1421. The absorptivity of a body is equal to its emissivity
At a particular temperature
For circular bodies
Under thermal equilibrium
None of these
✅ The correct answer is option C.
Engineering
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1422. Which of the following situations can be approximated to a steady state heat transfer system?
A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmosheric air at 35°C
10 kg of dry saturated steam at 8 kgf/cm² flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C
Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C
A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C
✅ The correct answer is option B.
1423. The units of resistance to heat transfer is
J.m⁻².K⁻¹
J.m⁻¹.K⁻¹
W.m⁻².K⁻¹
W⁻¹m²K
✅ The correct answer is option D.
1424. The value of Stefan-Boltazman constant in SI unit is
5.6697 x 10-8W/m².°K4
0.1714 x 10-8W/m².°K4
5.6697 x 10-8kcal/m² . °K4
0.1714 x 10-8kcal/m². °K4
✅ The correct answer is option A.
1425. Analogy between mass and heat transfer is not applicable in case of
Same velocity profile or equal eddy diffusivities
Thermal or pressure mass diffusion
Viscous heating or chemical reaction
Both B and C
✅ The correct answer is option D.
1426. The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid
Its evaporation loss
Excessive corrosion
Uneconomic LMTD
Decrease in heat exchanger efficiency
✅ The correct answer is option B.
1427. The actual temperature drop across the heating surface in an evaporator depends on the
Feed
Depth of liquid over heating surface
Pressure difference between steam chest and vapour space
All of the above
✅ The correct answer is option D.
1428. The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances.
Average
Geometric mean
Product
Sum
✅ The correct answer is option D.
1429. Boiling of milk in an open vessel is an example of __________ boiling.
Film
Sub-cooled
Saturated nucleate
None of these
✅ The correct answer is option A.
1430. A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions ? Assume that the conductive heat transfer co-efficient is infinitely large.
5 minutes
10 minutes
20 minutes
40 minutes
✅ The correct answer is option A.