13468-10-37P AID: 1825 | 05/12/2014

Shows the T-s diagram with steam as working fluid for the ideal reheat Rankine cycle as in Figure (1).

For the steam power plant which functions on a reheat Rankine cycle, pressure, specific enthalpy, specific entropy, specific volume, and temperature at state are , , , , and respectively.

(a)

Express the specific work input to the system.

(1)

Here, efficiency of pump is .

Refer to saturated water-pressure table, and interpret the values of , and at pressure .

Substitute for , for , and for in Equation (1).

Express the enthalpy of steam at state 2.

(2)

Substitute for , and for in Equation (2).

Express the isentropic efficiency of turbine 1.

(3)

Refer to superheated water table and interpret the values of , and at pressure , and temperature .

Since, the entropy at state 3 is equal to the entropy at state 4s, the entropy value of is .

Interpret the value of at pressure , and in superheated water table. Manipulate interpolation method.

(4)

Substitute 6.6956 for , 6.5850 for , 6.5995 for y, 2777.1 for , and 2828.3 for in Equation (4) to find x, which is the specific enthalpy at state 4s.

Hence,

Substitute for , 0.80 for , and for in Equation (3).

Express the quality of steam at state 6s.

(5)

Here, specific entropy of saturated liquid is , and specific entropy of is .

Refer to steam table and interpret the value of , and at pressure , and temperature .

Interpret the values of , and from saturated water-pressure table at pressure .

Substitute for , for , and for in Equation (5).

Express the specific enthalpy of steam at state 6s.

(6)

Refer to steam tables, and interpret the values of and at pressure .

Substitute for , for , and 0.9427 for in Equation (6).

Express the isentropic efficiency of turbine.

(7)

Substitute for , 0.80 for , and for in Equation (7).

The obtained value is greater than the value of saturated vapor at pressure . Hence it implies that it is a superheated vapor. Therefore, from superheated water table, find the temperature , at pressure , and enthalpy value .

Since, the temperature value is not available directly, manipulate interpolation method. Substitute 2687.5 for , 2592 for , 2664.8 for y, 50 for , and 100 for in Equation (4) to find x, which is .

Therefore, the temperature of steam at the exit of turbine is .

(b)

Express the specific work output from the turbine.

(8)

Here, specific work output from the turbine is .

Substitute for , for , for , and for in Equation (8).

Express the specific heat input to the Rankine cycle.

(9)

Here, specific heat input of the cycle is .

Substitute for , for , for and for in Equation (9).

Express the specific net work output of the cycle.

(10)

Substitute for , and for in Equation (10).

Express the thermal efficiency of the cycle.

(11)

Substitute for , and for in Equation (11).

Therefore, the thermal efficiency of the reheat Rankine cycle is .

(c)

Express the mass flow rate of steam

(12)

Here, rate of net work from the cycle is .

Substitute for , and for in Equation (12).

Therefore, the mass flow rate of steam is .