A Simple Two-Phase Frictional Multiplier Calculation Method

2004 ◽  
Author(s):  
M. M. Awad ◽  
Y. S. Muzychka
Keyword(s):  
Mass Flux ◽  
Homogeneous Model ◽  
Mass Effect ◽  
The Other ◽  
High Mass ◽  
Two Phase ◽  
Simple Method ◽  
Consistent Manner ◽  
Fluid Properties ◽  
Fanning Friction Factor

In this paper, a simple method for calculating two-phase frictional multiplier for total flow assumed liquid in the pipe φlo2 is presented. The homogeneous model is used to calculate the fluid properties (density and viscosity). The Churchill model is used to define the Fanning friction factor to take into account the effect of the mass flux on φlo2. Effect of stream pressure on φlo2 is also investigated. It is found that φlo2 decreases with increasing the stream pressure at a given mass quality and reaches 1 at the critical pressure. On the other hand, it is found that φlo2 increases with increasing the mass flux at a given mass quality. Comparison with other existing correlations for calculating φlo2 such as the Wallis correlation based on the homogeneous model without mass effect on φlo2, the Martinelli-Nelson correlation, the Chisholm correlation, and the Friedel correlation is presented. When the mass flux value becomes low, the effect of mass flux on φlo2 becomes small and present correlation approaches the Wallis correlation. Both the present correlation and the Wallis correlation approach the maximum two-phase frictional multiplier in a smooth consistent manner while the other correlations show a peaking effect at high mass qualities. The Friedel correlation shows better agreement with the present correlation than both the Martinelli-Nelson correlation and the Chisholm correlation. Comparison with results from other experimental test facilities for calculating φlo2 is also presented. Comparison with other experimental data shows better agreement with the present correlation than the Martinelli-Nelson correlation.

Three Boiling Instability Modes in Silicon Microchannels

2003 ◽  
Author(s):  
H. Y. Wu ◽  
Ping Cheng
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
High Mass ◽  
Flow Mode ◽  
High Heat Flux ◽  
Pressure Oscillations ◽  
Two Phase ◽  
Experimental Conditions ◽  
Instability Modes ◽  
Temperature And Pressure

Depending on the heat flux, mass flux, and subcooling of inlet water, three boiling instability modes in silicon microchannels are possible. These are: the LTAF (Liquid/Two-phase Alternating Flow) mode, the CTF (Continuous Two-phase Flow) mode, and the LTVAF (Liquid/Two-phase/Vapor Alternating Flow) mode. It is found that the LTAF mode occurs at low heat flux and high mass flux, and has medium-amplitude temperature and pressure oscillations. The CTF mode appears at the medium heat flux and medium mass flux, and has small-amplitude temperature and pressure oscillations. The LTVAF mode appears at high heat flux and low mass flux, and has large-amplitude temperature and pressure oscillations. During the two-phase period of the LTAF mode, bubbly flow is found to be the dominant flow pattern. Some peculiar flow patterns are observed during the two-phase period of CTF and LTVAF modes under the experimental conditions.

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.

Two-phase flow boiling in a microfluidic channel at high mass flux

2020 ◽  
Vol 32 (9) ◽  
pp. 093309 ◽  
Author(s):  
Chanyoot Keepaiboon ◽  
Ahmet Selim Dalkilic ◽  
Omid Mahian ◽  
Ho Seon Ahn ◽  
Somchai Wongwises ◽  
...  
Keyword(s):  
Mass Flux ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Microfluidic Channel ◽  
High Mass ◽  
Phase Flow ◽  
Two Phase

Two-Phase Pressure Drop of Ammonia in a Mini/Micro-Channel

2010 ◽  
Author(s):  
M. Hamayun Maqbool ◽  
Bjo¨rn Palm ◽  
R. Khodabandeh ◽  
Rashid Ali
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Homogeneous Model ◽  
Working Fluid ◽  
Uniform Heat Flux ◽  
Internal Diameter ◽  
Two Phase ◽  
Frictional Pressure Drop ◽  
Phase Pressure

Experiments have been performed to investigate two-phase pressure drop in a circular vertical mini-channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. A uniform heat flux is applied to the test section by DC power supply. Two phase frictional pressure drop variation with mass flux, vapour quality and heat flux was determined. The experimental results are compared to predictive methods available in literature for frictional pressure drop. The Homogeneous model and the correlation of Mu¨ller Steinhagen et al. [14] are in good agreement with our experimental data with MAD of 27% and 26% respectively.

scholarly journals An Assessment of Suitability of a SIMPLE VOF/PLIC-CSF Multiphase Flow Model for Rising Bubble Dynamics

2012 ◽  
Vol 4 (1) ◽  
pp. 65-83 ◽  
Author(s):  
S. Senthil Kumar ◽  
Y. M. C. Delauré
Keyword(s):  
Bubble Dynamics ◽  
Stokes Equations ◽  
Piecewise Linear ◽  
Navier Stokes ◽  
Simple Type ◽  
Two Phase ◽  
Simple Method ◽  
Navier Stokes Equations ◽  
Two Fluids ◽  
Fluid Properties

A Volume of Fluid (VOF) – Youngs' model for the solution of an incompressible immiscible two-phase flows is presented. The solver computes the flow field by solving the family of Navier Stokes equations on a fixed (Eulerian) Staggered Cartesian grid using the Finite Volume formulation of Semi-Implicit Pressure Linked Equation (SIMPLE) method and tracks the position of interface between two fluids with different fluid properties by Piecewise Linear Interface Construction (PLIC) Method. The suitability of the SIMPLE type implementation is assessed by investigating the dynamics of free rising bubbles for different fluid properties and flow parameters. The results obtained with the present numerical method for rising bubbles in viscous liquids are compared with reported numerical and experimental results.

Experimental Study on Two-Phase Heat Transfer of FC-72 in Microchannels Heat Sink

2009 ◽  
Author(s):  
Xiao Hu ◽  
Guiping Lin ◽  
Hongxing Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Rate ◽  
Mass Flux ◽  
Heat Sink ◽  
Heat Fluxes ◽  
High Mass ◽  
Two Phase ◽  
Two Phase Heat Transfer

A closed-loop two-phase microchannels cooling system using a micro-gear pump was built in this paper. The microchannels heat sink was made of oxygen-free copper, and 14 parallel microchannels with the dimension of 0.8mm(W)×1.5mm(D)×20mm(L) were formed by electric spark drilling followed by linear cutting which separated the channels from each other. The heat transfer performance was evaluated by the fluid temperature, the pressure drop across the micro-channels and the volumetric flow rate. Experiments were performed with refrigerant FC-72 which spanned the following conditions: initial pressure of Pin = 73 kPa, mass velocity of G = 94 – 333 kg/m2s, outlet quality of xe,out = 0 – superheat and heat flux of q″= 25–140 W/cm2. The result showed that, the maximum heat flux achieved 96 W/cm2, as the heating surface temperature was kept below 85 °C and critical heat flux occurred in the condition of low flow rate. Average two-phase heat transfer coefficients increased with the heat flux at low mass flux (G = 94 and 180 kg/m2s) and all heat fluxes, high mass flux (G = 333 kg/m2s) and all heat fluxes, and moderate mass fluxes (G = 224kg/m2s) under low and moderate heat fluxes (q″<110 W/cm2 for G = 224 kg/m2s), which was a feature of nucleate boiling mechanism. Pressure drop through microchannels heat sink was found to be below 4kPa.

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