586 ENGINEERING THERMODYNAMICS
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\M-therm\Th12-3.pm5
Some undesirable properties of mercury are listed below :
- Since the latent heat of mercury is quite low over a wide range of desirable condensation
temperatures, therefore, several kg of mercury must be circulated per kg of water evapo-
rated in binary cycle.
- The cost is a considerable item as the quantity required is 8 to 10 times the quantity of
water circulated in binary system.
- Mercury vapour in larger quantities is poisonous, therefore, the system must be perfect
and tight.
Fig. 12.35 shows the schematic line diagram of binary vapour cycle using mercury and
water as working fluids. The processes are represented on T-s diagram as shown in Fig. 12.36.
Mercury
turbine
Mercury electric
generator Steam
turbine
Steam electric
generator
Steam
condenser
Water feed pump
Superheater
Mercury condenser or
Steam generator
Mercury feed pump
Mercury
generator
Fig. 12.35. Line diagram of binary vapour cycle.
Analysis of Binary vapour cycle :
hhg 1 = Heat supplied per kg of Hg (mercury) vapour formed in the mercury boiler.
hhg 2 = Heat lost by one kg of Hg vapour in the mercury condenser.
hs = Heat given per kg of steam generated in the mercury condenser or steam boiler.
Whg = Work done per kg of Hg in the cycle.
Ws = Work done per kg of steam in the steam cycle.
ηs = Thermal efficiency of the steam cycle.
ηhg = Thermal efficiency of the Hg cycle.
m = Mass of Hg in the Hg cycle per kg of steam circulated in the steam cycle.
The heat losses to the surroundings, in the following analysis, are neglected and steam
generated is considered one kg and Hg in the circuit is m kg per kg of water in the steam cycle.
Heat supplied in the Hg boiler
ht = m × hhg 1 ...(12.14)
Work done in the mercury cycle
= m. Whg ...(12.15)
Work done in the steam cycle
= 1 × Ws ...(12.16)
