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Section-A(iii)

Section-A(iii). Properties of steam & steam Generators. Syllabus (ME-101-F). Section-A Introduction to machine tools Basic Concepts of thermodynamics Properties of steam & steam generators Section-B Refrigeration & Air conditioning. Hydraulic turbines & pumps. Section-C

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Section-A(iii)

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  1. Section-A(iii) Properties of steam & steam Generators For more info. : www.goodwisher.com

  2. Syllabus(ME-101-F) • Section-A • Introduction to machine tools • Basic Concepts of thermodynamics • Properties of steam & steam generators • Section-B • Refrigeration & Air conditioning. • Hydraulic turbines & pumps. • Section-C • Power transmission methods & devices • Stresses & strains • Section-D • Introduction to manufacturing system(NC & CNC Machining) For more info. : www.goodwisher.com

  3. Topics • Formation of steam at constant pressure • Thermodynamic properties of Steam • Use of steam tables • Measurement of dryness fraction by throttling calorimeter. For more info. : www.goodwisher.com

  4. THERMODYNAMIC PROPERTIES OF STEAM • WET STEAM:-when steam contains moisture in suspension , it is said to be wet. • Dry saturated steam:-when wet steam is further heated & it does not contain any suspended particles of water , it is called dry saturated steam. • Superheated steam:-when dry steam is further heated at a constant pressure for raising its temperature , it is said to be superheated. For more info. : www.goodwisher.com

  5. THERMODYNAMIC PROPERTIES OF STEAM(Contd….) • Dryness fraction:-it is the ratio of mass of actual dry steam to the mass total quantity of mixture. x= Where , mg is mass of dry steam mf is mass of water in suspension For more info. : www.goodwisher.com

  6. THERMODYNAMIC PROPERTIES OF STEAM(Contd….) • Latent heat of vapourisation :-it is the amount of heat absorbed to evaporate 1 Kg of water at its boiling point without change in temperature.Denoted by hfg • Sensible heating:-it is the amount of heat absorbed by 1 Kg of water , when heated at constant pressure from from freezing point to the temperature of formation of heat.Denoted by hf For more info. : www.goodwisher.com

  7. THERMODYNAMIC PROPERTIES OF STEAM(Contd….) • Enthalpy of steam:-it is the amount of heat absorbed by water from freezing plus heat absorbed during evaporation.it is denoted by hg • Wet steam:- h=hf+xhfg • dry steam:-(x=1) h=hf+hfg • Superheated steam hsup=total heat for dry steam + heat for superheated steam hsup=hf+ hg + cp(tsup-t) For more info. : www.goodwisher.com

  8. THERMODYNAMIC PROPERTIES OF STEAM(Contd….) • Specific volume:-it is the volume of steam per unit mass. • Wet steam:- Volume of 1Kg steam=xVg+(1-x)vf • Dry steam:-(x=1) Volume of 1 Kg steam=Vg • Superheated steam:-dry steam is further heated at constant temperature. For more info. : www.goodwisher.com

  9. THERMODYNAMIC PROPERTIES OF STEAM(Contd….) • Entropy of steam:-heating & evaporation of water during steam formation takes place at constant pressure. • Wet steam:- S=entropy of water + entropy change during evaporation S=Sf+xSfg • Dry steam(x=1):- S=Sf+Sfg For more info. : www.goodwisher.com

  10. Formation of steam at constant pressure. VAPOUR STATE VAPOURISATION Temperature 100o C LIQUID STATE MELTING 0o C SOLID STATE -10 LATENT HEAT OF FUSION SENSIBLE HEATING LATENT HEAT OF VAPORISATION SUPERHEATING For more info. : www.goodwisher.com

  11. Formation of ice at constant pressure • Consider 1Kg of ice under pressure say p & temperature say -10o C ; If we heat it gradually keeping pressure constant , following changes takes place. • The volume of ice will increase with the increase in temperature , till it reaches freezing point(0o C). • When we add more heat ,ice starts melting(no rise in temperature)till whole ice is melted & converted to water. • Gradual addition of more heat leads to rise in temperature till water reaches boiling point(100o C) • On heating further water will turn into steam , temperature remaining constant. The steam if contains some water particles in suspension is called wet steam , in later stage water will evaporate & steam is called dry steam. • If dry steam is further heated keeping pressure constant , the process is called superheating . Steam so obtained is called superheated steam. For more info. : www.goodwisher.com

  12. Steam tables • Properties of steam such as pressure , temperature , specific volume ,enthalpy , entropy etc. can be experimentally detemined & tabulated & are available in a form called steam table. • For Engg. Calculations , these values are picked from steam table & not calculated each time from equations. For more info. : www.goodwisher.com

  13. Throttling & measurement of dryness fraction • Throttling is a flow process during which pressure drops & enthalpy remains constant. • Throttling reduces the temperature of steam but increases the dryness fraction of wet steam , which may become dry or superheated. • This forms the principle of throttling calorimeter (a device used to measure the quality of wet steam). For more info. : www.goodwisher.com

  14. THROTTLING CALORIMETER THROTTLE VALVE SAMPLING TUBE CONTROL SCREW PIPE CARRYING STEAM AT PRESSURE P1 PRESSURE GAUGE P2 OUTLET For more info. : www.goodwisher.com

  15. Throttling calorimeter. • Pipe A carries wet steam at pressur P1,whose dryness fraction is to be determined. • A portion of steam is taken by sampling tube through holes provided for this purpose. • Steam is then throttled at low pressure usually atmospheric pressure. • Throttling operation is controlled by adjusting the position of throttle valve with a control screw. • The throttled steam then passes thru’ a container where its pressure & temperature are noted. • Note:-working of throttling apparatus would be successful only if steam becomes superheated or atleast dry after throttling operation. • Enthalpy before throttling=enthalpy after throttling • h1=hsup • hf+xhfg=hf+ hg + cp(tsup-t) • This helps to determine the value of dryness fraction x For more info. : www.goodwisher.com

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