# The refrigeration



## aati badri (27 أكتوبر 2010)

http://www.refrigerationbasics.com/1024x768/rb1.htm
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## aati badri (27 أكتوبر 2010)

http://www.refrigerationbasics.com/1024x768/*******s.htm


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## aati badri (27 أكتوبر 2010)

_*Introduction to the Refrigeration Trade*_ 
contact | order | pricing | readme | requirements | sample sections | shipping options | SI Units | teachers 
Available on CD-ROM from Seaside Computing, this introductory refrigeration training course is presented in a clear interesting manner utilizing interactive graphics and logically organized material, all from a mechanics perspective. Learn about the mechanical refrigeration process and how to diagnose and troubleshoot refrigerant side, air side, and electrical side problems.*Refrigeration Training*

There are a great number of technical publications dealing with refrigeration training but few are written from a mechanics perspective. This one is. It illustrates the mechanical refrigeration process and related topics with straight forward explanations and graphics. It's intent is to make it easy to understand important concepts and terminology. Traditional refrigeration textbooks cover such a large scope of material and in such great detail that rudimentary concepts often become lost in the process. Refrigeration Basics is an introduction to the Refrigeration Trade and focuses on creating a solid foundation which can be built upon readily. Learning about refrigeration is a never ending process and well understood fundamentals make learning more advanced concepts much easier. This interactive CD-ROM is a preparation for anyone interested in entering the air conditioning and refrigeration trade and is an introduction to some of the immediate problems one will face in the field. It is designed for those who: *are considering going into the refrigeration trade or trade college
*wish an easily understandable overview of HVAC/R (Heating Ventilation Air Conditioning/Refrigeration)
*wish a reference of basic refrigeration concepts
*are interested in these topics.



*Version II - Standard*Version II is available at the original economic price. See the online sample sections and try the interactive electrical troubleshooting boards.*Learn to Troubleshoot*




*Version III - Professional*The Version III release contains everything from the previous version as well as an amazing 100 interactive troubleshooting boards with fully functional test instruments. Learn the basics and then develop your troubleshooting skills on various types of refrigeration and air conditioning systems. All 100 boards utilize high and low side pressure gauges, a 9 point digital thermometer for measuring refrigerant, air, and water temperatures and of course an Amp/Ohm/Volt meter which measures all test points on the electrical schematics. Click the thumbnail images below for larger screen shots. (actual boards are full screen) 
In 2004, version III troubleshooting boards gained SI Units capability. The temperature meter could now be toggled to display Imperial units in ؛F or SI Units in ؛C. The refrigerant gauges could be toggled to display PSIG or kPa. As of March, 2007, version III now has SI capability throughout the entire ebook. All textual references to Imperial units can now be viewed in their SI unit counterparts. Diagrams and graphics which used to be in Imperial units only, can now be toggled to display SI Units. A new section called Systems of Measurement has been added to Refrigeration Basics.*Version III interactive troubleshooting board screen shots:
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_*click for more Version III features*_
*Features (Both Versions)**Interactive Graphics*[SIZE=-1]Sequential overlaid graphics are used to clearly illustrate the topic at hand. Buttons allow interactive back and forth control for logical comparisons.[/SIZE]*Animated Graphics*[SIZE=-1]Animations are used to clearly demonstrate concepts like heat flow and the mechanical workings of things like reciprocating, scroll and rotary compressors and bimetal warp switches.[/SIZE]*Full Screen Graphics*[SIZE=-1]Many sections, especially the troubleshooting boards use full screen graphics. The need to side scroll is eliminated because Refrigeration Basics senses your screen resolution and loads the page designed for your particular resolution. All resolutions are supported and exact full screen implementation is provided for [640x480], [800x600], [1024x768][/SIZE]*Actively Linked Index*[SIZE=-1]The *******s section is presented in a logical learning progression. There is also a linked Index to quickly locate topics. The links take you instantly to the exact spot on the specific page that covers the topic.[/SIZE]*Actively Linked Review Questions*[SIZE=-1]Each section has review questions which link to the spot on the appropriate page that covers the topic.[/SIZE]*PT Chart Refrigerant Data Base*[SIZE=-1]92 Pressure/Temperature Charts linked by ASHRAE and Trade Name Index. Each PT Chart also shows chemical formula, chemical name, recommended oil and if it is a blend lists the ODS refrigerant that it replaces.[/SIZE]*Interactive Refrigerant Side Diagnostics*[SIZE=-1]The relationship between refrigerant side parameters are explored with the interactive Causes & Effects tutorial. Although this course starts off with the basics it lets the participant advance to the point where complex refrigerant side parameters are dealt with in an interactive way.[/SIZE]*Interactive Electrical Troubleshooting*[SIZE=-1]After being presented with electrical basics, learn to troubleshoot electrical schematics with built in faults with simulated Amp/Volt/Ohm meters.[/SIZE]*Exam marks itself*[SIZE=-1]100 question, multiple choice exam fully tests participants grasp of the material. Submit button displays participant's mark in percentage.[/SIZE] 
*Browse Sample Sections*



*Secure Online Ordering*[SIZE=-1]Click this link to access our secure online order form



[/SIZE][SIZE=+1]*Online Order Form*[/SIZE]*Pricing** is located in the product drop down list on the order form*




[SIZE=-1]Our order form is secured using a Comodo Digital Certificate. This ensures that all information you send to us via the World Wide Web will be encrypted.[/SIZE]



*New for 2009:**Gas Fitter Basics*Visit GasFitterBasics.com to check out Seaside Computing's latest interactive training product. Gas Fitter Basics contains 100 interactive troubleshooting boards with built in faults and a 100 question exam just like Refrigeration Basics.


