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VAPOUR POWER CYCLES 603

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Unsolved Examples

1. A simple Rankine cycle works between pressure of 30 bar and 0.04 bar, the initial condition of steam
   being dry saturated, calculate the cycle efficiency, work ratio and specific steam consumption.
   [Ans. 35%, 0.997, 3.84 kg/kWh]


2. A steam power plant works between 40 bar and 0.05 bar. If the steam supplied is dry saturated and the
   cycle of operation is Rankine, find :
   (i) Cycle efficiency (ii) Specific steam consumption.
   [Ans. (i) 35.5%, (ii) 3.8 kg/kWh]


3. Compare the Rankine efficiency of a high pressure plant operating from 80 bar and 400°C and a low
   pressure plant operating from 40 bar 400°C, if the condenser pressure in both cases is 0.07 bar.
   [Ans. 0.391 and 0.357]


4. A steam power plant working on Rankine cycle has the range of operation from 40 bar dry saturated
   to 0.05 bar. Determine :
   (i) The cycle efficiency (ii) Work ratio
   (iii) Specific fuel consumption. [Ans. (i) 34.64%, (ii) 0.9957, (iii) 3.8 kg/kWh]


5. In a Rankine cycle, the steam at inlet to turbine is saturated at a pressure of 30 bar and the exhaust
   pressure is 0.25 bar. Determine :
   (i) The pump work (ii) Turbine work
   (iii) Rankine efficiency (iv) Condenser heat flow
   (v) Dryness at the end of expansion.
   Assume flow rate of 10 kg/s. [Ans. (i) 30 kW, (ii) 7410 kW, (iii) 29.2%, (iv) 17900 kW, (v) 0.763]


6. In a regenerative cycle the inlet conditions are 40 bar and 400°C. Steam is bled at 10 bar in regenerative
   heating. The exit pressure is 0.8 bar. Neglecting pump work determine the efficiency of the cycle.
   [Ans. 0.296]


7. A turbine with one bleeding for regenerative heating of feed water is admitted with steam having enthalpy
   of 3200 kJ/kg and the exhausted steam has an enthalpy of 2200 kJ/kg. The ideal regenerative feed water
   heater is fed with 11350 kg/h of bled steam at 3.5 bar (whose enthalpy is 2600 kJ/h). The feed water
   (condensate from the condenser) with an enthalpy of 134 kJ/kg is pumped to the heater. It leaves the
   heater dry saturated at 3.5 bar. Determine the power developed by the turbine. [Ans. 16015 kW]


8. A binary-vapour cycle operates on mercury and steam. Saturated mercury vapour at 4.5 bar is supplied
   to the mercury turbine, from which it exhaust at 0.04 bar. The mercury condenser generates saturated
   steam at 15 bar which is expanded in a steam turbine to 0.04 bar.
   (i) Find the overall efficiency of the cycle.
   (ii) If 50000 kg/h of steam flows through the steam turbine, what is the flow through the mercury
   turbine?
   (iii) Assuming that all processes are reversible, what is the useful work done in the binary vapour cycle
   for the specified steam flow?
   (iv) If the steam leaving the mercury condenser is superheated to a temperature of 300°C in a super-
   heater located in the mercury boiler, and if the internal efficiencies of the mercury and steam tur-
   bines are 0.85 and 0.87 respectively, calculate the overall efficiency of the cycle. The properties of
   saturated mercury are given below :

p (bar) t (°C) hf hg sf sg vf vg

(kJ/kg) (kJ/kg K) (m^3 /kg)

4.5 450 63.93 355.98 0.1352 0.5397 79.9 ×10–6 0.068

0.04 216.9 29.98 329.85 0.0808 0.6925 76.5 × 10–3 5.178

[Ans. (i) 52.94%, (ii) 59.35 × 10^4 kg/h, (iii) 28.49 MW, (iv) 46.2%]