Fundamentals of Refrigeration and Air-Conditioning (course ) 2

2.1 Basic vapour compression cycle

A liquid boils and condenses – the change between the liquid and
gaseous states – at a temperature which depends on its pressure,
within the limits of its freezing point and critical temperature. In
boiling it must obtain the latent heat of evaporation and in condensing
the latent heat must be given up again.
The basic refrigeration cycle (Figure 2.1) makes use of the boiling
and condensing of a working fluid at different temperatures and,
therefore, at different pressures.


Heat is put into the fluid at the lower temperature and pressure
and provides the latent heat to make it boil and change to a vapour.
This vapour is then mechanically compressed to a higher pressure
and a corresponding saturation temperature at which its latent heat
can be rejected so that it changes back to a liquid.



The total cooling effect will be the heat transferred to the working
fluid in the boiling or evaporating vessel, i.e. the change in enthalpies
between the fluid entering and the vapour leaving the evaporator.
For a typical circuit, using the working fluid Refrigerant 22,
evaporating at  – 5°C and condensing at 35°C, the pressures and
enthalpies will be as shown in Figure 2.2.



Enthalpy of fluid entering evaporator = 91.4 kJ/kg
Enthalpy of saturated gas leaving evaporator = 249.9 kJ/kg
Cooling effect = 249.9 – 91.4 = 158.5 kJ/kg
A working system will require a connection between the condenser
and the inlet to the evaporator to complete the circuit. Since these
are at different pressures this connection will require a pressure-
reducing and metering valve. Since the reduction in pressure at
this valve must cause a corresponding drop in temperature, some
of the fluid will flash off into vapour to remove the energy for this
cooling. The volume of the working fluid therefore increases at the
valve by this amount of flash gas, and gives rise to its name, the
expansion valve. (Figure 2.3.)



2.2 Coefficient of performance
Since the vapour compression cycle uses energy to move energy,
the ratio of these two quantities can be used directly as a measure
of the performance of the system. This ratio, the coefficient of
performance, was first expressed by Sadi Carnot in 1824 for an


ideal reversible cycle, and based on the two temperatures of the
system, assuming that all heat is transferred at constant temperature
(see Figure 2.4). Since there are mechanical and thermal losses in
a real circuit, the coefficient of performance (COP) will always be
less than the ideal Carnot figure. For practical purposes in working







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Fundamentals of Refrigeration and Air-Conditioning (course)


 Refrigeration: The process of removing heat.
Air-conditioning: A form of air treatment whereby temperature,
humidity, ventilation, and air cleanliness are all controlled within
limits determined by the requirements of the air conditioned
enclosure.


1.1 Basic physics – temperature

The general temperature scale now in use is the Celsius scale, based
nominally on the melting point of ice at 0°C and the boiling point
of water at atmospheric pressure at 100°C. (By strict definition, the
triple point of ice is 0.01°C at a pressure of 6.1 mbar.) On the
Celsius scale, absolute zero is – 273.15°C.
In the study of refrigeration, the Kelvin or absolute temperature scale
is also used. This starts at absolute zero and has the same degree
intervals as the Celsius scale, so that ice melts at + 273.16 K and
water at atmospheric pressure boils at + 373.15 K.




1.2 Heat

Refrigeration is the process of removing heat, and the practical
application is to produce or maintain temperatures below the
ambient. The basic principles are those of thermodynamics, and
these principles as relevant to the general uses of refrigeration are
outlined in this opening chapter.
Heat is one of the many forms of energy and mainly arises from
chemical sources. The heat of a body is its thermal or internal
energy, and a change in this energy may show as a change of
temperature or a change between the solid, liquid and gaseous
states.
Matter may also have other forms of energy, potential or kinetic,
depending on pressure, position and movement. Enthalpy is the
sum of its internal energy and flow work and is given by:
H = u + Pv
In the process where there is steady flow, the factor Pv will not
2 Refrigeration and Air-Conditioning
change appreciably and the difference in enthalpy will be the quantity
of heat gained or lost.
Enthalpy may be expressed as a total above absolute zero, or any
other base which is convenient. Tabulated enthalpies found in
reference works are often shown above a base temperature of
– 40°C, since this is also – 40° on the old Fahrenheit scale. In any
calculation, this base condition should always be checked to avoid
the errors which will arise if two different bases are used.
If a change of enthalpy can be sensed as a change of temperature,
it is called sensible heat. This is expressed as specific heat capacity,
i.e. the change in enthalpy per degree of temperature change, in
kJ/(kg K). If there is no change of temperature but a change of
state (solid to liquid, liquid to gas, or vice versa) it is called latent
heat. This is expressed as kJ/kg but it varies with the boiling
temperature, and so is usually qualified by this condition. The
resulting total changes can be shown on a temperature–enthalpy
diagram (Figure 1.1).



Example 1.1 For water, the latent heat of freezing is 334 kJ/kg and
the specific heat capacity averages 4.19 kJ/(kg K). The quantity of
heat to be removed from 1 kg of water at 30°C in order to turn it
into ice at 0°C is:
4.19(30 – 0) + 334 = 459.7 kJ
Example 1.2 If the latent heat of boiling water at 1.013 bar is 2257
kJ/kg, the quantity of heat which must be added to 1 kg of water at
30°C in order to boil it is:
Fundamentals 3
4.19(100 – 30) + 2257 = 2550.3 kJ
Example 1.3 The specific enthalpy of water at 80°C, taken from
0°C base, is 334.91 kJ/kg. What is the average specific heat capacity
through the range 0–80°C?
334.91/(80 – 0) = 4.186 kJ/(kg K)


1.3 Boiling point

The temperature at which a liquid boils is not constant, but varies
with the pressure. Thus, while the boiling point of water is commonly
taken as 100°C, this is only true at a pressure of one standard
atmosphere (1.013 bar) and, by varying the pressure, the boiling
point can be changed (Table 1.1). This pressure–temperature
property can be shown graphically (see Figure 1.2).



The boiling point is limited by the critical temperature at the upper
end, beyond which it cannot exist as a liquid, and by the triple point
at the lower end, which is at the freezing temperature. Between
these two limits, if the liquid is at a pressure higher than its boiling
pressure, it will remain a liquid and will be subcooled below the
saturation condition, while if the temperature is higher than
saturation, it will be a gas and superheated. If both liquid and
vapour are at rest in the same enclosure, and no other volatile
substance is present, the condition must lie on the saturation line.
At a pressure below the triple point pressure, the solid can change
directly to a gas (sublimation) and the gas can change directly to a
solid, as in the formation of carbon dioxide snow from the released
gas.
The liquid zone to the left of the boiling point line is subcooled
liquid. The gas under this line is superheated gas.



1.4 General gas laws

Many gases at low pressure, i.e. atmospheric pressure and below for
water vapour and up to several bar for gases such as nitrogen, oxygen
and argon, obey simple relations between their pressure, volume
and temperature, with sufficient accuracy for engineering purposes.
Such gases are called ‘ideal’.
Boyle’s Law states that, for an ideal gas, the product of pressure
and volume at constant temperature is a constant:
pV = constant


1.5 Dalton’s law

Dalton’s Law of partial pressures considers a mixture of two or
more gases, and states that the total pressure of the mixture is equal
to the sum of the individual pressures, if each gas separately occupied
the space.


Example 1.7 A cubic metre of air contains 0.906 kg of nitrogen of
specific gas constant 297 J/(kg K), 0.278 kg of oxygen of specific
gas constant 260 J/(kg K) and 0.015 kg of argon of specific gas
constant 208 J/(kg K). What will be the total pressure at 20°C?

pV = mRT
V = 1 m3
so p = mRT
For the nitrogen pN = 0.906 × 297 × 293.15 = 78 881 Pa
For the oxygen pO = 0.278 × 260 × 293.15 = 21 189 Pa
For the argon pA = 0.015 × 208 × 293.15 = 915 Pa
—————
Total pressure = 100 985 Pa
(1.009 85 bar)



1.6 Heat transfer

Heat will move from a hot body to a colder one, and can do so by
the following methods:
1. Conduction. Direct from one body touching the other, or through
a continuous mass
2. Convection. By means of a heat-carrying fluid moving between
one and the other
3. Radiation. Mainly by infrared waves (but also in the visible band,
e.g. solar radiation), which are independent of contact or an
intermediate fluid.
Conduction through a homogeneous material is expressed directly
by its area, thickness and a conduction coefficient. For a large plane
surface, ignoring heat transfer near the edges:






The exception to this is the effect of solar radiation when
considered as a cooling load, such as the air-conditioning of a building
which is subject to the sun’s rays. At the wavelength of sunlight the
absorptivity figures change and calculations for such loads use
tabulated factors for the heating effect of sunlight. Glass, glazed
tiles and clean white-painted surfaces have a lower absorptivity, while
the metals are higher.


1.7 Transient heat flow

A special case of heat flow arises when the temperatures through
the thickness of a solid body are changing as heat is added or
removed. This non-steady or transient heat flow will occur, for example,
when a thick slab of meat is to be cooled, or when sunlight strikes
on a roof and heats the surface. When this happens, some of the
heat changes the temperature of the first layer of the solid, and the
remaining heat passes on to the next layer, and so on. Calculations
for heating or cooling times of thick solids consider the slab as a
number of finite layers, each of which is both conducting and
absorbing heat over successive periods of time. Original methods of
solving transient heat flow were graphical [1, 5], but could not
easily take into account any change in the conductivity or specific
heat capacity or any latent heat of the solid as the temperature
changed.
Complicated problems of transient heat flow can be resolved by
computer. Typical time–temperature curves for non-steady cooling
are shown in Figures 16.1 and 16.2, and the subject is met again in
Section 26.2.



1.8 Two-phase heat transfer

Where heat transfer is taking place at the saturation temperature of
a fluid, evaporation or condensation (mass transfer) will occur at
the interface, depending on the direction of heat flow. In such
cases, the convective heat transfer of the fluid is accompanied by
conduction at the surface to or from a thin layer in the liquid state.
Since the latent heat and density of fluids are much greater than
the sensible heat and density of the vapour, the rates of heat transfer
are considerably higher. The process can be improved by shaping
the heat exchanger face (where this is a solid) to improve the drainage
of condensate or the escape of bubbles of vapour. The total heat
transfer will be the sum of the two components.
Rates of two-phase heat transfer depend on properties of the
volatile fluid, dimensions of the interface, velocities of flow and the

extent to which the transfer interface is blanketed by fluid. The
driving force for evaporation or condensation is the difference of
vapour pressures at the saturation and interface temperatures.
Equations for specific fluids are based on the interpretation of
experimental data, as with convective heat transfer.
Mass transfer may take place from a mixture of gases, such as the
condensation of water from moist air. In this instance, the water
vapour has to diffuse through the air, and the rate of mass transfer
will depend also on the concentration of vapour in the air. In the
air–water vapour mixture, the rate of mass transfer is roughly
proportional to the rate of heat transfer at the interface and this
simplifies predictions of the performance of air-conditioning coils
[1, 5, 9].






in the next section we will discuss the The refrigeration cycles




Funny Facts About Skyscrapers

Eiffel Tower

The Eiffel Tower was the world's tallest building when completed in 1889. It was built for the Universal Exposition to demonstrate that iron can be as strong as stone while being infinitely lighter. And, indeed, wrought iron tower is twice as high as the Washington Monument and masonry, however, that weighs 70,000 tons less! It is repainted every seven years, with 50 tons of dark brown paint.


The Housing Construction Insurance

Called "the father of the skyscraper," the Home Insurance Building was built in Chicago in1885 (and demolished in 1931), was 138 feet high and 10 stories. It was the first building to be used effectively to support a skeleton of steel beams and columns, allowing you to have many windows of traditional masonry structures. But this method of new construction made people worry that the building would fall, leading to the city to halt construction until it could investigate the safety of the structure.


The Chrysler Building

In 1929, the automobile magnate Walter Chrysler was involved in an intense race in the Bank of Manhattan Trust Company to build the tallest skyscraper in the world. Just when it seemed that the bank had captured the coveted title, workers at Chrysler Building kidnapped a thin needle hidden inside the building through the top of the roof to win the contest (subsequently lost the title four months later to the Empire State Building). Chrysler is also decorated their building to reflect their cars, with hubcaps, mudguards, and hood ornaments.


The Empire State Building

The Empire State Building is designed to be a lightning rod. In fact, it is struck by lightning about 100 times a year?


Citicorp Center

Citicorp Center in New York (915 feet, 59 floors, built in 1977) was the first U.S. skyscraper to contain a mass damper to swing control of the building. The structure was also the site of an upcoming disaster. During construction, instead of solder joints as specified, the manufacturer of the bolts. One year after completion, with the hurricane season fast approaching, the construction chief engineer discovered the change and realized the joints would be too weak to withstand hurricane force winds, which could lead to building collapse in a dense urban neighborhood. To correct the problem, a team of workers was hired to weld two steel plates inch thick in each of the 200 screwed. Six weeks on the job three months to repair the hurricane She was off the coast of North Carolina, heading to New York. Fortunately, a few hours before New York was the face of emergency evacuation, the hurricane turned toward the sea. This crisis was kept secret from the public for nearly 20 years.


Petronas Towers
Petronas Towers in the form of plants is based on an eight-pointed star, common in Malaysian Islamic patterns. The towers have many window cleaners windows to take a month to clean each tower! You can get a close look at the building in the movie Entrapment, starring Catherine Zeta-Jones and Sean Connery.


The Sears Tower in Chicago, Illinois

To strengthen the John Hancock Center against Chicago's famous winds, engineers included five enormous diagonal braces on the exterior walls of the building. These diagonal block the view of two windows on each floor. A rental agent intelligent, however, has made these windows without light a status symbol and it actually costs more money to rent these rooms!


Center First Interstate World


First Interstate World Center (Library Tower) in Los Angeles is only 26 miles from San Andreas fault and is designed to withstand an earthquake of August. 3 or higher on the Richter scale, with a massively reinforced central core and lighter columns around the perimeter. This design makes it flexible, so it can withstand the vigorous shaking from side to side without breaking, however, rigid, so that it can withstand the force of the wind.


Sears Tower


On a clear day one can see four states from the top of Sears Tower in Chicago: Illinois, Indiana, Wisconsin and Michigan. To ensure that your vision is clear, the building has six machines mounted robotic window washing on the roof.

How Skyscrapers Work ( Introduction)

Throughout the history of architecture, has been a constant search for the height. Thousands of workers working in the pyramids of ancient Egypt, the cathedrals of Europe and a host of other towers, all trying to create something impressive. People build skyscrapers primarily because they are convenient - you can create a lot of real estate a relatively small land area. But ego and grandeur often play an important role in the field of construction, as it did in earlier civilizations.


Until relatively recently, we could only go as high. After a certain point, it simply was not possible to continue building up. In the late 1800s, new technology is redefining the boundaries. Suddenly, it was possible to live and work in colossal towers, hundreds of feet above the ground.


The Twin Towers

When the twin towers of World Trade Center were hit on September 11, 2001, seemed at first that could remain standing. But in less than two hours, both towers had collapsed on the floor.

The fight against gravity

The main obstacle in building up the force of gravity. Imagine carrying a friend on his shoulders. If the person is fairly light, can help quite well for itself. But if I had to put someone else on the shoulders of his friend (build your tower higher), the weight would probably be too much for you to carry alone. To make a tower that is "high-multiple people," it takes more people at the bottom to support the weight of the world above.


The Empire State Building in New York. The view from the 86th floor observatory is building one of the main attractions of New York.

In normal buildings made of bricks and mortar, you have to keep a lower wall thickening as the construction of new upper floors. After reaching a certain height, this is very impractical. If there is almost no space on the lower floors, which is the point in making a tall building?

Using this technology, people are not building many buildings over 10 stories - was not feasible. But in late 1800, a number of converging developments and circumstances, and the engineers were able to break the upper limit - and then some. The social circumstances that led to the skyscraper were the growing metropolitan centers of America, especially Chicago. Businesses all wanted their offices near the city center, but there was enough space. In these cities, architects needed a way to extend the metropolis upward instead of outward.

The main technological advance that made skyscrapers possible was the development of mass iron and steel production (see How Iron and Steel Work for details). The new manufacturing process has helped produce long beams of solid iron. Essentially, this gave architects a new set of basic elements to work with them. Narrow, relatively lightweight metal beams could support much more weight than the brick walls in older buildings, while a fraction of the space. With the advent of the Bessemer process, the first efficient method for mass production of steel, the architects moved away from iron. Steel, which is even lighter and stronger than iron, has allowed to build even taller buildings.

Grids giant beam

The central support structure of a skyscraper is its steel skeleton. Metal riveted beams end to end to form vertical columns. At each floor level, these vertical columns are connected to the beam horizontal beams. Many buildings have diagonal beams running between the beams, as additional structural support.


This giant three-dimensional grid - called the super structure - all the weight on the building are transferred directly to the vertical columns. This concentrates the downward force caused by gravity in relatively small areas where the columns rest at the base of the building. This concentrated force is then spread out underneath the building infrastructure.

In a typical skyscraper substructure, each vertical column sits on an equal spread. The column rests directly on a cast iron plate that sits on top of a grid. The grid is basically a stack of horizontal steel beams, lined side by side in two or more layers (see diagram below). The grid rests on a thick concrete slab directly on the hard earth beneath the earth. Once the steel is in place, the whole structure is covered with concrete.


This structure expands out lower on the ground, in the same way a pyramid extending outward as you lower. This distributes the concentrated weight of the columns on a wide area. Ultimately, the full weight of the building sits directly on the hard clay material under the ground. In very heavy buildings, the basis of mass media other pillars of concrete footings that extend all the way to the rock layer of the earth.

An important advantage of the steel skeleton structure is that the exterior walls - called the curtain wall - just support its own weight. This allows the architects of the building open as much as they want, in marked contrast to the thick walls of traditional buildings. In many skyscrapers, especially those built in the 1950s and '60s, the curtain walls are made almost entirely of glass, giving the occupants a spectacular view of the city.

Making it functional

In the last section, we saw that the iron and steel making new process opened the possibility of tall buildings. But this is only half the picture. Before skyscrapers skyscraper could become a reality, engineers had to be practical.


73 The Empire State Building elevator can move 600-1400 feet (183-427 meters) per minute. A maximum speed, you can travel from the lobby to the 80th floor in 45 seconds.

Once you get more than five or six floors, stairs become a fairly inconvenient technology. Skyscrapers would never have worked without the coincident emergence of the technology of the elevator. From the passenger elevator was installed first in Haughwout department store in New York in 1857, elevator shafts have been an important part of designing skyscrapers. In most skyscrapers, the elevator shafts are the core of the building.

By deciphering the structure of the elevator is a balancing act of sorts. As you add more floors of a building to increase the occupancy of the building. When more people obviously need more elevators or the lobby will fill up with people waiting in line. But elevator shafts occupy much space, so you lose floor space for every elevator you add. To make more room for people, you have to add more plants. Deciding on the appropriate number of floors and elevators is one of the most important parts of a building design.

Building safety is also an important consideration in the design. Skyscrapers would not have worked so well without the advent of new building materials resistant to fire in 1800. These days, skyscrapers also equipped with sophisticated spray equipment that puts out most fires before they spread very far. This is extremely important when you have hundreds of people who live and work thousands of feet above a safe exit.

Architects also pay special attention to the comfort of building occupants. The Empire State Building, for example, was designed so that their occupants would always be within 30 feet (ft) from a window. The building of the Commerzbank in Frankfurt, Germany has tranquil indoor garden areas built in front of the building office areas, a climbing spiral structure. A building is only successful when the architects have focused not only on structural stability, but also usability and occupant satisfaction.

Wind Resistance

In addition to the vertical force of gravity, skyscrapers also have to deal with the horizontal force of the wind. Most skyscrapers can easily move several feet in any direction, like a swaying tree, without damaging its structural integrity. The main problem with this horizontal movement is how it affects the people inside. If the building moves a substantial horizontal distance, the occupants will undoubtedly feel.

The most basic method for controlling horizontal roll to just tighten the structure. At the point where the horizontal beams attached to the vertical column, bolts of the construction crew and solder them on the top and bottom and side. This move makes the whole steel super structure more like a unit, as a stick instead of a flexible skeleton.


The Chrysler Building in New York.

For tallest skyscrapers, tighter connections do not really do the trick. To maintain these buildings to sway in large measure, the engineers have to build particularly strong core through the center of the building. The Empire State Building, Chrysler Building and other skyscrapers of that time, the area around the central axis of the lift is reinforced by a sturdy steel frame, braced with diagonal beams. Most recent buildings have one or more cores of concrete built in the center of the building.

Making buildings more rigid also braces against earthquake damage. Basically, the entire building moves with the horizontal vibration of the earth, so the steel skeleton is not twisted and strained. While this helps protect the structure of skyscrapers, you can be pretty rough with the occupants, and can also cause much damage to furniture and loose equipment. Several companies are developing new technologies to counteract the horizontal movement to dampen the strength of the vibration. For more information on these systems, check out how smart structures will work.

Some buildings already use advanced shock absorbers compensating for wind. Citicorp Center in New York, for example, uses a tuned mass damper. In this complex system of hydraulic oil systems push a weight of 400 tonnes of concrete and back in one of the top floors, shifting the weight of the entire building from side to side. A sophisticated computer system carefully monitors how the wind is changing the building and moves the weight accordingly. Some similar systems of the building weight change based on the movement of giant pendulums.

The vertical variations

As seen in previous sections, the skyscrapers of all shapes and sizes. The concept of steel frame makes for a very flexible structure. The columns and beams are like a giant erector set pieces. The only real limit is the imagination of architects and engineers to put the pieces together.


Onward and upward

The world's tallest "title passes regularly from skyscraper to skyscraper. This is one of the most competitive contests in construction. Architects and engineers wholeheartedly embrace the challenges of building higher, and businesses and cities are a popular choice for the glory of dominating the competition. The current champion is the Petronas Towers in Malaysia (see box on previous section.)

In all respects, the race is far from over skyscrapers. More than 50 proposed buildings that would break the current record. Some of the most conservative structures already under construction. But the most ambitious buildings in the group are only theoretical at the moment. Is it possible? According to some experts in engineering, the real limitation is money, not technology. Super tall buildings that require heavy-duty materials and deep, fortified bases. The workers need to develop cranes and pumping systems to get materials and concrete to the upper level. In total, putting one of these buildings could easily cost tens of billions of dollars.

In addition, there would be logistical problems with the elevators. To make the upper floors of a building with 200 floors, easy access, you would need a large bank of elevators, which occupy a large area in the center of the building. An easy solution to this problem is to fix the elevators so that only up to cover part of the building. Passengers who want to go to the top will lift halfway down and then take another elevator the rest of the road.

Experts are divided about how high you can really go in the near future. Some say it could build a kilometer high (5,280 feet or 1. 609 m) development with existing technology, while others say they would need to develop lighter, stronger materials, faster elevators and advanced control dampers before these buildings were viable. Hypothetically speaking, most engineers will not impose an upper limit. Future advances technology could lead to sky-high cities, many experts say, housing a million people or more.

Whether it will actually arrive is another matter. We may be forced to build higher up in the future, just to keep their land. When it builds up, you can concentrate more on the development of an area, instead of distributing natural areas untapped. Skyscraper cities are also highly desirable: Most companies can be grouped in a city, reducing commuting time.

But the main force behind the skyscraper race could become the vanity base. When the height monumental, once the gods and kings honored, now glorifies corporations and cities. These structures come from a very basic desire - everyone wants to be the largest building in the block. This unit has been an important factor in the development of skyscrapers in the last 120 years and is a good bet to continue to push the buildings in the coming centuries.

reinforced plastic - Carbon fiber

Carbon fiber reinforced plastic (CFRP or CRP) is a very strong, light and expensive composite material or fiber reinforced plastic. Similar to glass reinforced plastic, which is sometimes simply called fiberglass, the composite material is commonly known by the name of its reinforcing fibers (carbon fiber). Plastic is most often epoxy, but other plastics such as polyester, vinyl ester or nylon, are also sometimes used. Some compounds contain carbon fiber and glass fiber reinforcement. Less commonly, graphite-reinforced plastic term is also used.

Many applications in aerospace and automotive fields, as well as in sailboats, and particularly in modern bikes, where these qualities are important. It is increasingly common in small consumer products, as well as laptops, tripods, fishing rods, frames of racquet sports, stringed instrument bodies, classical guitar strings, and drum shells.


Compound

The choice of matrix can have a profound effect on the properties of the finished product compound. A common plastic for this application is epoxy, and materials produced with this methodology are often referred to generically as compounds. A way to produce pieces of graphite epoxy layers of cloth carbon fiber cloth in a mold to form the final product. The alignment and weave of the fibers of the fabric is carefully chosen to maximize the strength and stiffness properties of the resulting material. In the most demanding applications all air is evacuated from the mold, but in applications where cost is more important than structural rigidity, this step is omitted. The mold is filled with epoxy and is heated or air cured. The resulting rigid group does not corrode in water and is very strong, especially for its weight. If the mold contains air, small air bubbles will be present in the material, reducing strength. Most composite parts are manufactured by draping cloth over a mold, either pre-impregnated with epoxy resin in the fibers (also known as prepreg), or "painted" on it. Hobby or cosmetic parts are often made in this way, as well as high performance aerospace components. High performance parts molds are often vacuum bagged and / or autoclaved.

The large number of (often manual) work required for the manufacture of composite materials has so far limited their use in applications requiring a large number of complicated parts.

The chemistry and manufacturing techniques such as epoxy thermosetting plastics are often unsuitable for mass production. A potential savings and improved performance as is to replace the epoxy matrix with a thermoplastic material such as nylon or polyketone. Boeing's entry in the Joint Strike Fighter competition included a carbon fiber wing delta-shaped reinforced thermoplastics, but the difficulties in making this part contributed to Lockheed Martin won the competition.

Process

The process in which most of CFRP is varied, depending on the piece being created, the finish (not glossy) is necessary, and how many of this particular piece will be produced.

For simple pieces that relatively few copies are needed (1-2 per day) a vacuum bag can be used. A fiberglass or aluminum mold is polished, waxed, and has a release agent applied before the fabric and resin applied and the vacuum is pulled and set aside to allow the piece to cure (harden). There are two ways to apply the resin into the cloth into a vacuum mold. One is called a wet tray, where two-part resin is mixed and applied before being placed in the mold and placed in the bag. The other is a resin induction system, where you place the dry fabric and mold in the bag, while the vacuum pulls the resin through a tube into the bag, then through a tube with holes or something similar to the resin evenly distributed throughout the tissue. Wire loom works perfectly for a tube that requires holes in the bag. Both methods require the application of resin to work hand to spread the resin evenly for a glossy finish, with tiny pinholes. A third method of construction of composite materials is known as a dry pan. In this case, the carbon fiber material is already impregnated with resin (pre-preg) and applied to the mold in a manner similar to the adhesive film. The assembly is then placed in a vacuum to cure. The dry tray method has the least amount of resin waste and can achieve lighter constructions than wet tray. In addition, due to greater amounts of resin are more difficult to bleed out tray methods wet prepreg parts generally have fewer imperfections. pin removal resin minimum quantities usually require the use of autoclave pressure to flush out the waste gases.

A quicker method uses a compression mold. This is a two-piece (male and female) mold usually made of fiberglass or aluminum which is screwed together with the fabric and resin between them. The benefit is that, once bolted together, is relatively clean and can be transferred or stored without a vacuum until after curing. However, molds require a lot of material to hold together through many uses under that pressure.

Many carbon fiber parts are created with a single layer of carbon fabric and filled with fiberglass. A chopper gun can be used to quickly create these pieces. Once a thin layer is created from carbon fiber, the chopper gun is a pneumatic tool that cuts a roll of fiberglass and resin spray at the same time, so the fiberglass and the resin is mixed on the spot. The resin is either external mix, where the hardener and resin sprayed separately, or internal, blending the inside, which requires cleaning after each use.

In ways difficult or impossible (like a tube) a filament winder can be used to make parts.

Automotive uses

CFRP is widely used in motor racing, especially in Formula One and IndyCar racing. The high cost of carbon fiber is mitigated by the relationship of material unsurpassed strength-to-weight and low weight is essential for racing high performance cars. Racecar manufacturers have also developed methods to make carbon fiber pieces strength in a particular direction, so it is strong in a load direction, but weak in directions that little or no load is placed on the member. Conversely, manufacturers developed omnidirectional carbon fiber fabrics to use force in all directions. This type of carbon fiber assembly is the most widely used in the safety cell "monocoque chassis mount race cars high performance.

Several supercars over the past few decades have incorporated CFRP extensively in their manufacture, they use for their monocoque chassis and other components. Examples include the Koenigsegg CCR, Koenigsegg CCX, McLaren F1, Mercedes McLaren SLR, Bugatti Veyron, Bugatti EB110, Pagani Zonda, Ferrari Enzo and Porsche Carrera GT.

Until recently, the material has had limited use in mass production of cars because the expense involved in terms of materials, equipment, and the relatively small number of people with experience of working with him. Recently, several mainstream vehicle manufacturers such as General Motors and BMW have started to use carbon fiber technology in road cars every day.

Chevrolet is using carbon fiber in a special version of its flagship sports, the Corvette. The Z06, a special high performance version of the Corvette, including carbon fiber body weight forward and increase the rigidity of the body instead of glass reinforced plastic found in the standard Corvette.

BMW produces carbon fiber reinforced plastic in its plant in Landshut. To make the roof of the BMW M3 CSL, for example, five layers of carbon fiber cloth are placed in a press of 1,800 tons, which is epoxy resin transfer molding and heat-cured in a robot-automated process. The resulting roof is half the weight of an equivalent steel roof.

The use of the material has been more readily adopted by low volume manufacturers like TVR who use it primarily for creating body panels for some of its high-end cars because of their greater strength and reduced weight compared with plastic reinforced glass used for most of their products.

Often street racers or fans tuners will purchase a carbon fiber hood, spoiler or body panel as part of the market for accessories for your vehicle. However, these pieces are rarely made of full carbon fiber. They are often just a single layer of carbon fiber laminated fiberglass for the "look" of CF. It is common for these parts to remain unpainted to accentuate the look of carbon fiber fabric.

Civil engineering applications

CFRP has recently become something of a hot topic in the field of structural engineering, surprisingly, for reasons of cost-effectiveness. For example, many old bridges in the world were designed to tolerate much lower service loads than they are today subject to, and compared with the cost of replacing the bridge, reinforcing it with CFRP is quite cheap. Due to the incredible stiffness of carbon fiber, which can be used under stretches to help prevent excessive deflections, or wrapped around the beams to limit shear stresses. Since 2005, the Westgate Bridge in Melbourne, is the world's largest bridge to be strengthened with carbon fiber laminates [1].

Much research is being done now with CFRP as reinforcement within concrete structures such as beams and bridge decks. The material has many advantages over conventional steel, especially that it is much more rigid and resistant to corrosion. There are, however, some doubts among the engineering community about implementing these new materials until a more real world has been made.

Other applications

One area where CFRP has found a good use in the manufacture of bicycles, especially high-end racing bikes. The vibration absorption properties of CFRP do to have a less severe travel, while providing weight reduction compared to traditional bike tube materials such as aluminum or steel. The choice of tissue can be carefully selected to maximize stiffness. The exploitation of the variety of forms can be constructed in CFRP has further increased rigidity and aerodynamic considerations also allowed in the profiles of the tube. carbon fiber frames, forks, handlebars, seatposts and crank arms are becoming common in the middle-and higher-priced bikes. CFRP holders are used in most of the new racing bike.

Another widespread use of carbon fiber is in the manufacture of fishing rods. Its high flexibility and low weight make it ideal to feel every bite.

Most modern rowing shells are made of carbon fiber, which significantly reduces the weight of the boat.

A system for resin transfer molding has been developed by Wilson Benesch advanced composite structures can be created. This manufacturing technology creates the most rigid and lightweight speaker cabinet. The damping properties are exceptional, do not give the same vibration similar to that absorbs the skills are in high-performance cycles. The combination of these properties makes it possible to achieve the lowest possible sound out of the cabinet. No distortion of the cabinet by a more accurate transducer.

Recycling

A major concern is the use of full life cycle of materials such as carbon fiber reinforced plastics have an almost infinite life. Some companies [2] are succeeding in the recycling of carbon fiber. The strategy focuses on the recycling of milling, compounding or shredding recycled carbon fiber, and the use of search for the final product in several industrial applications (including carbon fiber applications less stringent than those required by , say, the aerospace industry). It is also commonly used in electronics such as laptops, to reduce total weight and improve durability.

Bring the customer intelligence with the iPhone (Q & A)

 Customer intelligence on your iPhone



In a recent conversation about predictive analytics, I learned how Wal-Mart Stores used statistical models to better understand the patterns and trends of its customers - and how companies can use this data to a competitive price to dominate a market.

Imagine that the same type of customer intelligence, delivered almost instantaneously, in the hands of store managers on-site or corporate executives on your iPhone or IPAD.

That's what Medallia, a provider of customer feedback and software performance data, is intended to provide a new offer this week on the heels of the new iPhone announcement in April. Medallia obtains its information from all the requests it receives from the survey hotels, shops, banks and other consumer services.

According Medallia CEO and co-founder Borge Hald, these data, when properly extracted, you can let an executive of Nike brand, for example, knowing what customers think about Kobe Bryant new shoes in the U.S. regions, or may allow the administrator of a Four Seasons hotel to say that the new corporate headquarters concierge services the best responses received from customers. Apple iPhone IPAD offering an easy to use for these data, helping managers make decisions in near real time.

