CHAPTER 4 - SOURCE MODEL Flashcards
These are selected to describe how materials are discharged from the process
Source Models
This pertains when the material is ejected from holes and cracks in tanks and
pipes, leaks in flanges, valves and pumps, and severed or ruptured pipes.
Limited aperture release
It is subsequently used to describe how the material is transported downwind and dispersed to some concentration levels.
Dispersion Models
This model converts the incident-specific results into effects on people, such as injury or death, and structures.
Effects Models
This pertains to large holes developed in the process unit, releasing a substantial
amount of material in a short time.
Wide aperture release
This is designed to prevent the overpressuring of tanks and process vessels.
Relief Systems
What will happen if the liquid is stored under pressure above its atmospheric
boiling point and the leak is below the liquid level?
It will result in a stream of liquid flashing partially into vapor
What will happen if the leak is located in the vapor space above the liquid inside a
tank?
It will result in either a vapor stream or a two-phase stream composed of
vapor and liquid, depending on the physical properties of the material.
This force between the moving liquid and the wall of the leak converts some of
the kinetic energy of the liquid into thermal energy, resulting in a reduced
velocity.
Frictional Forces
This is the complicated function of Reynolds number of the fluid escaping
through the leak and the diameter of the hole.
Discharge Coefficient
Frictional forces between a liquid and the wall of a pipe convert kinetic energy
into
Thermal Energy
What is the driving force for the movement of a liquid in the pipe?
The pressure difference across the pipe
A type of flow that is characterized by smooth, layered fluid movement is known
as
Laminar Flow
The Reynolds number is a dimensionless quantity used to predict the onset of
turbulence. A low Reynolds number indicates:
Laminar Flow
Which of the following factors contributes to turbulence in fluid flow?
High Reynolds Number
In a pipe system, what happens to the pressure as the pipe diameter decreases?
Decreases
What is the primary function of a valve in a piping system?
Control fluid flow
A Function of the Reynolds number and the roughness of the pipe ε.
Fanning friction factor
A method that defines the excess head loss in terms of two constants (reynolds
number and pipe internal diameter)
2-K Method
It is the maximum downstream pressure resulting in maximum flow through a
hole or pipe.
Choked pressure
This is characterized by releasing the gas through a small crack with large
frictional losses.
Throttling
Which of the following statements is valid for downstream pressures less than
𝑃choked ?
The velocity of the fluid at the throat of the leak is the velocity of sound at the
prevailing conditions.
For sharp-edged orifices with a Reynolds number greater than 30,000 and not choked,
what is the constant discharge coefficient?
0.61
For choked flows, the discharge coefficient __________ as the downstream pressure
decreases.
Increases
1.
For this type of discharge, most of the pressure energy is converted into kinetic energy,
source models require only the diameter of the leak
Free Expansion
In the context of modeling vapor flow through pipes, which of the following best
describes adiabatic flow?
Rapid vapor flows through insulated pipes without heat exchange with
surroundings.
The phenomenon where a liquid rapidly evaporates due to a leak in a pressurized
container, causing some of the liquid to turn into vapor explosively, is known as?
Flashing
The type of vapor flow that occurs through an insulated pipe with no heat exchange is
called?
Adiabatic Flow
What happens to the temperature of a superheated liquid during flashing?
It decreases to the new boiling point as vaporization occurs.
Why are numerical models required for real vapor flow through pipes?
Because no generalized accurately capture the intermediate behavior
For flashing liquids composed of multiple miscible substances, the flash calculation
becomes more complex because?
The more volatile components flash preferentially.
In isothermal flow of gas in a pipe with friction, the gas velocity is assumed to be?
Below sonic velocity
Which of the following must be considered when a flashing liquid escapes through pipes
or holes?
Two-phase flow conditions.
What provides the driving force for gas transport in the isothermal flow through the
pipe?
Pressure gradient across the pipe
Who identified that the expansion factor reaches a maximum 𝑌g in both adiabatic and
isothermal gas flow scenarios?
Keith and Crowl
In isothermal flow conditions, the temperature of the gas is?
Constant across the entire pipe length
In the adiabatic choked flow of gas through a pipe, the maximum velocity is typically
reached at?
The end of the pipe
What is a distinguishing feature of the adiabatic flow case compared to the isothermal
case?
There is no heat exchange with the surroundings in adiabatic flow
1.
At the end of the pipe in isothermal flow, the pressure is?
Equal to the pressure of the surroundings
In the modeling of vapor flow through pipes, which two special cases are primarily
considered?
Adiabatic and isothermal flow behavior
The initial stage of boiling is usually controlled by the heat transfer from _____?
Ground
The realistic releases represent the incident outcomes with a low probability of
occurring. Worst-case releases are those that assume almost catastrophic failure of the
process.
The first statement is true
All the models, including consequence models, have uncertainties. These uncertainties
arise because of
An incomplete understanding of the geometry of the release, unknown or poorly
characterized physical properties, a poor understanding of the chemical or
release process, and unknown or poorly understood mixture behavior.
How is heat transferred to a liquid boiling from a pool?
From the ground by conduction and convection, and by radiation from the sun or
other sources
1.
Realistic release incident for process pipes smaller than 2 inches.
Assume a full bore rupture
How are uncertainties treated in consequence modeling?
By dispersion modeling to obtain conservative estimates
If an internal company study is being completed to determine the actual consequences of
plant releases, then the realistic cases would be selected. However, if a study is being
completed to meet the requirements of the EPA Risk Management Plan, then the worst
case releases must be used.
Both statements are true
The method for liquid pool evaporation or boiling works adequately for,
Liquefied natural gas (LNG) and perhaps for ethane and ethylene
For any particular modeling study several receptors might be present that require the
same decisions for conservative design. For example, dispersion modeling based on a
ground-level release will minimize the consequence for the surrounding community but
will not minimize the consequence for plant workers at the top of a process structure.
Both statements are false
Guidelines for selection process for worst-case incidents, except one;
Use calculated total release rate at set pressure; assume all material released is
airborne.
