Nucleate Boiling Bubble Dynamics in a PDMS Microchannel With a Single Nucleation Site

2011 ◽  
Author(s):  
Haojie Wang ◽  
Xipeng Lin ◽  
David M. Christopher
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Working Fluid ◽  
Heater Surface ◽  
Short Period ◽  
Pdms Microchannel ◽  
Very High

The bubble dynamics for flow boiling in a single microchannel was experimentally studied in the present work. A platinum heater was used as the nucleation site in a 0.1 mm hydraulic diameter PDMS (Polydimethylsiloxane) microchannel with FC72 as the working fluid. A high speed camera was used to visualize the bubble dynamics. The results show that the bubbles grow much slower than predicted by standard correlations due to the very large convective heat transfer to the liquid flowing around the bubble in the microchannel. The results also show that the bubble departure frequency, heat flux and bubble departure diameter are well correlated by two dimensionless parameters that also include the effect of the properties. Finally, the results suggest very high speed dryout and rewetting of the heater surface during the bubble growth with a very short period of more complete rewetting of the heater surface when a bubble separates from the main vapor stem.

Bubble Dynamics on Nanostructured Cu Surfaces

2008 ◽  
Author(s):  
Chen Li ◽  
Nikhil Koratkar ◽  
G. P. Peterson
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Ccd Camera ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Working Fluid ◽  
Visualization System ◽  
Boiling Process ◽  
Order Of Magnitude

Nucleate boiling performance was enhanced up to an order of magnitude through direct deposition of Cu nanorods on a planar Cu surface. The methodology that enables order of magnitude improvement in boiling performance without fabricating complicated surface structures or changing the working fluid will have broad impact on metal-liquid type two-phase heat exchangers. In this study, discussion was focused on bubble dynamics on the nanostrucured Cu surfaces. We observed striking differences in bubble dynamics through nucleation boiling process for the nanostructured surface including smaller bubble diameters, higher release frequencies and nucleation site density, and large fluctuations in bubble diameter prior to release. These differences during the boiling process are responsible for the enhanced heat transfer. High quality images were captured through a well-designed visualization system, which comprises of a high-speed charge-coupled device (CCD) camera, microscope and data acquisition system. This visualization study aims to quantitatively study the bubble dynamics on the nanostructured Cu surfaces.

A Photographic Study on the Effects of Hydrophobic-Spot Size and Subcooling on Local Film Boiling

2013 ◽  
Author(s):  
Bambang Joko Suroto ◽  
Masahiro Tashiro ◽  
Sana Hirabayashi ◽  
Sumitomo Hidaka ◽  
Masamichi Kohno ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Bubble Dynamics ◽  
Pure Water ◽  
Nucleate Boiling ◽  
Spot Size ◽  
Copper Surface ◽  
Film Boiling ◽  
Working Fluid ◽  
Boiling Regime

The effects of hydrophobic circle spot size and subcooling on local film boiling phenomenon from the copper surface with single PTFE (Polytetrafluoroethylene) hydrophobic circle spot at low heat flux has been investigated. The experiments were performed using pure water as the working fluid and subcooling ranging from 0 and 10K. The heat transfer surfaces are used polished copper block with single PTFE hydrophobic circle spot of diameters 2, 4 and 6 mm, respectively. A high-speed camera was used to capture bubble dynamics and disclosed the sequence of the process leading to local film boiling. The result shows that local films boiling occurs on the PTFE circle spot at low heat flux and was triggered by the merging of neighboring bubbles. The study also showed that transition time required for change from nucleate boiling regime to local film boiling regime depends on the diameter of the hydrophobic circle spot and the subcooling. A stable local film boiling occurs at the smallest diameter of hydrophobic spot. Subcooling cause the local film boiling occur at negative superheat and oscillation of bubble dome.

Dynamics of Contact Angle During Growth and Liftoff of Bubbles at a Single Nucleation Site in Flow Boiling

2004 ◽  
Author(s):  
Wangcun Jia ◽  
Vijay K. Dhir
Keyword(s):  
Contact Angle ◽  
High Speed ◽  
Flow Boiling ◽  
Nucleation Site ◽  
Contact Angles ◽  
Working Fluid ◽  
Wafer Surface ◽  
Photographic Images ◽  
Flow Boiling Heat Transfer ◽  
Processing Program

Contact angle is a critical parameter needed in the mechanistic models for the prediction of flow boiling heat transfer. In this paper, variations of upstream and downstream contact angles for a single vapor bubble in flow boiling on horizontal and vertical surfaces were investigated experimentally. The nucleation site is a well-characterized cavity, which was etched on a highly polished silicon wafer surface using micro-fabrication techniques. Water at one atmosphere pressure was used as the working fluid. Photographic images of the bubble were recorded during its inception, growth and liftoff by using high-speed video system and analyzed by an image-processing program. The results provide clean data on the dependence of upstream and downstream contact angles on surface orientation and flow velocity.