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## aati badri (27 أكتوبر 2010)

*Part 1*





This section explains in basic terms the principals that are used to create the refrigeration effect. Graphics and animation's are used in an attempt to make it easy to understand the concepts involved. First of all, did you know that there is no such thing as cold? You can describe something as cold and everyone will know what you mean, but cold really only means that something contains less heat than something else. All there really is, is greater and lesser amounts of heat. The definition of refrigeration is _The Removal and Relocation of Heat._ So if something is to be refrigerated, it is to have heat removed from it. If you have a warm can of pop at say 80 degrees Fahrenheit and you would prefer to drink it at 40 degrees Fahrenheit, you could place it in your fridge for a while, heat would somehow be removed from it, and you could eventually enjoy a less warm pop. (oh, all right, a cold pop.) But lets say you placed that 40 ؛F pop in the freezer for a while and when you removed it, it was at 35 ؛F. See what I mean, even "cold" objects have heat ******* that can be reduced to a state of "less heat *******". The limit to this process would be to remove all heat from an object. This would occur if an object was cooled to _Absolute Zero_ which is -460 ؛F or -273 ؛C. They come close to creating this temperature under laboratory conditions and strange things like electrical superconductivity occur.
*How do things get colder?*




The latter two are used extensively in the design of refrigeration equipment. If you place two objects together so that they remain touching, and one is hot and one is cold, heat will flow from the hot object into the cold object. This is called _conduction._ This is an easy concept to grasp and is rather like gravitational potential, where a ball will try to roll down an inclined plane. If you were to fan a hot plate of food it would cool somewhat. Some of the heat from the food would be carried away by the air molecules. When heat is transferred by a substance in the gaseous state the process is called _convection._ And if you kicked a glowing hot ember away from a bonfire, and you watched it glowing dimmer and dimmer, it is cooling itself by _radiating_ heat away. Note that an object doesn’t have to be glowing in order to radiate heat, all things use combinations of these methods to come to equilibrium with their surroundings. So you can see that in order to refrigerate something, we must find a way to expose our object to something that is colder than itself and nature will take over from there. We are getting closer to talking about the actual mechanics of a refrigerating system, but there are some other important concepts to discuss first. *The States of Matter*They are of course; solid, liquid and gas. It is important to note that heat must be added to a substance to make it change state from solid to liquid and from liquid to a gas. It is just as important to note that heat must be removed from a substance to make it change state from a gas to a liquid and from a liquid to a solid. *The Magic of Latent Heat*



Long ago it was found that we needed a way to quantify heat. Something more precise than "less heat" or "more heat" or "a great deal of heat" was required. This was a fairly easy task to accomplish. They took 1 Lb. of water and heated it 1 degree Fahrenheit. The amount of heat that was required to do this was called 1 BTU _(British Thermal Unit)._ The refrigeration industry has long since utilized this definition. You can for example purchase a 6000 BTUH window air conditioner. This would be a unit that is capable of relocating 6000 BTU's of heat per hour. A unit with a capacity of 12,000 BTUH would be called a one Ton unit. There are 12,000 BTU's in 1 Ton. The metric system of measurement specifies the Calorie as the basic unit of heat. A Calorie is the amount of heat that is required to raise the temperature of one gram of water through one degree Celsius. A larger unit of heat is the KiloCalorie (1000 Calories) or the amount of heat required to raise the temperature of a liter of water through one degree Celsius. The SI-system uses the Joule as a unit of heat. It's a multiple of the metric fundamental unit of energy, the erg, and is intended to replace the calorie.



To raise the temperature of 1 LB of water from 40 ؛F to 41 ؛F would take 1 BTU To raise the temperature of 1 LB of water from 177 ؛F to 178 ؛F would also take 1 BTU However, if you tried raising the temperature of water from 212 ؛F to 213 ؛F you would not be able to do it. Water boils at 212 ؛F and would prefer to change into a gas rather than let you get it any hotter. Something of utmost importance occurs at the boiling point of a substance. If you did a little experiment and added 1 BTU of heat at a time to 1 LB of water, you would notice that the water temperature would increase by 1 degree Fahrenheit each time. That is until you reached 212 ؛F Then something changes. You would keep adding BTU's, but the water would not get any hotter! It would change state into a gas and it would take 970 BTU's to vapourize that entire pound of water. This is called the Latent Heat of Vapourization and in the case of water it is 970 BTU's per pound. 
So what! you say. When are you going to tell me how the refrigeration effect works? Well hang in there, you have just learned about 3/4 of what you need to know to understand the process. What keeps that beaker of water from boiling when it is at room temperature? If you say it's because it is not hot enough, sorry but you are wrong. The only thing that keeps it from boiling is the pressure of the air molecules pressing down on the surface of the water. When you heat that water to 212 ؛F and then continue to add heat, what you are doing is supplying sufficient energy to the water molecules to overcome the pressure of the air pressing down on it's surface and allow them to escape from the liquid state. If you took that beaker of water to outer space where there is no air pressure the water would flash into a vapour instantly. If you took that beaker of water to the top of Mt. Everest where there is much less air pressure than at lower altitudes, you would find that much less heat would be needed to boil the water. (it would boil at a lower temperature than 212 ؛F). So water boils at 212 ؛F at normal atmospheric pressure. Lower the pressure and you lower the boiling point. Therefore we should be able to place that beaker of water under a bell jar and have a vacuum pump extract the air from within the bell jar and watch the water come to a boil even at room temperature. This is indeed the case! A liquid requires heat to be added to it in order for it to overcome the air pressure pressing down on its' surface if it is to evaporate into a gas. We just learned that if the pressure above the liquids surface is reduced it will evaporate easier. We could look at it from a slightly different angle and say that when a liquid evaporates it absorbs heat from the surrounding area. So, finding some fluid that evaporates at a handier boiling point than water (IE: lower) was one of the first steps required for the development of mechanical refrigeration. Chemical Engineers spent years experimenting before they came up with appropriate chemicals for the job. They developed a family of hydroflourocarbon refrigerants which had extremely low boiling points. These chemicals would boil at temperatures below 0 ؛F at atmospheric pressure. So finally, we can begin to describe the mechanical refrigeration process.


