Definitions and Fluid Properties Flashcards
Most significant properties which distinguish liquids from gases
bulk modulus of elasticity
density
Fluid definition
a substance that continuously deforms when subjected to shear stresses
Newton’s second law of motion
Force is proportional to time rate of change of momentum
Temperature rise when a high-speed gas is brought to rest without heat transfer
Equation for measuring fluid velocity through pressure rise when the fluid is brought to rest
Heat transfer is positive if
…added to the system
….added to the fluid as it passes through control volume
Work is positive if
….done by the system
(e.g. expansion of boundaries of a system)
…done by fluid as it passes through a control volume
(e.g. work done by a fluid as it passes through a turbine)
Energy may be defined as the capacity to
do work
e may be called the energy content, and consists of
kinetic energy
potential energy
internal energy
the inequality of Clausius
another second law axiom using entropy
enthalpy
usefule form of first and second laws of thermodynamics
(considering only pdv work being done)
compressibility factor
definition of specific heat at constant pressure
definition of specific heat at constant volume
for a perfect gas, equation relating R, cp, and cv
definition of isentropic
adiabatic and reversible
isentropic flow equations
polytropic process
n=0 constant pressure process
n=1 isothermal process
n=gamma isentropic process
Molecular spacing in gases
order of magnitude larger than the size of the individual molecules
Molecular spacing in liquids
same order of magnitude of size as the molecules
Density of standard air
1.225 kg/m3
specific volume
volume occupied by a unit mass of a substance
specific weight definition
force of gravity on the mass contained in a unit volume of a substance
specific weight equation
Is specific weight a true fluid property (strictly speaking)?
No, because it depends on the local gravitational acceleration.
specific gravity equation
When reporting specific gravity, what else should be noted?
temperatures of both the liquid in question and the reference temperature of water
average bulk modulus of elasticity
bulk modulus for water at 20 degC
variation of K (bulk modulus) for water between 0 degC and 100 degC
a few percent
isothermal elastic modulus of a gas
isentropic elastic modulus of a gas
equation for velocity of sound in any medium
velocity of sound in a perfect gas
surface tension units
energy per unit area of surface or force per unit length
surface tension description
work done in bringing molecules to the surface (result of difference in mutual attraction between liquid molecules near a surface compared with those farther within the mass of liquid)
increase in energy of a spherical bubble r when expanding to (r+dr)
work done in expanding bubble (force from the difference in pressure inside and outside the bubble times the distance dr the force moves)
equate the increase in energy to the work done for the expanding bubble
general curved surface relation with principal radii r1 and r2
equilibrium relation for liquid-gas interface in contact with a solid surface
contact angle for wetting
contact angle for non-wetting
mercury contact angle for many surfaces
130-150 degrees
(non-wetting)
capillary action
the rise of a column of liquid in a small tube due to surface tension
capillary balance
weight of the liquid column in the tube and the peripheral force around the tube circumference
capillary rise equation
(solve for h in capillary balance equation)
capillary action due to wetting contact angle
capillary action due to non-wetting contact angle
rise of liquid
depression of liquid
surface tension of water in air
about 0.073 N/m
approximate reduction of surface tension of water due to addition of wetting agents
about one-half
If a liquid and its vapor coexist in equilibrium, the vapor is called a ____ vapor and the pressure exerted by this saturated vapor is called the _____ ______.
saturated
vapor pressure
Vapor pressure is a function of ______ for a given substance.
temperature
