Wednesday, September 26, 2012

What is Management?


Management:
Management is a universal phenomenon. It is a very popular and widely used term. All organizations – business, political, cultural, or social are involved in management because it is the management which helps and directs the various efforts towards a definite purpose.
According to Harold Koontz, “Management is an art of getting things done through and with the people in formally organized groups. It is an art of creating an environment in which people can perform and individuals and can co-operate towards attainment of group goals.”
According to F.W. Taylor, “Management is an art of knowing what to do, when to do and see that it is done in the best and cheapest way.”
Management is a purposive activity. It is something that directs group’s efforts towards the attainment of certain Pre-determined goals. It is the process of working with and through others to effectively achieve the goals of the organization, by efficiently using limited resources in the changing world. Of course, these goals may vary form one enterprise to another. E.g. For one enterprise it may be launching of new products by conducting market surveys and for other it may be profit maximization by minimizing cost.
Management involves creating an internal environment. It is the management which puts into use the various factors of production. Therefore, it is the responsibility of management to create such conditions which are conducive (beneficial) to maximum efforts so that people are able to perform their task efficiently and effectively. It includes ensuring (conforming) availability of raw materials, determination of wages and salaries, formulation of rules and regulations etc.

Importance of management:
It helps in achieving group goals:
 It arranges the factors of production, assembles and organizes the resources, integrates the resources in effective manner to achieve goals. It directs group efforts towards achievement of pre-determined goals. By defining objective of organization clearly there would be no waste of time, money, and effort. Management convers disorganized resources of men, machines, money etc. into useful enterprise. These resources are coordinated, directed and controlled in such a manner that enterprise work towards attainment of goals.
Optimum Utilization of Resources:
Management utilizes all the physical and human resources productively. This leads to efficacy (efficiency) in management. Management provides maximum utilization of scarce (rare) resources by selecting its best possible alternate use in industry from out of various uses. It makes use of experts, professional and these services leads to use of their skills, knowledge, and proper utilization and avoids wastage. If employees and machines are producing its maximum there is no under employment of any resources.
Reduces costs:
It gets maximum results through minimum input by proper planning and by using minimum input and getting maximum output. Management uses physical, human, and financial resources in such a manner which results in best combination. This helps in cost reduction.
Establishes sound organization:
No overlapping of efforts (smooth and coordinated functions). To establish sound organizational structure is one of the objectives of management which is in tune with objective of organization and for fulfillment of this, it establishes effective authority and responsibility relationship i.e. who is accountable to whom, who can give instructions to whom, who are superiors and who are subordinates. Management fills up various positions with right persons, having right skills, training, and qualification. All jobs should be cleared to everyone.
Establishes equilibrium:
It enables the organization to survive in changing demand of keeps in touch with the changing environment. With the change in external environment, the initial co-ordination of organization must be changed. So it adapts organization to changing demand of market/ changing need of societies. It is responsible for growth and survival of organization.
Essentials for prosperity of society:
Efficient management leads to better economical production which helps in turn to increase the welfare of people. Good management makes a difficult task easier by avoiding wastage of scarce resource. It improves standard of living. It increases the profit which is beneficial and society will get maximum output at minimum cost by creating employment opportunities which generate income in hands. Organization comes with new products and researches beneficial for society.

Tuesday, July 10, 2012

Cavitation in hydraulic turbine: causes and effects


Cavitation in hydraulic turbine: causes and effects
Cavitation is formation of vapor bubbles in the liquid flowing through any Hydraulic Turbine. Cavitation occurs when the static pressure of the liquid falls below its vapor pressure. Cavitation is most likely to occur near the fast moving blades of the turbines and in the exit region of the turbines

Causes of Cavitation

The liquid enters hydraulic turbines at high pressure; this pressure is a combination of static and dynamic components. Dynamic pressure of the liquid is by the virtue of flow velocity and the other component, static pressure, is the actual fluid pressure which the fluid applies and which is acted upon it. Static pressure governs the process of vapor bubble formation or boiling. Thus, Cavitation can occur near the fast moving blades of the turbine where local dynamic head increases due to action of blades which causes static pressure to fall. Cavitation also occurs at the exit of the turbine as the liquid has lost major part of its pressure heads and any increase in dynamic head will lead to fall in static pressure causing Cavitation.

Detrimental Effects of Cavitation

The formation of vapor bubbles in cavitation is not a major problem in itself but the collapse of these bubbles generates pressure waves, which can be of very high frequencies, causing damage to the machinery. The bubbles collapsing near the machine surface are more damaging and cause erosion on the surfaces called as cavitation erosion. The collapses of smaller bubbles create higher frequency waves than larger bubbles. So, smaller bubbles are more detrimental to the hydraulic machines.

Smaller bubbles may be more detrimental to the hydraulic machine body but they do not cause any significant reduction in the efficiency of the machine. With further decrease in static pressure more number of bubbles is formed and their size also increases. These bubbles coalesce with each other to form larger bubbles and eventually pockets of vapor. This disturbs the liquid flow and causes flow separation which reduces the machine performance sharply. Cavitation is an important factor to be considered while designing Hydraulic Turbines.

Avoiding Cavitation

To avoid cavitation while operating Hydraulic Turbines parameters should be set such that at any point of flow static pressure may not fall below the vapor pressure of the liquid. These parameters to control cavitation are pressure head, flow rate and exit pressure of the liquid. The control parameters for cavitation free operation of hydraulic turbines can be obtained by conducting tests on model of the turbine under consideration. The parameters beyond which cavitation starts and turbine efficiency falls significantly should be avoided while operation of hydraulic turbines.

