Gas Phase Distribution Effects on Heat Transfer in Upward Vertical Bubbly Channel Flows

2016 ◽  
Author(s):  
Haden Hinkle ◽  
Deify Law
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Bubble Size ◽  
Single Phase ◽  
Volume Fraction ◽  
Phase Distribution ◽  
Vertical Channel ◽  
Channel Flows ◽  
Two Phase ◽  
Ansys Fluent

Two-phase (non-boiling) flows have been shown to increase heat transfer in channel flows as compared with single-phase flows. The present work explores the effects of gas phase distribution such as volume fraction and bubble size on the heat transfer in upward vertical channel flows. A two-dimensional (2D) channel flow of 10 cm wide by 100 cm high is studied numerically. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT. The bubble size is characterized by the Eötvös number. The volume fraction and the Eötvö number are varied parametrically to investigate their effects on Nusselt number of the two-phase flows. All simulations are compared with a single-phase flow condition.

Eulerian–Eulerian Modeling of Convective Heat Transfer Enhancement in Upward Vertical Channel Flows by Gas Injection

2017 ◽  
Vol 10 (2) ◽  
Author(s):  
Deify Law ◽  
Haden Hinkle
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Volume Fraction ◽  
Phase Distribution ◽  
Vertical Channel ◽  
Channel Flows ◽  
Two Phase ◽  
Air Volume ◽  
Eotvos Number

Two-phase bubbly flows by gas injection had been shown to enhance convective heat transfer in channel flows as compared with that of single-phase flows. The present work explores the effect of gas phase distribution such as inlet air volume fraction and bubble size on the convective heat transfer in upward vertical channel flows numerically. A two-dimensional (2D) channel flow of 10 cm wide × 100 cm high at 0.2 and 1.0 m/s inlet water and air superficial velocities in churn-turbulent flow regime, respectively, is simulated. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS fluent. The bubble size is characterized by the Eötvös number. The inlet air volume fraction is fixed at 10%, whereas the Eötvös number is maintained at 1.0 to perform parametric studies, respectively, in order to investigate the effect of gas phase distribution on average Nusselt number of the two-phase flows. All simulations are compared with a single-phase flow condition. To enhance heat transfer, it is determined that the optimum Eötvös number for the channel with a 10% inlet air volume fraction has an Eötvös number of 0.2, which is equivalent to a bubble diameter of 1.219 mm. Likewise, it is determined that the optimum volume fraction peaks at 30% inlet air volume fraction using an Eötvös number of 1.0.

Experimental Modeling of Light Phase Effect on Heat Transfer in Rod Bundle

2013 ◽  
Author(s):  
O. N. Kashinsky ◽  
P. D. Lobanov ◽  
A. S. Kurdyumov ◽  
N. A. Pribaturin ◽  
S. E. Volkov
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Phase Distribution ◽  
Transfer Enhancement ◽  
Light Phase ◽  
Two Phase ◽  
Injection Point ◽  
Rod Bundle ◽  
Fraction Distribution ◽  
Gas Liquid Flow

Experiments in two-phase gas-liquid flow in a vertical bundle of rods were performed. The void fraction distribution and heat transfer from heated central rod were considered. Comparisons for cases of single phase and two-phase flows are presented. Gas addition to the flow results in heat transfer enhancement. The position of gas injection point plays a significant role on heat transfer characteristics. A non uniform gas phase distribution around the central rod of the bundle was obtained.

Comparison of Single and Two-Phase Models for the Study of Mixed Convection Flows With Nanofluids

2010 ◽  
Author(s):  
Mahmood Akbari ◽  
Amin Behzadmehr ◽  
Nicolas Galanis
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Mixed Convection ◽  
Single Phase ◽  
Volume Fraction ◽  
Solid Particles ◽  
Two Phase ◽  
Prediction Ability ◽  
Numerical Predictions ◽  
Phase Models

The single phase and three different two phase models (Volume of fluid, Mixture and Eulerian) are used to analyse laminar mixed convection flow of Al2O3-water nanofluids in a horizontal tube, in order to evaluate their prediction ability. The flow is considered steady and developing. The fluid’s physical properties are temperature dependent whereas those of the solid particles are constant. A uniform heat flux is applied at the fluid-solid interface. Two different Reynolds numbers and three different volume fractions have been considered. The governing three-dimensional partial differential equations are elliptical in all directions and coupled. Predicted convective heat transfer coefficients, velocity, and temperature profiles, as well as secondary flow’s velocity vectors and temperature contours are compared at different axial positions. To validate the comparisons and verify the accuracy of the results, the numerical predictions are compared with corresponding experimental data. There are essentially no differences between the predictions of the two-phase models; however their results are significantly different from those of the single-phase approach. Two-phase model results are closer to the experimental data, but they show an unrealistic increase in heat transfer for small changes of the particle volume fraction. Hydrodynamically, the two-phase and single-phase approaches perform almost the same but their thermal predictions are quite different.

