Visualization and Analysis of Venting From a Single Microchannel Two-Phase Copper Heat Exchanger

2009 ◽  
Author(s):  
Milnes P. David ◽  
Julie Steinbrenner ◽  
Josef Miler ◽  
Kenneth E. Goodson
Keyword(s):  
Vapor Phase ◽  
Liquid Flow ◽  
Air Injection ◽  
Flow Structures ◽  
Static System ◽  
Two Phase ◽  
Flow Rates ◽  
System Pressure ◽  
The Impact ◽  
Injection Rates

Two-phase microfluidic cooling solutions have the potential to meet the thermal and geometric requirements of high performance microprocessors. However, rapid nucleation and growth of the vapor phase in the micro-scale flow structures produce detrimental rise in the system pressure and create flow instabilities. In our previous work we developed a novel solution to these problems: to locally vent the vapor formed in the microstructures by capping the flow structures with porous, hydrophobic membranes that allow only the trapped vapor phase to escape the system. In this paper we present the results from a visualization study of this venting process in a copper microchannel with a porous hydrophobic Teflon membrane wall and determine the impact of varying flow conditions on the venting process. We tested liquid flow rates of 0.1, 0.25 and 0.5 ml/min with air injection rates varying from 0.2 to 6 ml/min, corresponding to mass qualities of 0.1% to 7%. Bubbly/slug and wavy flows are dominant at the lower liquid and air flow rates, with wavy-stratified and stratified flows becoming dominant at higher air injection rates. At the highest liquid flow rate, plug and annular flows were common. Analysis finds that venting effectiveness is insensitive to Reliq until the point where non-contact flow structures such as annular become dominant and result in a loss of effective venting area. We also find that venting area changes linearly with mass quality and that the maximum venting effectiveness can be improved by increasing the venting area or raising the total static system pressure. However, venting effectiveness is fundamentally limited by the membrane conductance.

The effect of two-phase flow regime on hydrodynamics and mass transfer in a horizontal-tube gas-liquid reactor

1985 ◽  
Vol 50 (3) ◽  
pp. 745-757 ◽  
Author(s):  
Andreas Zahn ◽  
Lothar Ebner ◽  
Kurt Winkler ◽  
Jan Kratochvíl ◽  
Jindřich Zahradník
Keyword(s):  
Mass Transfer ◽  
Pressure Drop ◽  
Flow Regime ◽  
Liquid Flow ◽  
Horizontal Tube ◽  
Liquid Holdup ◽  
Two Phase ◽  
Flow Rates ◽  
Type Relation ◽  
Good Agreement

The effect of two-phase flow regime on decisive hydrodynamic and mass transfer characteristics of horizontal-tube gas-liquid reactors (pressure drop, liquid holdup, kLaL) was determined in a cocurrent-flow experimental unit of the length 4.15 m and diameter 0.05 m with air-water system. An adjustable-height weir was installed in the separation chamber at the reactor outlet to simulate the effect of internal baffles on reactor hydrodynamics. Flow regime maps were developed in the whole range of experimental gas and liquid flow rates both for the weirless arrangement and for the weir height 0.05 m, the former being in good agreement with flow-pattern boundaries presented by Mandhane. In the whole range of experi-mental conditions pressure drop data could be well correlated as a function of gas and liquid flow rates by an empirical exponential-type relation with specific sets of coefficients obtained for individual flow regimes from experimental data. Good agreement was observed between values of pressure drop obtained for weirless arrangement and data calculated from the Lockhart-Martinelli correlation while the contribution of weir to the overall pressure drop was well described by a relation proposed for the pressure loss in closed-end tubes. In the region of negligible weir influence values of liquid holdup were again succesfully correlated by the Lockhart-Martinelli relation while the dependence of liquid holdup data on gas and liquid flow rates obtained under conditions of significant weir effect (i.e. at low flow rates of both phases) could be well described by an empirical exponential-type relation. Results of preliminary kLaL measurements confirmed the decisive effect of the rate of energy dissipation on the intensity of interfacial mass transfer in gas-liquid dispersions.

