Centrifuge

    A centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and less density. There are many different kinds of centrifuges, including those for very specialised purposes.

     Theory

     Protocols for centrifugation typically specify the amount of acceleration to be applied to the sample, rather than specifying a rotational speed such as revolutions per minute. The acceleration is often quoted in multiples of g, the acceleration due to gravity at the Earth's surface. This distinction is important because two rotors with different diameters running at the same rotational speed will subject samples to different accelerations. The acceleration can be calculated as the product of the radius and the square of the angular velocity.

Compressor

     A compressor is a mechanical device that takes in a medium and compresses it to a smaller volume. Compressors can either increase or decrease a given mass to a lower or higher pressure. A mechanical or electrical drive is typically connected to a pump that is used to compress the medium.

Compressors have many everyday uses, such as:

• Air conditioners, (car, home)
• Air pumps
• Home and industrial refrigeration
• High pressure car washes
• Hydraulic compressors for industrial machines
• Air compressors for industrial manufacturing

     Compressors are used by many industries that depend on the power of compressed gas or fluid to power manufacturing processes of all kinds.

There are several different compressor types:

• Rotary screw compressor
  Two helical rotors force gas into a chamber that decreases in size, thereby increasing the pressure of the gas. The screws in the rotary screw compressor can be lubricated with oil or non-lubricated. Oil-free compressors are used for gas that must remain clean and uncontaminated. Rotary screw compressors are typically sized from 30-200 horsepower.

• Reciprocating compressor
  One or more pistons are moved inside a cylinder to increase the gas pressure. This is similar to a combustion engine without the ignition of fuel. Just like a car, the pistons generate much heat so the reciprocating compressor is typically cooled by air or water. Multi-stage reciprocating compressors pass the compressed gas from one cylinder to another, increasing the pressure in each stage. Most industrial compressors are multi-stage, ranging from one to 500 or more horsepower.

• Centrifugal compressor
  Centrifugal compressors speed up and compress gas via a rotor with blades. Centrifugal force is used to force the air or gas to an outer chamber under higher pressure. Centrifugal compressors are designed to operate above 75-80% speed. Surging can occur below these speeds. This makes the centrifugal compressor ideal for continuous high duty operation.

 

Heat Exchanger

     A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. They are widely used in petroleum refineries, chemical plants, petrochemical plants, natural gas processing, refrigeration, power plants, air conditioning and space heating. One common example of a heat exchanger is the radiator in a car, in which a hot engine-cooling fluid, like antifreeze, transfers heat to air flowing through the radiator.

     Flow arrangement

     Heat exchangers may be classified according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is most efficient, in that it can transfer the most heat. See countercurrent exchange. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger.

     For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the exchanger. The exchanger's performance can also be affected by the addition of fins or corrugations in one or both directions, which increase surface area and may channel fluid flow or induce turbulence.

Types of heat exchangers

1.Shell and Tube heat exchanger

     A typical heat exchanger, usually for higher-pressure applications, is the shell and tube heat exchanger which consists of a series of tubes, through which one of the fluids runs. The second fluid runs over the tubes to be heated or cooled. The set of tubes is called tube bundle, and may be composed by several types of tubes,: plain, logitudinally finned, etc.

2.Plate heat exchanger

     Another type of heat exchanger is the plate heat exchanger. One is composed of multiple, thin, slightly-separated plates that have very large surface areas and fluid flow passages for heat transfer. This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger. Advances in gasket and brazing technology have made the plate type heat exchanger increasingly practical. In HVAC applications, large heat exchangers of this type are called plate-and-frame; when used in open loops, these heat exchangers are normally of the gasketed type to allow periodic disassembly, cleaning, and inspection. There are many types of permanently-bonded plate heat exchangers such as dip-brazed and vacuum-brazed plate varieties, and they are often specified for closed-loop applications such as refrigeration. Plate heat exchangers also differ in the types of plates that are used, and the configurations of those plates. Some plates may be stamped with "chevron" or other patterns, where others may have machined fins and/or grooves.

3.Regenerative heat exchanger

     A third type of heat exchanger is the regenerative heat exchanger. In this, the heat from a process is used to warm the fluids to be used in the process, and the same type of fluid is used either side of the heat exchanger. (These heat exchangers can be either plate and frame or shell and tube construction.) Also see: Countercurrent exchange, Regenerator, Economizer

4.Adiabatic Wheel heat exchanger

     A fourth type of heat exchanger uses an intermediate fluid or solid store to hold heat, which is then moved to the other side of the heat exchanger to be released. Two examples of this are adiabatic wheels, which consist of a large wheel with fine threads rotating through the hot and cold fluids, and fluid heat exchangers. This type is used when it is acceptable for a small amount of mixing to occur between the two streams.

