** Company: ** DRDO

1. The velocity profile u in the boundary layer over a flat plate is given by . where U is the free stream velocity, y is the vertical distance of the velocity point from the flat plate and d is the boundary layer thickness. The displacement thickness of the boundary layer is

(A) (B) (C) (D)

2. Which of the following statements is INCORRECT about thixotropic fluids?

(A) Apparent viscosity depends on the time of shearing

(B) Thixotropy is an irreversible process

(C) Thixotropic fluid shows shear thinning behavior

(D) Thixotropic fluids are in general non-Newtonian fluids.

3. A small liquid droplet of radius 1 mm and density 900 kg/m3 is rising up in a column of water. What is the terminal rise velocity of the drop if creeping flow conditions are assumed?(Given: viscosity of water = 1 cp, Gravitational constant g = 10 m/s2 )

(A) m/s (B) m/s (C) m/s (D) m/s

4. Which of the following is NOT RECOMMENDED to increase the collection efficiency of a cyclone separator?

(A) Increase in particle density

(B) Decrease in gas temperature

(C) Increase in particle diameter

(D) Increase in gas flow rate

Statement for Linked Answer – Questions 5 and 6:

In a fluidized bed operation, spherical particles of 1 mm diameter are packed to a height of 1.0 meter. The porosity of this bed is measured to be 0.4. At the minimum fluidization with air the bed height expands to 1.2 meter.

(Given: Particle density = 1200 kg/m3, Gravitational constant g = 10 m/s2 ).

5. The porosity of the bed at minimum fluidization is

(A) 0.4 (B) 0.3 (C) 0.5 (D) 0.6

6. The approximate value of pressure drop in the bed at minimum fluidization will be

(A) 3600 N/m2 (B) 7200 N/m2 (C) 6000 N/m2 (D) 3000 N/m2

7. In a centrifugal filter the inside radius of the filter basket is R2 and radius of the inner surface of liquid is R1. The centrifuge is rotating with an angular speed ?. Which of the following is true about the pressure drop ?P from the centrifugal action?

(A) ?P µ ?1/2 (B) ?P µ (R22 + R12)

(C) ?P µ (R22 – R12) (D) ?P µ ?

8. In a dry crushing operation the mean diameter of the feed and product particles are 100 mm and 1 mm, respectively. The sphericity of the feed and product particles are 0.5 and 1.0, respectively. If the feed particles of 200 mm diameter with the same sphericity are handled at the same feed rate, what will be the percentage increase in power requirement assuming that the product remains the same?

(A) (B) (C) (D)

9. Which of the following is INCORRECT about the boundary layer development over flat infinite plate?

(A) The fluid velocity at solid-liquid interface is zero

(B) The shear rate inside the boundary layer is not zero

(C) The boundary layer thickness increases with distance from the leading edge

(D) The flow in the boundary layer close to the leading edge is turbulent

10. Which of the following velocity field represents an irrotational flow for x, y > 0, x ? y?

(A) V = 2 yi – 2x .j

(B) V = 2 xi – 3y,j

(C) V = xy i – xy j

(D) V = xy i + xy j

11. In a laminar flow between two parallel plates separated by a distance H, the head loss varies

(A) directly as H (B) inversely as H2

(C) directly as H2 (D) inversely as H3

12. Two viscous liquids are to be blended by passing through a pipe. Which of the following would be the most suitable condition for axial mixing?

(A) Creeping flow (B) Low Reynolds number flow

(C) High Reynolds number flow (D) Plug flow

13. A U-tube manometer measures

(A) absolute pressure at a point

(B) local atmospheric pressure at a point

(C) difference in total energy between two points

(D) difference in pressure between two points

14. What will happen to the heat loss if foam insulation, with thermal conductivity 0.09 W/m-K is added to a 5 cm outer diameter pipe carrying hot water? (Heat transfer coefficient on the outer surface = 10 W/m2-K)

(A) Increases (B) Decreases

(C) First increases then decreases (D) Remains constant

15. Biot number (hL/k) is important for which mode of heat transfer?

(A) Natural convection (B) Forced convection

(C) Transient heat conduction (D) Radiation

16. The temperature distribution in a 0.25 m thick wall is given as T (°C) = 250 + bx – cx2,

where x (in meter) is the position of a point with respect to the surface of the wall which is at higher temperature. The thermal conductivity of the wall is 5.95 W/m-°C. What will be the value of b if the surface at x = 0 is insulated?

(A) 0 (B) 1 (C) – 1 (D) 0.5

17. When momentum diffusivity is greater than the thermal diffusivity, the velocity boundary layer

(A) develops faster than the thermal boundary layer

(B) develops slower than the thermal boundary layer

(C) grows together

(D) disappears

18. An aluminium ball of area 0.5 m2 and mass 10 kg is cooled in ambient at 25 °C. When the temperature of the ball is 125 °C, it is found to cool at the rate of 6 °C/min. What will be the surface heat transfer coefficient?

(Given, Cp = 0.5 kJ/kg-°C)

(A) 0.5 W/m2-°C (B) 0.01 W/m2-°C

(C) 0.05 W/m2-°C (D) 0.l W/m2-°C

19. Water at 25 °C enters a pipe with internal diameter 2 cm having a constant wall heat flux of 1 KW/m2. The flow is hydro dynamically and thermally fully developed. What will be the difference between the local wall temperature and the local mean (bulk) temperature? (Thermal conductivity of pipe = 0.4 W/m-°C; Nusselt Number = 5.0)

(A) 5 °C (B) 15 °C (C) 10 °C (D) 50 °C

20. When some liquid nitrogen spills on the floor of a laboratory, the droplets move so briskly that they appear to be dancing before they disappear. This phenomenon

(A) is related to pool boiling (B) is related to film boiling

(C) is related to nucleate boiling (D) has nothing to do with boiling

21. Consider sphere 1 enclosed by sphere 2 as shown in the following figure. The area of sphere 2 is double the area of sphere 1. What are the various view factors (F1I, F12, F21, F22)?

(A) 0, 0.5, 0.5, 1 (B) 0.5, 1, 1, 0.5

(C) 0.5, 0.5, 0, 1 (D) 0, 1, 0.5, 0.5

22. A triple-effect evaporator is concentrating a liquid that has no appreciable elevation in boiling point. The temperature of the steam to the first effect is 110 °C and the boiling point of the solution in the last effect is 50 °C. The ratio of the heat transfer resistance of the first effect to that of the overall heat transfer resistance is 0.2. At what temperature will the liquid boil in the first effect?

(A) 95 °C (B) 98 °C (C) 90 °C (D) 92 °C

23. Gas A is being cracked on a catalyst as per the reaction, A?2B+C in such a way that A diffuses to the cracking surface and B diffuses back, while C is not diffusing. At steady state what will be the ratio of molar flux of A to the total molar flux?

(A) 1/3 (B) –1 (C) 2 (D) 2/3

24. The eddy momentum diffusivity, the thermal diffusivity and the mass diffusivity will be same for most of the gases when

(A) both Prandtl and Schmidt numbers are equal to 1.2

(B) both Prandtl and Schmidt numbers are equal to 10.0

(C) both Prandtl and Schmidt numbers are equal to 0.1

(D) both Prandtl and Schmidt numbers are equal to 1.0

25. According to surface renewal theory, the average mass transfer coefficient is directly proportional to

(A) DAB (B) (C) (D)