Questions and answers for exam Preparation

MCQs

Heat Radiation, Thermal Properties Of Matter, Dual Nature Of Matter

Total Questions : 247 | Page 22 of 25 pages

Question 211. The interchange factor is also known as

Equivalent emissivity
Irradiation
Radiosity
Shape factor

Discuss Question

Answer: Option A. -> Equivalent emissivity
Answer: (a).Equivalent emissivity

Question 212. For the same type of shapes, the value of radiation shape factor will be higher when

Surfaces are closer
Surfaces are larger and held closer
Surfaces are moved further apart
Surfaces are smaller and held closer

Discuss Question

Answer: Option B. -> Surfaces are larger and held closer
Answer: (b).Surfaces are larger and held closer

Question 213. Two parallel square plates, each 4 m² area, are large compared to a gap of 5 mm separating them. One plate has a temperature of 800 K and surface emissivity of 0.6, while the other has a temperature of 300 K and surface emissivity of 0.9. Find the net energy exchange by radiations between the plates

61.176 k W
51.176 k W
41.176 k W
31.176 k W

Discuss Question

Answer: Option B. -> 51.176 k W
Answer: (b).51.176 k W

Question 214. The furnace of a boiler is laid from fire clay brick with outside lagging from the plate steel, the distance between the two is quite small compared with the size of the furnace. The brick setting is at an average temperature of 365 K whilst the steel lagging is at 290 K. Calculate the radiant heat flux. Assume the following emissivity values
For brick = 0.85
For steel = 0.65

352.9 W/m²
452.9 W/m²
552.9 W/m²
652.9 W/m²

Discuss Question

Answer: Option A. -> 352.9 W/m²
Answer: (a).352.9 W/m²

Question 215. A cavity in the shape of a frustum of a cone has diameter 30 cm and 60 cm and the height is 80 cm. If the cavity is maintained at temperature of 800 K, determine the heat loss from the cavity when the smaller diameter is at the bottom

6577 W
2367 W
8794 W
3675 W

Discuss Question

Answer: Option A. -> 6577 W
Answer: (a).6577 W

Question 216. Two black discs each of diameter 50 cm are placed parallel to each other concentrically at a distance of one meter. The discs are maintained at 1000 K and 500 K. Calculate the heat flow between the discs when the disks are connected by a cylindrical black no-flux surface

2417.68 W
3417.68 W
4417.68 W
5417.68 W

Discuss Question

Answer: Option D. -> 5417.68 W
Answer: (d).5417.68 W

Question 217. Two black discs each of diameter 50 cm are placed parallel to each other concentrically at a distance of one meter. The discs are maintained at 1000 K and 500 K. Calculate the heat flow between the discs when no other surface is present

317.27 W
417.27 W
517.27 W
617.27 W

Discuss Question

Answer: Option B. -> 417.27 W
Answer: (b).417.27 W

Question 218. Reflectivity is defined as

Fraction of total energy transmitted by the body
Fraction of energy reflected by the body
Fraction of total energy absorbed by the body
Fraction of total energy absorbed and radiated by the body

Discuss Question

Answer: Option B. -> Fraction of energy reflected by the body
Answer: (b).Fraction of energy reflected by the body

Question 219. A thin metal plate of 4 cm diameter is suspended in atmospheric air whose temperature is 290 K. This plate attains a temperature of 295 K when one of its face receives radiant energy from a heat source at the rate of 2 W. If heat transfer coefficient on both surfaces of the plate is stated to be 87.5 W/m 2 K, workout the energy lost by reflection

0.8 W
0.3 W
0.9 W
0.10 W

Discuss Question

Answer: Option C. -> 0.9 W
Answer: (c).0.9 W

Question 220. The value of reflectivity depends upon
(i) Body temperature
(ii) Wavelength of reflected radiation
(iii) Nature of surface of body
Identify the correct statement