Theory of Producing Vapour

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Theory of Producing Vapour

• P M V Subbarao
• Professor
• Mechanical Engineering Department
• I I T Delhi

Creation of the Working Fluid using A Pure
Substance ....
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Triple Point

• Water
• Triple point temperature 273.17 K
• Triple point pressure 0.6113 kPa
• Ammonia
• Triple point temperature  195.2 K
• Triple point pressure  6.111 kPa

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Production of Vapour Ancient Method
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Production of Vapour Modern Method
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Rudolf Christian Karl Diesel

• Diesel was born in Paris, France in 1858 the
  second of three children of Elise and Theodor
  Diesel.
• At age 14, Rudolf wrote a letter to his parents
  stating that he wanted to become an engineer.
• Diesel was graduated in January 1880 with highest
  academic honours.

• Started working as director of company working
  on design and construction of a modern
  refrigeration and ice plant from 1981.
• In early 1890, Diesel moved to Berlin.
• Diesel understood thermodynamics and the
  theoretical and practical constraints on fuel
  efficiency.
• He first worked with steam, his research into
  thermal efficiency and fuel efficiency leading
  him to build a steam engine using ammonia vapour.

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• He spent many months in a hospital, followed by
  health and eyesight problems.
• He then began designing an engine based on the
  Carnot cycle, and in 1893, Diesel published a
  treatise entitled
• Theorie und Konstruktion eines rationellen
  Wärmemotors zum Ersatz der Dampfmaschine und der
  heute bekannten Verbrennungsmotoren.
• Theory and Construction of a Rational Heat-engine
  to Replace the Steam Engine and Combustion
  Engines Known Today.

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Starting from Liquid State
Let's consider the results of heating liquid from
20C
For Ammonia Pressure must be greater than 857.5kPa
For Ammonia Pressure must be greater than 2.339
kPa
20?C
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State 1
Liquid Ammonia _at_ 1 MPa
Liquid Water _at_ 100 kPa
20?C

• In the compressed liquid region, the properties
  of the liquid are approximately equal to the
  properties of the saturated liquid state at the
  temperature.

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State 2 Saturated Liquid

• Process 1-2
• The temperature and specific volume will increase
  from the compressed liquid, or subcooled liquid,
  state 1, to the saturated liquid state 2.

state 2
Saturated Liquid Ammonia _at_ 1 MPa 24.9?C
Saturated Liquid Water _at_ 100 kPa 99.62?C
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State 3 Equilibrium Mixture of Saturated Liquid
Vapour

• Process 2-3
• At state 2 the liquid has reached the temperature
  at which it begins to boil, called the saturation
  temperature, and is said to exist as a saturated
  liquid.
• Properties at the saturated liquid state are
  noted by the subscript f and v2 vf.
• During the phase change both the temperature and
  pressure remain constant.
• Water boils at 99.62C when the pressure is
  100kPa .
• Ammonia boils at 24.99C when the pressure is
  1000 kPa ).
• At state 3 the liquid and vapor phase are in
  equilibrium and any point on the line between
  states 2 and 3 has the same temperature and
  pressure.

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State 4 Saturated Vapour

• Process 3-4
• At state 4 a saturated vapor exists and
  vaporization is complete.
• The subscript g will always denote a saturated
  vapor state.
• Note v4 vg.

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Saturated Water Vs Saturated Steam
Temperature Pressure Specific Volume, m3/kg   Specific Volume, m3/kg  
0C MPa Saturated Liquid Saturated Vapour

100 0.1013 0.001044 1.673
120 0.1985 0.00106 0.8919
150 0.4759 0.00109 0.3928
200 1.554 0.001156 0.1274
250 3.973 0.001251 0.05013
300 8.581 0.001404 0.02167
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Saturated Liquid Ammonia Vs Saturated Vapour
Ammnia
Temperature Pressure Specific Volume, m3/kg   Specific Volume, m3/kg  
0C MPa Saturated Liquid Saturated Vapour

100 6.254 0.002188 0.01784
120 9.107 0.002589 0.01003
132.3 11.33 0.004255 0.004255
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State 5 Superheated Vapour

• Process 4-5
• If the constant pressure heating is continued,
  the temperature will begin to increase above the
  saturation temperature.
• State 5 is called a superheated state because T5
  is greater than the saturation temperature for
  the pressure.

Superheated Ammonia _at_ 1 MPa 300?C
Superheated Water _at_ 100 kPa 300?C
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Constant Pressure Process
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The Theory of Producing Steam

• Water and steam can be easily used as heat
  carriers in heating systems.
• Water boils and evaporates at 100C under
  atmospheric pressure.
• By higher pressure, water evaporates at higher
  temperature - e.g. a pressure of 10 bar equals
  an evaporation temperature of 179.90C.
• At a constant pressure of 10 MPa the saturation
  temperature is 311.10C.

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Wet Vapour

• Wet vapour is a mixture of vapour and liquid
  water at same temperature and pressure.
• Saturation pressure is the pressure at which the
  liquid and vapor phases are in equilibrium at a
  given temperature.
• Saturation temperature is the temperature at
  which the liquid and vapor phases are in
  equilibrium at a given pressure.
• Saturation Pressure is function of temperature or
  vice versa.
• T F(p)

The Wagner-Ambrose equation
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Equations for Saturation Conditions of Water
Saturation Properties of Water
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Many Constant Pressure Processes

• If all of the saturated liquid states are
  connected, the saturated liquid line is
  established.

• If all of the saturated vapor states are
  connected, the saturated vapor line is
  established.

• These two lines intersect at the critical point
  and form what is often called the steam dome.

The critical point of water is 374.14oC, 22.09
MPa
The critical point of ammonia is 132.3oC, 11.33
MPa
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Density of Saturated Liquid
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Density of Saturated Vapour
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The Vapour Dome

• The region between the saturated liquid line and
  the saturated vapor line is called by these
  terms
• Saturated liquid-vapor mixture region,
• Wet region,
• Two-phase region, and just
• The saturation region.
• The trend of the temperature following a constant
  pressure line is to increase with increasing
  volume.
• The trend of the pressure following a constant
  temperature line is to decrease with increasing
  volume.

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Peculiar Nature of Wet Vapour

• Pressure and temperature are not independent
  properties.
• Either p V or T V are independent pair.
• P v or T v can also be considered.
• A new property is to be defined for steam for
  ease of design.
• This is called Quality or dryness fraction of wet
  steam.

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Quality and Saturated Liquid-Vapor (Wet) Mixture

• Now, lets review the constant pressure heat
  addition process for water shown in Figure.
• The state 3 is a mixture of saturated liquid and
  saturated vapor.
• How do we locate it on the T-v diagram?
• To establish the location of state 3 a new
  parameter called the quality x is defined as

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• The quality is zero for the saturated liquid and
  one for the saturated vapor (0?x ? 1).
• The average specific volume at any state 3 is
  given in terms of the quality as follows.
• Consider a mixture of saturated liquid and
  saturated vapor.
• The liquid has a mass mf and occupies a volume
  Vf.
• The vapor has a mass mg and occupies a volume Vg.

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Volume of Wet Mixture