What is main difference between nozzles and diffusers?
4 Answers
Nozzle
A nozzle is a device of uniformly varying cross sectional duct in which velocity of fluid increases on the expense of Pressure energy(below image is example of application of nozzle)
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Diffuser
A diffuser is a device opposite to nozzle,
In which pressure energy increases on the expense of kinetic energy of fluid.
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Source- My second year engineering text book
Edit:
Shows how exactly the nozzle works
A nozzle is a device of uniformly varying cross sectional duct in which velocity of fluid increases on the expense of Pressure energy(below image is example of application of nozzle)
Diffuser
A diffuser is a device opposite to nozzle,
In which pressure energy increases on the expense of kinetic energy of fluid.
Source- My second year engineering text book
Edit:
Shows how exactly the nozzle works
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A nozzle is a device which accelerates fluid. During this process, velocity of fluid increases with decreasing pressure.
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A diffuser is a device which slows down fluid. That means, velocity of fluid decreases with increasing pressure.
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The 1st law of thermodynamics:
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No work is involved in nozzles and diffusers:
ΣWj=0
The change of potential energy of fluid flowing into and out of nozzles and diffusers is negligible because of almost no height change.
(epot)out – (epot)in≈0 → g∙(zout – zin)≈0
Nozzles and diffusers are also regarded as steady-flow engineering device, so the term at the right-hand side equals zero:
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Furthermore, mout=min because of conservation of mass.
So now we obtain a simplified expression for nozzles and diffusers:
q + (hin +o.5∙c2in) – (hout+o.5∙c2out) =0
q + (hin –hout) + 0.5∙ (c2in – c2out) =0
where
We notice that velocity appears in the equation of energy balance, so the conservation of mass is usually taken into consideration in order to solve the problems:
ρin∙cin∙Ain= ρout∙cout∙Aout
where
Another necessary equation is the law of ideal gas:
p= ρ∙R∙T
where
A diffuser is a device which slows down fluid. That means, velocity of fluid decreases with increasing pressure.
The 1st law of thermodynamics:
No work is involved in nozzles and diffusers:
ΣWj=0
The change of potential energy of fluid flowing into and out of nozzles and diffusers is negligible because of almost no height change.
(epot)out – (epot)in≈0 → g∙(zout – zin)≈0
Nozzles and diffusers are also regarded as steady-flow engineering device, so the term at the right-hand side equals zero:
Furthermore, mout=min because of conservation of mass.
So now we obtain a simplified expression for nozzles and diffusers:
q + (hin +o.5∙c2in) – (hout+o.5∙c2out) =0
q + (hin –hout) + 0.5∙ (c2in – c2out) =0
where
- q=heat transferred per unit mass
- hin= specific enthalpy of inlet fluid
- hout= specific enthalpy of outlet fluid
- cin= velocity of inlet fluid
- cout= velocity of outlet fluid
We notice that velocity appears in the equation of energy balance, so the conservation of mass is usually taken into consideration in order to solve the problems:
ρin∙cin∙Ain= ρout∙cout∙Aout
where
- A= section area
- ρ=density
Another necessary equation is the law of ideal gas:
p= ρ∙R∙T
where
- p=pressure
- R=specific gas constant
- T=temperature
So usually we need three equations to solve the problems related to nozzles and diffusers:
The conservation of energy:
q + (hin – hout) + 0.5∙ (c2in – c2out) =0
The conservation of mass:
ρin∙cin∙Ain= ρout∙cout∙Aout
The law of ideal gas:
p= ρ∙R∙T
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