scholarly journals Analytical Investigation into Effects of Capillary Force on Condensate Film Flowing over Horizontal Semicircular Tube in Porous Medium

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Tong-Bou Chang ◽  
Bai-Heng Shiue ◽  
Yi-Bin Ciou ◽  
Wai-Io Lo
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Capillary Force ◽  
Heat Transfer Performance ◽  
Capillary Forces ◽  
Gravity Force ◽  
Transfer Performance ◽  
Capillary Suction ◽  
Condensate Film ◽  
Energy Balance Approach

A theoretical investigation is performed into the problem of laminar filmwise condensation flow over a horizontal semicircular tube embedded in a porous medium and subject to capillary forces. The effects of the capillary force and gravity force on the condensation heat transfer performance are analyzed using an energy balance approach method. For analytical convenience, several dimensionless parameters are introduced, including the Jakob number Ja, Rayleigh number Ra, and capillary force parameter Boc. The resulting dimensionless governing equation is solved using the numerical shooting method to determine the effect of capillary forces on the condensate thickness. A capillary suction velocity can be obtained mathematically in the calculation process and indicates whether the gravity force is greater than the capillary force. It is shown that if the capillary force is greater than the condensate gravity force, the liquid condensate will be sucked into the two-phase zone. Under this condition, the condensate film thickness reduces and the heat transfer performance is correspondingly improved. Without considering the capillary force effects, the mean Nusselt number is also obtained in the present study as N u   ¯ | V 2 ∗ = 0 = 2 R a   D a / J a 1 / 2 ∫ 0 π 1 + cos   θ 1 / 2 d θ .

Boiling/Evaporation Heat Transfer Augmentation Using Subchannels-Inserted Metal Porous Media

2013 ◽  
Author(s):  
Kazuhisa Yuki ◽  
Masahiro Uemura ◽  
Koichi Suzuki ◽  
Ken-ichi Sunamoto
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Electronic Devices ◽  
High Heat Flux ◽  
Transfer Performance ◽  
Power Electronic ◽  
Copper Particles ◽  
Evaporation Heat

Two-phase flow loop system using a metal porous heat sink is proposed as a cooling system of the future power electronic devices with a heat load exceeding 300W/cm2. In this paper, as the first step, the heat transfer performance of the porous heat sink is evaluated under high heat flux conditions and the applicability and some engineering issues are discussed. The porous medium, which is fabricated by sintering copper particles, has a functional structure with several sub-channels inside it to enhance phase-change as well as discharge of generated vapor outside the porous medium. This porous heat sink is attached onto a heating chip and removes the heat by evaporating cooling liquid passing through the porous medium against the heat flow. Experiments using 30 kW of heating system show that the heat transfer performance of a copper-particles-sintered porous medium with the sub-channels exceeds 800W/cm2 in both high and low subcooling cases and achieves 300W/cm2 at a wall temperature of 150 °C (Tin = 70 °C) and 130 °C (Tin = 70 °C). These results prove that this porous heat sink is applicable enough for cooling 300 W/cm2 class of power electronic devices.

Heat Transfer Characteristics of Horizontal Nano-Structured Oscillating Heat Pipes

2019 ◽  
Author(s):  
Tingting Hao ◽  
Huiwen Yu ◽  
Xuehu Ma ◽  
Zhong Lan
Keyword(s):  
Heat Transfer ◽  
Heat Input ◽  
Capillary Force ◽  
Heat Transfer Performance ◽  
Filling Ratio ◽  
Water Evaporation ◽  
Working Fluid ◽  
Transfer Performance ◽  
Structured Surface ◽  
Inner Surface

Abstract Working fluid in the oscillating heat pipe (OHP) with low turn number (< 9) positioned in the horizontal heat mode could not easily backflow to the evaporator due to the absence of gravity. In this paper, copper OHP with superhydrophilic nano-structured inner surface by introducing additional capillary force was investigated through the visualization and thermal experiments. OHPs with 6 turns, charged with pure water as the working fluid, were fabricated with copper, and nano-structured inner surface and tested for comparison. Contact angles of water on the copper and superhydrophilic surface were 36.7 and 0 deg. The filling ratio of water was 50%, 65%, and 80%, respectively. Startup performance, thermal resistance, and liquid slug oscillation of OHPs were investigated experimentally at the heat input of 100–380 W. Experimental results showed that OHPs with the superhydrophilic nano-structured surface showed an enhanced heat transfer performance due to the nanostructure-induced capillary action for water in the horizontal direction. The optimum filling ratio was 65% in this work. Dryout was observed in the OHPs with the filling ratio of 50% at the heat input higher than 220 W. At the filling ratio of 80%, the working fluid was accumulated in the adiabatic and condensation section, and the driving force due to the water evaporation in evaporator was not high enough to activate the movements of liquid slugs. Heat transfer performance of OHP with nano-structured surface was higher than that of bare copper surface by introducing the additional capillary force.

scholarly journals MHD Heat Transfer in W-Shaped Inclined Cavity Containing a Porous Medium Saturated with Ag/Al2O3 Hybrid Nanofluid in the Presence of Uniform Heat Generation/Absorption

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3457 ◽  
Author(s):  
Mohamed Dhia Massoudi ◽  
Mohamed Bechir Ben Hamida ◽  
Hussein A. Mohammed ◽  
Mohammed A. Almeshaal
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Aspect Ratio ◽  
Heat Generation ◽  
Heat Transfer Performance ◽  
Convection Heat Transfer ◽  
Hybrid Nanofluid ◽  
Transfer Performance ◽  
Convection Heat ◽  
Uniform Heat

In this paper, a 2D numerical study of natural convection heat transfer in a W-shaped inclined enclosure with a variable aspect ratio was performed. The enclosure contained a porous medium saturated with Ag/Al2O3 hybrid nanofluid in the presence of uniform heat generation or absorption under the effect of a uniform magnetic field. The vertical walls of the enclosure were heated differentially; however, the top and bottom walls were kept insulated. The governing equations were solved with numerical simulation software COMSOL Multiphysics which is based on the finite element method. The results showed that the convection heat transfer was improved with the increase of the aspect ratio; the average Nusselt number reached a maximum for an aspect ratio (AR) = 0.7 and the effect of the inclination was practically negligible for an aspect ratio of AR = 0.7. The maximum heat transfer performance was obtained for an inclination of ω = 15 and the minimum is obtained for ω = 30 . The addition of composite nanoparticles ameliorated the convection heat transfer performance. This effect was proportional to the increase of Rayleigh and Darcy numbers, the aspect ratio and the fraction of Ag in the volumetric fraction of nanoparticles.

EXPERIMENTAL INVESTIGATION ON THE HEAT TRANSFER PERFORMANCE OF HEAT PIPES IN COOLING HEV LITHIUM-ION BATTERIES

2018 ◽  
Vol 49 (17) ◽  
pp. 1745-1760
Author(s):  
Faiza M. Nasir ◽  
Mohd Zulkifly Abdullah ◽  
Mohd A. Ismail
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Lithium Ion Batteries ◽  
Heat Transfer Performance ◽  
Lithium Ion ◽  
Heat Pipes ◽  
Transfer Performance

Computation of heat-transfer performance via CFD

2017 ◽  
Author(s):  
E. O. Pankova ◽  
Dudley Brian Spalding
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Transfer Performance
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