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## aati badri (27 أكتوبر 2010)

*Part 2*

* Main Components*





There are 4 main components in a mechanical refrigeration system. Any components beyond these basic 4 are called accessories. The compressor is a vapour compression pump which uses pistons or some other method to compress the refrigerant gas and send it on it's way to the condenser. The condenser is a heat exchanger which removes heat from the hot compressed gas and allows it to condense into a liquid. The liquid refrigerant is then routed to the metering device. This device restricts the flow by forcing the refrigerant to go through a small hole which causes a pressure drop. And what did we say happens to a liquid when the pressure drops? If you said it lowers the boiling point and makes it easier to evaporate, then you are correct. And what happens when a liquid evaporates? Didn't we agree that the liquid will absorb heat from the surrounding area? This is indeed the case and you now know how refrigeration works. This component where the evaporation takes place is called the evaporator. The refrigerant is then routed back to the compressor to complete the cycle. The refrigerant is used over and over again absorbing heat from one area and relocating it to another. Remember the definition of refrigeration? (the removal and relocation of heat) *Heat Transfer Rates*One thing that we would like to optimize in the refrigeration loop is the rate of heat transfer. Materials like copper and aluminium are used because they have very good thermal conductivity. In other words heat can travel through them easily. Increasing surface area is another way to improve heat transfer. Have you noticed that small engines have cooling fins formed into the casting around the piston area? This is an example of increasing the surface area in order to increase the heat transfer rate. The hot engine can more easily reject the unwanted heat through the large surface area of the fins exposed to the passing air. Refrigeration heat transfer devices such as air cooled condensers and evaporators are often made out of copper pipes with aluminium fins and further enhanced with fans to force air through the fins. *Metering Device*We will now take a closer look at the individual components of the system. We will start with the metering device. There are several types but all perform the same general function which is to cause a pressure drop. There should be a full column of high pressure liquid refrigerant (in the liquid line) supplying the inlet of the metering device. When it is forced to go through a small orifice it loses a lot of the pressure it had on the upstream side of the device. The liquid refrigerant is sort of misted into the evaporator. So not only is the pressure reduced, the surface area of the liquid is vastly increased. It is hard to try and light a log with a match but chop the log into toothpick sized slivers and the pile will go up in smoke easily. The surface area of zillions of liquid droplets is much greater than the surface area of the column of liquid in the pipe feeding the metering device. The device has this name because it meters the flow of refrigerant into the evaporator. The next graphic shows a capillary line metering device. This is a long small tube which has an inside diameter much smaller than a pencil lead. You can imagine the large pressure drop when the liquid from a 1/4" or 3/8" or larger pipe is forced to go through such a small opening. The capillary line has no moving parts and can not respond to changing conditions like a changing thermal load on the evaporator. Some labels have been added showing the names of some of the pipes. 



*The Evaporator*The metering device has sprayed low pressure droplets of refrigerant into the evaporator. The evaporator could be the forced air type and could be constructed of many copper tubes which conduct heat well. To further enhance heat transfer the pipes could have aluminium fins pressed onto them. This vastly increases the surface area that is exposed to the air. And this type of evaporator could have a fan motor sucking air through the fins. The evaporator would be capable of reducing the temperature of air passing through the fins and this is a prime example of the refrigeration effect. If that evaporator was located in a walk in cooler, the air would be blown out into the box and would pick up heat from the product; let's say it is a room full of eggs. The flow of heat would be egg core/egg shell/circulating air/aluminium fins/copper evaporator pipe/liquid droplet of refrigerant. The droplet of refrigerant has the capability of absorbing a large quantity of heat because it is under conditions where it is just about ready to change state into a gas. We have lowered it's pressure, we have increased surface areas and now we are adding heat to it. Just like water, refrigerants also have ratings for Latent Heats of vapourization in BTU's per LB. When heat is picked up from the air stream, the air is by definition cooled and is blown back out into the box to take another pass over the eggs and pick up more heat. This process continues until the eggs are cooled to the desired temperature and then the refrigeration system shuts off and rests. But what about our droplet of refrigerant. By now it might have picked up so much heat that it just couldn't stand it anymore and it has evaporated into a gas. It has served it's purpose and is subjected to a suction coming from the outlet pipe of the evaporator. This pipe is conveniently called the suction line. Our little quantity of gas joins lots of other former droplets and they all continue on their merry way to their next destination.*The Compressor*



The compressor performs 2 functions. It compresses the gas (which now contains heat from the eggs) and it moves the refrigerant around the loop so it can perform it's function over and over again. We want to compress it because that is the first step in forcing the gas to go back into a liquid form. This compression process unfortunately adds some more heat to the gas but at least this process is also conveniently named; _The Heat of Compression._ The graphic shows a reciprocating compressor which means that it has piston(s) that go up and down. On the down stroke refrigerant vapour is drawn into the cylinder. On the upstroke those vapours are compressed. There are thin valves that act like check valves and keep the vapours from going back where they came from. They open and close in response to the refrigerant pressures being exerted on them by the action of the piston. The hot compressed gas is discharged out the...you guessed it; discharge line. It continues towards the last main component. *The Condenser*The condenser is similar in appearance to the evaporator. It utilizes the principles to effect heat transfer as the evaporator does. However, this time the purpose is to reject heat so that the refrigerant gas can condense back into a liquid in preparation for a return trip to the evaporator. If the hot compressed gas was at 135 ؛F and the air being sucked through the condenser fins was at 90 ؛F, heat will flow downhill like a ball wants to roll down an inclined plane and be rejected into the air stream. Heat will have been removed from one place and relocated to another as the definition of refrigeration describes. As long as the compressor is running it will impose a force on the refrigerant to continue circulating around the loop and continue removing heat from one location and rejecting it into another area.*Superheat and Slugging*There is another very common type of metering device called a TX Valve. It's full name is _*T*hermostatic E*x*pansion *V*alve_, and you will be thankful to know that its' short form is TXV. (It can also be called TEV) This valve has the additional capability of modulating the refrigerant flow. This is a nice feature because if the load on the evaporator changes the valve can respond to the change and increase or decrease the flow accordingly. The next graphic shows this type of metering device and you will note that another component has been added along with it.



