Instantaneous Optical Measurement of the Temperature at the Interface Between a Wall and a Thin Liquid Film

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Brian E. Fehring ◽  
Roman W. Morse ◽  
Jason Chan ◽  
Kristofer M. Dressler ◽  
Evan T. Hurlburt ◽  
...  
Keyword(s):  
Laser Beam ◽  
Liquid Film ◽  
Solid Wall ◽  
Incident Angle ◽  
Thin Liquid Film ◽  
Index Of Refraction ◽  
High Temporal Resolution ◽  
Flow Measurements ◽  
Vapor Interface ◽  
Liquid Vapor

Abstract Instantaneous temperature measurements at the interface between a solid wall and a thin, unsteady liquid film are performed using thermoreflectance, a nonintrusive optical technique with high temporal resolution. A laser beam is directed at a wall–liquid interface, and the intensity of the light reflected at that interface is measured by a photodiode. The intensity of the reflected light varies with the index of refraction of the liquid at the wall. The index of refraction is a function of temperature, which enables the instantaneous measurement of the wall temperature. In the presence of thin liquid films, reflections from the liquid–vapor interface at the free surface of the film generate noise in the measurements. We demonstrate that orienting the laser beam at a large incident angle, close to total internal reflection, minimizes noise from the liquid–vapor interface while increasing the sensitivity of the measurement. The thermoreflectance technique is validated in an unsteady two-phase annular flow. Measurements of temperature fluctuations less than 1 K in amplitude are achieved, with an uncertainty of 0.1 K.

Heat Transfer and Pressure Drop Characteristics of Condensation for R410A in a 3.78mm Circular Tube Under Normal and Micro Gravity

2016 ◽  
Author(s):  
Jingzhi Zhang ◽  
Wei Li ◽  
Tom I.-P. Shih ◽  
Yonghai Zhang ◽  
Yanping Shi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Transfer Coefficients ◽  
Bottom Part ◽  
Vapor Interface ◽  
Heat Transfer Coefficients ◽  
Micro Gravity ◽  
Liquid Vapor

Heat transfer and pressure drop characteristics of condensation for R410A inside horizontal tubes (dh = 3.78 mm) under normal and micro gravity are investigated numerically. The Volume of Fluid method is used to acquire liquid-vapor interface, while the low-Reynolds form of the Shear Stress Transport k∼ω (SST k∼ω) model is adopted to taking turbulent effect into account. The results indicate that the heat transfer coefficients decrease with increasing gravity accelerations, while the frictional pressure gradients increase with increases in gravity accelerations. The liquid film accumulates at the bottom of the tube, leading to a very thin liquid film attached to the upper part of inner tube wall. This accumulation effect decreases with decreases in gravitational accelerations. A more symmetrical liquid-vapor interface is obtained at lower gravity. The average liquid film thickness is nearly the same for different gravity accelerations at the same vapor quality (δave≈56 μm at x = 0.9 and δave≈230 μm at x = 0.5). The local heat transfer coefficients increase with increasing gravity at the top of the tube and decrease with increases in gravity at the bottom, while the bottom part of the tube has a limited contribution to the global heat transfer coefficient for stratified flow regime. The numerical data obtained under normal gravity agree well with well-known empirical correlations.

Molecular Dynamics Study on Explosive Boiling of Thin Liquid Argon Film on Nanostructured Surface Under Different Wetting Conditions

2015 ◽  
Author(s):  
Sheikh Mohammad Shavik ◽  
Mohammad Nasim Hasan ◽  
A. K. M. Monjur Morshed
Keyword(s):  
Molecular Dynamics ◽  
Liquid Film ◽  
Solid Surface ◽  
Solid Wall ◽  
Thin Liquid Film ◽  
Liquid Argon ◽  
Spatial And Temporal Variation ◽  
Phase System ◽  
Explosive Boiling ◽  
System Pressure

Molecular dynamics (MD) simulations have been performed to investigate the boiling phenomena of thin liquid film adsorbed on a nanostructured solid surface with particular emphasis on the effect of wetting condition of the solid surface. The molecular system consists of liquid and vapor argon, and solid platinum wall. The nanostructures which reside on top of the solid wall have shape of rectangular block. The solid-liquid interfacial wettability, in other words whether the solid surface is hydrophilic or hydrophobic has been altered for different cases to examine its effect on boiling phenomena. The initial configuration of the simulation domain comprised a three phase system (solid platinum, liquid argon and vapor argon) which was equilibrated at 90 K. After equilibrium period, the wall temperature was suddenly increased from 90 K to 250 K which is far above the critical point of argon and this initiates rapid or explosive boiling. The spatial and temporal variation of temperature and density as well as the variation of system pressure with respect to time were closely monitored for each case. The heat flux normal to the solid surface was also calculated to illustrate the effectiveness of heat transfer for different cases of wetting conditions of solid surface. The results show that the wetting condition of surface has significant effect on explosive boiling of the thin liquid film. The surface with higher wettability (hydrophilic) provides more favorable conditions for boiling than the low-wetting surface (hydrophobic) and therefore, liquid argon responds quickly and shifts from liquid to vapor phase faster in case of hydrophilic surface.

