26 April 2017

Work transfer in thermodynamics

A close system and its surroundings can interact in two ways :

  • By work transfer 
  • By heat transfer 
Both are those are called interactions and these bring about changes in the properties of the system. 
In thermodynamics mainly studies these energy interactions and the associated property changes of the system.

Work Transfer :
Work is one of the basic modes of energy transfer. In mechanics, the action of a force on a moving body is called work. A force is a means of transmitting an effect from one body to another. An effect of that certain distance can be performed by a body. The product of force and distance is the same to accomplish the same effect. 

What is work?
The work is done by a force as it acts upon a body moving in the direction of the force.

The action of a force through a distance is called mechanical work. The product of the force and distance moved parallel to the force is the magnitude of mechanical work.

W = F * d

In thermodynamics, work transfer is considered as occurring between the system and the surroundings.

Work is said to be done by a system if the sole effect on things external to the system can be reduced to the raising of a weight.

When work is done by a system, it is arbitrarily taken to be positive.
When work is done on a system, it is taken to be negative. 

The symbol used for work transfer is W.

The unit of work is N.m or Joule. 1 N.m = 1 Joule 

The rate at which work is done is called power.

There are various types of work transfer which can get involved between them. 
  • pdV work
  • Electrical work 
  • Shaft work 
  • Paddle-wheel work or Stirring work 
  • Flow work 
  • Work was done in stretching a wire
  • Work was done in changing the area of a surface film
  • The magnetization of a para-magnetic solid