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.

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.

Numerical Study on the Mechanism of Heat Transfer Enhancement in Fe3O4 Nanoferrofluids With Magnetic Field

2019 ◽  
Author(s):  
Chenfei Wang ◽  
Dongdong Gao ◽  
Minli Bai ◽  
Peng Wang ◽  
Yubai Li
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Fe3o4 Nanoparticles ◽  
Volume Fraction ◽  
Numerical Study ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Enhancement Of Heat Transfer

Abstract Nanofluids is reported to significantly enhance heat transfer but with little cost of pressure loss. To further the enhancement of heat transfer using Fe3O4 nanofluids, a magnetic field is employed to control the trajectory of Fe3O4 nanoparticles. A numerical study is conducted with commercial soft ANSYS FLUENT and the simulations are done with a two-phase flow approach named Euler-Lagrange. By comparing heat transfer of laminar flow in a horizontal tube with magnetic field or not, various volume fraction (0.5%/2%) and Reynolds numbers (Re = 200–1000) are considered. Results show that magnetic field contributes an average 4% promotion in convective heat transfer coefficients compared with the condition of no magnet. The mechanism of the enhancement of heat transfer with magnetic field is explored based on the analysis of velocity field. Fe3O4 Nanoparticles move up and down under the magnetic force, and convective heat transfer is enhanced because of the disturbance of the Fe3O4 nanoparticles. Slip flow between the base fluid and nanoparticles also contributes to the enhancement of heat transfer.

Experimental Model of Temperature-Driven Nanofluid

2006 ◽  
Vol 129 (6) ◽  
pp. 697-704 ◽  
Author(s):  
A. G. Agwu Nnanna
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Small Volume ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Isothermal Condition ◽  
Carrier Fluid ◽  
Small Volume Fraction ◽  
The Impact

This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm Al2O3–H2O nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, 0.2⩽ϕ⩽2% the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction ϕ>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for Nuϕ as a function of ϕ and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

scholarly journals Convective Heat Transfer of Ethanol/Polyalphaolefin Nanoemulsion in Mini- and Microchannel Heat Exchangers for High Heat Flux Electronics Cooling

2021 ◽  
Author(s):  
Jaime Rios ◽  
Mehdi Kabirnajafi ◽  
Takele Gameda ◽  
Raid Mohammed ◽  
Jiajun Xu
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Phase Flow ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Flow And Heat Transfer

The present study experimentally and numerically investigates the flow and heat transfer characteristics of a novel nanostructured heat transfer fluid, namely, ethanol/polyalphaolefin nanoemulsion, inside a conventionally manufactured minichannel of circular cross section and a microchannel heat exchanger of rectangular cross section manufactured additively using the Direct Metal Laser Sintering (DMLS) process. The experiments were conducted for single-phase flow of pure polyalphaolefin (PAO) and ethanol/PAO nanoemulsion fluids with two ethanol concentrations of 4 wt% and 8 wt% as well as for two-phase flow boiling of nanoemulsion fluids to study the effect of ethanol nanodroplets on the convective flow and heat transfer characteristics. Furthermore, the effects of flow regime of the working fluids on the heat transfer performance for both the minichannel and microchannel heat exchangers were examined within the laminar and transitional flow regimes. It was found that the ethanol/PAO nanoemulsion fluids can improve convective heat transfer compared to that of the pure PAO base fluid under both single- and two-phase flow regimes. While the concentration of nanoemulsion fluids did not reflect a remarkable distinction in single-phase heat transfer performance within the laminar regime, a significant heat transfer enhancement was observed using the nanoemulsion fluids upon entering the transitional flow regime. The heat transfer enhancement at higher concentrations of nanoemulsion within the transitional regime is mainly attributed to the enhanced interaction and interfacial thermal transport between ethanol nanodroplets and PAO base fluid. For two-phase flow boiling, heat transfer coefficients of ethanol/PAO nanoemulsion fluids were further enhanced when the ethanol nanodroplets underwent phase change. A comparative study on the flow and heat transfer characteristics was also implemented between the traditionally fabricated minichannel and additively manufactured microchannel of similar dimensions using the same working fluid of pure PAO and the same operating conditions. The results revealed that although the DMLS fabricated microchannel posed a higher pressure loss, a substantial heat transfer enhancement was achieved as compared to the minichannel heat exchanger tested under the same conditions. The non-post processed surface of the DMLS manufactured microchannel is likely to be the main contributor to the augmented heat transfer performance. Further studies are required to fully appreciate the possible mechanisms behind this phenomenon as well as the convective heat transfer properties of nanoemulsion fluids.

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