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BARC 2021 ME: Subject Revision Quiz 3

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Question 1

Two long rods of same diameter, one made of aluminium (k= 250 W/m°C) and other made of copper (k= 400 W/m°C) have one of their ends inserted in furnace. Both the rods are exposed to same environment. At a distance of 125mm from the furnace end, the temperature of the aluminium rod is 120°C. At what distance from the furnace end the same temperature will reach in copper rod.

Question 2

An oil cooler in a high performance engine has an outside area 0.12 m2 and surface temperature of 65°C . At any intermediate time air moves over the surface of the cooler at a temperature of 30°C and given heat transfer coefficient equal to Find out the heat transfer rate?

Question 3

A body placed in all enclosure (which may be assumed black body) is in thermal equilibrium with it. Which of the following is true for emissivity (ϵ) and absorptivity (α) of the body?

Question 4

If the temperature of a solid surface changes from to , then its emissive power changes in the ration of nearly

Question 5

Air at 25°C blows over a flat plate of 40×60 cm size maintained at 120°C . The convective heat transfer coefficient is 20 W/m2K.The heat loss from the plate would be.

Question 6

A fluid having a density of 1 g/cc is in a state with Grashof number 2 × 106 and prandtl number 0.7. Assuming acceleration due to gravity as 10 m/s2, calculate the Rayleigh number?

Question 7

The chemical formula for R-134 is:

Question 8

Two rods, one of length l and the other of length 2l , are made of the same material and have same diameter. Both ends of the longer rod are maintained at 100 °C. One end of the shorter rod is maintained at 100 °C while the other end is insulated. Both rods are exposed to the same environment at 40 °C. The temperature at the insulated end is measaured to be 55 °C The temperature at the midpoint of the longer rod would be:

Question 9

Gas refrigerator working on reverse Brayton cycle is with pressure ratio is 4. If the specific heat ratio for gas is 1.5, then what will be the COP of the cycle.

Question 10

The COP of domestic air conditioner in comparison to domestic refrigerator will be

Question 11

Consider an ideal VCRS (Vapor compression refrigeration cycle), for which the enthalpy of refrigerant before and after the evaporator are 75 kJ/kg and 180 kJ/kg respectively. Determine the refrigerant flow for each ton of refrigeration required:

Question 12

A sphere of diameter of D/2 is surrounded by a cube of size D, then what will be the view factor of F21?

Question 13

A double-pipe counter-flow heat exchanger transfers heat between two water streams. Tube side water at 19 liter/s is heated from 10 °C to 38 °C. Shell side water at 25 liter/s is entering at 46 °C. Assume constant properties of water; density is 1000 kg/m3 and specific heat is 4186 J/kg.K. The LMTD (in °C) is __________

Question 14

A new heat exchanger is replaced by old one which transfer 15% more heat Assuming that both heat exchanger has same temperature difference & same effective surface area. Find the fouling of old heat exchanger if overall heat transfer coefficient of new heat exchanger is 220 W/m2°C.

Question 15

When the Brayton cycle working in the pressure limits of p1 and p2 is reversed and operated as a refrigerator, what is the ideal value of COP for such a cycle?

Question 16

Heat transfer rates are often described by non-dimensional parameters such as Nusselt Number (Nu), Prandtl number (Pr). Reynolds number (Re), Grashoff (Gr), Biot number (Bi) , fourier number (F0). Which of the following relations is true for forced convection ?

Question 17

Air at 15°C DBT, 60% of relative humidity is heated to 45°C using an electric heater. The surface temp. of the coil is 55°C. Then what will be contact factor of heating coil.

Question 18

Match List-I with List-II and select the correct answer using the code given below the lists:
A) Radiation heat transfer
B) Conduction heat transfer
C) Forced convection
D) Transient heat flow
1) Fourier number
2) Wien’s displacement law
3) Fourier law
4) Stanton number

Question 19

During which component of vapour compression refrigeration system, the enthalpy remains constant:

Question 20

A counter flow type air heater has an area of 80 m2. The overall heat transfer coefficient is 200 W/m2-K and heat capacity of both the hot and cold stream is 3200 W/K. The effectiveness of heat exchanger will be.
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