Impact of Bubble Size on Flow Response to Transient Pressure Drop Through Converging Nozzle

2020 ◽  
Author(s):  
Aleksey Garbaly ◽  
Thomas Shepard
Keyword(s):  
Transient Response ◽  
Liquid Flow ◽  
Speed Of Sound ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Bubbly Flows ◽  
Chamber Pressure ◽  
Convergent Nozzle ◽  
Flow Rates ◽  
The Impact

Abstract For homogenous two-phase bubbly flows, the theoretical speed of sound is dramatically reduced at moderate void fractions to speeds much lower than the speed of sound for either single phase. This theoretical speed of sound would suggest a propensity for bubbly flows to reach choked conditions when traveling through a convergent nozzle. However, for a bubbly flow to be considered homogenous requires assumptions that may not be realized in practical applications. In this experimental study, a bubbly flow was sent through a convergent nozzle before entering a large chamber. By setting steady flow conditions upstream and then reducing the chamber pressure via a vacuum pump, the transient response in terms of gas and liquid flow rates and upstream channel pressure was determined. The bubble size was carefully varied from ∼0.3–1 mm while holding gas and liquid flow rates constant in order to study how bubble size affects the transient flow characteristics. High-speed imaging was used for measuring the bubbles. Experiments were also conducted at two gas-liquid mass flow ratios. Results are presented to demonstrate the impact of bubble size and gas-liquid ratio on the transient response of upstream gas and liquid flow rates, upstream pressure and exit Mach number to the lowering of pressure downstream of the convergent nozzle. Results are presented both for flows that remained in the bubbly regime and for flows that transitioned to an annular flow regime during a trial.

Unified Model for Gas-Liquid Pipe Flow Via Slug Dynamics: Part 2 — Model Validation

2002 ◽  
Author(s):  
Hong-Quan Zhang ◽  
Qian Wang ◽  
Cem Sarica ◽  
James P. Brill
Keyword(s):  
Experimental Data ◽  
Liquid Flow ◽  
Pipe Flow ◽  
Flow Behavior ◽  
Two Phase ◽  
Flow Rates ◽  
Inclination Angles ◽  
Gas Liquid Flow ◽  
Extensive Experimental Data ◽  
Good Agreement

In Zhang et al. [1], a unified hydrodynamic model is developed for prediction of gas-liquid pipe flow behavior based on slug dynamics. In this study, the new model is validated with extensive experimental data acquired with different pipe diameters, inclination angles, fluid physical properties, gas-liquid flow rates and flow patterns. Good agreement is observed in every aspect of the two-phase pipe flow.

Aerodynamic Performance of Turbine Center Frames With Purge Flows—Part I: The Influence of Turbine Purge Flow Rates

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Stefan Zerobin ◽  
Andreas Peters ◽  
Sabine Bauinger ◽  
Ashwini Bhadravati Ramesh ◽  
Michael Steiner ◽  
...  
Keyword(s):  
Measurement Data ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Flow Structures ◽  
Flow Rates ◽  
Purge Flow ◽  
Mass Flows ◽  
The Individual ◽  
The Impact ◽  
First Time

This two-part paper deals with the influence of high-pressure turbine (HPT) purge flows on the aerodynamic performance of turbine center frames (TCF). Measurements were carried out in a product-representative one and a half-stage turbine test setup. Four individual purge mass flows differing in flow rate, pressure, and temperature were injected through the hub and tip, forward and aft cavities of the unshrouded HPT rotor. Two TCF designs, equipped with nonturning struts, were tested and compared. In this first part of the paper, the influence of different purge flow rates (PFR) is discussed, while in the second part of the paper, the impact of the individual hub and tip purge flows on the TCF aerodynamics is investigated. The acquired measurement data illustrate that the interaction of the ejected purge flow with the main flow enhances the secondary flow structures through the TCF duct. Depending on the PFR, the radial migration of purge air onto the strut surfaces directly impacts the loss behavior of the duct. The losses associated with the flow close to the struts and in the strut wakes are highly dependent on the relative position between the HPT vane and the strut leading edge (LE), as well as the interaction between vane wake and ejected purge flow. This first-time experimental assessment demonstrates that a reduction in the purge air requirement benefits the engine system performance by lowering the TCF total pressure loss.

