Monday, July 27, 2009

Robots Take Wing

In many ways, autonomous robots are like toddlers. They need to learn their limits. They must also discover how to play nice with others. And, like toddlers, they often fall down trying.
Nowhere was this more on evident than the Hanover Fair display of German automation specialist, Festo AG & Co. One side of the company's long space was crammed with pneumatic and electrical actuators and control systems similar to those in the booths around it. The other side contained the toys. These included a wall of lightweight pylons that interacted by moving as people walked by and a huge aquarium containing three mechanical penguins that interacted with one another as they swam.
Festo has a history of producing audacious autonomous robots for Hanover Fair, and these displays were no exception. Yet the company's most impressive display was taking place above the heads of the onlookers, where three flying penguins interacted with one another in tight airspace above Festo's booth.
Penguins, of course, cannot fly. Festo's AirPenguins, however, are balloons with bodies made of carbon fiber rod and extruded polyurethane foam under metalized foil. Each one measures 3.7 meters long and 0.9 meter deep with a 2.5-meter wingspan. Each flying penguin carries a complete control system, battery pack, an assortment of sensors, and servos to power the wings, nose, and tail. The entire ensemble weighs one kilogram.
Providing consistent yet autonomous behaviors to Festo's AirPenguin proved a major challenge for Kristof Jebens and Agalya Nagarathinam, an engineering team based in Gärtringen, Germany.
To enable the AirPenguins to interact with one another in their confined airspace—just 3.5 meters above the area of the Festo booth—Jebens first had to synchronize their wing movements through use of a wireless timing signal. "Without synchronization, if they came close, the turbulence would suck them in and they would crash," Jebens said. By eliminating a turbulence sensor, Jebens and Nagarathinam could concentrate on what was really important: avoiding the AirPenguin's most feared predator—the building's air conditioning system.
Festo had been down this road before. One year at Hanover Fair, the company featured manta ray-like balloons with wings that moved up and down. The large, flat surfaces made a perfect target for a downdraft. When the balloons flew under an air conditioning vent, any downdraft would push them into the booth.
The AirPenguins are far more versatile. Their wings not only move up and down, but also pivot to propel them forward like a swimmer doing the breaststroke. Their nose and tail bend also, allowing them to lean into turns like a real penguin in the water for faster response.
To take advantage of this mechanical flexibility, Jebens and Nagarathinam designed the AirPenguins to carry an array of sensors. For instance, a receiver enables the balloons to triangulate their position in space by listening to three ultrasonic stations located around the Festo booth. They are also equipped with a compass and three-axis accelerometer, which tell the AirPenguin if it is level or tilted, and allow the robot to calculate yaw for more-precise quick turns.
The AirPenguins also contain an air pressure sensor sensitive enough to calculate altitude to within 10 centimeters. When Jebens and Nagarathinam tested the system in Festo's high-roofed corporate lounge, that sensor worked fine. At Hanover Fair, where Festo's booth is always crowded, updrafts from the body heat of visitors and drafts from open doors made it harder for the AirPenguins to use pressure data to determine their height. The AirPenguins, however, could deduce their height from the ultrasonic beacons around the booth.
The ultrasonic receiver and pressure sensors alert the AirPenguin when a draft of cold air from the air conditioner is pushing it down. The robot might try to fly around the flow of cold air or dive into it to increase its speed and then turn sharply away.
Sometimes it works. Other times, the AirPenguins crash. When the balloons are flying, Festo technicians hold backup controls in case anything goes wrong. In the end, while Festo's AirPenguins show complex behaviors, they also have a lot of conventional automation safeguards built in as well. "
You have to do that if you want to have a nice show," Jebens said. "Sometimes, if you try to make them more adaptive, it doesn't work as well. For the software to adapt, you need lots of cycles. We don't want it to start learning while all the visitors are coming to the booth."
In other words, clean the toddlers up before company comes and hope that in a few years, they will have learned how to behave and play nice with others on their own.

Friday, July 17, 2009

Mechanical engineering

Mechanical Engineering is an Engineering discipline that involves the application of principle of physics and chemistry for analysis, design, manufacturing, and maintenance of various systems. Mechanical engineering is one of the oldest and broadest engineering disciplines.
It requires a solid understanding of core concepts including mechanics, kinematics, thermodynamics, fluid mechanics, and energy. Mechanical engineers use the core principles as well as other knowledge in the field to design and analyze manufacturing plants, industrial equipment and machinery, heating and cooling systems, motor vehicles, aircraft, watercraft, robotics, medical devices and more.



