Ideal Brayton cycle efficiency for gas turbine with P V and T S diagram

The ideal cycle for gas turbine is Brayton or jule cycle. The Brayton cycle has two constant pressure and two isentropic processes. In this video, i have explained PV and TS diagram of Brayton cycle. This video will show you the Analysis of Brayton cycle, and at the end of the video, you will get the equation to find the thermal efficiency of a simple gas turbine power plant. The analysis of Brayton is carried out with the following assumptions: 1) Compression and expansion are isentropic. 2) Pressure losses in the system are neglected. 3) Heat losses in the system are neglected. 4) specific heat of working fluid is taken constant throughout the cycle. Considering the 1kg of working fluid.

Gas Turbine Engine Fuel

The gas turbine engine can be operated with gas, liquid and solid fuels. However, this statement is not true for all gas turbine engine. The selection of fuel for gas turbine is dependent on type of cycle, size and length of engine and application of gas turbine engine. The most important requirement of a gas turbine fuel are 
(1) composition should provide proper combustion and rapid burning,
(2) the product of combustion should contain a minimum of mater which might get deposited on the turbine blades or the heat exchanger,
(3) highest heating value per kg or m^3 volume specially for aircraft engine.


The modern gas turbine are normally operated on the following fuels:
a) Gaseous fuels: Natural gas, Blast furnace gas, Producer gas, Sewage gas, etc.…
b) Liquid fuels: Kerosene, Gasoline, Residual oils, etc.…
c) Solid Fuels: Coal


The solid fuel (Coal) is normally used in closed cycle gas turbine. The main problem with using solid fuel in the case of open cycle plans is of reducing the level of flyash in the gases leaving the combustion chamber so that the blades of the turbines are not eroded. For this, it is necessary to ensure proper cleaning of the combustion gases from fine ash and dust. Before the gas enters the turbine, it is purified with help of the various flyash collectors. The use of coal as a fuel of open cycle gas turbine is under the development. Coal is burnt in two methods. In the first method, the coal is completely or partially gasified and fuel gas produced is supplied to gas turbine combustor. In other method, pressurized bubbling or circulating fluidized bed, where fuel gas, after it is adequately filtered, expands in the gas turbine. Coal is usually considered as a gas turbine fuel in combined cycle power plant.

Liquid oil like kerosene, gasoline, etc. are easily used in a gas turbine combustor. Residual oils can be used as fuel in gas turbine. If the viscosity of the oil is high, some heating arrangement required.

What are the pros and cons of using closed cycle gas turbines?

As we know that in open cycle gas turbine power plant, the fuel is mixed with air in the combustion chamber and the combustion gases are expanded in the gas turbine which causes erosion and corrosion of turbine blades and therefore it is necessary to use fuel superior quality in the combustion chamber in order to minimize erosion and corrosion. This negative effect overcome in case closed gas turbine power plant. In the closed gas turbine power plant, the same air or working fluid is circulated over and over again. The working medium is not mixed with fuel, but it is heated by the burning of fuel in a separate supply of air in the combustion chamber and the transferring this heat to the working fluid which passes through tubes fitted in the combustion chamber. The working fluid does not come in to direct contact with products of combustion. The other disadvantage of open cycle gas turbine gas turbine plant is that the turbine exhaust is discharged into the atmosphere resulting in rejection of heat of exhaust gases to the atmosphere. In case of closed cycle these heat are recovered in a heat exchanger or recooler.

The working fluid (air or any other suitable gas such as helium, argon, hydrogen, and neon) coming out from compressor is heated in the heat exchanger (heater) by an external source at constant pressure. The high temperature and high pressure air coming out from the external heater is passed through the gas turbine. The working fluid coming out from the turbine is cooled to its original temperature in the heat exchanger (cooler) using external heating source before passing in the compressor. In the closed cycle, the working fluid is continuously circulated through compressor, cooler, heater and turbine without its change of phase, the required heat addition and rejection taken place in the heater and cooler respectively.

The performance characteristics, component elements and analysis for open cycle apply equally as well as to the closed cycle gas turbine.

Advantages of closed cycle over open cycle:
1) In the closed cycle gas turbine, the working medium is heated externally and the fuel does not mix with it, hence any inexpensive solid fuel such as coal can be used to heat the working fluid. Also need for filtration of the incoming air is completely eliminated.
2) They are kept free from product of combustion. Hence absence of corrosion and abrasion of the interiors of turbines and compressors extends the life of the plant and maintains the efficiency of the plant constant throughout its life.
3) The working medium is at relatively high internal pressure. So, specific volume is less and the dimensions of the compressors and turbines can be reduced and the maximum unit capacity can be increased. 
4) A working medium such as helium, argon, hydrogen, neon may be used which has very good physical properties compared to those of air. For example thermal conductivity of hydrogen is about 6.8 times that of air and therefore require smaller heat exchanger.
5) The closed cycle can be operated with highest efficiencies in comparison to open cycle plants at an equal initial temperature of working fluid.
6) The power output at constant speed can be varied by adding or substracting the working fluid and thus altering the weight of the charge. This gives improved part load efficiency as compared to open cycle gas turbine.
7) High heat transfer can be possible

Disadvantages of closed cycle:
1) In closed cycle gas turbine considerable quantity of cooling water is required.
2) Heat addition to the working medium takes place through heat exchanger, hence full heat of fuel fired is not utilized.
3) Additional equipments such as externally fired heater, cooler are required, the plant and its operation makes additional complexity.

