Important Thermodynamic Equations and Formulas

By Mike Pauken

Part of Thermodynamics For Dummies Cheat Sheet

Thermodynamics is filled with equations and formulas. Here’s a list of the most important ones you need to do the calculations necessary for solving thermodynamics problems.

  • Combustion equations:

    • Air-fuel ratio:

      image0.png

    • Hydrocarbon fuel combustion reaction:

      image1.png

  • Compressibility calculations:

    • Compressibility factor Z: Pv = ZRT

    • Reduced temperature:

      image2.png

    • Reduced pressure:

      image3.png

    • Pseudo-reduced specific volume:

      image4.png

  • Efficiency equations:

    • Thermal efficiency:

      image5.png
      image6.png

    • Coefficient of performance (refrigerator):

      image7.png

    • Coefficient of performance (heat pump):

      image8.png

  • Energy equations:

    image9.png
    image10.png
    image11.png

  • Entropy equations:

    • Entropy change for ideal gas, constant specific heat:

      image12.png
      image13.png

    • Entropy change for ideal gas, variable specific heat:

      image14.png

    • Irreversibility for a process:

      image15.png

  • Ideal-gas formulas:

    • Ideal-gas law: Pv = RT

    • Gas constant:

      image16.png

    • Ratio of specific heats:

      image17.png

    • Isentropic process for ideal gas:

      image18.png

  • Moist air properties:

    • Relative humidity:

      image19.png

    • Specific humidity:

      image20.png

  • Properties of mixtures:

    • Quality liquid-vapor mixture:

      image21.png

    • Saturated mixture property, y: y = yf + x · yfg

  • Work calculations:

    • Isobaric process: Wb = P0(V2 – V1)

    • Polytropic process:

      image22.png

    • Isothermal process of an ideal gas:

      image23.png

    • Shaft power:

      image24.png

    • Spring work:

      image25.png