Study of Flow Boiling Characteristics of a Microchannel Using High Speed Visualization

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Rashid Ali ◽  
Björn Palm ◽  
Claudi Martin-Callizo ◽  
Mohammad H. Maqbool
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Indium Tin Oxide ◽  
High Speed ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Fused Silica ◽  
Internal Diameter ◽  
Electrically Conductive ◽  
Heated Length

This paper presents the visualization results obtained for an experimental study of R134a during flow boiling in a horizontal microchannel. The microchannel used was a fused silica tube having an internal diameter of 781 μm, a heated length of 191 mm, and was coated with a thin, transparent, and electrically conductive layer of indium-tin-oxide (ITO) on the outer surface. The operating parameters during the experiments were: mass flux 100–400 kg/m2 s, heat flux 5–45 kW/m2, saturation temperatures 25 and 30 °C, corresponding to saturation pressures of 6.65 bar and 7.70 bar and reduced pressures of 0.163 and 0.189, respectively. A high speed camera with a close up lens was used to capture the flow patterns that evolved along the channel. Flow pattern maps are presented in terms of the superficial gas and liquid velocity and in terms of the Reynolds number and vapor quality plots. The results are compared with some flow pattern maps for conventional and micro scale channels available in the literature. Rigorous boiling and increased coalescence rates were observed with an increase in the heat flux.

Flow Boiling Characteristics for R1234ze(E) in 1.0 and 2.2 mm Circular Channels

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Cristiano Bigonha Tibiriçá ◽  
Gherhardt Ribatski ◽  
John Richard Thome
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
High Speed ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Internal Diameter ◽  
Steel Tubes ◽  
Experimental Campaign ◽  
Microscale Flow ◽  
Flow Boiling Heat Transfer

Experimental flow boiling heat transfer results are presented for horizontal 1.0 and 2.2 mm I.D. (internal diameter) stainless steel tubes for tests with R1234ze(E), a new refrigerant developed as a substitute for R134a with a much lower global warming potential (GWP). The experiments were performed for these two tube diameters in order to investigate a possible transition between macro and microscale flow boiling behavior. The experimental campaign includes mass velocities ranging from 50 to 1500 kg/m2 s, heat fluxes from 10 to 300 kW/m2, exit saturation temperatures of 25, 31 and 35 °C, vapor qualities from 0.05 to 0.99 and heated lengths of 180 mm and 361 mm. Flow pattern characterization was performed using high speed videos. Heat transfer coefficient, critical heat flux and flow pattern data were obtained. R1234ze(E) demonstrated similar thermal performance to R134a data when running at similar conditions.

Experimental Measurements and CFD Evaluation of the Onset Flow Boiling at Low Pressure and High Subcooling Flow of R-11 Within Vertical Annulus

2014 ◽  
Author(s):  
Y. Bouaichaoui ◽  
R. Kibboua ◽  
M. Matkovič
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Fluid Model ◽  
Computer Code ◽  
Computational Method ◽  
Subcooled Boiling ◽  
Two Phase ◽  
Local Flow ◽  
Wide Range

The knowledge of the onset of subcooled boiling in forced convective flow at high liquid velocity and subcooling is of importance in thermal hydraulic studies. Measurements were performed under various conditions of mass flux, heat flux, and inlet subcooling, which enabled to study the influence of different boundary conditions on the development of local flow parameters. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow carried out with the computer code ANSYS-CFX-13. A computational method based on theoretical studies of steady state two phase forced convection along a test section loop was released. The calculation model covers a wide range of two phase flow conditions. It predicts the heat transfer rates and transitions points such as the Onset of Critical Heat Flux.

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.

Single Phase and Flow Boiling Heat Transfer of Water and Ethanol in a Mini-Channel Array

2010 ◽  
Author(s):  
M. W. Alnaser ◽  
K. Spindler ◽  
H. Mu¨ller-Steinhagen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Single Phase ◽  
Flow Boiling ◽  
Video Camera ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Speed Video Camera

