1994-4-i-ht A small black body with a surface area \(A_1\) having no concavities is surrounded by a large black surface of area \(A_2\). Match the view factors.
I. \(F_{21}\)
II. \(F_{22}\)
1997-1-12-ht
In thermal radiation, for a black body
1997-2-10-ht The thermal radiative flux from a surface of emissivity 0.4 is 22.68 kW/m\(^2\). The approximate surface temperature (K) is (Stefan-Boltzmann’s constant = \(5.67\times 10^{-8}\) W/m\(^2\).K\(^4\))
2000-1-13-ht A sphere of radius, \(R_1\) is enclosed in a sphere of radius, \(R_2\). The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is
2001-1-9-ht
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
2004-18-ht
For an ideal black body
2011-17-ht Consider two black bodies with surfaces \(S_1\) (area = 1 m2) and \(S_2\) (area = 4 m2). They exchange heat only by radiation. 40% of the energy emitted by \(S_1\) is received by \(S_2\). The fraction of energy emitted by \(S_2\)
that is received by \(S_1\) is
2014-11-ht
In a completely opaque medium, if 50% of the incident monochromatic radiation is absorbed, then which of the following statements are CORRECT?
2015-13-ht Two infinitely large parallel plates (I and II) are held at temperatures \(T_{\text {I}}\) and \(T_{\text {II}}\) (\(T_{\text {I}} > T_{\text {II}}\)) respectively, and placed at a distance of \(2d\) apart in vacuum. An infinitely large flat radiation
shield (III) is placed in parallel in between I and II. The emissivities of all the plates are equal. The ratio of the steady state radiative heat fluxes with and without the shield is: 
2017-39-ht Let \(I_{b\lambda }\) be the spectral blackbody radiation intensity per unit wavelength about the wavelength \(\lambda \). The blackbody radiation intensity emitted by a blackbody over all wavelengths is
1994-2-m-ht A body at 925 K emits an energy of \(1.42\times 10^{11}\sigma \) W/m\(^2\) (\(\sigma \) is Stefan Boltzmann constant) in the wavelength band between 3 \(\mu \)m to 4\(\mu \)m. The fraction of this energy in the total energy emitted over the entire wavelength
range is equal to ––––-
2013-18-ht A hole of area 1 cm2 is opened on the surface of a large spherical cavity whose inside temperature is maintained at 727oC. Assuming black body radiation, the rate at which the energy is emitted (in W) by the cavity through the hole,
up to 3 digits after the decimal point, is ____________ The value of Stefan-Boltzmann constant is \(5.67\times 10^{-8}\) W/m2.K4
1994-3-e-ht The maximum in the emissive power of a surface at a temperature \(T_1\) occurs at a wavelength of \(\lambda _1\). If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of \(0.5\lambda _1\). (True/False).
1994-3-j-ht
A medium is always required for heat to be transferred. (True/False).
ME-2009-53-54-ht Radiative heat transfer is intended between the inner surfaces of two very large isothermal parallel metal plates. While the upper plate (designated as plate 1) is a black surface and is the warmer one being maintained at 727oC, the lower plate
(plate 2) is a diffuse and gray surface with an emissivity of 0.7 and is kept at 227oC. Assume that the surfaces are sufficiently large to form a two-surface enclosure and steady-state conditions to exist. Stefan-Boltzmann constant is given
as \(5.67\times 10^{-8}\) W/m2.K4. (i) The irradiation (in kW/m2) for the upper plate (plate 1) is {#1} (ii) If plate 1 is also a diffuse and gray surface with an emissivity value of 0.8, the net radiation heat exchange (in kW/m2) between plate 1 and plate 2 is {#2}
1998-2-12-ht The radiation heat flux from a heating element at a temperature of 800\(^\circ \)C, in a furnace maintained at 300\(^\circ \)C is 8 kW/m\(^2\). The flux when the element temperature is increased to 1000\(^\circ \)C for the same furnace temperature is
2006-45-ht An insulated cylindrical pipe of 0.2 m diameter has a surface temperature of 45oC. It is exposed to black body surroundings at 25oC. The emissivity and absorptivity of the insulation surface are 0.96 and 0.93, respectively. The convective
heat transfer coefficient outside the insulation surface is 3.25 W/ (m2.K). The Stefan-Boltzmann constant is \(5.67 \times 10^{-8}\) W/(m2.K4). The surrounding fluid may be assumed to be transparent. Find the percentage
contribution from radiation, to the total heat transfer rate to the surroundings.
