Introduction of Turbo Machinery

Turbo machinery is mainly of two types, one that add  energy (Pumps), and other that extract energy (Turbines). The prefix turbo- is a Latin word which means  “spin’’ or “whirl,’’.



The pump is the oldest fluid-energy-transfer device known. At least two designs
date before Christ: (1) the undershot-bucket waterwheels, or norias, used in Asia and Africa (1000 B.C.) and (2) Archimedes’ screw pump (250 B.C.), still being manufactured today to handle solid-liquid mixtures. Paddlewheel turbines were used by the Romans in 70 B.C., and Babylonian windmills date back to 700 B.C.









Machines which deliver liquids are simply called pumps, but if gases are involved,
three different terms are in use, depending upon the pressure rise achieved. If the pressure rise is very small (a few inches of water), a gas pump is called a fan; up to 1 atm, it is usually called a blower; and above 1 atm it is commonly termed a compressor.

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Rivet Types

The standard structural or machine rivet has a cylindrical shank and is either hot- or cold-driven.
Following are types of rivets.

Various Types of Rivets

(a) Counter Sunk Head.

(b) Counter sunk Head with chamfered top.

(c) Counter sunk Head with round top.

(d) Globe head.

• Boiler Rivet:It is simply a large rivet with cone head.
• Cooper's Rivet:  A cooper's rivet, used for barrel-hoop joints, is a solid rivet with a head like that is in figure below which has a shank end that is chamfered.

 

• Shoulder Rivet: A shoulder rivet has a shoulder under the head.
• A tank rivet, used for sheet-metal work, is a solid rivet with a button, countersunk, flat, or truss head.
• A tinner's rivet, used for sheet-metal work, is a small solid rivet with a large flat head.
• A compression or cutlery rivet consists of a tubular rivet and a solid rivet. The hole and shank are sized to produce a drive fit when the joint is assembled.
• A blind rivet is intended for use where only one side of the joint is within reach. The blind side is the side that is not accessible.

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Rivets

A rivet is a fastener that has a head and a shank and is made of a deformable material. It is used to join several parts by placing the shank into holes through the several parts and creating another head by upsetting or deforming the projecting shank.

 

Advantages of Rivets:

• Low cost
•  Can be used to fasten automatic or repetitive assembly
•  Permanent joints
•  Usable for joints of unlike materials such as metals and plastics
•  Wide range of rivet shapes and materials

•  Large selection of riveting methods, tools, and machines 

Riveted joints, however, are not as strong under tension loading as are bolted
joints and the joints may loosen under the action of vibratory tensile or shear forces acting on the members of the joint. Unlike with welded joints, special sealing methods must be used when riveted joints are to resist the leakage of gas or fluids.

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Mechanical Engineering by Shigley

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Equation of Continuity

The continuity equation is simply a mathematical expression of the principle of conservation of mass. For a control volume that has a single inlet and a single outlet, the principle of conservation of mass states that, for steady-state flow, the mass flow rate into the volume must equal the mass flow rate out. The continuity equation for this situation is expressed by Equation below

 

For a control volume with multiple inlets and outlets, the principle of conservation of mass requires that the sum of the mass flow rates into the control volume equal the sum of the mass flow rates out of the control volume. The continuity equation for this more general situation is expressed by Equation given below.

 

One of the simplest applications of the continuity equation is determining the change in fluid velocity due to an expansion or contraction in the diameter of a pipe.

 

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Heat Exchangers

Heat exchangers are devices that are used to transfer thermal energy from one fluid to another without mixing the two fluids.

The transfer of thermal energy between fluids is one of the most important and frequently used processes in engineering. The transfer of heat is usually accomplished by means of a device known as a heat exchanger. Common applications of heat exchangers in the nuclear field include boilers, fan coolers, cooling water heat exchangers, and condensers. The basic design of a heat exchanger normally has two fluids of different temperatures separated by some conducting medium. The most common design has one fluid flowing through metal tubes and the other fluid flowing around the tubes. On either side of the tube, heat is transferred by convection. Heat is transferred through the tube wall by conduction.