The TXV has a sensing bulb attached to the outlet of the evaporator. This bulb senses the suction line temperature and sends a signal to the TXV allowing it to adjust the flow rate. This is important because if not all the refrigerant in the evaporator changes state into a gas, there would be liquid refrigerant ******* returning down the suction line to the compressor. That could be disastrous to the compressor. A liquid can not be compressed and if a compressor tries to compress a liquid something is going to break and it's not going to be the liquid. The compressor can suffer catastrophic mechanical damage. This unwanted situation is called _liquid slugging_. The flow rate through a TXV is set so that not only is all the liquid hopefully changed to a gas, but there is an additional 10 ؛F safety margin to *insure* that all the liquid is changed to a gas. This is called _Superheat._ At a given temperature any liquid and vapour combination will always be at a specific pressure. There are charts of this relationship called PT Charts which stands for Pressure/Temperature Chart. If all the liquid droplets in an evaporator have changed state into a gas, and they still have 1/4 of the evaporator remaining to travel through, this gas will pick up more heat from the load being imposed on the evaporator and even though it is at the same pressure, it will become hotter than the PT Chart says it should be. This heat increase over and above the normal PT relationship is called superheat. It can only take place when there is no liquid in the immediate area and this phenomena is used to create an insurance policy of sorts. Usually TXV's are set to maintain 10 ؛F of superheat and by definition that means that the gas returning to the compressor is several degrees away from the risk of having any liquid *******. A compressor is a vapour compression pump and must not attempt to compress liquid. That extra component that got added in along with the TX Valve is called a receiver. When the TXV reduces the flow there has to be somewhere for the unneeded refrigerant to go and the receiver is it. Note that there is a dip tube in the outlet side to insure that liquid is what is fed into the liquid line. Liquid must be provided to the TXV not a mixture of liquid and gas. The basic premise is to change a liquid to a gas so you don't want to waste any of the evaporator's capacity by injecting useless vapour into it. The line that comes from the condenser and goes to the receiver is also given a name. It's called the condensate line.
*Accessories*Even though there are only 4 basic components to a refrigeration system there are numerous accessories that can be added. The next graphic shows a _liquid line filter_ and a _sight glass_. The filter catches unwanted particles such as welding slag, copper chips and other unwanted debris and keeps it from clogging up important devices such as TX Valves. It has another function as well. It contains a desiccant which can absorbs a minute quantity of water. (a mere drop or two) Hopefully a proper evacuation removed all the air and moisture ******* during the installation of the equipment. The sight glass is a viewing window which allows a mechanic to see if a full column of liquid refrigerant is present in the liquid line.




Earlier we discussed heat transfer rates and mentioned surface area as one of the factors. Let's put some fins on our condenser and evaporator. While we are at it lets also add a couple of fan motors to move air through those fins. They are conveniently called the condenser fan motor and evaporator fan motor.


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## aati badri (27 أكتوبر 2010)

*Part 3*

To make our cyber space refrigeration system a little more realistic lets separate the evaporator away from the compressor section and put it inside an insulated box. The left over components can now be called a _Condensing Unit._ The insulated box does not conduct heat well. If we lower the temperature of a refrigerated product inside the box we want to slow down the rate of thermal gain from the rest of the world outside the box. There has been oil added to the compressor sump to keep the moving parts inside the compressor lubricated. The suction line returning to the compressor has been sloped to aid in returning oil to the compressor. The oil is slowly depleted from the sump by getting entrained in the refrigerant and proper piping practices must be used to insure its' return. Also notice that the liquid line has been made smaller. The same quantity of refrigerant can be contained in a much smaller pipe when it is in the liquid form. The suction line has been connected to its' proper place on the evaporator; the bottom. Consider the direction of flow, the liquid refrigerant (which probably contains oil stolen from the compressor) enters the top of the evaporator and now has gravity on its' side to return the oil where to it belongs (just like the sloped suction line).



Consider the heat flow within the insulated box. The evaporator is constantly recirculating air in a forced convection loop around the box. As the cold air passes over the product to be refrigerated, once again we see a thermal transfer taking place. If there were a bunch of boxes of warm eggs placed in the cooler some of their heat ******* would be picked up by the cold air and that air is sucked back into the evaporator. We know what happens then. The heat is transferred through the fins, through the tubing, and into the refrigerant and carried away. That same air has been cooled and is once again discharged back over the product. The next graphic shows this loop and the pink and blue colours represent air with more heat ******* and less heat ******* respectively.



The next graphic is a more pictorial representation of what an actual installation might look like.



*Summary*I hope you enjoyed the original Refrigeration Basics section. It covered a lot of material but this was done by just barely skimming the surface of things. You should now have a general idea of what refrigeration is and how it is accomplished. There are of course many issues that must be looked at in much greater depth. We will try to do this in the same easy to understand fashion using pictures, animation's and interactive objects where possible. You may jump around all you want to different areas of this book however it has been designed in a way where subsequent sections are often based on the previous sections information. You will probably find things easier to comprehend by following the sections in the order they are presented


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## aati badri (27 أكتوبر 2010)

*Definitions*

* Temperature*


[SIZE=-1]*English[/SIZE]*[SIZE=-1]*Metric[/SIZE]*[SIZE=-1]*Fahrenheit*[/SIZE][SIZE=-1]*Rankine*[/SIZE][SIZE=-1]*Celsius*[/SIZE][SIZE=-1]*Kelvin*[/SIZE] 
Temperature scales are a way of describing how hot a substance is. A lump of matter contains energy. There are many forms of energy, one of them is Kinetic energy and measuring temperature is a way of measuring how furiously the molecules contained in a lump of substance are moving about. This molecular activity causes what we perceive as the temperature of an object. A refrigeration mechanic must be able to deal with temperatures in various scales. Traditionally the English system has been used (Fahrenheit degrees) and a whole series of familiar capacity measurements like Horse Power, BTU's, Tons, and PSI have been the norm. However the metric system which is supposed to be easier to work with is becoming popular in many locations. In both systems there are standard and absolute temperature scales. Try experimenting with the above temperature converter. Type a value in any one of the input boxes and click on the Convert Button. Here are several interesting values to try: -40 ؛F, 0 ؛R, 40 ؛F, 373 ؛K, 21 ؛C *Fahrenheit*The Fahrenheit temperature scale was developed by no less than Fahrenheit himself back in the early 1700's. It was based on scientifically observable occurrences such as human body temperature and melting ice. Those points were assigned arbitrary values which made sense at the time. The newly created number scale was widened for easier reading and when boiling water was measured at 212 degrees, Fahrenheit changed the value of freezing water from 30 to 32 degrees to achieve the more attractive scale of 180 degrees between water's freezing and boiling points. There are 180 degrees in 1/2 of a circle and this was a temptation too great to resist. *Celsius*

