Conduction with Heat Generation

This quiz contains multiple-choice problems on the dielectric effect and heat generation through various mechanisms, including plane wall, cylinder and sphere.

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The temperature drop in a plane wall with uniformly distributed heat generation can be decreased by reducing

Wall thickness Heat generation rate Thermal conductivity Surface area

Generally heat generated depends on some parameters. It is directly proportional to

Time Conductivity Voltage Distance between plates

Consider a 1.2 m thick slab of poured concrete (k = 1.148 W/m degree) with both of side surfaces maintained at a temperature of 20 degree Celsius. During its curing, chemical energy is released at the rate of 80 W/m3. Workout the maximum temperature of concrete

30.73 degree celsius 29.73 degree celsius 28.73 degree celsius 27.73 degree celsius

The insulating material used in dielectric heating is

Coal Silver Coin Wool

What maximum thickness of concrete can be poured without causing the temperature gradient to exceed 98.5 degree Celsius per meter anywhere in the slab? Consider a 1.2 m thick slab of poured concrete (k = 1.148 W/m degree) with both of side surfaces maintained at a temperature of 20 degree Celsius. During its curing, chemical energy is released at the rate of 80 W/m3. Workout the maximum temperature of concrete

2.64 m 3.64 m 4.64 m 5.64 m

In the case of heat conduction through a plane wall, which of the following is not a correct assumption?

Steady-state

Three-dimensional heat flow

Volumetric heat generation must be constant

K must be constant

If Q{X} is heat generated at a distance ‘x’, then heat conducted out at a distance (x + dx) will be

Q{X} + 3*(dQ{X}/dx)*d x

2Q{X} + (dQ{X}/dx)*d x

(dQ{X}/d x)*d x

Q{X} + (dQ{X}/dx)*d x

Some notable examples of uniform heat generation within the conducting medium are
(i) Energy of a nuclear reactor
(ii) Liberation of energy due to some exothermic chemical reactions
(iii) Resistance heating in electrical appliances
Which of these statements are correct?

i, ii and iii

i and ii

i and iii

Only ii

For a plane wall of thickness l with uniformly distributed heat generation q{g} per unit volume, the temperature t{0} at mid plane is given by

t{0} = q{g}l^(2)/2k + t{w}

t{0} = q{g}l^(2)/4k + t{w}

t{0} = q{g}l^(2)/8k + t{w}

t{0} = q{g}l^(2)/16k + t{w}

Consider a slab of thickness δ with one side (x = 0) insulated and another side (x = δ) maintained at constant temperature. The rate of uniform heat generation within the slab is q{g} W/m^3. Assuming the heat conduction is in steady-state, and one dimensional along the x direction, the maximum temperature in the slab would occur at x equal

δ/2

zero

δ/4

Suppose heat is conducted due to electrons where i = I/A and p is the resistivity, then

q{g} = 2i^(2)p

q{g} = 3i^(2)p

q{g} = i^(2)p

q{g} = 4i^(2)p

In case when both the surfaces of plane wall are at different temperature, we get an expression, i.e., T{MAX} – T{W{2}} /T{W{1}} – T{W{2}} = (B + 1)^(2)/4B
What is the value of B?

(q{g}*δ^(2)/2k) (T{W{1}} – T{W{2}})

(q{g}*δ^(3)/3k) (T{W{1}} – T{W{2}}

(q{g}*δ^(4)/4k) (T{W{1}} – T{W{2}}

(q{g}*δ^(5)/5k) (T{W{1}} – T{W{2}}

Which of the following materials can be quickly heated by applying high frequency?

Coal

Engines

Rubber

Textiles

There occurs heat conduction and internal heat generation at uniform rates within the conduction medium itself in the following cases:
(i) Drying of concrete
(ii) Chemical processes
(iii) Fuel elements in a nuclear reaction
Choose the correct option.

i only

ii only

i and iii

i, ii and iii

The unit for specific resistance is

Ω mm^2/m

Ω mm

Ω/m

Ω mm/m

Quiz/Test Summary

Title: Conduction with Heat Generation

Questions: 15