STEADY FLOW ENERGY EQUATION FOR NOZZLE AND DIFFUSER

We were discussing various basic concepts of thermodynamics such as “Thermodynamic system, boundary and surrounding” in our recent post. We have also discussed the “pure substances” and also “Mass balance and energy balance fora steady flow process” in the field of thermal engineering.

Today we will see here the steady flow energy equation for nozzle and diffuser with the help of this post. Finally we will also see here the applications of nozzle and diffuser. After this post, we will see the steady flow energy equation for throttling devices in our next post.

Let us first see here the basic concepts of nozzle and diffuser

Nozzle is an engineering device which will accelerate the fluid and hence fluid velocity or kinetic energy of fluid will be increased while pressure of fluid will be reduced.

Diffuser is an engineering device which will decelerate the fluid and hence fluid velocity or kinetic energy of fluid will be decreased while pressure of fluid will be increased.

Following figure displayed here, indicates the nozzle and diffuser and also it indicates the variation of velocity and pressure with the help of the curve as shown in following figure.

Let us consider the case of nozzle and let us write here the steady flow energy equation

Here, heat energy transfer or work energy transfer across the system boundary will be zero and change in potential energy will also be zero. Therefore we will have following equation as displayed here.

When, velocity at the inlet section V₁ is small as compared to the discharged velocity or velocity at exit section V₂, in that case we will have following equation because V₁² will be too much low as compared to V₂² and therefore we can ignore the term (V₁²/2) and hence we will have following equation as displayed here.

We must note it here that above equations is also valid for diffuser.

Applications of nozzle and diffuser

Nozzles and diffusers are normally used in various applications such as jet engines, rockets, garden hoses and spacecraft too.

We will see the “Throttling devices” and also “Carnot cycle” in our upcoming posts.

Do you have suggestions? Please write in comment box

Reference:

Engineering thermodynamics by P.K. Nag

Engineering thermodynamics by R. K. Rajput

Image courtesy: Google

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