Important Thermodynamic Equations and Formulas

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:

    

  • Hydrocarbon fuel combustion reaction:

    

• Compressibility calculations:

  • Compressibility factor Z: Pv = ZRT

  • Reduced temperature:

    

  • Reduced pressure:

    

  • Pseudo-reduced specific volume:

    

• Efficiency equations:

  • Thermal efficiency:

    
    

  • Coefficient of performance (refrigerator):

    

  • Coefficient of performance (heat pump):

    

• Energy equations:

  
  
  

• Entropy equations:

  • Entropy change for ideal gas, constant specific heat:

    
    

  • Entropy change for ideal gas, variable specific heat:

    

  • Irreversibility for a process:

    

• Ideal-gas formulas:

  • Ideal-gas law: Pv = RT

  • Gas constant:

    

  • Ratio of specific heats:

    

  • Isentropic process for ideal gas:

    

• Moist air properties:

  • Relative humidity:

    

  • Specific humidity:

    

• Properties of mixtures:

  • Quality liquid-vapor mixture:

    

  • Saturated mixture property, y: y = y_f + x · y_fg

• Work calculations:

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

  • Polytropic process:

    

  • Isothermal process of an ideal gas:

    

  • Shaft power:

    

  • Spring work: