Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H35: Bubbles: Heat Transfer and Boiling |
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Chair: Chihiro Inoue, University of Tokyo Room: Ballroom B |
Monday, November 23, 2015 10:35AM - 10:48AM |
H35.00001: Visco-capillarity in Sparkling Fireworks Chihiro Inoue, Emmanuel Villermaux A unique toy firework called sparkling fireworks is popular in Japan for 400 years, but the physics behind the beauty remains a hidden mystery. Sparkling fireworks are made by a twisted paper simply wrapping 0.1g of black powder at the lower end. Ignited there, the powder melts in a fireball of molten salts, and streaks of light are ejected. The beautiful fragile streaks are visible from the black body radiation of the hot surface of the ejected droplets. The droplets suddenly fragment up to ten times successively and their light streaks traces are like pine needles. We have already clarified why the droplets are ejected through the bursting of a gas bubble on the mother fireball, leading to successive fragmentations by micro explosions. To quantify phenomenon, we measure the diameter and the ejection velocity of the droplets. It is found that not only inertia and capillarity of the liquid matter, but also its viscosity is important (the Ohnesorge number is about 0.1). The droplets ejection velocity is determined by the liquid surface tension and viscosity, and separate from the mother drop on a visco-capillarity time scale. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H35.00002: Experimental study of combustion of decane, dodecane and hexadecane with polymeric and nano-particle additives Mohsen Ghamari, Albert Ratner Recent studies have shown that adding combustible nano-particles could have promising effects on increasing burning rate of liquid fuels. Combustible nano-particles could enhance the heat conduction and mixing within the droplet. Polymers have also higher burning rate than regular hydrocarbon fuels because of having the flame closer to the droplet surface. Therefore adding polymeric additive could have the potential to increase the burning rate. In this study, combustion of stationary fuel droplets of n-Decane, n-Dodecane and n-Hexadecane doped with different percentages of a long chain polymer and also a very fine nano carbon was examined and compared with the pure hydrocarbon behavior. In contrast with hydrocarbon droplets with no polymer addition, several zones of combustion including a slow and steady burning zone, a strong swelling zone and a final fast and fairly steady combustion zone were also detected. In addition, increasing polymer percentage resulted in a more extended swelling zone and shorter slow burning zone in addition to a shorter total burning time. Addition of nano-particles also resulted in an overall increased burning rate and shortened burning time which is due to enhanced heat conduction within the droplet. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H35.00003: Fragment structure from vapor explosions during the impact of molten metal droplets into a liquid pool Nadia Kouraytem, Er Qiang Li, Ivan Uriev Vakarelski, Sigurdur Thoroddsen High-speed video imaging is used in order to look at the impact of a molten metal drop falling into a liquid pool. The interaction regimes are three: film boiling, nucleate boiling or vapor explosion. Following the vapor explosion, the metal fragments and different textures are observed. It was seen that, using a tin alloy, a porous structure results whereas using a distinctive eutectic metal, Field's metal, micro beads are formed. Different parameters such as the metal type, molten metal temperature, pool surface tension and pool boiling temperature have been altered in order to assess the role they play on the explosion dynamics and the molten metal's byproduct. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H35.00004: High Frequency Stable Oscillate boiling Fenfang Li, Silvestre Roberto Gonzalez-Avila, Claus Dieter Ohl We present an unexpected regime of resonant bubble oscillations on a thin metal film submerged in water, which is continuously heated with a focused CW laser. The oscillatory bubble dynamics reveals a remarkably stable frequency of several 100 kHz and is resolved from the side using video recordings at 1 million frames per second. The emitted sound is measured simultaneously and shows higher harmonics. Once the laser is switched on the water in contact with the metal layer is superheated and an explosively expanding cavitation bubble is generated. However, after the collapse a microbubble is nucleated from the bubble remains which displays long lasting oscillations. Generally, pinch-off from of the upper part of the microbubble is observed generating a continuous stream of small gas bubbles rising upwards. The cavitation expansion, collapse, and the jetting of gas bubbles are detected by the hydrophone and are correlated to the high speed video. We find the bubble oscillation frequency is dependent on the bubble size and surface tension. A preliminary model based on Marangoni flow and heat transfer can explain the high flow velocities observed, yet the origin of bubble oscillation is currently not well understood. