Properties of Steam
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Questions and Answers

What occurs at the critical point of a substance?

  • The distinction between liquid and gas phases disappears. (correct)
  • The substance can only exist in a gas phase.
  • The liquid and gas phases separate into distinct phases.
  • The substance can only exist in a liquid phase.

    • What is the characteristic of the critical point in terms of phase transition?

  • There is no distinct phase transition. (correct)
  • The phase transition only occurs at low pressures.
  • There is a sudden and abrupt change from liquid to gas.
  • The phase transition only occurs at high temperatures.

    • What is the term for the amount of heat required to change the temperature of a substance without changing its phase?

  • Superheat
  • Sensible heat (correct)
  • Total heat
  • Latent heat

    • What is the term for the energy required to overcome the pressure-volume work done during a process?

    <p>Pressure-volume work</p> Signup and view all the answers

    What is the term for steam that is heated above its saturation temperature without changing its pressure?

    <p>Superheated steam</p> Signup and view all the answers

    What is the term for a mixture of steam and water droplets that occurs when steam is not fully superheated?

    <p>Wet steam</p> Signup and view all the answers

    What is a significant benefit of steam's low viscosity?

    <p>It makes steam easy to flow and penetrate small spaces.</p> Signup and view all the answers

    What is the primary reason why steam is an effective sterilizer?

    <p>It can kill bacteria and other microorganisms at temperatures above 160°C (320°F).</p> Signup and view all the answers

    What is the unique combination of temperature and pressure at which a substance coexists in all three phases?

    <p>Triple point</p> Signup and view all the answers

    At what temperature and pressure does ice, water, and steam coexist in equilibrium?

    <p>Temperature: 0.01°C (32.018°F), Pressure: 611.73 pascals (0.0886 atm)</p> Signup and view all the answers

    What happens to steam when it condenses back into liquid water?

    <p>It releases its heat energy.</p> Signup and view all the answers

    What is the term for the temperature and pressure above which a substance cannot be liquefied, regardless of pressure?

    <p>Critical point</p> Signup and view all the answers

    What is the dryness fraction of a steam mixture that consists entirely of water?

    <p>0</p> Signup and view all the answers

    What is the internal energy of steam a measure of?

    <p>the total energy stored in the steam, including both sensible and latent energy</p> Signup and view all the answers

    What occurs during the external work of evaporation?

    <p>the steam does work against the external pressure to occupy the increased volume</p> Signup and view all the answers

    What is the internal latent heat of vaporization?

    <p>the amount of heat energy required to change the phase of a substance from liquid to vapor without a change in temperature</p> Signup and view all the answers

    What is the relationship between specific volume and density?

    <p>specific volume is inversely proportional to density</p> Signup and view all the answers

    What is enthalpy a measure of?

    <p>the total energy content of a substance, including both its internal energy and the product of its pressure and volume</p> Signup and view all the answers

    What does enthalpy represent in the context of steam?

    <p>The total heat content per unit mass of the steam, including internal energy and pressure-volume work</p> Signup and view all the answers

    What is the primary difference between internal energy and enthalpy?

    <p>Internal energy represents the total energy stored within the steam, while enthalpy includes the energy associated with the steam's volume change under pressure</p> Signup and view all the answers

    What happens to the entropy of a system when it undergoes a phase change from liquid to vapor?

    <p>Entropy increases because the vapor is more disordered than the liquid</p> Signup and view all the answers

    What is the quality of a two-phase liquid-vapor mixture?

    <p>The ratio of the mass of the vapor to the total mass of both vapor and liquid</p> Signup and view all the answers

    What is the significance of the saturation temperature for water at 1.014 bar?

    <p>It is the temperature at which the phase change from liquid to vapor occurs at 1.014 bar</p> Signup and view all the answers

    What is the purpose of an enthalpy-entropy chart?

    <p>To plot the total heat of a system against its entropy</p> Signup and view all the answers

    What does the enthalpy-pressure chart typically represent?

    <p>Refrigeration cycle analysis</p> Signup and view all the answers

    What is the significance of the critical point in a saturated phase?

    <p>It is an important property of enthalpy</p> Signup and view all the answers

    What is the purpose of the barrel calorimeter?

    <p>To find the dryness fraction of steam</p> Signup and view all the answers

    What is the characteristic of a saturated liquid or vapour?

    <p>It has one independent variable</p> Signup and view all the answers

    What is the advantage of using a barrel calorimeter?

    <p>It gives better results if the dryness fraction of steam is greater than 0.95</p> Signup and view all the answers

    What is the significance of the lines of constant dryness fraction in a h-s chart?

    <p>They are drawn in the wet region</p> Signup and view all the answers

    In a Separating Calorimeter, what happens to the wet steam when it strikes the perforated cup?

    <p>It undergoes a sudden reversal of direction of motion.</p> Signup and view all the answers

    What is the advantage of using a Separating Calorimeter?

    <p>It can determine the dryness fraction of very wet steam.</p> Signup and view all the answers

    What is the purpose of the partially-opened valve in a Throttling Calorimeter?

    <p>To decrease the pressure of the steam.</p> Signup and view all the answers

    What is the disadvantage of using a Throttling Calorimeter?

    <p>It can only determine the dryness fraction of very wet steam.</p> Signup and view all the answers

    What is the purpose of the separator in a Combined Separating and Throttling Calorimeter?

    <p>To separate some part of the moisture from the steam.</p> Signup and view all the answers

    When is a Combined Separating and Throttling Calorimeter used?

    <p>When the steam is very wet and the pressure after throttling is not low enough.</p> Signup and view all the answers

    What is the advantage of using a Throttling Calorimeter?

    <p>It can determine the dryness fraction of very dry steam.</p> Signup and view all the answers

    In a Separating Calorimeter, how is the weight of steam passing through the jacket determined?

    <p>By passing the escaping steam into a bucket of water.</p> Signup and view all the answers

    What is the disadvantage of using a Separating Calorimeter?

    <p>It leads to inaccuracy due to incomplete separation of water.</p> Signup and view all the answers

    What is the result of throttling the steam in a Throttling Calorimeter?

    <p>The steam becomes superheated.</p> Signup and view all the answers

    Study Notes

    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.

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    Description

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

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