Numerical Analysis of Mixed Convection of Nanofluids Inside a Vertical Channel

2016 ◽  
Vol 13 (03) ◽  
pp. 1650012 ◽  
Author(s):  
M. B. Akgül ◽  
M. Pakdemirli
Keyword(s):  
Mixed Convection ◽  
Single Phase ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Vertical Channel ◽  
Eulerian Model ◽  
Two Phase ◽  
Thermal Fields ◽  
Laminar Mixed Convection ◽  
Effective Particle

Laminar mixed convection of an Al[Formula: see text]O[Formula: see text]/water nanofluid inside a vertical channel is investigated numerically. Single-phase and two-phase Eulerian models are employed to analyze flow and thermal fields of the nanofluid in conjunction with the suitable expressions for the particle viscosity and effective particle thermal conductivity. The results of two-phase Eulerian model are compared with the single-phase model and with the published experimental data. Effects of the solid volume fraction, Reynolds number and Grashof number on the heat transfer performance of the nanofluid are investigated and discussed in detail.

Computational Modeling of Extreme Heat Flux Microcooler for GaN-Based HEMT

2015 ◽  
Author(s):  
Hyoungsoon Lee ◽  
Yoonjin Won ◽  
Farzad Houshmand ◽  
Catherine Gorle ◽  
Mehdi Asheghi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Simulation Models ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Ansys Fluent ◽  
Heat Transfer Coefficients ◽  
Gan Hemt ◽  
Simulation Results ◽  
The Impact

This study explores an extreme heat flux limit of microcooler for GaN-based HEMTs (high electron mobile transistors) which have local power densities exceeding 30 kW/cm2 using both solid conduction simulation and single-phase/two-phase conjugate simulations. Solid conduction simulation models are developed for full geometry of the microcooler to account for the overall thermal resistances from GaN HEMT to working fluid. This allows investigating the temperature distribution of the suggested microcooler. Parametric studies are also performed to investigate the impact of geometries and heat transfer coefficients on the junction temperature. The solid conduction simulation results using COMSOL Multiphysics agree well with single-cell ANSYS Fluent simulation results. Separately, fluid-solid conjugate CFD (Computational Fluid Dynamics) simulation models provide the detailed flow information in the microchannel using a single-channel geometry with symmetry boundary conditions. Single-phase CFD simulations obtain the lower bound of total pressure drop and heat transfer coefficient at the microchannel walls for a mass velocity range of G = 6000–24000 kg/m2-s. The local temperatures and velocity distributions are reported that can help with identifying the locations of the maximum velocity and recirculation regions that are susceptible to dryouts. Two additional alternative tapered inlet designs are proposed to alleviate the significant pressure loss at the entrance of the SiC channel. The impact of the tapered inlet designs on pressure drops and heat transfer coefficients is also investigated. Two-phase simulations in microchannel are conducted using Volume-of-Fluid (VOF) method embedded in ANSYS Fluent to investigate two-phase flow patterns, flow boiling, and temperature distributions within the GaN HEMT device and SiC etched mircochannels. A user-defined function (UDF) accounts for the phase change process due to boiling at the microchannel walls. The results show that the time relaxation factor, ri has a strongly influence on both numerical convergence and flow solutions.

scholarly journals Gas–Liquid Two-Phase Flow and Heat Transfer without Phase Change in Microfluidic Heat Exchanger

Fluids ◽  
2021 ◽  
Vol 6 (4) ◽  
pp. 150
Author(s):  
Maksim P. Vasilev ◽  
Rufat Sh. Abiev
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Experimental Studies ◽  
Performance Criterion ◽  
Phase Flow ◽  
Segmented Flow ◽  
Two Phase ◽  
Intensification Of Heat Exchange

This work presents an experimental study of the possibility of intensifying in microfluidic heat exchangers (MFHE) by creating a two-phase segmented flow (gas–liquid). Measurements of convective heat transfer were carried out using an MFHE, consisting of six channels 1 × 1 mm. Experimental studies have shown that segmented flow makes it possible to increase the Nusselt number of a laminar flow in MFHE up to 1.67 and reduce thermal resistance up to 1.7 times compared to single-phase flow. At the same time, it was found that the intensification of heat exchange by a two-phase flow is observed only for the range of the volume fraction of gas from 10 to 30%. In addition, the calculation of the thermal performance criterion, including both thermal and hydraulic parameters (friction factor), also confirmed the promise of using the Taylor segmented flow as a method for single-phase heat transfer intensifying in microchannels.

