Stabilization of Flow Boiling in Microchannels Using Pressure Drop Elements and Fabricated Nucleation Sites

2005 ◽  
Vol 128 (4) ◽  
pp. 389-396 ◽  
Author(s):  
Satish G. Kandlikar ◽  
Wai Keat Kuan ◽  
Daniel A. Willistein ◽  
John Borrelli
Keyword(s):  
Pressure Drop ◽  
Flow Boiling ◽  
Inlet Pressure ◽  
Superheated Liquid ◽  
Working Fluid ◽  
Vapor Bubbles ◽  
Liquid Environment ◽  
Nucleation Sites ◽  
Boiling Process ◽  
Flow Configurations

The flow boiling process suffers from severe instabilities induced due to nucleation of vapor bubbles in a superheated liquid environment in a minichannel or a microchannel. In an effort to improve the flow boiling stability, several modifications are introduced and experiments are performed on 1054×197μm parallel rectangular microchannels (hydraulic diameter of 332μm) with water as the working fluid. The cavity sizes and local liquid and wall conditions required at the onset of nucleation are analyzed. The effects of an inlet pressure restrictor and fabricated nucleation sites are evaluated as a means of stabilizing the flow boiling process and avoiding the backflow phenomenon. The results are compared with the unrestricted flow configurations in smooth channels.

Experimental Evaluation of Pressure Drop Elements and Fabricated Nucleation Sites for Stabilizing Flow Boiling in Minichannels and Microchannels

2005 ◽  
Author(s):  
Satish G. Kandlikar ◽  
Daniel A. Willistein ◽  
John Borrelli
Keyword(s):  
Pressure Drop ◽  
Experimental Evaluation ◽  
Flow Boiling ◽  
Superheated Liquid ◽  
Working Fluid ◽  
Vapor Bubbles ◽  
Liquid Environment ◽  
Nucleation Sites ◽  
Boiling Process ◽  
Flow Configurations

The flow boiling process suffers from severe instabilities induced due to nucleation of vapor bubbles in a minichannel or a microchannel in a superheated liquid environment. In an effort to improve the flow boiling stability, several modifications are introduced and experiments are performed on 1054 × 197 μm microchannels with water as the working fluid. The cavity sizes and local liquid and wall conditions required at the onset of nucleation are analyzed. The effects of an inlet pressure restrictor and fabricated nucleation sites are evaluated as a means of stabilizing the flow boiling process and avoiding the backflow phenomena. The results are compared with the unrestricted flow configurations in smooth channels.

Flow Boiling Heat Transfer in a Silicon Microchannel Heat Sink Using Liquid Crystal Thermography

2008 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Tariq Ahmad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Microchannel Heat Sink

The present study focuses on the experimental investigation of boiling heat transfer characteristics and pressure drop in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 295 μm, width of 254 μm, and a length of 16 mm. Un-encapsulated Thermochromic liquid Crystals (TLC) are used in the present work to enable nonintrusive and high spatial resolution temperature measurements. This measuring technique is used to provide accurate full and local surface-temperature and heat transfer coefficient measurements. Experiments are carried out for mass velocities ranging between 290 to 457 kg/m2.s and heat fluxes from 6.04 to 13.06 W/cm2 using FC-72 as the working fluid. Experimental results show that the pressure drop increases as the exit quality and the flow rate increase. High values of heat transfer coefficient can be obtained at low exit quality (xe < 0.2). However, the heat transfer coefficient decreases sharply and remains almost constant as the quality increases for an exit quality higher than 0.2.

Flow Boiling on Heterogeneous Wetting Surface in a Vertical Narrow Microchannel

2020 ◽  
Author(s):  
Yuhao Lin ◽  
Junye Li ◽  
Kan Zhou ◽  
Wei Li ◽  
Kuang Sheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Working Fluid ◽  
Hydrophilic Surface ◽  
Structured Surfaces ◽  
Boiling Process

Abstract The micro structured surfaces have significant impact on the flow patterns and heat transfer mechanisms during the flow boiling process. The hydrophobic surface promotes bubble nucleation while the hydrophilic surface supplies liquid to a heating surface, thus there is a trade-off between a hydrophobic and a hydrophilic surface. To examine the effect of heterogeneous wetting surface on flow boiling process, an experimental investigation of flow boiling in a rectangular vertical narrow microchannel with the heterogeneous wetting surface was conducted with deionized water as the working fluid. The heat transfer characteristics of flow boiling in the microchannel was studied and the flow pattern was photographed with a high-speed camera. The onset of flow boiling and heat transfer coefficient were discussed with the variation of heatfluxes and mass fluxes, the trends of which were analyzed along with the flow patterns. During the boiling process, the dominated heat transfer mechanism was nucleate boiling, with numerous nucleate sites between the hydrophilic/hydrophobic stripes and on the hydrophobic ones. In the meantime, after the merged bubbles were constrained by the channel walls, it would be difficult for them to expand towards upstream since they were restricted by the contact line between hydrophilic/hydrophobic stripes, thereby reduce the flow instability and achieve remarkable heat transfer performance.

