

Flow Patterns and Heat Transfer in Thin Liquid Films on Walls With Straight, Meandering and Zigzag Mini-Grooves

2008 ◽  
Author(s):  
Karsten Lo¨ffler ◽  
Hongyi Yu ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Patterns ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Transport Processes ◽  
Temperature Fields ◽  
Film Stability ◽  
Falling Films ◽  
Falling Liquid Films

Thin liquid films flowing along solid walls are widely used in technological applications in which high rates of heat and mass transport are required. The transport processes can be further intensified by using structured walls. In the present work hydrodynamics and heat transfer in falling liquid films on heated vertical and inclined walls with mini-grooves are studied experimentally and theoretically/numerically. The experiments are performed with straight, meandering and zigzag mini-grooves. The film dynamics is investigated using a confocal chromatic sensoring (CHR) technique. The flow patterns and the temperature of the liquid-gas interface are visualized using the high-speed infrared thermography. The wall temperature distribution is measured with thermocouples. A numerical model for description of the velocity and temperature fields in the thermal entrance region of the falling films on smooth and structured walls is developed. This model is based on the solution of the Graetz-Nusselt problem for falling films on grooved plates. We show that the mini-grooves significantly affect the flow patterns, film stability and heat transfer in falling liquid films. Using grooved walls leads to the increase of the maximal attainable heat transfer rate.

Cooling of Microelectronics by Shear-Driven Liquid Films

2006 ◽  
Author(s):  
Oleg Kabov
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
High Speed ◽  
Liquid Films ◽  
Vapor Flow ◽  
Air Cooling ◽  
Film Rupture ◽  
Computer Chips ◽  
Speed Computer ◽  
Very High

The recent development of microelectronics is closely linked to the problem of thermal regulation. The levels of heat generation in high-speed computer chips are now approaching very high values and they are on the edge of exceeding the capabilities of today’s air-cooling techniques. Thin liquid films may provide very high heat transfer intensity and may be used for cooling of microelectronics. A particularly promising technological solution is a set-up where heat is transferred to a very thin liquid film driven by a forced gas or vapor flow in a micro-channel. However, development such a cooling system requires significant advances in fundamental research, since the stability of joint flow of liquid film and gas is rather complex problem. Flow patterns, heat transfer laws and film rupture mechanisms for shear-driven locally heated liquid film flows remain only partially understood. The paper focuses upon shear-driven liquid film evaporative cooling of high-speed computer chips. The recent progress that has been achieved through conducting theoretical and numerical modeling as well as new experimental data has been discussed.

scholarly journals AN ANALYSIS OF THE LIQUID FILMS BREAK-UP USING THE COMPUTER VISION TECHNIQUE

2021 ◽  
Vol 61 (1) ◽  
pp. 253-269
Author(s):  
Lucie Měšťanová ◽  
Ondřej Bartoš
Keyword(s):  
Image Processing ◽  
Wind Tunnel ◽  
High Speed ◽  
Optical Measurement ◽  
Liquid Films ◽  
Light Extinction ◽  
Steam Turbines ◽  
Droplet Distribution ◽  
Novel Approach ◽  
Unfavourable Effect

The aim of this paper is to introduce a novel approach for analysing the droplet formation in a transonic flow. The method suggested in this work is based on the combination of the measured data from the wind tunnel by an optical measurement and image processing. A new wind tunnel was developed for the study of the liquid film atomization at high speed flows similar to ones that can be found in steam turbines. The coarse droplets in steam turbines are formed from the liquid films on the blades and inner casings. The coarse droplets formed on the stator blades don´t follow the bulk flow and collide with the following moving blades. These collisions cause erosion and corrosion processes, which have an unfavourable effect on the reliability and the efficiency of the low pressure stages of steam turbines. The tunnel is equipped with a standard instrumentation for the measurement of the flow properties and for the analysis of the size distribution of the droplets. Two measurement methods were used for the measurement of the size of the droplets, photogrammetry and light scattering. In this paper, the image processing of the captured images is discussed. The images were taken by a camera with a telecentric lens. The paper contains an assessment of three image processing methods used for the measurement of the droplet distribution by the light extinction. Moreover, the formation of the droplets is captured on the trailing edge of the profile in the flow. The results bring a new view on the formation of droplets at high speeds.

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