In this video we will learn first law of thermodynamics in a practical way.Detailed description of above video lecture is given below.
Applications of First Law of Thermodynamics
First law of thermodynamics when it is applied to an open system has got tremendous applications all across industries. Using this law you can predict how much is the pressure drop across the nozzle, or how much is the energy required by the pump to pump the fluid out, or what is the heat transfer in heat exchanger, or what is the amount of work produced by the turbine.
|Fig.1 Industrial applications of first law of thermodynamics for an open system|
First Law for Closed System
We will understand how first law is applied for a thermodynamic system by analyzing a simple example, an example of piston cylinder arrangement. Here the cylinder has got some gas inside it. Assume there is no air leakage to the surrounding. So this is an example of closed system where mass does not change. Assume the gas is absorbing some heat Q from the surrounding; also assume that this gas is able to push the piston upwards due to high pressure of gas. So the gas is doing some work on the piston with quantity W.
|Fig.2 Piston-cylinder arrangement to demonstrate first law for a closed system|
First Law for an Open System
Now we are going to open the system, or open the cylinder as shown below.
|Fig.3 A piston-cylinder open system made by making the cylinder open|
|Fig.4 Defining a control volume for energy balance|
Concept of Flow work & Enthalpy – More Useful Form of First Law
But for an open system the term W, work done by the gas should be carefully examined. Here the gas is doing work to push the cylinder up, plus it is doing work to suck the fluid in or eject the fluid out. Or to maintain the flow gas has to do some work. This kind of work, the work which is required to maintain the flow is known as flow work. So the total work done by the system will be summation of visible work and flow work.
One Application of First Law
We will work out one interesting example using firs law equation in this section. A pump problem, where fluid is getting pumped from point 1 to point 2.
|Fig.5 Work required by the pump for pumping fluid from state 1 to 2 is to be calculated|