Closed-Loop Flow Boiling Module With a Plated Heat Sink

2007 ◽  
Author(s):  
Hitoshi Sakamoto ◽  
Kazuyuki Mikubo
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Cold Plate ◽  
Vapor Bubbles ◽  
Cross Sectional ◽  
Heat Rejection ◽  
Attractive Option ◽  
Cooling Module ◽  
Water Holding

A compact flow boiling module was developed for cooling a 100-W class package of about one-inch square in size. The cold plate, where heat is transferred from the package was made with a porous plating inside to augment boiling heat transfer. Heat transfer increased by a maximum of 50 percent when an organic refrigerant HFE-7100 was used, while the conditions for heat rejection to the ambient were kept unchanged. The heat rejection was achieved with an 80-mm fan with a matching corrugated fin radiator, whose effectiveness limits the overall size of the cooling module. The microscopic structure in the cold plate negatively influenced boiling of water, holding large patches of vapor bubbles on the surface. When the convective effect was increased by decreasing the cross sectional area of the channel by 10 times, heat transfer was further augmented approximately by 2 folds, making the use of the organic refrigerant an attractive option as the working fluid.

scholarly journals Effects of Dissolved Air on Subcooled Flow Boiling of a Dielectric Coolant in a Microchannel Heat Sink

2005 ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Instability ◽  
Flow Boiling ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Process ◽  
Dissolved Air

The effects of dissolved air in the dielectric liquid FC-77 on flow boiling in a microchannel heat sink containing 10 parallel channels, each 500 μm wide and 2.5 mm deep, were experimentally investigated. Experiments were conducted before and after degassing, at three flow rates in the range of 30 to 50 ml/min. The dissolved air resulted in a significant reduction in wall temperature at which bubbles were first observed in the microchannels. Analysis of the results suggests that the bubbles observed initially in the undegassed liquid were most likely air bubbles. Once the boiling process is initiated, the wall temperature continues to increase for the undegassed liquid, while it remains relatively unchanged in the case of the degassed liquid. Prior to the inception of boiling in the degassed liquid, the heat transfer coefficients with the undegassed liquid were 300–500% higher than for degassed liquid, depending on the flow rate. The heat transfer coefficients for both cases reach similar values at high heat fluxes (over 120 kW/m2) once the boiling process with the degassed liquid was well established. The boiling process induced a significant increase in pressure drop relative to single-phase flow; the pressure drop for undegassed liquid was measured to be higher than for degassed liquid once the boiling process became well established in both cases. Flow instabilities were induced by the boiling process, and the magnitude of the instability was quantified using the standard deviation of the measured pressure drop at a given heat flux. It was found that the magnitude of flow instability increased with increasing heat flux in both the undegassed and degassed liquids, with greater flow instability noted in the undegassed liquid.

Preliminary Results of Pressure Drop Modeling During Flow Boiling in Open Microchannels With Uniform and Tapered Manifolds (OMM)

2013 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Full Potential ◽  
Transfer Coefficients ◽  
Open Microchannel

Flow boiling with microchannel can dissipate high heat fluxes at low surface temperature difference. A number of issues, such as instabilities, low critical heat flux (CHF) and low heat transfer coefficients, have prevented it from reaching its full potential. A new design incorporating open microchannels with uniform and tapered manifold (OMM) was shown to mitigate these issues successfully. Distilled, degassed water at 80 mL/min is used as the working fluid. Plain and open microchannel surfaces are used as the test sections. Heat transfer and pressure drop performance for uniform and tapered manifold with both the surfaces are discussed. A low pressure drop of 7.5 kPa is obtained with tapered manifold and microchannel chip at a heat flux of 263 W/cm2 without reaching CHF. The pressure drop data is further compared with the homogenous model and the initial results are presented.

Research on the Flow Boiling Characteristics of Water in a Multi-Furcated Tree-Shaped Mini-Channel

2012 ◽  
Vol 629 ◽  
pp. 691-698 ◽  
Author(s):  
Chen Yan ◽  
Chang Wei ◽  
Shu Sheng Zhang
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Constant Wall Temperature ◽  
Boiling Process ◽  
Simulation Results ◽  
Temperature Heating ◽  
The Heat Transfer Coefficient

A new multi-furcated structure of tree-shaped mini-channel was proposed in this paper. Numerical simulation was conducted to analyze the flow boiling and bubble growth characteristics of water in the mini-channel. By using the constant wall temperature heating method, the model was divided into different sub-regions according to different wall temperatures. Typical bubbly flow and slug flow patterns were obtained through the monitoring of the boiling process. The simulation results showed that when the convective heat transfer dominated, the pressure drop maintained minor and stable; while the nucleate boiling dominated, the pressure drop increased significantly and fluctuated within a certain range. Moreover, with the increase of vapor quality, the heat transfer coefficient increased first and then decreased. It is also found that the geometric structure of the multi-furcated tree-shaped mini-channel had a great impact on the heat transfer characteristics, and simulation results agreed well with the theoretical values.

