Two Phase Flow Patterns and Cooling Power of Mixed Refrigerant in Micro Cryogenic Coolers

2012 ◽  
Author(s):  
Ryan Lewis ◽  
Hayley Schneider ◽  
Yunda Wang ◽  
Ray Radebaugh ◽  
Y. C. Lee
Keyword(s):  
Liquid Flow ◽  
High Speed ◽  
Single Phase ◽  
Liquid Fraction ◽  
Cryogenic Cooling ◽  
Cooling Power ◽  
Vapor Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Power Draw

Micro cryogenic coolers (MCCs) operating in the Joule-Thomson cycle with mixed refrigerants offer an attractive way to decrease the size, cost, and power draw required for cryogenic cooling. Recent studies of MCCs with mixed refrigerants have, when employing pre-cooling, shown pulsating flow-rates and oscillating temperatures, which have been linked to the refrigerant flow regime in the MCC. In this study we investigate those flow regimes. Using a high-speed camera and optical microscopy, it is found that the pulsations in flow correspond to an abrupt switch from single-phase vapor flow to single-phase liquid flow, followed by 2-phase flow in the form of bubbles, liquid slugs, and liquid slug-annular rings. After this period of 2-phase flow, the refrigerant transitions back to single-phase vapor flow for the cycle to repeat. Under different pre-cooling temperatures, the mole fraction of the vapor-phase refrigerant, as measured by molar flow-rate, agrees reasonably well with the quality of the refrigerant at that temperature as calculated by an equation of state. The frequency of pulsation increases with liquid fraction in the refrigerant, and the volume of liquid in each pulse only weakly increases with increasing liquid fraction. The cooling power of the liquid-flow is up to a factor of 7 greater than that of the 2-phase flows and single-phase vapor flow.

Comparing the Enhancement of Heat Transfer Caused by Sliding Gas Bubbles and by Sliding Vapor Bubbles in Subcooled Flow in a Minichannel

2013 ◽  
Author(s):  
Khaled E. Albahloul ◽  
D. Keith Hollingsworth ◽  
Larry C. Witte ◽  
Arif B. Ozer
Keyword(s):  
Heat Transfer ◽  
Liquid Flow ◽  
High Speed ◽  
Single Phase ◽  
Imaging System ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Lower Wall ◽  
Vapor Bubbles ◽  
Two Phase

Studies published over the past decade have established the importance of sliding bubbles in enhancing the heat transfer in subcooled two-phase flow in channels small enough to confine the bubbles. Recent work in this laboratory (Ozer et al., 2011, 2012) proposed that the primary enhancement mechanism is a single-phase convective mechanism: the transport of cold fluid nearer the wall due to the mixing behind the bubble. This is in contrast to two phase-change mechanisms: distributed bubble nucleation and the evaporation of the liquid microlayer between a sliding bubble and the surface. The work reported here explores this hypothesis by comparing the heat transfer enhancement produced by injected air bubbles to Ozer’s measurements obtained with naturally nucleated vapor bubbles. Data were collected under similar conditions in a highly subcooled laminar flow of Novec 649 in a horizontal rectangular minichannel of 1.21 to 1.484 mm channel spacing. The channel was formed by an electrically heated metallic upper wall and an unheated transparent lower wall. For the air/liquid flow, bubbles were injected at either a single point on the lower wall or through a sintered metal plug. The latter system produced a more channel-filling distribution of bubbles. A high-speed imaging system recorded the bubble motion and liquid crystal thermography recorded time-averaged surface temperature data. The comparison is presented in the form of the streamwise evolution of surface temperatures and the enhancement in time-averaged Nusselt number. Also, results for the passage of a single air bubble are presented. The air/liquid flow produced a Nu enhancement of between 120–350% compared to a single-phase flow at the same conditions. The passage of the single gas bubble produced a decrease in the wall temperature directly behind the bubble of 2–5 °C. The Nu enhancement produced by the air/liquid data and the nucleated vapor data is well correlated to appropriate dimensionless groups involving bubble diameter and frequency. The results from both data sets support the contention that a transient transport/mixing model developed previously for the vapor/liquid case captures the dominant single-phase convective mechanism in sliding bubble flows in highly confined channels.