Hald I met this week to discuss the management of customer experience and new mobile application.


Q: What do you mean by "customer experience management," and why does it matter?
Hald: Customer experience management (CEM) goes by a lot of names--customer intelligence, enterprise feedback management, even social CRM, to name a few--but it is the practice of using customer feedback to improve operations and sales. Not to be confused with CRM, which focuses on streamlining the sales cycle, CEM is actually a complementary system that is more focused on the actual interactions customers have with brands.
Currently, it's the big brands in hospitality, retail, and financial services that have made investments in customer experience. What we found with our customers was that though the initial goal for most of them was to save risky customers from switching brands, they also saw a boost in revenue. In fact, our clients are in sectors that were hit the hardest by the recession, but they all saw revenue growth during this period.
How do you see customer analytics delivering value over the iPhone?
Hald: Ultimately, we want to help companies become better at listening to customers and acting on that feedback. Call centers, Web surveys, social networks like Facebook and Twitter, online forums, and receipt-based surveys are all hard-to-monitor sources of customer experience intel.
Customer intelligence is used for decision making from a local level to the boardroom. Most people who interact with customers don't sit behind a desk all day, so we needed to put information on something that's carried with them--like their iPhone. Now, whether you're the CIO, a branch employee walking the floors, or a manager in the back office, you get real-time alerts and analytics about performance and customer sentiment.
Do companies pay more attention to social and mobile Web?
Hald: Well, sales revenue is tied tightly to brand names, so a lot of attention shifts to social networks and the mobile Web. Our clients are household names, so if a conversation is taking place across social forums that could impact their brand, they care.
Pundits such as Bruce Temkin, Jeremiah Owyang, and Charlene Li at Altimeter have been big proponents of brands navigating their social personas with customers and listen to the "voice of the customer."
In large part, I agree with them, but I am always telling clients not to let social media overplay its part. Fact is, 80 percent of customer referrals still take place offline, and the case could be that only 4 percent of your customers are online, driving 90 percent of the social conversation. The value in CEM software is extracting customer intelligence from the right channels.

Life's First Energy Source-new theory

A compound known as dark pyrophosphite could have been a source of energy that allowed the first life on Earth to form, scientists say now.

From the smallest bacteria in the human body complex, all living things require a molecule called ATP-transport energy to survive. Often compared to a "rechargeable battery," ATP chemical energy stored in a form that can be used by organic matter.

"You need enzymes to produce ATP, and ATP you need to make enzymes," said researcher Terence Kee, University of Leeds in England. "The question is: Where does the power before any of these things existed? We think the answer may lie in simple molecules such as pyrophosphate, which is chemically very similar to the ATP, but has the potential to transfer energy without enzymes. "

Dark, but important

Before the theories of how life arose from chemistry only have seen a similar compound, but independent pyrophosphate was known as the predecessor to the more complex and more efficient ATP.

Phosphate has four oxygen atoms attached to a central phosphorus atom, and is present in all living cells. When the two phosphates and lose a water molecule, form pyrophosphate.

Pyrophosphite, however, rarely encountered, the chemist Robert Shapiro of New York University told LiveScience. "Even in my Google search for it, I have the query:" does not mean pyrophosphate? '"

The presence of "one or two little thorny issues" with his rival molecule [] pyrophosphate had left some questions unanswered, Kee said in a telephone interview.

The two main problems were that the pyrophosphate does not seem to be available in significant quantities in the geological record of minerals, and does not react well without catalyst (which did not exist then), according to Kee.

On the other hand, the team has found that pyrophosphite Kee would be "relatively easy to prepare from minerals that are known to exist in iron meteorites." The routes to the production of this molecule are simpler than those proposed for the pyrophosphate, Kee said.

Although similarly produced by dehydration, and similar in composition, except that it has some oxygen atoms replaced by hydrogen, pyrophosphite is rare. Only three minerals pyrophosphite exist, as opposed to "many phosphate minerals," said Kee.

The darkness of the chemical in the earth is not a sign of its irrelevance. It is very unstable in oxygen-rich environment today (ie, breaks down into other molecules quickly), but it is a superior catalyst (jump starting) for certain chemical reactions, Kee said, citing as evidence yet publish.

Lateral thinking

Altered Kee called the theory "more a process of lateral thinking that a" new concept ".

"It is strange that so little pyrophosphite and its ability to act as transfer agent of phosphorus have been known for some time, but has not been previously proposed to be important for pre-biotic" he said. "I suspect that because no one had considered the need for him or could have been pre-biotic accessible."

Interestingly, the machines that manufacture artificial DNA experiments pyrophophite regularly used in their assembly process, said Shapiro.

The researchers detail their theory pyrophosphate as an energy source of life in a recent issue of the journal Chemical Communications.