Experimental Investigation of Flow Boiling Pressure Drop of R134A in a Microscale Horizontal Smooth Tube

2011 ◽  
Vol 3 (1) ◽  
Author(s):  
Cristiano Bigonha Tibiriçá ◽  
Jaqueline Diniz da Silva ◽  
Gherhardt Ribatski
Keyword(s):  
Pressure Drop ◽  
High Speed ◽  
Flow Boiling ◽  
Smooth Tube ◽  
Working Fluid ◽  
Prediction Methods ◽  
Internal Diameter ◽  
Two Phase ◽  
Pressure Drops ◽  
Frictional Pressure Drop

This paper presents new experimental flow boiling pressure drop results in a microscale tube. The experimental data were obtained under diabatic conditions in a horizontal smooth tube with an internal diameter of 2.32 mm. Experiments were performed with R134a as working fluid, mass velocities ranging from 100 kg/m2 s to 600 kg/m2 s, heat flux ranging from 10 kW/m2 to 55 kW/m2, saturation temperatures of 31°C, and exit vapor qualities from 0.20 to 0.99. Flow pattern characterization was also performed from images obtained by high-speed filming. Pressure drop gradients up to 48 kPa/m were measured. These data were carefully analyzed and compared against 13 two-phase frictional pressure drop prediction methods, including both macro- and microscale methods. Comparisons against these methods based on the data segregated according to flow patterns were also performed. Overall, the method by Cioncolini et al. (2009, “Unified Macro-to-Microscale Method to Predict Two-Phase Frictional Pressure Drops of Annular Flows,” Int. J. Multiphase Flow, 35, pp. 1138–1148) provided quite accurate predictions of the present database.

scholarly journals Effects of Dissolved Air on Subcooled Flow Boiling of a Dielectric Coolant in a Microchannel Heat Sink

2006 ◽  
Vol 128 (4) ◽  
pp. 398-404 ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Instability ◽  
Flow Boiling ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Process ◽  
Dissolved Air

The effects of dissolved air in the dielectric liquid FC-77 on flow boiling in a microchannel heat sink containing ten parallel channels, each 500μm wide and 2.5mm deep, were experimentally investigated. Experiments were conducted before and after degassing, at three flow rates in the range of 30-50ml∕min. The dissolved air resulted in a significant reduction in wall temperature at which bubbles were first observed in the microchannels. Analysis of the results suggests that the bubbles observed initially in the undegassed liquid were most likely air bubbles. Once the boiling process is initiated, the wall temperature continues to increase for the undegassed liquid, whereas it remains relatively unchanged in the case of the degassed liquid. Prior to the inception of boiling in the degassed liquid, the heat transfer coefficients with the undegassed liquid were 300-500% higher than for degassed liquid, depending on the flow rate. The heat transfer coefficients for both cases reach similar values at high heat fluxes (>120kW∕m2) once the boiling process with the degassed liquid was well established. The boiling process induced a significant increase in pressure drop relative to single-phase flow; the pressure drop for undegassed liquid was measured to be higher than for degassed liquid once the boiling process became well established in both cases. Flow instabilities were induced by the boiling process, and the magnitude of the instability was quantified using the standard deviation of the measured pressure drop at a given heat flux. It was found that the magnitude of flow instability increased with increasing heat flux in both the undegassed and degassed liquids, with greater flow instability noted in the undegassed liquid.

Experimental Study on the Effect of Stabilization on Flow Boiling Heat Transfer in Microchannels

2006 ◽  
Author(s):  
Wai Keat Kuan ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Instabilities ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Cross Sectional ◽  
Flow Configuration ◽  
Flow Boiling Heat Transfer ◽  
Boiling Process

The effect of flow instabilities on flow boiling heat transfer in microchannels is investigated using water as the working fluid. The experimental test section has six parallel rectangular microchannels with each having a cross sectional area of 1054 × 197 microns. Flow restrictors are introduced at the inlet of each microchannel to stabilize the flow boiling process and avoid the backflow phenomena. The mass flow rate, inlet temperature of water, and the electric current supplied to the resistive cartridge heater are controlled to provide quantitative heat transfer information. The results are compared with the unrestricted flow configuration.

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