Development


Applications of mechanical engineering are found in the records of many ancient and medieval societies throughout the globe. In ancient Greece, the works of Archimedes (287 BC–212 BC) and Heron of Alexandria (c. 10–70 AD) deeply influenced mechanics in the Western tradition. In China, Zhang Heng (78–139 AD) improved a water clock and invented a seismometer, and Jun (200–265 AD) invented a chariot with differential gears. The medieval Chinese horologist and engineer Su Song (1020–1101 AD) incorporated an escapement mechanism into his astronomical clock tower two centuries before any escapement could be found in clocks of medieval Europe, as well as the world's first known endless power-transmitting chain drive
During the years from 7th to 15th century, the era called the Islamic golden age, there have been remarkable contributions from Muslims in the field of mechanical technology, Al Jaziri, who was one of them wrote his famous "Book of Knowledge of Ingenious Mechanical Devices" in 1206 presented many mechanical designs. He is also considered to be the inventor of such mechanical devices which now form the very basic of mechanisms, such as crank and cam shafts.
During the early 19th century in England and Scotland, the development of machine tools led mechanical engineering to develop as a separate field within engineering, providing manufacturing machines and the engines to power them.[ The first British professional society of mechanical engineers was formed in 1847, thirty years after civil engineers formed the first such professional society. In the United States, the American Society of Mechanical Engineers (ASME) was formed in 1880, becoming the third such professional engineering society, after the American Society of Civil Engineers (1852) and the American Institute of Mining Engineers (1871). The first schools in the United States to offer an engineering education were the United States Military Academy in 1817, an institution now known as Norwich University in 1819, and Rensselaer Polytechnic Institute in 1825. Education in mechanical engineering has historically been based on a strong foundation in mathematics and science.
The field of mechanical engineering is considered among the broadest of engineering disciplines. The work of mechanical engineering ranges from the depths of the ocean to outer space.

Salaries and workforce statistics


The total number of engineers employed in the U.S. in 2004 was roughly 1.4 million. Of these, 226,000 were mechanical engineers (15.6%), second only to civil engineers in size at 237,000 (16.4%). The total number of mechanical engineering jobs in 2004 was projected to grow 9% to 17%, with average starting salaries being $50,236 with a bachelor's degree, $59,880 with a master's degree, and $68,299 with a doctorate degree. This places mechanical engineering at 8th of 14 among engineering bachelors degrees, 4th of 11 among masters degrees, and 6th of 7 among doctorate degrees in average annual salary.The median annual income of mechanical engineers in the U.S. workforce is roughly $63,000. This number is highest when working for the government ($72,500), and lowest when doing general purpose machinery manufacturing in the private sector ($55,850).
Canadian engineers make an average of $29.83 per hour with 4% unemployed. The average for all occupations is $18.07 per hour with 7% unemployed. Twelve percent of these engineers are self-employed, and since 1997 the proportion of female engineers has risen to 6%.
Mechanical Engineering is the second highest paid profession in the UK behind medicine. A Mechanical Engineer with a CEng Status earns an average of £55,000 a year. It is also recognized that Mechanical Engineers are happy workers according to national statistics in 2006

Modern tools

Many mechanical engineering companies, especially those in industrialized nations, have begun to incorporate computer-aided engineering (CAE) programs into their existing design and analysis processes, including 2D and 3D solid modeling computer-aided design (CAD). This method has many benefits, including easier and more exhaustive visualization of products, the ability to create virtual assemblies of parts, and the ease of use in designing mating interfaces and tolerances.
Other CAE programs commonly used by mechanical engineers include product lifecycle management (PLM) tools and analysis tools used to perform complex simulations. Analysis tools may be used to predict product response to expected loads, including fatigue life and manufacturability. These tools include finite element analysis (FEA), computational fluid dynamics (CFD), and computer-aided manufacturing (CAM).
Using CAE programs, a mechanical design team can quickly and cheaply iterate the design process to develop a product that better meets cost, performance, and other constraints. No physical prototype need be created until the design nears completion, allowing hundreds or thousands of designs to be evaluated, instead of a relative few. In addition, CAE analysis programs can model complicated physical phenomena which cannot be solved by hand, such as viscoelasticity, complex contact between mating parts, or non-Newtonian flows
As mechanical engineering begins to merge with other disciplines, as seen in mechatronics, multidisciplinary design optimization (MDO) is being used with other CAE programs to automate and improve the iterative design process. MDO tools wrap around existing CAE processes, allowing product evaluation to continue even after the analyst goes home for the day. They also utilize sophisticated optimization algorithms to more intelligently explore possible designs, often finding better, innovative solutions to difficult multidisciplinary design problems.


