Basic Energy Concepts

Question 1

Identify energy and work forms.

Answer 1

Energy can be used to produce work, and work can be done to increase the energy content of a system

Question 2

Explain the difference between the state and the phase of a working substance.

Answer 2

A phase change usually indicates a gross change in molecular or atomic spacing, while a state change is a change in an intensive property.

Question 3

State the definition of a thermodynamic process.

Answer 3

A thermodynamic process occurs whenever a working substance changes state

Question 4

State the First Law of Thermodynamics.

Answer 4

Energy cannot be created or destroyed. One kind of energy can be transformed into another kind of energy, but the sum of energies entering a process must equal the sum of energies stored in or leaving a process.

Question 5

Perform conversions from work and energy to the equivalent amount of heat.

Answer 5

Q + E in = W/J + E out

Question 6

Define the terms in Q + E in = W/J + E out

Answer 6

Q = heat transferred to or from system (Btu)E in = total energy of the working fluid entering the system (Btu)W = work done by or to the system (ft lbf)J = Joule’s constant (778 ft lbf /Btu)E out = total energy of the working fluid leaving the system (Btu)

Question 7

Explain the application of enthalpy in the General Energy Equation.

Answer 7

Enthalpy is a term (H) for the total of internal energy (U) and Pressure (P), Volume (V) energy of a working fluid.

Question 8

Perform calculations applying the General Energy Equation to steady flow systems.

Answer 8

Q +mhin =mhout+ W/JQ =rate of heat transfer to or from the system (Btu/hr)m=mass flow rate of the working fluid (lbm/hr)hin=specific enthalpy of the working fluid entering the system (Btu/lbm)hout=specific enthalpy of the working fluid leaving the system (Btu/lbm)W =rate of work done by or to the system (ft lbf /hr)J =Joule’s constant (778 ft lbf /Btu)

Question 9

Perform calculations applying the General Energy Equation to non-flow processes.

Answer 9

U1+ Q = U2+ W/JU1=initial internal energy of the process (Btu)Q =heat transfer to or from the process (Btu)U2=final internal energy of the process (Btu)W =work performed by or to the process work performed on the process (ft lbf)J =Joule’s constant (778 ft lbf /Btu)

Question 10

Identify the relationship between work in a non-flow process and the P-udiagram representation of the process.