Effects of Superhydrophobic and Superhydrophilic Surfaces on Heat Transfer and Oscillating Motion of an Oscillating Heat Pipe

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Tingting Hao ◽  
Xuehu Ma ◽  
Zhong Lan ◽  
Nan Li ◽  
Yuzhe Zhao
Keyword(s):  
Heat Transfer ◽  
Superhydrophobic Surface ◽  
Thin Liquid Film ◽  
Maximum Amplitude ◽  
Line Length ◽  
Copper Surface ◽  
Working Fluid ◽  
Liquid Slug ◽  
Vapor Interface ◽  
Liquid Vapor

The effects of superhydrophobic surface and superhydrophobic and superhydrophilic hybrid surface on the fluid flow and heat transfer of oscillating heat pipes (OHPs) were investigated in the paper. The inner surfaces of the OHPs were hydrophilic surface (copper), hybrid surface (superhydrophilic evaporation and superhydrophobic condensation section), and uniform superhydrophobic surface, respectively. Deionized water was used as the working fluid. Experimental results showed that superhydrophobic surface influenced the slug motion and thermal performance of OHPs. Visualization results showed that the liquid-vapor interface was concave in the OHP with copper surface. A thin liquid film existed between the vapor plug and the wall of the OHP. On the contrary, the liquid-vapor interface took a convex profile in the OHP with superhydrophobic surface and the liquid-vapor interface contact line length in the hybrid surface OHP was longer than that in the uniform superhydrophobic surface OHP. The liquid slug movements became stronger in the hybrid surface OHPs as opposed to the copper OHP, while the global heat transfer performance of the hybrid surface OHPs increased by 5–20%. Comparing with the copper OHPs, the maximum amplitude and velocity of the liquid slug movements in the hybrid surface OHPs increased by 0–127% and 0–185%, respectively. However, the maximum amplitude and velocity of the liquid slug movements in the uniform superhydrophobic OHPs was reduced by 0–100% and 0–100%, respectively. The partial dryout phenomenon took place in OHPs with uniform superhydrophobic surface. The liquid slug movements became weaker and the thermal resistance was increased by 10–35% in the superhydrophobic surface OHPs.

Visualization of the Evaporating Liquid-Vapor Interface in Micropillar Arrays

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Dion S. Antao ◽  
Solomon Adera ◽  
Edgardo Farias ◽  
Rishi Raj ◽  
Evelyn N. Wang
Keyword(s):  
Capillary Pressure ◽  
Evaporation Rate ◽  
Thin Liquid Film ◽  
Monochromatic Light ◽  
Unit Cell ◽  
Vapor Interface ◽  
Viscous Loss ◽  
Liquid Vapor ◽  
Micropillar Array ◽  
Micropillar Arrays

We captured interesting static and dynamic behavior of the liquid-vapor interface in well-defined silicon micropillar arrays during thermally driven evaporation of water from the microstructured surface. The 3-D shape of the meniscus was characterized via laser interferometry where bright and dark fringes result from the interference of incident and reflected monochromatic light due to a variable thickness thin liquid film (FIG. 1). During steady state evaporation experiments, water was supplied to the sample with a syringe pump at 10 μL/min. FIG. 2a and 2b show a SEM image of a typical fabricated micropillar array and a schematic of the experimental setup, respectively. When water wicks through the micropillar array, the meniscus in a unit cell (four pillars in FIG. 1) assumes an equilibrium shape depending on the location from the liquid source/reservoir and the ambient conditions (ambient evaporation at Qin = 0 W). At this point, the meniscus is pinned at the top of the pillars. As the evaporation rate increases due the applied heat flux, the meniscus increases in curvature, thus increasing the capillary pressure to sustain the higher evaporation rate. This is evidenced by the increasing number of fringes in the unit cell when Qin is increased (0 W, 0.11 W, 0.44 W, and 0.99 W, FIG. 1a-1d respectively). Beyond a maximum curvature, the meniscus de-pins from the pillar top surface and recedes within the unit cell. This occurs when the capillary pressure generated at this curvature, cannot balance the viscous loss resulting from flow through the micropillar array. We observed that this receding shape was independent of the applied heat, and only depended on the micropillar array geometry and the intrinsic wettability of the material. Representative meniscus profiles along the diagonal direction of the unit cell obtained from image analysis of FIG. 1 at various Qin are shown in FIG. 2c.

