Question

Compressing a substance in the Liquid versus Gas Phases EXAMPLE 7-12 Determine the compressor work input required to compress steam isentropi- cally from 100 kPa to 1 MPa, assuming that the steam exists as (a) satu- T rated liquid and (b) saturated vapor at the inlet state. SOLUTION Steam is to be compressed from a given pressure to a specified pressure isentropically. The work input is to be determined for the cases of steam being a saturated liquid and saturated vapor at the inlet. Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible. 3 The process is given to be isentropic. Analysis We take first the turbine and then the pump as the system. Both are control volumes since mass crosses the boundary. Sketches of the pump and the turbine together with the T-s diagram are given in Fig. 7-42. (a) In this case, steam is a saturated liquid initially, and its specific volume is V, Vo1001- 0.001043 mkg CTable A-5) which remains essentially constant during the process. Thus, - (0.001043 m'kg)01000 - 100) kPa1 kPa m -0.94 kJ/kg 1 kJ (b) This time, steam is a saturated vapor initially and remains a vapor during the entire compression process. Since the specific volume of a gas changes considerably during a compression process, we need to know how v varies

Answer 1