scholarly journals Influence of Blade Type on the Flow Structure of a Vortex Pump for Solid-Liquid Two-Phase Flow

Machines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 353
Author(s):  
Hui Quan ◽  
Yanan Li ◽  
Lei Kang ◽  
Xinyang Yu ◽  
Kai Song ◽  
...  
Keyword(s):  
Flow Structure ◽  
Liquid Flow ◽  
Single Phase ◽  
Solid Phase ◽  
Internal Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Vortex Pump ◽  
Solid Liquid

Vortex pumps have good non-clogging performance owing to their impellers being retracted into retraction cavities, but they are much less efficient than ordinary centrifugal pumps. In this paper, numerical simulations were performed on a model of the 150WX200-20 vortex pump for four different blade types, and the influence of blade structure on pump performance was determined. The simulations revealed the existence of axial vortices in the flow passage between the blades in the impeller region. The geometric characteristics of these axial vortices were more regular in two-phase solid-liquid flow than single-phase liquid flow. The presence of the solid phase reduced the vortex strength compared with the single-phase flow and suppressed the increase in size of the secondary circulation vortex. It was found, however, that the blade shape had a greater influence on the circulating flow than the presence of the solid phase. The flow state of the medium flowing out of the impeller domain had a direct effect on the circulating flow with this effect being related to the law governing the flow of the medium in the flow channel between the blades. It was found that the performance of a front-bent blade was the best and that of a curved blade the worst. This influence of blade type on the internal flow structure was used to further explain the relationship between the internal flow structure and the external characteristics of the vortex pump, the understanding of which is crucial for blade selection and hydraulic optimization.

Visualization of Confined Jet Impingement With Boiling Using Time-Resolved Stereo-PIV

2015 ◽  
Author(s):  
Matthew J. Rau ◽  
Tianqi Guo ◽  
Pavlos P. Vlachos ◽  
Suresh V. Garimella
Keyword(s):  
Flow Field ◽  
Heat Source ◽  
Liquid Flow ◽  
Heated Surface ◽  
Jet Impingement ◽  
Vapor Flow ◽  
Wall Jet ◽  
Phase Flow ◽  
Two Phase ◽  
Time Resolved

Two-phase liquid-vapor flow field measurements of confined jet impingement with boiling are performed using time-resolved stereo particle image velocimetry (stereo-PIV). A single circular jet of water, impinges normally from a 3.75 mm-diameter orifice onto a submerged circular heat source at an orifice-to-target spacing of 4 jet diameters. The impinging jet outflow including the vapor generated at the heat source are confined between the jet orifice plate and the bottom test section wall. Fluorescent seeding particles (10 μm in diameter) and time-resolved PIV measurements (taken at a sampling rate of 750 Hz) allow for imaging of the instantaneous interactions between the liquid and vapor structures. Liquid-phase velocity vectors within the two-phase flow field (with high vapor fractions) are presented as a function of heat flux at jet Reynolds numbers of 5,000 and 15,000 and contrasted with single-phase flow. The time-resolved measurements are used to highlight the influence of the vapor phase on the liquid flow field. It is found that bubble formation effectively blocks the developing wall-jet flow on the heated surface. The resulting liquid flow field in the confinement gap is dominated by vapor motion rather than by the entrainment from the developing wall jet.

Pressure Drop During Two-Phase Flow of R134a and R32 in a Single Minichannel

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Single Phase ◽  
Two Phase Flow ◽  
Vapor Flow ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Roughness Effects ◽  
Two Phase ◽  
Adiabatic Flow

