Conduction Through a Composite Wall MCQ

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• A composite wall of a furnace has two layers of equal thickness having thermal conductivities in the ratio 2:3. What is the ratio of the temperature drop across the two layers?
  ক

  2:3

  খ

  3:2

  গ

  1:2

  ঘ

  log e 2 : log e 3
• A composite slab has two layers having thermal conductivities in the ratio of 1:2. If the thickness is the same for each layer then the equivalent thermal conductivity of the slab would be
  ক

  1/3

  খ

  2/3

  গ

  2

  ঘ

  4/3
• “Radiation cannot be affected through vacuum or space devoid of any matter”. True or false
  ক

  True

  খ

  False
• A pipe carrying steam at 215.75 degree Celsius enters a room and some heat is gained by surrounding at 27.95 degree Celsius. The major effect of heat loss to surroundings will be due to
  ক

  Conduction

  খ

  Convection

  গ

  Radiation

  ঘ

  Both conduction and convection
• Find the heat flow rate through the composite wall as shown in figure. Assume one dimensional flow and take k 1 = 150 W/m degree k 2 = 30 W/m degree k 3 = 65 W/m degree k 4 = 50 W/m degree AB = 3 cm, BC = 8 cm and CD = 5 cm. The distance between middle horizontal line from the top is 3 cm and from the bottom is 7 cm
  ক

  1173.88 W

  খ

  1273.88 W

  গ

  1373.88 W

  ঘ

  1473.88 W
• Heat is transferred from a hot fluid to a cold one through a plane wall of thickness (δ), surface area (A) and thermal conductivity (k). The thermal resistance is
  ক

  1/A (1/h1 + δ/k + 1/h2)

  খ

  A (1/h1 + δ/k + 1/h2)

  গ

  1/A (h1 + δ/k + h2)

  ঘ

  A (h1 + δ/k + 1/h2)
• Let us say thermal conductivity of a wall is governed by the relation k = k0 (1 + α t). In that case the temperature at the mid-plane of the heat conducting wall would be
  ক

  Av. of the temperature at the wall faces

  খ

  More than average of the temperature at the wall faces

  গ

  Less than average of the temperature at the wall faces

  ঘ

  Depends upon the temperature difference between the wall faces
• A composite wall is made of two layers of thickness δ1 and δ2 having thermal conductivities k and 2k and equal surface area normal to the direction of heat flow. The outer surface of composite wall are at 100 degree Celsius and 200 degree Celsius. The minimum surface temperature at the junction is 150 degree Celsius. What will be the ratio of wall thickness?
  ক

  1:1

  খ

  2:1

  গ

  1:2

  ঘ

  2:3
• Three metal walls of the same thickness and cross sectional area have thermal conductivities k, 2k and 3k respectively. The temperature drop across the walls (for same heat transfer) will be in the ratio
  ক

  3:2:1

  খ

  1:1:1

  গ

  1:2:3

  ঘ

  Given data is insufficient
• A composite wall generally consists of
  ক

  One homogenous layer

  খ

  Multiple heterogeneous layers

  গ

  One heterogeneous layer

  ঘ

  Multiple homogenous layers