Adiabatic Process - Physical Engineering - Lecture Slides, Slides of Engineering Physics

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Physics

Adiabatic Process, Isothermal Process & Heat

And Carnot Engine

Adiabatic Process

Adiabatic Processes

P-V Diagrams

p

V

f

i

Isotherm

Isobar

Adiabat

Isochor

Such a process can occur if the

container of the system has thermally-

insulated walls or the process happens

in an extremely short time, so that

there is no opportunity for significant

heat exchange. The term "adiabatic"

literally means impassable

Adiabatic process occurs when the gas

expands or is compressed rapidly,

particularly when the gas is contained

in an insulated cylinder.

Adiabatic Expansion

• dq=
• dU=dw
• for an ideal gas,

CVdT = -pexdV

• if reversible,

pex = p = nRT/V

• therefore,

CV(dT/T) = -nR(dV/V)

q

q

w

Reversible Adiabatic Expansion

R

T V T V

V

V

T

T

V

V

R

T

T

C

i

c f

c

f

i

R

C

i

f

i

f

i

f V m

f i

V m

where c C /

ln ln

V, m

,

,

Reversible Adiabatic Expansion

  f f i i

c i

c i

c f

c f

i

c i i f

c f f

i

c f

c

p V p V

p V p V

V nR

pV V nR

p V

T V T V f i





 

  

  

















 1  1

Examples Of Adiabatic Process

Two examples of adiabatic processes are the

cooling of a rising parcel of air, due to the

expansion of molecules (particles made by the

combination of two or more atoms) within the

parcel and the warming of a falling parcel of air,

due to the compression of molecules within the

parcel. (An air parcel is a small volume of air

that has a consistent temperature throughout

and experiences minimal mixing with the

surrounding air.)

The process which is carried out at a

constant temperature and hence

the condition for the Boyle’s Law on

the gas is fulfilled

Therefore when the gas

expands or compressed

isothermally, the product of

its pressure and volume

during the process remain

constant.

Examples of Isothermal Process

• Example1:

Boiling of water in the open air. In general most isobaric phase changes are isothermal. In this example the system does work as the steam-produced pushes against the atmosphere as it expands. Neither the heat Q , the work W , or the change in internal energy ΔU are zero. In this case Q = mLv since the water change phases.