The 2nd Law and Entropy for 27/10/05

Look for uncomplicated definitions and try not to stray. This can become complicated!

The Carnot cycle does provide an excellent example of reversible processes and can also be used to explain why an engine cannot achieve 100% efficiency.
Mechanical work can be completely converted to heat but why can`t heat be completely converted to work?

The Second Law of Thermodynamics. 27/10/05

Look at the definitions of the 2nd law and select those which you feel are most meaningful. For example, look at Kelvin-Planck and Clausius.
When asked to define Entropy, it`s important that you stay on course and be content to give a definition that is sufficient and remains relevent to the work for this part of the course.
Think of the reversible adiabatic process and the significance of entropy in this context.
Use the Carnot cycle to give an example of a heat transfer processes that can be considered reversible.
What processes make up the Carnot cycle?
Can you explain how it is impossible for an engine to achieve 100% efficiency?

Heat energy and work energy are mutually convertible one into the other but there is an important difference. Mechanical work can be completely converted into heat energy but heat energy cannot be completely converted into work.
Therefore in the Carnot cycle, there is always a loss to a colder body and the efficiency of an engine can never be 100%.

The 2nd Law indicates the way in which heat can be converted to mechanical work.

For Thursday 13 October 2005

Torsion:

The torsion equation.
Calculating `J` values

Torsion of a stepped shaft with common value of Torque.

Torque diagrams: show how the torue is distributed from a motor to a pulley system.


Thermodynamics:

The Gas Laws PV/T=C and PV=mRT

Non flow E E Q= (U2-U1) + W

Steady Flow E E :

H1 + KE1 + PE1 + Q = H2 + KE2 + PE2 + W + losses

Mass Continuity Equation

Refrigeration Cycle and the importance of (h2-h1) using chart and verifying with tables.

For Monday 10/10/05
Criteria of Failure - Factors of Safety

1) Maximum Principal Stress (useful for brittle materials)

2) Maximum Principal Strain (useful for concrete)

3) Maximum Shear Stress (Tresca)

4) Maximum Strain Energy (values required may be obtained from experimentation)

5) Maximum Shear Strain Energy ( Von Mises)

------------------------------------------------------------
MEP Statics and Dynamics

Distance, Time, Velocity and Acceleration for linear and Angular motion.
The area under the Velocity- Time graph will give the distance travelled in metres.
The gradient of the diagonal line will give the acceleration.

Acceleration= (final velocity-initial velocity)/ time.

For 6/10/05
Using the steady flow energy equation. Work and Heat transfer.
Refrigeration.

The basic cycle.
1-2 Compression:Increase in pressure (from 100% dry to Superheated vapour)
2-3 Condensing (from Superheated vapour to Liquid)
3-4 Expansion Valve: Decrease in pressure
4-1 Evaporation Liquid to dry saturated vapour.

The change in Enthalpy between 1 and 2 will be significant.

Processes:

Polytropic
Adiabatic
Isothermal
Know the formulae for Q and W and be able to manipulate the equations between Pressure, Volume and Temperature.

Design for manufacture Wednesday 5/10/05

1) List and describe the elements of the design process.

2) List the factors which influence a design. describe how maintenance, ergonomices and materials influence the final decision.

3) List and describe the various stages of design documentation.

Calculate the Direct Stress and the Strain at 2 suitable points on the graph.
The material is H C Copper (99.99% cu)
A= 20 mm2
l=25.25 mm

Typical values of Stress/ Extension
1) F= 1500N and x=0.5mm
20 F= 3000N and x= 1mm.

Also, give a definition of Hooke`s Law and comment on whether the law has been verified by the findings of the test.