In theory the Celsius scale should be much easier to work with. It is based on calling the freezing point of water zero and the boiling point of water 100. There are therefore 100 degrees between those 2 points. The Celsius temperature scale is also referred to as the "Centigrade" scale. Centigrade means "consisting of or divided into 100 degrees. I wonder what a comfortable room of 70؛ F would be in Celsius? If you don't happen to have a conversion calculator at your disposal you can always rely on the following 2 formulae: 





*Kelvin*

Scientists use the Kelvin scale, which is based on the Celsius scale, but has no negative numbers. Instead of basing it's zero point on the freezing point of water, it bases it's zero point on _Absolute Zero._ which is the theoretical temperature where all heat has been removed from a substance. Hence any amount of heat added creates a positive temperature. Negative numbers can mess up a scientist's mathematical calculations. You will find that in refrigeration, we too must use absolute temperature scales for some things. At Absolute Zero scientists believe that molecular motion would stop. *Rankine*

Rankine is the English version of an absolute temperature scale. Add 460 degrees to Fahrenheit temperatures to obtain the Rankine temperature. Input 0؛ in the Rankine box on the calculator above and you will see why. 





*Heat*


Temperature is a qualitative measurement. Heat is a quantitative measurement. The temperature "quality" of a object describes how hot it is but not the total amount of heat it actually contains. Here's a silly example which makes clear the distinction. Let's say we have two blocks of iron. One is a mere cubic inch, the other is 10 feet cubed. We heat each of them to 150 ؛F and you verify this with some sort of thermometer. They both have the same temperature but do they both contain the same amount of heat? When you throw the little cube in your swimming pool nothing noticeable happens to the temperature of the pool water but when you toss in the huge iron chunk the pool water can be measured to rise somewhat over time. If there was a noticeable amount of heat transfer from the large chunk of iron but not from the small chunk of iron then surely the large chunk contained more heat than the small one even though they were at the same temperature. The temperature of an object is a reflection of the kinetic energy of the atoms or molecules that make it up. Fast molecules = high kinetic energy = high temperature. On the other hand heat represents the total amount of kinetic energy in an object. Heat is measured in BTU's. Recall that 1 BTU is the amount of heat required to change the temperature of 1 Lb. of water through 1؛ F. So it would take 2 BTU to raise the temperature of 2 Lb. of water through 1؛ F. And it would take 30 BTU to raise the temperature of 3 Lb. of water by 10؛ F. BTU's (or their metric counterparts) Larger quantities of heat in the Imperial system are described with the term _Ton_. 12,000 BTU = 1 Ton. A building might have a 3 Ton Air Conditioning system which would be equivalent to 36,000 BTUH. 
*Specific Heat*


Specific heat capacity is the amount of heat required to change temperature of a given quantity of a substance by one degree. Specific heat may be measured in Btu/lb ؛F or kJ/kg ؛K. Different substances have different heat holding capabilities and thermal properties. Just because 1 Lb. of water will change precisely through 1؛ F when 1 BTU is applied to it does not necessarily mean that the same thing will happen with 1 Lb. of copper or 1 Lb. of steel or 1 Lb. of ice cream. There is a need to be able to specify those differences and the method utilized is to compare all substances to water. Water is given a specific heat value of 1. This means that 1 BTU is required to change the temperature of 1 Lb. of water through 1؛ F. The specific heat of water can also be described in the metric system. The metric specific heat of water is 1 calorie per gram per degree Celsius. This value also works out to 1. In other words it would take 1 calorie of heat to raise the temperature of 1 gram of water through 1 degree Celsius. Specific heat is a dimensionless quantity. It is purely a number having no unit of measurement associated with it. In Refrigeration specific heat values are used to calculate capacity requirements for refrigerating known quantities of product. For example one might need to be able to select refrigeration equipment capable of cooling 5000 Lb. of beef from 55 ؛F to -20؛ F. A calculation like that must take into consideration the fact that the specific heat of a substance usually is different above and below it's freezing point. 
*Latent Heat*


Latent Heat is the heat given up or absorbed by a substance as it changes state. It is called latent because it is not associated with a change in temperature. Each substance has a characteristic latent heat of fusion, latent heat of vapourization, latent heat of condensation and latent heat of sublimation. 



*Sensible Heat*


Sensible Heat is associated with a temperature change, as opposed to latent heat. This is so-called because it can be sensed by humans. If the air in a building was to be heated from 60 ؛F to 70 ؛F only sensible heat would be involved. However, if the air in a building was to be cooled from 80 ؛F to 70 ؛F and humidity was to be removed from the air at the same time, then both sensible and latent heats would be involved. *Insulator*


Electrical wires are coated with an insulating material so electricity stays in the conductor (wire). Thermal insulation on the other hand tries to keep heat from transferring. Thermal insulation does not stop heat transfer, it only slows down the rate of transfer. The greater the amount and quality of insulation, the greater the insulating effect and the slower is the thermal transfer. There is insulation inside cooler and freezer walls and in the perimeter walls of conditioned spaces. If fiberglass batting is being used it should be noted that the glass fibers are actually a poor insulator. It is the tiny pockets of trapped air in-between the fibers that actually are responsible for the insulating effect. 
*Conductor*


The chart below shows the specific heat values of several materials. Notice the very small specific heat value that copper has. This means it would take a mere .09 BTU to raise 1 Lb. of copper through 1 ؛F. Copper has a bigger temperature change for the same heat input compared to many other materials. Copper transfers heat readily and would not make a very good insulator, it conducts heat too well. The smaller the specific heat number, the better of a conductor a material is. You can see why heat transfer devices like evaporators and condensers are made from materials like aluminum and copper. 
*Material**Specific Heat* (Btu/Lb. ؛F)
as well as (kcal/kg ؛C)*Specific Heat* (calorie/gram °C)
as well as (kcal/kg ؛C)*Specific Heat* (kJ/kg K)Water11 4.19Ice 32 ؛F
0.490.492.09Wood max
0.480.482.01Ice -4 ؛F
0.470.471.97Ice -40 ؛F
0.430.431.8Ice -112 ؛F
0.350.351.47Wood min
0.320.321.34Air
0.240.241.01Concrete
0.230.20.8Aluminum
0.220.220.9Glass
0.200.20.84Iron 
0.120.11
0.45Copper
0.090.090.39
*Pressure*


