Question 51. “A solid which extend itself infinitely in all directions of space is termed as finite solid”. Choose the correct answer

Question 52. 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. Calculate the time required to heat the pieces to 600 degree Celsius. Assume the following property values
Density = 7850 kg /m³
Specific heat = 480 J/kg K
Conductivity = 40 W/m degree

Question 53. The quantity h L C/k is known as

Question 54. Identify the correct relation between Biot number and Fourier number

Question 55. Fourier number is given by

Question 56. For a plat plate (thickness δ, breadth b and height h) the heat exchange occurs from both the sides. The characteristics length is equal to

Question 57. A person is found dead at 5 pm in a room whose temperature is 20 degree Celsius. The temperature of body is measured to be 25 degree Celsius, when found and heat transfer coefficient is estimated to be 8 W/m² K. Modeling the body as a 30 cm diameter, 1.7 cm long cylinder. Estimate the time of death of person.

Question 58. A thermocouple junction in the form of 4 mm radius sphere is to be used to measure the temperature of a gas stream. The junction is initially at 35 degree Celsius and is placed in a gas stream which is at 300 degree Celsius. The thermocouple is removed from the hot gas stream after 10 seconds and kept in still air at 25 degree Celsius with convective coefficient 10 W/m² K. Find out the time constant of the thermocouple. Assume the thermos-physical properties as given below:
h = 37.5 W/m² K
p = 7500 kg/m³
c = 400 J/kg K

Question 59. The following data pertains to the junction of a thermocouple wire used to measure the temperature of the gas stream.
Density = 8500 kg/m³, specific heat = 325 J/kg K, thermal conductivity = 40 W/m K and the heat transfer coefficient between the junction and gas = 215 W/m² K.
If thermocouple junction can be approximated as 1 mm diameter sphere, determine how long it will take for the thermocouple to read 99% of the initial temperature difference.

Question 60. What percentage of water an average human body can have?