Enhancement of Forced Convection Subcooled Film Boiling Heat Transfer Using Gas Sheet Collapse by Electric Field Application

2018 ◽  
Vol 26 (02) ◽  
pp. 1850011
Author(s):  
Mitsuhiro Uemura
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Cooling Rate ◽  
Forced Convection ◽  
Boiling Heat Transfer ◽  
Pure Water ◽  
Field Application ◽  
Wire Surface ◽  
Cooling Period ◽  
Cooling Method

Enhancement of forced-convection boiling heat transfer by electric field is investigated experimentally. When a high-temperature horizontal filament is immersed in water, a gas sheet is formed around and the above filament due to liquid boiling, in the early immersion process. This gas-sheet markedly decreases the boiling cooling rate of the filament. Here, forced collapse of the gas sheet is attempted by imposing an electric field to enhance the boiling cooling rate, In the experiments, a horizontal platinum wire of 0.5[Formula: see text]mm in diameter is immersed in pure water under atmospheric pressure, and a DC voltage up to 600[Formula: see text]V is applied between the wire surface and an electrode made of glass placed 10[Formula: see text]mm apart. The whole boiling curve is measured under different applied voltages and wire-falling velocities in 0.5 to 2.0[Formula: see text]m/s range, and at subcooling of 60[Formula: see text]K. The experimental results show that the electric field is effective in promoting the disintegration of the gas sheet. Under the tested conditions, boiling cooling rate increased two-fold for an applied electric field of 600[Formula: see text]V/cm. This result shows that the use of an electric field to break up the gas-sheet has resulted in a remarkable increase in the cooling rate at high superheats during initial cooling period, which is even greater than that used in the existing material manufacturing processes by the rapid cooling method, and therefore, this method may contribute to developing new materials.

Numerical Analysis on Nanofluid Forced Convection in Ducts With Triangular Cross Sections

2011 ◽  
Author(s):  
O. Manca ◽  
S. Nardini ◽  
D. Ricci ◽  
S. Tamburrino
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Forced Convection ◽  
Cross Sections ◽  
Fluid Dynamic ◽  
Pure Water ◽  
Convection Flow ◽  
Uniform Heat Flux ◽  
Surface Shear Stress ◽  
Surface Shear

Heat transfer of fluids is very important to many industrial heating or cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by enhancing the thermal conductivity of the working fluids. An innovative way of improving the fluid thermal conductivity is to introduce suspended small solid nanoparticles in the base fluids. In this paper a numerical investigation on laminar forced convection flow of a water–Al2O3 nanofluid in a duct having an equilateral triangular cross section is performed. The hydraulic diameter is set equal to 1.0×10−2 m. A constant and uniform heat flux on the external surfaces has been applied and the single-phase model approach has been employed. The analysis has been run in steady state regime for a nanoparticle size equal to 38 nm, considering different volume particle concentrations. The CFD code Fluent has been employed in order to solve the tri-dimensional numerical model. Results are presented in terms of temperature and velocity distributions, surface shear stress and heat transfer convective coefficient, Nusselt number and required pumping power profiles. Comparison with results related to the fluid dynamic and thermal behaviors in pure water are carried out in order to evaluate the enhancement due to the presence of nanoparticles in terms of volumetric concentration.

Experimental Verification of Analytical Prediction of Pool Boiling CHF Incorporating the Effects of EHD and Contact Angle

2015 ◽  
Author(s):  
Ichiro Kano ◽  
Takahiro Sato ◽  
Naoki Okamoto
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Electric Field ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Contact Angles ◽  
Dielectric Liquid ◽  
Working Fluid ◽  
Analytical Prediction ◽  
Compound Effect

Boiling heat transfer enhancement via compound effect of Electro-Hydro-Dynamic (EHD) and contact angle has been experimentally and analytically investigated. A fluorinated dielectric liquid (Asahi Glass Co. Ltd, AE-3000) was selected as the working fluid. Pool boiling heat transfer in the saturated liquid was measured at atmospheric pressure. In order to change the contact angle between the boiling surface and the dielectric liquid, the different materials Cu, Cr, NiB, Sn, and mixture of 5 and 1.5 micro meter diamond particles were electrically deposited on a boiling surface. The critical heat flux (CHF) for different contact angles showed 20.5 ∼ 26.9 W/cm2 which was −7 ∼ 25 % of that for a non-coated Cu surface (21.5 W/cm2). Upon application of a −5 kV/mm electric field to the micro structured surface (the mixture of 5 and 1.5 micro meter particles), a CHF of 99 W/cm2 at a superheat of 33.5 K was obtained. The previous theoretical equation of pool boiling predicted the CHF with the electric field and without the electrode.

2618 Forced Convection Boiling Heat Transfer of Carbon Dioxide near Critical Pressure in a Mini-channel

2008 ◽  
Vol 2008.3 (0) ◽  
pp. 193-194
Author(s):  
Yasuhiko TANAKA ◽  
Isao ISHIHARA ◽  
Mamoru OZAWA ◽  
Hisashi UMEKAWA ◽  
Ryosuke MATSUMOTO
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Forced Convection ◽  
Boiling Heat Transfer ◽  
Critical Pressure
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