scholarly journals Simulation of Boiling Flow Experiments Close to CHF with the Neptune_CFD Code

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
Boštjan Končar ◽  
Borut Mavko
Keyword(s):  
Volume Fraction ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Heated Wall ◽  
Wall Region ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Boiling Flow ◽  
Flow Experiments ◽  
Near Wall

A three-dimensional two-fluid code Neptune_CFD has been validated against the Arizona State University (ASU) and DEBORA boiling flow experiments. Two-phase flow processes in the subcooled flow boiling regime have been studied on ASU experiments. Within this scope a new wall function has been implemented in the Neptune_CFD code aiming to improve the prediction of flow parameters in the near-wall region. The capability of the code to predict the boiling flow regime close to critical heat flux (CHF) conditions has been verified on selected DEBORA experiments. To predict the onset of CHF regime, a simplified model based on the near-wall values of gas volume fraction was used. The results have shown that the code is able to predict the wall temperature increase and the sharp void fraction peak near the heated wall, which are characteristic phenomena for CHF conditions.

Some Measurements in Subcooled Flow Boiling of Refrigerant-113

1991 ◽  
Vol 113 (1) ◽  
pp. 216-223 ◽  
Author(s):  
A. Hasan ◽  
R. P. Roy ◽  
S. P. Kalra
Keyword(s):  
Flow Boiling ◽  
Fluid Model ◽  
Annular Channel ◽  
Heated Wall ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Boiling Flow ◽  
Phase Temperature ◽  
Two Fluid Model ◽  
Two Fluid

Measurements of local vapor phase residence time fraction, liquid phase temperature, and heated wall temperature were carried out in subcooled flow boiling of Refrigerant-113 through a vertical annular channel. Data are reported for two fluid mass velocities and two pressures over a range of wall heat flux. Estimates of typical vapor bubble size and velocity are given. Some comparisons with a one-dimensional two-fluid model of subcooled boiling flow are also presented.

scholarly journals Interface Tracking Simulation for Subcooled Flow Boiling Using VOSET Method

2021 ◽  
Vol 8 ◽  
Author(s):  
Kong Ling ◽  
Shuai Zhang ◽  
Wenxing Liu ◽  
Xiaowei Sui ◽  
Wenquan Tao
Keyword(s):  
Heat Transfer ◽  
Volume Fraction ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Interface Tracking ◽  
Time Averaging ◽  
Subcooled Flow Boiling ◽  
Moving Interface ◽  
Subcooled Flow ◽  
Boiling Flow

This article presents a numerical simulation on subcooled flow boiling at a high-pressure condition. An interface tracking method, VOSET, was used to handle the moving interface, and conjugate heat transfer between the wall and the fluid was included in the numerical model. In order to consider the evaporation on the microlayer below a growing bubble, a depletable micorlayer model was employed. Our simulation illustrated typical processes of subcooled boiling flow including bubble sliding, coalescence, detachment and annihilation, and revealed many mechanisms in increasing the heat transfer coefficient. A transition in flow regime from isolated bubbly flow to elongated bubbly flow was reproduced by our simulations. The void fraction obtained by time-averaging the volume fraction of the vapor phase under various flow conditions was analyzed.

Multi-Scale Near-Wall Averaging and Two-Phase Logarithmic Law for a CFD Two-Fluid Model

2014 ◽  
Author(s):  
Avinash Vaidheeswaran ◽  
John R. Buchanan ◽  
Paul Guilbert ◽  
Martin Lopez de Bertodano
Keyword(s):  
Volume Fraction ◽  
Fluid Model ◽  
Wall Region ◽  
Two Phase ◽  
Averaging Technique ◽  
Multi Scale ◽  
Logarithmic Law ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Near Wall

A considerable amount of work has been done in the past to improve the solution methodology using the two-fluid model in the near-wall region. This includes the works of Larrateguy et al. [1], and Moraga et al. [2], based on a multi-scale bubble-center averaging technique. However one shortcoming is that the primitive variables must be recovered from the bubble-center averaged variables. This makes it difficult to implement it in a commercial CFD code. The current research focuses on an engineering approach to overcome this issue. A multi-scale near-wall averaging technique is proposed which separates the effects of bubble dynamics from its geometry in this region. In addition, the averaged volume fraction profile makes the CFD approach consistent with the modified logarithmic law of Marie et al. [3]. A step function volume fraction distribution was assumed in the near-wall region while developing the theory. However, the volume fraction prediction obtained from CFD calculations is not uniform in this region. The proposed near-wall averaging technique resolves this issue and makes the CFD implementation of the modified wall function approach consistent with the theory of Marie et al. [3].