2009-33-ht
A well-insulted hemispherical furnace (radius = 1 m) is shown below:
The self-view factor of radiation for the curved surface 2 is
2010-37-ht
The view factor matrix for two infinitely long co-axial cylinders, shown in the figure below, is
2012-33-ht For the enclosure formed between two concentric spheres as shown below (\(R_2=2R_1\)), the fraction of radiation leaving the surface area \(A_2\) that strikes itself is 
ME-2008-54-ht
A hollow enclosure is formed between two infinitely long concentric cylinders of radii 1m and 2 m respectively. Radiative heat exchange takes place between the inner surface of the larger cylinder (surface-2) and the outer surface of the smaller cylinder (surface-1). The radiating surfaces are diffuse and the medium in the enclosure is non-participating. The fraction of the thermal radiation leaving the larger surface and striking itself is
1990-4-iv-ht A black body of finite dimensions at 1000 K is inserted into an infinite medium at 300 K. Given Stefan Boltzmann constant as \(1.8 \times 10^{-8}\) W/m\(^2\).K\(^4\), the radiative heat transfer coefficient in (W/m\(^2\).K) is ––––-
1991-15-ii-ht A horizontal steam pipe 20 m long, 50 mm ID, 60 mm OD losses 13.5 kW heat to the surroundings at 310 K. The pipe carries steam at 500 K. Given that the convective heat transfer coefficient \(h_c = 1.65 (\Delta T)^{0.25}\) W/m\(^2\).K and the Stefan-Boltzmann
constant = \(5.67 \times 10^{-8}\) W/m\(^2\).K\(^4\). Find the emissivity of the bare surface of the pipe.
1992-15-a-ht Consider three infinite parallel plates. Plate 1 is maintained at 1227\(^\circ \)C and plate 3 is maintained at \(-174^\circ \)C. Emissivities are equal to that of a black body. Plate 2 is placed between plates 1 and 3, and receives no heat from external
sources. What is the temperature of plate 2 (in \(^\circ \)C)?
1993-21-a-i-ht A solid cube of side 30 cm at an initial temperature of 1000 K is kept in vacuum at absolute zero temperature. Calculate the time (in hour) required to cool it to 500 K. The material has the following properties:
Density = 2700 kg/m\(^3\); Specific
heat = 0.9 kJ/kg.K; Emissivity = 0.1. The Stefan-Boltzmann constant, \(\sigma =5.669\times 10^{-8}\) W/m\(^2\).K\(^4\).
2016-42-ht The space between two hollow concentric spheres of radii 0.1 m and 0.2 m is under vacuum. Exchange of radiation (uniform in all directions) occurs only between the outer surface (\(S_1\)) of the smaller sphere and the inner surface (\(S_2\)) of the larger
sphere. The fraction (rounded off to the second decimal place) of the radiation energy leaving \(S_2\), which reaches \(S_1\) is ____________
ME-2016-S3-42-ht Two large parallel plates having a gap of 10 mm in between them are maintained at temperatures \(T_1 = 1000\) K and \(T_2 = 400\) K. Given emissivity values, \(\varepsilon _1 = 0.5, \ \varepsilon _2 = 0.25\) and Stefan-Boltzmann constant \(\sigma
= 5.67\times 10^{-8}\) W/(m2.K4
Last Modified on: 03-May-2024
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