Pressure is what occurs when a force is applied over an area. More specifically, pressure is the ratio of the force acting on a surface to the area of the surface. The equation for pressure represents this rather straightforwardly; *P=F/A *This equation means that Pressure equals Force divided by Area. Let's look at a couple of very simple examples. As is demonstrated in the sketches below, the same weight can exert completely different pressures depending on how much surface area it is spread out over. Note that in the Imperial System when you multiply FT by Lbs you get a unit called FT Lb. (pronounced Foot Pounds) This is a legitimate unit of pressure however. However refrigeration pressures in the Imperial System are measured in pounds per square inch not pounds per square foot. This is abbreviated to PSI. Refrigeration gauges are zeroed to 1 Atm pressure and the units are then called PSIG. (as in PSI Gauge) The calculations shown in the metric picture yield pressure units in kg/m2 (kilograms per meter squared). This is also a legitimate unit of pressure however kPa (kilopascals) are the pressure units that you will see on Metric refrigeration gauges. As with temperature, pressure has many different scales that can be used and can be described with the English system or the Metric system. We seldom deal with gravitational forces as shown in the diagram although it is an important concept to be aware of. Rather, we deal with the pressures and temperatures of gases and that is what the next section is all about.


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## محمود عزت احمد (27 أكتوبر 2010)

بارك الله فيك


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## aati badri (27 أكتوبر 2010)

Refrigeration Engineer.com

http://www.refrigeration-engineer.com/


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## سليمان سعد الدين (27 أكتوبر 2010)

والله شئ جميل شكراً جزيلاً على هذا المجهود الرائع ولك كل الشكر والتقدير .


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## aati badri (27 أكتوبر 2010)

محمود عزت احمد قال:


> بارك الله فيك


 مشكور وربنا يسكنك جوار هذا الحرم


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## aati badri (27 أكتوبر 2010)

*Definitions*
*Part 2*
*Energy*

Energy is the capacity of a system to do work where "system" refers to any physical system, not just a refrigeration system.*Enthalpy*

Enthaply is the total amount of heat in one Lb. of a substance. It's units are therefore BTU/Lb. The metric counter part is kJ/Kg. (kilo joules/kilogram)*Entropy*

Entropy measures the energy dispersion in a system divided by temperature. This ratio represents the tendency of energy to spread out, to diffuse, to become less concentrated in one physical location or one energetic state. That spreading out is often done by molecules because molecules above absolute zero always have energy inside of them. That's why they are incessantly speeding through space and hitting each other and rotating and vibrating in a gas or liquid. Entropy is measured in BTU per Lb. per degree change for a substance. 



 *Mollier Charts*

Mollier charts are used in designing and analyzing performance of vapour compression refrigeration systems. Each refrigerant has it's own chart which is a graph of the Enthalpy of a refrigerant during various pressures and physical states. Mollier charts are also called Pressure-Enthalpy diagrams. Pressure is shown on the verticle axis, enthalpy is on the horizontal axis. You can compare Imperial versus SI Unit Mollier Charts by clicking on the buttons below the chart.




 The above chart is for refrigerant MP39. You can see that pressure and enthalpy are the units on the verticle and horizontal axis. Several other parameters are also shown on the chart including temperature, volume, saturation quality and entropy.




The series of graphics above shows how the refrigeration cycle is graphed onto the pressure-enthalpy chart and goes into details about how certain parameters can be determined from the chart.


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## aati badri (27 أكتوبر 2010)

*Charging**Part 1*Click back and forth between buttons 1 and 2 and see how many differences in operation you can find between the two systems. Can you come to a conclusion about the operation of these two systems? When you are done click the Answers button to find out if you came to the correct conclusions.




There are some points that should be made about the preceding example. A sight glass that is not full (while the system is operating) may indicate an undercharged system. However there are other things that can cause that symptom as well. For example, if the LL Filter (Liquid Line Filter) was partially clogged but still allowing some flow, the sight glass wouldn't be full yet the system could be fully charged. That condition is called a _High Side Restriction._ Fortunately there is a simple way to identify this situation. A partially clogged filter/drier can cause enough pressure drop to lower the temperature of the liquid passing through it making the drier and downstream liquid line cold. This is the refrigeration effect taking place and the drier and liquid line can even get cold enough to allow frost to form. If the liquid line feeding the filter/drier is 105 ؛F and the shell of the filter/drier cold to the touch, the high side restriction will be obvious. 
The key to diagnosing a malfunctioning system is to gather as many symptoms as you can. Several symptoms consistent with a potential cause are more likely to lead you in the right direction than a single indicator. You must also eliminate other possible causes as with the high side restriction example. 
It is logical that an undercharge will cause higher than normal superheat. Normal operation is to have as much of the evaporator as possible filled with liquid in order to pick up heat when it changes state. At the same time it must not be so full that there is no room left over for superheating the vapour. With undercharged conditions there is a lack of liquid and a surplus of vapour in the evaporator. That translates to a great deal of evaporator area that is available for superheating. Hence undercharge and high superheat go hand in hand. The refrigerant pressure in the evaporator is affected by the thermal loads imposed on the evaporator, the removal of vapour from the continual suction of the compressor as well as the continual addition of refrigerant from the metering device. With an undercharged system the metering device can not feed the evaporator at the rate it is supposed to because there is not a full column of liquid in the liquid line. There also may be lower than normal high side pressure pushing liquid through the TXV. Without the required feed rate to the evaporator, the compressor tends to empty out the low side. That's why the suction pressure becomes lower than normal. This also explains why an over sized compressor will also cause lower than normal suction pressure. (The greator suction capacity removes vapours at a faster rate than the rest of the system was designed to keep up with.) The Discharge Pressure is the result of compressing the low side vapours. So lower suction pressure tends to lower the high side pressure. However there are other forces also affecting the high side pressure. This is especially true if the system has some type of head pressure control. For example, a water cooled system has a water regulator valve that may totally mask the high side pressure from the symptoms you would expect with an undercharge. It will reduce the water flow trying to maintain it's head pressure setting and can possibly maintain normal high side pressure with undercharged conditions. Air cooled systems that have some form of head pressure control will also mask the expected symptoms. Measuring several parameters will reduce the number of possibilities and narrow the number of possible causes of problem.