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H35.00005: Pool Boiling Enhancement on Textured Surfaces using Acoustic Actuation Thomas Boziuk, Marc Smith, Ari Glezer Boiling heat transfer on submerged textured heated surfaces is enhanced using ultrasound actuation. The heated surface is textured using an array of open microchannels that advantageously separate the nucleation sites on the surface and inhibit the transition to film boiling, which significantly increases the critical heat flux compared to a smooth surface of the same planform dimensions. The present investigation shows that the formation and evolution of vapor bubbles on the heated surface can be substantially altered by a highly directional ultrasound (1.7 MHz) beam, and leads to significant enhancement in heat transfer, including reduced surface superheat and increased critical heat flux (exceeding 55{\%}). The effects of the beam incidence and azimuthal angle on vapor formation, advection, and resulting effect on surface superheat are investigated experimentally in a liquid test cell. Heat transfer enhancement characterized by changes in the boiling curve (i.e., superheat and CHF) varies with surface texturing and is also dependent on acoustic beam orientation relative to the surface texture pattern. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H35.00006: Cooling of hot bubbles by surface texture during the boiling crisis Navdeep Dhillon, Jacopo Buongiorno, Kripa Varanasi We report the existence of maxima in critical heat flux (CHF) enhancement for pool boiling on textured hydrophilic surfaces and reveal the interaction mechanism between bubbles and surface texture that governs the boiling crisis phenomenon. Boiling is a process of fundamental importance in many engineering and industrial applications but the maximum heat flux that can be absorbed by the boiling liquid (or CHF) is limited by the boiling crisis. Enhancing the CHF of industrial boilers by surface texturing can lead to substantial energy savings and reduction in greenhouse gas emissions on a global scale. However, the fundamental mechanisms behind this enhancement are not well understood, with some previous studies indicating that CHF should increase monotonically with increasing texture density. However, using pool boiling experiments on a parametrically designed set of plain and nano-textured micropillar surfaces, we show that there is an optimum intermediate texture density that maximizes CHF and further that the length scale of this texture is of fundamental significance. Using imbibition experiments and high-speed optical and infrared imaging, we reveal the fundamental mechanisms governing the CHF enhancement maxima in boiling crisis. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H35.00007: Verification and validation of a GPU-based multi-resolution direct numerical simulation of multiphase flow with phase change Christopher J. Forster, Marc K. Smith Nucleate boiling processes span a large range of length scales, ranging from O(1 $\mu$m) to O(0.1 m), that arise due to steep gradients in the density and temperature near the liquid-vapor interface and the contact line. The Wavelet Adaptive Multiresolution Representation (WAMR) method is a general and robust technique for providing grid adaptivity around sharp features in the solutions of partial differential equations and is capable of resolving the large disparity of length scales present in nucleate boiling. A new flow solver based on the WAMR method and specifically parallelized for a GPU computing architecture has been developed. The compressible formulation of the Navier-Stokes equations is used in the flow solver and a preconditioned dual time-stepping integration scheme provides accurate solutions for flows approaching the incompressible limit. The WAMR method provides a direct measure of the local error over the entire grid and coupling spatial error control with adaptive time integration allows for $\textit{a priori}$ control of the error in the solution. Verification and validation cases, including single vapor bubble growth, will be presented to demonstrate the efficiency and accuracy of the method for solving nucleate boiling problems. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H35.00008: Sliding bubbles on a hot horizontal wire in a subcooled bath Alexis Duchesne, Charles Dubois, Herv\'e Caps When a wire is heated up to the boiling point in a liquid bath some bubbles will nucleate on the wire surface. Traditional nucleate boiling theory predicts that bubbles generate from active nucleate site, grow up and depart from the heating surface due to buoyancy and inertia. However, an alternative scenario is presented in the literature for a subcooled bath: bubbles slide along the horizontal wire before departing. New experiments were performed by using a constantan wire and different liquids, varying the injected power. Silicone oil, water and even liquid nitrogen were tested in order to vary wetting conditions, liquid viscosities and surface tensions. We explored the influence of the wire diameter and of the subcooled bath temperature. We observed, of course, sliding motion, but also a wide range of behaviors from bubbles clustering to film boiling. We noticed that bubbles could change moving sense, especially when encountering with another bubble. The bubble speed is carefully measured and can reach more than 100 mm/s for a millimetric bubble. We investigated the dependence of the speed on the different parameters and found that this speed is, for a given configuration, quite independent of the injected power. We understand these phenomena in terms of Marangoni effects. [Preview Abstract] |
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