Subdisciplines

The field of mechanical engineering can be thought of as a collection of many mechanical disciplines. Several of these subdisciplines which are typically taught at the undergraduate level are listed below, with a brief explanation and the most common application of each. Some of these subdisciplines are unique to mechanical engineering, while others are a combination of mechanical engineering and one or more other disciplines. Most work that a mechanical engineer does uses skills and techniques from several of these subdisciplines, as well as specialized subdisciplines. Specialized subdisciplines, as used in this article, are more likely to be the subject of graduate studies or on-the-job training than undergraduate research. Several specialized subdisciplines are discussed at the end of this section.


Mechanics
Mohr's circle, a common tool to study stresses in a mechanical element
Mechanics is, in the most general sense, the study of forces and their effect upon matter. Typically, engineering mechanics is used to analyze and predict the acceleration and deformation (both elastic and plastic) of objects under known forces (also called loads) or stresses. Subdisciplines of mechanics include
Statics, the study of non-moving bodies under known loads
Dynamics (or kinetics), the study of how forces affect moving bodies
Mechanics of materials, the study of how different materials deform under various types of stress
Fluid mechanics, the study of how fluids react to forces
Continuum mechanics, a method of applying mechanics that assumes that objects are continuous (rather than discrete)
Mechanical engineers typically use mechanics in the design or analysis phases of engineering. If the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. Dynamics might be used when designing the car's engine, to evaluate the forces in the pistons and cams as the engine cycles. Mechanics of materials might be used to choose appropriate materials for the frame and engine. Fluid mechanics might be used to design a ventilation system for the vehicle , or to design the intake system for the engine.


Kinematics

Kinematics is the study of the motion of bodies (objects) and systems (groups of objects), while ignoring the forces that cause the motion. The movement of a crane and the oscillations of a piston in an engine are both simple kinematic systems. The crane is a type of open kinematic chain, while the piston is part of a closed four bar linkage.
Mechanical engineers typically use kinematics in the design and analysis of mechanisms Kinematics can be used to find the possible range of motion for a given mechanism, or, working in reverse, can be used to design a mechanism that has a desired range of motion.



Mechatronics and robotics


Training FMS with learning robot SCORBOT-ER 4u, workbench CNC Mill and CNC Lathe
Mechatronics is an interdisciplinary branch of mechanical engineering, electrical engineering and software engineering that is concerned with integrating electrical and mechanical engineering to create hybrid systems. In this way, machines can be automated through the use of electric motors, servo-mechanisms, and other electrical systems in conjunction with special software. A common example of a mechatronics system is a CD-ROM drive. Mechanical systems open and close the drive, spin the CD and move the laser, while an optical system reads the data on the CD and converts it to bits. Integrated software controls the process and communicates the contents of the CD to the computer.
Robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. These robots may be of any shape and size, but all are preprogrammed and interact physically with the world. To create a robot, an engineer typically employs kinematics (to determine the robot's range of motion) and mechanics (to determine the stresses within the robot).
Robots are used extensively in industrial engineering. They allow businesses to save money on labor, perform tasks that are either too dangerous or too precise for humans to perform them economically, and to insure better quality. Many companies employ assembly lines of robots, and some factories are so robotized that they can run by themselves. Outside the factory, robots have been employed in bomb disposal, space exploration, and many other fields. Robots are also sold for various residential applications.


Structural analysis


Structural analysis and Failure analysis

Structural analysis is the branch of mechanical engineering (and also civil engineering) devoted to examining why and how objects fail. Structural failures occur in two general modes: static failure, and fatigue failure. Static structural failure occurs when, upon being loaded (having a force applied) the object being analyzed either breaks or is deformed plastically, depending on the criterion for failure. Fatigue failure occurs when an object fails after a number of repeated loading and unloading cycles. Fatigue failure occurs because of imperfections in the object: a microscopic crack on the surface of the object, for instance, will grow slightly with each cycle (propagation) until the crack is large enough to cause ultimate failure.
Failure is not simply defined as when a part breaks, however; it is defined as when a part does not operate as intended. Some systems, such as the perforated top sections of some plastic bags, are designed to break. If these systems do not break, failure analysis might be employed to determine the cause.
Structural analysis is often used by mechanical engineers after a failure has occurred, or when designing to prevent failure. Engineers often use online documents and books such as those published by ASM to aid them in determining the type of failure and possible causes.
Structural analysis may be used in the office when designing parts, in the field to analyze failed parts, or in laboratories where parts might undergo controlled failure tests.


Thermodynamics

Thermodynamics is an applied science used in several branches of engineering, including mechanical and chemical engineering. At its simplest, thermodynamics is the study of energy, its use and transformation through a system. Typically, engineering thermodynamics is concerned with changing energy from one form to another. As an example, automotive engines convert chemical energy (enthalpy) from the fuel into heat, and then into mechanical work that eventually turns the wheels.
Thermodynamics principles are used by mechanical engineers in the fields of heat transfer, thermofluids, and energy conversion. Mechanical engineers use thermo-science to design engines and power plants, heating, ventilation, and air-conditioning (HVAC) systems, heat exchangers, heat sinks, radiators, refrigeration, insulation, and others.


