Properties of Steam
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What is the primary reason why steam is an effective sterilizer?

  • Its high energy content makes it a powerful cleaning agent
  • Its high viscosity allows it to penetrate small spaces
  • Its low density makes it difficult for bacteria to survive
  • It can reach temperatures above 160°C (320°F) (correct)
  • At what temperature and pressure does the triple point of water occur?

  • 0.01°C (32.018°F) and 611.73 pascals (0.0886 atm) (correct)
  • 100°C (212°F) and 1 atm
  • 20°C (68°F) and 0.5 atm
  • 0°C (32°F) and 1 atm
  • What is the primary advantage of steam in heating and cooling applications?

  • Its high energy content makes it a powerful cleaning agent
  • Its low viscosity makes it easy to flow and penetrate small spaces
  • Its ability to expand rapidly when heated makes it useful for power generation
  • Its excellent heat transfer properties make it useful for heating and cooling applications (correct)
  • What happens to the energy content of steam when it condenses back into liquid water?

    <p>It is released as heat</p> Signup and view all the answers

    What is the primary characteristic of the critical point of a substance?

    <p>It is the temperature and pressure above which a substance cannot be liquefied</p> Signup and view all the answers

    What is the primary reason why steam is used in power generation and mechanical work?

    <p>Its ability to expand rapidly when heated makes it useful for power generation and mechanical work</p> Signup and view all the answers

    What is the primary characteristic of a substance at its critical point?

    <p>The density of the liquid phase is identical to the gas phase.</p> Signup and view all the answers

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

    <p>Sensible heat</p> Signup and view all the answers

    What occurs when steam is heated above its saturation temperature at a given pressure?

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

    What is the term for 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?

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

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

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

    At what temperature and pressure does water exhibit a critical point?

    <p>374°C (680°F) and 22.1 megapascals (220 atm)</p> Signup and view all the answers

    What is the definition of the dryness fraction of steam?

    <p>The proportion of steam in the wet steam mixture</p> Signup and view all the answers

    Which of the following is NOT a characteristic of wet steam?

    <p>It has a higher internal energy</p> Signup and view all the answers

    What is the purpose of considering the external work of evaporation in thermodynamic analyses?

    <p>To evaluate the energy transfers and efficiency in steam systems</p> Signup and view all the answers

    What is the physical significance of the internal latent heat of vaporization?

    <p>It represents the energy needed to break the intermolecular bonds within the liquid phase</p> Signup and view all the answers

    How does the specific volume of steam change with an increase in temperature and pressure?

    <p>It decreases with an increase in temperature and pressure</p> Signup and view all the answers

    What is the enthalpy of a substance?

    <p>A measure of 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 is the primary advantage of using enthalpy in analyzing heat transfer processes involving steam?

    <p>It takes into account the energy associated with the steam's pressure-volume work.</p> Signup and view all the answers

    What is the definition of internal energy in thermodynamics?

    <p>The sum of all microscopic forms of energy within a substance.</p> Signup and view all the answers

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

    <p>To determine the mass fraction of vapor in the mixture.</p> Signup and view all the answers

    What is the typical temperature range covered by an enthalpy-entropy chart?

    <p>Up to 800 degrees Celsius.</p> Signup and view all the answers

    What is the primary difference between enthalpy and internal energy?

    <p>Enthalpy includes the energy associated with pressure-volume work, while internal energy does not.</p> Signup and view all the answers

    What happens to the entropy of water as it undergoes a phase change from liquid to vapor?

    <p>It increases.</p> Signup and view all the answers

    What is the purpose of defining a base or datum for internal energy, enthalpy, and entropy?

    <p>To establish a reference point for changes in these properties</p> Signup and view all the answers

    What do the lines of constant pressure and temperature coincide on a h-s chart in a two-phase region?

    <p>Represent a constant volume process</p> Signup and view all the answers

    What is the primary purpose of a barrel calorimeter?

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

    What is the relationship between the quality of steam and the masses of saturated liquid and vapour?

    <p>m = mf + mg, V = Vf + Vg, mV = mfvf + mgvg</p> Signup and view all the answers

    What is the characteristic of the saturation state of a liquid and its vapour?

    <p>Only one independent variable is required to fix the state</p> Signup and view all the answers

    What is the primary difference between a pure substance and a mixture?

    <p>A pure substance has one degree of freedom, while a mixture has two degrees of freedom</p> Signup and view all the answers

    What is the main reason why the separating calorimeter gives inaccurate results?

    <p>Due to incomplete separation of water</p> Signup and view all the answers

    What is the purpose of the perforated sampling tube in the throttling calorimeter?

    <p>To take a sample of wet steam from the steam main</p> Signup and view all the answers

    What is the advantage of the throttling calorimeter?

    <p>It can be used to find the dryness fraction of very dry steam</p> Signup and view all the answers

    What is the purpose of the separator in the combined separating and throttling calorimeter?

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

    Why is the gauge G not required in the separating calorimeter?

    <p>Because it is not necessary when the weight of steam is measured</p> Signup and view all the answers

    What happens to the steam in the throttling calorimeter?

    <p>It is superheated to a higher temperature</p> Signup and view all the answers

    When is the combined separating and throttling calorimeter used?

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

    What is the limitation of the separating calorimeter?

    <p>It gives inaccurate results for very wet steam</p> Signup and view all the answers

    What is the purpose of the mercury manometer in the throttling calorimeter?

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

    What is the main advantage of the combined separating and throttling calorimeter?

    <p>It can be used for both very wet and very dry steam</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 high energy content, low viscosity, and ability to transfer heat efficiently. Discover its uses in heating, cooling, and sterilization.

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