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

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Kan Zhou ◽  
Hua Zhu ◽  
Wei Li ◽  
Junye Li ◽  
Kuang Sheng ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Rectangular Microchannel ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Recently, microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging and integration. In this study, an experimental investigation of subcooled flow boiling in a high-aspect-ratio rectangular microchannel was conducted with de-ionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and the imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, onset of nucleate boiling (ONB), and flow patterns of subcooled flow boiling were investigated with the aid of instrumental measurements and a high-speed camera. The slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, with lower superheat required of boiling incipience for lower mass fluxes. Meanwhile, the initiative superheat and heat flux of onset of nucleate boiling were compared with the existing correlations in the literature with good agreement. As for the flow visualization images, slug flow and reverse backflow were observed, where transient local dryout as well as rewetting occurred. A facile image processing tool was developed to profile the transient development and progression of the liquid–vapor interface and partial dryout patches in microchannels, which proved that the physical quantities of bubble dynamics for the elongation period during subcooled boiling could be well detected and calculated.

An Experimental Study on Flow Boiling Characteristics of pHEMA Nano-Coated Surfaces in a Microchannel

2016 ◽  
Author(s):  
Abdolali Khalili Sadaghiani ◽  
Yağmur Şişman ◽  
Gözde Özaydın İnce ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Rectangular Microchannel ◽  
Camera System ◽  
Coated Surfaces

In this study, the effect of pHEMA (Polyhydroxyethylmethacrylate) nanostructure coated surfaces on flow boiling was investigated in a rectangular microchannel. Experiments were conducted using deionized water as the working fluid to investigate flow boiling in a microchannel with dimensions of 14 cm length, 1.5 cm width, and 500 μm depth. The effect of pHEMA coatings (coated on 1.5 × 1.5 cm2 silicon plates) on heat transfer coefficients and flow patterns was assessed and supported using a high speed camera system. Although the contact angle decreases on nano-coated surfaces, due to surface porosity, boiling heat transfer coefficient increases. Furthermore, visualization results indicated that uncoated surfaces experienced a smaller nucleate boiling region. It was also observed that dryout occurs at higher heat fluxes for coated surfaces.

Two-Phase Flow in Microchannels

2001 ◽  
Author(s):  
G. Hetsroni ◽  
A. Mosyak ◽  
Z. Segal
Keyword(s):  
Heat Sink ◽  
High Speed ◽  
Single Phase ◽  
Flow Boiling ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Two Phase ◽  
Infrared Radiometry ◽  
Phase Water

Abstract Experimental investigation of a heat sink for electronics cooling is performed. The objective is to keep the operating temperature at a relatively low level of about 323–333K, while reducing the undesired temperature variation in both the streamwise and transverse directions. The experimental study is based on systematic temperature, flow and pressure measurements, infrared radiometry and high-speed digital video imaging. The heat sink has parallel triangular microchannels with a base of 250μm. According to the objectives of the present study, Vertrel XF is chosen as the working fluid. Experiments on flow boiling of Vertrel XF in the microchannel heat sink are performed to study the effect of mass velocity and vapor quality on the heat transfer, as well as to compare the two-phase results to a single-phase water flow.

Effects of Parameters on the Two-Phase Flow Instability in a Microchannel

2018 ◽  
Author(s):  
Yefei Liu ◽  
Yang Liu ◽  
Xingtuan Yang ◽  
Liqiang Pan
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Flow Instability ◽  
Working Fluid ◽  
Two Phase ◽  
Short Period ◽  
Period Oscillation ◽  
Data Acquisition Card ◽  
Series Of Experiments ◽  
Vertical Microchannel

Series of experiments are conducted in a single microchannel, where subcooled water flows upward inside a transparent and vertical microchannel. The cross section of the channel is rectangle with the hydraulic diameter of 2.8mm and the aspect ratio of 20. The working fluid is 3–15K subcooled and surface heat flux on the channel is between 0–3.64 kW/m2, among which two-phase instability at low vapor quantity may occur. By using a novel transparent heating technique and a high-speed camera, visualization results are obtained. The parameters are acquired with a National Instruments Data Acquisition card. In the experiments, long-period oscillation and short-period oscillation are observed as the primary types of instability in a microchannel. Instability characteristics represented from signals correspond well with the flow pattern. Moreover, effects of several parameters are investigated. The results indicate that the oscillating period generally increases with the heat flux density and decreases with inlet subcooling, while the effects of inlet resistance are more complex.

