MCQs
Total Questions : 71
| Page 3 of 8 pages
Answer: Option C. -> 3.6 (α T)^1/2
Answer: (c).3.6 (α T)^1/2
Answer: (c).3.6 (α T)^1/2
Question 22. A mild steel plate 5 cm thick and initially at 40 degree Celsius temperature is suddenly exposed on one side to a fluid which causes the surface temperature to increase to and remain at 90 degree Celsius. Calculate maximum time that the slab be treated as a semi-infinitely body
For steel, thermal diffusivity = 1.25 * 10¯⁵ m²/s
For steel, thermal diffusivity = 1.25 * 10¯⁵ m²/s
Answer: Option B. -> 200 seconds
Answer: (b).200 seconds
Answer: (b).200 seconds
Question 23. Water pipes are to be buried underground in a wet soil (thermal diffusivity = 2.78 * 10¯³ m²/s) which is initially at 4.5 degree Celsius. The soil surface temperature suddenly drops to -5 degree Celsius and remains at this value for₁0 hours. Calculate the minimum depth at which the pipe be laid if the surrounding soil temperature is to remain above 0 degree Celsius. The soil may be considered as semi-infinite solid
Answer: Option D. -> 0.167 m
Answer: (d).0.167 m
Answer: (d).0.167 m
Answer: Option C. -> α S,T – α S,A = sin (2 π n T)
Answer: (c).α S,T – α S,A = sin (2 π n T)
Answer: (c).α S,T – α S,A = sin (2 π n T)
Question 25. The temperature variation of a thick brick wall during periodic heating or cooling follows a sinusoidal waveform. During a period of 24 hours, the surface temperature ranges from 25 degree Celsius to 75 degree Celsius. Workout the time lag of the temperature wave corresponding to a point located at 25 cm from the wall surface. Thermo-physical properties of the wall material are; thermal conductivity = 0.62 W/m K; specific heat = 450 J/kg K and density = 1620 kg/m³
Answer: Option B. -> 6.245 hour
Answer: (b).6.245 hour
Answer: (b).6.245 hour
Answer: Option A. -> Triangular
Answer: (a).Triangular
Answer: (a).Triangular
Answer: Option D. -> Attain 63.2% of the value of initial temperature difference
Answer: (d).Attain 63.2% of the value of initial temperature difference
Answer: (d).Attain 63.2% of the value of initial temperature difference
Answer: Option A. -> True
Answer: (a).True
Answer: (a).True
Question 29. A thermocouple junction of spherical form is to be used to measure the temperature of the gas stream. The junction is at 20 degree Celsius and is placed in a gas stream which is at 200 degree Celsius. Make calculations for junction diameter needed for the thermocouple to have thermal time constant of one second.
Assume the thermos-physical properties as given below
k = 20 W/ m K
h = 350 W/m² K
c = 0.4 k J/kg K
p = 8000 kg/m³
Assume the thermos-physical properties as given below
k = 20 W/ m K
h = 350 W/m² K
c = 0.4 k J/kg K
p = 8000 kg/m³
Answer: Option B. -> 0.656 mm
Answer: (b).0.656 mm
Answer: (b).0.656 mm
Answer: Option C. -> p V c/h A
Answer: (c).p V c/h A
Answer: (c).p V c/h A