Technical drawing and CNC


A CAD model of a mechanical double seal
Drafting parts. A technical drawing can be a computer model or hand-drawn schematic showing all the dimensions necessary to manufacture a part, as well as assembly notes, a list of required materials, and other pertinent information. A U.S. mechanical engineer or skilled worker who creates technical drawings may be referred to as a drafter or draftsman. Drafting has historically been a two-dimensional process, but computer-aided design (CAD) programs now allow the designer to create in three dimensions.
Instructions for manufacturing a part must be fed to the necessary machinery, either manually, through programmed instructions, or through the use of a computer-aided manufacturing (CAM) or combined CAD/CAM program. Optionally, an engineer may also manually manufacture a part using the technical drawings, but this is becoming an increasing rarity, with the advent of computer numerically controlled (CNC) manufacturing. Engineers primarily manually manufacture parts in the areas of applied spray coatings, finishes, and other processes that cannot economically or practically be done by a machine.
Drafting is used in nearly every subdiscipline of mechanical engineering, and by many other branches of engineering and architecture. Three-dimensional models created using CAD software are also commonly used in finite element analysis (FEA) and computational fluid dynamics (CFD).


Frontiers of research

Mechanical engineers are constantly pushing the boundaries of what is physically possible in order to produce safer, cheaper, and more efficient machines and mechanical systems. Some technologies at the cutting edge of mechanical engineering are listed below (see also exploratory engineering).


Micro Electro Mechanical Systems (MEMS)

Micron-scale mechanical components such as springs, gears, fluidic and heat transfer devices are fabricated from a variety of substrate materials such as silicon, glass and polymers like SU8. Examples of MEMS components will be the accelerometers that are used as car airbag sensors, gyroscopes for precise positioning and microfluidic devices used in biomedical applications.


Composites

Composites or composite materials are a combination of materials which provide different physical characteristics than either material separately. Composite material research within mechanical engineering typically focuses on designing (and, subsequently, finding applications for) stronger or more rigid materials while attempting to reduce weight, susceptibility to corrosion, and other undesirable factors. Carbon fiber reinforced composites, for instance, have been used in such diverse applications as spacecraft and fishing rods.


Mechatronics


Mechatronics is the synergistic combination of mechanical engineering, electronic engineering, and software engineering. The purpose of this interdisciplinary engineering field is the study of automata from an engineering perspective and serves the purposes of controlling advanced hybrid systems.


Nanotechnology

At the smallest scales, mechanical engineering becomes nanotechnology and molecular engineering—one speculative goal of which is to create a molecular assembler to build molecules and materials via mechanosynthesis. For now this goal remains within exploratory engineering.


Finite Element Analysis

This field is not new, as the basis of Finite Element Analysis (FEA) or Finite Element Method (FEM) dates back to 1941. But evolution of computers has made FEM a viable option for analysis of structural problems. Many commercial codes such as ANSYS, Nastran and ABAQUS are widely used in industry for research and design of components.
Other techniques such as Finite Difference Method (FDM) and Finite Volume Method (FVM) are employed to solve problems relating heat and mass transfer, fluid flows, fluid surface interaction etc.

Monday, July 13, 2009

Mecanical or Electrical Gauges.



We receive many questions asking which is better, electrical or mechanical gauges. Both mechanical and electrical gauges are equally accurate. The determining factors more involve installation and application than gauge accuracy. Our new "Full Sweep" electric gauges combine the electric gauge wiring with a full sweep dial face like the mechanical gauge. This short list of advantages should help you to make the decision for your specific application.
Mechanical Gauge Advantages
Full 270° sweep, makes them easier to read accurately.
Mechanical gauges do not require 12V power to operate. They make direct physical contact with the item they are reading. They do this through tubing or lines, which eliminates the need for electric signals.
Ideal for vehicles that operate on voltages other than 12V, with no voltage at all (magneto applications) or operate on a battery with no generator.


Electrical Gauge Advantages
90° sweep.
No large connectors and tubing coming out the back.
Can be mounted in more unusual positions without connections showing.
Easier to install in tight areas.
Easier to install a great distance from the item being measured.
Stops fluids from entering the passenger compartment.

Low Temp 60° - 210° Water TemperatureIdeal for drag race teams.
Includes all the advantages of an electric gauge (easy to connect, easier to install in tight places, etc...).

Full 270° sweep, makes it easier to read acurately.