Evaporation and Nucleate Boiling of an Individual Droplet on Surfaces

2005 ◽  
Author(s):  
X. D. Wang ◽  
G. Lu ◽  
X. F. Peng ◽  
B. X. Wang
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Bubble Dynamics ◽  
Imaging System ◽  
Dynamical Behavior ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Dynamical Process ◽  
Boiling Regime ◽  
Film Evaporation

A visual study was conducted to investigate the evaporation and nucleate boiling of a water droplet on heated copper, aluminum, or stainless surfaces with temperature ranging from 50°C to 112°C. Using a high-speed video imaging system, the dynamical process of the evaporation of a droplet was recoded to measure the transient variation of its diameter, height, and contact angle. When the contact temperature was lower than the saturation temperature, the evaporation was in film evaporation regime, and the evaporation could be divided into two stages. When the surface temperature was higher than the saturation temperature, the nucleate boiling was observed. The dynamical behavior of nucleation, bubble dynamics droplet were detail observed and discussed. The linear relationships of the average heat flux vs. temperature of the heated surfaces were found to hold for both the film evaporation regime and nucleate boiling regime. The different slopes indicated their heat transfer mechanism was distinct, the heat flux decreased in the nucleate boiling regime more rapidly than in the film evaporation due to the strong interaction between the bubbles.

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.

Heat Transfer Coefficient Measurement for Downward-Facing Heat Transfer on Curved Rectangular Water Channel

2016 ◽  
Author(s):  
Jun Yeong Jung ◽  
Yong Hoon Jeong
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Flow Boiling ◽  
Water Channel ◽  
Outer Wall ◽  
Reactor Vessel ◽  
Working Fluid ◽  
Heater Surface ◽  
Ir Camera ◽  
Lower Head

In-Vessel Retention by External Reactor Vessel Cooling (IVR-ERVC) is method of removing the decay heat by cooling reactor vessel after corium relocation, and is also one of severe accident management strategies. Estimating heat transfer coefficients (HTCs) is important to evaluate heat transfer capability of the ERVC. In this study, the HTCs of outer wall of reactor vessel lower head were experimentally measured under the IVR-ERVC situation of Large Loss of Coolant Accident (LLOCA) condition. Experimental equipment was designed to simulate flow boiling condition of ERVC natural circulation, and based on APR+ design. This study focused on effects of real reactor vessel geometry (2.5 m of radius curvature) and material (SA508) for the HTCs. Curved rectangular water channel (test section) was design to simulate water channel which is between the reactor vessel lower head outer wall and thermal insulator. Radius curvature, length, width and gap size of the test section were respectively 2.5 m, 1 m, 0.07 m and 0.15 m. Two connection parts were connected at inlet and outlet of the test section to maintain fluid flow condition, and its cross section geometry was same with one of test section. To simulate vessel lower head outer wall, thin SA508 plate was used as main heater, and test section supported the main heater. Thickness, width, length and radius curvature of the main heater were 1.2 mm, 0.07 m, 1 m and 2.5 m respectively. The main heater was heated by DC rectifier, and applied heat flux was under CHF value. The test section was changed for each experiment. The HTCs of whole reactor vessel lower head (bottom: 0 ° and top: 90 °) were measured by inclining the test section, and experiments were conducted at four angular ranges; 0–22.5, 22.5–45, 45–67.5 and 67.5–90 °. DI water was used as working fluid in this experiment, and all experiments were conducted at 400 kg/m2s of constant mass flux with atmospheric pressure. The working fluid temperatures were measured at two point of water loop by K-type thermocouple. The main heater surface temperatures were measured by IR camera. The main heater was coated by carbon spray to make uniform surface emissivity, and the IR camera emissivity calibration was also conducted with the coated main heater. The HTCs were calculated by measured main heater surface temperature. In this research, the HTC results of 10, 30, 60 and 90 ° inclination angle were presented, and were plotted with wall super heat.

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