compressor

Compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.

Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible, while some can be compressed, the main action of a pump is to pressurize and transport liquids.

Types of compressors
The main types of gas compressors are illustrated and discussed below:

Reciprocating compressor

A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure.

A reciprocating compressor uses the reciprocating action of a piston inside a cylinder to compress refrigerant. As the piston moves downward, a vacuum is created inside the cylinder. Because the pressure above the intake valve is greater than the pressure below it, the intake valve is forced open and refrigerant is sucked into the cylinder. After the piston reaches its bottom position it begins to move upward. The intake valve closes, trapping the refrigerant inside the cylinder. As the piston continues to move upward it compresses the refrigerant, increasing its pressure. At a certain point the pressure exerted by the refrigerant forces the exhaust valve to open and the compressed refrigerant flows out of the cylinder. Once the piston reaches it top-most position, it starts moving downward again and the cycle is repeated.





Centrifugal Compressors
The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is then converted to an increase in potential energy/static pressure by slowing the flow through a diffuser.

Centrifugal compressors use the rotating action of an impeller wheel to exert centrifugal force on refrigerant inside a round chamber (volute). Refrigerant is sucked into the impeller wheel through a large circular intake and flows between the impellers. The impellers force the refrigerant outward, exerting centrifugal force on the refrigerant. The refrigerant is pressurized as it is forced against the sides of the volute. Centrifugal compressors are well suited to compressing large volumes of refrigerant to relatively low pressures. The compressive force generated by an impeller wheel is small, so chillers that use centrifugal compressors usually employ more than one impeller wheel, arranged in series. Centrifugal compressors are desirable for their simple design and few moving parts.





Rotary Compressors
In a rotary compressor the refrigerant is compressed by the rotating action of a roller inside a cylinder. The roller rotates eccentrically (off-centre) around a shaft so that part of the roller is always in contact with the inside wall of the cylinder. A spring-mounted blade is always rubbing against the roller. The two points of contact create two sealed areas of continuously variable volume inside the cylinder. At a certain point in the rotation of the roller, the intake port is exposed and a quantity of refrigerant is sucked into the cylinder, filling one of the sealed areas. As the roller continues to rotate the volume of the area the refrigerant occupies is reduced and the refrigerant is compressed. When the exhaust valve is exposed, the high-pressure refrigerant forces the exhaust valve to open and the refrigerant is released. Rotary compressors are very efficient because the actions of taking in refrigerant and compressing refrigerant occur simultaneously.

What is Humidification?

Humidification is the artificial regulation of humidity in home environments, industrial environments, and health care applications such as artificial respiration. To be comfortable, people require a certain amount of ambient humidity -- not too high, and not too low. Adequate humidification in a manufacturing environment stabilizes moisture in wood, paper, and textiles, while preventing warping in glue joints. In all environments, humidification reduces fire risk and static electricity while making the area feel comfortable.

Areas in which delicate components such as electronics are assembled require precisely tuned humidity levels. Humidification is achieved using liquid atomisers which distribute moisture to the area, coupled with accurate sensors which measure ambient humidity.

In humidification, two quantities are commonly used. Absolute humidification is expressed in grams of moisture per cubic volume of air, while the more commonly used relative humidification is expressed as a ratio between the amount of moisture currently in the air and the maximum moisture the air could hold before condensation occurs. A typical comfortable level of relative humidification is between 35% and 50%. Excess humidity can cause the growth of mold or fungus. Too little humidity can cause static discharge or the accumulation of unwanted dust, contributing to allergies.

Many humidifiers are cheap and require little maintenance. In industrial settings, they are often hung from the ceiling among duct work. Humidification is intimately tied to heating and cooling systems. The level of humidity in the air is also a function of the temperature. Therefore, humidity control systems are often integrated with cooling systems.

Humidification systems are designed by mechanical engineers and are also linked to ventilation systems. Given adequate ventilation from the outside, the humidity of an indoor environment will tend to reach equilibrium with the humidity outside. Humidification is also used to "relax" old documents that have become wrinkled with age.