Mechanical pencil

A mechanical pencil looks very much like a ballpoint pen, but the fine writing tip is of lead or graphite. The first mechanical pencil was invented in Britain in the early 1820s, and patented by John Hawkins and Sampson Mordon in 1822. A mechanical pencil opens just like a normal pen, but instead of refilling it with a new ink cartridge, a length of specially manufactured pencil lead is fed into the writing barrel. Once the mechanical pencil is closed, lead can be pushed through the barrel in small increments -- as it is used -- by clicking the tip of the pen, depressing a ratchet button, or twisting the cone of the barrel, depending on the model. The advantage of a mechanical pencil is that the lead is so thin that it's always sharp, allowing precise and uniform strokes without the hassle of constant sharpening. This makes the mechanical pencil ideal for architects, draftsman, engineers, and anyone else that requires the convenience of a pen with the flexibility of an erasable pencil. One leading manufacturer of pens offers a liquid lead mechanical pencil. The graphite in this case, is in solution, behaving much like ink as it rolls from the ballpoint-like tip. However, once the fluid is absorbed into the paper and dries, only erasable graphite is left. This mechanical pencil purportedly writes with the fluid motion of a pen, while offering all the advantages of a pencil. It retails for less than $3 (US dollars), and is refillable. Aside from the convenience of never having to sharpen a mechanical pencil, they are also environmentally friendly, saving wood and eliminating the wood shavings of traditional pencils. An exception to this rule would be disposable mechanical pencils. Fortunately, there is little reason to buy a disposable model when refillable models are so cheap. Many leading manufacturers of pens make mechanical pencils, and several types of lead are available from soft to hard. Mechanical pencils can be purchased in sets with a matching mechanical pen, or individually. They range in quality from plastic barrels to enamel, gold or silver, and prices vary accordingly.

Friday, July 3, 2009

BASIC AIR CONDITIONING

BASIC AIR CONDITIONING
SYSTEM DESIGN

INIRODUCTION

Air conditioning system design is a broad and sometimes complex field with many Aspect to consider and many options available for selection of the final system for a particular project.Air conditioning system is design is more than just a technical exercise and in order to Design an air conditioning system we need to understand what air conditioning is, what The clients needs are, what constraints there are on the design and what the architect trying to achieve. That is, we need to know the technical aspects of air conditioning system As well as the effect of the design of the other members of the project team. The design process involves a mix of technical interpersonal and management skills. This paper covers a typical air conditioning system design process.
So how do we go about designing air conditioning system? first of all we need to understand. What air conditioning is.

THE TECHNICAL ASPECT

Air conditioning is the treatment of the environment to achieve a set of required conditioning the field of building services it usually relates to air providing comforts For the building occupants but could also cover other situation such as fumigation and specialist storage environments. this presentation will deal only with treatment of air for Comforts conditions. The environmental condition, which is controlled in a given design, may include:
Ø Dry bulb temperature
Ø Moisture contents of the air (humidity, both relative and absolutes)
Ø Air movements
Ø Air quality

The need for control of these variables and there control points will be based on the Clients requirements. For example, if a factory owner wants to provide some limited Cooling for their factory .then dry bulb temperature control over a fairly wide range would probably suffice. However if a pharmaceutical manufacture wants to provide suitable condition for theirs manufacturing process, then we would needs to controls all the above variables to close tolerance. Air quality is control by filtration system, and an air movement is controlled by the distribution system. These aspects of air conditioning system design are worth separate Discussion and there own paper .we will look at the control of temperature and moisture control only. A useful tool to help visualize the control of temperature and moisture control is the Psychometric chart. Atmospheric air is a mixture of air and water vapour.The psychometric chart is a graph showing the various concentration of water vapor in the air and the associated temperatures, densities and energy contents. The task of the air conditioning system is to control the temperature and moisture Contents of the air by one or more of the following process.

Ø Heating
Ø Cooling
Ø Dehumidification
Ø Humidification


The Metabolic Rate

The rate at which body produces heat is called the metabolic rate. The heat produce by a
normal healthy person while sleeping is called the basal metabolic rate which is of the order of 60W.The maximum value may be 10 times much as this for a person engaged in sustained hard work.
The temperature of the body remains comparatively constant at about 36.9 C(98.4)for tissues or the skin and abt 37.2 C for the deep tissues or the core. it is found that the body temperature in the morning after sleep is about 0.5C less than its temperature in the afternoon. A value of 40.5C (104.9F) is considered serious and 43.5C (110F) is certainly fatal..
Human comfort is influenced by physiological factor determined by the rate of heat
generation within the body and the rate of heat dissipation to the environment


OUTSIDE DESIGN CONDITION:

It is observed that there is kinds of sinusoidal relationship the air dry bulb temperature and the sun time. For example, in the month of June in a certain locality where the sun rise is at about 5 am. and the sunset at about 7pm.the time of minimum temperature falls at about 4 pm.,i.e.,whith laps of about 12 hours.
As regards relative humidity, it is seen that it reaches a minimum value in the afternoon.
Since the mean daily maximum dry bulb temperature occurs between 1 pm., it is reasonable to assume that the minimum relative humidity would occur during the same period.

