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STUDY GUIDE · GKU 5

Thermodynamics study guide (Mechanical Engineering)

Thermodynamics is bookkeeping for energy plus one rule about direction. The first law says energy is conserved, so every problem is a balance: what enters as heat, work and flowing mass equals what leaves plus what is stored. The second law says that every real process degrades some energy, and that sets the best possible efficiency of any engine, refrigerator or heat pump. Both laws need property values, which come from the ideal-gas equation for gases and from steam and refrigerant tables for substances that change phase. The ETEC handout groups this into two units: pure substances and ideal gases, then power and refrigeration cycles, where the laws are applied to closed systems, control volumes, components (turbines, pumps, compressors, heat exchangers) and complete cycles. In this guide the cycles are worked out as the Otto, Diesel, dual, Brayton, Rankine and vapour-compression cycles, followed by combustion. Four sections go beyond the handout because the app's practice questions draw on them: gas mixtures and moist air, the steam power station, gas, diesel and combined-cycle stations with cogeneration, and desalination; each says so at the start.

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Structured by the official ETEC subject standard for this topic: every listed topic and learning outcome, with formulas, figures and worked examples. The full sections are available to members in the app.

SKU 5.1 · Pure substances and ideal gases

  1. Systems, properties, temperature and pressure

    The vocabulary every thermodynamics problem uses: system and control volume, property and state, temperature, pressure and the forms of energy.

  2. Pure substances, phase change and property tables

    What happens when water boils, how the T–v and P–T diagrams map the phases, and how to find a state and its properties in the steam tables.

  3. Ideal gases and real gases

    The ideal-gas equation, specific heats, when a gas stops being ideal, and how the generalized compressibility chart corrects for it.

  4. Gas mixtures and moist air (psychrometrics)

    Beyond the handout: properties of non-reacting ideal-gas mixtures, and the humidity ratio, relative humidity, dew point and wet-bulb temperature of moist air.

SKU 5.2 · Power and refrigeration cycles

  1. Work and heat: how energy crosses a boundary

    The difference between heat and work, the sign convention, and moving-boundary work for the common processes of a gas.

  2. First law for closed systems

    The energy balance for a fixed mass, applied to ideal gases, solids and liquids, and steam in tanks and piston–cylinders.

  3. Mass and energy balances for steady-flow devices

    Conservation of mass and the steady-flow energy equation for nozzles, turbines, compressors, pumps, throttling valves, mixing chambers and heat exchangers, with isentropic efficiencies.

  4. Second law: heat engines, refrigerators and the Carnot limits

    The Kelvin–Planck and Clausius statements, reversible and irreversible processes, the Carnot efficiency and COP limits, and how to test a performance claim.

  5. Entropy and entropy generation

    Entropy as a property, the increase-of-entropy principle, entropy changes of pure substances, solids and liquids and ideal gases, and the entropy balance for closed systems and steady flow.

  6. Exergy, irreversibility and second-law efficiency

    Exergy (availability) of heat and of flowing streams, exergy destruction as the dead-state temperature times the entropy generated, and first- and second-law efficiencies of turbines, pumps and heat exchangers.

  7. Reciprocating-engine cycles: Otto, Diesel and dual

    Air-standard analysis of spark-ignition and compression-ignition engines: efficiency, cycle temperatures, mean effective pressure, and how the three cycles compare.

  8. Gas-turbine (Brayton) cycle

    The ideal and actual Brayton cycle, the back-work ratio, the effect of component efficiencies, and regeneration, intercooling and reheating in gas-turbine power stations.

  9. Steam power cycles: Rankine, reheat and feedwater heating

    The Rankine cycle and the ways to raise its efficiency, the open feedwater heater, steam rate, and an exergy-destruction analysis of a steam plant.

  10. Refrigeration and heat-pump cycles

    The vapour-compression cycle on a P–h diagram, cooling capacity, COP of refrigerators and heat pumps, the second-law view of their losses, and other refrigeration systems.

  11. Fuels and combustion

    Theoretical and excess air, air–fuel ratio, product composition and dew point, heat released from enthalpies of formation, heating values, adiabatic flame temperature and boiler efficiency.

  12. Power stations and the steam plant

    Beyond the handout: how power stations are classified, the layout of a steam plant, steam generators, steam turbines and plant water systems, with load and capacity factors.

  13. Gas, diesel and combined-cycle stations, cogeneration and emissions

    Beyond the handout: diesel generating sets, combined gas–steam cycles, cogeneration and its utilization factor, and the environmental impact of power generation.

  14. Seawater desalination: MSF, MED and reverse osmosis

    Beyond the handout: how thermal (multi-stage flash, multi-effect) and membrane (reverse osmosis) desalination work, and how their performance is measured.

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