Question 61. According to lumped system analysis, solid possesses thermal conductivity that is

Question 62. What is the value of characteristics length for cylinder?

Question 63. During heat treatment, cylindrical pieces of 25 mm diameter, 30 mm height and at 30 degree Celsius are placed in a furnace at 750 degree Celsius with convective coefficient 80 W/m² degree. Find the value of biot number if thermal conductivity is 40 W/m degree

Question 64. “An infinite solid is one which extends itself infinitely in all directions of space”. Identify the correct option

Question 65. What is the value of characteristics length for cube?

Question 66. What is the value of characteristics length for sphere?

Question 67. A single cylinder 2-stroke engine operates at 1500 rpm. Calculate the depth where the temperature wave due to variation in cylinder is damped to 1% of its surface value. For the cylinder material, thermal diffusivity = 0.042 m²/hr

Question 68. At a certain time instant, the temperature distribution in a long cylindrical fire tube can be represented approximately by the relation
T = 650 + 800 r – 4250 r²
Where temperature t is in degree Celsius and radius r is in meter. Find the rate of heat flow such that the tube measures: inside radius 25 cm, outside radius 40 cm and length 1.5 m.
For the tube material
K = 5.5 W/m K
α = 0.004 m²/hr

Question 69. The temperature distribution at a certain time instant through a 50 cm thick wall is prescribed by the relation
T = 300 – 500 x – 100 x² + 140x³
Where temperature t is in degree Celsius and the distance x in meters has been measured from the hot surface. If thermal conductivity of the wall material is 20 k J/m hr degree, calculate the heat energy stored per unit area of the wall

Question 70. A large plane wall, 40 cm thick and 8 m² area, is heated from one side and temperature distribution at a certain time instant is approximately prescribed by the relation:
T = 80 – 60 x +12 x² + 25 x³ – 20 x⁴
Where temperature t is in degree Celsius and the distance x in meters. Make calculations for heat energy stored in the wall in unit time.
For wall material:
Thermal conductivity = 6 W/m K and thermal diffusivity = 0.02 m²/hr