Power Plant Engineering

114 POWER PLANT ENGINEERING

Example 8. Calculate the day length on a horizontal surface at New Delhi (28°35′ N, 77°12′ E)

on December 1.

Solution. Day length = (2/15) cos–1(– tan Φ. tan δ)

Day length =

2

15 cos

• 1 [– tan 28.58° tan (– 22.11°)]

= 10.30 h.
Example 9. Determine solar time corresponding to 1430 h (IST) at Bombay (190°07′ N, 72°51′
E) on July 1. In India standard time is based on 82.50° E.
Solution. Solar time = 1430 h – 4(82.50 – 72.85) minutes + (– 4 minutes)
= 1430 h – 38.6 minutes – 4 minutes
= 1347 h.
Example 10. A 100 mW vapour-dominated system uses saturated steam from a well with a shut-
off pressure of 28 bar. Steam enters the turbine at 5.5 bar and condenses at 0.15 bar. The turbine
polytropic efficiency is 0.82 and the turbine-generator combined mechanical efficiency is 0.9. The cool-
ing tower exist is at 20°C. Calculate the necessary steam flow, the cooling water flow and the plant
efficiency and heat rate if reinjection occurs prior to cooling tower.

Solution.

7

1

S.T.

(^52)
Cooling
To w e r
Direct
Contact
Condenser
Steam-jet
Ejector
Condenser Pump
Alternate
Rejectors
Rejector Well
6 Ground
5
4
Fig. 2.49. Vapour-dominated Power Plant.
T
3
5 2 ′^2
S
1
7
6
Fig. 2.50. T-s Diagram.