Heat and Work: Part 2 Conservation of Energy Heat Engines Second Law of Thermodynamics Energy Efficiency OTEC.

Heat and Work: Part 2

• Conservation of Energy

• Heat Engines

• Second Law of Thermodynamics

• Energy Efficiency

• OTEC

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

Equilibrium of Heat Loss

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?

Heat Engines

Two basic types of heat engines

• What are they?

Vapor or Rankine Cycle

• Steam engines

• Heat pumps

Gas Cycle

• Automobiles (Internal Combustion)

• Jet Engines (External Combustion)

• Where is the fuel burned?

• What does the force from burning move?

Ocean Thermal Energy Conversion

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?

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

Ideal Case

• A completely reversible process

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

Heat Pumps-How They Cool

Why Pump from Ground Rather Than Air?

Heat Pump in Winter

Why Do Animals Burrow ?