Shock jump and mass flux calculations through cryogenic two-phase flow nozzle

1999 ◽  
Author(s):  
I. Akmandor ◽  
Toshio Nagashima
Keyword(s):  
Mass Flux ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Shock Jump

Two-phase flow regimes of condensing R-134a at low mass flux in rectangular microchannels

2017 ◽  
Vol 84 ◽  
pp. 92-103 ◽  
Author(s):  
Michael A. Vanderputten ◽  
Tabeel A. Jacob ◽  
Maria Sattar ◽  
Nouman Ali ◽  
Brian M. Fronk
Keyword(s):  
Mass Flux ◽  
Two Phase Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Rectangular Microchannels ◽  
Low Mass ◽  
R 134A

Transient Response of BWR Core Flow During Simulated Generator Load Rejection Event

2009 ◽  
Author(s):  
Masahiro Furuya ◽  
Takashi Hara ◽  
Shinya Mizokami
Keyword(s):  
Mass Flux ◽  
Two Phase Flow ◽  
Differential Pressure ◽  
Phase Flow ◽  
Two Phase ◽  
Core Flow ◽  
Initial Stage ◽  
Rapid Flow ◽  
Fine Control ◽  
Automatic Controllers

Integral Effects Test (IET) was conducted to investigate the effects of flow redistribution during the generator load rejection event by using the SIRIUS-F facility, which simulates boiling two-phase flow in a BWR core. Owing to the automatic controllers of a recirculation pump inverter and fine-control valves in the facility, the time series of signals of heat flux and mass flux were observed to agree well with those of target rapid flow-decrease events in the previous experimental series. This paper addresses the simulated generator load rejection event, during which the flow and power gradually decrease and the flow takes a turn toward recovery. As a result of the two-parallel channel experiment, mass flux of a hot channel is lower than that of the other during the initial stage. When the void fraction becomes smaller, mass flux of the hot channel is observed to become higher. This phenomenon can be accurately demonstrated with the TRAC-BF1 code as well. The code does, therefore, predict the boiling two-phase flow in a BWR core even at such flow-decrease event. During the event, differential pressure along each channel between the upper and lower plena decreases by several tens of kPa. The relative perturbations of the differential pressure between both channels, however, remain less than 0.4%, which is a significantly small amount. In conclusion, the differential pressures between the upper and lower plena of two-parallel channels are, therefore, identical to each other regardless of the power.

Variations of Buoyancy-Induced Mass Flux From Single-Phase to Two-Phase Flow in a Vertical Porous Tube With Constant Heat Flux

1999 ◽  
Vol 121 (3) ◽  
pp. 646-652 ◽  
Author(s):  
T. S. Zhao ◽  
Q. Liao ◽  
P. Cheng
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
Single Phase ◽  
Two Phase Flow ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Constant Heat ◽  
Two Phase ◽  
Porous Tube

This paper presents an experimental study of a buoyancy-induced flow of water with phase-change heat transfer in a vertical porous tube heated at a constant heat flux. Experiments were carried out from subcooled liquid flow to connective boiling by varying the imposed heat fluxes. At a prescribed heat flux the steady-state mass flux of water, as well as the temperatures along the tube wall and along the centerline of the packed tube, were measured. It is shown that for both single-phase flow and the two-phase flow with a rather low vapor fraction, the induced mass flux increased as the heat flux was increased. However, as the imposed heat flux was increased further, the induced mass flux dropped drastically, and remained relatively constant afterwards. The influences of various parameters such as the porous tube diameter, the particle sizes, and the hydrostatic head on the induced mass flux are also examined.

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%.

Two-Phase Flow Regime Transitions in Microchannel Tubes: The Effect of Hydraulic Diameter

2000 ◽  
Author(s):  
John W. Coleman ◽  
Srinivas Garimella
Keyword(s):  
Flow Regime ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Small Diameter ◽  
Flow Patterns ◽  
Hydraulic Diameter ◽  
Intermittent Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Mechanisms

Abstract An experimental investigation of two-phase flow mechanisms during condensation of refrigerant R134a in small diameter round and rectangular tubes was conducted. A 4.91 mm round tube, and four round tubes with hydraulic diameters ranging from 1 mm – 4 mm were studied to characterize the influence of tube miniaturization on the flow mechanisms. For each tube under consideration, flow mechanisms were recorded over the entire range of qualities 0 < x < 1, and for five different mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Approximately 50 data points were recorded for each tube to obtain a comprehensive understanding of the effects of geometry, mass flux and quality on the phase-change flow mechanisms. The flow mechanisms were categorized into four different flow regimes: intermittent flow, wavy flow, annular flow, and dispersed flow. In addition, the large amount of data over a wide range of test conditions enabled the delineation of several different flow patterns within each flow regime, which provides a clearer understanding of the different modes of two-phase flow. Transition lines between the respective flow patterns and regimes on these maps were established based on the experimental data. It was found that the intermittent flow regime becomes larger as the tube hydraulic diameter is decreased. Also, the size of the wavy flow regime decreases for the small diameter tubes, and disappears completely for the 1 × 1 mm square tube. These maps and transition lines can be used to predict the flow pattern or regime that will be established for a given mass flux, quality and tube geometry.

