A saturated-interface-volume phase change model for simulating flow boiling

Abstract

High-fidelity simulation of flow boiling in microchannels remains a challenging problem, but the increasing interest in applications of microscale two-phase transport highlights its importance. In this paper, a volume of fluid (VOF)-based flow boiling model is proposed with features that enable cost-effective simulation of two-phase flow and heat transfer in realistic geometries. The vapor and liquid phases are distinguished using a color function which represents the local volume fraction of the tracked phase. Mass conservation is satisfied by solving the transport equations for both phases with a finite-volume approach. In order to predict phase change at the liquid-vapor interface, evaporative heat and mass source terms are calculated using a novel, saturated-interface-volume phase change model. This phase change model is formulated to anchor the interfacial temperature at saturation within each iteration, and thereby acts as a robust constant-temperature boundary condition. Unlike other available phase-change models, the source terms are coupled with the local temperature explicitly; therefore, numerical oscillations around the interface temperature are not observed during iterations within a time step, which reduces the numerical cost. In addition, the reference frame is set to move with the vapor slug to artificially increase the local velocity magnitude in the thin liquid film region in the relative frame. This reduces the influence of numerical errors resulting from calculation of the surface tension force, and thus suppresses the development of spurious currents. As a result, non-uniform meshes may be used which can efficiently resolve high-aspect-ratio geometries and flow features. The overall numerical expense is significantly reduced. The proposed saturated-interface-volume model is first validated against a one-dimensional Stefan problem, and then used to simulate the growth of a vapor bubble flowing in a heated, 2D axisymmetric microchannel. The bubble motion, bubble growth rate, liquid film thickness, and local heat transfer coefficient along the wall are compared against previous numerical studies. A three-dimensional flow boiling problem is studied to demonstrate the cost effectiveness of the present approach and to highlight the transport mechanisms it can reveal in more complex domains. § Submitted for possible publication in

Dynamics of magnetic modulation of ferrofluid droplets for digital microfluidic applications

“…The Volume of Fluid (VOF) model was used in the present work to perform transient three dimensional simulations. The VOF method has been shown to be useful for simulating diverse problems such as evaporative cooling [43], pipeline corrosion [44], heat transfer in oscillating heat pipes [45], interaction of waves with coastal structures [46], liquid dessicant dehumidification [47], drop impact [48], and flow boiling [49]…”

An experimental method for controlled generation and characterization of microchannel slug flow boiling

“…Several recent studies have developed multiphase numerical models for flow boiling that account for complex vapor-liquid interfacial transport phenomena [14][15][16][17][18]. For example, Pan et al.…”

“…For example, Pan et al. [17] demonstrated a cost-effective approach for modeling microchannel flow boiling using a volume-of-fluid (VOF) approach coupled with a saturated-interface-volume phase change model and a moving-reference-frame method that suppresses spurious currents [19]. The growth of single, evaporating vapor bubbles flowing in heated microchannels was simulated.…”

“…Despite the recent significant advances in modeling, these state-of-the-art techniques are still validated using test problems for which simplistic analytical solutions are available [15,17,18,21,22], comparison to temporally and spatially averaged transport quantities that can be easily measured experimentally [16], or cross-comparison between the different numerical modeling approaches [17]. There is a clear need for high-fidelity benchmark experimental data that can be used as a common basis for validation of sophisticated flow boiling models.…”

Boiling heat transfer by using the VOSET method based on unstructured grids

“…随后, Agarwal等人 [4] 采用VOF方法成功 预测了水平膜态沸腾气泡的生长和传热特征, 计算得 到的努塞尔数仅比Klimeno关联式 [5] 低7.6%. Yuan等 人 [6] 将VOF方法拓展至适体坐标, 模拟了强制对流膜 态沸腾, 计算得到的气液界面演化过程与实验吻合良 好. Pan等人 [7] 基于VOF法, 提出了一种可大大减少计 算时间的相变模型, 模型源项与当地温度耦合显式求 解, 得到了较为准确的微通道内气泡生长运动、液膜 厚度以及壁面传热系数. LS方法已被用于求解各种沸 腾问题, Son和Dhir [8] 首先采用LS方法求解了膜态沸腾 问题.…”