1
GATE ME 2002
Subjective
+5
-0
A copper tube of $$20$$ $$mm$$ outer diameter, $$1$$ $$mm$$ thickness and $$20$$ $$m$$ long (Thermal conducti-vity$$= 400$$ $$W/mK$$) is carrying saturated steam at $${150^ \circ }C$$ (Convective $$HTC\,\, = \,\,150\,\,W/{m^2}K$$). The tube is exposed to an ambient temperature of $${27^ \circ }C.$$ The convective $$HTC$$ of air is $$5\,W/{m^2}K.$$ Glass wool is used for insulation (Thermal conductivity $$= 0.075\,\,W/mK$$). If the thickness of the insulation used is $$5$$ $$mm$$ higher than the critical thickness of insulation, calculate the rate of heat lost by the steam and the rate of steam condensation in $$kg/hr$$ (The enthalpy of condensation of steam $$= 2230\,\,kJ/kg$$)
2
GATE ME 2001
Subjective
+5
-0
A composite wall, having unit length normal to the plane of paper, is insulated at the top and bottom as shown in the figure. It is comprised of four different materials $$A, B, C$$ and $$D.$$
Dimensions are \eqalign{ & {H_A} = {H_D} = 3cm, \cr & {H_B} = {H_C} = 1.5cm, \cr & {L_1} = {L_3} = 0.05m,\,\,\,\,\,\,\,\,\,\,{L_2} = 0.1m \cr} Thermal conductivity of the materials are \eqalign{ & {K_A} = {K_D} = 50\,\,\,W/mK, \cr & {K_B} = 10\,\,W/mK,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{K_C} = 1\,\,W/mK \cr}
The fluid temps and $$HTC$$(see fig) are \eqalign{ & {T_1} = {200^ \circ }C,\,\,\,\,{h_1} = 50\,\,W/{m^2}K, \cr & T{}_2 = {25^ \circ }C,\,\,\,\,{h_2} = 10\,\,W/{m^2}K, \cr}\$

Assuming one dimensional heat transfer condition. Determine the rate of heat transfer through the wall.

3
GATE ME 1998
Subjective
+5
-0
A gas filled tube has $$2$$ $$mm$$ inside diameter and $$25$$ $$cm$$ length. The gas is heated by an electrical wire of diameter $$50$$ microns ($$0.05$$ $$mm$$) located along the axis of the tube. Current and voltage drop across the heating element are $$0.5$$ amps and $$4$$ volts, respectively. If the measured wire and inside tube wall temperatures are $${175^ \circ }C$$ and $${150^ \circ }C$$ respectively, find the thermal conductivity of the gas filling the tube.
4
GATE ME 1993
Subjective
+5
-0
An electric hot plate is maintained at a temperature of $${350^ \circ }C,$$ and is used to keep a solution boiling at $${95^ \circ }C.$$ The solution is contained in cast iron vessel of wall thickness $$25mm,$$ which is enameled inside to a thickness of $$0.8mm$$. The heat transfer coefficient for the boiling solution is $$5.5$$ $$kW/{m^2}K$$ and the thermal conducti-vities of cast iron and enamel are $$50$$ and $$1.05W/mK,$$ respectively. Calculate the $$OHTC$$ and the rate of heat transfer per unit area.
GATE ME Subjects
Engineering Mechanics
Machine Design
Strength of Materials
Heat Transfer
Production Engineering
Industrial Engineering
Turbo Machinery
Theory of Machines
Engineering Mathematics
Fluid Mechanics
Thermodynamics
General Aptitude
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