1
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 $$$\eqalign{ & {H_A} = {H_D} = 3cm, \cr & {H_B} = {H_C} = 1.5cm, \cr & {L_1} = {L_3} = 0.05m,\,\,\,\,\,\,\,\,\,\,{L_2} = 0.1m \cr} $$$ GATE ME 2001 Heat Transfer - Conduction Question 3 English

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.

2
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.
3
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.
4
GATE ME 1988
Numerical
+5
-0
Steam is flowing through an insulated steel pipe shown in the fig, is losing heat to the surroundings. The details are as follows

Inner radius of steel pipe $$=50mm,$$
Outer radius of the steel pipe $$=57mm,$$
Outer radius of insulation $$=157 mm,$$
Thermal conductivity of steel $$=43$$ $$W/mK$$
Thermal conductivity of insulating material $$=0.1$$ $$W/mK$$
Heat transfer coefficient on steam side $$ = 570W/{m^2}K$$
Heat transfer coefficient on air side $$ = 12W/{m^2}K,$$
Temperature of steam $$ = {500^ \circ }C$$
Temperature of surroundings $$ = {30^ \circ }C$$

GATE ME 1988 Heat Transfer - Conduction Question 1 English

Calculate the heat loss per meter length of pipe and temp of the outer surface of the insulation.

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