Lecture 04

Question 1

How are conduction and convection different from thermal radiation?

Answer 1

Conduction and convection are passive modes, which means they need a medium. Thermal radiation is active by emission from a surface.

Question 2

What does the first law of thermo say about a control volume?

Answer 2

The increase in the amount of energy stored in a control volume must equal the amount of energy that enters the control volume minus the amount of energy that leaves the control volume.

Question 3

What is the formula for total change in energy os a system?

Answer 3

deltaEsubSYS=sumQ-sumW

Question 4

When is heat positive and when is heat negative? How about work?

Answer 4

Heat is positive when there’s an increase in heat, and negative when there is a decrease in heat. Work is positive when work is being done BY a system and negative when it is done ON a system.

Question 5

Using the rate approach (and ignoring work), what is the energy equation used in this class?

Answer 5

d/dt(EsubSYS)=sum(q.in)-sum(q.out)+sum(q.gen)

Question 6

What does the assumption of steady-state conditions do to the rate equation?

Answer 6

d/dt(EsubSYS)=0

Question 7

What does the assumption that L=0 do to the rate equation?

Answer 7

d/dt(EsubSYS)=0

Volume becomes a surface (this is good for steady and unsteady)

Question 8

Do example problems posted on sakai.

Answer 8

Okay