Assignment 3
- 1. ASSIGNMENT 3 1. (a) In a steam power plant, 2.8 kg/s of dry saturated steam at a pressure of 30 bar is produced by a steam boiler. Feed water enters the boiler at a temperature of 38 C. Assuming the changes in kinetic and potential energy are negligible, determine the rate of heat energy supplied to the boiler, if 350 kJ/s of heat energy is lost from the boiler to its surroundings; (7753 kJ/s) (b) The steam from the boiler in 1(a) is superheated to a temperature of 450 C before entering a turbine at 30 bar. In the turbine, the steam expands to a pressure of 0.42 bar and exhausts with the dryness fraction of 0.95. If 130 kJ/s of heat energy is lost from the turbine casing to its surroundings and the changes in kinetic and potential energy are negligible, determine the power developed by the turbine. (2168 kJ/s) 2. (a) In a steam power plant, 2.8 kg/s of superheated steam at a pressure of 40 bar and a temperature of 450 ºC enters a steam turbine and leaves as wet steam at a pressure of 1.2 bar and a dryness fraction of 0.95. If 125 kJ/s of heat energy is lost to its surroundings through its casing, and the changes in kinetic and potential energy are negligible, determine the power developed by the turbine. (2001 kJ/s) (b) In the steam plant of 2(a), the wet steam exhausted from the turbine enters the steam condenser. It condenses at constant pressure and leaves the condenser as saturated water. Assuming the changes in kinetic and potential energy are negligible, determine the rate of heat rejected from the condenser to its surroundings. (5969 kJ/s) 3. (a) In a hotel, a steam boiler operates at a constant pressure of 5 bar. Wet steam is produced at a rate of 1.2 kg/s with a dryness fraction of 0.68. Feed water enters the boiler at a temperature of 28 ºC. If 30 kJ/s of heat energy is lost to its surroundings through its casing, and the changes in kinetic and potential energy are negligible, determine the rate of heat energy supplied to the boiler. (2378.2 kJ/s) (b) The wet steam from the boiler in 3(a) is mixed with the cold water at a temperature of 28 ºC in the mixing chamber to produce a continuous supply of hot water at a temperature of 75 ºC. Assuming no heat is lost to its surroundings, and the changes in kinetic and potential energy are negligible, determine the mass flow rate of cold water and hot water. (10.74 kg/s, 11.94 kg/s)
- 2. 4. In a hotel, wet steam and cold water are mixed in the mixing chamber to produce a continuous supply of hot water. Wet steam at a pressure of 5.0 bar and dryness fraction of 0.62 is mixed with cold water at a pressure of 5.0 bar and a temperature of 29 C in the mixing chamber. Assume no heat is lost to its surroundings and the changes in kinetic and potential energy are negligible. (a) If the mixing chamber is required to produce hot water at a pressure of 5.0 bar and a temperature of 70 C, determine the ratio between the mass flow rates of the wet steam and the cold water. (b) If 0.6 kg/s of wet steam is mixed with the 5.2 kg/s of cold water, determine the temperature of hot water. (0.1037, 74.16 C)