Consider the flow of water through a clear tube. It is sometimes possible to observe cavitation in the throat created by pinching off the tube to a very small diameter as sketched. We assume incompressible flow with negligible gravitational effects and negligible irreversibility's. You will learn later (Chap. 5) that as the duct cross-sectional area decreases, the velocity increases and the pressure decreases according to

respectively, where V₁ and V₂ are the average velocities through cross-sectional areas A₁ and A₂. Thus, both the maximum velocity and minimum pressure occur at the throat. 

(a) If the water is at 208C, the inlet pressure is 20.803 kPa, and the throat diameter is one-twentieth of the inlet diameter, estimate the minimum average inlet velocity at which cavitation is likely to occur in the throat. 

(b) Repeat at a water temperature of 50°C. Explain why the required inlet velocity is higher or lower than that of part (a).

Transcribed Image Text:

pV/²= P₂ + 2 V₁A₁ = V₂A₂ and P₁ + p- 2