Ingenieria

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  • Publicado : 24 de agosto de 2012
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Table of content

Nomenclature……………………………………………………………………………………4
Introduction………………………………………………………………………………………5
Theory……………………………………………………………………………………………5
Impulse stage……………...………………………………………………………………………7
Discussion and results……………………………………………………………………………12
Final Design…………...…………………………………………………………………………15
References………………………………………………………………………………………16

Nomenclature
Symbols |Description of each symbol | Units |
Δh | Change in Enthalpy | Btu/lbm |
ν | Specific volume | ft3/lbm |
ѡ | Stage work | Btu/lbm |
m | Mass Flow Rate | lbm/s |
g | Gravitational constant | ft/s2 |
c | Conversion Factor | lbm.ft |
ѡnet | Net work | Btu/lbm |
Wnet | Energy flow rate | KW |
rm | Mid-radius | ft |
η | Stage Efficiency | --- |
ѱ | Loading factor | --- |
V |Absolute Velocity | ft/s |
W | Relative Velocity | ft/s |
U | Blade Velocity-Inlet to stator | ft/s |
α | Angle made by absolute and relative velocities | (°)Degrees |
β | Angle made by absolute and relative velocities | (°) Degrees |

Introduction
In a previous project, we analyzed and design a steam power plant, where we were focus in optimized the efficiency of a steam power plantincluding open feed water heaters. In the following project, our aim is to design an impulse stage for a steam turbine that is used in a power plant that is based in the Rankin cycle. Since we are looking for an optimized type of energy generation, the impulse stage in a steam turbine plays an important role to obtain higher effectiveness. The same constraints used to design the steam power plant andimportant results such as the mass flow rate and the net work needed to run the power plant will be used to design the impulse stage for the steam turbine. In this project, we will find the number of blades, their size, and the angle of position that will give the best efficiency in the impulse stage.
Theory

Figure 1. Axial Flow in a Rotor.
The porpuse of a steam turbine is to convert theenergy that a continous flow of a fluid has into a rotational mechanical energy obtained from the movement of a shaft. This means that a steam turbine can be divided in two parts, whereas the first part converts the heat from the steam to kinetic energy and the second part converts the kinetic energy to work. To do this, the steam turbine must be divided in a series of stages that makes
possiblethe convertion from heat to work. A stage is composed by a stator and rotor, this means that the turbine has multiple stages due to the distribution of the energy along the turbine. A stator consists of stationary nozzles or vanes while the rotor is made up of a shaft, disc and many blades. In the stator the heat is converted into kinetic energy, while in the rotor the kinetic energy isconverted into work through the shaft. There are two types of stages, impulse stage and reaction stage. In the impulse stage most of the heat is transformed to work, nevertheless, it has a lower efficiency compared to the reaction stages. Usually, in large turbines the impulse stage is the first stage followed by a series of various reaction stages. The impulse is really important in the design of aturbine due to its contribution to the overall size of the turbine; the impulse can influence the diameter and the length of the entire turbine. A steam turbine is a complex machine, that depending on the application, it can be divided in different blocks that determine the high pressure (HP), intermediate pressure (IP) , and low pressure (LP) ranges, which make the entire design a challenging and longprocess. Consequently, we will be focus in the design of the impulse stage. The analysis and design of the impulse stage is based in the concept of cascade that consists in the analysis of the blade profile and the space between the blades. This method focuses on identical profile and equally spaced blades extending to infinity. Since the rotor is continuously rotating the number of blades...
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