Energy Balance on Open SystemOpen System is one in which there is Mass Flow

across its Boundaries

Types of Work

= Shaft Work + Flow Work

Shaft Work= Work Done by Process Fluid Moving Part within System

Flow Work = Work Done by Fluid at System Outlet – Work Done on Fluid at System Inlet

System(inlet Mass Flow Rate)

(inle

t Specific Internal Energy )

uin (inlet Velocity)

Zin (inlet elevation)

(Inlet Specific Volume)

Pin (Inlet Pressure)

(outlet Mass Flow Rate)

(outlet Specific Internal Energy)

uout (outlet Velocity)

Zout (outlet elevation)

(Outlet Specific Volume)

Pout(Outlet Pressure)

Illustration of Flow Work = PV Work

Dimensional Analysis

Flow Work is a State Function

Form of Energy Equation for Open System

Pipe

State Properties of Steam

(Table B.6)Prop. Of Saturated Steam

P T (Liq.Water)(Bars) (oC) M3/Kg M3/Kg KJoules/Kg KJoules/Kg

0.00611 0.01 0.001 206.2 Zero 2375.6

0.10 45.8 0.00101 14.67 191.8 2438.0

0.50 81.3 0.00103 3.24 340.5 2484.0

1.01325 100.0 0.001044 1.673 419.0 2506.5

Another State Function

Enthalpy = Internal Energy + Flow Work = A State Function

(Table B.6)Prop. Of Saturated Steam

P T(Bars) (oC) KJoules/Kg KJoules/Kg KJ/Kg KJ/Kg

0.00611 0.01 Zero 2375.6 +0.0 2501.6

0.10 45.8 191.8 2438.0 191.8 2584.8

0.50 81.3 340.5 2484.0 340.6 2646.0

1.01325 100.0 419.0 2506.5 419.1 2676.0

Heat of Vaporization

Internal Energy of Vaporization

Energy Balance for Open System with Multiple Feed & Product Streams

Energy Balance Equation

Simplification of First Law of Thermodynamics for Open System

Here All Terms are Rates of Energy &

Compare with First Law of ThermodynamicsFor Closed System

System

Here All Terms are Amounts of Energy &

Simplifications of Energy Balance for Open System

If Single Input & Single Output Stream

Simplifications:

If no Moving Parts in System

Shaft Work Rate = 0.0=

If System & Surroundings are at Same Temperature

Heat Transfer Rate = 0.0=

If Linear Velocities of All Streams are Equal

Neglect Kinetic Energy Term:

If all streams enter & leave process at the Same Height

Neglect Potential Energy Term:

If Specific Enthalpy is Same for All Streams& Because Mass is Conserved