Questions and answers for exam Preparation

MCQs

Total Questions : 448 | Page 35 of 45 pages

Question 341. Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be

Three
Four
Two
One

Discuss Question

Answer: Option A. -> Three

Question 342. Depending on the radiating properties, a body will be white when(Where a = absorptivity, p = reflectivity, x = transmissivity)

P = 0, x = 1 and a = 0
X = 0, a + p = 1
P = 0, x = 0 and a = 1
P=1, T = 0 and a = 0

Discuss Question

Answer: Option D. -> P=1, T = 0 and a = 0

Question 343. Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

k.
(dT/dx)
(dx/dT)
k.
k. (dT/dx)
k. (dx/dT)

Discuss Question

Answer: Option D. -> k.

Question 344. Air is best heated with steam in a heat exchanger of

plate type.
double pipe type with fin on steam side.
double pipe type with fin on air side.
shell and tube type.

Discuss Question

Answer: Option C. -> double pipe type with fin on air side.

Question 345. According to Prevost theory of heat exchange

It is impossible to transfer heat from low temperature source to t high temperature source
Heat transfer by radiation requires no medium
All bodies above absolute zero emit radiation
Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

Discuss Question

Answer: Option C. -> All bodies above absolute zero emit radiation

Question 346. Which of the following property of air does not increase with rise in temperature?

Thermal conductivity
Thermal diffusivity
Density
Dynamic viscosity

Discuss Question

Answer: Option C. -> Density

Question 347. Which of the following would lead to a reduction in thermal resistance?

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
In convection, stirring of the fluid and cleaning the heating surface.
In radiation, increasing the temperature and reducing the emissivity.
All of the above

Discuss Question

Answer: Option D. -> All of the above

Question 348. Total heat is the heat required to