Tutorial 8

A stationary gas-turbine power plant operates on a regenerative Brayton cycle

with the effectiveness of 90% ( 90%) with air as the working fluid. Air enters

the compressor at 95 kPa and 290 K and the turbine at 760 kPa and 1100 K. Heat

is transferred to air from an external source at a rate of 75000 kW. Determine the

power delivered by this plant. ( k 1.4)

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Tutorial 7 1. Consider an ideal refrigeration system that uses R-12 as the working fluid, as

shown below. Saturated liquid leaves the condenser at 40C and is throttled to 20C. The liquid and vapor at this temperature are separated, and the liquid is throttled to the evaporator temperature, 70C. Vapor leaving the evaporator is compressed to the saturation pressure corresponding to 20C, after which it is mixed with the vapor leaving the flash chamber. It may be assumed that both the flash chamber and the mixing chamber are well insulated to prevent heat transfer from the ambient. Vapor leaving the mixing chamber is compressed in the second stage of the compressor to the saturation pressure corresponding to the condenser temperature, 40C. Determine a) the coefficient of performance of the system, b) the coefficient of performance of a simple ideal refrigeration cycle operating over the same condenser and evaporator ranges as those of the two-stage compressor unit studied in this problem.

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mhoorfarTypewritten TextTutorial 9

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Tutorial 8 1. A piston/cylinder device contains 0.1 kg of a mixture of 40% methane ( 4CH ),

and 60% propane ( 83HC ) gases by mass at 300 K and 100 kPa. The gas is now slowly compressed in an isothermal process to a final pressure of 250 kPa. Find the work and heat transfer in this process. ( 4CHM 16 kg/kmol, 83HCM 44 kg/kmol, 4CHR 0.5183 kJ/kg.K, 83HCR 0.1886 kJ/kg.K)

2. A large air separation plant takes in ambient air (79% N2, 21% O2 by mole) at 100

kPa, 20C, at a rate of 25 kg/s. It discharges a stream of pure O2 gas at 200 kPa and 100C, and a stream of pure N2 gas at 100 kPa and 20C. The plant operates on an electrical power input of 2000 kW. Calculate the net rate of entropy change for the process. (

2OM 32 kg/kmol, 2NM 28 kg/kmol, 2Opc 0.918 kJ/kg.K, 2OR 0.2598 kJ/kg.K, 2NR 0.2968 kJ/kg.K)

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Tutorial 8+ solutionTutorial 9+ solutionTutorial 10+ solution