Pressure - Volume Correction

Pressure correction :

 We all are very much friendly with these words pressure and volume . When I say pressure, suddenly one picture comes in your mind is application of force on any surface area. OK, you are correct, but you know actually what is pressure and what is mechanism of developing pressure ..???
Pressure is nothing but the excitement of molecule which is present inside the air. If I heat the air inside a container at say 60 degree, the molecule of air is started exciting. Firstly when air is at N.T.P. condition the air molecule flows smoothly and that haven't that much energy, but when it is heated at some temperature the molecule are charging its own energy. And after getting some amount of energy to each molecule, they started travelling very fast and hit the container wall with some force. We can also say the molecule become mad and dashed the wall with stored energy. Once it hits the wall it destroy its energy. Once again it recharges its own energy and try to dashed against wall.
The addition of this all small small force make one big force and it create pressure by adding all forces upon the area on which it acts.

Pressure = force / area

Now the question comes what is pressure correction
Suppose is we consider a rectangular box with full of pressurised air and one pressure gauge is mounted on that box and take reading for pressure. Say pressure is 5 bar. But if we go towards CG of body, we get pressure some what 4.96 bar. This is called pressure correction.
Theoretically we say that the pressure is constant throughout the box but in actually its not constant. This is called pressure correction. This is because the hitting of molecule against wall. At surface, molecule get one face to hit. But at C.G. no surface is present. Due to this phenomena pressure correction comes in picture.

Volume correction :

Volume is another major parameter in engineering calculation. When I say volume, you all are started thing about multiplication of length x width x thickness. But you know what is actual meaning of volume ??

Let us take one square container in which the air is present at N.T.P. condition. Volume of that container in general terms is l x b x w. but in engineering language this is not a definition of volume. volume is nothing but a space in which one molecule of air can travel. in above example, air molecule can travel in whole container. That's why volume of container is l x b x w.
now the question rises, what is volume correction ?? if you read above five lines carefully then you also understand the correction factor. let us take same example of container. The volume, in which the molecule can travel is (l x b x w) - (self volume of that molecule). this is what volume correction. it means molecule cannot travel in whole container, i.e. l x b x w.  it can travel only in (l x b x w) - (self volume).  


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Thermodynamic - System, Surrounding, Boundary

If we want to do analysis properly on thermodynamic related things, we must devid the thing in three part. They are as below....

1. System

2. Surrounding

3. Boundary

1. System :

Thermodynamic system is a specified region in which we are concentrated for thermodynamic analysis. Or we can say that system is a volume of space containing the item chosen for thermodynamic analysis. The system and its boundary are always chosen by us while doing analysis. A system does not have to be fixed in space. It can move, deform and increase or decrease in size with time. Basically there are three different types of system...
1. Close System
2. Open System
3. Isolated System.

1.1  Close System :

It is a part of system in which mass does not cross the system boundary. But energy may cross system boundary.

This fundamental diagram shows the property of closed system. i.e. in this system only energy can transfer across boundary of system.

 

                             

                                       Closed System (a)

             Closed System (b)

These are the examples of closed system of thermodynamics. fig (a) shows one testing tube in which hot water takes about 75 degree. and in that we knows that glass is good conductor of heat, so in that heat is transfer from water to glass. but the volume of water is constant in test tube. So (Heat) Energy transfer without transfer of mass. Fig (b) shows one plastic jar. also plastic is a good conductor of heat. In this case also (Heat) energy can transfer without transfer of mass.

1.2  Open System :

It is a system in which, both mass and energy may cross system boundary.

This fundamental diagram shows the property of open system. i.e. In this system energy as well as mass can cross boundary of system.

           

Open System (a)

Open System (b)

These are some example of Open System of thermodynamics. Fig (a) shows one cup filled with hot coffee. Here we consider coffee mug with hot coffee as a system. In this case heat is transferred from coffee mug in to atmosphere as well as steam is evaporated from coffee. So heat as well as mass is transferred from system. Thus it called open system. Fig (b) shows a part of steam power plant i.e. Turbine. In this case mass is entering from one side and leaving from other side, and also heat enery is exchang between turbine and surrounding atmosphere. Thus is also called a Open System.

1.3  Isolated System :

It is a system in which, both mass and energy may not cross system boundary.

                        

                                     Isolated System (a)

   Isolated System (b)

Fig (a) shows fundamental diagram of the property of open system. i.e. In this system energy as well as mass cannot cross boundary of system. Fig (b) shows perfectly insulated Thermos. Which is the perfect example of Isolated System. In this case mass as well as energy are not crossing the system boundry. Thus it is called as Isolated System.

2. Surrounding :

If we want to learn simply about surrounding, then remember one thing, "OUTSIDE THE SYSTEM IS SURROUNDING".  But we have to remember one thing that surrounding also has one limited boundary.

For ex :
Suppose we performing an experiment of boiling water in properly air-conditioned room. Then our system is water, and surrounding for this system is cool air. we cannot consider outside room air as a surrounding. So Surrounding itself has boundary.

3. Boundary :

Boundary is nothing but an imaginary line which separates system and surrounding. Boundary is always shown by dotted lines across system. Heat and mass can cross this line to do some useful work.

Or if you understand more about system surrounding boundary you can watch the video (link given below) to understand more about it.

       https://www.youtube.com/watch?v=7BKllTsXhm0&feature=youtu.be

Thank You.

What is ENGINEERING THERMODYNAMICS...?

The term thermodynamics is derived from the Greek Word therme (heat) and dynamics (power or motion); thus thermodynamics means heat power or heat in motion. Thermodynamics is defined as the science of engineering that deals With the storage of energy, entropy, heat and Work, mutual conversation of heat and Work, exchange of energy and those properties of substances that govern the relation between heat and Work. Earlier, thermodynamics Was considered as a subject of science by Joule (1818-1889), Kelvin (1824-1907), Clausius (1822-1888) and Carnot (1792-1832). Later, Gibbs (1839-1903) extended its scope and now it is extensively used in branches of science and engineering to analyze physical and chemical changes. Experimental observation is the basis for thermodynamics. Based on these observations and results, certain basic laws are developed Which are known as the Zeroth, First, Second and Third laws of thermodynamics. A large part of the subject of thermodynamics deals With a study of energy. Energy can be defined as a capacity to produce change. The energy output of an I.C. engine supplies the capacity to move from one location to another. The energy output of a power plant supplies the capacity to produce a Wide variety of changes to operate motors, television sets and lights, etc.

Thermodynamics is the science of energy transfer and its effect on the physical properties of substances. It is based upon observations of common experience which have been formulated into thermodynamic laws. These laws govern the principles of energy conversion. The applications of the thermodynamic laws and principles are found in all fields of energy technology, notably in steam and nuclear power plants, internal combustion engines, gas turbines, air conditioning, refrigeration, gas dynamics, jet propulsion, compressors, chemical process plants, and direct energy conversion devices.

Or else you want to learn more about thermodynamics or you want to learn, what things are present in thermodynamics, you can see this video given below..

https://www.youtube.com/watch?v=9GMBpZZtjXM&list=PLD8E646BAB3366BC8

Thank you.