Q. The solar radiation that is felt at the earth’s surface includes

(i) Direct radiation that has passed through the atmosphere

(ii) Diffuse radiation from the sky

(iii) Absorbed radiation from the water

Identify the correct statement

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Q. When the sun lies at a mean distance from the earth, the heat flux from the sun to the outer edge of the atmosphere has been found to be

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

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

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

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

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

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

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

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

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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

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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

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Q. The interchange factor is also known as

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

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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

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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

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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?

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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

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

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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

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