Faculty of Engineering Technology, Universiti Malaysia Perlis (UniMAP)

PDT 277 – APPLIED THERMODYNAMICS

Prepared by:

Mohd Al-Hafiz Mohd Nawi, Eng.D.

Department of Mechanical Engineering Technology,

Faculty of Engineering Technology (FE-Tech),

Universiti Malaysia Perlis (UniMAP) Perlis.

Chapter 7:

Vapor & Combined Power Cycles

(Answer)

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[1] Why is the Carnot cycle not a realistic model for steam power

plants?

Answer

The Carnot cycle is not a realistic model for steam power plantsbecause (1) limiting the heat transfer processes to two-phase

systems to maintain isothermal conditions severely limits the

maximum temperature that can be used in the cycle, (2) the

turbine will have to handle steam with a high moisture content

which causes erosion, and (3) it is not practical to design a

compressor that will handle two phases.

[2] How do actual vapor power cycles differ from idealized ones?

Answer

The actual vapor power cycles differ from the idealized ones inthat the actual cycles involve friction and pressure drops in various

components and the piping, and heat loss to the surrounding

medium from these components and piping.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[3] Is it possible to maintain a pressure of 10 kPa in a condenser that isbeing cooled by river water entering at 20 °C?

Answer

Yes, because the saturation temperature of steam at 10 kPa is

45.81°C, which is much higher than the temperature of the cooling

water.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[4] A steady-flow Carnot cycle uses water as the working fluid. Water

changes from saturated liquid to saturated vapor as heat istransferred to it from a source at 250 °C. Heat rejection takes

place at a pressure of 20 kPa. Show the cycle on a T-s diagram

relative to the saturation lines, and determine (a) the thermal

efficiency, (b) the amount of heat rejected, and (c) the net work

output.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[5] Consider a steady-flow Carnot cycle with water as the working

fluid. The maximum and minimum temperatures in the cycle are350 and 60 °C. The quality of water is 0.891 at the beginning of the

heat-rejection process and 0.1 at the end. Show the cycle on a T-s

diagram relative to the saturation lines, and determine (a) the

thermal efficiency, (b) the pressure at the turbine inlet, and (c) the

net work output.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[6] A steam power plant operates on a simple ideal Rankine cycle

between the pressure limits of 3 MPa and 50 kPa. The temperatureof the steam at the turbine inlet is 300 °C, and the mass flow rate

of steam through the cycle is 35 kg/s. Show the cycle on a T-s

diagram with respect to saturation lines, and determine (a) the

thermal efficiency of the cycle and (b) the net power output of

the power plant.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[6] A steam power plant operates on a simple ideal Rankine cycle

between the pressure limits of 3 MPa and 50 kPa. The temperatureof the steam at the turbine inlet is 300 °C, and the mass flow rate

of steam through the cycle is 35 kg/s. Show the cycle on a T-s

diagram with respect to saturation lines, and determine (a) the

thermal efficiency of the cycle and (b) the net power output of

the power plant.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[7] Refrigerant-134a is used as the working fluid in a simple ideal

Rankine cycle which operates the boiler at 2000 kPa and thecondenser at 24 °C. The mixture at the exit of the turbine has a

quality of 93 percent. Determine the turbine inlet temperature, the

cycle thermal efficiency, and the back-work ratio of this cycle.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[7] Refrigerant-134a is used as the working fluid in a simple ideal

Rankine cycle which operates the boiler at 2000 kPa and thecondenser at 24 °C. The mixture at the exit of the turbine has a

quality of 93 percent. Determine the turbine inlet temperature, the

cycle thermal efficiency, and the back-work ratio of this cycle.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[8] A simple ideal Rankine cycle as in figure below which uses wateras the working fluid operates its condenser at 40 °C and its boiler

at 300 °C. Calculate the work produced by the turbine, the heat

supplied in the boiler, and the thermal efficiency of this cycle

when the steam enters the turbine without any superheating.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[8] A simple ideal Rankine cycle as in figure below which uses wateras the working fluid operates its condenser at 40 °C and its boiler

at 300 °C. Calculate the work produced by the turbine, the heat

supplied in the boiler, and the thermal efficiency of this cycle

when the steam enters the turbine without any superheating.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[8] A simple ideal Rankine cycle as in figure below which uses wateras the working fluid operates its condenser at 40 °C and its boiler

at 300 °C. Calculate the work produced by the turbine, the heat

supplied in the boiler, and the thermal efficiency of this cycle

when the steam enters the turbine without any superheating.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[9] Consider a 210-MW steam power plant that operates on a simple

ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500°C and is cooled in the condenser at a pressure of 10 kPa. Show

the cycle on a T-s diagram with respect to saturation lines, and

determine (a) the quality of the steam at the turbine exit, (b) the

thermal efficiency of the cycle, and (c) the mass flow rate of the

steam.

Lecturer Info

DEPARTMENT OF MECHANICAL ENGINEERING TECHNOLOGY,FACULTY OF ENGINEERING TECHNOLOGY,

UNIVERSITI MALAYSIA PERLIS (UniMAP)

Exercise

PDT277 – APPLIED THERMODYNAMICS UNIT 7 – VAPOR & COMBINED POWER CYCLES

[9] Consider a 210-MW steam power plant that operates on a simple

ideal Rankine cycle. Steam enters the turbine at 10 MPa and 500°C and is cooled in the condenser at a pressure of 10 kPa. Show

the cycle on a T-s diagram with respect to saturation lines, and

determine (a) the quality of the steam at the turbine exit, (b) the

thermal efficiency of the cycle, and (c) the mass flow rate of the

steam.