Properties of Steam

Properties of Steam

• Steam has a high energy content, which is released as heat when it condenses back into liquid water.
• Steam has a low viscosity, making it easy to flow and penetrate small spaces.
• Steam is much less dense than water, allowing it to expand and rise quickly.
• Steam is an excellent heat transfer medium, making it useful for heating and cooling applications.
• Steam is an effective sterilizer, killing bacteria and other microorganisms at temperatures above 160°C (320°F).
• Steam is a powerful cleaning agent, able to loosen and remove dirt and grime without chemicals.
• Steam expands rapidly when heated, making it useful for power generation and mechanical work.
• Steam condenses back into liquid water when cooled, releasing its heat energy in the process.

Triple Point

• The triple point is the temperature and pressure at which a substance coexists in all three phases: solid, liquid, and gas.
• For water, the triple point is at 0.01°C (32.018°F) and 611.73 pascals (0.0886 atm).
• At this point, ice, water, and steam are in equilibrium.

Critical Point

• The critical point is the temperature and pressure above which a substance cannot be liquefied, regardless of pressure.
• For water, the critical point is at 374°C (680°F) and 22.1 megapascals (220 atm).
• Characteristics of the critical point include:
  • No phase boundary between liquid and gas phases.
  • Substances display interesting behavior, such as increased compressibility and anomalous phenomena like critical opalescence.
  • No distinct phase transition.

Sensible Heat and Latent Heat

• Sensible heat is the amount of heat or energy required to change the temperature of a substance without changing its phase.
• Latent heat is the amount of heat absorbed or released during a phase transition at constant temperature.
• Example: Boiling water, where enough thermal energy is given to water to change its phase from liquid to vapor.

Superheat

• Superheating refers to heating a substance above its saturation temperature without changing its pressure.
• Example: When water is heated and reaches its boiling point at a given pressure, it begins to convert into steam. If more heat is added, the temperature of the steam increases further, resulting in superheated steam.
• Superheated steam carries more energy and can transfer more heat than saturated steam at the same pressure.

Total Heat (Enthalpy)

• Total heat, or enthalpy, is the total energy content of a substance, including both internal energy and the energy required to overcome the pressure-volume work done during the process.
• Enthalpy is calculated using the equation: h = u + Pv, where h is specific enthalpy, u is specific internal energy, P is pressure, and v is specific volume.

Wet Steam and Dryness Fraction (x)

• Wet steam is a mixture of steam and water droplets.
• Dryness fraction, or quality of steam, is the proportion of steam in the wet steam mixture, defined as x = (mass of vapor) / (mass of vapor + mass of water droplets).
• The dryness fraction ranges from 0 (all water) to 1 (all steam).

Internal Energy of Steam (u)

• Internal energy of steam represents the total energy stored in the steam, including both sensible and latent energy.
• Internal energy is calculated using the equation: u = h - pV.

External Work of Evaporation

• External work of evaporation refers to the work done by the expanding steam against the surrounding pressure during the phase change from liquid to vapor at constant temperature.

Internal Latent Heat

• Internal latent heat, or latent heat of vaporization, is the amount of heat energy required to change the phase of a substance from liquid to vapor without a change in temperature.

Specific Volume

• Specific volume is the volume occupied by a unit mass of the substance.
• Specific volume is inversely related to density and decreases as density increases.

Enthalpy

• Enthalpy is a measure of the total energy content of a substance, including both internal energy and the product of pressure and volume.

Internal Energy

• Internal energy represents the sum of all microscopic forms of energy within the substance.

Entropy

• Entropy is a measure of the disorder or randomness of a system.
• Entropy increases with the phase change from liquid to vapor because steam is more disordered than water molecules.

Phase Behaviour

• Phase change of 1 kg of liquid water at constant pressure, with temperature increasing until reaching the saturated liquid state.
• Further heating causes the liquid to evaporate at constant pressure, reaching the saturated vapor state.
• Additional heating increases the temperature and specific volume, resulting in superheated vapor.

Measurement of Steam Quality

• Measurement of steam quality involves determining the dryness fraction (x) using various methods, including calorimetry.
• Types of calorimeters used for measurement of steam quality include barrel calorimeter, separating calorimeter, throttling calorimeter, and combined separating and throttling calorimeter.

Learn about the characteristics of steam, including its energy content, viscosity, density, and uses in heat transfer and sterilization.