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Transcript
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 ?