High Heat Flux Subcooled Flow Boiling of Methanol in Microtubes

2015 ◽  
Author(s):  
Farzad Houshmand ◽  
Hyoungsoon Lee ◽  
Mehdi Asheghi ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Inner Diameter ◽  
Phase Pressure

As the proper cooling of the electronic devices leads to significant increase in the performance, two-phase heat transfer to dielectric liquids can be of an interest especially for thermal management solutions for high power density devices with extremely high heat fluxes. In this paper, the pressure drop and critical heat flux (CHF) for subcooled flow boiling of methanol at high heat fluxes exceeding 1 kW/cm2 is investigated. Methanol was propelled into microtubes (ID = 265 and 150 μm) at flow rates up to 40 ml/min (mass fluxes approaching 10000 kg/m2-s), boiled in a portion of the microtube by passing DC current through the walls, and the two-phase pressure drop and CHF were measured for a range of operating parameters. The two-phase pressure drop for subcooled flow boiling was found to be significantly lower than the saturated flow boiling case, which can lead to lower pumping powers and more stability in the cooling systems. CHF was found to be increasing almost linearly with Re and inverse of inner diameter (1/ID), while for a given inner diameter, it decreases with increasing heated length.

Droplet Formation in a Microchannel T-Junction With Different Step Structure Position

2020 ◽  
Vol 143 (7) ◽  
Author(s):  
Mohammad Yaghoub Abdollahzadeh Jamalabadi ◽  
Rasoul Kazemi ◽  
Mohammad Ghalandari
Keyword(s):  
Nusselt Number ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Flow Path ◽  
The Other ◽  
Two Phase ◽  
Fluid Behavior ◽  
Discrete Phase

Abstract In this study, numerical simulation of formation of droplet within T-shaped microchannel is investigated. Three-dimensional, transient and two-phase numerical solution for four different microchannels with different stepping positions in the flow path was performed. Various parameters such as volume fraction, Nusselt number, pressure, Reynolds number, and temperature are discussed. The results show that the location of stepped barriers in the flow path affects the process of droplet formation, its number and size in the microchannel and should be considered as an important factor in determining the fluid behavior in the microchannel. It was observed that by placing half of the step at the entrance and the other half after the entrance, the continuous phase (S3 mode) was formed in 37.5 s compared to the other modes. The droplets were also smaller in size and more in numbers. It was also observed that the maximum value for the Nusselt number was obtained for the S2 mode where the step was located just above the discrete-phase entrance. In addition, the pressure at the inlet was higher and the flow velocity increased after the step and its pressure decreased, and continued to decrease due to frictional path.

Vortex Simulation for Behavior of Solid Particles Falling in Air

2011 ◽  
Author(s):  
Hisanori Yagami ◽  
Tomomi Uchiyama
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Air Flow ◽  
Three Dimensional ◽  
Particle Diameter ◽  
Vortex Method ◽  
Solid Particles ◽  
Particle Volume ◽  
Two Phase ◽  
Spherical Region

The behavior of small solid particles falling in an unbounded air is simulated. The particles, initially arranged within a spherical region in a quiescent air, are made to fall, and their fall induces the air flow around them, resulting in the gas-particle two-phase flow. The particle diameter and density are 1 mm and 7.7 kg/m3 respectively. A three-dimensional vortex method proposed by one of the authors is applied. The simulation demonstrates that the particles are accelerated by the induced downward air flow just after the commencement of their fall. It also highlights that the particles are whirled up by a vortex ring produced around the downward air flow after the acceleration. The effect of the particle volume fraction at the commencement of the fall is also explored.

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