Cavitation MCQ Quiz in मराठी - Objective Question with Answer for Cavitation - मोफत PDF डाउनलोड करा
Last updated on Mar 20, 2025
Latest Cavitation MCQ Objective Questions
Top Cavitation MCQ Objective Questions
Cavitation Question 1:
The vapour pressure is the characteristic fluid property involved in the phenomenon of
Answer (Detailed Solution Below)
Cavitation Question 1 Detailed Solution
Explanation:
- Cavitation is the phenomenon of the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below the vapour pressure of the fluid and the sudden collapse of these bubbles in a region of higher pressure.
- In reaction turbines, the pressure of the working fluid changes gradually as it passes through the runner along with the change in its kinetic energy based on absolute velocity due to the impulse action between the fluid and the runner.
- At the exit of the rotor, the pressure of the working fluid is lowest, if the pressure falls below the vapour pressure of the working fluid then cavitation may occur at the outlet of the rotor.
- Due to cavitation, the metal of the runner vanes is gradually eaten away, which results in lowering the efficiency of the turbine.
Additional Information
Cavitation in Centrifugal Pump:
- In centrifugal pumps, the cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pumps, where the pressure is considerably reduced.
- Cavitation also occurs in reciprocating pumps if there is a high-velocity suction or discharge.
Cavitation Question 2:
To avoid gas bounding, the pump is:
Answer (Detailed Solution Below)
Cavitation Question 2 Detailed Solution
Explanation:
Priming
- It is an operation in which the suction pipe, casing of the pump, and a portion of the delivery pipe are completely filled up by an water from an outside source before starting the pump.
- In other words, priming is the process in which the impeller of a centrifugal pump will get submerged in liquid without any air trap inside. It is always advisable to start pump only after priming.
- Priming is an operation that generally that happens in the centrifugal pump.
- Priming is required in order to drive out the air voids present, which otherwise would make the operation of the pump ineffective.
Additional Information
Centrifugal pump:
- It works on the principle of the forced vortex, which means that when a certain mass of liquid is rotated with the external torque, the rise in pressure head of the rotating fluid takes place.
- Due to this high pressure the liquid can be lifted to a higher level.
- The action of the centrifugal pump is the reverse of radially inward flow reaction turbine ie radially outward flow, which takes water from the tailrace and delivers it to the headrace.
Cavitation Question 3:
The dimensionless parameter describing flow-induced boiling is known as ______.
Answer (Detailed Solution Below)
Cavitation Question 3 Detailed Solution
Explanation:
Cavitation:
It is defined as the phenomenon of the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure and the sudden collapsing of these vapour bubbles in a region of higher pressure. When the vapour pressure collapse, very high pressure is created.
It is defined as:
\(\mathbf{\sigma ~=~\frac{{{P_a}~ - ~{P_v}}}{{\frac{1}{2}\rho {V^2}}}}\)
Where Pa is the local pressure, Pv is vapor pressure ρ is the density of the fluid, V is the characteristic velocity of flow.
If the value of σ is negative, then cavitation will take place.
Boiling or cavitations may damage the pump.
Effects of cavitation:
(i) The metallic surfaces are damaged and cavities are formed on the surfaces.
(ii) Due to the sudden collapse of the vapour bubble, considerable noise and vibrations are produced.
(iii) Due to cavitation, the metal of the runner vanes and the draft tube is gradually eaten away, which results in lowering the efficiency of the turbine.
Cavitation Question 4:
In which case Cavitation phenomenon occurs?
Answer (Detailed Solution Below)
Cavitation Question 4 Detailed Solution
Explanation:
Cavitation is the phenomenon of the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below the vapour pressure of the fluid and the sudden collapse of these bubbles in the region of higher pressure.
In centrifugal pumps, the cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pump where the pressure is considerably low. So to avoid cavitation pressure on the suction side should be high. In order to determine whether cavitation will occur in any portion of the suction side of the pump, the critical value of Thoma’s cavitation factor is calculated.
The hydraulic machines subjected to cavitation are reaction turbines and centrifugal pumps.
Cavitation in turbine: In a reaction turbine (Francis Turbine) the cavitation may occur at the outlet of the runner or at the inlet of the draft tube where the pressure is considerably reduced.
Cavitation in Centrifugal Pump: In centrifugal pumps, the cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pumps, where the pressure is considerably reduced.
Cavitation also occurs in reciprocating pumps if there is a high-velocity suction or discharge.
Cavitation Question 5:
A reaction turbine works under 100 m head of water. The atmospheric pressure at the point of the turbine is 10.33 meters of water and vapour pressure of water is 0.33 meters of water of local temperature. Permissible Thoma's number value is 0.02. The height (in meters) of turbine above tail race free surface in meters, is
Answer (Detailed Solution Below)
Cavitation Question 5 Detailed Solution
Concept:
\(σ = \frac{{{H_{atm}} - {H_v} - {H_s}}}{H}\)
Calculation:
Given:
σ = 0.02, Hatm = 10.33 m, Hv = 0.33 m, H = 100 m
\(σ = \frac{{{H_{atm}} - {H_v} - {H_s}}}{H}\)
∴ Hs = 8 m
Cavitation Question 6:
The cavitation parameter σ is defined in terms of net positive suction head (NPSH) and net head H as
Answer (Detailed Solution Below)
Cavitation Question 6 Detailed Solution
Thoma's cavitation parameter (σ): It is the ratio of Net Positive Suction Head (NPSH) to the total head.
\(\sigma = \frac{{NPSH}}{H} = \frac{{\left( {\frac{{{P_A}}}{{\rho g}} - \frac{{{P_V}}}{{\rho g}} - z - {h_f}} \right)}}{H}\)
NPSH: It is defined as the net head developed at the suction port of the pump, in excess of the head due to the vapor pressure of the liquid at the temperature in the pump. NPSH must be positive for preventing the liquid from boiling. Boiling or cavitations may damage the pump. If NPSH reaches zero then the liquid starts boiling and cavitation starts.
Cavitation: It is defined as the phenomenon of formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure and the sudden collapsing of these vapor bubbles in a region of higher pressure. When the vapor pressure collapse, very high pressure is created.
Effects of cavitation:
(i) The metallic surfaces are damaged and cavities are formed on the surfaces.
(ii) Due to the sudden collapse of the vapor bubble, considerable noise and vibrations are produced.
(iii) Due to cavitation, the metal of the runner vanes and the draft tube is gradually eaten away, which results in lowering the efficiency of the turbine.
Cavitation Question 7:
Cavitation is a phenomenon that occurs in turbines due to:
Answer (Detailed Solution Below)
Cavitation Question 7 Detailed Solution
Explanation:
Cavitation:
- It is the formation of gas bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure i.e. low pressure.
- It is the phenomenon of the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below the vapour pressure of the fluid and the sudden collapsing of these bubbles in the region of higher pressure.
- In centrifugal pumps, cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pumps, where the pressure is considerably reduced.
- Hence if the pressure at the suction side of the pump drops below the vapour pressure of the liquid then the cavitation may occur.
Cavitation Question 8:
The cavitation and pitting can be prevented by creating which one of the following conditions?
Answer (Detailed Solution Below)
Cavitation Question 8 Detailed Solution
Concept-
Cavitation is the formation of vapour cavities in a liquid that are the consequence of forces acting upon the liquid.
It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities in the liquid where the pressure is relatively low.
When the pressure inside a pipe falls below the vapor pressure of the fluid, then cavitation occurs.
When subjected to higher pressure, the voids implode and can generate an intense shock wave and it damages the pipe material.
Pitting Corrosion is the localized corrosion of a metal surface confined to a point or small area that takes the form of cavities. Pitting corrosion is one of the most damaging forms of corrosion.
So to avoid the cavitation and pitting the pressure head has to be increased.
We have the energy equation,
\(\frac{P}{{\rho g}} + \;\frac{{{v^2}}}{{2g}} + Z = Constant\)
Where,
\(\frac{P}{{\rho g}}=\) Pressure head or Static head
V2 / 2g → Velocity head / Dynamic head / Kinetic head
Z = datum head
So considering the datum head to be constant, when the velocity head will be decreased then the pressure head will increase.
By increasing the pressure head the cavitation and pitting can be avoided.
So to avoid cavitation and pitting, we need to decrease the velocity head.Cavitation Question 9:
Cavitation in the pump occurs when
Answer (Detailed Solution Below)
Cavitation Question 9 Detailed Solution
Explanation:
Cavitation:
- It is the formation of gas bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapour pressure i.e. Vapor pressure of liquid is greater than local pressure.
- It is the phenomenon of formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below the vapour pressure of the fluid and sudden collapsing of these bubbles in the region of higher pressure.
- In centrifugal pumps, the cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pumps, where the pressure is considerably reduced.
- Hence if the pressure at the suction side of the pump drops below the vapour pressure of the liquid then the cavitation may occur.
Cavitation Question 10:
Cavitation in a centrifugal pump is caused by:
Answer (Detailed Solution Below)
Cavitation Question 10 Detailed Solution
Explanation:
Cavitation:
- Cavitation is the phenomenon of the formation of vapour bubbles of a flowing liquid in a region where the pressure of the liquid falls below the vapour pressure of the fluid and sudden collapsing of these bubbles in the region of higher pressure.
- In centrifugal pumps, cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pump where the pressure is considerably low. So to avoid cavitation pressure on the suction side should be high.
- In order to determine whether cavitation will occur in any portion of the suction side of the pump, the critical value of Thoma’s cavitation factor is calculated.
- The hydraulic machines subjected to cavitation are reaction turbines and centrifugal pumps.
Cavitation in Centrifugal Pump:
- In centrifugal pumps, cavitation may occur at the inlet of the impeller of the pump or at the suction side of the pumps, where the pressure is considerably reduced.
- Cavitation also occurs in reciprocating pumps if there is a high-velocity suction or discharge.
Cavitation in turbine:
- In a reaction turbine (Francis Turbine) the cavitation may occur at the outlet of the runner or at the inlet of the draft tube where the pressure is considerably reduced.