1
GATE ME 2005
MCQ (Single Correct Answer)
+2
-0.6
A small copper ball of $$5$$ $$mm$$ diameter at $$500$$ $$K$$ is dropped into an oil bath whose temperature is $$300$$ $$K.$$ the thermal conductivity of copper is $$400$$ $$W/m.$$ $$K,$$ its density $$9000\,\,kg/{m^3}$$ and its specific heat $$385\,J/kg.\,\,K.$$ if the heat transfer coefficient is $$250\,\,W/{m^2}K$$ and lumped analysis is assumed to be valid, the rate of fall of the temperature of the ball at the beginning of cooling will be, in $$K/s.$$
A
$$8.7$$
B
$$13.9$$
C
$$17.3$$
D
$$27.7$$
2
GATE ME 2004
MCQ (Single Correct Answer)
+2
-0.6
A spherical thermocouple junction of diameter $$0.706 mm$$ is to be used for the measurement of temperature of a gas stream. The convective heat transfer co-efficient on the bead surface is $$400W/{m^2}K.$$ Thermo-physical properties of thermocouple material are
$$k = 20W/mK,$$ $$C = 400J/kgK$$ and $$\rho = 8500\,\,kg/{m^3}.$$ If the thermocouple initially at $${30^ \circ }C$$ is placed in a hot stream of $${300^ \circ }C$$ the time taken by the bead to reach $${298^ \circ }C$$, is
A
$$2.35s$$
B
$$4.9s$$
C
$$14.7s$$
D
$$29.4s$$
3
GATE ME 1992
MCQ (Single Correct Answer)
+2
-0.6
Two rods, one of length $$L$$ and the other of length $$2L$$ are made of the same material and have the same diameter. The two ends of the longer rod are maintained at $${100^ \circ }C.$$ One end of the shorter end is maintained at $${100^ \circ }C.$$ while the other end is insulated. Both the rods are exposed to the same environment at $${40^ \circ }C.$$ The temperature at the insulated end of the shorter rod is measured to be $${55^ \circ }C.$$ The temperature at the mid-point of the longer rod would be
A
$${40^ \circ }C.$$
B
$${50^ \circ }C$$
C
$${55^ \circ }C$$
D
$${100^ \circ }C$$
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