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Radiant Heat Transfer

Radiant heat transfer is thermal energy transferred by means of electromagnetic
waves or particles.

Radiant heat transfer involves the transfer of heat by electromagnetic radiation that arises due to the temperature of a body. Most energy of this type is in the infra-red region of the electromagnetic spectrum although some of it is in the visible region. The term thermal radiation is frequently used to distinguish this form of electromagnetic radiation from other forms, such as radio waves, x-rays, or gamma rays. The transfer of heat from a fireplace across a room in the line of sight is an example of radiant heat transfer.


Radiant heat transfer does not need a medium, such as air or metal, to take place. Any material that has a temperature above absolute zero gives off some radiant energy. When a cloud covers the sun, both its heat and light diminish. This is one of the most familiar examples of heat transfer by thermal radiation.

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Convection

Heat transfer by convection is more difficult to analyze than heat transfer by conduction because no single property of the heat transfer medium, such as thermal conductivity, can be defined to describe the mechanism. Heat transfer by convection varies from situation to situation (upon the fluid flow conditions), and it is frequently coupled with the mode of fluid flow. In practice, analysis of heat transfer by convection is treated empirically (by direct observation).

Convection involves the transfer of heat by the motion and mixing of "macroscopic" portions of a fluid (that is, the flow of a fluid past a solid boundary). The term natural convection is used if this motion and mixing is caused by density variations resulting from temperature differences within the fluid. The term forced convection is used if this motion and mixing is caused by an
outside force, such as a pump. The transfer of heat from a hot water radiator to a room is an example of heat transfer by natural convection. The transfer of heat from the surface of a heat exchanger to the bulk of a fluid being pumped through the heat exchanger is an example of forced convection.

Convection heat transfer is treated empirically because of the factors that affect the stagnant film thickness:

• Fluid velocity
• Fluid viscosity
• Heat flux
• Surface roughness
• Type of flow (single-phase/two-phase)

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Conduction Heat Transfer

Conduction involves the transfer of heat by the interaction between adjacent molecules of a material. Heat transfer by conduction is dependent upon the driving "force" of temperature difference and the resistance to heat transfer. The resistance to heat transfer is dependent upon the nature and dimensions of the heat transfer medium. All heat transfer problems involve the temperature difference, the geometry, and the physical properties of the object being studied.

In conduction heat transfer problems, the object being studied is usually a solid. Convection problems involve a fluid medium. Radiation heat transfer problems involve either solid or fluid surfaces, separated by a gas, vapor, or vacuum. There are several ways to correlate the geometry, physical properties, and temperature difference of an object with the rate of heat transfer through the object. In conduction heat transfer, the most common means of correlation is through
Fourier’s Law of Conduction.

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Carnot’s Principle

With the practice of using reversible processes, Sadi Carnot in 1824 advanced the study of the second law by disclosing a principle consisting of the following propositions.

1.  No engine can be more efficient than a reversible engine operating between the same high temperature and low temperature reservoirs. Here the term heat reservoir is taken to mean either a heat source or a heat sink.
2.  The efficiencies of all reversible engines operating between the same constant temperature reservoirs are the same.
3. The efficiency of a reversible engine depends only upon the temperatures of the heat source and heat receiver.

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First Law of Thermodynamics Summary

• The First Law of Thermodynamics states that energy can neither be
created nor destroyed, only altered in form.


• In analyzing an open system using the First Law of Thermodynamics, the energy into the system is equal to the energy leaving the system.

• If the fluid passes through various processes and then eventually returns to the same state it began with, the system is said to have undergone a cyclic process. The first law is used to analyze a cyclic process.


• The energy entering any component is equal to the energy leaving that component at steady state.

• The amount of energy transferred across a heat exchanger is dependent
upon the temperature of the fluid entering the heat exchanger from both
sides and the flow rates of the fluids.

• A T-s diagram can be used to represent thermodynamic processes.

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First Law of Thermodynamics

The First Law of Thermodynamics states:

"Energy can neither be created nor destroyed, only altered in form".
For any system, energy transfer is associated with mass and energy crossing the control boundary, external work and/or heat crossing the boundary, and the change of stored energy within the control volume. The mass flow of fluid is associated with the kinetic, potential, internal, and "flow" energies that affect the overall energy balance of the system. The exchange of external work and/or heat complete the energy balance.






