Wednesday, 6 April 2016

BARC OCES/DGFS recruitment interview questions - Part 2

Hi,
I am glad to share some more questions asked in BARC OCES/DGFS recruitment interview for mechanical engineering discipline in 2015. These questions were shared by my colleague.
1.       Draw the shear force and bending moment diagrams for the following beam subjected to point load at the mid span. (Ref fig.1)

2.       In the above problem, replace the beam with a rope and draw the SFD & BMD. Which one will have more strength and Why? (Ref fig.1)
3.       What is the required load ‘W’ to be applied in order to make θ zero degrees? (Ref fig. 2)
Fig. 2

4.       Two steel balls, one is of volume V and the other is of volume 2V. Both contains same amount of sensible thermal energy 2000J in them. Which will have more temperature?
5.       Two spherical bodies of same diameter D, are connected by a string as shown in fig. 3. If the string is in tension, can both be of same material? Determine the weights of the two bodies. (Ref fig.3)

6.       For the bar shown in figure below, assuming 1-D axial heat conduction and completely insulated boundaries around and subjected to same temperature 1000 K at the ends at time t=0. If the initial temperature of the bar is 300K, draw the temperature profile along the length, at some typical instances for t>0. (Ref fig.4)
7.       There are two vessels, A and B, having same diameter and containing water to the same level. But one vessel has steel ball in it and they are heated from bottom at the same time. Draw the approximate average water temperature variation in them with respect to time. Does both require same amount of time to start boiling under same ambient pressure conditions? If not, which one requires more time? (Ref fig.5)

8.       For a reversible Carnot engine, find the relation between temperatures TH, TC and heats QH, QC.
9.       Tell all the laws of thermodynamics with application for each law.
10.   How can you find whether scaling occurred on condenser tubes or not?
11.   Draw the temperature profiles for shell side and tube side fluids for a typical condenser.
12.   What is the stress in the below bar subjected to force P1 at one end and force P2 at other end? (Ref fig.6)

All the very Best.!!!

1. 6th is a unsteady state problem how to solve such problems.
Can you answer this 10. How can you find whether scaling occurred on condenser tubes or not?

1. Hello Dinesh,
6th question is indeed an unsteady problem. Since they are asking only to draw the temperature profiles at some typical instances of time (t>0), you can approach problem like this... First see the typical shape of profile in transient heat conduction through infinite media (ref Incropera or Cengel). then draw that profile on both sides with 300 K in remaining middle portion. after some time, both the profiles start interacting. so, you can make next instance by rising the center portion temperature to certain higher value. then reduce the valley size to approach the horizontal profile (as both ends are at same temperature).

Question 10: scaling of heat exchanger tubes can be identified by comparing the pressure drop and overall duty of the exchanger with benchmark values. the benchmark values are nothing but those values obtained during initial operation of the heat exchanger. if pressure drop on tube side increases with same flow rate, then scaling might have occurred. duty of heat exchanger may or may not be affected depending on whether tube side transfer coefficient is dominating or not.

2. for horizontal (or flat) profile at the end you may denote time as "infinity"

2. in question no 2 for making theta to zero the value of p must be 0.

1. or we have to use equilibrium analysis.

2. 3. 