Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A7: Bubbles: Growth, Heat Transfer and BoilingBubbles
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Chair: Elias Balaras, George Washington University Room: 407 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A7.00001: Level set immersed boundary method for gas-liquid-solid interactions with phase-change Akash Dhruv, Elias Balaras, Amir Riaz, Jungho Kim We will discuss an approach to simulate the interaction between two-phase flows with phase changes and stationary/moving structures. In our formulation, the Navier-Stokes and heat advection-diffusion equations are solved on a block-structured grid using adaptive mesh refinement (AMR) along with sharp jump in pressure, velocity and temperature across the interface separating the different phases. The jumps are implemented using a modified Ghost Fluid Method (Lee et al., J. Comput. Physics, 344:381–418, 2017), and the interface is tracked with a level set approach. Phase transition is achieved by calculating mass flux near the interface and extrapolating it to the rest of the domain using a Hamilton-Jacobi equation. Stationary/moving structures are simulated with an immersed boundary formulation based on moving least squares (Vanella & Balaras, J. Comput. Physics, 228:6617-6628, 2009). A variety of canonical problems involving vaporization, film boiling and nucleate boiling is presented to validate the method and demonstrate the its formal accuracy. The robustness of the solver in complex problems, which are crucial in efficient design of heat transfer mechanisms for various applications, will also be demonstrated. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A7.00002: Numerical study of the bubbly flow regime in micro-channel flow boiling. Pramod Bhuvankar, Sadegh Dabiri Two-phase flow accompanied by boiling in micro-channel heat sinks is an effective means for heat removal from computer chips. We present a numerical study of flow boiling in micro-channels with conjugate heat transfer with a focus on the bubbly flow regime. The bubbles are assumed to nucleate at a pre-determined location and frequency. The Navier Stokes equations are solved using a single fluid formulation with the Front tracking method. Phase change is implemented using the deficit in heat flux across the bubble interface. The analytical solution for bubble growth in a superheated liquid is used as a benchmark to validate the mentioned numerical method. Water and FC-72 are studied as the operating fluids in a micro-channel made of Copper with a focus on hotspot mitigation. The micro-channel of cross-section $231\mu m$x$1000\mu m$, is used to study the effects of vertical up-flow, vertical down-flow and horizontal flow of the mentioned fluids on the heat transfer coefficients. A simple film model accounting for mass and energy conservation is applied wherever the bubble approaches closer than a cell width to the wall. The results of the simulation are compared with existing experimental data for bubble growth rates and heat transfer coefficients. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A7.00003: New Departure from Nucleate Boiling model relying on first principle energy balance at the boiling surface. Etienne Demarly, Emilio Baglietto Predictions of Departure from Nucleate Boiling have been a longstanding challenge when designing heat exchangers such as boilers or nuclear reactors. Many mechanistic models have been postulated over more than 50 years in order to explain this phenomenon but none is able to predict accurately the conditions which trigger the sudden change of heat transfer mode. This work aims at demonstrating the pertinence of a new approach for detecting DNB by leveraging recent experimental insights. The new model proposed departs from all the previous models by making the DNB inception come from an energy balance instability at the heating surface rather than a hydrodynamic instability of the bubbly layer above the surface (Zuber, 1959). The main idea is to modulate the amount of heat flux being exchanged via the nucleate boiling mechanism by the wetted area fraction on the surface, thus allowing a completely automatic trigger of DNB that doesn't require any parameter prescription. This approach is implemented as a surrogate model in MATLAB in order to validate the principles of the model in a simple and controlled geometry. Good agreement is found with the experimental data leveraged from the MIT Flow Boiling at various flow regimes. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A7.00004: Predicting bubble departure frequency in CFD from thermal boundary layer energy limit Ravikishore Kommajosyula, Emilio Baglietto Second generation boiling closures for CFD being developed at MIT aim at accurately capturing the subgrid scale phenomena to gain improved accuracy and extended applicability. Here we focus on the key aspect of predicting the bubble departure frequency, and replace the current correlation based methods with a physically based mechanistic model. While various attempts have been made in literature, they have all relied on the Hsu's criterion, which makes them highly dependent on the nucleation cavity size and not applicable to general CFD applications. A new approach is proposed to evaluate the bubble wait time, which is based on capturing the energy limit of the thermal boundary layer (TBL). The TBL develops during the short time span following bubble departure, when subcooled liquid quenches the surface, but as the TBL growth reaches a critical thickness its inertia increases and the excess heat is directed towards bubble nucleation. The energy limit is analyzed over an extended experimental database and a fully mechanistic model for predicting the bubble wait time is proposed. The new model can be used in conjunction with the bubble growth time to accurately predict the bubble departure frequency. