Work, Energy, and Power

Question 1

What is the meaning of energy in terms of thermodynamics

Answer 1

It is the capacity to perform work or to produce heat.

Question 2

What are the two types of energy and what are their difference?

Answer 2

Potential energy and Kinetic Energy
- the differ as potential energy is characterized as an energy at rest, and kinetic energy is characterized as energy in motion.

Question 3

What is the formula of Potential Energy (with respect to thermodynamics)?

Answer 3

PE = mgh/gc
where:
PE = potential energy (ft-lbf)
m = mass (lbm)
g = acceleration due to gravity (32.17 ft/s^2)
h = height of any reference (ft)
gc = gravitational constant (32.17 ft-lbm/lbf-s^2)

Question 4

What is the formula for Kinetic Energy?

Answer 4

KE = mv^2/2gc
where:
m = mass (lbm)
v = velocity ()
gc = gravitational constant (32.17 ft-lbm/lbf-s^2)

Question 5

What is internal energy?

Answer 5

internal energy is energy accumulated within the system associated with random particles along with potential energies of the molecules due to orientation
- unit: Btu (British thermal unit)

Question 6

What is the formula for internal energy? Define each factors.

Answer 6

ΔU = q + w
where:
ΔU = total change in internal energy that contains a system
q = heat transferred between the system and its surroundings
w = work done by or on the system

Question 7

what is specific internal energy?

Answer 7

• specific energy (u) is the internal energy per unit mass

- it is acquired through dividing the total internal energy by the total mass

Question 8

What is the formula for specific internal energy (u)? Define each factors.

Answer 8

u = U/m
where:
u = specific internal energy (Btu/lbm or J/kg)
U = total internal energy (Btu or J)
m = mass (lbm or kg)

Question 9

What is the difference between Internal energy (U) and the specific internal energy?

Answer 9

The difference is that, specific internal energy s just a fraction of the total internal energy

Question 10

What does PV Energy prove?

Answer 10

P-V energy proves that fluid under pressure has the capacity to perform work

Question 11

What does it mean by specific P-V energy?

Answer 11

Similar with specific internal energy (u), Pv or the specific PV energy is described as the pressure-volume per unit mass
Formula: Pv = PV/m
- it has something to do with mass
- it may be inside or outside the system

Question 12

What is the formula for specific PV energy? Define each factors and indicate their units

Answer 12

Pv = PV/m
where:
Pv = specific PV energy (ft-lbf/lbm)
P = pressure (psi or lbf/in^2) psi (multiply 144)
V = volume (ft3)
m = mass (lbm)

Question 13

What does specific enthalpy mean?

Answer 13

Defined with formula: 
h = u + Pv
- it has a connection with open systems
- extensive unit
- usually given with respect to a reference unit

Question 14

Explain the formula of specific enthalpy

Answer 14

h = u + Pv
where:
u = specific internal heat (Btu/lbm)
h = specific enthalpy
P = specific pressure in the system (lbf/ft^2)
v = specific volume of a system (ft^3/lbm)

Question 15

What is the standard atmospheric pressure? (in sea-level)

Answer 15

1 atm at 4 degree Celsius

Question 16

How is work defined in thermodynamics?

Answer 16

Work is not an energy but is defined as energy in transit.
Work is not a property of a system but it lets us understand how energies are transformed.
Work can be done by or on the system.
Work is also defined as mechanical systems as the action of a force is done through a distance.

Question 17

How do you describe work, with consideration to energy transfer?

Answer 17

When work is done by the system towards its surrounding, it obtains a positive value
If work is done on the system by its surrounding, we obtain a negative energy value