5.Fluid heat exchangers

     This is a heat exchanger with a gas passing upwards through a shower of fluid (often water), and the water then taken elsewhere before being cooled. This is commonly used for cooling gases whilst also removing certain impurities, thus solving two problems at once. It's widely used in espresso machines as an energy-saving method of cooling super-heated water to be used in the extraction of espresso.

6.Dynamic Scraped surface heat exchanger

     Another type of heat exchanger is called dynamic heat exchanger or scraped surface heat exchanger. This is mainly used for heating or cooling with high viscosity products, crystallization processes, evaporation and high fouling applications. Long running times are achieved due to the continuous scraping of the surface, thus avoiding fouling and achieving a sustainable heat transfer rate during the process.

Pump

     A pump is a device used to move liquids, or slurries. A pump moves liquids from lower pressure to higher pressure, and overcomes this difference in pressure by adding energy to the system (such as a water system). A gas pump is generally called a compressor, except in very low pressure-rise applications, such as in heating, ventilating, and air-conditioning, the equipment is known as fans or blowers.

     The earliest pump was described by Archimedes in the 3rd century BC and is known as the Archimedes screw pump. Pumps work by using mechanical forces to push the material, either by physically lifting, or by the force of compression.

Types

     Pumps fall into two major groups: rotodynamic pumps and positive displacement pumps. Their names describe the method for moving a fluid, such as water.

     Positive displacement pumps

     A positive displacement pump causes a liquid to move by trapping a fixed amount of fluid and then forcing (displacing) that trapped volume into the discharge pipe. Positive displacement pumps can be further classified as either rotary-type (for example the rotary vane pump) or reciprocating-type (for example the diaphragm pump).
     A common type is the Wendelkolben pump or the helical twisted Roots pump. The low pulsation rate and gentle performance of this Roots-type positive displacement pump is achieved due to a combination of its two 90° helical twisted rotors, and a triangular shaped sealing line configuration, both at the point of suction and at the point of discharge. This design produces a continuous and non-vorticuless flow with equal volume.

     Centrifugal Pumps

     Centrifugal Pumps are those which convert the Mechanical energy into Hydraulic energy by centrifugal force on the liquid. Hydraulic energy is in the form of Pressure energy. So if the mechanical energy is converted into pressure energy by centrifugal force on the liquid is called the centrifugal pumps. There are mainly two types of the Pumps. 1. Kinetic 2. Positive Displacement

     1.Kinetic Pumps

     1. Continuous energy addition 2. Conversion of added energy to increase in kinetic energy (increase in velocity) 3. Conversion increased velocity to increase in pressure 4. Conversion of Kinetic head to Pressure Head. 5. Meet all heads like Kinetic , Potential, and Pressu

     2. Positive Displacement

     1. Periodic energy addition 2. Added energy forces displacement of fluid in an enclosed volume 3. Fluid displacement results in direct increase in pressure

Turbine

     A turbine is a rotary engine that extracts energy from a fluid flow. Claude Burdin coined the term from the Latin turbinis, or vortex, during an 1828 engineering competition. The simplest turbines have one moving part, a rotor assembly, which is a shaft with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they rotate and impart energy to the rotor. Early turbine examples are windmills and water wheels.

     Gas, steam, and water turbines usually have a casing around the blades that focuses and controls the fluid. The casing and blades may have variable geometry that allows efficient operation for a range of fluid-flow conditions.

     A device similar to a turbine but operating in reverse is a compressor or pump. The axial compressor in many gas turbine engines is a common example.

Theory of operation

1.Impulse turbines 

     These turbines change the direction of flow of a high velocity fluid jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is no pressure change of the fluid in the turbine rotor blades. Before reaching the turbine the fluid's Pressure head is changed to velocity head by accelerating the fluid with a nozzle. Pelton wheels and de Laval turbines use this process exclusively. Impulse turbines do not require a pressure casement around the runner since the fluid jet is prepared by a nozzle prior to reaching turbine. Newton's second law describes the transfer of energy for impulse turbines.

