fluid and thermal engineering
TRANSCRIPT
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 1/20
Two-phase Flow and Heat Transfer(ME – 657)
by
Dr. Dipankar N. BasuAssistant Professor
Department of Mechanical Engg.
IIT Guwahati, Guwahati – 781039
Lecture 1
Introduction to Multiphase Flow
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 2/20
Course Outline
Importance & applications of multiphase flow
Fundamentals of two-phase flow Basic definitions & conservation equations
Comparison with single-phase systems
Identification of flow patterns
Mathematical modeling
Homogeneous flow, Separated flow & Drift flux models Simplified treatment of different flow regimes
Boiling heat transfer
Classifications: Pool & Flow boiling
Boiling curve
Bubble nucleation & boiling crisis Condensation heat transfer:
Drop-wise & Film-wise condensation
Simple modeling & analysis
Measurement of two-phase parameters
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 3/20
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 4/20
Multiphase Flow Systems: Some Examples
Examples of gas-liquid flow
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 5/20
Multiphase Flow Systems: Some Examples
Gas-solid flow
Liquid-liquid flow
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 6/20
Multiphase Flow Systems: Some Examples
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 7/20
Multiphase Flow Systems: Some Examples
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 8/20
Unique Features of Two-phase Flow
Analysis of two-phase flow is distinctly different from its single-phase
counter-part because of numerous factors, some of which are
mentioned below.
Presence of multiple (possibly), deformable and moving interface
Drastic change in fluid properties across the interface
Possible compressible nature of one or all the phases (particularlywhen gaseous medium is involved)
Involvement of several length and time scales
Strong dependence of the nature of flow stream on geometrical
orientation, method of initiating the flow and local condition
Different nature of interaction of phases with boundaries (walls)
Very high heat transfer coefficient associated with boiling and
condensation processes
Susceptibility of systems towards instabilities and fluctuations
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 9/20
Appearance of Different Flow Regimes
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 10/20
Two-phase Flow and Heat Transfer(ME – 657)
by
Dr. Dipankar N. BasuAssistant Professor
Department of Mechanical Engg.
IIT Guwahati, Guwahati – 781039
Lecture 2
Two-phase Flow Regimes
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 11/20
Flow Regimes in Vertical Adiabatic Flow (Upward)
These are the most common types of flow regimes appearing with
increasing fraction of lighter phase in the mixture.
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 12/20
Flow Regimes in Vertical Adiabatic Flow (Downward)
Bubbly
flow
Slug flow Falling
film flow
Bubbly falling
film flow
Churn flow Dispersed
annular flow
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 13/20
Flow Regimes in Horizontal Adiabatic Flow
Gravity plays a dominating role in deciding the flow regime
for horizontal and inclined tubes.
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 14/20
Flow Regimes in Horizontal Adiabatic Flow
All possible flow regimes may
not appear under every two-phase flow situation. Nature of
the flow regime depends
strongly on local flow
characteristics, including the
relative fraction of individual
phases, phasic velocities,
interfacial properties etc. It is
also possible to have different
transition regimes dominating
the flow domain.
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 15/20
Flow Regimes in Vertical Diabatic Flow
Here the location identified as x=0 signifies
the position of boiling boundary calculated
considering Thermodynamic equilibrium.However, due to the presence of non-
equilibrium subcooled boiling, small amount
of vapour generation can takes place prior
to this point. x=1 similarly identifies the
equilibrium location of the end of boiling.
Drop/Mist flow (appearsonly in heated channels)
Rate of heat addition and hence dx/dz plays a
crucial role in determining the presence or absence
of any particular flow pattern in diabatic channels.
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 16/20
Flow Regimes in Horizontal Diabatic Flow
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 17/20
Flow Pattern Map for Vertical Flow (Hewitt & Roberts, 1969)
This map was developed for
low-pressure air-water and
high-pressure steam-water
upward flow through smalldiameter (1-3 cm) tubes.
This is not the most accurate
presentation & serves mostly
as a rough guide.
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 18/20
Flow Pattern Map for Horizontal Flow (Baker, 1954)
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 19/20
Unified Flow Pattern Map (Taitel & Dukler, 1976)
7/29/2019 Fluid and Thermal Engineering
http://slidepdf.com/reader/full/fluid-and-thermal-engineering 20/20
Flow Pattern Map for Vertical Down-flow (Oshimowo & Charles, 1974)
This map was generated
for air & differentliquids in a channel of
2.54 cm diameter at
172 kPa pressure.