The film temperature at which the fluid properties (as Reynolds, Prandtl and Nusselt’s number are functions in fluid properties) are to be evaluated is given by Where Tb = mean bulk temperature and Tw = wall surface temperature

1.  2 (Tb + Tw)

2.  (Tb + Tw)/2

3.  2 (Tb - Tw)

4.  (Tb - Tw)/2

4

(Tb + Tw)/2

Explanation :
No Explanation available for this question

In free convection motion of fluid is caused

1.  By the weight of the fluid element

2.  By the hydrostatic force on the element

3.  By the buoyancy forces arising from variation in density of the fluid with the temperature

4.  None of these

4

By the buoyancy forces arising from variation in density of the fluid with the temperature

Explanation :
No Explanation available for this question

Nn = C rme Pnr represents heat transfer under

1.  Free convection

2.  Forced convection

3.  Combined convection

4.  None of these

4

Forced convection

Explanation :
No Explanation available for this question

According to Newton’s law of cooling the amount of heat transfer from a solid surface of area A at a temperature Ts to a fluid at temperature Tf is Where h = film heat transfer coefficient

1.  Q = hA/(Ts – Tf)

2.  Q = h/A(Ts – Tf)

3.  Q = hA(Ts – Tf)

4.  Q = (Ts – Tf)/hA

4

Q = hA(Ts – Tf)

Explanation :
No Explanation available for this question

The thickness of thermal and hydrodynamic boundary layer is equal if (Pr = Prandtl Number, Nu = Nusselt number)

1.  Pr = 1

2.  Pr > 1

3.  Pr < 1

4.  Pr = Nu

4

Pr = Nu

Explanation :
No Explanation available for this question

It is desired to increase the heat dissipation rate over the surface of an electronic device of spherical shape of 5 mm radius exposed to convection with h = 10 W/m2K by encasing it in a spherical sheath of conductivity 0.04 W/mK. For maximum heat flow the diameter of the sheath should be

1.  18 mm

2.  16 mm

3.  12 mm

4.  8 mm

4

18 mm

Explanation :
No Explanation available for this question

A copper wire of radius 0.5 mm is insulated with a sheathing of thickness 1 mm having a thermal conductivity of 0.5 W/m-K. The outside surface convective heat transfer coefficient is 10 W/m2-K. If the thickness of insulation sheathing is raised by 10 mm, then he electrical current carrying capacity of the wire wall

1.  Increase

2.  Decrease

3.  Remain the same

4.  Vary depending upon the electrical conductivity of the wire

4

Increase

Explanation :
No Explanation available for this question

The overall heat transfer coefficient will be

1.  692.5 W/m2k

2.  714.5 W/m2k

3.  742 W/m2k

4.  764.5 W/m2k

4

692.5 W/m2k

Explanation :
No Explanation available for this question

PVC sheets are produced by

1.  Melt spinning process

2.  Injection molding process

3.  Calendaring process

4.  Rotomolding process

4

Calendaring process

Explanation :
No Explanation available for this question

Green strength in powder metallurgy refers to the strength of

1.  The original material

2.  the powder before compaction

3.  The powder after compaction

4.   the product after sintering and compaction

4