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APPLIED MECHANICS THERMODYNAMICS CHAPTER 1 (UNITS :!!: (image image …
APPLIED MECHANICS THERMODYNAMICS
CHAPTER 1
3 fundamentals of fluid mechanics
Bernoulli's equation
linear momentum equation
= Newton's second law for fluid streams
determine the force caused by fluid flows
Reynolds transport theorem
Newton's second law
a = Fnet / m
OR
Fnet = m • a (1 Newton = 1 kg • m/s2)
conservation of kinetic, potential, and pressure energies of a fluid stream
their conversion during
idealized frictionless flow
Bernoulli's equation
Bernoulli's equation
limitation of the use of Bernoulli's equation
:<3:
when the
frictional effects
cannot be neglible.
their conversion via
friction loss
// mechanical energy loss = conversion of mechanical energy into thermal energy
enery equation = conservation of mechanical energy
DEFINITION
: is a relation b/w
pressure, velocity, and elevation
in
steady, incompressible, frictionless flow
. [in other words, for
the idealized flow
the fluid motion is governed by the
combined effects of pressure and gravity forces
].
NOTE: with assumption that neglects the
vicous effect
(~ in
the frictionless flow
) and s
urface tension
.
motion of a particle
EXERCISE SESSION 2
WORD FILE
FORMULARIUM_LAB SESSION
FORMULARIUM _LECTURE SESSIONS
energy equation
(see above for definition
fluid mechanics
=
mechanical energy
//
thermal energy
:red_flag:
mechanical energies and efficiency
of mechanical work devices
(pumps and turbines)
head loss
Fluid systems
=
transport
a fluid from one location to another with
a specific rate
velocity
elevation
In general, this system = mechanical energy + frictional effects
.
Because
A system can
generate
or
consume
mechanical work, such as turbine or pumps, fans, respectively.
NO conversion of nuclear, chemical, or thermal energies into mechanical energy.
NO heat transfer
BUT with constant temperature.
reversible turbine
coverts
pressure energy P/rho
into
mechanical energy
.
Meaning
NOTE: thermal energy is not included into the mechanical energy
mechanical energy
= KE + PE + Pr E :<3:
Mechanical energy = Kinetic energy + Potential energy + Pressure energy.
mechanical energy is
entropy free
Presure energy Pr E = P.v = P/rho = g.h
energy per unit volume (J/m3)
or energy per unit mass (J/kg)
J/m3 = J/kg = N/m2 = Pa
:<3:
(related to gage pressure) vs. flow energy (related to absolute pressure) :!:
EXAMPLE
Pr E
= Wmax, turbine :<3:
reference level = datum: at the bottom
h: height filled with water = the vertical distance of the point from the free surface.
At point A,
gage pressure
: P A = 0, and potential energy per unit mass: p eA= g.h
at point B,
gage pressure P B
= rho.g.h and p eB=0
For a perfect hydraulic turbine,
the work
w turbine
at point A = w turbine at point B = g.h (J/m3) or
= P.v
= P/rho
(kJ/kg)
Note that: at point A, w turbine = potential energy
At point B, w turnbine = pressure energy
For
a stationary fluid with constand density
SUM pressure energy and potential enery = constant
:!:
mechanical work = shaft work
shaft work in turbines, pumps, fans
mechanical efficiency
of a device/process
:<3:
pump efficiency
:
by supplying mechanical energy to the fluid by the pump (fan, compressor)
:<3:
W' pump, u:
useful pumping power supplied to the fluid
AND
: the increase in mechanical energy of the fluid :<3:
Motor efficiency
(
a pump is usually packed with its motor
)
turbine efficiency
:
by extracting mechanical energy from a fluid
where
=
the rate of decrease in the mechanical energy of the fluid
:<3:
Generator efficiency
(
a hydraulic turbine is usually packed with its generator
)
combined/overall efficiency
of pumps and turbines
UNITS :!!:
