Saturated Steam
Raise the temperature of water to its boiling point (Sensible Heat Transfer), after this liquid phase of water, will transfer to vapor phase or in simple water will start vapourising (Latent Heat Transfer). Now as long as the liquid water left temperature of the steam is same as that of water. So, saturated steam is formed when these both phase coexists ( liquid water and its vapor).
Superheated Steam
When all the water is vaporized, any subsequent addition of heat raises the steam’s temperature. Steam heated beyond the saturated steam level is called superheated steam.
WHY IS SATURATED STEAM GENERALLY PREFERABLE TO SUPERHEATED STEAM ??
Industries normally use saturated steam for heating, cooking, drying or other procedures. Superheated steam is used almost exclusively for turbines. The various types of steam have different energy exchange capacities and this justifies their different uses. Energy transfer capacity, also known as the heat transfer coefficient (U), is used to compare types of steam. Its value is determined by the number of watts that goes through per surface unit and per degree of temperature difference. The greater this value, the greater the heat transfer for a given situation.
Superheated steam only yields sensible heat in an exchanger. It must, therefore, cool down before heating another substance. Superheated steam stuck to a surface cools down while yielding energy to the exchanger. However, superheated steam farther away from the surface cannot easily cool down and yield its energy, because superheated steam is an insulator (a bad conductor of heat), as all gases.
REFERENCES
1) http://www.systhermique.com/steam-condensate/services/troubleshooting/superheated-steam/
2) http://www.tlv.com/global/TI/steam-theory/types-of-steam.html#superheat
No comments:
Post a Comment