2.Reaction turbines

     These turbines develop torque by reacting to the fluid's pressure or weight. The pressure of the fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages may be used to harness the expanding gas efficiently. Newton's third law describes the transfer of energy for reaction turbines.

     Turbine designs will use both these concepts to varying degrees whenever possible. Wind turbines use an airfoil to generate lift from the moving fluid and impart it to the rotor (this is a form of reaction). Wind turbines also gain some energy from the impulse of the wind, by deflecting it at an angle. Crossflow turbines are designed as an impulse machine, with a nozzle, but in low head applications maintain some efficiency through reaction, like a traditional water wheel. Turbines with multiple stages may utilize either reaction or impulse blading at high pressure. Steam Turbines are usually more impulse while Gas Turbines more reaction type designs. At low pressure the operating fluid medium expands in volume for small changes in pressure. Under these conditions (termed Low Pressure Turbines) blading becomes strictly a reaction type design with the base of the blade solely impulse. The reason is due to the effect of the rotation speed for each blade. As the volume increases, the blade height increases, and the base of the blade spins at a slower speed relative to the tip. This change in speed forces a designer to change from impulse at the base, to a high reaction style tip.

     Classical turbine design methods were developed in the mid 19th century. Vector analysis related the fluid flow with turbine shape and rotation. Graphical calculation methods were used at first. Formulas for the basic dimensions of turbine parts are well documented and a highly efficient machine can be reliably designed for any fluid flow condition. Some of the calculations are empirical or 'rule of thumb' formulae, and others are based on classical mechanics. As with most engineering calculations, simplifying assumptions were made.

     Modern turbine design carries the calculations further. Computational fluid dynamics dispenses with many of the simplifying assumptions used to derive classical formulas and computer software facilitates optimization. These tools have led to steady improvements in turbine design over the last forty years.

     The primary numerical classification of a turbine is its specific speed. This number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate. The specific speed is derived to be independent of turbine size. Given the fluid flow conditions and the desired shaft output speed, the specific speed can be calculated and an appropriate turbine design selected.

     The specific speed, along with some fundamental formulas can be used to reliably scale an existing design of known performance to a new size with corresponding performance.

     Off-design performance is normally displayed as a turbine map or characteristic.

Types of turbines

• Steam turbines are used for the generation of electricity in thermal power plants, such as plants using coal or fuel oil or nuclear power. They were once used to directly drive mechanical devices such as ship's propellors (eg the Turbinia), but most such applications now use reduction gears or an intermediate electrical step, where the turbine is used to generate electricity, which then powers an electric motor connected to the mechanical load.
• Gas turbine engines are sometimes referred to as turbine engines. Such engines usually feature an inlet, fan, compressor, combustor and nozzle (possibly other assemblies) in addition to one or more turbines.
• Transonic turbine. The gasflow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a transonic turbine the gasflow becomes supersonic as it exits the nozzle guide vanes, although the downstream velocities normally become subsonic. Transonic turbines operate at a higher pressure ratio than normal but are usually less efficient and uncommon. This turbine works well in creating power from water.
• Contra-rotating turbines. Some efficiency advantage can be obtained if a downstream turbine rotates in the opposite direction to an upstream unit. However, the complication may be counter-productive.
• Statorless turbine Multi-stage turbines have a set of static (meaning stationary) inlet guide vanes that direct the gasflow onto the rotating rotor blades. In a statorless turbine the gasflow exiting an upstream rotor impinges onto a downstream rotor without an intermediate set of stator vanes (that rearrange the pressure/velocity energy levels of the flow) being encountered.
• Ceramic turbine. The most poorly designed turbine blades (and vanes) are made from nickel-steel alloys and often require intricate air-cooling passages to prevent the metal from melting. In recent years, experimental ceramic blades have been manufactured and tested in gas turbines, with a view to increasing Rotor Inlet Temperatures and/or, possibly, eliminating aircooling.
• Shrouded turbine. Many turbine rotor blades have a shroud at the top, which interlocks with that of adjacent blades, to increase damping and thereby reduce blade flutter.
• Shroudless turbine. Modern practise is, where possible, to eliminate the rotor shroud, thus reducing the centrifugal load on the blade and the cooling requirements.
• Bladeless turbine uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine.
• Wind turbine. These normally operate as a single stage without nozzle and interstage guide vanes.

Water and wind turbines have a thermodynamic cycle that is part of weather.

• Francis Turbine. Widely used water turbine.
• Kaplan Turbine. Variation of the Francis Turbine.

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