Numerical modeling of the influence of bubbles on flow and heat transfer in the descending gas-liquid flow in a pipe

2012 ◽  
Vol 9 (1) ◽  
pp. 131-135
Author(s):  
M.A. Pakhomov
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Liquid Flow ◽  
Bubble Diameter ◽  
Gas Content ◽  
Two Phase ◽  
Eulerian Description ◽  
Flow And Heat Transfer ◽  
Gas Liquid Flow ◽  
The Mathematical Model

The paper presents the results of modeling the dynamics of flow, friction and heat transfer in a descending gas-liquid flow in the pipe. The mathematical model is based on the use of the Eulerian description for both phases. The effect of a change in the degree of dispersion of the gas phase at the input, flow rate, initial liquid temperature and its friction and heat transfer rate in a two-phase flow. Addition of the gas phase causes an increase in heat transfer and friction on the wall, and these effects become more noticeable with increasing gas content and bubble diameter.

CFD simulation of air effect on flow field characteristics of hydro-viscous clutch with constant speed difference

2018 ◽  
Vol 19 (2) ◽  
pp. 208
Author(s):  
Xudong Zheng ◽  
Fangwei Xie ◽  
Diancheng Wu ◽  
Xinjian Guo ◽  
Bing Zhang ◽  
...  
Keyword(s):  
Flow Field ◽  
Cfd Simulation ◽  
Power Transmission ◽  
Volume Fraction ◽  
Phase Distribution ◽  
Constant Speed ◽  
Distribution Law ◽  
Two Phase ◽  
Oil Film ◽  
Speed Difference

The purpose of this paper is to study the air effects on transmission characteristics of hydro-viscous clutch and reveal the distribution law of the flow field of the oil film. The computational-fluid-dynamics (CFD) simulation model of oil film with radial oil grooves between friction pairs is taken as the study object. Considering the air effects, the pressure field, two-phase distribution, transmission torque and temperature field of the oil film are analyzed comparatively by using the CFD technology. The results show that the presence of air changes the pressure and temperature distributions of the oil film. With increase of the absolute rotational speed, the air volume fraction increases and the radius value of the air-liquid boundary decreases under condition of constant speed difference, which makes the coverage rate of the oil film on the surface of the friction disks reduce and the transmission torque of the oil film decrease. These simulation results are attributed to the study of hydro-viscous-drive and its applications. This paper also can provide a theoretical basis for the mechanism of power transmission through oil film in the presence of air effects.

Experimental Study on Heat Transfer of Single-Phase Flow and Boiling Two-Phase Flow in Vertical Narrow Annuli

2002 ◽  
Author(s):  
Suizheng Qiu ◽  
Minoru Takahashi ◽  
Guanghui Su ◽  
Dounan Jia
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Two Phase Flow ◽  
Annular Channel ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Narrow Annuli ◽  
Narrow Gaps

Water single-phase and nucleate boiling heat transfer were experimentally investigated in vertical annuli with narrow gaps. The experimental data about water single-phase flow and boiling two-phase flow heat transfer in narrow annular channel were accumulated by two test sections with the narrow gaps of 1.0mm and 1.5mm. Empirical correlations to predict the heat transfer of the single-phase flow and boiling two-phase flow in the narrow annular channel were obtained, which were arranged in the forms of the Dittus-Boelter for heat transfer coefficients in a single-phase flow and the Jens-Lottes formula for a boiling two-phase flow in normal tubes, respectively. The mechanism of the difference between the normal channel and narrow annular channel were also explored. From experimental results, it was found that the turbulent heat transfer coefficients in narrow gaps are nearly the same to the normal channel in the experimental range, and the transition Reynolds number from a laminar flow to a turbulent flow in narrow annuli was much lower than that in normal channel, whereas the boiling heat transfer in narrow annular gap was greatly enhanced compared with the normal channel.

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