BRIEF HISTORY OF REFRIGERATION

The method of production of cold by mechanical process is quite recent. Long back in 1748, William coolen of Glasgow University produced refrigeration by creating partial Vacuum over ethyl ether, but he could not implement his experience in practice. The first development took place in 1834 when Perkins proposed a hand-operated compressor machine working on ether. Then in1851 came Gorrie, s air refrigeration machine, and in1856 Linde developed a machine working on ammonia.
The pace of development was slow in the beginning when steam engine was the only prime mover known to run the compressors. With the advent of electric motor and Consequent higher speed of the compressor, the scope of applications of refrigeration widened.the pace of development was considerably quickened in 1920 decade when due pont put in the market a family of new working substances, the fluoro-chloro derivates of Methane ,ethane ,etc.popularly known as chloro fluorocarbon or CFCs—under the name of Freons, since it has been found that chlorine atoms in Freons are responsible for the depletion of ozone layer in the upper atmosphere. Water vapors absorption machine by Carre.These developments account for the major commercial and industrial application in the field of refrigeration.
A phenomenon called Peltier effect was discovered in 1834 which is still not commercialized. Advances in cryogenics, a field of very low temperature refrigeration, were registered with the liquefaction of oxygen by pictet in 1877.Dewar made the famous Dewar flask in 1898 to store liquids at cryogenic temperatures. Then followed the liquefaction of other permanent gases including helium in 1908 by Ones which led to the discovery of the phenomenon of superconductivity. Finally in 1926,Giaque and Debye independently proposed adiabatic demagnetization of a paramagnetic salt to reach temperatures near absolute zero Two of the most common refrigeration application ,viz.,a window-type conditioner and a domestic refrigerator ,have been described in the following pages.

ROOM AIR CONDITIONER

Flowing figure shows schematic diagram of a typical window –type room air conditioner, which works according to the principle described below:
Consider that a room is maintained at constant temperature of 25C.In the air conditioner, the air from the room is drawn by a fan is made to pass over a cooling coil, the surface of which is maintained, say, at a temperature of 10C.After passing over the coil, the air is cooled (for example, 15C) before being supplied to the room. After picking up the room heat, the air is again return to the cooling coil at 25C.
Now, in the cooling coil, a liquid working substance called a refrigerant, such as CHCIF2 (monochloro-difluoro methane), also called Freon 22 by trade name,

Schematic diagram of a Room air conditioner

Or simply refrigerant 22 (R22) ,enter at a temperature of ,say,5C and evaporates, thus absorbing its latent heat of vaporization from the room air. This equipment in which the refrigerant evaporates is called an evaporator.
After evaporation, the refrigerant becomes vapour.To enable it to condense back and to release the heat –which it has absorbed from the room while passing through the vapor-its pressure is raised by a compressor. Following this the high pressure vapors enter the condenser. In the condensers, the outside atmospheric air, say, at a temperature of 45C in summer, is circulating by a fan. After picking up the latent heat of condensation from the condensing refrigerant, air is let out in to the environment ,say, at temperature of 55C.The condensation of refrigerant may occure,for example, at temperature of 60C
After condensation, the high pressure liquid refrigerant is reduced to the low pressure of the evaporator by passing it through pressure reducing device called the expansion device, and thus the cycle of operation is completed. A partition wall separates the high temperature side of the condenser from the low temperature side of the evaporator
The principle of working of large air conditioning plants is also the same, except that condenser is water cooled instead of being air cooled .

Unit of Refrigeration capacity:
The standard unit of refrigeration in vogue is ton refrigeration or simply ton denoted By the symbol TR.It is equivalent to the production of cold at the rate at which heat is to be removed from one US tone of water at 32 F to freeze it to ice at 32 F in one dayor 24 hours .Thus
1TR=1×2,0001b×144Btu/1b
24 hrs
=12,000Btu/hrs=200Btu/min
where the latent heat of fusion of ice has been taken as 144 Btu/1B.The term one ton refrigeration is a carry over from the time ice was used for cooling. In general 1TR always means 12,000Btu of heat removal per hours, irrespective of the working substance used and the operating condition, viz, temperature of refrigeration and heat rejuction.This unit of refrigeration is currently in used in the USA, the UK and India. in many countries, the standard MKS unit of kcal/hr is used

It can be sent that
1TR=12,000 BTU/hr
=12000 =3,024kcal/hrs
3.968
=50kcal/min =50 kcal/min
Also, since 1Btu =1.055kj,the conversion of ton in to equivalent SI unit is
1TR=12,000×1.055=12,600 kj/hours
=211 kj/min=3.5167K

Design for air conditioning of a 4 m high-story office building located at 30N latitude, the plan of which is shown in fig the following data are given
Fig.

