Q. Estimate the peak heat flux for water boiling at normal atmospheric pressure. The relevant thermo-physical properties are

p f (liquid) = 958.45 kg/m³
p g (vapor) = 0.61 kg/m³
h f g = 2.25 * 10⁶ J/kg
σ = 0.0585 N/m

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Q. A 1.0 mm diameter and 300 mm long nickel wire is submerged horizontal in water at atmospheric pressure. At burnout, the wire has a current of 195 A. Calculate the voltage at burnout. The relevant thermos-physical properties are

p f (fluid) = 959.52 kg/m³
p g (vapor) = 0.597 kg/m³
h f g = 2257000 J/kg
σ = 0.0533 N/m

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Q. Condensation refers to a change from the

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Q. Condensation process is very common in

(i) Boilers
(ii) Condensers
(iii) Evaporators

Identify the correct statements

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Q. The convective coefficients for condensation usually lie in the range

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Q. Drop wise condensation usually occurs on

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Q. Consider the following statements:

(i) If a condensing liquid does not wet a surface, then drop wise condensation will not take place on it
(ii) Drop wise condensation gives a higher transfer rate than film wise condensation
(iii) Reynolds number of condensing liquid is based on its mass flow rate
(iv) Suitable coating or vapor additive is used to promote film wise condensation

Identify the correct statement

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Q. Depending upon the behavior of condensate up on the cooled surface, the condensation process are classified into how many distinct modes?

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Q. A plate condenser was designed to be kept vertical. How would the condensation coefficient be effected if due to site constraints, it has to be kept at 60 degree to the horizontal?

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Q. Saturated steam is allowed to condense over a vertical flat surface and the condensate film flows down the surface. The local coefficient of heat transfer for condensation

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Q. In condensation over a vertical surface, the value of convection coefficient varies as

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Q. For film wise condensation on a vertical plane, the film thickness δ and heat transfer coefficient h vary with distance x from the leading edge as

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Q. What is the value of surface fluid constant for water-copper combination?

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Q. What is the value of surface fluid constant for water-brass combination?

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Q. Spherical bubbles of 3 mm diameter are observed in the bulk fluid boiling of water at standard atmospheric pressure. Assuming pure water vapor in the bubble and vapor pressure equal to 101.325 k N/m², calculate the temperature of the vapor

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Q. An electric wire of 1.25 mm diameter and 250 mm long is laid horizontally and submerged in water at 7 bar. The wire has an applied voltage of 2.2 V and carries a current of 130 amperes. If the surface of the wire is maintained at 200 degree Celsius, make calculations for the heat flux

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Q. Which of the following parameters affect burnout heat flux in the nucleate boiling region

(i) Heat of evaporation
(ii) Temperature difference
(iii) Density of vapor
(iv) Density of liquid
(v) Surface tension at the vapor-liquid interface

Mark the correct answer from the codes indicated below

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Q. All the following statements are correct, except

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Q. Milk spills over when it is boiled in an open vessel. The boiling of milk at this instant is referred to as

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Q. For laminar film condensation on a vertical plate, the velocity distribution at a distance δ from the top edge is given by

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