Post on 23-Jan-2016
description
FLOW PROCESSES
Total energy of a flowing fluid Total energy of a compressible system
consists of three parts Internal energy Kinetic energy Potential energy
For unit mass
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But, the fluid entering or leaving a control volume possesses an additional form of energy, called “flow energy”
Flow work or (energy)
Consider a fluid element of volume V from a flowing fluid
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Force acting on the imaginary piston
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Control volume
Total energy of a control volume
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Steady flow processes
A large number of engineering devices such as nozzles, compressors and turbines operate for long periods of time under same conditions, and are classified as steady flow devices.
Processes in these devices can be approximated to a process called steady flow process.
Steady flow process is defined as a process during which a fluid flows through a control volume steadily. This means the fluid properties can change from point to point within the control volume, but at any fixed location the properties remain the same.
Principles governing steady flow
Conservation of mass
Total mass entering the
control volume per unit time
Total mass entering the
control volume per unit time
Total mass leaving the
control volume per unit time
Total mass leaving the
control volume per unit time
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A = cross e sectional area (m2)V = Velocity (m/s)= density (kg/m3) = 1/vv = specific volume (m3/kg)
Principles governing steady flow
Conservation of energyTotal energy crossing the boundary as
heat and work per unit time
Total energy crossing the boundary as
heat and work per unit time
Total energy transported out of the
control volume per unit time
Total energy transported out of the
control volume per unit time
Total energy transported
into the control
volume per unit time
Total energy transported
into the control
volume per unit time
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Principles governing steady flow
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For a single stream of flow, mass flow rates are equal
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q and w are the heat and mass transfer to the control volume per unit mass of the
Principles governing steady flow
If the fluid experiences negligible change in kinetic and potential energy as it flows through the control volume, then the energy equation for single stream steady flow system is give by:
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