Impact of Channel Geometry on Two-Phase Flow Heat Transfer Characteristics of Refrigerants in Microchannel Heat Exchangers

1998 ◽  
Vol 120 (2) ◽  
pp. 485-491 ◽  
Author(s):  
T. S. Ravigururajan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Heat ◽  
The Heat Transfer Coefficient

Microchannel surfaces, often machined to 20 to 1000 μm in width and depth, are employed in high-heat-flux applications. However, a large number of variables, control the two-phase flow heat transfer coefficient. The pressure, the surface heat flux, and the mass flux significantly affect the thermal transport. Experiments were conducted on a setup that was built for testing microchannel heat exchanges. The parameters considered in the study are power input: 20 to 300 W, volume flow rate: 35 to 300 ml/min, quality: 0 to 0.5, inlet subcooling: 5 to 15°C. The results indicate that the heat transfer coefficient and pressure drop are functions of the flow quality, the mass flux, and, of course, the heat flux and the related surface superheat. The heat transfer coefficient decreases from a value of 12,000 W/m2-K to 9000, W/m2-K at 80°C, when the wall superheat is increased from 10 to 80°C. The coefficient decreases by 30 percent when the exit vapor quality is increased from 0.01 to 0.65.

Two-Phase Flow Patterns During Microchannel Vaporization of CO2 at Near-Critical Pressures

2003 ◽  
Author(s):  
Jostein Pettersen
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Bubble Formation ◽  
Glass Tube ◽  
Flow Patterns ◽  
High Mass ◽  
Phase Flow ◽  
Two Phase

Carbon dioxide (CO2 / R-744) is receiving renewed interest as a refrigerant, in many cases based on systems with microchannel heat exchangers that have high pressure capability, efficient heat transfer, and compact design. A good understanding of two-phase flow of evaporating CO2 in microchannels is needed to analyze and predict heat transfer. A special test rig was built in order to observe two-phase flow patterns, using a horizontal quartz glass tube with ID 0.98 mm, externally coated by a transparent resistive film. Heat flux was obtained by applying DC power to the film, and flow patterns were recorded at 4000 or 8000 frames per second by a digital video camera. Flow patterns were recorded for temperatures 20°C and 0°C, and for mass flux ranging from 100 to 580 kgm−2s−1. The observations showed a dominance of intermittent (slug) flow at low x, and wavy annular flow with entrainment of droplets at higher x. At high mass flux, the annular/entrained flow pattern could be described as dispersed. The aggravated dryout problem reported from heat transfer experiments at high mass flux could be explained by increased entrainment. Stratified flow was not observed in the tests with heat load. Bubble formation and growth could be observed in the liquid film, and the presence of bubbles gave differences in flow pattern compared to adiabatic flow. The flow pattern observations did not fit generalized maps or transition lines showed in the literature.

Periodic Oscillations in Natural Circulation Boiling System

2017 ◽  
Author(s):  
Xianbing Chen ◽  
Puzhen Gao ◽  
Qiang Wang ◽  
Yinxing Zhang ◽  
Jiawei Liu
Keyword(s):  
Mass Flux ◽  
Nuclear Power ◽  
Power Plants ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Natural Circulation ◽  
Flow Reversal ◽  
Phase Flow ◽  
Two Phase ◽  
Periodic Oscillations

Natural circulation has been widely used in some evolutionary and innovative nuclear power plants. Natural circulation systems are susceptible to flow instabilities which are undesirable in the nuclear power devices. An experimentally investigation of two phase flow instability in up-flow boing channel under natural circulation is presented in this paper. Flow instability with and without flow reversal have been found. A pulse signal of water temperature at the inlet of the test section can be detected when the channel suffers from flow reversal. Single phase and two phase flow alternate in the channel regardless of the occurrence of flow reversal. Periodic oscillations with multiple high-order harmonic waves are confirmed by applying Fast Fourier Transform to the time traces of flow rates. Period of flow instability which is the reciprocal of the frequency with the largest amplitude in the amplitude-frequency plane are obtained. Period of flow oscillation presents a nonlinear change with the increase of mass flux. Period of flow instability increases rapidly with the increase of mass flux and decreases slowly when it reaches the maximum value.

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