Q. What is the value of solar absorptivity for aluminum foil?

View solution

Q. What is the value of solar absorptivity for polished copper?

View solution

Q. Which one is having lowest value of solar absorptivity?

View solution

Q. What is the value of solar absorptivity for polished stainless steel?

View solution

Q. What is the value of solar absorptivity for white marble?

View solution

Q. What is the value of solar absorptivity for asphalt?

View solution

Q. What is the value of solar absorptivity for snow?

View solution

Q. Engineering problems of practical interest are involved with heat exchange between two or more surfaces, and this exchange is strongly dependent upon

(i) Radiative properties

(ii) Temperature levels

(iii) Surface geometrics

Identify the correct statements

View solution

Q. The fraction of the radiative energy that is diffused from one surface element and strikes the other surface directly with no intervening reflections is called

(i) Radiation shape factor

(ii) Geometrical factor

(iii) Configuration factor

Choose the correct answer

View solution

Q. The interchange factor is also known as

View solution

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

View solution

Q. A thin shield of emissivity E3 on both sides is placed between two infinite parallel plates of emissivities E1 and E2 and temperatures T1 and T2. If E1 = E2 = E3, then the fraction radiant energy transfer without shield takes the value

View solution

Q. The grey body shape factor for radiant heat exchange between a small body (emissivity = 0.4) in a large enclosure (emissivity = 0.5) is

View solution

Q. Two long parallel surfaces, each of emissivity 0.7 are at different temperatures and accordingly have radiation exchange between them. It is desired to reduce 75% of this radiant heat transfer by inserting thin parallel shields of equal emissivity 0.7 on both sides. What should be the number of shields?

View solution

Q. An enclosure consists of four surfaces 1, 2, 3 and 4. The view factors for radiation heat transfers are

F 11 = 0.1

F 12 = 0.4

F 13 = 0.25

The surface areas A 1 and A 2 are 4 m² and 2 m². The view factor F 41 is

View solution

Q. The value of shape factor depends on how many factors?

View solution

Q. A large plane, perfectly insulated on one face and maintained at a fixed temperature T 1 on the bare face, has an emissivity of 0.84 and loses 250 W/m² when exposed to surroundings at nearly 0 K. The radiant heat loss from another plane of the same size is 125 W/m² when bare face having emissivity 0.42 and is maintained at temperature T 2 is exposed to the same surroundings. Subsequently these two planes are brought together so that the parallel bare faces lie only 1 cm apart and the heat supply to each is so regulated that their respective temperatures T 1 and T 2 remains unchanged. Determine he net heat flux between the planes

View solution

Q. Interchange factor for body 1 completely enclosed by body 2 (body 1 is large) is given by

View solution

Q. A thermos flask has a double walled bottle and the space between the walls is evacuated so as to reduce the heat flow. The bottle surfaces are silver plated and the emissivity of each surface is 0.025. If the contents of the bottle are at 375 K, find the rate of heat loss from the thermos bottle to the ambient air at 300 K

View solution

Q. A 250 mm by 250 mm ingot casting, 1.5 m high and at 1225 K temperature, is stripped from its mold. The casting is made to stand on end on the floor of a large foundry whose wall, floor and roof can be assumed to be at 300 K temperature. Make calculation for the rate of radiant heat interchange between the casting and the room. The casting material has an emissivity of 0.85

View solution