Flow separation at the exit of the turbine in the draft tube causes vibrations which can damage the draft tube. To dampen the vibration and stabilize the flow air is injected in the draft tube. To totally avoid the flow separation and cavitation in the draft tube it is submerged below the level of the water in tailrace.

Pelton Turbine


Pelton Turbine

In a Pelton Turbine or Pelton Wheel water jets impact on the blades of the turbine making the wheel rotate, producing torque and power. Learn more about design, analysis, working principle and applications of Pelton Wheel Turbine.

Hydraulic Turbines are being used from very ancient times to harness the energy stored in flowing streams, rivers, and lakes. The oldest and the simplest form of a Hydraulic Turbine was the Waterwheel used for grinding grains. Different types of Hydraulic Turbines were developed with the increasing need for power. Three major types are Pelton Wheel, Francis, and Kaplan Turbine.

Design of Pelton Wheel Turbine

The Pelton Turbine has a circular disk mounted on the rotating shaft or rotor. This circular disk has cup shaped blades, called as buckets, placed at equal spacing around its circumference. Nozzles are arranged around the wheel such that the water jet emerging from a nozzle is tangential to the circumference of the wheel of Pelton Turbine. According to the available water head (pressure of water) and the operating requirements the shape and number of nozzles placed around the Pelton Wheel can vary.


Working Principle of Pelton Turbine

The high speed water jets emerging form the nozzles strike the buckets at splitters, placed at the middle of a bucket, from where jets are divided into two equal streams. These stream flow along the inner curve of the bucket and leave it in the direction opposite to that of incoming jet. The high speed water jets running the Pelton Wheel Turbine are obtained by expanding the high pressure water through nozzles to the atmospheric pressure. The high pressure water can be obtained from any water body situated at some height or streams of water flowing down the hills.
The change in momentum (direction as well as speed) of water stream produces an impulse on the blades of the wheel of Pelton Turbine. This impulse generates the torque and rotation in the shaft of Pelton Turbine. To obtain the optimum output from the Pelton Turbine the impulse received by the blades should be maximum for that, change in momentum of the water stream should be maximum possible. That is obtained when the water stream is deflected in the direction opposite to which it strikes the buckets and with the same speed relative to the buckets.
Pelton Turbine Hydroelectric Setup

A typical setup of a system generating electricity by using Pelton Turbine will have a water reservoir situated at a height from the Pelton Wheel. The water from the reservoir flows through a pressure channel to the penstock head and then through the penstock or the supply pipeline to the nozzles, from where the water comes out as high speed jets striking the blades of the Pelton Turbine. The penstock head is fitted with a surge tank which absorbs and dissipates sudden fluctuations in pressure.


For a constant water flow rate from the nozzles the speed of turbine changes with changing loads on it. For quality hydroelectricity generation the turbine should rotate at a constant speed. To keep the speed constant despite the changing loads on the turbine water flow rate through the nozzles is changed. To control the gradual changes in load servo controlled spear valves are used in the jets to change the flow rate. And for sudden reduction in load the jets are deflected using deflector plates so that some of the water from the jets does not strike the blades. This prevents over speeding of the turbine.

Kaplan Turbine


Kaplan Turbine

Kaplan Turbine is designed for low water head applications. Kaplan Turbine has propeller like blades but works just reverse. Instead of displacing the water axially using shaft power and creating axial thrust, the axial force of water acts on the blades of Kaplan Turbine and generating shaft power.

Most of the turbines developed earlier were suitable for large heads of water. With increasing demand of power need was felt to harness power from sources of low head water, such as, rivers flowing at low heights. For such low head applications Viktor Kaplan designed a turbine similar to the propellers of ships. Its working is just reverse to that of propellers. The Kaplan Turbine is also called as Propeller Turbine.

Design of Kaplan Turbine

To generate substantial amount of power from small heads of water using Kaplan Turbine it is necessary to have large flow rates through the turbine. Kaplan Turbine is designed to accommodate the required large flow rates. Except the alignment of the blades the construction of the Kaplan Turbine is very much similar to that of the Francis Turbine. The overall path of flow of water through the Kaplan Turbine is from radial at the entrance to axial at the exit. Similar to the Francis Turbine, Kaplan Turbine also has a ring of fixed guide vanes at the inlet to the turbine.


Unlike the Francis Turbine which has guide vanes at the periphery of the turbine rotor (called as runner in the case of Francis Turbine), there is a passage between the guide vanes and the rotor of the Kaplan Turbine. The shape of the passage is such that the flow which enters the passage in the radial direction is forced to flow in axial direction. The rotor of the Kaplan Turbine is similar to the propeller of a ship. The rotor blades are attached to the central shaft of the turbine. The blades are connected to the shaft with moveable joints such that the blades can be swiveled according to the flow rate and water head available.
The blades of the Kaplan Turbine are not planer as any other axial flow turbine; instead they are designed with twist along the length so as to allow swirling flow at entry and axial flow at exit.

Working of the Kaplan Turbine

The working head of water is low so large flow rates are allowed in the Kaplan Turbine. The water enters the turbine through the guide vanes which are aligned such as to give the flow a suitable degree of swirl determined according to the rotor of the turbine. The flow from guide vanes pass through the curved passage which forces the radial flow to axial direction with the initial swirl imparted by the inlet guide vanes which is now in the form of free vortex.

The axial flow of water with a component of swirl applies force on the blades of the rotor and loses its momentum, both linear and angular, producing torque, and rotation (their product is power) in the shaft. The scheme for production of hydroelectricity by Kaplan Turbine is same as that for Francis Turbine.