Heat Transfer

Question: For a laminar flow of fluid in a circular tube, ‘h1’ is the convective heat transfer co-efficient at velocity ‘V1’. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is
[A].

1.26 h1

[B].

0.794 h1

[C].

0.574 h1

[D].

1.741 h1

Answer: Option B

Explanation:

No answer description available for this question.

Question: For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of
[A].

1

[B].

1.74

[C].

6.1

[D].

37

Answer: Option C

Explanation:

No answer description available for this question.

Question: A composite flat wall of a furnace is made of two materials ‘A’ and ‘B’. The thermal conductivity of ‘A’ is twice of that of material ‘B’, while the thickness of layer of ‘A’ is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material ‘A’ is
[A].

125

[B].

133

[C].

150

[D].

160

Answer: Option D

Explanation:

No answer description available for this question.

Question: Heat transfer by natural convection is enhanced in system with
[A].

high viscosity.

[B].

high co-efficient of thermal expansion.

[C].

low temperature gradients.

[D].

low density change with temperature.

Answer: Option B

Explanation:

No answer description available for this question.

Question: In a heat exchanger, floating head is provided to
[A].

facilitate cleaning of the exchanger.

[B].

increase the heat transfer area.

[C].

relieve stresses caused by thermal expansion.

[D].

increase log mean temperature gradient.

Answer: Option C

Explanation:

No answer description available for this question.

Question: Heat transfer occurs by natural convection because change in temperature causes difference in
[A].

viscosity

[B].

density

[C].

thermal conductivity

[D].

heat capacity

Answer: Option B

Explanation:

No answer description available for this question.

Question: In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of
[A].

concentrations

[B].

chemical potentials

[C].

activity co-efficients

[D].

mass transfer co-efficients

Answer: Option A

Explanation:

No answer description available for this question.

Question: A multiple effect evaporator as compared to a single effect evaporator of the same capacity has
[A].

lower heat transfer area.

[B].

lower steam economy.

[C].

higher steam economy.

[D].

higher solute concentration in the product.

Answer: Option C

Explanation:

No answer description available for this question.

Question: The advantage of backward feed multiple effect evaporators over forward feed units is that
[A].

heat sensitive material can be handled.

[B].

there is no additional cost of pumping.

[C].

most concentrated liquid is at highest temperature.

[D].

equal heat transfer co-efficients exist in various effects.

Answer: Option C

Explanation:

No answer description available for this question.

Question: Indirect contact heat exchangers are preferred over direct contact heat exchangers, because
[A].

heat transfer co-efficient are high.

[B].

there is no risk of contamination.

[C].

there is no mist formation.

[D].

cost of equipment is lower.

Answer: Option B

Explanation:

No answer description available for this question.