Consider the following statements:
1. Temperature of the surface.
2. Emissivity of the surface.
3. Temperature of the air in the room.
4. Length and diameter of the pipe.
The parameter(s) responsible for loss of heat from at hot surface in a room would include
Thermal radiation exhibit characteristics similar to those of….
Consider two infinitely long blackbody concentric cylinders with a diameter ratio D2/D1 = 3. The shape factor for the outer cylinder with itself will be
On a summer day, a scooter rider feels more comfortable while on the move than while at a stop light because
Assertion (A): In a furnace, re-radiation from the walls has the same wavelength as the incident radiation from the heat source.
Reason (R): Surfaces at the same temperature radiate at the same wavelength.
If a body is at 2000K, the wavelength at which the body emits maximum amount of radiation is
Solar radiation of 1200 W/m2 falls perpendicularly on a gray opaque surface of emissivity 0.5. If the surface temperature is 50oC and surface emissive power is 600 W/m2, the radiosity of that surface will be
The shape factor of a hemispherical body placed on a flat surface with respect to itself is
Two large parallel grey plates with a small gap, exchange radiation at the rate of 1000 W/m2 when their emissivities are 0.5 each. By coating one plate, its emissivity is reduced to 0.25. Temperatures remain unchanged. The new rate of heat exchange shall become
Match List-I (Type of radiation) with List-II (Characteristic) and select the correct answer using the codes given below the lists:
|
|
List-I |
|
List-II |
|
A. |
Black body |
1. |
Emissivity does not depend on wavelength |
|
B. |
Grey body |
2. |
Mirror like reflection |
|
C. |
Specular |
3. |
Zero reflectivity |
|
D. |
Diffuse |
4. |
Intensity same in all directions |
Through a finned heat engine placed in atmospheric air, the major heat transfer is due to
On a summer day, when fan is blowing a person feels more comfortable. What does fan motion do?
Name the quantity which signifies the ratio of temperature gradient at a surface to a reference temperature gradient?
Nusselt number is given by
The convective surface coefficient ‘h’ is directly proportional to?
Which of the following explains newton’s law of cooling?
The region of fluid motion near plate in which temperature gradient exist is
Ratio of actual velocity to sonic velocity is
Free convection of heat flow does not depends on
Ratio of inertia force to viscous force is known as
Ratio of heat capacity of fluid flowing through pipe to the conductivity of pipe material is
If the radius of any current carrying conductor is less than the critical radius, then the addition of electrical insulation will enable the wire to carry a higher current because
The thermal conductivity of thermal insulation applied to a hollow spherical vessel containing very hot material is 0.5 W/mK. The convective heat transfer coefficient at the outer surface of insulation is 10 W/m2K. What is the critical radius of the sphere?
A hollow pipe of 1 cm outer diameter is to be insulated by thick cylindrical insulation having thermal conductivity 1 W/mK. The surface heat transfer coefficient on the insulation surface is 5 W/m2K. What is the minimum effective thickness of insulation for causing the reduction in heat leakage from the insulated pipe?
A metal rod of 2 cm diameter has a conductivity of 40 W/mK, which is to be insulated with an insulating material of conductivity of 0.1 W/mK. If the convective heat transfer coefficient with the ambient atmosphere is 5W/m2K, the critical thickness of insulation will be
