Electrohydrodynamically Enhanced Convective Boiling: Relationship Between Electrohydrodynamic Pressure and Momentum Flux Rate

1999 ◽  
Vol 122 (2) ◽  
pp. 266-277 ◽  
Author(s):  
J. E. Bryan ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Momentum Flux ◽  
Saturation Temperature ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Convective Boiling ◽  
The Mean ◽  
R 134A

The relationship between the mean radial electrohydrodynamic (EHD) pressure and the rate of the axial momentum flux and its influence on heat transfer enhancement and pressure drop in EHD-enhanced convective boiling of R-134a in a horizontal smooth tube was investigated in detail. A simple theory, which included the characteristics of two-phase flow, was developed to determine the mean radial EHD pressure. It was shown that the amount of heat transfer enhancement and the pressure drop penalty were dependent upon the size of the mean radial EHD pressure relative to the rate of the axial momentum flux. The influence of the mass flux, change in quality, and saturation temperature on the mean radial EHD pressure relative to the rate of the axial momentum flux was also studied. This study has provided a greater understanding of EHD enhancement of the convective boiling heat transfer. [S0022-1481(00)01802-8]

Visualization of the Heat Transfer Enhancement During Condensation in a Microfin Tube

2006 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Luca Doretti ◽  
Simone Mancin ◽  
Luisa Rossetto ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Saturation Temperature ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Vapor Quality ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Plain Tube ◽  
The Heat Transfer Coefficient

Microfins tubes are largely used in refrigeration industry for in-tube refrigerant condensation, because of the heat transfer enhancement when compared to equivalent smooth tubes under the same operating conditions. But not much evidence about the effect of microfins on the condensation flow patterns is available in the open literature. There is agreement in the open literature that the mechanisms of heat transfer are intimately linked with the prevailing two-phase flow regime. The present authors have recently measured the heat transfer coefficient during condensation of R410A in a microfin tube. The heat transfer enhancement in this tube can be experimentally evaluated by comparing those coefficients to the ones measured by Cavallini et al. (2001) in a plain tube, at the same operating conditions. The same operative conditions (saturation temperature, vapor quality and mass flux), occurring during the heat transfer measurements, were reproduced in a different section for visualization of flow patterns during condensation of R410A. The flow visualization has been carried out both in the plain tube and in the microfin tube. The objective of the present paper is to present the heat transfer enhancement during condensation of R410A and to show the flow visualized at the same operating condition for both the smooth and the microfin tube, aiming to link the heat transfer enhancement to the flow pattern variation.

Numerical investigation of EHD effects on heat transfer enhancement and flow pattern of R-134a two phase flow

2016 ◽  
Vol 82 ◽  
pp. 63-71 ◽  
Author(s):  
Pedram Hanafizadeh ◽  
Mahla Gharahasanlo ◽  
Sadegh Ahmadi ◽  
Shahab Zeraati ◽  
M.A. Akhavan-Behabadi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Pattern ◽  
Numerical Investigation ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Transfer Enhancement ◽  
Two Phase ◽  
R 134A

Effects of Particle Shape on Nanofluids Laminar Forced Convection in Helically Coiled Tubes

2017 ◽  
Author(s):  
Fang Liu ◽  
Yang Cai
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Particle Shape ◽  
Spherical Nanoparticles ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Laminar Forced Convection ◽  
Shape And Size

In this study, effects of particle morphology (shape and size) on nanofluids laminar forced convection in helically coiled tubes are investigated numerically using Eulerian-Lagrangian two-phase approach. The laminar forced convective heat transfer and pressure drop of Al2O3-water nanofluids containing nanoparticles with various particle shapes (sphere, platelet, blade, cylinder and brick) and sizes at different volume fractions in the developing and fully developed regions are investigated using the validated two-phase model. It is found that the nanofluids containing platelet particle shape has the highest heat transfer enhancement, which is followed by nanofluids containing cylinder, blade, sphere and brick nanoparticle shapes, respectively. Non-spherical nanoparticles with larger aspect ratio, small particle size and a suitable particle volume concentration are beneficial for heat transfer enhancement of forced convection. Heat transfer efficiency reaches minima at Re of 1250 for laminar forced convection with 1% volume fraction. The correlations of Nusselt number and pressure drop with nanoparticle shape and size were developed to predict convective heat transfer of nanofluids containing spherical nanoparticles and non-spherical nanoparticles.

Implication of geometrical configuration on heat transfer enhancement in converging minichannel using nanofluid by two phase mixture model: A numerical analysis

2020 ◽  
pp. 095440892096469
Author(s):  
Md. Faizan ◽  
Sukumar Pati ◽  
Pitamber R Randive
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Straight Channel ◽  
Particle Loading ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Phase Mixture ◽  
Converging Angle

In the present study laminar forced convective flow of nanofluid through a converging minichannel is investigated numerically by employing two phase mixture model. The heat transfer enhancement and the corresponding pressure drop are analyzed for the following range of parameters: Reynolds number (700 ≤ Re ≤ 1650), particle volume concentration (0% ≤ ϕ ≤ 4%) and converging angle (θ = 0.029°, 0.043° and 0.05°). The results indicate that there is a considerable increase in pressure drop coupled with enhancement in heat transfer rate with particle loading due to the improvement in the thermal properties of the resulting mixture. The pressure drop in the converging channel increases with the converging angle. The pressure drop augments as high as 2 times by advancing the particle loading from 0% to 4%. The wall temperature decreases appreciably by 34 K and heat transfer coefficient is enhanced by as high as 98% from Re =  700, ϕ = 0% and straight channel to Re =1650, Hout = 2.75mm and ϕ = 4%. The enhancement in heat transfer and corresponding increase in pressure drop as compared to equivalent straight channel is presented by the performance factor, which increases with decrease in converging angle. There is a significant concern of the pumping power with increase in converging angle, volume fraction and Reynolds number.

Mechanism of Annular Two-Phase Flow Heat Transfer Enhancement and Pressure Drop Penalty in the Presence of a Radial Electric Field—Turbulence Analysis

2003 ◽  
Vol 125 (3) ◽  
pp. 478-486 ◽  
Author(s):  
Y. Feng ◽  
J. Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Electric Field ◽  
Heat Transfer Enhancement ◽  
Annular Flow ◽  
Radial Electric Field ◽  
Phase Flow ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Flow Heat

The mechanism of heat transfer enhancement and pressure drop penalty in the presence of a radial electric field for the two-phase (liquid/vapor) annular flow is presented. The turbulence spectral theory shows that the radial electric field fluctuation changes the turbulent energy distribution, especially in the radial direction. Consequently, the Reynolds stresses are directly affected by the applied electric field. The analysis reveals that the influence of the applied electric field on the turbulence distribution in an annular two-phase flow leads to the changes in the heat transfer and the pressure drop. The magnitudes of the heat transfer enhancement and the pressure drop penalty are strongly related to the ratio of the radial pressure difference generated by the EHD force to the axial frictional pressure drop. The existing experimental data agree with the predictions of the analysis presented in this paper. The analysis developed here can be a valuable tool in properly predicting the two-phase annular flow heat transfer enhancement and pressure drop penalty in the presence of a radial electric field for both convective boiling and condensation processes.

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