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## aati badri (27 أكتوبر 2010)

*Charging**Part 2*Let us assume that you have located and repaired the leak which caused the undercharged conditions. You now wish to top up the refrigerant charge and have hooked up a jug of the appropriate refrigerant. Click the Charge button to open the low side hand wheel on the gauge set and start charging. Notice all the things that change as you are charging. The yellow colour is used to indicate the route that the refrigerant takes when you allow flow from the jug. Gas will flow because the pressure in the jug is greater than the pressure in the low side of the system. High pressure flows to low pressure just as high temperature flows to low temperature. When you open the low side hand wheel you can see the suction pressure increasing on the low side gauge. You can also notice a slight increase in high side pressure and you now know why. 





You can see that there is a liquid/vapour interface in the refrigerant jug and that you are drawing refrigerant from the vapour portion. This vapour is being introduced into the suction of the compressor and there is nothing wrong with that. This method works well with small to medium sized systems but if you need to charge a large system you might be there for very long time indeed. If you vapour charge for several minutes you will notice a decrease in available pressure from the jug. You will also notice that the jug is getting colder and colder. That makes sense because we know low pressure goes hand in hand with low temperature. We can't get away from the laws of physics. When you draw off some vapour from the jug the _Pressure Temperature Relationship_ forces some liquid to flash into a gas to make up for the vapour you just removed and keep the Pressure Temperature Relationship in balance. But by changing state that liquid has created the refrigeration process and removed heat from the surrounding area which in this case is the rest of the liquid refrigerant in the drum. If you continue vapour charging long enough the drum may get so cold that you lose all of your pressure differential and can no longer continue. One solution is to warm up the *******s of the jug. Don't even think of playing a torch on the jug. You must never do that. A safe method to warm up a jug is to place it in a pail of warm water or if you prefer run warm water over the jug in a sink. Keep a gauge in place so you can monitor the pressure at all times. Develop safe working habits, there are more than enough dangerous circumstances to go around without creating any of your own. We are still in need of a method to charge a large system...


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## aati badri (27 أكتوبر 2010)

*Charging**Part 3*
A liquid charging valve is an access valve which is installed downstream of the King Valve. This location allows for some fancy manoeuvring. Note in the diagram below that the high side hose has been removed from the DSV and that the DSV has been back seated and capped off as it is no longer needed. The high side hose has been relocated to the liquid charging valve and is sensing high side pressure from that location instead. In this case the liquid charging valve is a Schraeder Valve but it could also have been another service valve. The pressure is still the same other than perhaps some tiny bit of pressure drop from frictional losses through the condenser. When you measure high side pressure from the DSV it is called True Head Pressure. It can still be called Head Pressure as measured from anywhere on the high side of the system but the distinction of being called True Head Pressure is reserved for measurements from the DSV location.We are looking for a way to charge with liquid refrigerant rather than vapour and the first problem to overcome is getting liquid out of the jug. Refer to the diagram below and click Button 2 for the solution. So now we have access to liquid and we have our hose hooked up to a place where it would be fine to introduce it but there is another problem. The pressure in the high side of the system may be equal to or higher than the pressure in the jug so we might not get any flow. But what if we pump down the low side...click Button 3 to front seat the King Valve. The low side empties. Note that the Liquid charging Valve is now part of the low side. The pressure reading on the high side gauge is indicating the same low pressure as the low side gauge. We now have a pressure differential between the liquid in the jug and the liquid line where it is safe to introduce liquid. Press Button 4 to start charging liquid. Notice that the sight glass starts to show liquid, the suction gauge pressure increases and the high side gauge reflects the pressure from the jug, not from the high side of the system. Press 5 to continue charging. Are you noticing that the amount of area being used for superheating is decreasing? (An increasing amount of the evaporator is being used for evaporation so there is less room left over for excessive superheating) We may achieve a fuller Sight Glass but this is not a reflection of system operating conditions. We do not have a loop, we have a front seated King Valve. All the refrigerant you are adding is merely being relocated into the isolated high side. First it changes to a gas in the evaporator, then it is in a form to be safely drawn into the compressor and finally it is condensed in the condenser and ends up in the receiver which starts to fill up.With the system in the present configuration there is no way of telling us whether we have yet added sufficient refrigerant. We should be monitoring the weight of the jug so we know how much refrigerant has been added and periodically closing the red hand wheel and opening the King Valve to see how things are progressing. Be cautious not to overcharge the system using this method. When you get close to being complete it can be a wise decision to complete charging by the vapour charging method so it is not so easy to overshoot the correct charge.If you happen to have a refrigerant jug with 2 valves then there is no need to invert the jug to get liquid. Press 6 to see a dual valve jug. The red valve controls flow through a dip tube which is submerged into the liquid level.



We have gone over several techniques about manipulating a system through use of it's valves and charging refrigerant. There is of course a great deal more to diagnosing and understanding the refrigerant side of systems than we have touched on so far. To do that we must start dealing with specific values and that is what we shall do next.


