THERMODYNAMICS - CHAPTER 3
ENERGY TRANSFER AND GENERAL ANALYSIS
TOTAL ENERGY OF A SYSTEM E (kJ)
in the absence of other forms, E includes internal, kintetic, and potential energies (also other forms)
= 
thermal
mechanical enery e mech
Mechanical energy of a flowing fluid per unit mass 
❤
potential energy
electric
magnetic
chemical
nuclear
microscopic forms
macroscopic forms
Sum of E microscopic = internal energy
- related to molecular structure and degree of molecular activity
OR
pe = g. z (kJ/kg)
z: elevation of the center of gravity of a system relative to some arbitrarily selected reference level
mass flow rate (kg/s)
Energy flow rate
: 
Thermal = Sensible + Latent
Internal = Sensible + Latent + Chemical + Nuclear
static vs. dynamic forms
static forms: The total energy of a system, can be contained or stored in a system
dynamic forms (or energy interactions): The form of energy not stored in a system
E transfer in a closed system
HEAT TRANSFER
WORK
driving force = temparature difference
Heat transfer per unit mass: q = Q/m (kJ/kg)
Amount of heat transfer Q when heat transfer rate Q' = constant (kJ): Q = Q'.Δt
Q when heat transfer rate is changed with time Q = ∫ t1 to t2 of Q'.dt
adiabatic syst : no heat with its surroundings Q = 0 🚩
HT mechanisms (slide 11 - chapter 3)
conduction
convection
radiation
E transfer = force acting through a distance
to RAISE a body
to ACCELERATE a body
w = change in the potential energy of the body
W = change in the kinetic energy of the body
non-mechanical forms
mechanical forms:
- there must be a force acting on the boundary.
– the boundary must move.
Work = Force x Distance OR W = F . s (kJ)
when force is not constant: W = ∫ 1 to 2 of F. ds
Shaft work: A force F acting through a moment arm r
generates a torque T
W sh = F.s with s = (2pi.r) n as F acts through a distance s
Power transmitted through the shaft W' sh = shaft work done per unit time
- with n' =
SPRING WORK
When the length of the spring changes by a differential amount dx under the influence of a force F, the work done is 
For linear elastic springs, the displacement
x is proportional to the force applied; OR F = k.x (kN) with k: spring constant (kN/m).
The displacement of a linear spring doubles when the force is doubled
W spring = 1/2 k (x2^2 - x1^2)
x1 and x2: the initial and the final displacements
Work done on Elastic solid bars - SLIDE 17
Electrical work - SLIDE 18
Power = work done per unit time W' (kW)
Work done per unit mass w = W/m (kJ/kg)
Some definitions for a thermodynamic cycle
A process: the final and initial states are identical
AND
∆U = 0 for a whole numbers of cycles.
composed of processes that cause the working fluid to undergo a series of state changes through a process or a series of processes
first law for a closed system operating in a thermodynamic cycle
∆E cycle = Q net - W net
AND
Q net = W net
OR: Q in - Q out = W out - W in
Energy conversion efficiiencies
Performance = Desired output / Required input
Efficiency of a water heater
SEE microscopic energies
internal: see microscopic forms
heat transfer
work
kinetic enery KE
OR kinetic energy per unit mass
❤
Rate of mechanical energy of a
flowing fluid 
Mechanical energy change of a fluid during incompressible flow per unit mass (kJ/kg) 
Rate of mechanical energy change of a fluid during incompressible flow (kW) 
total energy of a system on a unit mass
e = E / m (kJ/kg)
remarks for KE and PE: for stationary processes, there is NO change in KE and PE. In other words,for the stationary processes ΔE = ΔU ❤
HEAT = HEAT TRANSFER
adiabatic processes = NO heat transfer. NOTE: adiabatic process is different from isothermal processes. ❤
IMPORTANT CHARACTERISTICS OF HEAT AND WORK TRANSFERS P. 63
FIRST LAW OF THERMODYNAMICS
: 
While the mechanisms of Energy Transfer, E in and E out:
E in - E out = (Q in - Q out) + (W in - W out) + (M in - M out)
- adiabatic processes: NO heat transfer
- closed system: NO mass transfer
For a closed system undergoing a cycle ( a cycle: the final state is identical to the initial state) or Ein = E out, therefore:
W net,out = Qnet, in (or W = Q)
W net, out = W out - W in (when sign convention is used)
Q net, in = Q in - Q out
Note the differential form
Energy change of a system during a process
AND
WITH
MECHANICAL EFFICIENCY OF A DEVICE OR A PROCESS
= 
For pumps
w' pump,u: the useful pumping power supplied to the fluid.
OUTLINES:
understanding of the most important points
- What is E, e, and E'
- what are the forms of E and the three common forms
- what is the 1st law of thermodynamics
- what is mechanical energy, mechanical efficiency of pumps and turbines
What is the motor efficiency?
EXERCISE
how to define property values of pure substances?
https://www.rose-hulman.edu/~adams1/courses/me301/files/Property_algorithm.pdf