Plan of building for example
Plaster on inside =11/4cm

Outside wall construction =20cm concrete block
Partition wall construction=33cm brick
Roof construction =20cm RCC slab with 4cm asbestos cement board
Floor construction =20cm concrete
Densities, brick =2000kg/m3
Concrete =1900kg/m3
Plaster = 1885kg/m3
Asbestos board =520kg/m3
Fenestration =2m×11/2m glass
(Weather stripped loose fit) U=5.9wm-2 k-1
Doors =11/2m×2m wood panels
U=0.63 Wm-2 k-1
Outdoors-design condition=43C DBT,27C WBT
Indoor-design condition =25C DBT, 50% RH
Daily range =31C to 43C =12C
Occupancy =100
Light =15,000W florescent
Assumed by pass factor of coil: 0.15
Find the room sensible and latent heat loads, and also the grand total heat load.
Solution
Thermal conductivities from table 18.1
k glass =0.78 Wm-1 k-1
k concrete =1.73 Wm-1 k-1
k brick =1.32 Wm-1 k-1
k plaster =8.65 Wm-1 k-1
k asbestos =0.154Wm-1 k-1

Assumed film coefficients
ƒ=23 Wm-2 k-1
ƒi=7 Wm-2 k-1
Outside wall
1/U=1/23+0.1/1.32+0.2/1.73+1/7+0.0125
U=7 Wm-2 k-1
Partition wall
1/U=1/7+0.33/1.32+1/7+2 (0.0125)/8.65

U=1.86 Wm-2 k-1
Roof
1/U=1/23+0.2/9+0.04/0.154+0.0125/8.65+1/7
U=2.13 Wm-2 k-1
Floor
1/U=1/7+0.2/9
Area and volume of space
A= (27) (17) =459m2
V= (459) (4) =1836m2

Ventilation rate of office
QV/person=0.28 cmm (from Table 16.2)
Qv=0.28(100) =28cmm

Number of air changing of ventilation air
(28)(60)/1836=0.92(satisfactory)
Mass of wall per unit area
Outside wall: 0.2(1900) + (2000) +0.0125(1885)
=604 kg/m2


Partition wall: 0.33 (2000) + 2(0.0125) (1885) =707 kg/m2

Roof: 0.2(1900) + 0.04 (520) =401 kg/m2
Correction for equivalent temperature differential
For daily range of 12C=12-11.1 =0.45C
2
For (t-ti)of 18C = 18-8.3=9.7C
Total correction= -0.45+9.7=9.25C
Equivalent temperature differential in C, from Table 18.9 and 18.10 and
Incorporating correction:
2 p.m. 3 p.m. 4 p.m 5 p.m 6 p.m 7 p.m
West wall 14.4 14.8 15.2 16.5 17.5
North wall 9.6 10.2 9.6 11.3 11.7
South wall 13.1 14.7 16.0 17.4 17.8
Roof (exposed) 24.0 25.8 28.0 29.7 30.5 30.2
__


Rates of solar gain through glass on June 21 W/m2 from Table 17.8(d)
2pm 3pm 4pm 5pm
West glass 309 451 508 492
North glass 44 44 51 91
South glass 47 44 38 32
_____________________________________________________________
Door area = 11/2×2=3m2
Glass area
West glass=4(2×11/2) =12m2
North glass=2×11/2 =3m2
South glass =2(2×11/2) =6m2
Outside wall areas
West wall = (27) (4)-12=96m2
North wall= (10) (4)-3-3=34m2
South wall = (17) (4)-3-6=59m2
Partition wall area
East wall= (27) (4)-3=105m2
North wall= (7) (4) =28m2
Estimated time of maximum cooling load:
From the above calculation, it is obvious that the major components of the variable
Cooling loads are solar and transmission heat gains through the west wall and glass
And the roof. Of these glass and roof loads are the predominant loads. The roof load
Is maximum at 6 pm.when the equivalent temperature differential is 30.5C.The solar
gain through the west glass has a maximum value of 508 w/m2 at 4 pm.Thus the time
Of maximum loads is most likely to be near 5pm. Heat transfer through floor:
Assume a temperature difference of 2.5 C across the floor wind pressure
Assume a wind velocity of kmp, we have
Δp=0.00047(15) =0.11cm H2O
Infiltration rate for window, from table 18.11 for 0.11 wind pressure
=2.5m3/h/m crack
Length of crack for 7 window=7<2(2+11/2)>=49m
SHL=75W/person
LHL=55W/person
Other assumption
Only 10%of the supply duct outside the condition space
No return duct outside the conditioned space
Fan horsepower,5 per cent of RSH
The detail of cooling loads calculation are given on the calculation sheet in table
Calculation sheet fir cooling load Estimation
Space used for office
Size 27×17=459m2×4=1836m2
Estimate for 5 pm LOCAL TIME SUN TIME
HOURSE OF OPERATION DAY TIME
Conditions DB WB %RH DP h, kj/kg kg/kg
Outdoors 43 27 29 21.3 85.0 0.016
ROOM 25 18 50 15.7 50.85 0.01
Difference 18 34.15 0.006
OUTDOOR AIR
100 PEOPLE×0.28cmm/PERSON=28cmm
VENTILATION cmm=28

