Mechanical Engineering - Heat and Mass Transfer - Heat Transfer

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Question - 1

Heat transfer takes place according to

  • A zeroth law of thermodynamics
  • B first law of thermodynamics
  • C second law of thermodynamics
  • D third law of thermodynamics

Question - 2

Using thermal electrical analogy in heat transfer, match List I (Electrical quantities) with List" (Thermal quantities) and select the correct answer using the codes given below the lists.

List I List II
P. Voltage 1. Thermal resistance
Q. Current 2. Thermal capacity
R. Resistance 3. Heat flow
S. Capacitance 4. Temperature
  • A P Q R S 2 3 1 4
  • B P Q R S 4 1 3 2
  • C P Q R S 2 1 3 4
  • D P Q R S 4 3 1 2

Question - 3

The equivalent thermal conductivity of the wall as shown in the figure below is

  • A \(\frac { { K }_{ 1 }+{ K }_{ 2 } }{ 2 } \)
  • B \(\frac { { K }_{ 1 }{ K }_{ 2 } }{ { K }_{ 1 }+{ K }_{ 2 } } \)
  • C \(\frac { 2{ K }_{ 1 }{ K }_{ 2 } }{ { K }_{ 1 }+{ K }_{ 2 } } \)
  • D \(\sqrt { { K }_{ 1 }{ K }_{ 2 } } \)

Question - 4

Heat flows through a composite slab, as shown in the figure given below. The depth of the slab is 1 m. The values of K are in W/m-K. The overall thermal resistance in K/W is

  • A 17.2
  • B 21.9
  • C 28.6
  • D 39.2

Question - 5

In the given figure, consider one-dimensional heat conduction in Y- direction. Temperature of point Pis 80 0C and Q = 1 W/m2. If K = 1 W/m-K, then at steady state, the temperature of point Q is

  • A zero
  • B 77 0C
  • C 80 0C
  • D Data insufficient

Question - 6

A flat plate has thickness 5 cm, thermal conductivity 1 W/m-K, convective heat transfer coefficients on its two flat faces of 10 W/m2-K and 20 W/m2-K. The overall heat transfer coefficient for such a flat plate is

  • A 5 W/m2-K
  • B 6.33 W/m2-K
  • C 20 W/m2-K
  • D 30 W/m2-K

Question - 7

A steady two-dimensional heat conduction takes place in the body shown in the figure below. The normal temperature gradients over surfaces P and Q can be considered to be uniform. The temperature gradient \(\frac { \partial T }{ \partial x } \) at surface Q is equal to 10 K/m. Surfaces P and Q are maintained at constant temperatures as shown in the figure, while the remaining part of the boundary is insulated. The body has a constant thermal conductivity of 0.1 W/m-K. The values of \(\frac { \partial T }{ \partial y } \) and \(\frac { \partial T }{ \partial x } \) at surface P are

  • A \(\frac { \partial T }{ \partial x } =20K/m,\frac { \partial T }{ \partial y } =0\)
  • B \(\frac { \partial T }{ \partial x } =0,\frac { \partial T }{ \partial y } =10K/m\)
  • C \(\frac { \partial T }{ \partial x } =10K/m,\frac { \partial T }{ \partial y } =10K/m\)
  • D \(\frac { \partial T }{ \partial x } =0,\frac { \partial T }{ \partial y } =20K/m\)

Question - 8

There is a steady one-dimensional heat conduction through a slab. If T1 = 70 °C and T2 =30 °C, then temperature of point P is

  • A 40 0C
  • B 43.3 0C
  • C 45 0C
  • D 47 0C

Question - 9

Upto the critical radius of insulation

  • A convection heat loss will be less than conduction heat loss
  • B heat flux will decrease
  • C added insulation will increase heat loss
  • D added insulation will decrease heat loss

Question - 10

Water jacketed copper rod of D m diameter is used to carry the current. The water, which flows continuously maintains the rod temperature at T10C during normal operation at I A. The electrical resistance of the rod is known to be R Ω/m. If the coolant water ceased to be available and the heat removal diminished greatly, the rod would eventually melt. What is the time required for melting if the melting point of the rod material is Tmp? (CP is specific heat, p is density of the rod material an L is the length of the rod.)

  • A \(\rho \left( \frac { \pi { D }^{ 2 } }{ 4 } \right) { C }_{ P }\frac { \left( { T }_{ mp }-{ T }_{ l } \right) }{ { l }^{ 2 }R } \)
  • B \(\frac { \left( { T }_{ mp }-{ T }_{ l } \right) }{ \rho l^{ 2 }R } \)
  • C \(\frac { \rho \left( { T }_{ mp }-{ T }_{ l } \right) }{ { l }^{ 2 } } \)
  • D \(\frac { { C }_{ p }\left( { T }_{ mp }-{ T }_{ l } \right) }{ { l }^{ 2 }R } \)