The First Law of Thermodynamics is referred to as the Conservation of Energy principle, meaning that energy can neither be created nor destroyed, but rather transformed into various forms as the fluid within the control volume is being studied. The energy balance spoken of here is maintained within the system being studied. The system is a region in space (control volume) through which the fluid passes. The various energies associated with the fluid are then observed as they cross the boundaries of the system and the balance is made.

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Thermodynamics Processes

A thermodynamic process is the succession of states that a system passes through. Processes can be described by any of the following terms:

Cyclic process - a series of processes that results in the system returning to its original state
Reversible process - a process that can be reversed resulting in no change in the system or surroundings
Irreversible process - a process that, if reversed, would result in a change to the system or surroundings
Adiabatic process - a process in which there is no heat transfer across the system boundaries
Isentropic process - a process in which the entropy of the system remains unchanged
Polytropic process - the plot of Log P vs. Log V is a straight line, PVn = constant

Throttling process - a process in which enthalpy is constant h1 = h2, work = 0, and which is adiabatic, Q=0.

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Temperature and Pressure (Brief)

 Temperature
Temperature is a measure of the molecular activity of a substance. The greater the movement of molecules, the higher the temperature. It is a relative measure of how "hot" or "cold" a substance is and can be used to predict the direction of heat transfer.

Pressure:

Pressure is a measure of the force exerted per unit area on the boundaries of a substance (or system). It is caused by the collisions of the molecules of the substance with the boundaries of the system. As molecules hit the walls, they exert forces that try to push the walls outward. The forces resulting from all of these collisions cause the pressure exerted by a system on its surroundings. Pressure is frequently measured in units of lbf/in2 (psi).

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Thermodynamics Properties in brief

Thermodynamics properties can be mainly classified as :

1. Intensive Properties
2. Extensive Properties

• Intensive properties are those that are independent of the amount of mass.
• Extensive properties are those that vary directly with the mass.

Specific volume  is the total volume (V) of a substance divided by the
total mass (m) of that substance.

• Density is the total mass (m) of a substance divided by the total
volume (V) occupied by that substance.

• Specific gravity (S.G.) is a measure of the relative density of a substance
as compared to the density of water at a standard temperature.

• Humidity is the amount of moisture (water vapor) in the air. It can be
measured in absolute or relative units.

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Mechanical Engineering: How a boiling water reactor works

Mechanical Engineering: How a boiling water reactor works: The basic principle is simple: nuclear energy is used to produce steam, the steam drives a turbine, and the turbine powers a generat...

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How a boiling water reactor works

The basic principle is simple: nuclear energy is used to produce steam, the steam drives a turbine, and the turbine powers a generator, which produces electricity.

Boiling water reactor

In a boiling water reactor, the nuclear reaction heats the water inside the reactor tank, causing it to boil. This creates the steam that drives the turbine. The turbine powers the generator, which in turn produces electricity.The steam is cooled in a condenser, and the resulting water sent back  into the reactor and heated again.

 


The Boiling Water Reactor (BWR)
 (Source: http://www.nrc.gov/reading-rm/basic-ref/students/animated-bwr.html)
 



1. The reactor
Uranium atoms are split inside the reactor, producing heat. This causes the water to boil and turn to steam.
2. The turbine
Steam is released into the turbine, causing the blades to rotate at speeds up to 3,000 rpm.
3. The generator
The turbine powers a generator, which produces electricity.
4. The transformer
A transformer converts the electricity into a high-voltage current. This is then sent to the power grid via high-tension wires.
5. Sea water
To cool the steam back into water, a huge amount of sea water is pumped into the condenser via pipes about the same diameter as a finger. When this water is pumped back into the sea, it is about ten degrees warmer than it was before it entered the condenser. The sea water circulates through a closed system, and never comes in contact with the reactor water.
6. The condenser
In the condenser, the cold water running through the pipes cools the steam into water. This is pumped back into the reactor.

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