Consider the following phenomena (i) Boiling (ii) Free convection in air (iii) Forced convection in air (iv) Conduction in air Identify the correct sequence (heat transfer coefficient)

Consider with respect to HusserI's concept of phenomena.
1. Phenomena is a substantial unity that has real properties, real parts and real changes.
2. Phenomena is no substantial unity, that has no real parts and no real changes.
3. Phenomena has no nature, but only essence.
4. Phenomena have no essence, but only nature.

A

Only (1) is true

B

Only (2) and (3) are true

C

Only (1) and (3) are true

D

Only (1), (3) and (4) are true

A stream of air at 100 kPa pressure and 300 K is flowing on the top surface of a thin flat sheet of solid naphthalene of length 0.2 m with a velocity of 20 m/sec. The other data are: Mass diffusivity of naphthalene vapor in air = 6 * 10 –6 m2/sec Kinematic viscosity of air = 1.5 * 10 –5 m2.sc Concentration of naphthalene at the air-solid naphthalene interface = 1 * 10 – 5 kmol/m3 Calculate the overage mass transfer coefficient over the flat plate. Note: For heat transfer over a flat plate, convective heat transfer coefficient for laminar flow can be calculated by the equation. Nu = 0.664 ReL1/2 Pr1/3 you may use analogy between mass and heat transfer.

A

0.014 m/sec

B

0.015 m/sec

C

0.016 m/sec

D

0.013 m/sec

Forced air flows over a convection heat exchanger in a room heater, resulting in a convective heat transfer coefficient 1.136 k W/m2 K. The surface temperature of heat exchanger may be considered constant at 65 degree Celsius, and the air is at 20 degree Celsius. Determine the heat exchanger surface area required for 8.8 k W of heating

A

0.272 m2

B

0.472 m2

C

0.172 m2

D

0.672 m2

The determination of a value of Nusselt number or the convective film coefficient forms a basis for the computation of heat transfer by convection. Towards that end, following approaches have been suggested (i) Non-dimensional analysis and experimental correlations (ii) Hydrodynamic concept of velocity boundary layer (iii) Reynolds similarity between the mechanism of fluid friction in the boundary layer and the transfer of heat by convection Identify the correct one

A

i, ii and iii

B

i and ii

C

ii and iii

D

i and iii

Experimental results indicate that the local heat transfer coefficient h g for flow over a flat plate with an extremely rough surface is approximated by the relation h x = a x -0.12 Where a is a constant coefficient and x is distance from the leading edge of the plate. What is the relation between this local heat transfer coefficient and the average heat transfer coefficient for a plate of length x?

A

1.136 h x

B

2.136 h x

C

3.136 h x

D

4.136 h x

Consider the following statements for Nucleate boiling: 1. For water, the critical heat flux does not exceed 1 MW/m2. 2. Nucleate boiling is the most desirable boiling regime in practice because of high heat transfer rates. 3. Heat flux increases at a higher rate with increase in temperature. Which of the above statements is/are correct?

A

1 only

B

2 only

C

1 and 3 only

D

2 and 3 only

A polished metal pipe 5 cm outside diameter and 370 K temperature at the outer surface is exposed to ambient conditions at 295 K temperature. The emissivity of the surface is 0.2 and the convection coefficient of heat transfer is 11.35 W/m2 degree. Calculate the overall coefficient of heat transfer by the combined mode of convection and radiation

A

11.04 W/m2 degree

B

12.04 W/m2 degree

C

13.04 W/m2 degree

D

14.04 W/m2 degree

Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place

A

Between two bodies in physical contact with each other

B

Between two bodies not in physical contact with each other

C

From one part of a body to the another part of the same body

D

Both B & C