Dynamics of the critical liquid-vapor interface close to a solid wall

1988 ◽  
Vol 127 (3) ◽  
pp. 188-190 ◽  
Author(s):  
A. Łcrossed cap.Lsakowski ◽  
Łcrossed cap.L.A. Turski
Keyword(s):  
Solid Wall ◽  
Vapor Interface ◽  
Liquid Vapor

Thin Film Evaporation Model With Retarded van der Waals Interaction

2013 ◽  
Author(s):  
Michael S. Hanchak ◽  
Marlin D. Vangsness ◽  
Nadina Gheorghiu ◽  
Jamie S. Ervin ◽  
Larry W. Byrd ◽  
...  
Keyword(s):  
Thin Film ◽  
Solid Wall ◽  
Van Der Waals ◽  
Van Der Waals Interaction ◽  
Working Fluid ◽  
Interface Temperature ◽  
Vapor Interface ◽  
Adsorbed Film ◽  
Flux Profile ◽  
Liquid Vapor

In phase change heat transfer equipment, three-phase contact regions exist that consist of a solid wall and the liquid and vapor phases of a working fluid. When the working fluid fully wets the solid wall, a microscopic thin film adjoining the meniscus is present called the adsorbed film. Upon heating, a non-uniform evaporative flux profile develops with a maximum value occurring within the transition between the adsorbed film and the intrinsic meniscus. It is important to study the heat transfer characteristics of this region to gain better fundamental understanding and useful design principles. The adsorbed film occurs when the driving potential for evaporation is opposed by the presence of intermolecular forces, represented analytically by the disjoining pressure, which acts to thicken a wetting film. The model presented includes lubrication theory of the liquid flow within the film, heat conduction across the film from the heated wall to the liquid-vapor interface, kinetic theory evaporation from the interface to the vapor phase, and disjoining pressure based on a retarded van der Waals interaction. The retarded van der Waals interaction is derived from Hamaker theory, the summation of retarded pair potentials for all molecules for a given geometry. When combined, the governing equations form a third-order, nonlinear differential equation for the film thickness versus distance, which is solved numerically using iteration of the initial film curvature in order to match the far-field curvature of the meniscus. Also, iteration is required at each length step to determine the liquid-vapor interface temperature. Useful outputs of the model include the liquid-vapor interface temperature and the evaporative mass flux profile. The model is calibrated to in-house experiments that employ an axisymmetric capillary feeder to provide a thin film of n-octane onto a substrate of silicon, where the gas phase is air saturated with vapor. The film thickness versus radial distance is measured using reflectometry and interferometry.

Effects of Roughness of Solid Surface With Nano-Relief on Liquid-Wall Contact Angle

2007 ◽  
Author(s):  
Wei Qu ◽  
Yuhua Li ◽  
Yan Zhou ◽  
Tongze Ma
Keyword(s):  
Contact Angle ◽  
Liquid Film ◽  
Solid Wall ◽  
Thin Liquid Film ◽  
Contact Angles ◽  
Disjoining Pressure ◽  
Roughness Height ◽  
Phase Change Heat Transfer ◽  
Liquid Wall ◽  
Space Phase

The liquid-wall contact angle reflects the liquid wettability, the front size of thin liquid film, it is important for micro space phase change heat transfer. The smooth solid wall is supposed to have a periodic nano-relief, which has a roughness height and a roughness angle microscopically. The analytical contact angles are derived by the adsorptive potential and the disjoining pressure of adsorbed thin liquid film, depends on the scales of nano-relief and outside applying conditions. The results show that the adsorptive potential and the disjoining pressure of adsorbed thin liquid film will be affected by the nano-relief significantly when the roughness height is closer to the thickness of adsorbed thin liquid film. For apolar working fluids, if the roughness is medium, the analytical liquid contact angles are of the order of 0.010∼0.10 degree; if the roughness is extremely, then nano-relief of surface will exert stronger influences on the contact angles, the contact angle is nearly 90 degrees.

Numerical Simulation of Bubble Dynamics in the Presence of Boron in the Liquid

2001 ◽  
Author(s):  
Qiang Bai ◽  
V. K. Dhir
Keyword(s):  
Numerical Simulation ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Thin Liquid Film ◽  
Dynamic Change ◽  
Nucleate Boiling ◽  
Reactor Power ◽  
Vapor Interface ◽  
Fuel Rod ◽  
Liquid Vapor

Abstract Deposition of boron on the fuel rod cladding during boiling of water containing boron can depress the neutron flux and lead to a decrease in nuclear reactor power output. There is practically little precise information on the temperature field, the gradients of chemical concentration and deposition of boron on the cladding surface. The objective of the present work is to simulate the nucleate boiling process along with velocity, temperature and concentration fields of aqueous boron in the vicinity of the cladding of a fuel rod. As a first step in solving the complete problem, two-dimensional numerical simulation of a bubble growth on a horizontal surface is considered. A finite difference scheme is used to solve the equations governing conservation of mass, momentum, energy and species concentration. The calculation domain is divided into macro and micro regions. In macro-region, the governing equations are used to calculate the distributions of velocity, temperature, and concentration. The Level Set method is used to capture the evolving liquid-vapor interface. For micro-region, lubrication theory is used, which includes the disjoining pressure in the thin liquid film. The solutions for micro-region and macro-region are matched at the outer edge of the micro-layer. A dilute aqueous Boron solution is considered in the simulation. From numerical simulations, the dynamic change in concentration distribution of boron during the bubble growth shows that the precipitation of boron can occur near the advancing and receding liquid-vapor interface when the ambient boron concentration level is 0.003.

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