The bubble diameter at the time of detachment from the surface can be worked out from the relation proposed by Fritz and is given by(Where, β is the angle of contact)

C d β [2 σ/g (p t – p v)]^5/2

C d β [2 σ/g (p t – p v)]^3/2

C d β [2 σ/g (p t – p v)]^1/2

C d β [2 σ/g (p t – p v)]^5/2

All the following statements are correct, except

In subcooled heating, the temperature of the heating surface is more than the boiling point of the liquid

Nucleate boiling gets promoted on a smooth surface

In subcooled heating, the temperature of the heating surface is more than the boiling point of the liquid

Film boiling region is usually avoided in commercial equipment

There occurs transition from nucleate to film boiling burn-out point on the boiling curve

Mark the wrong statement with respect to laminar flow condensation on a vertical plate

At a definite point on the heat transfer, the film coefficient is directly proportional to thermal conductivity and inversely proportional to thickness of film at the point

The rate of condensation heat transfer is maximum at the upper edge of the plate and progressively decreases as the lower edge is approached

The average heat transfer coefficient is two third of the local heat transfer coefficient at the lower edge of the plate

At a definite point on the heat transfer, the film coefficient is directly proportional to thermal conductivity and inversely proportional to thickness of film at the point

The film thickness increases as the fourth root of the distance down the upper edge

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

Increases with increasing thickness of film

Remains constant at all heights of the surface

Decreases with increasing distance from the top of the surface

Increases with increasing thickness of film

Increases with increasing temperature differential between the surface and vapour

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?

4.53% reduction in condensation coefficient

1.53% reduction in condensation coefficient

2.53% reduction in condensation coefficient

3.53% reduction in condensation coefficient

4.53% reduction in condensation coefficient

In nucleate pool boiling, the heat flux depends on

Liquid properties, material and condition of the surface

Material and roughness of the surface

Liquid properties and material of the surface

Consider an elemental control volume for mass balance continuity equation. Which one of the following is correct?

Value of 2 is 2 u + d v/d x (d x)

Value of 1 is 2 v + d u/d x (d y)

Value of 2 is u + d u/d y (d x)

Value of 1 is v + d u/d x (d y)

Value of 2 is 2 u + d v/d x (d x)

Heat flux increases with temperature excess beyond the Leiden-frost point due to

Occurrence of subcooled boiling

Radiation effect becomes predominant

Occurrence of subcooled boiling

Leiden-frost expansion is related to

Condensation of vapor on a cold surface

Exchange of heat between two solids

Boiling of liquid on a hot surface

Which of the following is a wrong statement in the context of a convective heat transfer coefficient in laminar film condensation?The heat transfer coefficient varies as

– ¼ power of acceleration due to gravity

¼ power of enthalpy of evaporation

– ½ power of dynamic viscosity

A plate condenser of dimensions l * b has been designed to be kept with side l in the vertical position. However due to oversight during erection and installation, it was fixed with side b vertical. How would this affect the heat transfer? Assume laminar conditions and same thermos-physical properties and take b = l/2

The condenser should be installed with shorter side horizontal

The condenser should be installed with longer side horizontal

The condenser should be installed with longer side vertical

The condenser should be installed with shorter side vertical

With increase in excess temperature, the heat flux in boiling

Decreases, then increases and again decreases

Increases, then decreases and again increases

Kirk bride criterion is given by

h = 0.0087 (Re)^0.4 [k³ p² g/δ²]^1/3

h = 0.0057 (Re)^0.4 [k³ p² g/δ²]^1/3

h = 0.0067 (Re)^0.4 [k³ p² g/δ²]^1/3

h = 0.0077 (Re)^0.4 [k³ p² g/δ²]^1/3

h = 0.0087 (Re)^0.4 [k³ p² g/δ²]^1/3

62 + Mcqs in Condensation And Boiling in Heat Transfer Page 1 McqOptions

1.	For n-tubes in a vertical column of the tube bank pattern, identify the correct statement.(Where, D is the diameter of a single tube in the bank)
A.	D e = n D
B.	D e = n² D
C.	D e = (1/n) D
D.	D e = D
Answer» B. D e = n² D