Condensation in minichannels is widely used in air-cooled condensers for the automotive and air-conditioning industry, heat pipes, and compact heat exchangers. The knowledge of pressure drops in such small channels is important in order to optimize heat transfer surfaces. Most of the available experimental work refers to measurements obtained within multiport smooth extruded tubes and deal with the average values over the number of parallel channels. In this context, the present authors have set up a new test apparatus for heat transfer and fluid flow studies in single minichannels. This paper presents new experimental frictional pressure gradient data, relative to single-phase flow and adiabatic two-phase flow of R134a and R32 inside a single horizontal minitube, with a 0.96 mm inner diameter and with not-negligible surface roughness. The new all-liquid and all-vapor data are successfully compared against predictions of single-phase flow models. Also the two-phase flow data are compared against a model previously developed by the present authors for adiabatic flow or flow during condensation of halogenated refrigerants inside smooth minichannels. Surface roughness effects on the liquid-vapor flow are discussed. In this respect, the friction factor in the proposed model is modified, in order to take into consideration also effects due to wall roughness.

Computational Simulation of High-Speed Steady Homogeneous Two-Phase Flow in Complex Piping Systems

1982 ◽  
Vol 104 (4) ◽  
pp. 272-277
Author(s):  
D. B. Bliss ◽  
T. R. Quackenbush ◽  
M. E. Teske
Keyword(s):  
High Speed ◽  
Single Phase ◽  
Two Phase Flow ◽  
Computational Simulation ◽  
State Equation ◽  
Phase Flow ◽  
Two Phase ◽  
Subcooled Liquid ◽  
Constant Area ◽  
Piping Systems

A study was undertaken to predict steady flow conditions in two-phase steam/water flows in safety/relief discharge piping systems. The homogeneous-equilibrium model was used for the two-phase flow along with the ASME Steam Tables in subroutine form as a state equation. The approach can also accommodate single-phase flows of superheated steam or subcooled liquid. Subroutines were developed to simulate flows through isentropic area changes, abrupt area changes, adiabatic constant area pipes with friction, valves, two-phase shock waves, and mass addition at pipe junctions. These subroutines were combined to predict conditions in arbitrary complex piping systems. Sample calculations which treat both single line and multiple-branch piping systems are included.

scholarly journals Experimental Study on Hydraulic Characteristics of Pneumatic Lifting Pump

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 388
Author(s):  
Juanli Zuo ◽  
Fengchao Li ◽  
Ning Zhang ◽  
Denghui He ◽  
Wen Wang ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Flow Rate ◽  
Liquid Flow ◽  
High Speed ◽  
Two Phase Flow ◽  
Liquid Flow Rate ◽  
Bubble Formation ◽  
Phase Flow ◽  
Hydraulic Characteristics ◽  
Two Phase

A pneumatic lifting pump is used in sewage treatment, offshore oil production, and other fields because of its simple structure and strong practicability. In order to study its internal hydraulic characteristics and gas-liquid two-phase flow, this paper carries out experimental research on the influence of different air intake modes and riser diameters on the performance of a pneumatic lifting pump. The air-water two-phase flow pattern in the riser and motion characteristics of bubble formation at the nozzle are obtained by a high-speed camera. Through theoretical analysis, the theoretical model of a pneumatic lifting pump is established, and experimental results verify the theoretical model well. The results show that when the submergence ratio is constant, the lifting efficiency decreases with the smaller intake area under different intake areas; and the influences of different holes distributions on liquid flow rate and lifting efficiency are not significant under the same intake area. At the same submergence ratio, the smaller the riser diameter, the smaller the final lifting liquid flow rate and the larger the lifting efficiency peak value.

Characteristics of Water Flow in a Vertical Micro Tube

2003 ◽  
Author(s):  
Xiaoping Wang ◽  
Makoto Watanabe ◽  
Masahiro Shoji
Keyword(s):  
High Speed ◽  
Single Phase ◽  
Transient Flow ◽  
Capillary Tube ◽  
Excess Pressure ◽  
Phase Flow ◽  
Two Phase ◽  
Pressurized Water ◽  
Tube Wall Temperature ◽  
Tube Exit