A test rig was constructed to investigate flow boiling in an electrically heated horizontal mini-channel array. The test section is made of copper and consists of twelve parallel mini-channels. The channels are 1 mm deep, 1 mm wide and 250 mm long. The test section is heated from underneath with six cartridge heaters. The channels are covered with a glass plate to allow visual observations of the flow patterns using a high-speed video-camera. The wall temperatures are measured at five positions along the channel axis with two resistance thermometers in a specified distance in heat flow direction. Local heat transfer coefficients are obtained by calculating the local heat flux. The working fluids are deionised water and ethanol. The experiments were performed under near atmospheric pressure (0.94 bar to 1.2 bar absolute). The inlet temperature was kept constant at 20°C. The measurements were taken for three mass fluxes (120; 150; 185 kg/m2s) at heat fluxes from 7 to 375 kW/m2. Heat transfer coefficients are presented for single phase forced convection, subcooled and saturated flow boiling conditions. The heat transfer coefficient increases slightly with rising heat flux for single phase flow. A strong increase is observed in subcooled flow boiling. At high heat flux the heat transfer coefficient decreases slightly with increasing heat flux. The application of ethanol instead of water leads to an increase of the surface temperature. At the same low heat flux flow boiling heat transfer occurs with ethanol, but in the experiments with water single phase heat transfer is still dominant. It is because of the lower specific heat capacity of ethanol compared to water. There is a slight influence of the mass flux in the investigated parameter range. The pictures of a high-speed video-camera are analysed for the two-phase flow-pattern identification.

Flow Boiling in a Parallel Strip Fin Heat Sink With Nonuniform Heat Flux Conditions

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Kexian Ren ◽  
Ze Miao ◽  
Bo Yang ◽  
Tongzhi Yang ◽  
Weixing Yuan
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Thermal Load ◽  
High Speed ◽  
Flow Boiling ◽  
Uniform Heat Flux ◽  
High Speed Camera ◽  
Pressure Drops ◽  
Boiling Process ◽  
Parallel Strip

Abstract This study investigates the thermal performance of a parallel strip fin heat sink (PSFHS) under various heat flux conditions at a flowrate of 100 ml/min, including uniform heat flux and nonuniform heat flux. The heat sink consists of 150 fins with a width of 1 mm, a height of 5.5 mm, and a pitch of 1 mm and has a Z-type inlet/outlet arrangement. Nine separate heaters offer thermal load to the heat sink in order to provide a uniform or nonuniform heat flux. The flow boiling process is captured by a high-speed camera. The temperatures of the heaters have been measured under the uniform and nonuniform heat flux conditions. In addition, the pressure drops inside the heat sink are also obtained. A minichannel heat sink (MCHS) with the same channel dimensions and inlet/outlet configuration is tested too. A comparison between MCHS and PSFHS is discussed in detail, which helps to understand the flow boiling characteristic in PSFHS.

Flow Boiling Visualization of R-134a in a Vertical Channel of Small Diameter

2007 ◽  
Author(s):  
Claudi Marti´n-Callizo ◽  
Bjo¨rn Palm ◽  
Wahib Owhaib ◽  
Rashid Ali
Keyword(s):  
Flow Pattern ◽  
Annular Flow ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
R 134A ◽  
Heated Length

The present work reports on flow boiling visualization of refrigerant R-134a in a vertical circular channel with internal diameter of 1.33 mm and 235 mm in heated length. Quartz tube with a homogeneous ITO-coating is used allowing heating and simultaneous visualization. Flow patterns have been observed along the heated length with the aid of a digital camera with close-up lenses. From the flow boiling visualization, seven distinct two-phase flow patterns have been observed: Isolated bubbly flow, confined bubbly flow, slug flow, churn flow, slug-annular flow, annular flow, and mist flow. Two-phase flow pattern observations are presented in the form of flow pattern maps. Finally, the experimental flow pattern map is compared to models developed for conventional sizes as well as to a microscale map for air-water mixtures available in the literature, showing a large discrepancy.

Flow Pattern, Heat Transfer and Pressure Drop Behaviors of Micro-Channel Flow Boiling

2018 ◽  
Author(s):  
Sira Saisorn ◽  
Pochai Srithumkhant ◽  
Pakorn Wongpromma ◽  
Maturose Suchatawat ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Flow Boiling ◽  
Flow Direction ◽  
Saturation Pressure ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Stainless Steel Tube

Two-phase flow of R-134a with high confinement number was experimentally carried out in this study. Flow boiling conditions for different orientations were controlled to take place in a stainless steel tube having a diameter of 0.5 mm. Based on a saturation pressure of 8 bar, a heat flux range of 2–26 kW/m2, and a mass flux range of 610–815 kg/m2s, a constant surface heat flux condition was controlled by applied DC power supply on the test section. The flow behaviors were described based on flow pattern and pressure drop data while heat transfer mechanisms were explained by using heat transfer coefficient data. In this work, nucleate boiling was observed, and the importance of the change in the flow direction was neglected, corresponding to the confinement number of around 1.7.

