ChECal and Momentra Flashcards
Laminar flow
*Re < 2100
*Fluid travels smoothly or in streamlined paths
Turbulent flow
*Re > 4000
*Occurs at high velocity and low dynamic viscosity.
Fluid
Phase of Matter that can flow and take up the shape of its container
Nozzle
Decreases pressure to increase velocity
Nominal diameter
*Size of the pipe
Pipe Schedule
*Way pipe wall thickness is mentioned
*1000P/S
*P = max allowable stress
*S = max service stress
BFD vs PFD vs P&ID
BFD:
*Logical sequence of processes
*Feeds and products
PFD:
*Equipment and Pumps
*Pipes and Fittings
*Material Balance
*Instrumentation
*Operating pressure and temperature
*Callout Sheets
P&ID:
*Equipment and Pumps
*Pipes and Fittings
*Material Balance
*Instrumentation, and Electrical control loops
*Voting and Sparing Philosophy
*More Detailed Callout Sheets (include design pressure, material, insulation, etc)
Unit Operation vs Unit Process
Unit Operation:
*Reversible
*Physical transformation of the feed
*Fluid flow, Mechanical operations, Mass transfer
Unit Process:
*Irreversible
*Chemical transformation of the feed
*Chemical reactors
NON NEWTONIAN:
Pseudoplastic
Dilatant
Bingham plastic
*Pseudoplastic
-Shear thinning
*Dilatant
-Shear thickening
*Bingham plastic
-Requires shear threshold before thickening
Shear thinning fluids
AKA Pseudoplastic fluids
Shear thickening fluids
AKA Dilatant fluids
It is a liquid that does not flow at all until a threshold shear stress is attained.
Bingham fluids
Fluid whose viscosity is independent of shear rate
Newtonian fluids
Fluid whose shear stress is directly proportional to the shear rate
Newtonian Fluids
Discipline of fluid mechanics which studies the relationship between fluid deformation and stress.
Rheology
Viscosity decreases with increase in
shear rate.
Pseudoplastic
e.g. clay, milk and cement
Viscosity increases with increase in shear rate
Dilatant
e.g. Quicksand
No-slip condition
Velocity of the
fluid must equal that of the adjacent wall
Internal energy
All other energy present in a unit mass, such as, rotational and vibrational energy in chemical bonds.
Potential energy
Energy present because of the position of the mass in a gravitational field.
Kinetic energy
Energy present because of the translational or rotational motion of the mass
Shear stress decreases with time at a constant shear rate.
Thixotropic
Shear stress increases with time at a constant shear rate.
Rheopectic
Mechanical Energy
Type of energy that is work or can be directly converted to work.
The fluid property, due to which, mercury does not wet the glass is
surface tension
viscosity
cohesion
adhesion
surface tension
The normal stress is the same in all directions at a point in a fluid, when the fluid is ___
non-viscous.
incompressible.
both (a) and (b).
having no motion of one fluid layer relative to the other.
having no motion of one fluid layer relative to the other.
The head loss in turbulent flow in a pipe varies
as velocity
as (velocity)^2
inversely as the square of diameter
inversely as the velocity
as (velocity)^2
The net positive suction head (NPSH) of a centrifugal pump is defined as the sum of the velocity head and the pressure head at the ____
discharge.
suction.
suction minus vapor pressure of the liquid at suction temperature.
discharge minus vapor pressure of the liquid at the discharge temperature.
suction minus vapor pressure of the liquid at suction temperature.
The velocity profile for turbulent flow through a closed conduit is ___
logarithmic
parabolic
hyperbolic
linear
logarithmic
The velocity profile for laminar flow through a closed conduit is ___
logarithmic
parabolic
hyperbolic
linear
parabolic
Water hammer in a pipeline results from the _____
bursting of pipelines due to closure by a valve.
rapid pressure change due to a rapid change in the rate of flow.
pressure increase due to closure of a valve resulting in decrease in rate of flow.
none of these.
rapid pressure change due to a rapid change in the rate of flow.
Which of the following denotes the effect of compressibility in fluid flow ?
Weber number
Mach number
Euler number
Reynolds number
Mach number
Nominal size of the discharge pipe of a pump is usually __________ the nominal size of the inlet pipe.
smaller than
larger than
same as
twice
smaller than
If the discharge of a centrifugal pump is throttled, then its suction lift ____
increases
decreases
remains unchanged
data insufficient to predict
increases
In fluid flow, cavitation is caused, if the ___
fluid velocity decreases to zero.
total energy decreases.
both (a) and (b).
flow pressure approaches its vapor pressure at the prevailing temperature.
flow pressure approaches its vapor pressure at the prevailing temperature.
Cavitation vs Air Entrainment vs Suction Vortex
*Cavitation
-Sudden implosion of vapor to cause shockwaves in pump
*Air Entrainment
-simply air in fluid. May not be related to suction pressure level
*Suction Vortex
-Highly unstable and dance around, resulting in radial force.
Why Cavitation happens?
- Vapor in suction
- Air / Vapor entrainment
- Recirculation - liquid can’t exit pump
Co-efficient of velocity is __________ the coefficient of discharge.
less than
more than
equal to
not related to
more than
All pipes of a particular nominal size have the same ___
inside diameter
outside diameter
thickness
none of these
outside diameter
PREVENTING CAVITATION:
1.Heights
Increase surface height
2. Temperature
Reduce
3. Pressure
Pressurize tank
4. Line Length and Size
Shorten line, Enlarge pipe
DECREASE NPSHr
*Lower RPM pump
*Use oversized pump
*Use parallel pumps
PUMPS IN SERIES/PARALLEL:
1. Head
2. Volume
- Head
Series: Additive
Parallel: Equal - Volume
Series: Equal
Parallel: Additive
When Pumps in Series are used?
*BOOSTER: To increase NPSHa
Affinity Law:
Q,H,P vs N,D
Exponents of N and D:
1. Very
2. Hard
3. Problems
FANS vs BLOWER vs COMPRESSOR
Fans: < 1 psig
Blower: 1-50 psig
Compressor: > 50 psig
For a particle settling in water at its terminal settling velocity, which of the following is true ?
Buoyancy = weight + drag
Weight = buoyancy + drag
Drag = buoyancy + weight
Drag = weight
Weight = buoyancy + drag
Kasi Buoyancy = weight - drag
Shear stress in a fluid flowing in a round pipe
varies parabolically across the cross-section.
remains constant over the cross-section.
is zero at the centre and varies linearly with the radius.
is zero at the wall and increases linearly to the centre.
is zero at the centre and varies linearly with the radius.
What causes cavitation in centrifugal pump ?
High suction pressure
Low barometric pressure
Low suction pressure
High suction velocity
Low suction pressure
A hydraulic ram acts as a/an __________ pump.
centrifugal
reciprocating
impulse
parallel cylinder
impulse
The friction factor for turbulent flow in a hydraulically smooth pipe ___
depends only on Reynolds number.
does not depend on Reynolds number.
depends on the roughness.
none of these.
depends only on Reynolds number.