1
GATE ME 2016 Set 1
MCQ (Single Correct Answer)
+1
-0.3
A plastic sleeve of outer radius $${r_0} = 1\,\,mm$$ covers a wire (radius $$r = 0.5$$ $$mm$$) carrying electric current. Thermal conductivity of the plastic is $$0.15\,\,W/m$$-$$K$$. The heat transfer coefficient on the outer surface of the sleeve exposed to air is $$25$$ $$W/{m^2}$$-$$K$$. Due to the addition of the plastic cover, the heat transfer from the wire to the ambient will
A
increases
B
remain the same
C
decreases
D
be zero
2
GATE ME 2015 Set 2
Numerical
+1
-0
If a foam insulation is added to a $$4cm$$ outer diameter pipe as shown as figure, the critical radius of insulation (in $$cm$$) is ________. GATE ME 2015 Set 2 Heat Transfer - Conduction Question 37 English
Your input ____
3
GATE ME 2014 Set 4
MCQ (Single Correct Answer)
+1
-0.3
As the temperature increases, the thermal conductivity of a gas
A
increases
B
decreases
C
remains constant
D
increases up-to a certain temperature and then decreases
4
GATE ME 2014 Set 3
MCQ (Single Correct Answer)
+1
-0.3
Consider a long cylindrical tube of inner and outer radii, $${r_i}$$ and $${r_0}$$ , respectively, length, $$L$$ and thermal conductivity, $$k.$$ Its inner and outer surfaces are maintained at $${T_i}$$ and $${T_0}$$ , respectively $$\left( {{T_i}\,\,\, > \,\,\,{T_0}} \right).$$ Assuming one-dimensional steady state heat conduction in the radial direction, the thermal resistance in the wall of the tube is
A
$${1 \over {2\pi kL}}\ell n\left( {{{{r_i}} \over {{r_0}}}} \right)$$
B
$${L \over {2\pi {r_i}k}}$$
C
$${L \over {2\pi kL}}\ell n\left( {{{{r_0}} \over {{r_i}}}} \right)$$
D
$${L \over {4\pi kL}}\ell n\left( {{{{r_0}} \over {{r_i}}}} \right)$$
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