Chapter: 08 POWER CYCLES

Power CYCLEs

A Vapour Power Station: a bird’s eye view Vapour Power Systems

Vapour Power Systems POWER CYCLES: There are four principal control volumes involving components: Turbine Condenser Pump Boiler All energy transfers by work and heat are taken as positive in the directions of the arrows on the schematic and energy balances are written accordingly. Vapour Power Systems

The processes are: Vapour Power Systems VAPOUR POWER CYCLE: Process~1-2: vapor expands through the turbine developing work Process~2-3: vapor condenses to liquid through heat transfer to cooling water Process~3-4: liquid is pumped into the boiler requiring work input Process~4-1: liquid is heated to saturation and evaporated in the boiler through heat transfer from the energy source Vapour Power Systems

IDEALIZATION: Born: 1 June 1796, in Palais du Petit-Luxembourg, Paris, France Died: 24 August, 1832 (age 36) Paris, France Nationality: French Fields: Physicist and engineer Vapour Power Systems

Vapour Power Systems CARNOT CYCLE: Four Processes in CARNOT cycle: Turbine: Isentropic Condenser: Isothermal Pump: Isentropic Boiler: Isothermal Vapour Power Systems

why is this impractical? CARNOT CYCLE: why is this impractical? Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Processes in RANKINE cycle: 1 2 3 4 Processes in RANKINE cycle: Turbine: Isentropic Condenser: Isobaric Pump: Isentropic Boiler: Isobaric Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Turbine: Isentropic 1 2 3 4 Processes in RANKINE cycle: Turbine: Isentropic Condenser: Isobaric Pump: Isentropic Boiler: Isobaric Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Processes in RANKINE cycle: 1 2 3 4 Processes in RANKINE cycle: Turbine: Isentropic Condenser: Isobaric Pump: Isentropic Boiler: Isobaric Vapour Power Systems

Wcycle = Qin – Qout Vapour Power Systems Ideal RANKINE CYCLE: 1 2 3 4 Energy Analysis: 1 2 3 4 Wcycle = Qin – Qout Vapour Power Systems

Each component is analyzed as a control volume at steady state. IDEALIZATION: Engineering model: Each component is analyzed as a control volume at steady state. The turbine and pump operate adiabatically. Kinetic and potential energy changes are ignored. Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Energy Analysis ¬ Component wise: 1 2 3 4 Vapour Power Systems

Vapour Power Systems Ideal RANKINE CYCLE: Performance Parameters: Net Power output: Efficiency: Steam Rate: Vapour Power Systems

Gas Power Cycle

Gas Power Cycle

Gas Power Cycle:  OTTO CYCLE  DIESEL CYCLE

Gas Power Cycles OTTO CYCLE

Gas Power Cycles Thermodynamic Analysis

Gas Power Cycles

Gas Power Cycles pressure

Thermodynamic Analysis Gas Power Cycles pressure Thermodynamic Analysis The Diesel cycle is executed in a closed system, and disregarding the changes in kinetic and potential energies

Power Cycles A steam turbine plant operates on Rankine cycle with steam entering turbine at 40 bar, 350ºC and leaving at 0.05 bar. Steam leaving turbine condenses to saturated liquid inside condenser. Feed pump pumps saturated liquid into boiler. Determine the net work per kg of steam and the cycle efficiency assuming all processes to be ideal. Also show cycle on T-s diagram. Also determine pump work per kg of steam considering linear variation of specific volume. [Ans. Net work per kg of steam = 1081.74 kJ/kg, Cycle efficiency = 36.67%, Pump work per kg of steam = 4.02 kJ/kg]

Power Cycles A four stroke SI engine has the compression ratio of 6 and swept volume of 0.15 m3. Pressure and temperature at the beginning of compression are 98 kPa and 60ºC. Determine the pressure, volume and temperatures at all salient points if heat supplied to it is 150 kJ/kg. Also find out work done, efficiency and mean effective pressure of cycle assuming cp = 1 kJ/kg · K, cv = 0.71 kJ/kg · K. Also plot the cycle on T-S diagram. [Ans. Net Work = 76.75 kJ, = 51.17%, m.e.p. = 511.67 kPa]

Power Cycles In an IC engine using air as working fluid, total 1700 kJ/kg of heat is added during combustion and maximum pressure in cylinder does not exceed 5 MPa. Compare the efficiency of following two cycles used by engine: (a) cycle in which combustion takes place isochorically. (b) cycle in which half of heat is added at constant volume and half at constant pressure. Temperature and pressure at the beginning of compression are 100ºC and 103 kPa. Compression and expansion processes are adiabatic. Specific heat at constant pressure and volume are 1.003 kJ/kg · K and 0.717 kJ/kg · K. [Ans. Otto = 50.83%; mixed = 56.47%]

Power Cycles