2.	The excess temperature range 50 degree Celsius < d t < 200 degree Celsius is indicative of the region of
A.	Interface evaporation
B.	Nuclear boiling
C.	Partial film boiling
D.	Stable film boiling
Answer» D. Stable film boiling

3.	The bubble diameter at the time of detachment from the surface can be worked out from the relation proposed by
A.	Stanton
B.	Fritz
C.	Fourier
D.	Nusselt
Answer» C. Fourier

4.	The nucleate pool boiling is influenced by the following factors(i) Pressure(ii) Liquid properties(iii) MaterialIdentify the correct statements
A.	1, 2 and 3
B.	2 only
C.	1 and 2
D.	2 and 3
Answer» B. 2 only

5.	The bubble diameter at the time of detachment from the surface can be worked out from the relation proposed by Fritz and is given by(Where, β is the angle of contact)
A.	C d β [2 σ/g (p t – p v)]
B.	C d β [2 σ/g (p t – p v)]^3/2
C.	C d β [2 σ/g (p t – p v)]^1/2
D.	C d β [2 σ/g (p t – p v)]^5/2
Answer» D. C d β [2 σ/g (p t – p v)]^5/2

6.	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 interfaceMark the correct answer from the codes indicated below
A.	i, ii, iii and v
B.	i, iii, iv and v
C.	i, ii, iii and iv
D.	i, iii and v
Answer» C. i, ii, iii and iv

7.	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
A.	100.217 degree Celsius
B.	200.217 degree Celsius
C.	300.217 degree Celsius
D.	400.217 degree Celsius
Answer» B. 200.217 degree Celsius

8.	What is the value of surface fluid constant for water-brass combination?
A.	0.004
B.	0.005
C.	0.006
D.	0.007
Answer» D. 0.007

11.	For laminar film condensation on a vertical plate, the mass flow rate of the condensate per unit depth of the film at any position x is given by
A.	p g δ ³/ 3
B.	p g δ³/ 3 σ
C.	p g δ²/ 3 σ
D.	p g δ²/ 3
Answer» C. p g δ²/ 3 σ

12.	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
A.	δ decreases, h increases
B.	Both δ and h increases
C.	δ increases, h decreases
D.	Both δ and h decreases
Answer» D. Both δ and h decreases

13.	The outer surface of a vertical tube is 1.25 m long and outer diameter is 50 mm is exposed to saturated steam at atmospheric pressure. If the tube surface is maintained at 80 degree Celsius by the flow of cooling water through it, determine the rate of heat transfer to the coolant
A.	47648 W
B.	12345 W
C.	19879 W
D.	97123 W
Answer» D. 97123 W

17.	What is the value of Reynolds number in terms of mass flow rate?(Where, δ is length of the plate and b is width of the plate)
A.	4 m/δ b
B.	2 m/δ b
C.	3 m/δ b
D.	m /δ b
Answer» B. 2 m/δ b

18.	What is the value of characteristics length in turbulent film condensation?(Where, δ is length of the plate)
A.	δ
B.	3 δ
C.	2 δ
D.	4 δ
Answer» E.

19.	The transition from laminar to turbulent flow occurs at a critical Reynolds number of
A.	1800
B.	2200
C.	2600
D.	3000
Answer» B. 2200

20.	A 0.10 cm diameter and 15 cm long wire has been laid horizontally and submerged in water at atmospheric pressure. The wire has a steady state voltage drop of 14.5 V and a current of 42.5 A. Determine the heat flux of the wire.The following equation applies for water boiling on a horizontal submerged surfaceH = 1.54 (Q/A)^0.75 = 5.58 (d t)³ W/m² K where Q/A is the heat flux rate in W/m² and d t is the temperature difference between surface and saturation.
A.	1.308 * 10⁸ W/m²
B.	1.308 * 10⁷ W/m²
C.	1.308 * 10⁶ W/m²
D.	1.308 * 10⁵ W/m²
Answer» D. 1.308 * 10⁵ W/m²

