What are steam tables, and how are they used?

Short Answer:

Steam tables are reference charts that give important thermodynamic properties of water and steam at various pressures and temperatures. These properties include enthalpy, entropy, specific volume, internal energy, and saturation temperature/pressure. Steam tables are essential for engineers to perform calculations related to boilers, turbines, condensers, and other steam-based systems.

Steam tables are used to find the exact values of steam properties at a given condition (like pressure or temperature), which helps in designing, analyzing, and improving steam systems. They save time and improve accuracy by avoiding complex formulas and using directly available data.

Detailed Explanation:

Steam tables and their usage

In thermodynamics, especially in the study of steam power systems, engineers often need to know how steam behaves at different pressures and temperatures. Since water and steam do not follow simple equations under all conditions, scientists have experimentally measured and compiled data into easy-to-use formats called steam tables.

These tables help find the state of water or steam, whether it is saturated, superheated, or compressed, and also provide necessary values for energy and work calculations in thermal machines like boilers, turbines, condensers, and heat exchangers.

What Steam Tables Contain

Steam tables are usually divided into the following sections:

  1. Saturation Temperature Table
  • Lists thermodynamic properties at different saturation temperatures.
  • For each temperature, it provides:
    • Saturation pressure
    • Specific enthalpy (hf, hfg, hg)
    • Specific volume (vf, vg)
    • Entropy (sf, sfg, sg)
  1. Saturation Pressure Table
  • Lists data at different saturation pressures.
  • For each pressure, you get similar values as the temperature table.
  1. Superheated Steam Table
  • Gives steam properties when temperature is above the saturation temperature at a given pressure.
  • Includes enthalpy, entropy, specific volume for superheated conditions.
  1. Compressed Liquid Table (less common)
  • Provides properties of water at pressures above saturation pressure, below boiling.

Key Symbols Used in Steam Tables

  • hf = Enthalpy of saturated liquid
  • hfg = Latent heat of vaporization
  • hg = Enthalpy of saturated vapor (hf + hfg)
  • sf, sfg, sg = Entropy values (similar to enthalpy)
  • vf, vg = Specific volume of liquid and vapor
  • T = Temperature
  • P = Pressure

These values are mostly given in kJ/kg for energy and m³/kg for volume.

How to Use Steam Tables

Example 1: Saturated Steam

Suppose the pressure in a boiler is 10 bar, and you want to find the saturation temperature and enthalpy.

  • Go to the saturation pressure table.
  • At 10 bar, you will find:
    • Saturation temperature ≈ 179.91°C
    • Enthalpy of water (hf) ≈ 762.8 kJ/kg
    • Latent heat (hfg) ≈ 2014.5 kJ/kg
    • Enthalpy of steam (hg) ≈ 2777.3 kJ/kg

Example 2: Superheated Steam

If steam at 10 bar is heated to 300°C, you go to the superheated steam table under 10 bar and locate the row for 300°C to find:

  • Enthalpy
  • Specific volume
  • Entropy

These values help calculate turbine work, efficiency, and heat transfer.

Applications of Steam Tables

  1. Boiler Calculations
    To find how much energy is required to convert water into steam.
  2. Turbine Analysis
    To calculate work output from steam as it expands in turbines.
  3. Heat Exchanger Design
    Helps find temperature and enthalpy difference across steam pipes.
  4. Energy Audits
    Used to assess energy usage and losses in thermal systems.
  5. Steam Cycle Analysis
    Steam tables are essential in drawing and analyzing Rankine cycles.
Conclusion

Steam tables are essential reference tools in mechanical engineering that provide detailed data on the properties of water and steam. These tables help engineers perform accurate thermal and energy calculations without deriving equations. Used widely in power plants, heating systems, and industrial processes, steam tables are key to understanding the behavior of steam under various pressure and temperature conditions, enabling better design, analysis, and efficiency of steam-based equipment.