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.
The simple pitot tube measures the __________ pressure.
static
dynamic
total
none of these
total
Manometers measure the __________ pressure.
vacuum as well as the atmospheric
difference in
absolute
gage
difference in
The fluid property which matters for fall-ing rain drops to acquire spherical shape is its ___
pressure
height of descend
viscosity
surface tension
surface tension
Venturimeter and orificemeter measures the __________ of the fluid.
pressure
maximum velocity
average velocity
point velocity
average velocity
During ageing of fluid carrying pipes, the ___
pipe becomes smoother with use.
friction factor increases linearly with time.
absolute roughness decreases with time.
absolute roughness increases linearly with time.
absolute roughness increases linearly with time.
Check in a centrifugal pump is ___
provided in the discharge line.
generally a globe valve.
provided to prevent liquid from backing up through the pump when the pump is turned off or accidently stops running.
all (a), (b) and (c).
all (a), (b) and (c).
Where does the maximum stress occur in case of laminar flow of incompressible fluid in a closed conduit of diameter ‘d’?
At the centre
At d/4 from the wall
At the wall
At d/8 from the wall
At the wall
In an incompressible fluid, the density is ____
greatly affected by moderate changes in pressure.
greatly affected only by moderate changes in temperature.
not affected with moderate change in temperature & pressure.
sensible to changes in both temperature & pressure.
not affected with moderate change in temperature & pressure.
Define Priming
Preparing the pump by removing the air and filling it up with water.
Prevent cavitation / pump damage
What are Self Priming Pumps?
Has the ability to use liquid stored in its housing to generate a vacuum on the suction line.
WORK OF COMPRESSION:
Adiabatic
Isothermal
*Adiabatic - Maximum
*Isothermal - Minimum
COOLING OF COMPRESSION:
Isentropic
Polytropic
Isothermal
*Isentropic - No Cooling
*Polytropic - Some Cooling
*Isothermal - Maximum Cooling
Types of Pumps
Centrifugal / Dynamic Pumps:
*Smaller size, Smaller cost
*Impellers pass to the fluid to imparting kinetic energy
*Produces pressure by creating flow
Positive Displacement Pumps:
*Larger size, larger cost
*Requires safety valve
*Self priming
*High viscosity
*Encloses definite amount of fluid and exits the discharge
*Produces flow by creating pressure
When to use:
*Gravity Flow
*Centrifugal
*Positive Displacement
*Gravity Flow
-< 50 kPag needed to move liquid
*Centrifugal
-Default choice
*Reciprocating
- Low flowrates and high viscosity
*Rotary
-High flowrates and high viscosity
Turbine
Compresses gas to increase its pressure to transfer in gas plants
Types of Positive Displacement Pumps
*Rotary
-Achieves pumping through meshing of gears, lobes, etc
*Reciprocating
-Uses valve to traps liquid inside and direct liquid to certain areas
Types of Centrifugal Pumps
- Axial Flow
*High Flow, Low Pressure
*Flow PARALLEL to impeller shaft - Mixed Flow
*Medium Flow, Medium Pressure
* Greater then 90 deg - Radial Flow
*Low Flow, High Pressure
*Flow PERPENDICULAR to impeller shaft
What is a Compressor?
Device that increases gas pressure by decreasing its volume
What is a pump?
Device responsible for moving liquids
Minimum data required for line sizing
- v,p,u
- Pipe length
- Fittings
When are pumps not required?
- Gravity flow
- Pressurized storage
Implications of below Minimum flow for Pumps
*Pitted/worn impeller vanes
*Overheated casing/bearings
*Excessive noise or vibration
*Broken shafts
*Mechanical seal failures
*Poor performance efficiency
Based on two pressure measurements how can you estimate gas flow?
v = 2*dP/density
Difference of Newtonian vs Non-Newtonian fluids
*Newtonian - viscosity independent of shear rate
*Non-Newtonian - viscosity dependent of shear rate
Exothermic vs Endothermic Process
Exothermic - releases heat
Endothermic -absorbs heat
Valve Types:
Gate Valves
*Linear
*On-Off
+Most economical on/off
-Prone to leaks and breakage vs ball valves
-Cause water hammer
Valve Types:
Glove Valves
*Flow Regulating
+Versatile in different fluids and temperature
+Low chance of leakage
-Creates large pressure drop
Valve Types:
Knife Valve
*Small diameter
*Flow Regulating
Valve Types:
Ball Valve
*Quick Acting
*On-Off Control
+Most secure against leaks
+Most durable
+Quarter-turn valve (No water hammer)
-Most expensive
Valve Types:
Butterfly Valve
*For D>12 inch
*Quick Acting
*On-Off Control
*Flow Regulating
Valve Types:
Pressure Relief Valve
Relieves pressure from equipment operating LIQUIDS
Valve Types:
Pressure Safety Valve
Relieves pressure from equipment operating GASES
Valve Types:
Check Valve
*Non-Return Valve
PUMP CURVE:
Run Out
*Head produced at maximum flow
*Cavitation, vibration and overloading of the driver.
PUMP CURVE:
Shut-off Head
Head produced when the pump operates with fluid but with no flow rate.
PUMP CURVE:
BEP
*Best Efficiency Point
*Flow rate and head at which the pump efficiency is the maximum
PUMP CURVE:
Carry Out
Operates in the far right of its curve with poor efficiency.
PUMP CURVE:
Sweet Area
Area near the BEP
Importance of Pump Curve
*Graphical representation of head and efficiency given flowrate
*Pump selection
System Curve
*Curve representing the head of pump given flow rate
Break Horsepower
external power supplied to the pump
Water Horsepower
useful power actually delivered to the fluid
Criteria for Line Sizing
*Operating Parameters
-Velocity
-Pressure Drop
*Pump Efficiency
*Liquid Transported
*Transport Equipment Used
*NPSHa/NPSHr Ratio
Minimum Flow Rate
*Flow rate reported by pump manufacturer
*Below this, pump will start vibrating, heating up and fail prematurely
When NOT to use Recirculation Line?
*Closed circulating systems
*Pumps in Batch services
*Small pumps
*Pumps with control valve
Choked Flow
*Liquids
*Gases
*Liquids
-Liquid pressure is lower than vapor pressure –> Cavitation
*Gases
-Choked pressure = below which NO FURTHER INCREASE in mass flow
Connect pipes of ___ diameter:
a. Same
b. Different
a. Same
Coupling - permanent
Union - removable
b. Different
Reducer or Expander
Solvent
Substance that dissolves solutes
Octane Number
*Anti-Knocking Number
*Ability of fuel to resist knocking when ignited
*Volume i-octane/ Total Volume
*i-Octane and n-Heptane
Cetane Number
*Diesel Performance Number
*Measure delay to ignite diesel fuel (higher number = lower delay)
*Cetane (C16H34) and Methyl Naphthalene
Newtonian vs Non-Newtonian Fluids
*Newtonian
- Viscosity INDEPENDENT of shear rate
*Non-Newtonian
- Viscosity DEPENDENT of shear rate
Fluidization
Process of passing through gas to a bed of solids to exhibit fluid-like properties
Pyrolysis vs Combustion
*Pyrolysis
-Thermal decomposition of organic matter with an absence of oxygen into shorter hydrocarbon chains
*Combustion
-Decomposition of organic matter with presence of oxygen into CO2, CO and H2O
COMPRESSORS:
*Surge Point
*Stonewall Point
Surge Point
*Reversal of flow when capacity is reduced to a point where insufficient pressure to maintain flow.
Stonewall Point (Choking)
*Discharge pressure falls, but airflow no longer increases due to physical limitations
Valve Types:
Diaphragm Valve
*Regulating Flow
*Corrosive Fluids
Pipes with same nominal diameter but different schedule have the same ____
inner diameter
Shear rate
Rate at which one layer of fluid slides over another layer
Pitot Tube
- Measures local velocity only
+Negligible pressure drop
Orifice Meter
*Measure LIQUID flow through pressure difference
- Higher pressure drop than venturi meter
- Cannot be used for dirty fluids
+ CHEAPER and REMOVABLE
Venturi Meter
*Measure LIQUID AND GAS flow through pressure difference
+ Lower pressure drop than orifice meter
+ Can handle higher flowrates than orifice meter
- EXPENSIVE and PERMANENT
Ultrasonic Meters
*Ideal for CORROSIVE and DIRTY fluids
*Uses Doppler effect (calculate how fast radiation is reflected back)
+CHEAP
Positive Displacement Meters
*Used to accurately measure fluid flow (for recipes)
- For CLEAN and VISCOUS fluids only
Variable Area Meters
+CHEAP
+NO POWER DEMAND
+Low pressure drop
- Low accuracy
-Glass prone to breakage
Oscillation Meters
*Measure oscillation of tubes (sine waves)
*For CLEAN and NON-VISCOUS fluids
*High accuracy, repeatability and low maintenance
Turbine Meters and Paddlewheel Meters
*Turbine Meters
+More accurate
-More expensive
-More pressure drop (though very small)
-More susceptible to fouling
*Paddlewheel Meters
+Cheaper
+Less pressure drop
-Less accuracy
Why Acceleration Head for Centrifugal pump is NOT ZERO while Positive Displacement pump is ZERO?
Acceleration head: Head required to accelerate velocity from zero to some value
*Centrifugal pump: Flow is assumed constant
*PD pump: Flow is fluctuating
Lift vs Head
*Lift
-Liquid level power than pump.
-Pump creates vacuum to force liquid to flow.
*Head
-Liquid level higher than pump
COMPRESSORS:
*Centrifugal
*Axial Flow
*Positive Displacement
*Centrifugal
+Most common
+High flowrate
*Axial Flow
+Compressors for turbines
*Positive Displacement
+High pressure head and low flowrate
+Used for air
-Prone to leaking
Assumptions of Bernoulli Equation
*Steady flow
*Incompressible
No shaft work and heat transferNegligible viscous effects (friction) compared to pressure, elevation and kinetic heads
Subsonic and Supersonic Flow:
P, V, T, Ma Relation to Nozzles and Diffusers
*Subsonic NOZZLE and Supersonic DIFFUSER
-Decrease P and T
+Increase V and Ma
*Supersonic NOZZLE and Subsonic DIFFUSER
-Decrease V and Ma
+Increase P and T
Why fuel is sweetened?
- Higher heating values
- Better odor, oxygen stability and color
Explain Dalton’s, Henry’s and Raoult’s Laws
Dalton
Pi = sum yi*Pt
Henry (non ideal)
Pi = H * xi
Amount dissolved gas proportional to its partial pressure
Raoult’s (ideal)
Pi = Psat * xi
Partial pressure of gas proportional to both vapor pressure and dissolved gas
Vertical vs Horizontal Separators
*Vertical Separator
-For high liquid/gas ratio
-Space limitations
-High amounts of solids
*Horizontal Separator
-For low liquid/gas ratio
-For three-phase separation
-Separating foaming crude oil
Pipes with nominal size of above ___ is equal to its ___ diameter
14”
Outside diameter
COMPRESSORS in:
*Parallel
*Series
*Series
-Flow: Constant
-Pressure: Additive
*Parallel
-Flow: Additive
-Pressure: Greater than lower-pressure compressor
Compressor Surging
- Pressure high enough such that there is reversal of flow / unsustainable flow
- Equivalent to deadheading in pumps
