Breakdown of Liquid Film around a Vapor Bubble Generated by Direct-Contact Evaporation in a Liquid-Liquid System

2003 ◽  
Vol 2003 (0) ◽  
pp. 331-332
Author(s):  
Katsuhiko KADOGUCHI
Keyword(s):  
Liquid Film ◽  
Vapor Bubble ◽  
Direct Contact ◽  
Liquid System

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.

Experimental Observation of Nucleate Boiling Entrainment in a Liquid Film

2021 ◽  
Author(s):  
Junpei Tabuchi ◽  
Yuki Narushima ◽  
Kenichi Katono ◽  
Tomio Okawa
Keyword(s):  
Liquid Film ◽  
Forced Convection ◽  
Vapor Bubble ◽  
Water Surface ◽  
Annular Flow ◽  
Nucleate Boiling ◽  
Vapor Bubbles ◽  
Droplet Entrainment ◽  
Bubble Bursting ◽  
Filament Breakup

Abstract Many studies have been conducted on droplet entrainment in an annular flow regime, but little is known about droplet entrainment caused by nucleate boiling. In this report, visualization results of droplet entrainment caused by nucleate boiling are described. We observed two processes of droplet entrainment. The first one causes bubble bursting at a water surface. The second one causes filament breakup which occurs when the vapor bubble reaches and collapses at the interface between air and liquid. From comparison of the phenomena for the two processes, we found that the diameters of the droplets and vapor bubbles were considerably different. Using the results of this research allows the effect of forced convection to be taken into account. In the future, we plan to expand the amount of data and develop a boiling entrainment model under forced convection conditions.

Experimental Study and Modeling of the Intermediate Section of the Nonisothermal Constrained Vapor Bubble

1998 ◽  
Vol 120 (1) ◽  
pp. 166-173 ◽  
Author(s):  
M. Karthikeyan ◽  
J. Huang ◽  
J. Plawsky ◽  
P. C. Wayner
Keyword(s):  
Liquid Film ◽  
Vapor Bubble ◽  
Thermal Conductance ◽  
Width Ratio ◽  
Operating Pressure ◽  
Governing Parameter ◽  
Constrained Vapor Bubble ◽  
Operating Limits ◽  
Large Length ◽  
Intermediate Section

The generic nonisothermal constrained vapor bubble (CVB) is a miniature, closed heat transfer device capable of high thermal conductance that uses interfacial forces to recirculate the condensate on the solid surface constraining the vapor bubble. Herein, for the specific case of a large length-to-width ratio it is equivalent to a wickless heat pipe. Experiments were conducted at various heat loads on a pentane/quartz CVB to measure the fundamental governing parameter fields: temperature, pressure, and liquid film curvature. An “intermediate” section with a large effective axial thermal conductivity was identified wherein the temperature remains nearly constant. A one-dimensional steady-state model of this intermediate section was developed and solved numerically to yield pressure, velocity, and liquid film curvature profiles. The experimentally obtained curvature profiles agree very well with those predicted by the Young-Laplace model. The operating temperature of the CVB was found to be a function of the operating pressure and not a function of the heat load. Due to experimental design limitations, the fundamental operating limits of the CVB were not reached.

Direct contact condensation of vapor on turbulent, falling liquid film

1992 ◽  
Vol 49 (1) ◽  
pp. 31-48 ◽  
Author(s):  
V. Dharma Rao ◽  
J. Saibabu ◽  
P. K. Sarma
Keyword(s):  
Liquid Film ◽  
Direct Contact ◽  
Falling Liquid Film ◽  
Contact Condensation

scholarly journals Heat Transfer in Direct Contact with Thermal Media Case of Non-boiling in Liquid-Liquid System

1965 ◽  
Vol 29 (1) ◽  
pp. 2-7,a1
Author(s):  
Masao Hashizume ◽  
Hayao Okamoto ◽  
Yoshikazu Motoki
Keyword(s):  
Heat Transfer ◽  
Direct Contact ◽  
Liquid System

Performance Predictions of a Moisture Management Device for Fuel Cell Applications

2006 ◽  
Author(s):  
J. D. Killion ◽  
S. Garimella
Keyword(s):  
Mass Transfer ◽  
Liquid Film ◽  
Direct Contact ◽  
Operating Conditions ◽  
Equivalent Resistance ◽  
Moisture Management ◽  
Performance Predictions ◽  
And Performance ◽  
Louvered Fins ◽  
Rectangular Tubes

Moisture management in proton-exchange-membrane fuel cells is crucial to durability and performance. This frequently requires external humidification of the reactant gas streams to maintain sufficient humidity levels at the membranes, especially at higher operating temperatures. Direct-contact humidifiers using louvered fins brazed to rectangular tubes, similar to those frequently employed in automotive condensers and radiators, can be used to humidify a gas stream. A gas stream in which liquid water is sprayed flows through the passages formed by the louvered fins counter-current to a heating fluid flowing in the rectangular tubes sandwiching the fins. A mathematical model of this type of direct-contact humidifier is presented. The equations of energy and mass conservation are simultaneously solved for a number of segments along the humidifier. An equivalent resistance network is used to capture the temperature profile of the fins and liquid film surrounding them. The thickness of the liquid film is calculated from a shear balance at the film interface. The heat and mass transfer analogy is used with empirically derived transfer coefficients to solve the coupled heat and mass transfer problem in the gas phase. Predicted results are presented for typical operating conditions corresponding to a wide range of fuel cell operating conditions. The results show how the humidification process varies along the length of the humidifier. It is also shown that, although evaporation of the liquid film takes place throughout the entire humidifier, the direction of sensible heat transfer between the gas and liquid film can switch at some distance along the humidifier. This confirms the need for the equivalent resistance network model of the fin and film since simple fin efficiency models would fail in this situation. The model provides a basis for design optimization and performance predictions for this type of direct-contact moisture management device.

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