Fluid flow and heat transfer in micro-channel has received attention in developing electronic element cooling systems and in designing thermal elements of micro machines and refrigerators. In the present experiment, pressurized water in the chamber flushed out of a vertical capillary tube of 0.5mm in inner diameter and 1150mm in length. The outer surface of the tube was insulated. The chamber excess pressure was changed from 0.1 MPa to 0.6 MPa and also the inlet water temperature was widely varied. At low excess pressures, the flow is liquid single-phase flow but at high excess pressures, phase change (flushing) takes place inside and/or near the exit end of the tube and the flow becomes two-phase flow of oscillatory or intermittent. Mass flow rate as well as tube wall temperature (distribution and fluctuation) were measured, and the aspect of flushing at the tube exit end was observed using high-speed video movie. It is found that the flow regime can be classified into three (single-phase, two-phase and transient flow regimes) depending on the chamber excess pressure.

scholarly journals Application of RQA and SOM for identification of two-phase flow patterns during boiling in horizontal minichannel

2021 ◽  
Vol 321 ◽  
pp. 02008
Author(s):  
Hubert Grzybowski ◽  
Iwona Zaborowska ◽  
Romuald Mosdorf
Keyword(s):  
Pressure Drop ◽  
Liquid Flow ◽  
Slug Flow ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Inner Diameter

In the paper, numerical methods of data analysis recurrence quantification analysis (RQA) and self-organizing map (SOM) have been used to analyse pressure drop oscillations during the flow boiling in minichannel. The performed analysis allows us to identify flow patterns based on the character of the pressure drop oscillations. The following two-phase flow patterns have been identified: liquid flow, liquid flow with small vapour bubble, slug flow, long slug flow and confined bubble flow. In the experiment, the open-loop boiling system in a circular horizontal minichannel with an inner diameter of 1 mm was investigated. The two-phase flow patterns at the outlet of the heated section were observed through the glass tube (with an inner diameter of 1 mm) and recorded by a high-speed camera Phantom v1610.

Transient Local Resolution of Flow Boiling in a Microchannel With a Streamlined Pin Fin

2018 ◽  
Author(s):  
Anatoly Parahovnik ◽  
Yingying Wang ◽  
Yoav Peles
Keyword(s):  
High Speed ◽  
Single Phase ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Temperature Measurements ◽  
Phase Flow ◽  
Two Phase ◽  
Pin Fin ◽  
Boiling Process ◽  
Microchannel Device

Flow boiling around a single streamlined pin fin in a microchannel with engineering fluid, HFE-7000, was experimentally studied. A micro heater and an array of resistance temperature detectors (RTDs) were integrated into the microchannel device to enable heating and local temperature measurements on the microchannel internal wall. Thermal behavior as a function of position, heat flux, mass flux, and pressure was investigated for single phase flow and flow boiling. High-speed visualization of the two-phase flow was used to identify pertinent flow patterns and to complement the surface temperature measurements. It was found that the nucleate boiling regime and the periodic behavior of the boiling process was strongly dependent on the system’s pressure.

Gas-Liquid Flow Through Horizontal Eccentric Annuli: CFD and Experiments Compared

2011 ◽  
Author(s):  
Mehmet Sorgun ◽  
Reza E. Osgouei ◽  
M. Evren Ozbayoglu ◽  
A. Murat Ozbayoglu
Keyword(s):  
Liquid Flow ◽  
High Speed ◽  
Two Phase Flow ◽  
Flow Behavior ◽  
Flow Patterns ◽  
Phase Flow ◽  
Cfd Model ◽  
Flow Loop ◽  
Two Phase ◽  
Gas Liquid Flow

Although flow of two-phase fluids is studied in detailed for pipes, there exists a lack of information about aerated fluid flow behavior inside a wellbore. This study aims to simulate gas-liquid flow inside horizontal eccentric annulus using an Eulerian-Eulerian computational fluid dynamics (CFD) model for two-phase flow patterns i.e., dispersed bubble, dispersed annular, plug, slug, churn, wavy annular. To perform experiments using air-water mixtures for various in-situ air and water flow rates, a flow loop was constructed. A digital high speed camera is used for recording each test dynamically for identification of the liquid holdup and flow patterns. Results showed that CFD model predicts frictional pressure losses with an error less than 20% for all two-phase flow patterns when compared with experimental data.

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