Essential hydraulics fluid power basic

FLUID POWER SYSTEM

Fluid power system is power transmission system in which, the transmission of power takes place by means of “oil under pressure” or “compressed air”.

If “oil under pressure” is used in the system for power transmission, then the system is called “hydraulic system”.

If “compressed air” is used in the system for the power transmission then the system is called “pneumatic system”.

If large force and low speed is needed, then hydraulic system should be selected.

Because, oil is incompressible. Its volume will not change with increase in pressure. Pressure can be increased to any amount, nothing happens to volume of oil.

More the pressure of oil, more will be the force developed.

Hydraulic systems are slower in operation because, oil has more viscosity. Oil can not flow fast as compressed air.

If less force and higher speed is required, then pneumatic system should be selected.

As air is compressible in nature, it can not be pressurized to large amount of pressure. Since the pressure of compressed air is less (about 10 bar), force developed is also less.

Pneumatic systems are faster in operation because, air has very less viscosity. It can flow very quickly. Air rushes in to the cylinder once the valve is opened and within no time, the cylinder extends.

If compressed air is readily available in the industry, then pneumatic system is preferred.

In many industries, air compressed plant is already installed, as compressed air is needed for different processes. In such case, we can use the compressed air for operating pneumatic system.

Advantage of fluid power system:

1.       Fluid power system avoids mechanical linkage (such as belts pulley, chains, sprockets, gears etc.) to a greater extent.

2.       Hence, breakdowns are reduced and production will increase.

3.       “design and construction” of fluid power system is easy, simple and compact, as pipes are flexible, can be bent and accommodated in the available space.

4.       Automatic and safety circuits are possible, which is very important to increase rate of production and safety to avoid accidents.

5.       Fluid power system are more flexible to cope-up with the design changes. Any modification in design can easily in the existing and the fluid power system.

6.       Vibration and noise, wear ad ear etc. are reduced, as the mechanical linkages are replaced by the pipes.

7.       If overloaded, the system stalls, the system starts working once the load is reduced.

8.       Maintenance, servicing, lubrication etc. are simple and easy.

What can a jobless mechanical engineering fresher in India do to get hired if he has a good knowledge of AutoCAD, catia and ansys?

well, before i give answer of question, i want to say that Mechanical engineer are awesome. being Mechanical engineer is not a joke. only smart and hard working person can become an engineer. and you have good knowledge of AutoCAD, catia and ansys which is your plus point. but you want job. and before you get job all you have to take care is “Apply to company only if they really require your expertise”. other wise you have some other option such as:

• go to foreign and use your skill to help those companies which really require your skills.
• prepare for government exams and you are engineer so you have habit of studying hard so it will be very easy as compare to other graduates to crack exam.
• open classes for engineering students and start teaching AutoCAD, catia & ansys and also start taking orders from other industries for designing.
• analyze your situation and situation of market by using your operation research skills which you already studied during your engineering and take decision. you should proud of having knowledge of everything and being scientist of Mechanism.

open cycle gas turbine power plant

A simple cycle gas turbine consists of a (1) compressor, (2) combustion chamber and (3) gas turbine.

In the open cycle gas turbine, ambient air enters at the compressor and after the compression of air, fuel is burned in the air itself to raise it to high temperature and then product of combustion are passed on to the turbine for expansion. After delivering the work combustion products are finally rejected to atmosphere. In the open cycle the working medium is continuously replaced by fresh air and fuel. It works on the joule cycle and Brayton cycle.

The air is sucked in by the compressor from the atmosphere through the filter which removes the dust from the air. The rotary blades of the compressor push the air between the stationary blades to raise its pressure to 4-5 atmosphere. Hence the air is available at high pressure at output of the compressor. Then high pressure air passes through combustion chamber, in which heat added to the air at constant pressure by burning the fuel and raises temperature (about 1650) of working medium. This high temperature must be brought down to the level so that the thermal stresses in the turbine blades do not become excessive. This is achieved by allowing the reminder air to enter the combustion chamber at downstream to mix and cool down the combustion gases. The products of combustion comprising of mixture of gases at high pressure and temperature are passes through the gas turbine. These gases in passing over the turbine blades expand and thus result in motion of rotor and finally discharged to the atmosphere at the temperature about 540.

Advantage of open cycle:

         I.            Simplicity: There are only few rotating parts as turbine, compressor and gear train driving the auxilliaries. Hence problem of vibration and lubrication is not so severe. The ignition system is also simple compared to closed cycle.

