Answer & Solution
Answer: Option
C
Solution:
In fluid mechanics, the term "vena contracta" refers to the narrowest portion of the flow downstream from a fluid flow measurement device, such as an orifice or a nozzle. It is the point where the cross-sectional area of the flow is the smallest. While certain characteristics may hold true at the vena contracta, it is not accurate to say that streamlines are parallel throughout the jet at this point.
At the vena contracta, the streamlines are not parallel; instead, they tend to converge due to the contraction of the flow. This phenomenon is a result of the Bernoulli's principle, which states that the velocity of a fluid increases as the cross-sectional area of the flow decreases.
The other options are correct statements:
Option A: The pressure intensity at vena contracta is atmospheric
This statement is correct. At the vena contracta, the pressure intensity (pressure) is generally lower than atmospheric due to the increased velocity of the flow.
Option B: Contraction is least at vena contracta
This statement is correct. The vena contracta is the point of maximum contraction in the flow downstream of a fluid measurement device.
Option D: Coefficient of contraction is always less than one
This statement is correct. The coefficient of contraction (Cc) is a dimensionless factor that represents the ratio of the actual minimum area of flow (throat area) to the theoretical minimum area of flow. Since the actual area is smaller than the theoretical area, the coefficient of contraction is always less than one.
Therefore, the correct answer is Option C: Stream lines are parallel throughout the jet at vena contracta, as this statement is not accurate.