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## aati badri (27 أكتوبر 2010)

*Controls**Part 1*Refrigeration systems require operating controls so they can cycle on and off to maintain a certain temperature. They also require safety controls to stop operation if unsafe conditions occur. There are many varieties of controls. Different types respond to temperature, pressure, humidity, liquid levels, other controls, manual intervention and other things.*Thermostatic Control*



Lets add a basic control system to a refrigeration system. First we need to know what loads there are to be controlled. The image on the left shows a small split system for a walk in cooler with 3 electrical devices; a compressor, condenser fan motor and evaporator fan motor. Those 3 electrical devices are represented on the _ladder schematic_ shown below. This type of wiring diagram has branch runs all shown as parallel circuits going from the left line (L1) to the neutral line (N). They look like the rungs in a ladder hence the name ladder schematic. The EFM (Evaporator Fan Motor) must run all the time so that the box temperature stays uniform and the thermostat senses the average box temperature not some pocket of stratified air. Press the Off Cycle Button to see the circuit through the EFM. Now Press the On Cycle Button to close the T-Stat and call for refrigeration. The T-Stat "makes" on a rise of temperature. Notice that the COMPR (compressor) and the CFM (Condenser Fan Motor) both come on. A T-Stat that "makes on a rise" is a cooling T-Stat. A T-Stat that "makes on a fall" is a heating T-Stat.





Also note that just because the wiring on the left side of the T-Stat is not coloured red when the T-Stat is open, that does not mean there is no electricity there. There is a full electrical potential on that line and if you were to come along and stick your finger at that point you would be shocked. The red coloured wiring indicates the logical flow routes. Non red wires are not necessarily without voltage potential. 
The graph below shows how an operating control cycles. The control is set to start refrigeration if the box warms up to 40 ؛F That's called the _Cut In_ point. The system keeps running until it reaches the _Cut Out_ point which is 37 ؛F where it shuts off and awaits the next call for cooling. In this example there is a 3 ؛F differential between the cut in and cut out points. The differential must be wide enough that the equipment does not short cycle. Short cycling means to turn on and off too rapidly. Starting is hard on the equipment, so you want to keep the number of starts per hour to a reasonable amount, not an excessive amount. The 40 ؛F point is a very special temperature. It is the standard cut in point for most refrigeration systems. Above 40 ؛F bacterial growth rates in stored food increase dramatically. Below 40 ؛F bacteria growth rate is subdued. The cut out point is more of a compromise than anything else. Some products may store better at colder temperatures but colder temperatures might adversely affect other products in the same box. There is also a concern about keeping the evaporator from icing up. There is no active defrost system in a standard refrigeration system. (defrost systems are only a standard item with freezers) If a refrigeration system was set to cut in at 36 ؛F and cut out at 33 ؛F and the evaporator was operating with a 7 ؛F TD to the box air, the temperature of the evaporator fins would be 29 ؛F to 26 ؛F during the run cycle. Since the freezing point of water is 32 ؛F, you can see that moisture in the air would sublimate onto the evaporator surface and grow into thicker and thicker layers of ice. Not only does ice act like an insulator and reduce thermal transfer, it can totally block airflow through the evaporator fins and virtually stop thermal transfer. Some people try to push this wall a little and it is possible to squeak out a degree or 2 colder than a 40 ؛F cut in point. However, anything more than a couple of degrees will risk icing the evaporator. A countering force is the _"off cycle defrost"_ effect. Since a typical refrigerator is designed to maintain 40 ؛F, the recirculating air will tend to melt ice build up on the evaporator during the times it has it has cycled off. There are of course refrigeration systems that are designed to operate in the 35 ؛F (and colder) range. However these typically have some form of defrost system. Systems that are designed to operate below 32 ؛F are freezers with defrost systems and they typically operate in temperature ranges like: 0 ؛F, -10 ؛F, -15 ؛F as well as much colder.


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## aati badri (27 أكتوبر 2010)

The adjustment knob on a commercial T-Stat sets the cut in point. The differential is adjustable by setting a slider inside the enclosure. Thermostatic controls are manufactured with an wide range of variations. They have fixed differentials, adjustable differentials, different operating ranges and various accuracy’s , various electrical load ratings, different types of sensors, electro-mechanical, electronic 

 etc.


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## aati badri (27 أكتوبر 2010)

The sensing bulb of the control should be mounted so that it senses the evaporator inlet air. During the off cycle the constant fan recirculates the air in the box. The temperature of the air becomes an average of the product temperature, the wall temperature, any infiltrated air and any other loads such as caused by a person entering the box. When the air temperature reaches the cut in point of the control it brings on refrigeration. When refrigeration is operating, 40 ؛F air passes through the evaporator and drops in temperature several degrees. That's why the sensor can not be placed in or near the discharge air stream. If it was placed there, the control would think that the whole box was cold and shut off the system as soon as it started. It is the average box temperature that should be monitored, not the discharge air temperature. Some thermostatic controls are designed with a capillary line temperature sensor which is intended to be inserted between the evaporator fins on units that have a tendency to ice up. A commercial cooler in a hot environment which is constantly being accessed would tend to ice up. A _Constant Cut In Control,_ also known as a beverage cooler control forces an off cycle defrost at the end of each run cycle. The control will remain open until the evaporator has reached a temperature which indicates that any frost accumulated during the previous run cycle has been melted. This type of control is used in appliances like beverage coolers. Adjusting the knob on this type of control changes only the Cut Out setting, the Cut In setting remains fixed.


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## م. رياض النجار (28 أكتوبر 2010)

مشكور يابشمهندس
:59::75::59:​


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## aati badri (28 أكتوبر 2010)

riyadh1 قال:


> مشكور يابشمهندس
> 
> 
> :59::75::59:​


 العفو يا هندسة
طبعا منقول
بس نسيت
اعذرني


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## hamadalx (28 أكتوبر 2010)

حاجة جميلة جدا يابشمهندس


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## م محمد حمدى السيد (14 ديسمبر 2010)

مشكووووووووووووور


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## دكتور صبرى سعيد (14 ديسمبر 2010)

ايه الجمال ده ، اللي ما يعرف لغة ح يفهم من الشرائح اللي بتتكلم من غيركلام 
اكرمك الله بمحبته و برضاه و توفيقه و قضله


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## aati badri (7 سبتمبر 2011)

سليمان سعد الدين قال:


> والله شئ جميل شكراً جزيلاً على هذا المجهود الرائع ولك كل الشكر والتقدير .


 شكرا صديقي م سليمان
يظهر انه حضرتك اتداخلت وانا انزل المادة فلة ارىمداخلتك
فلك العتبى حتى ترضى


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## aati badri (7 سبتمبر 2011)

اشكر كل من مر من هنا وشجعني
وكل من مر من هنا ولم يفعل


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