16.	In nucleate pool boiling, the heat flux depends on
A.	Liquid properties, material and condition of the surface
B.	Material of the surface only
C.	Material and roughness of the surface
D.	Liquid properties and material of the surface
Answer» B. Material of the surface only

21.	For water evaporating at atmospheric pressure, the burnout occurs at temperature excess slightly above
A.	25 K
B.	55 K
C.	75 K
D.	105 K
Answer» C. 75 K

22.	Fritz criterion is given by
A.	h = 1.973 (Q/A)^0.45
B.	h = 1.973 (Q/A)^0.55
C.	h = 1.973 (Q/A)^0.65
D.	h = 1.973 (Q/A)^0.75
Answer» E.

23.	Consider the following statements regarding nucleate boiling(i) The temperature of the surface is greater than the saturation temperature of the liquid(ii) Bubbles are created by the expansion of entrapped gas oil vapor at small cavities in the surface(iii) The temperature is greater than that in film boiling(iv) The heat transfer from the surface to the liquid is greater than that in the film boilingWhich of these statements are correct?
A.	1 and 3
B.	1, 2 and 4
C.	2, 3 and 4
D.	1, 2 and 3
Answer» C. 2, 3 and 4

25.	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 arep f (fluid) = 959.52 kg/m³p g (vapor) = 0.597 kg/m³h f g = 2257000 J/kgσ = 0.0533 N/m
A.	6.15 V
B.	7.15 V
C.	8.15 V
D.	9.15 V
Answer» C. 8.15 V

26.	The temperature of the liquid is below the saturation temperature and boiling takes place only in vicinity of the heated surface. This type of boiling is known as
A.	Subcooled
B.	Forces
C.	Saturated
D.	Pool
Answer» B. Forces

27.	Consider the following phenomena(i) Boiling(ii) Free convection in air(iii) Forced convection in air(iv) Conduction in airIdentify the correct sequence (heat transfer coefficient)
A.	3 – 4 – 1 – 2
B.	4 – 1 – 3 – 2
C.	4 – 3 – 2 – 1
D.	4 – 2 – 3 – 1
Answer» E.

29.	The convective coefficients for condensation usually lie in the range
A.	30-300 W/m² K
B.	60-3000 W/m² K
C.	300-10000 W/m² K
D.	2500-10000 W/m² K
Answer» E.

31.	Determine the length of a 25 cm outer diameter tube if the condensate formed on the surface of the tube is to be same whether it is kept vertical or horizontal
A.	61.5 cm
B.	71.5 cm
C.	81.5 cm
D.	91.5 cm
Answer» C. 81.5 cm

32.	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 condensationIdentify the correct statement
A.	1 and 2
B.	2, 3 and 4
C.	4 only
D.	1, 2 and 3
Answer» E.

Explore topic-wise MCQs in Heat Transfer.

For n-tubes in a vertical column of the tube bank pattern, identify the correct statement.(Where, D is the diameter of a single tube in the bank)

The excess temperature range 50 degree Celsius < d t < 200 degree Celsius is indicative of the region of

The bubble diameter at the time of detachment from the surface can be worked out from the relation proposed by

The nucleate pool boiling is influenced by the following factors(i) Pressure(ii) Liquid properties(iii) MaterialIdentify the correct statements

The bubble diameter at the time of detachment from the surface can be worked out from the relation proposed by Fritz and is given by(Where, β is the angle of contact)

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 interfaceMark the correct answer from the codes indicated below

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

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

All the following statements are correct, except

Mark the wrong statement with respect to laminar flow condensation on a vertical plate

For laminar film condensation on a vertical plate, the mass flow rate of the condensate per unit depth of the film at any position x is given by

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

The outer surface of a vertical tube is 1.25 m long and outer diameter is 50 mm is exposed to saturated steam at atmospheric pressure. If the tube surface is maintained at 80 degree Celsius by the flow of cooling water through it, determine the rate of heat transfer to the coolant

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

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?

