Heat and Work: Part 2

1
Heat and Work Part 2

• Conservation of Energy
• Heat Engines
• Second Law of Thermodynamics
• Energy Efficiency
• OTEC

2
Energy in the News

• Possible solutions to Energy Problems
• 1) Smart Buildings and Machines
• 2) Superconductive Cables
• 3) Fewer Phantom Loads
• 4) Distributed Generation
• A) Solar Cells
• B) Wind
• C) Diesel Generators
• D) Microturbines
• E) Fuel Cells

3
Equilibrium of Heat Loss
4
Heat Loss

• Hypothermia-what causes it? Basic physics
• Lakes-ice and summer warmth. Why retained?
• Space blankets-very thin-what do they do?
• Why cold when standing near a window in winter?
• Why warm near a fire?

5
Heat Engines
6
Two basic types of heat engines

• What are they?

7
Vapor or Rankine Cycle

• Steam engines
• Heat pumps

8
Gas Cycle

• Automobiles (Internal Combustion)
• Jet Engines (External Combustion)
• Where is the fuel burned?
• What does the force from burning move?

9
Ocean Thermal Energy Conversion
10
Practicalities of OTEC

• Maximum Efficiency (Carnot efficiency)
• 100 ( Thigh-Tlow)/Thigh
• T in degrees Kelvin
• What is more efficient?
• Thermal engines with large or small temperature
  differences?
• When will it be 100 efficient?

11
Second Law of Thermodynamics

• Entropy (Disorder) always increases Unless energy
  is added
• Examples
• Kids room
• Spontaneous heat flow (Hot to Cold yes, never
  cold to hot)
• Waste Heat is always present

12
Ideal Case

• A completely reversible process
• Do common heat engines use reversible processes,
  why or why not?

13
Heat Pumps-How They Cool
14
Why Pump from Ground Rather Than Air?
15
Heat Pump in Winter
16
Why Do Animals Burrow ?