1511. The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe )
K/h0
2K/h0
hi/K
2hi/K
✅ The correct answer is option A.
1514. A hot body will radiate heat most rapidly, if its surface is
White & rough
Black & rough
White & polished
Black & polished
✅ The correct answer is option B.
1517. A graph between __________ is called Wilson plot.
1/U Vs . 1/v0.8
1/v0.8 Vs . U
V0.8 Vs . U
1/U Vs . 1/V
✅ The correct answer is option A.
1520. In pipe flow, heat is transferred from hot wall to the liquid by
Conduction only
Forced convection only
Forced convection and conduction
Free and forced convection
✅ The correct answer is option C.
1522. In Biot number, the characteristic length used is the ratio of the __________ of the solid.
Volume to surface area
Perimeter to surface area
Surface area to volume
Surface area to perimeter
✅ The correct answer is option A.
1524. The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface)
K/h0
2K/h0
h0/K
h0/2K
✅ The correct answer is option B.
1489. Radiation heat losses from satisfactorily insulated high pressure boilar may be about __________ percent.
1
7
18
26
✅ The correct answer is option B.
1491. The main purpose of providing fins on heat transfer surface is to increase the
Temperature gradient
Mechanical strength of the equipment
Heat transfer area
Heat transfer co-efficient
✅ The correct answer is option C.
1493. A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to 65° C in __________ minutes.
10
>10
<10
Either B or C, depends on the mass of the body
✅ The correct answer is option B.
1495. Which of the following is unimportant in forced convection?
Reynolds number
Prandtl number
Grashhoff number
None of these
✅ The correct answer is option C.