N5 Power Machines STEAM GENETATION

ialegodi@gmail.com 082 396 7717 STEAM GENERATION Type of steam Enthalpy of steam Volume of steam v(m 3 / kg) h kJ / kg Vwet  xvg @ pressure( initial volume), Wet steam hwet  m(hf  xhfg  hw ) volume entering superheater, volume leaving evaporator) Dry saturated hdry  m(hfg  hw ) Vdry  Vg @ pressure n  1  hsup  1941 Superheated hsup  mhg  Cp s t ss  t s   hw  Vsup  n    (final volume, P  volume leaving superheated steam) Other formulas under steam generations: Enthalpy of the: Formula 1. Sensible heat H sensible  mhf @ pressure hf @ t w  2. Latent heat H latent  mhfg @ pressure 3. Superheat H sup erheat  mCp s (t ss  t s ) POSSIBLE QUESTIONS: 1. Steam which contains 3, 5% moisture enters a super heater at a pressure of 3 MPa. The steam is then superheated to a temperature of 350 C at constant pressure. Calculate the following with the aid of steam table: 1.1. The enthalpy transferred in the superheater in kJ/kg 1.2. The volume of steam entering the superheater 1.3. The volume of superheated steam leaving the superheater 2. 10 kg of water, at a pressure of 920 kPa and a temperature of 60 C is heated at the boiling point, then to dry saturated steam and then to superheat, with a temperature of 210 C . The specific heat capacity of superheated steam is 2, 1 kJ/kg. C and that of water is 4, 187 kJ/kg.K Calculate the following with the aid of steam table: Downloaded from hlayiso.com

ialegodi@gmail.com 082 396 7717 2.1. The enthalpy of the sensible heat 2.2. The enthalpy of the latent heat 2.3. The enthalpy of the superheat 2.4. The enthalpy of the total heat required for superheating the water in MJ 2.5. The saturated temperature 3. 1 kg of supply water at 0 C is changed to wet steam with a dryness fraction of 0, 82 and at a pressure of 1, 4 MPa. The wet steam is then heated at the same pressure to form superheated steam which has a volume of 0, 1568 m 3 . The specific heat capacity of superheated steam is 2, 15 kJ/kg. C Calculate the following with the aid of steam tables: 3.1. The enthalpy of the superheated steam 3.2. The temperature of the superheated steam 3.3. The initial volume entering the superheater 3.4. The change in specific volume 4. 11, 5 kg of water at a pressure of 880 kPa and a temperature of 48 C is heated to boiling point, then dry saturated steam and then to superheat, with a temperature of 210 C . The specific capacity of superheated steam is 2, 1 kJ/kg. C and that of water is 4, 187 kJ/kg.K Calculate the following with the aid of steam table: 4.1. The enthalpy of the sensible heat 4.2. The enthalpy of the latent heat 4.3. The enthalpy of the superheat 4.4. The enthalpy of the total heat required for superheating the water in MJ 4.5. The saturated temperature 5. Steam which contains 4, 2% moisture enters a superheater at a pressure of 4 MPa. The steam is then superheated to a temperature of 400 C at constant pressure. Downloaded from hlayiso.com

ialegodi@gmail.com 082 396 7717 Calculate the following with the aid of steam tables: 5.1. The heat transferred in the superheater in kJ/kg 5.2. The volume of steam entering the superheater 5.3. The volume of superheated steam leaving the superheater 6. Water which has a mass of 8, 5 kg and a temperature of 40, 3 C is used to form steam at a pressure of 980 kPa. The steam is then superheated to a temperature of 214 C . The specific heat capacity of superheated steam is 2, 1 kJ/kg.K Calculate with the aid of steam tables: 6.1. The sensible heat 6.2. The latent heat 6.3. The superheat 6.4. The total heat required to superheat the steam 6.5. The saturated temperature 7. With the aid of steam table, calculate the following: 7.1. The enthalpy found in 2 kg of steam which has a pressure of 480 kPa and is 7, 3% 7.2. The enthalpy of a kilogram of steam which has a pressure of 1, 5 MPa, a temperature of 396c and the specific heat capacity of steam is 2, 1 kJ/kg. C 7.3. The dryness fraction of wet steam which has an enthalpy of 2 650 kJ/kg at a pressure of 1, 3 MPa 7.4. The heat required to change 2, 3 kg of water from a temperature of 31 C to dry saturated steam at a pressure of 1 000 kPa 8. Supply water enters a boiler at a pressure of 60, 1 C and the pressure in the boiler is 4 MPa. The steam formed is superheated to 310 C and the superheated steam is 2, 1 kJ/kg. C . Calculate the specific volume of the steam per kilogram Downloaded from hlayiso.com

ialegodi@gmail.com 082 396 7717 9. Calculate the total heat and specific volume required to form 8 kg of steam in each of the following conditions of steam if the temperature of the boiling water is 40, 3 C and the pressure of the boiler is 1 000 kPa. 9.1. The dryness fraction of steam is 0, 82 9.2. The steam dry sat1urated 9.3. The steam is superheated with a temperature of 110 C and the specific heat capacity is 2, 4 kJ/kg. C The internal energy of the vapour (study examples in page 114) Steam before expansion (it can either be wet, dry or superheated) = steam after expansion (it can either be wet, dry saturated or superheated) U 1  int ernalenergy of the vapour  h1  P1V1 if the steam at the inlet is wet steam which means h1  hwet and V1  Vwet  U 2  int ernal energy after exp ansio2n h2  P2V2  same thing applies here if the steam is sup erheated steamh1  hsup and V2  Vsup U  mU 2  U 1  3, 5 kg of steam is expanded from 2 000 kPa and 300 C to a pressure of 280 kPa. The specific heat capacity of superheated steam is 2, 1 kJ/kg.K. The steam is 10% at the latter pressure. Calculate the total change of the internal energy Other activities page 116 activity 8. 2 No: 1-3 10. 4 673, 5 kJ of heat is dissipated from 1, 75 kg of wet steam which is at a pressure of 2 000 kPa. The supply water which is used to form the steam entering the evaporator is 26, 6 C . The wet steam is then superheated to 350 C . The specific heat capacity of water is 4, 187 kJ/kg.K Calculate the following: 10.1. The dryness fraction of the wet steam 10.2. The change in enthalpy from wet steam to superheated steam for 1 kg of steam 10.3. The increase in specific volume of the steam for 1 kg of steam Downloaded from hlayiso.com