Important Terms & Notes Conceptual Physics Mar. 13, 2014
Thermodynamics Class Problem Set #2-1 1.Can 375J of work be performed by a system if 875J of heat is added to it if the system’s internal energy increases by 500J? Will there be any residual energy available to perform additional work? ΔQ = ΔE i + W 857J = 500J + 375J 875J = 875J ????
Thermodynamics Class Problem Set #2-2 A Mechanical Engineer has available to a project a fuel that can generate heat at a rate of 15,000J/minute. The engineer is also responsible for a system that can perform “work” at a rate of 100J/second while increasing its internal energy at a rate of 500J/minute. Can the engineer’s system, using the fuel available to this project, perform work at a rate of 100J/sec.
Thermodynamics Class Problem Set #2-2 ΔQ = ΔE i + W W = ΔQ - ΔE i W= 100J/sec * 60 sec/minute = 6000J/minute W = ΔQ - ΔE i ? 6,000J/min. = 15,000J/min. – 1,000J/min. 6,000J/min. < 14,000J/min. therefore yes. The engineer might consider using a less powerful, probably less expensive fuel to use.
Chapter 24 Review Questions Questions No Heat is gained or Lost by the System. 10a. The Air temperature increases during adiabatic compression. 10b. The Air temperature decreases during adiabatic expansion. 11. The temperature of rising air generally cools as it rises.
Chapter 24 Review Questions Questions (cont.) 12. The temperature of falling air generally increases as it rises. 13. Since heat, of itself, will only flow from hot to cold, in order to force heat to flow from cold to hot work MUST be performed. 14. Three processes occurring in every heat engine High Temperature, Low temperature, Work Done
Chapter 24 Review Questions Questions (cont.) 15. Thermal Pollution is the undesirable heat expulsion from a process. 16. No. According to the Carnot Efficiency (which is based on the temperature difference between processes) a Heat Engine cannot achieve 100% efficiency even if the effects of friction are removed. Ideal Efficiency = (T hot – T cold )/T hot
Adiabatic The term applied to the expansion or compression of a gas occurring without the gain or loss of heat. Example: Automobile Engine
Heat Engine A Device that Changes Internal Energy into Mechanical Energy
The Heat Engine Carnot engine diagram (modern) - where heat flows from a high temperature T H furnace through the fluid of the "working body" (working substance) and into the cold sink T C, thus forcing the working substance to do mechanical work W on the surroundings, via cycles of contractions and expansions. mechanical work
Carnot Efficiency The Ideal maximum percentage of input energy that can be converted into work in a heat engine. Ideal Efficiency = (T hot – T cold )/T hot
Entropy A measure of the amount of disorder in a system. ΔS = Δ Q/T