       II.            Flexibility: since different processes within the cycle take part in separate components, a great variety in the arrangement of the system is possible.

     III.            Low weight and size: The weight in kg. per KW developed is less.

    IV.            Independent system: Open cycle gas turbine power plant, except those having intercooler, does not require cooling water. There fore the plant is independent of cooling medium and becomes self-contained.

      V.            Fuels: Almost any hydrocarbon fuel from high octane gasoline to heavy diesel oils including some solid fuels can be burned in the combustion chamber.

    VI.            Warm-up time: After the turbine has been brought up to speed by the starting motor and the fuel ignited the gas turbine will accelerate from cold start to full load without a warm up time. This is particularly important in stand by emergency plants.

Disadvantage of open cycle:

            I.            Part load performance: The part load efficiency of the open cycle plant decreases rapidly as the considerable percentage of power developed by the turbine, is used to drive the compressor. Also, the system is sensitive to the changes in components efficiency.

          II.            Sensitivity: Since system sensitive to the component efficiency, particularly that of compressor. The efficiency of compressor is affected by change in the atmospheric conditions such as temperature ad humidity of air at the inlet and foreign matter contained in the air.

        III.            High air rate: The simple open cycle gas turbine has a very high air rate as compared to other prime movers. However, the air rate may be lowered by intercooling and reheating.

       IV.            Erosion and corrosion: The working fluid is mixture of air and fuel. Since air contains dirt being deposited on the compressor blades. Due to carbon and other foreign deposits from combustion in the combustion chamber, turbine and regenerator, it is necessary that the dust should be prevented from entering into the compressor in order to minimized erosion and depositions on the blades and passages of the compressor and turbine.

         V.            In the simple open cycle, the turbine exhaust is discharged into atmosphere. Since turbine exhaust contain large amount of heat resulting in loss of heat.

Classification of Gas Turbine Power Plant

The gas turbine can be classified as follows:

1)      According to types of combustion process

                                 I.            Constant volume or explosion type gas turbine: This type of Gas turbine works on Atkinson cycle in which combustion of air fuel mixture is takes place at constant volume, hence air and fuel mixture should be isolated from compressor. This is possible by valves in the combustion chamber, resulting in an intermittent combustion which inherently impairs smooth running of machine. This type of turbine has better thermal efficiency than a constant pressure cycle gas turbine. The main disadvantages of this type of gas turbine is that complexity in mechanical system and pressure difference and velocity of hot gases are not constant, so turbine speed fluctuates. The constant volume combustion type gas turbine is not popular in practical use. The constant volume gas turbines are absolute in use.

                               II.            Constant pressure or continuous combustion type gas turbine: This type of gas turbine works on Brayton cycle in which combustion of air fuel mixture is takes place at constant pressure.

2)      According to direction of flow

                                 I.            Axial flow gas turbine

                               II.            Radial flow gas turbine.

3)      According to action of expanding gases

                                 I.            Impulse gas turbine

                               II.            Impulse- Reaction gas turbine

4)      According to path of working substance

                                 I.            Open cycle gas turbine plants: In the open cycle gas turbine, ambient air enters at the compressor and after the compression of air, fuel is burned in the air itself to raise it to a high temperature and then product of combustion is passed on to the turbine for expansion and which after delivering the work are finally ejected to atmosphere. In the open cycle the working medium is continuously replaced by fresh air and fuel.

                               II.            Closed cycle gas turbine plants: In the closed cycle gas turbine power plant, the same air or the working fluid is circulated over and over again. The working medium is not mixed with fuel, but it is heated by the burning of fuel in separate supply of air in the combustion chamber and transferring this heat to the working fluid which passes through tubes fitted in the combustion chamber. The working fluid does not come into direct constant with product of combustion.

                             III.            Semi-closed cycle gas turbine plants: Semi-closed cycle gas turbine plant is combination of open and closed cycle, in which some part of working fluid is recirculated to the plant and another part of working fluid flows into and from the atmospheric air.

5)      According to thermodynamic cycle

                                 I.            Simple cycle

                               II.            Simple cycle with intercooling: in which the air is cooled between stages of compression.

                             III.            Simple cycle with regeneration: in which the air after compression is heated with help of exhaust gases coming from turbine.

                            IV.            Simple cycle with reheating: in which combustion products (gases) after part of expansion in high pressure turbine is reheated in second combustion chamber and then it is expanded in the low pressure turbine.

                              V.            Simple cycle with intercooling, regeneration and reheating.

6)      According to shaft configuration

                                 I.            Single shaft engine: - Examples: Turbojet engine, Turboshaft engine.

                               II.            Multi-shaft engine: - Example: Two shaft engine with power turbine, Turbojet engine, industrial slit shaft engine, Twin-spool engine.

7)      According to applications

                                 I.            Power or industrial gas turbines

                               II.            Aviation or aircraft turbines