A. Called the view factor
B. Called the angle of vision
C. Proportional to the square of the distance between surfaces
D. Expressed in terms of radians
Related Mcqs:
- 200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 × 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)?
A. 0.5
B. 0.05
C. 0.1
D. 0.15 - The ratio of total radiating power to the absorptivity of the body depends upon the _____________ as per Kirchoff‟s law?
A. Wavelength of radiation
B. Nature of the body
C. Temperature of the body
D. None of these - As per Kirchoff‟s law, the ratio of the total radiating power to the absorptivity of a body depends on the_______________?
A. Temperature of the body only
B. Wavelength of monochromatic radiation
C. Both A. and B.
D. Nature of material of body - The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m2. The flux, when the element temperature is increased to 1000°C for the same furnace temperature is_____________________?
A. 11.2 kW/m2
B. 12.0 kW/m2
C. 14.6 kW/m2
D. 16.5 kW/m2 - Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the_________________?
A. Existence of thermal boundary layer
B. Temperature gradient produced due to density difference
C. Buoyancy of the bubbles produced at active nucleation site
D. None of these - In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is______________________?
A. 2000
B. 4000
C. 5000
D. 6000 - Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface ?
A. Liquid density
B. Liquid viscosity
C. Hot surface temperature
D. Interfacial tension - The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C- 1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m-2.°C-1. The rate of heat loss from the outer surface in W.m-2is__________________?
A. 165.4
B. 167.5
C. 172.5
D. 175 - Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be_________________?
A. 0.35
B. 0.45
C. 0.55
D. 0.85 - The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by__________________?
A. Painting the surface black
B. Painting the surface white (with aluminium paint)
C. Giving the surface a mirror finish
D. Roughening the surface
