Types of Forces and Newton's Laws of Motion in a Steam Turbine - Essay Example

Types of Forces and Newtons Laws of Motion in a Steam Turbine The fundamental definition of force in physics is thatit is a pull or a push acting on an object. Forces in physics play important roles in various fields without which life could be difficult because of careful work. In essence, therefore, through force, work is made easier. Steam turbines are devices for obtaining mechanical work from the energy stored in steam (Woodruff 32). High energy steam enters the turbine and leaves after giving up much of the energy. This high-pressure steam is expanded in nozzles creating a high-velocity jet of steam that in turn converts the heat energy available in steam into kinetic energy. Centrifugal pumps also called displacement pumps employ the concepts of forces in physics in their operation (eHow par 5). Newtons laws of motion which are useful in the analysis of the operation of centrifugal pumps are derivatives of force. Steam turbines apply the basic principles of thermodynamics in their operation. Superheated steam at high temperature and pressure enters the turbine. There are two main types of turbines based on the forces that act on them, to turn the turbine wheel, namely; Impulse turbines and Reaction turbines. The high energy steam is converted into kinetic energy using nozzles in impulse based turbines. For a reaction turbine, the steam is converted into kinetic energy that is sent to the blades of the turbine. A force created on the blades due to the difference in pressure provided motion to the turbine. If a generator is attached to the shaft of the turbine, electricity is produced stored and utilized in various appliances. Applying the first law of thermodynamics the rate at which work is developed per unit mass can be obtained assuming there is no heat transfer to the immediate environment and that there is no net that kinetic energy and potential energies in comparison to the specific enthalpy of the system (eHow par. 7) The following diagrams show the basic features of a steam turbine According to Newtons second law of motion, the change in momentum produces impulsive force, a force that acts on a body for a short time creating an enormous change in momentum (Woodruff 33). These impulse turbines are made up of rings of nozzles followed by rings of blades. Notably, high pressure, high energy steam is allowed into the nozzles then it is let into a region of lower pressure, high velocity in a different direction. As a result, the changing direction and high velocity produce impulsive force that acts in the direction of rotation of the turbines. Thus according to Newtons second law of motion, the rate of change in momentum is directly proportional to the external force producing the change and it takes place in the direction of the force (Woodruff 32). A notable feature of the Impulse turbine is the presence of fixed nozzles that orient the steam flow into high-speed jets (Wikipedia par. 3). These jets contain significantly high kinetic energy which is transferred to the turbine to cause shaft rotation. A drop in pressure across the stationary blades with a net increase in steam velocity occurs. As a result, as the steam passes through the nozzles its pressure decreases from the inlet as it advances to the exit. As a result of the high ratio expansion of the steam, the steam leaves the nozzle at very high velocity and as such, a significant portion of maximum velocity in the steam leaves to the moving blades. Furthermore, the law of moment of momentum requires that moments of external forces acting on a fluid occupying the control volume be equal to the net time change of angular momentum flux through the control volume. The net loss in the energy due to the high exit velocity is commonly termed as carry over velocity useful in understanding the operation of the turbine (eHow par. 2). The second type of steam turbines based on forces that act on them are the Reaction turbines. These turbines primarily apply Newton’s third law of motion that states that for every action force there is always reaction force. These type of turbines are made up of rings of fixed blades to the casing. A row of blades is tightly mounted on the rotor of the turbine (Woodruff par. 4). These blades are shaped in such a way that they provide a narrowing passage which behaves like a nozzles. Therefore, increasing the velocity of steam it is important to notice that the increase in velocity of steam results in change in direction and an impulsive force is created and therefore the more correct name for this type of turbines is impulse- reaction because the two types of forces are experienced simultaneously. In addition, reaction turbine consists of rotors blades arranged to form convergent nozzles. As the steam accelerates through this nozzle, Newton’s third law of motion comes into play producing a reaction force due to incident steam. The steam is directed onto the rotor by fixed constant vanes of the stator. As it leaves the stator, it creates a jet that covers the entire circumference of the rotor. As explained above the steam then changes direction and increases its speed in relation to the speed of the blades of the turbine. A pressure decline across both the rotor on which steam decelerates and the stator through which steam accelerates indicating the amount of work done in driving the turbine. The effect of expansion of steam over the moving blades is an increase in the velocity at the exit end. This implies that for good efficiency, the relative velocity at the exit is always bigger than the relative velocity at the inlet (Woodruff 36). Lastly, Newton’s first law of motion is equally useful in understanding the operation of a steam turbine. This law states that the body will always remain in its state of rest or if moving, it continues moving steadily or in a straight line unless acted upon by external forces. The first part of the law is evident from daily experience for instance, a coin resting on the floor shall remain there unless force acts on it. The second part of the law useful for Steam turbines states that if it is set in motion and left to move, it virtually keeps on moving unless an external force such as friction acts. From this understanding then, if friction is eliminated when the turbine is in motion, it is possible to have the turbine running forever with undiminished velocity (Woodruff par. 6). Thus to increase efficiency of turbines, practices such as lubrication are adopted in steam turbines. In conclusion, therefore modern turbines employ both impulse and reaction forces and concepts in varying degrees. It is important to notice that Newton’s second law describes the transfer of energy for impulse turbines. Turbines with multiple stages may employ either reaction or impulsive forces at high pressure. Steam turbines that traditionally are known to have more impulse than reaction are evolving into reaction turbines similar to those applied in gas turbines. Furthermore, these turbines employ the fundamental laws of thermodynamics in their operation and the understanding of the relationship between enthalpy and the work done by the system. In addition, Velocity triangles and Newtons laws of motion are useful in understanding the basic performance principles of the turbines and enable manufacturers to improve their efficiency (eHow par. 4). Work Cited eHow. “How a steam turbine works”, 2014. Web. 22 November, 2014. www.ehow.com/how does_501161_how turbine-pumps- work.html Wikipedia. “Steam turbine”, 17th November, 2014. Web. 22 November, 2014. http//en.wikipedia.org/wiki/steam_turbine. Woodruff, Everett B, Herbert B. Lammers, and Thomas F. Lammers. Steam Plant Operation. New York: McGraw-Hill, 2012. Print. [4] [5]http://www.aircav.com/histturb.html Read More