# A furnace is made of a red brick wall of thickness 0.5 m and conductivity 0.7 W/mk. For the same heat loss and temperature drop, this can be replaced by a layer of diatomite earth of conductivity 0.14 W/mk and thickness

1.  0.5 m

2.  0.1 m

3.  0.2 m

4.  0.5 m

4

0.1 m

Explanation :
No Explanation available for this question

# Up to the critical radius of insulation

1.  Added insulation will increase heat loss

2.  Added insulation will decrease heat loss

3.  Convention heat loss will be less than conduction heat loss

4.   Heat flux will decrease

4

Added insulation will increase heat loss

Explanation :
No Explanation available for this question

# Which of the following would lead to a reduction in thermal resistance

1.  In conduction, reduction in the thickness of the material and an increase in the thermal conductivity

2.  In convection, stirring of the fluid and clearing the heating surface

3.  In radiation, increasing the temperature and reducing the emissivity

4.  All of these

4

All of these

Explanation :
No Explanation available for this question

# The temperature distribution in a stainless fin (thermal conductivity 0.17 W/cm 0C) of constant cross-sectional area of 2 cm2 and length of 1 cm, exposed to an ambient of 400 C (with a surface heat transfer coefficient of 0.0025 W/cm2 0C) is given by (T - T∞) = 3x2 – 5x + 6. Where T is in 0C and x is in cm. If base temperature is 1000 C, then the heat dissipated by the fin surface will be

1.  6.8 W

2.  3.4 W

3.  1.7 W

4.  0.17 W

4

6.8 W

Explanation :
No Explanation available for this question

# Heat pipe is widely used now-a-days because it acts as

1.  An insulator

2.  Conductor & Insulator

3.  A superconductor

4.  A fin

4

Conductor & Insulator

Explanation :
No Explanation available for this question

# In current carrying conductors, if the radius of the conductor is less than the critical radius, then addition of electrical insulation is describe, as

1.  It reduces the heat loss from the conductor and thereby enables the conductor to carry a higher current

2.  It increases the heat loss from the conductor and thereby enables the conductor to carry a higher current

3.  It increases the thermal resistance of the insulation and thereby enables the conductor to carry a higher current

4.  It radius the thermal resistance of the insulation and thereby enables the conductor to carry a higher current

4

It increases the heat loss from the conductor and thereby enables the conductor to carry a higher current

Explanation :
No Explanation available for this question

# The heat transfer Q, the work done W and the change in internal energy U are all zero in the case of

1.  A rigid vessel containing steam at 1500 C left in the atmosphere which is at 250 C

2.  1 kg of gas contained in a insulated cylinder expanding as the piston move slowly outwards

3.  A rigid vessel containing ammonia gas connected through a valve to a evacuated rigid vessel, the vessel, the value and the connecting pipes being well insulated and the valve being opened and after a time, conditions though the two vessel becoming uniform

4.  1 kg or air flowing adiabatically from the atmosphere into a previously evacuated bottle

4

A rigid vessel containing ammonia gas connected through a valve to a evacuated rigid vessel, the vessel, the value and the connecting pipes being well insulated and the valve being opened and after a time, conditions though the two vessel becoming uniform

Explanation :
No Explanation available for this question

# Heat transfer takes place according to

1.  Zeroth Law of Thermodynamics

2.  First Law of Thermodynamics

3.  Second Law of Thermodynamics

4.   Third Law of Thermodynamics

4

Second Law of Thermodynamics

Explanation :
No Explanation available for this question

# It is desired to increase the heat dissipation rate over the surface of an electronic device of spherical shape of 5 mm radius exposed to convection with h = 10 w/m2 K by encasing it in a spherical sheath of conductivity 0.04 W/m K. For maximum heat flow, the diameter of the sheath should be

1.  18 mm

2.  16 mm

3.  12 mm

4.  8 mm

4

18 mm

Explanation :
No Explanation available for this question

# Consider the following statements pertaining to heat transfer through fins: 1. Fins are equally effective irrespective of whether they are on the hot side or cold side of the fluid 2. The temperature along the fin is variable and hence the rate of heat transfer varies along the elements of the fin 3. The fins may be made of materials that have a higher thermal conductivity than the material of the wall 4. Fins must be arranged at right angles to the direction of flow of the working fluid Of these statements

1.  1 and 2 are correct

2.  2 and 4 are correct

3.  1 and 3 are correct

4.  2 and 3 are correct

4