Pressure Drop in a Capillary Tube in Boiling Two-Phase Flow

2003 ◽  
Author(s):  
Fumito Kaminaga ◽  
Baduge Sumith ◽  
Kunihito Matsumura
Keyword(s):  
Pressure Drop ◽  
Vapor Phase ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Capillary Tube ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
System Pressure ◽  
Phase Pressure

Two-phase pressure drop is experimentally examined in a flow boiling condition in a tube of diameter 1.45 mm using water in ranges of pressure from 10 to 100 kPa, mass flux from 18 to 152 kg/m2s, heat flux from 13 to 646 kW/m2, and exit quality from 0.02 to 0.77. Also, pressure drop in an adiabatic air-water two-phase flow is measured at atmospheric pressure using the same test section and mass flux ranges of liquid and gas as those in the flow boiling. Decreasing system pressure the pressure drop significantly increases at a given mass flux. Influence of vapor phase on the pressure drop is found to be large both in the adiabatic and the diabatic conditions. The frictional pressure drop correlation for the adiabatic two-phase flow is developed and applied to predict pressure drop in the flow boiling. But it cannot give satisfactory predictions. The Chisholm correlation calculating a two-phase pressure drop multiplier is modified to account the influence of vapor phase in a capillary tube and the modified correlation can predict the pressure drop in the flow boiling within an error of 20%.

Experimental Study of Gas-Liquid Pressurization Performance and Critical Gas Volume Fractions of a Multiphase Pump

2021 ◽  
Author(s):  
Liang Chang ◽  
Qiang Xu ◽  
Chenyu Yang ◽  
Xiaobin Su ◽  
Xuemei Zhang ◽  
...  
Keyword(s):  
Liquid Flow ◽  
Volume Fraction ◽  
Extreme Points ◽  
Transition Flow ◽  
Two Phase ◽  
Flow Rates ◽  
Multiphase Pump ◽  
Gas Liquid Flow ◽  
Relative Errors ◽  
Gas Volume

Abstract Gas entrainment may cause pressurization deterioration and even failure of pumps under conditions of high inlet gas volume fraction (GVF). When the inlet GVF increases to a critical value, an obvious deterioration performance of pump occurs. Air-water pressurization performance and inlet critical GVFs of a centrifugal multiphase pump are investigated experimentally under different inlet pressures and gas-liquid flow rates. To determine the first and second critical GVFs, a new method is proposed by computing the local extreme points of the second derivative of performance curves. New prediction correlations for two critical GVFs are established with relative errors lower than ±10% and ±8%. Boundaries of three different flow patterns and the transition flow rates are determined and presented by critical GVFs on the flow pattern diagram. Moreover, boundaries of maximum pressurization are determined by performance curve clusters and a power function correlation of gas-liquid flow rates when reaching the maximum pressurization is established. With the increase of inlet pressure from 1MPa to 5MPa, two-phase pressurization performance is significantly increased; occurrences of pressurization deterioration are obviously delayed with the first and second critical GVFs increasing by maximums of 8.2% and 7.1%.

Flashing Flow of Initially Subcooled Water in Convergent–Divergent Nozzles

1977 ◽  
Vol 99 (2) ◽  
pp. 263-268 ◽  
Author(s):  
V. E. Schrock ◽  
E. S. Starkman ◽  
R. A. Brown
Keyword(s):  
Liquid Flow ◽  
Phase Region ◽  
Phase Flow ◽  
Equilibrium Flow ◽  
Two Phase ◽  
Flow Rates ◽  
Discontinuous Transition ◽  
Pressure Profiles ◽  
Step Model ◽  
Bernoulli Flow

This paper presents results from a research program conducted a number of years ago on the problem of flashing flow of water in nozzles. In a previous paper [1] we presented results for the case of stagnation states in the low quality two-phase region. The present paper reports results for stagnation states in the subcooled region at pressures up to 9.05 × 103 kN/m2 and subcooling from 0 to 60° C. Pressure profiles and flow rates are reported. The results are compared with limiting cases of Bernoulli flow (meta-stable liquid flow) and homogeneous equilibrium flow. As expected neither was able to predict the experimental results. A two-step model based upon nucleation delay, “discontinuous” transition to two-phase flow followed by frozen composition gave reasonable predictions of the flowrates and pressure profiles in the convergent section.

