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Thermodynamics - Lecture - 5

IMPORTANT FOR SOLVING PROBLEMS

Heat (Q)

Specific Heat Capacity (C)

Relation Between The Cp, Cv and R

Internal Energy (U)

Enthalpy (H)

Workdone (W)

Pressure Unit Conversion

Sign Convention Of Work and Heat

 

Relationship Between Temperature Scales

Three Temperature Scales,

Fahrenheit

Celsius

Kelvin


Convert a temperature from its representation on

The Fahrenheit ( F) scale to the Celsius (C) value:

C = 5/9(F - 32)

The Celsius (C) value to Fahrenheit ( F) scale :

F = 9/5C + 32

Kelvin(k):

0°C = 273K


Heat (Q)

Q is the heat supplied to the system, m is the mass of the system, c is the specific heat capacity of the system and ΔT is the change in temperature of the system.

Q=m×c×ΔT

Or

Q=W+ ΔU


Specific heat capacity (C)

In The Form Of Heat, To One Unit Of Mass Of The Substance In Order To Cause An Increase Of One Unit In Its Temperature.

Unit - J/Kg.K

Specific heat capacity at constant pressure (Cp )

Cp = 1.005 KJ/Kg.K

Specific heat capacity at constant volume (Cv)

Cv = 0.716 KJ/Kg.K

Relation Between The Cp, Cv and R

Characteristic Gas Constant (R) = Cp - Cv

For Gas (R)=1.005-0.716

R = 0.289 KJ/Kg.K

For Ratio (γ) = Cp / Cv

For air (γ) = 1.4


Internal Energy (U)

Heat Energy Stored in the Gas at a Given Temperature

Unit = Joule

U = m. Cv (T2-T1)

Enthalpy (h)

Total Heat of the substance which is equal to the SUM of Internal Energy (U) and Flow work (PxV)

Unit = Joule

Enthalpy (H) = U+PV

H=m.Cp (T2-T1)


Work Done (W)

Displacement of Work

Wok Done (W) = Pressure x Change in Volume

= P.dV


Pressure unit conversion

Pressure units are

Pascal

Bar

N/m2


Pascal to N/m2

1 Pa = 1 N/m2


Bar to N/m2

1 Bar = 10 5  N/m2

105  N/m2  = 100 x 1000 N/m2

= 100 KN/m2


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