Fault of Electric Cable
Energy Bands in Crystals
Gallium Arsenide Semiconductor
Atomic Energy Levels
Electric Pressure Cooker
Steam Dryness Fraction
Superheated Steam and Steam Phase Diagram
Vapour Properties Mollier Chart Heat Capacities
What is Steam Flashing?
How to Calculate Steam Consumption During Plant Start Up
Effective Steam Distribution System
What is Water Hammer?
Steam Boiler | Working principle and Types of Boiler
Methods of Firing Steam Boiler
Fire Tube Boiler | Operation and Types of Fire Tube Boiler
Water Tube Boiler | Operation and Types of Water Tube Boiler
Steam Boiler Furnace Grate Firebox Combustion Chamber of Furnace
Feed Water and Steam Circuit of Boiler
Boiler Feed Water Treatment Demineralization Reverse Osmosis Plant Deaerator
Coal Combustion Theory
Fluidized Bed Combustion | Types and Advantages of Fluidized Bed Combustion
Steam Condenser of Turbine
Jet Condenser | Low Level High Level Ejector Jet Condenser
Surface Steam Condenser
Economics of Power Generation
Cooling Tower Useful Terms and Cooling Tower Performance
Cooling Tower Material and Main Components
Power Plant Fire Protection System
Hydrant System for Power Plant Fire Protection
Medium Velocity Water Spray or MVWS System for Fire Protection
Foam Fire Protection System
Fire Detection and Alarm System
Gas Extinguishing System
Electric Power Generation
Power Plants and Types of Power Plant
Thermal Power Generation Plant or Thermal Power Station
Hydro Power Plant | Construction Working and History of Hydro power plant
Nuclear Power Station or Nuclear Power Plant
Diesel Power Station
Why Supply Frequency is 50 Hz or 60 Hz?
Economiser in Thermal Power Plant | Economiser
MHD Generation or Magneto Hydro Dynamic Power Generation
Cogeneration | Combined Heat and Power
Thermoelectric Power Generators or Seebeck Power Generation
Cost of Electrical Energy
Gas Turbine Power Plant
Solar Energy Solar Electricity
Solar Energy System | History of Solar Energy
Types of Solar Power Station
Components of a Solar Electric Generating System
What is photovoltaic effect?
Staebler Wronski Effect
Working Principle of Photovoltaic Cell or Solar Cell
Characteristics of a Solar Cell and Parameters of a Solar Cell
Solar Cell Manufacturing Technology
What is a Solar PV Module?
What is Standalone Solar Electric System?
Engineering Thermodynamics Part 1
Science of Engineering Thermodynamics Part 2
Basic Law of Conservation and First Law of Thermodynamics
Carnot Cycle and Reversed Carnot Cycle
Enthalpy Entropy and Second Law of Thermodynamics
Rankine Cycle and Regenerative Feed Heating
Rankine Cycle for Closed Feed Water Heaters and Rankine Cycle Cogeneration
Ideal Verses Actual Rankine Cycle
Rankine Cycle Efficiency Improvement Techniques
Basic Wind Energy
Wind Turbine | Working Types and History of Wind Turbine
Theory of Wind Turbine
Steam Dryness Fraction
What is Dryness Fraction?Steam is said to be dry saturated when at that particular pressure its temperature is equal to the boiling point. It is difficult to produce dry saturated steam in practice and steam will often contains water droplets. So steam generated in the drum of the boiler is often wet and contains some moisture. If the moisture content of the steam is 7% by mass, then the dryness fraction of the steam is said to be 0.93 and that means the steam is only 93% dry. Evaporation Enthalpy of wet steam is expressed as a product of specific enthalpy (hfg) and dryness fraction (x). Heat content of the wet steam and dry saturated steam are different. Dry saturated steam is having higher heat content (useable energy) than the wet steam. Actual Enthalpy of Evaporation Actual total Enthalpy of wet steam Where hf is Liquid Enthalpy. Density of water is higher than that of the steam, so the specific volume of the water is far lesser than that of the specific volume of the steam.
Thus the droplets of water in the wet steam will occupy negligible-space and the specific volume of the wet-steam is less than that of the dry steam and given by the formula: Actual specific volume = x vg Where, vg is the specific volume of dry saturated steam
Steam Phase DiagramRelation of enthalpy and temperature corresponding to different pressure range is graphically represented in Phase Diagram.
Liquid Enthalpy (hf) on Phase DiagramWhen water is heated from 0oC to its saturation temperature at atmospheric pressure it follows the saturated liquid line until it has received all its liquid enthalpy hf and is represented by (A-B) on Phase diagram.
Enthalpy of Saturated Steam (hfg)Any further heat addition results in change in phase to saturated steam and is represented by (hfg) on phase diagram i.e B-C
Dryness Fraction (x)When heat is applied then the liquid start changing its phase from liquid to vapour and then the dryness fraction of the mixture starts increasing i.e moving towards unity. In the phase diagram dryness fraction of the mixture is 0.5 at exactly mid of the line B-C. Similarly at point C on the phase diagram dryness fraction value is 1.
Line C-DPoint C is in the saturated vapour line, any further heat addition results in increasing the steam temperature i.e beginning of steam super-heating represented by line C - D
Liquid ZoneRegion towards left side of the saturated liquid line
Super Heat ZoneRegion towards right side of the saturated vapour line
Two Phase ZoneArea between the saturated liquid and saturated vapour line is mixture liquid and vapour. Mixture with varied dryness fractions.
Critical PointIt is the Apex point where saturated liquid and saturated vapour lines meet. Enthalpy of evaporation diminishes to zero at critical point, it means that water changes directly to steam at critical point and thereafter. Maximum temperature which liquid can attain or exist is equivalent to critical point.
Critical Point ParametersTemperature 374.15°C, Pressure 221.2 bar, values above this are super-critical values and are useful in increasing the efficiency of the Rankine Cycle.
What is Flash Steam?Flash steam is produced when water pressure is reduced from high to a low pressure, then the water is at higher temperature than that of saturation temperature at low pressure. Thus this excess heat energy is released at low pressure in the foam of flashing and the steam thus produced is “Flash Steam”.
Flashing of SteamIt is the excess energy or enthalpy available (due to fall in pressure) will flashes/evaporate some portion of the water/condensate when pressure falls. Amount of Flash steam produced is given by the formula: hf at 6 bar = 697.22 kJ/Kg hf at 0 bar = 417.5 kJ/Kg hfg at 0 bar = 2258 kJ/Kg Flash steam generation for the condensate for values as given in Figure:1 = 0.124 Kg of steam/per Kg of water OR = 12.4 %
Flash Steam EffectsFollowing are the areas where Flash steam effect should be given due consideration other it may lead to water hammer:
- Condensate-receiver tank vent sizing
- Steam-traps discharge piping.
- Condensate return line sizing.