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Understanding Thermodynamics in Mechanical Engineering

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devaki
12 diapositives · 242 Views · Oct 03, 2014

Explore concepts in thermodynamics, Carnot efficiency, entropy, and heat engines in mechanical engineering with practical problem sets and review questions.

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Understanding Thermodynamics in Mechanical Engineering
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  1. Important Terms & Notes Conceptual Physics Mar. 13, 2014

  2. Thermodynamics Class Problem Set #2-1 • 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 = ΔEi + W 857J = 500J + 375J 875J = 875J ????

  3. 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.

  4. Thermodynamics Class Problem Set #2-2 ΔQ = ΔEi + W W = ΔQ - ΔEi W= 100J/sec * 60 sec/minute = 6000J/minute W = ΔQ - ΔEi ? 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.

  5. Chapter 24 Review QuestionsQuestions 9 - 16 9. 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.

  6. Chapter 24 Review QuestionsQuestions 9 - 16 (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

  7. Chapter 24 Review QuestionsQuestions 9 - 16 (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 = (Thot – Tcold)/Thot

  8. Adiabatic • The term applied to the expansion or compression of a gas occurring without the gain or loss of heat. • Example: Automobile Engine

  9. Heat Engine A Device that Changes Internal Energy into Mechanical Energy

  10. The Heat Engine Carnot engine diagram (modern) - where heat flows from a high temperature TH furnace through the fluid of the "working body" (working substance) and into the cold sink TC, thus forcing the working substance to do mechanical workW on the surroundings, via cycles of contractions and expansions.

  11. Carnot Efficiency • The Ideal maximum percentage of input energy that can be converted into work in a heat engine. • Ideal Efficiency = (Thot – Tcold)/Thot

  12. Entropy • A measure of the amount of disorder in a system. ΔS = Δ Q/T