Fourier’s law
Newton’s law of cooling
Fick’s law
None of these
✅ The correct answer is option B.
Engineering
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1382. Value of Prandtl number for water ranges from
L to 2
5 to 10
100 to 500
1000 to 2000
✅ The correct answer is option B.
1383. A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m³ and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m².K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is
555
55.5
0.55
0.15
✅ The correct answer is option D.
1384. Economy of an evaporator is influenced by the
Steam pressure
Feed temperature
Number of effect
Both B & C
✅ The correct answer is option D.
1385. A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,
The cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant
Both the spheres will emit equal amount of radiation per unit time in the beginning
Both will absorb equal amount of radiation from the surrounding in the beginning
Both B & C
✅ The correct answer is option D.
1386. The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is
1.66
88.66
3.66
Dependent on NRe only
✅ The correct answer is option C.
1387. Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator?
Long vertical evaporator
Horizontal tube evaporator
Agitated film evaporator
Calenderia vertical tube evaporator
✅ The correct answer is option C.
1388. As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the
Temperature of the body only
Wavelength of monochromatic radiation
Both A and B
Nature of material of body
✅ The correct answer is option A.
1389. Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is
Thin walled having the value of Ao Ai/< 2
Thick walled
Having the value of Ao/Ai > 2
Both B and C
✅ The correct answer is option A.
1390. In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is
Minimum
Maximum
Zero
Infinity
✅ The correct answer is option C.