Quiz: Mechanical Engineering

Exam: DFCCIL

Topic: Fluid Mechanics/Machines

Each question carries 2 mark

Negative marking: 1/3 mark

Time: 10 Minutes

Q1. Using Blasius equation, the friction factor for turbulent flow through pipes varies as:

(a) Re^(-1)

(b) Re^(-0.5)

(c) Re^(-0.33)

(d) Re^(-0.25)

Q2. In reaction turbine:

(a) kinetic energy is appreciable as the fluid leaves the runner and enters the draft tube

(b) the vanes are partly filled

(c) total energy of fluid is converted to kinetic energy in the runner

(d) it is exposed to the atmosphere

Q3. The unit discharge, Q(u )and unit speed, Nu curve for a turbine is shown in figure. Curve B is for

(a) Francis turbine

(b) Kaplan turbine

(c) Pelton turbine

(d) Propeller turbine

Q4. Kaplan turbine-

(a) has poor part-load efficiency

(b) is used where high head is available

(c) has inlet adjusted guided vanes

(d) has adjustable runner blades

Q5. Bluff body is the body of such a shape that pressure drag as compared to friction drag is

(a) Same

(b) More

(c) Less

(d) Zero

Q6. According to Nikuradse’s the boundary behaves hydrodynamically smooth when

(a) (k/δ)>10

(b) (k/δ)>0.25

(c) (k/δ)<0.25

(d) (k/δ)<8

Q7. The head loss in a sudden expansion from 6 cm diameter pipe to 12 on diameter pipe in terms of velocity v_1 in the smaller diameter pipe is

(a) 3/16.(V_1^2)/2g

(b) 5/16.(V_1^2)/2g

(c) 7/16.(V_1^2)/2g

(d) 9/16.(V_1^2)/2g

Q8. An air vessel is provided at the summit in the syphon in order to

(a) to maintain pressure difference

(b) to increasing discharge

(c) to increase velocity

(d) None of these

Q9. For measuring flow by a venturi-meter, it should be installed in ** _**.

(a) Vertical line

(b) Horizontal line

(c) Inclined line with upward flow

(d) in any direction and in any location

Q10. Which one of the following statements is correct? While using boundary layer equation, Bernoulli’s equation

(a) can be used anywhere

(b) can be used only outside the boundary layer

(c) can be used only inside the boundary layer

(d) cannot be used either inside or outside the boundary layer

Solutions

S1. Ans.(d)

Sol. Friction factor according to Blasius equation,

f=0.316/(Re^(1⁄4) )

f ∝1/(Re^(1⁄4) )

f ∝ Re^((-1)⁄4)

f ∝ Re^(-0.25)

S2. Ans.(a)

Sol. in Case of reaction turbine, Kinetic energy is appreciable as the fluid leaves the runner and enters the draft tube. Draft tube converts this Kinetic energy into useful Pressure energy.

S3. Ans.(a)

Sol. Graph represent the Francis turbine. G.O is Gate open

S4. Ans.(d)

Sol. Kaplan turbine has adjustable runner blade due to that it has high part load efficiency.

S5. Ans.(b)

Sol. when pressure force is dominated to friction force which both are component of drag force is the condition when submerge body is bluff body.

S6. Ans.(c)

Sol. as per Nikuradse’s

K/δ<0.25=Hydrodynamically smooth. 0.256=Rough

Here, δ = Thickness of laminar. Sublayer

K = Avg height of surface roughness

S7. Ans.(d)

Sol.

h_f=(V_1^2)/2g [1-A_1/A_2 ]^2

A_1=π/4 d_1^2=π/4 (6)^2=9π cm^2

A_2=π/4 d_2^2=π/4 (12)^2=36π cm^2

h_f=(V_1^2)/2g [1-9π/36π]^2=(3/4)^2.(V_1^2)/2g=9/16 .(V_1^2)/2g

S8. Ans.(d)

Sol. Air vessel is provided to maintain the continuity of flow.

S9. Ans.(b)

Sol. Venturi meter has no effect on its reading with its position of placing. It is the device which is independent about its position.

S10. Ans.(b)

Sol. Bernoulli’s equation can be used only outside the boundary layer, Bernoulli’s equation can be applied only for frictionless flow but inside the boundaries there is irrotational flow and in disorganized form