Multiple choice questions (MCQ) on Fluid machinery / Turbo machines

1. Which one of the following helps in avoiding cavitation in centrifugal pumps?

a. Low suction pressure                        b. High delivery pressure

c. Low delivery pressure                        d. High suction pressure

 

2. Which one of the following is the purpose of a surge tank in a Pelton turbine station?

a. It acts as a temporary storage during load changes            b. It prevents hydraulic jump

c. It prevents surges at the transformer                                 d. It prevents water hammer due to sudden reduction in load

 

3. A jet of water issues from a nozzle with a velocity of 20 m/s and it impinges normally on a flat plate moving away from it at 10m/s. If the cross sectional area of the jet is 0.02m2 and the density of water is taken as 1000 kg/m2, then the force developed on the plate will be

a. 10N                           b. 100N             c. 1000N                       d. 2000N

 

4. In the case of pelton turbine installed in a hydraulic power plant, the gross head available is the vertical distance between

a. forebay and tail race              b. reservoir level and turbine inlet

c. forebay and turbine inlet        d. reservoir level and tail race

 

5. A hydraulic couplings belongs to the category of

a. power absorbing machines                 b. power developing machines

c. energy generating machines               d. energy transfer machines

 

6. For pumping molasses, it is preferable to employ

a. reciprocating pump                b. centrifugal pump with double shrouds

c. open impeller pump               d. multistage centrifugal pump

 

7. In case of a centrifugal pump, cavitation will occur if

a. it operates above the minimum net positive suction head

b. it operates below the minimum net positive suction head

c. the pressure at the inlet of the pump is above the atmospheric pressure

d. the pressure at the inlet of the pump is equal to the atmospheric pressure

 

8. Cavitation in a centrifugal pump is likely to occur at the

a. impeller exit               b. impeller inlet              c. diffuser exit               d. involute casing

 

9. Manometric efficiency of a centrifugal pump is defined as the ratio of

a. suction head to the head imparted by the impeller to water

b. head imparted by the impeller to water to the suction head

c. manometric head to the head imparted by the impeller to water

d. head imparted by the impeller to water to the manometric head

 

10. Specific speed of a turbine is given by

a. N(P)1/2/H3/4                                   b. N(Q)1/2/H5/4                                  c. N(P)1/2/H5/4                                   d. N(H)1/2/P5/4

 

11. In the case of Francis turbine, velocity ratio is defined as V3/√2 gH where H is the available head and V3 is the

a. absolute velocity at the draft tube inlet                       b. mean velocity of flow in the turbine

c. absolute velocity at the guide vane inlet                    d. flow velocity at the rotor inlet

 

12. Consider the following statements:

a. A reverse jet protects Pelton turbine from over speeding

b. Runner blades of Francis turbine are adjustable

c. Draft tube is used invariably in all reaction turbine installations

d. Surge shafts is a protective device on penstock

Of these statements

a. 1 and 2 are correct                 b. 2 and 3 are correct

c. 3 and 4 are correct                 d. 1 and 4 are correct

 

13. Cavitation damage in the turbine runner occurs near the

a. inlet on the concave side of the blades           b. outlet on the concave side of the blades

c. outlet on the convex side of the blades          d. inlet on the convex side of the blades

 

 14. In hydraulic power-generation systems, surge tanks are provided to prevent immediate damage to

a. draft tube                 b. turbine                      c. tail race                     d. penstocks

 

15. A centrifugal pump delivers water at the rate of 50 litres/s against a total head of 40 metres. Then the power required to drive the pump is

a. 2 kW             a. 15.2 kW                    c. 19.6 kW                    d. 25.8 kW

 

16. Consider the following characteristics:

1. The fluid enters the pump axially and is discharged radially

2. Maximum efficiency may be of the order of 90%

3. Development of a low head

4. A limited suction capacity

Which of the above characteristics are possessed by axial flow pumps?

a. 1 and 2                     b. 2 and 3                     c. 2 and 4                     d. 3 and 4

 

17. Match list 1 with list 2 and select the correct answer using the codes given below the lists:                                  

List 1 List 2
A. Head race 1. Channel, tunnel or pipes through which water is carried from reservoir to the turbine
B. Tail race 2. Reservoir water level
C. Penstock 3. Diverging tube discharging water from the turbine to the atmosphere
D. Draft tube 4. The level at which water is discharged at atmospheric pressure

Codes:

A          B          C          D

a.         1          3          2          4

b.         2          4          1          3

c.         1          4          2          3

d.         2          3          1          4

 

18. Which one of the following correctly expresses the specific speed of a turbine and a pump, respectively?

a. NQ1/2/H3/4, NP1/2/H5/4                 b. NP1/2/H3/4, NQ1/2/H5/4

c. NP1/2/H5/4, NQ1/2/H3/4                 c. NP1/2/H7/4, NQ1/2/H3/4

19. Match list 1 with 2 and select the correct answer using the codes given below the lists

List 1 (Turbines)                         List 2 (Specific speeds in MKS units)

A. Kaplan turbine                                   1. 10 to 35

B. Francis turbine                                  2. 35 to 60

C. Pelton wheel with single jet                3. 60 to 300

D. Pelton wheel with two or more jets     4. 300 to 1000

 

Codes:             A          B          C          D

a.                      4          3          1          2

b.                     3          4          2          1

c.                      3          4          1          2

d.                     4          3          2          1

 

20. A centrifugal pump having an impeller of 10 cm diameter discharges 40 litre/second when running at 1000 rpm. The corresponding speed of a geometrically similar pump having an impeller of 40 cm diameter and 0.8 m3/s discharge will be

a. 276.4 rpm                  b. 298.3 rpm                 c. 312.5 rpm                  d. 358.2 rpm