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Questions and Answers
What is the critical point of a substance?
What is the critical point of a substance?
What is the primary advantage of steam as a heat transfer medium?
What is the primary advantage of steam as a heat transfer medium?
What happens to the densities of the liquid and gas phases at the critical point?
What happens to the densities of the liquid and gas phases at the critical point?
At what temperature can steam be used as an effective sterilizer?
At what temperature can steam be used as an effective sterilizer?
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What is sensible heat?
What is sensible heat?
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What is the primary advantage of steam in cleaning applications?
What is the primary advantage of steam in cleaning applications?
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What is latent heat?
What is latent heat?
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What is superheat?
What is superheat?
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What happens to steam when it is cooled?
What happens to steam when it is cooled?
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What is enthalpy?
What is enthalpy?
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What is the triple point of water?
What is the triple point of water?
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What is the critical point of a substance?
What is the critical point of a substance?
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What is the dryness fraction of a mixture of steam and water?
What is the dryness fraction of a mixture of steam and water?
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What is the internal energy of steam?
What is the internal energy of steam?
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What is the external work of evaporation?
What is the external work of evaporation?
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What is the internal latent heat of steam?
What is the internal latent heat of steam?
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What is the specific volume of steam?
What is the specific volume of steam?
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What is enthalpy?
What is enthalpy?
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What is the relationship between enthalpy H, internal energy U, pressure p, and volume V?
What is the relationship between enthalpy H, internal energy U, pressure p, and volume V?
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What does a vertical line in the h-s chart represent?
What does a vertical line in the h-s chart represent?
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What is the purpose of drawing lines of constant dryness fraction (x) in the wet region of the h-s chart?
What is the purpose of drawing lines of constant dryness fraction (x) in the wet region of the h-s chart?
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What is the type of calorimeter used to measure steam quality when the dryness fraction is greater than 0.95?
What is the type of calorimeter used to measure steam quality when the dryness fraction is greater than 0.95?
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What is the number of independent properties required to fix the state of a pure substance?
What is the number of independent properties required to fix the state of a pure substance?
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What is the purpose of drawing lines of constant temperature in the superheated region of the h-s chart?
What is the purpose of drawing lines of constant temperature in the superheated region of the h-s chart?
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What does enthalpy represent for steam?
What does enthalpy represent for steam?
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What is internal energy typically measured in?
What is internal energy typically measured in?
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What happens to entropy when there is a phase change from liquid to vapor?
What happens to entropy when there is a phase change from liquid to vapor?
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What is the quality x of a two-phase liquid-vapor mixture defined as?
What is the quality x of a two-phase liquid-vapor mixture defined as?
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What does an enthalpy-entropy chart describe?
What does an enthalpy-entropy chart describe?
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What state is reached when the system is heated at constant pressure and reaches 100o C at 1.014 bar?
What state is reached when the system is heated at constant pressure and reaches 100o C at 1.014 bar?
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What is the purpose of the perforated cup in the separating calorimeter?
What is the purpose of the perforated cup in the separating calorimeter?
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What is the advantage of using a separating calorimeter?
What is the advantage of using a separating calorimeter?
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What is the purpose of the partially-opened valve in the throttling calorimeter?
What is the purpose of the partially-opened valve in the throttling calorimeter?
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What is the disadvantage of using a separating calorimeter?
What is the disadvantage of using a separating calorimeter?
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What is the advantage of using a throttling calorimeter?
What is the advantage of using a throttling calorimeter?
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What happens to the steam in the throttling calorimeter?
What happens to the steam in the throttling calorimeter?
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What is the purpose of the mercury manometer in the throttling calorimeter?
What is the purpose of the mercury manometer in the throttling calorimeter?
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What is the purpose of the combined separating and throttling calorimeter?
What is the purpose of the combined separating and throttling calorimeter?
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When is the combined separating and throttling calorimeter used?
When is the combined separating and throttling calorimeter used?
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What happens to the steam in the combined separating and throttling calorimeter?
What happens to the steam in the combined separating and throttling calorimeter?
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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 unique properties of steam, including high energy content, low viscosity, low density, and excellent heat transfer. Test your knowledge of steam's characteristics and applications.