Numerical Modeling of Vapor Bubbles During Flow Boiling Inside Microchannels

2018 ◽  
pp. 293-323
Author(s):  
Abhijit Mukherjee
Keyword(s):  
Numerical Modeling ◽  
Flow Boiling ◽  
Vapor Bubbles

Numerical Study of the Effect of Inlet Constriction on Bubble Growth During Flow Boiling in Microchannels

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Vapor Bubbles ◽  
Reversed Flow ◽  
Cross Sectional ◽  
Parallel Microchannels ◽  
Energy Equations

Flow boiling through microchannels is characterized by nucleation of vapor bubbles on the channel walls and their rapid growth as they fill the entire channel cross-section. In parallel microchannels connected through a common header, formation of vapor bubbles often results in flow maldistribution that leads to reversed flow in certain channels. The reversed flow is detrimental to the heat transfer and leads to early CHF condition. One way of eliminating the reversed flow is to incorporate flow restrictions at the channel inlet. In the present numerical study, a nucleating vapor bubble placed near the restricted end of a microchannel is numerically simulated. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid-vapor interface is captured using the level set technique. The results show that with no restriction the bubble moves towards the nearest channel outlet, whereas in the presence of a restriction, the bubble moves towards the distant but unrestricted end. It is proposed that channels with increasing cross-sectional area may be used to promote unidirectional growth of the vapor plugs and prevent reversed flow.

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.

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.

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.

Design Considerations for the Effects of Liquid Compressibility in Microchannel Flow Boiling

2006 ◽  
Author(s):  
David W. Fogg ◽  
Ken E. Goodson
Keyword(s):  
Single Channel ◽  
Flow Boiling ◽  
Vapor Bubbles ◽  
Confined Geometries ◽  
Local Pressure ◽  
Eulerian Model ◽  
Forced Convective Flow ◽  
Pressure Perturbations ◽  
Vapor Formation ◽  
Chip Geometry

Forced convective flow boiling in microchannels is characterized by the nucleation and rapid growth of vapor bubbles in confined geometries. Confined boiling flows are highly transient yielding periods of rapid vapor formation followed by a refilling of the channel with liquid. This behavior in a single microchannel with constant flow rates can only be correlated with the growth of single bubbles in the channel. Using a one-dimensional Lagrangrian-Eulerian model, Fogg and Goodson [1] showed that reflections of these pressure waves create local pressure depressions that may trigger nucleation at temperatures not predicted by incompressible analysis. This study extends the work of Fogg and Goodson [1] by examining the influence of channel and chip geometry on the propagation of pressure perturbations within microchannels. A set of equations are proposed to estimate the amplitude of the initial pulse and its evolution through various geometries such as converging/diverging channels and sudden expansions/contractions. Simulations of two single channel experimental structures show that the flow delivery condition plays a minimal role in the reflection and propagation of pressure perturbations and that channel design may impact the nucleation characteristics of microchannels.

An Experimental Investigation on the Effects of Heat and Mass Flux on Vapor Bubble Growth Characteristics in a Microchannel

2009 ◽  
Author(s):  
Zachary Edel ◽  
Abhijit Mukherjee
Keyword(s):  
Flow Rate ◽  
Heat Exchangers ◽  
Bubble Growth ◽  
High Speed ◽  
Flow Boiling ◽  
Bubble Formation ◽  
Flow Characteristics ◽  
Vapor Bubbles ◽  
Constant Flow Rate ◽  
Temperature Liquid

Micro heat exchangers are emerging as one of the most effective cooling technologies for high power-density applications. The design of micro heat exchangers is complicated by the presence of alternating flow regimes, which give way to flow boiling instability. Bubble formation inside microchannels can be correlated directly to flow boiling instability and can regulate flow characteristics and wall heat transfer when the bubbles grow to reach the microchannel hydraulic diameter. In this study, the growth of vapor bubbles in a single microchannel was examined using an experimental setup capable of measuring coolant flow rate, inlet and outlet liquid temperatures, and channel wall surface temperature. Liquid flow rate and wall heat flux were systematically varied while a high-speed camera was used to capture images of vapor bubbles forming in the channel. These images were used to compare bubble growth rates for a constant flow rate. The results provide fundamental understanding of the bubble growth process.

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