Thermodynamic fundamentals and definitions

Thermodynamic fundamentals and definitions

(a) A thermodynamic system consists of matter contained in a region of space delineated by a closed surface that separates the system from its environment/surroundings.

Describe what is meant if a system is said to be:

i) Open

ii) Closed

iii) Diathermal

iv) Adiabatic

v) Isolated

(b) A thermodynamic system can often be decomposed into smaller subsystems that can themselves be considered as thermodynamic systems. The separation between two subsystems is referred to as a wall or boundary. The enclosure which separates a system from its environment consists of one or several walls. Describe what is meant if

a wall is said to be:

i) Fixed

ii) Movable

iii) Permeable

iv) Impermeable

v) Diathermal

vi) Adiabatic

(c) Write out in full, the definition of the First Law of Thermodynamics. Also, provide the energy conservation equations for both an isolated system as well as an open system. In the case of an open system, give an explanation for each form/type of power that can occur when a system interacts with its environment.[GH1]

Question 2: Gas laws

(a) There are three fundamental gas laws which describe the relationship between the pressure, temperature, volume and amount of an ideal gas. Provide the name, mathematical relation, and explanation of each of these three ideal gas laws.

(b) These three ideal gas laws rely on making several simplifying assumptions, which fortunately for us, prove to be more than reasonable for mathematically governing most “every day” applications. Please list these assumptions.

Question 3: Application of the First Law

0.35 kg’s of air is contained in a vertical piston?cylinder assembly fitted with an electrical resistor. The atmospheric pressure is 101.325 kPa and the piston has a mass of 45 kg and a face area of 0.12 m2. An electrical current is passed through a resistive heating element

which causes the air contained within the cylinder to expand in volume by 0.045 m3.

During this process, the specific energy of the air increases by 41.8 kJ/kg. Assuming that the piston-cylinder assembly is insulated (and thus there is no heat loss to the environment) and frictional losses between the cylinder wall and the piston can be considered to be negligible, determine the heat transfer from the heating element to the air for a system consisting of:

(a) the air alone,

(b) the air and the piston

(c) What can you conclude about the value of the heat transfer Q in both cases? Include a simple diagram illustrating the arrangement as well as the system boundaries in each case. [GH4]

(c) What is meant if a thermodynamic process is said to be “polytropic”? what is the polytropic index for the following specific cases whereby a process is:

(i) Isobaric

(ii) Isochoric

(iii) Isothermal

(iv) Isentropic[GH2]

(d) If you have 1 Kg of a gas with a specific gas constant of 260 J/Kg.K which is compressed according to a polytropic process such that the temperature of the gas increases by 60 degC, determine the polytropic index of this process if 3000 J of work is done on the system.[GH3]