Interview Short Question



Q. What is condensation heat transfer?

Ans. The conversion of vapor into liquid at saturation on cooling is called condensation. In this Tsur is less than Tsat. On change of phase it loses latent heat which is quite high. Thus heat flows to the cold surface.

Q. What are the various types of condensation?

Ans. There are two types of condensation namely

i. Film condensation
ii. Drop-wise condensation

Q. What is film condensation?

Ans. When the liquid formed wets the surface and forms a film (continuous flow of liquid) it is called film condensation. In this liquid flows over the cooled vertical surface under the action of gravity.  The layer thickness increases continuously in thickness because of more condensation. This liquid film offers thermal resistance and reduces heat transfer between vapor and surface. Hence heat transfer in film boiling is much less.

Q. What are various types of film condensation?

Ans. There are two types film condensations

i. Laminar film condensation when Reynolds number is less than 1800
ii. Turbulent film condensation when Reynolds number is greater than 1800

Q. What is laminar film condensation?

Ans. Velocity of liquid in the condensate film is less or Re <1800.

Liquid flows under the action of gravity on a vertical plate.

Flow is laminar and properties of fluid are constant.

Heat transfer is purely by conduction and temperature variation is linear.

Q. Write the empirical correlations for heat transfer coefficient in laminar film condensation.

Ans. Local heat transfer coefficient

hx = ((ρll -ρv) k3g hfg)/(4µx(Tsat-Tsur))1/4

Heat transfer coefficient at the end of the plate

hL = ((ρ2k3ghfg)/(4µL(Tsat—Tsur))1/4

Average heat transfer coefficient

hav= (4/3) hL = (4/3)((ρ2k3ghfg)/(4µL(Tsat—Tsur))1/4

Q. What is turbulent film condensation?

Ans. When the Re >1800.

Velocity of film is quite high.

There is eddy’s current formation in a turbulent flow.

There is more heat transfer in turbulent than in laminar film condensation.

Q. Write the empirical correlations for heat transfer coefficient in turbulent film condensation?

Ans. Heat transfer coefficient over a vertical plate

hav (turbu)= 0.0077(ρl l -ρv)k3 g)/(µL2))1/3 Re0.4

Heat transfer coefficient  for condensation on the outside of a horizontal tube

Hav =0.0725 ((ρl l –ρv)k3 g hfg)/(µl (Tsat—Tsur)D))1/4

Heat transfer coefficient for condensation inside of a horizontal tube

hav =0.555 ((ρll –ρv)k3g hfg)/(µl (Tsat—Tsur)D))1/4

where hfg= hfg + (3/8) Cpl (Tsat —Tsur)

https://mesubjects.net/wp-admin/post.php?post=14131&action=edit                      MCQ Boiling

https://mesubjects.net/wp-admin/post.php?post=6455&action=edit                    MCQ Condensation

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