Work Transfer

Work transfer

Work is defined as the form of energy and the energy intransient , i.e., the energy which can transfer.

The Work Transfer is a boundary phenomenon i.e., work is said to be transferred only when the work crosses the boundary of the system .

For heat transfer

Work Transfer is

  • Boundary phenomenon
  • Energy in transition i.e., intransient
  • Path function
  • Not a Property
  • Inexact differential
  • Cyclic integral is zero

Work done or transfer can be written like –

∆W ( ✓ )

But cannot write like

dW ( × ) , because work is inexact differential.

Types of work transfer :

  1. Displacement work
  2. Stirrer work / shaft work / paddle wheel work
  3. Electrical work
  4. Flow work

• Displacement work :

When the force acts upon the system and it undergoes a change in its position , i.e., displacement occurs then work is said to be done .

The three parameters exists here which are , force , displacement and angle between the line of action of force and displacement.

Note : Here force will be the conservative force.

Therefore ,

Work = ∆W

Here , this displacement work is applicable only for

(i) Reversible Process

(ii) Closed system

Sign convention :

  • Work is done on the system is negative.
  • Work is done by the system is positive.

Note : Area under the PV diagram denotes the work transfer.

• Stirrer Work / Paddle Wheel work / Shaft work :

Stirrer work is the work produced due to the enforcement of the Torque which causes the angular displacement of stirrer .

Here , consider

T = Torque

N = Number of revolutions of stirrer

∆ W = Stirrer work

then ,

∆W = Torque × 2π N

stirrer work

• Electrical work :

The work produced due to the unit current flow across unit voltage for unit time is known as Electrical work .

Here ,

I = Current

V = Voltage

t = time

∆W = Electrical work

Therefore ,

∆W = I × V × t

Electrical work

• Flow Work :

The work required by the fluid to enter or exit from a control volume where mass is involved , such work is Flow work.

Flow work = P .dV

Therefore , flow work per mass = P. dV / p.dV

Here ,

P = Pressure

dV = Volume

p = density

Since , 1/p = v { specific volume }

Flow work / mass = P . v