Textile industry

The textile industry is primarily concerned with the production of yarn, and cloth and the subsequent design or manufacture of clothing and their distribution. The raw material may be natural, or synthetic using products of the chemical industry.

The industrial processes

Cotton is the world's most important natural fibre. In the year 2007, the global yield was 25 million tons from 35 million hectares cultivated in more than 50 countries.

There are five stages

• Cultivating and Harvesting
• Preparatory Processes
• Spinning
• Weaving
• Finishing

Spinning

Spinning is a major industry. It is part of the Textile manufacturing process where three types of fibre are converted into yarn, then fabric, then textiles. The textiles are then fabricated into clothes or other artifacts. There are many three industrial processes available at this time used to spin yarn, and a handicraft community that use hand spinning techniques. Spinning is the twisting together of drawn out strands of fibres to form yarn, though it is colloquially used to describe the process of drawing out, inserting the twist, and winding onto bobbins.

Most spinning today is done using break or open-end spinning, this is a technique where the staples are blown by air into a rotating drum, where they attach themselves to the tail of formed yarn that is continually being drawn out of the chamber. Other methods of break spinning use needles and electrostatic forces.This method has replace the older methods of ring and mule spinning. It is also is easily adapted forartificial fibres.

The spinning machines takes the roving, thins it and twists it, creating yarn which it winds onto a bobbin.

In mule spinning the roving is pulled off a bobbin and fed through some rollers, which are feeding at several different speeds.This thins the roving at a consistent rate. If the roving was not a consistent size, then this step could cause a break in the yarn, or could jam the machine. The yarn is twisted through the spinning of the bobbin as the carriage moves out, and is rolled onto a cop as the carriage returns. Mule spinning produces a finer thread than the less skilled ring spinning.

• The mule was an intermittent process, as the frame advanced and returned a distance of 5ft.It was the descendant of 1779 Crompton device. It produces a softer less twisted thread that was favoured for fines and for weft.
• The ring was a descendant of the Arkwright water Frame 1769. It was a continuous process, the yarn was coarser, had a greater twist and was stronger so was suited to be warp. Ring spinning is slow due to the distance the thread must pass around the ring, similar methods have improved on this; such as flyer and bobbin and cap spinning.

Sewing thread, was made of several threads twisted together, or doubled.

The pre-industrial techniques of Hand spinning with spindle or Spinning wheel are continue to be practised as a handicraft or hobby, and enable wool or unusual vegetable and animal staples to be creatively used.

• Checking

This is the process where each of the bobbins is rewound to give a tighter bobbin.

• Folding and twisting

Plying is done by pulling yarn from two or more bobbins and twisting it together, in the opposite direction that in which it was spun. Depending on the weight desired, the yarn may or may not be plied, and the number of strands twisted together varies.

Weaving

Weaving is a textile craft in which two distinct sets of yarns or threads are interlaced to form afabric or cloth. The threads which run lengthways are called the warp and the threads which run across from side to side are the weft or filling.

Cloth is usually woven on a loom, a device that holds the warp threads in place while filling threads are woven through them. Weft is an old English word meaning "that which is woven". A fabric band which meets this definition of cloth (warp threads with a weft thread winding between) can also be made using other methods, including tablet weaving, back-strap, or other techniques without looms.

The way the warp and filling threads interlace with each other is called the weave. The majority of woven products are created with one of three basic weaves: plain weave, satin weave, or twill. Woven cloth can be plain (in one colour or a simple pattern), or can be woven in decorative or artistic designs, including tapestries. Fabric in which the warp and/or weft is tie-dyed before weaving is called ikat.

Though traditional handweaving and spinning remain popular crafts, nowadays the majority of commercial fabrics in the West are woven on computer-controlled Jacquard looms. In the past, simpler fabrics were woven on dobby looms, while the Jacquard harness adaptation was reserved for more complex patterns. Some believe the efficiency of the Jacquard loom, with its Jacquard weaving process, makes it more economical for mills to use them to weave all of their fabrics, regardless of the complexity of the design.