Q. Reflectivity is defined as

View solution

Q. Of the radiant energy 350W/m² incident upon a surface 250W/m² is absorbed, 60W/m² is reflected and the remainder is transmitted through the surface. Workout the value for reflectivity for the surface material

View solution

Q. 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

View solution

Q. The value of reflectivity depends upon
(i) Body temperature

(ii) Wavelength of reflected radiation

(iii) Nature of surface of body

Identify the correct statement

View solution

Q. When a surface absorbs a certain fixed percentage of striking radiation the surface is called

View solution

Q. Which one is true regarding gases?

View solution

Q. Thin glass plate is an example of

View solution

Q. Radiant energy with an intensity of 800 W/m² strikes a flat plate normally. The absorptivity is thrice the reflectivity and twice the transmissivity. Determine the rate of reflection

View solution

Q. Which one is true for opaque body?

View solution

Q. Energy strikes a vertical hemispherical plate with an intensity of 640 W/m². The absorptivity is thrice the transmissivity and twice the reflectivity. Determine the rate of transmission

View solution

Q. The absorptivity of a surface depends upon

(i) Direction of reflected radiation
(ii) Temperature of the surface
(iii) Composition

Identify the correct statements

View solution

Q. What is the absorptivity of gray body?

View solution

Q. A body that reflects all the incident thermal radiations is called a

View solution

Q. Energy strikes a vertical hemispherical plate with an intensity of 640 W/m². The absorptivity is thrice the transmissivity and twice the reflectivity. Determine the rate of absorption

View solution

Q. Let 220 W/m² of radiant energy is absorbed by a convex surface, 90 W/m² is reflected and 40 W/m² is transmitted through it. What is the value of absorptivity?

View solution

Q. For a grey surface

View solution

Q. Which quantity can be neglected for gases?

View solution

Q. Absorptivity of a body is equal to its emissivity

View solution

Q. Electromagnetic waves strikes a hot body maintained at 900 degree Celsius which has a reflectivity of 0.66 and a transmissivity of 0.022. Let the absorbed flux be 60 W/m². Determine the rate of incident flux

View solution

Q. Radiation heat transfer is characterized by

View solution