Critical Heat Flux During Subcooled Flow Boiling of Alumina Nanofluids in a Narrow Channel

2010 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Pure Water ◽  
Pressure Fluctuations ◽  
Narrow Channel ◽  
Inlet Temperature ◽  
Subcooled Flow Boiling ◽  
Narrow Channels

This work reported an experimental study of flow boiling of pure water and aqueous alumina nanofluids in a 0.5 millimetre narrow channel. An open-ended stainless steel microchannel system is constructed where liquids are supplied by a syringe pump and heated by a variable DC power source, with synchronized measurement of the surface temperature distribution along the channel and pressure fluctuations associated with bubbles. The effect of nanoparticle concentration, inlet subcooling and mass flow rate and on critical heat flux in a microchannel is investigated. A modest increase in CHF is observed for nanofluids, being higher at higher particle concentrations and higher inlet subcoolings. Regular fluctuations in temperature and pressure signals suggest a cyclic boiling events occurring in the narrow channel; the large pressure fluctuation, coupling with the surface temperature and inlet temperature fluctuations, would affect flow boiling mechanisms in narrow channels.

Development of Advanced High Heat Flux Cooling System for Power Electronics

2009 ◽  
Author(s):  
Yasuhisa Shinmoto ◽  
Shinichi Miura ◽  
Koichi Suzuki ◽  
Yoshiyuki Abe ◽  
Haruhiko Ohta
Keyword(s):  
Heat Flux ◽  
Power Electronics ◽  
Critical Heat Flux ◽  
Heating Surface ◽  
Narrow Channel ◽  
High Heat ◽  
High Heat Flux ◽  
Gap Size ◽  
Narrow Channels ◽  
Very High

Recent development in electronic devices with increased heat dissipation requires severe cooling conditions and an efficient method for heat removal is needed for the cooling under high heat flux conditions. Most researches are concentrated on small semiconductors with high heat flux density, while almost no existing researches concerning the cooling of a large semiconductor, i.e. power electronics, with high heat generation density from a large cooling area. A narrow channel between parallel plates is one of ideal structures for the application of boiling phenomena which uses the cooling for such large semiconductors. To develop high-performance cooling systems for power electronics, experiments on increase in critical heat flux (CHF) for flow boiling in narrow channels by improved liquid supply was conducted. To realize the cooling of large areas at extremely high heat flux under the conditions for a minimum gap size and a minimum flow rate of liquid supplied, the structure with auxiliary liquid supply was devised to prevent the extension of dry-patches underneath flattened bubbles generated in a narrow channel. The heating surface was experimented in two channels with different dimensions. The heating surfaces have the width of 30mm and the lengths of 50mm and 150mm in the flow direction. A large width of actual power electronics is realizable by the parallel installation of the same channel structure in the transverse direction. The cooling liquid is additionally supplied via sintered metal plates from the auxiliary unheated channels located at sides or behind the main heated channel. To supply the liquid to the entire heating surface, fine grooves are machined on the heating surface for enhance the spontaneous liquid supply by the aid of capillary force. The gap size of narrow channels are varied as 0.7mm, 2mm and 5mm. Distribution of liquid flow rate to the main heated channel and the auxiliary unheated channels were varied to investigate its effect on the critical heat flux. Test liquids employed are R113, FC72 and water. The systematic experiments by using water as a test liquid were conducted. Critical heat flux values larger than 2×106W/m2 were obtained at both gap sizes of 2mm and 5mm for a heated length of 150mm. A very high heat transfer coefficient as much as 1×105W/m2K was obtained at very high heat flux near CHF for the gap size of 2mm. This paper is a summary of experimental results obtained in the past by the present authors.

Heat Transfer Characteristics and Flow Pattern Visualization for Flow Boiling in a Vertical Narrow Microchannel

2018 ◽  
Author(s):  
Kan Zhou ◽  
Junye Li ◽  
Zhao-zan Feng ◽  
Wei Li ◽  
Hua Zhu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Lower Mass ◽  
Subcooled Flow Boiling ◽  
Mass Fluxes ◽  
Subcooled Flow

For improving the functionality and signal speed of electronic devices, electronic components have been miniaturized and an increasing number of elements have been packaged in the device. As a result there has been a steady rise in the amount of heat necessitated to be dissipated from the electronic device. Recently microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging, In the present study an experimental study of subcooled flow boiling in a high-aspect-ratio, one-sided heating rectangular microchannel with gap depth of 0.52 mm and width of 5 mm was conducted with deionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, flow pattern and onset of nucleate boiling of subcooled flow boiling were investigated through instrumental measurements and a high speed camera. It was found that the slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, and the slope was greater for lower mass fluxes, with lower superheat required for boiling incipience. As for the visualization images, for relatively lower mass fluxes the bubbles generated were larger and not easy to depart from the vertical upward placed narrow microchannel wall, giving elongated bubbly flow and reverse backflow. The thin film evaporation mechanism dominated the entire test section due to the elongated bubbles and transient local dryout as well as rewetting occurred. Meanwhile the initiative superheat and heat flux of onset of nucleate boiling were compared with existing correlations in the literature with good agreement.

Development of an Experimental Facility for Investigating Critical Heat Flux of Saturated Flow Boiling of Refrigerant-123 in Microchannels

2005 ◽  
Author(s):  
Wai Keat Kuan ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Test Facility ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Experimental Facility ◽  
Copper Block ◽  
Saturated Flow ◽  
Cartridge Heater

An experimental facility is developed to investigate critical heat flux (CHF) of saturated flow boiling of Refrigerant-123 (R-123) in microchannels. Six parallel Microchannels with cross sectional area of 0.2 mm × 0.2 mm are fabricated on a copper block, and a Polyvinyl Chloride (PVC) cover is then placed on top of the copper block to serve as a transparent cover through which flow patterns and boiling phenomena could be observed. A resistive cartridge heater is used to provide a uniform heat flux to the microchannels. The experimental test facility is designed to accommodate test sections with different microchannel geometries. The mass flow rate, inlet pressure, inlet temperature of Refrigerant-123, and the electric current supplied to the resistive cartridge heater are controlled to provide quantitative information near the CHF condition in microchannels. A high-speed camera is used to observe and interpret flow characteristics of CHF condition in microchannels.

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.

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