In nucleate pool boiling, the heat flux depends on

What is the value of Reynolds number in terms of mass flow rate?(Where, δ is length of the plate and b is width of the plate)

What is the value of characteristics length in turbulent film condensation?(Where, δ is length of the plate)

The transition from laminar to turbulent flow occurs at a critical Reynolds number of

For water evaporating at atmospheric pressure, the burnout occurs at temperature excess slightly above

Fritz criterion is given by

Consider an elemental control volume for mass balance continuity equation. Which one of the following is correct?

The temperature of the liquid is below the saturation temperature and boiling takes place only in vicinity of the heated surface. This type of boiling is known as

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

Heat flux increases with temperature excess beyond the Leiden-frost point due to

The convective coefficients for condensation usually lie in the range

Leiden-frost expansion is related to

Determine the length of a 25 cm outer diameter tube if the condensate formed on the surface of the tube is to be same whether it is kept vertical or horizontal

For laminar film condensation on a vertical plate, the gravitational acceleration g is replaced by

Condensation refers to a change from the

The phenomenon of stable film boiling is referred to as

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

Which parameter is responsible for commencement of the turbulent flow?

The heat flux in nucleate boiling varies in accordance with

The critical Reynolds number for transition from laminar to turbulent film condensation is

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

Which of the following is a wrong statement in the context of a convective heat transfer coefficient in laminar film condensation?The heat transfer coefficient varies as

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

When evaporation takes place at the liquid-vapor interface, the heat transfer is solely due to free convection and the film coefficient follows the relation

Drop wise condensation usually occurs on

With increase in excess temperature, the heat flux in boiling

Condensation process is very common in(i) Boilers(ii) Condensers(iii) EvaporatorsIdentify the correct statements

The boiling phenomenon is known to occur in how many forms?

Kirk bride criterion is given by

Estimate the peak heat flux for water boiling at normal atmospheric pressure. The relevant thermo-physical properties arep f (liquid) = 958.45 kg/m³p g (vapor) = 0.61 kg/m³h f g = 2.25 * 10⁶ J/kgσ = 0.0585 N/m

33.	For laminar film condensation on a vertical plate, the gravitational acceleration g is replaced by
A.	4 g sin α
B.	3 g sin α
C.	2 g sin α
D.	g sin α
Answer» E.

34.	Condensation refers to a change from the
A.	Solid to a liquid phase
B.	Vapor to a liquid phase
C.	Liquid to a solid phase
D.	Liquid to a vapor phase
Answer» C. Liquid to a solid phase

35.	The phenomenon of stable film boiling is referred to as
A.	Nucleate effect
B.	Boiling regimes
C.	Leiden frost effect
D.	Von karma effect
Answer» D. Von karma effect

36.	Depending upon the behavior of condensate up on the cooled surface, the condensation process are classified into how many distinct modes?
A.	1
B.	2
C.	3
D.	4
Answer» C. 3

37.	Which parameter is responsible for commencement of the turbulent flow?
A.	Fourier number
B.	Reynolds number
C.	Stanton number
D.	Nusselt number
Answer» C. Stanton number

38.	The heat flux in nucleate boiling varies in accordance with
A.	h f g
B.	(h f g)⁴
C.	1/(h f g)²
D.	(h f g)³
Answer» D. (h f g)³

39.	The critical Reynolds number for transition from laminar to turbulent film condensation is
A.	2000
B.	1900
C.	1800
D.	1700
Answer» D. 1700

40.	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
A.	0.0915 * 10⁶ W/m²
B.	0.1915 * 10⁶ W/m²
C.	0.2915 * 10⁶ W/m²
D.	0.3915 * 10⁶ W/m²
Answer» D. 0.3915 * 10⁶ W/m²

41.	Which of the following is a wrong statement in the context of a convective heat transfer coefficient in laminar film condensation?The heat transfer coefficient varies as
A.	– ¼ power of acceleration due to gravity
B.	½ power of density of liquid
C.	¼ power of enthalpy of evaporation
D.	– ½ power of dynamic viscosity
Answer» B. ½ power of density of liquid

43.	What is the value of surface fluid constant for water-copper combination?
A.	0.010
B.	0.011
C.	0.012
D.	0.013
Answer» E.