Subcooled Flow Boiling With Microbubble Emission in a Michrochannel

2009 ◽  
Author(s):  
Koichi Suzuki ◽  
Tomoyuki Nomura ◽  
Chungpyo Hong ◽  
Kazuhisa Yuki
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Atmospheric Condition ◽  
High Heat ◽  
Hydraulic Diameter ◽  
Maximum Pressure ◽  
High Heat Flux ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Subcooled flow boiling of water has been investigated for the horizontal multi-microchannel of which hydraulic diameter is 150μm for unit channel. Eleven rectangular microchannels are made on a top of copper heating block of 5.25mm × 5.25mm. The outlet of the channel is opened to the atmospheric surroundings and the maximum pressure in the channel is lower than 25mmHg. The boiling test is performed under the nearly atmospheric condition. The experimental results are discussed compared with subcooled boiling of water in a microchannel of 155μm in hydraulic diameter with Platinum film microheater of 2000μm in length and 200μm in width obtained by Ping Cheng and his co-workers. According to the authors’ previous experiments on subcooled flow boiling in mini and conventional channels, the critical heat flux decreases with decreasing of the hydraulic diameter of the channel. The boiling in the microchannel turns to film boiling after reaching CHF without microbubble emission boiling (MEB) regardless of liquid subcooling and liquid velocity even if the boiling condition is the same as MEB in the minichannels. In the high heat flux region, whole of the microchannels is completely covered with large coalescing bubbles. The results are much different from those of experiments with Platinum film microheater, which have 14.41 MW/m2 of heat flux in MEB. It is difficult to introduce liquid–vapor exchange including MEB for the large capacitance heat sink in microchannel boiling.

Correlation for Flow Boiling Critical Heat Flux in Thin Rectangular Channels

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Futoshi Tanaka ◽  
Takashi Hibiki ◽  
Kaichiro Mishima
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Rectangular Channels ◽  
Hydraulic Design ◽  
Wide Range ◽  
Outlet Flow ◽  
Triggering Mechanisms ◽  
Small Channels ◽  
Heated Length

The effect of heated length on critical heat flux (CHF) in thin rectangular channels under atmospheric pressure has been studied. CHF in small channels has been widely studied in the last decades but most of the studies are based on flow in round tubes and number of studies focused on rectangular channels is relatively small. Although basic triggering mechanisms, which lead to CHF in thin rectangular channels, are similar to that of tubes, applicability of thermal hydraulic correlations developed for tubes to rectangular channels are questionable since heat transfer in rectangular channels are affected by the existence of nonheated walls and the noncircular geometry of channel circumference. Several studies of CHF in thin rectangular channels have been reported in relation to thermal hydraulic design of research reactors and neutron source targets and correlations have been proposed, but the studies mostly focus on geometrical conditions of the application of interest and therefore effect of channel parameters exceeding their interest is not fully understood. In his study, CHF data for thin rectangular channels have been collected from previous studies and the effect of heated length on CHF was examined. Existing correlations were verified with data with positive quality outlet flow but none of the correlations successfully reproduced the data for a wide range of heated lengths. A new CHF correlation for quality region applicable to a wide range of heated lengths has been developed based on the collected data.

Development of a Transparent Heater to Measure Surface Temperature Fluctuations Under Spray Cooling Conditions

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
A. R. Griffin ◽  
A. Vijayakumar ◽  
R.-H. Chen ◽  
K. B. Sundaram ◽  
L. C. Chow
Keyword(s):  
Surface Temperature ◽  
Indium Tin Oxide ◽  
High Speed ◽  
Quartz Substrate ◽  
Sampling Rate ◽  
Temperature Fluctuations ◽  
Spray Cooling ◽  
Fused Silica ◽  
Measure Surface Temperature ◽  
Lift Off

A heater designed to monitor surface temperature fluctuations during pool boiling and spray cooling experiments while the bubbles are simultaneously being observed has been fabricated and tested. The heat source was a transparent indium tin oxide (ITO) layer commercially deposited on a fused quartz substrate. Four copper-nickel thin film thermocouples (TFTCs) on the heater surface measured the surface temperature, while a thin layer of sapphire or synthetic fused silica provided electrical insulation between the TFTCs and the ITO. The TFTCs were microfabricated using the lift-off process to deposit the nickel and copper metal films. The TFTC elements were 50μm wide and overlapped to form a 25×25μm2 junction. A DAQ program recorded the TFTC voltages at a sampling rate of 50kHz and sent a trigger to a high-speed camera to synchronize bubble images with the surface temperature data. As the bubbles and their contact rings grew over the TFTC junction, correlations between bubble behavior and surface temperature changes were demonstrated.

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