Modeling and Simulation Challenges in Embedded Two Phase Cooling: DARPA’s ICECool Program

2015 ◽  
Author(s):  
Kaiser Matin ◽  
Avram Bar-Cohen ◽  
Joseph J. Maurer
Keyword(s):  
Heat Transfer ◽  
Modeling And Simulation ◽  
Coefficient Of Thermal Expansion ◽  
Operating Conditions ◽  
Electrical Performance ◽  
Two Phase ◽  
Modeling Tools ◽  
Analysis And Design ◽  
System Pressure ◽  
The Impact

Modeling and simulation of two-phase phenomena, as well as their impact on electrical performance and physical integrity are critical to the success of embedded cooling strategies. In DARPA’s Intrachip/Interchip Embedded Cooling (ICECool) program, thermal/electrical/mechanical co-simulation and modeling tools are being applied to the analysis and design of RF GaN MMIC (Monolithic Microwave Integrated Circuit) Power Amplifiers (PA) and digital ICs, with the ultimate goal of achieving greater than 3X electronic performance improvement. This paper addresses various simulation strategies and numerical techniques adopted by the DARPA ICECool performers, with attention devoted to co-simulation through coupled iterations of thermal, mechanical and electrical behavior for capturing device characteristics and predicting reliability and “best in class” simulations that can provide an understanding of device behavior during rugged operating conditions impacted by multi-physics environments. The effect of CTE (Coefficient of Thermal Expansion) mismatch on bond and structural integrity, the impact of cooling fluid choice on performance, the factors affecting erosion/corrosion in the microchannels, as well as electro-migration limits and joule heating effects, will also be addressed. A separate discussion of various two-phase issues, including interface tracking, system pressure drops, conjugate heat transfer, estimating near wall heat transfer coefficients, and predicting CHF (Critical Heat Flux) and dryout is also provided.

Flow Regime Evolution in Long, Serpentine Microchannels With a Porous Carbon Paper Wall

2008 ◽  
Author(s):  
Julie E. Steinbrenner ◽  
Eon Soo Lee ◽  
Fu-Min Wang ◽  
Chen Fang ◽  
Carlos H. Hidrovo ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Flow Regime ◽  
Liquid Flow ◽  
Liquid Water ◽  
Two Phase Flow ◽  
Pem Fuel Cells ◽  
Carbon Paper ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Rates

An important function of the gas delivery channels in Proton Exchange Membrane (PEM) fuel cells is the evacuation of liquid water created at the cathode. The resulting two-phase flow can become an obstacle to reactant transport and a source of parasitic losses. The present work examines the behavior of two-phase flow in 500 μm × 500 μm × 60 cm channels with distributed water injection through a porous carbon paper wall to gain understanding of the physics of flows relevant to fuel cell water management challenges. Flow regime maps based on local gas and liquid flow rates are constructed for experimental conditions corresponding to current densities between 0.5 and 1 A/cm2 and stoichiometric coefficients from 1 to 4. Flow structures are analyzed along the entire length of the channel. It is observed that slug flow is favored to plug flow at high air flow rates and low liquid flow rates. Stratified flow dominates at high liquid flow rates. Along the axial flow direction, the flow regime consistently transitions from intermittent to wavy to stable stratified flow. This progression is quantified using a parameter of flow progression which characterizes the degree of development of the two-phase flow toward the stable stratified condition. This parameter is discussed in relation to fuel cell operating conditions. It provides a metric for analyzing liquid water removal mechanisms in the cathode channels of PEM fuel cells.

Experimental and Numerical Development of a Two-Phase Venturi Flow Meter

2004 ◽  
Vol 126 (3) ◽  
pp. 457-467 ◽  
Author(s):  
Euge^nio S. Rosa ◽  
Rigoberto E. M. Morales
Keyword(s):  
Liquid Flow ◽  
Fluid Model ◽  
Algebraic Model ◽  
Venturi Tube ◽  
Gas Content ◽  
Test Facility ◽  
Model Parameters ◽  
Flow Meter ◽  
Two Phase ◽  
Flow Rates

An algebraic model is developed access the gas and the liquid flow rates of a two-phase mixture through a Venturi tube. The flow meter operates with upward bubbly flows with low gas content, i.e., volumetric void fraction bellow 12%. The algebraic model parameters stem from numerical modeling and its output is checked against the experimental values. An indoor test facility operating with air-water and air-glycerin mixtures in a broad range of gas and liquid flow rates reproduces the upward bubbly flow through the Venturi tube. Measurements of gas and liquid flow rates plus the static pressure acroos the Venturi constitute the experimental database. The numerical flow modeling uses the isothermal, axis-symmetric with no phase change representation of the Two-Fluid model. The numerical output feeds the Venturi’s algebraic model with the proper constants and parameters embodying the two-phase flow physics. The novelty of this approach is the development of each flow meter model accordingly to its on characteristics. The flow predictions deviates less than 14% from experimental data while the mixture pipe Reynolds number spanned from 500 to 50,000.

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