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A7.00005: Stochastic automata to simulate wettability effects in phase change heat transfer Daniel Attinger, Christian Marcel, Alejandro Clausse, Christophe Frankiewicz, Amy Rachel Betz Surface wettability is a key physical property in phase change heat transfer that influences heat-removal mechanisms and/or their relative relevance. A stochastic automata model is provided with rules to simulate pool boiling heat transfer considering the influence of the contact angle [1]. Free bubbles are modeled as a population of virtual spheres that change their geometric properties with simple stochastic rules. The model is validated against published experimental pool boiling data, showing excellent agreement with the boiling curve, as well as with the activation of nucleation sites, in a statistical sense. The sensitivity of the model parameters is studied to assess their influence and relevance. The model also provides information about the behavior of other near-wall relevant quantities, such as the interfacial area density and bubble detachment frequency. The computing time is about two orders of magnitude lower than that required by continuum methods to simulate pool boiling. [1] C. Marcel, A. Clausse, C. Frankiewicz, A. Betz, and D. Attinger, "Numerical investigation into the effect of surface wettability in pool boiling heat transfer with a stochastic-automata model," International Journal of Heat and Mass Transfer, vol. 111, pp. 657-665, 2017. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A7.00006: The rate of size change of a bubble containing a vapor and a non-condensable gas Enrique Rame, R. Balasubramaniam The rate of size change of a bubble containing a vapor and a non-condensable gas E. Ram\'e and R. Balasubramaniam When a vapor bubble is surrounded by subcooled liquid, the vapor condenses at a rate determined by the rate of heat loss from the bubble to the surroundings. Alternatively a bubble of pure gas surrounded by a liquid will dissolve at a rate proportional to the mass transfer rate into the liquid by dissolution. In this talk we will present analysis of the rate of change of bubble size when the bubble contains vapor and a non-condensable gas that is soluble in the liquid. The problem has application in the bubble management of heat transfer fluids that have high affinity for non-condensables such as air. [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A7.00007: Counter-current thermocapillary migration of bubbles in self-rewetting liquids Robson Nazareth, Pedro S\'{a}enz, George Karapetsas, Khellil Sefiane, Omar Matar, Prashant Valluri Thermocapillary migration of bubbles has been studied since Young described a bubble rising in a pure, quiescent liquid subject to a vertical temperature gradient. Pure liquids usually exhibit a linearly-decreasing dependence of surface tension on temperature. Here, we consider so-called `self-rewetting' fluids where surface tension is a parabolic function of temperature with a defined minima. Specifically, we target the counter-current thermocapillary migration of a bubble under temperature gradient. We present DNS using the Basilisk solver to resolve the two-phase continuity, momentum, and energy equations with a VoF method to capture the interface. The simulations agree with the experimental and the theoretical findings of Shanahan and Sefiane (2014). Two distinct regimes are revealed: i) ``steady migration'' where the bubble migrates against flow to an equilibrium position at the surface tension minimum; and ii) ``sustained oscillations'' where the bubble undergoes steady oscillations around the equilibrium position after a transient migration period. We map these in Re and Ca number parameter space and explain sustained oscillations when Ca \textless O($10^{-4})$ , and their damping in the range O($10^{-4})$ \textless Ca \textless O($10^{-2})$. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A7.00008: Single-bubble boiling under Earth's and low gravity. Boris Khusid, Ezinwa Elele, Qian Lei, John Tang, Yueyang Shen Miniaturization of electronic systems in terrestrial and space applications is challenged by a dramatic increase in the power dissipation per unit volume with the occurrence of localized hot spots where the heat flux is much higher than the average. Cooling by forced gas or liquid flow appears insufficient to remove high local heat fluxes. Boiling that involves evaporation of liquid in a hot spot and condensation of vapor in a cold region can remove a significantly larger amount of heat through the latent heat of vaporization than force-flow cooling can carry out. Traditional methods for enhancing boiling heat transfer in terrestrial and space applications focus on removal of bubbles from the heating surface. In contrast, we unexpectedly observed a new boiling regime of water under Earth's gravity and low gravity in which a bubble was pinned on a small heater up \quad to 270\textdegree C and delivered a heat flux up to 1.2 MW/m$^{\mathrm{2}}$ that was as high as the critical heat flux in the classical \quad boiling regime on Earth$. $Low gravity measurements conducted in parabolic flights in NASA Boeing 727. The heat flux in flight and Earth's experiments was found to rise linearly with increasing the heater temperature. We will discuss physical mechanisms underlying heat transfer in single-bubble boiling. \quad . [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A7.00009: Behavior of a laser-induced bubble: effects of the volume variation of the liquid Sennosuke Kawamoto, Yoshiyuki Tagawa We investigate both experimentally and theoretically the behavior (growth and contraction) of a laser-induced bubble generated in a narrow tube opened at one end. In experiments, the bubble behavior is observed using a high-speed camera. Immediately after the illumination of a laser pulse to a point inside a liquid, a generated bubble expands mainly toward the open end of the tube. The expanding bubble ejects a certain amount of liquid from the tube, resulting in the volume change of the liquid inside the tube. In order to describe the behavior of the bubble, we develop a model considering the volume variation of the liquid in the equation of motion. The boundary condition of this model is set at the open end as atmospheric pressure for the entire process. It is found that our model can describe the bubble behavior better than conventional models. Our results suggest the possibility of volumetric control with nano-litter precision for practical liquid transportation technologies using microjets. [Preview Abstract] |
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