Page 124 - Mechanical Engineer's Data Handbook

THERMODYNAMICS AND HEAT TRANSFER 1 I3

T

A bleed pressure pb is selected to correspond to the
saturation temperature t,.
4 \
\ '1 -'fb; '1 -sf2
Dryness fractions: xb =- 2-
-2
a 'Pgb Sfg2
3
2
S Enthalpy: h, =h,, + xbhfg,; h2 = hf, + xzhfg2
Quantity of bled steam y=- hfb-hfZ kg/kg total steam
3.6.3 Rankine cycle with reheat hb-h2
Work done per kg steam W=(h,-h,)+(l-y)(h,-h2)
At point 2 the steam is reheated to point 6 and passed Heat supplied per kg steam Q= (h, -hfb)
through a second turbine. W
W=(h, -hz)+ (h6-h7) Cycle efficiency 4 = -
Q=(hl-h3)+(h6-h2) Q
The value of p6 is found using T6= TI (usually) and 3600 kg kW h '
sgz, = s, from which h6 is found. The value of h, is found Specific steam consumption (SSC) = ~ W ~
using s, = s6.

s

3.6.4 Regenerative cycle

Turbine inlet conditions pl, t,, h,
Turbine outlet conditions p,, t,, h,
Bleed steam conditions p,, t,, h,

(tl +t2)
For maximum efficiency tb=-
2