CRITICAL HEAT FLUX AND SUBCOOLED FLOW BOILING WITH SMALL HEATED REGIONS ON STRAIGHT AND CONCAVE-CURVED WALLS

1994 ◽  
Author(s):  
P. S. Wu ◽  
Terrence W. Simon
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Curved Walls

scholarly journals Alumina Nanoparticle Pre-Coated Tubing Enhancing Subcooled Flow Boiling Critical Heat Flux

2009 ◽  
Author(s):  
Bao Truong ◽  
Lin-wen Hu ◽  
Jacopo Buongiorno ◽  
Thomas McKrell
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Nanoparticle Deposition ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

Nanofluids are engineered colloidal dispersions of nano-sized particle in common base fluids. Previous pool boiling studies have shown that nanofluids can improve critical heat flux (CHF) up to 200% for pool boiling and up to 50% for subcooled flow boiling due to the boiling induced nanoparticle deposition on the heated surface. Motivated by the significant CHF enhancement of nanoparticle deposited surface, this study investigated experimentally the subcooled flow boiling heat transfer of pre-coated test sections in water. Using a separate coating loop, stainless steel test sections were treated via flow boiling of alumina nanofluids at constant heat flux and mass flow rate. The pre-coated test sections were then used in another loop to measure subcooled flow boiling heat transfer coefficient and CHF with water. The CHF values for the pre-coated tubing were found on average to be 28% higher than bare tubing at high mass flux G = 2500 kg/m2 s. However, no enhancement was found at lower mass flux G = 1500 kg/m2 s. The heat transfer coefficients did not differ much between experiments when the bare or coated tubes were used. SEM images of the test sections confirm the presence of a nanoparticle coating layer. The nanoparticle deposition is sporadic and no relationship between the coating pattern and the amount of CHF enhancement is observed.

Critical Heat Flux (CHF) of Subcooled Flow Boiling of Alumina Nanofluids in a Horizontal Microchannel

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Nanoparticle Deposition ◽  
Common Features ◽  
Surface Temperature Distribution ◽  
Subcooled Flow ◽  
Pattern Development ◽  
Subsequent Modification

This work investigates subcooled flow boiling of aqueous based alumina nanofluids in 510 μm single microchannels with a focus on the effect of nanoparticles on the critical heat flux. The surface temperature distribution along the pipe, the inlet and outlet pressures and temperatures are measured simultaneously for different concentrations of alumina nanofluids and de-ionized water. To minimize the effect of nanoparticle depositions, all nanofluid experiments are performed on fresh microchannels. The experiment shows an increase of ∼51% in the critical heat flux under very low nanoparticle concentrations (0.1 vol %). Different burnout characteristics are observed between water and nanofluids, as well as different pressure and temperature fluctuations and flow pattern development during the stable boiling period. Detailed observations of the boiling surface show that nanoparticle deposition and a subsequent modification of the boiling surface are common features associated with nanofluids, which should be responsible for the different boiling behaviors of nanofluids.

Influence of Test Tube Material on Subcooled Flow Boiling Critical Heat Flux in Short Vertical Tube

2006 ◽  
Author(s):  
Koichi Hata ◽  
Masahiro Shiotsu ◽  
Nobuaki Noda
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Vertical Tube ◽  
Test Tube ◽  
304 Stainless Steel ◽  
Tube Material ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

The steady state subcooled flow boiling critical heat flux (CHF) for the flow velocities (u = 4.0 to 13.3 m/s), the inlet subcoolings (ΔTsub,in = 48.6 to 154.7 K), the inlet pressure (Pin = 735.2 to 969.0 kPa) and the increasing heat input (Q0exp(t/τ), τ = 10, 20 and 33.3 s) are systematically measured with the experimental water loop. The 304 Stainless Steel (SUS304) test tubes of inner diameters (d = 6 mm), heated lengths (L = 66 mm) and L/d = 11 with the inner surface of rough finished (Surface roughness, Ra = 3.18 μm), the Cupro Nickel (Cu-Ni 30%) test tubes of d = 6 mm, L = 60 mm and L/d = 10 with Ra = 0.18 μm and the Platinum (Pt) test tubes of d = 3 and 6 mm, L = 66.5 and 69.6 mm, and L/d = 22.2 and 11.6 respectively with Ra = 0.45 μm are used in this work. The CHF data for the SUS304, Cu-Ni 30% and Pt test tubes were compared with SUS304 ones for the wide ranges of d and L/d previously obtained and the values calculated by the authors’ published steady state CHF correlations against outlet and inlet subcoolings. The influence of the test tube material on CHF is investigated into details and the dominant mechanism of subcooled flow boiling critical heat flux is discussed.

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