SWINGING
REVOLVING____________PEOPLE ×___________cmm/PERSON=cmm
DOORS
OPEN 3 DOORS×1.9813cmm/DOOR=17.8cmm
DOORS
EXAUST _____________________________________________=cmm
FAN
CRACK 49m×2.5/60 cmm/m=2.0cm
INFILTRATION cm

LOAD CALCULATIONS
ITEM AREA OR SUN GAIN OR FACTOR W
QUANTITY TEMP.DIFF.OR
HUMIDITY
DIFF.
SENSIBLE HEAT
SOLAR GAIN-GLASS
EAST GLASS -m2 ___ ___ ___
WEST GLASS 12m2 492 __ 5,900
NORTH GLASS 3m2 91 __ 270
SOUTH GLASS 6m2 32 __ 190
SKY LIGHT -m2 __ __ __

SOLAR TRANSMITION GAIN-WALLS AND ROOF
EAST WALL -m2 __ ___ ___
WEST WALL 96m2 16.5 3.5 5,540
NORTH WALL 34m2 11.3 3.5 1,345
SOUTH WALL 59m2 17.4 3.5 3,590
ROOF-SUN 459m2 29.7 2.13 29.035
ROOF-SHADED -m2 __ __ __

TRANSMITION GAIN- OTHERS
DOORS 9m2 18 0.63 100
ALL GLASS (12+3+6) m2 18 5.9 2,230
PARTITION (108+28) m2 15.5 1.86 3,930
CEILING -m2 __ __ __
FLOOR 459 2.5 6.05 6,940
INFILTRATION 19.8cmm 18 20.4 7,270

INTERNAL HEAT GAIN
PEOPLE 100 __ 75 7,500
POWER __ __ __ __
LIGHT 15,000 __ 1.25 18,750
APPLIANCES __ __ __ __
ADDITIONAL __ __ __ __

_________________
SUB TATAL 92,690
STORAGE (Neglected) __ __ __ __
SAFETY
FACTOR 5% 4,635
ROOM SENSIBLE HEAT 103,090
SUPPLY DUCT
SUPPLY DUCT
HEAT GAIN 0.5%+LEAKAGE O.5%+Fan 5% 5,560
HP
OUTDOOR AIR
BY PASSED 28cmm 18C 20.4×0.15 1540
EFECTIVE ROOM SENSIBLE HEAT 104,425
LATENT HEAT
INFILTRATION 19.8cmm 0.006 50,000 5,940
PEOPLE 100 --- 55 5,500
STEAM -- -- -- --
APPLIANCES -- -- -- --
ADDITIONAL -- -- -- --
VAPOR TRANS -- -- -- --
_________________________
SUB TOTAL 11,440
SAFETY FACTOR 5% 570
ROOM LATENT HEAT 12,010
SUPLY DUCT
LEAKAGE LOSS 0.5% 60
OUTDOOR AIR
BY PASSED 28 0.006 50,000×0.15 1,260
EFFECTIVE ROOM LATENT HEAT 13,330
EFFECTIVE ROOM TOTAL HEAT 117,755

OUTDOOR AIR TOTAL HEAT (on equipment)
SENSIBLE 28cmm 18 20.4× (1-0.15) 8740
LATENT 28cmm 0.006 50,000× (1-0.15) 7140
RETURN 0%+RETURN DUCT 0%PUMP %+DEUH. %
DUCT LEAKAGE GAIN PIPE
HEAT GUN GAI


GRAND TOTAL HEAT

133,635(38TR)
Note
Many designers do not like in to account the filtration loads separately. It is consider to be taken care of by ventilation air if the ventilation cmm is designer is greater than filtration cmm.one such simplified loads estimation calculation sheet fir the ground, first and third floor of television studio building, without considering infiltration loads. note that in such a case, there is actually no infiltration as the room is under positive pressure. There is, however, infiltration which is equivalent to exhaust of the room air.

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