Why does the heat flux decrease when the temperature increases way above the nucleate boiling point?

Steam bubbles no longer break away from the solid surface of the channel

What is the term KL in the giver equation of Nusselt number for nucleate boiling heat transfer correlations? Nub = ( frac{( frac{q}{A})D_b}{(T_s-T_{sat})k_L} )

Thermal conductivity of the film

Thermal conductivity of the vapour

Thermal conductivity of the liquid

Thermal conductivity of the film

Thermal conductivity of the Bubble

The Nusselt number for nucleate boiling is correctly represented by which equation?

Nu= ( frac{Q}{A} ) Db(Ts-Tsat) KL

Nu= ( frac{Q}{A} ) Db xa0 xa0(Ts-Tsat) KL

Nu= ( frac{Q}{A} ) Db(Ts-Tsat) KL

Nu= ( frac{Q}{A} ) Db (Ts-Tsat) xa0 xa0KL

Nu= ( frac{Q}{A} ) Db KL xa0 xa0(Ts-Tsat)

The heat flux Q/A depends on the specific heat of the liquid Cf as which one of the following given?

Q/A = f hfg [(pf pg) g/ ]0.5 [Cf dt/hfg p Csf]

Q/A= f hfg [(pf pg) g/ ]0.55 [Cf dt/hfg p] 3

Q/A = f hfg [(pf pg) g/ ]0.6 [Cf dt/hfg p Csf]3

Q/A = f hfg [(pf pg) g/ ]0.5 [Cf dt/hfg p Csf]3

Q/A = f hfg [(pf pg) g/ ]0.5 [Cf dt/hfg p Csf]

What is the relation between the vapour temperature and the liquid temperature on nucleation for a bubble inside the fluid?

Tv Tsat = (2 /r pg) Rv Tv2pv hfg

Tv Tsat = (2 /r pg) Rv Tv/pv hfg

Tv Tsat = (2 /r pg) Rv Tv2/pv hfg

Tv Tsat = (2 /r pg) Rv Tv2pv hfg

9 + Mcqs in Boilers Boiling Curve Calculations in Heat Transfer Operations Page 1 McqOptions

1.	Avoiding the Critical heat flux is an engineering problem in heat transfer applications, such as nuclear reactors, where fuel plates must not be allowed to overheat. To cope with this, what measure can be taken?
A.	Decrease the pressure
B.	Increase the pressure
C.	Add more water
D.	Add turbulence
Answer» C. Add more water

Discussion

2.	Why does the heat flux decrease when the temperature increases way above the nucleate boiling point?
A.	Steam bubbles no longer break away from the solid surface of the channel
B.	Radiation takes over
C.	Convection takes over
D.	Fouling occurs
Answer» B. Radiation takes over

Discussion

3.	What is the term KL in the giver equation of Nusselt number for nucleate boiling heat transfer correlations? Nu_b = ( frac{( frac{q}{A})D_b}{(T_s-T_{sat})k_L} )
A.	Thermal conductivity of the vapour
B.	Thermal conductivity of the liquid
C.	Thermal conductivity of the film
D.	Thermal conductivity of the Bubble
Answer» C. Thermal conductivity of the film

Discussion

4.	The Nusselt number for nucleate boiling is correctly represented by which equation?
A.	Nu= ( frac{Q}{A} ) D<sub>b</sub> xa0 xa0(T<sub>s</sub>-T<sub>sat</sub>) K<sub>L</sub>
B.	Nu= ( frac{Q}{A} ) D<sub>b</sub>(T<sub>s</sub>-T<sub>sat</sub>) K<sub>L</sub>
C.	Nu= ( frac{Q}{A} ) D<sub>b</sub> (T<sub>s</sub>-T<sub>sat</sub>) xa0 xa0K<sub>L</sub>
D.	Nu= ( frac{Q}{A} ) D<sub>b</sub> K<sub>L</sub> xa0 xa0(T<sub>s</sub>-T<sub>sat</sub>)
Answer» B. Nu= ( frac{Q}{A} ) D<sub>b</sub>(T<sub>s</sub>-T<sub>sat</sub>) K<sub>L</sub>

Discussion

5.	The heat flux Q/A depends on the specific heat of the liquid C_f as which one of the following given?
A.	Q/A= <sub>f</sub> h<sub>fg</sub> [(p<sub>f</sub> p<sub>g</sub>) g/ ]<sup>0.55</sup> [C<sub>f</sub> dt/h<sub>fg</sub> p] <sup>3</sup>
B.	Q/A = <sub>f</sub> h<sub>fg</sub> [(p<sub>f</sub> p<sub>g</sub>) g/ ]<sup>0.6</sup> [C<sub>f</sub> dt/h<sub>fg</sub> p C<sub>sf</sub>]<sup>3</sup>
C.	Q/A = <sub>f</sub> h<sub>fg</sub> [(p<sub>f</sub> p<sub>g</sub>) g/ ]<sup>0.5 </sup>[C<sub>f</sub> dt/h<sub>fg</sub> p C<sub>sf</sub>]<sup>3</sup>
D.	Q/A = <sub>f</sub> h<sub>fg</sub> [(p<sub>f</sub> p<sub>g</sub>) g/ ]<sup>0.5</sup> [C<sub>f</sub> dt/h<sub>fg</sub> p C<sub>sf</sub>]
Answer» D. Q/A = <sub>f</sub> h<sub>fg</sub> [(p<sub>f</sub> p<sub>g</sub>) g/ ]<sup>0.5</sup> [C<sub>f</sub> dt/h<sub>fg</sub> p C<sub>sf</sub>]

Discussion

6.	Consider a situation when evaporation takes place at the liquid-vapour interface in which the heat transfer is mainly due to free convection then the Nusselt Number for the film follows which one of the following relation?
A.	Nu = F<sub>1</sub> Gr F<sub>2</sub> Pr
B.	Nu = 4 F<sub>1</sub> Gr F<sub>2</sub> Pr
C.	Nu = 2 F<sub>1</sub> Gr F<sub>2</sub> Pr
D.	Nu = 3 F<sub>1</sub> Gr F<sub>2</sub> Pr
Answer» B. Nu = 4 F<sub>1</sub> Gr F<sub>2</sub> Pr

Discussion

7.	Spherical bubbles of diameter 3 mm are observed in the bubble boiling phase of water at 1 atmosphere pressure. Assuming pure water vapour is present inside the bubbles, calculate the temperature of that vapour. Given Surface tension = 73mN/m
A.	nR/p<sub>g</sub>f<sub>g</sub> = 0.000014
B.	119.387
C.	200.217
D.	300.217
E.	400.217
Answer» B. 119.387

Discussion

8.	What is the relation between the vapour temperature and the liquid temperature on nucleation for a bubble inside the fluid?
A.	T<sub>v</sub> T<sub>sat</sub> = (2 /r p<sub>g</sub>) R<sub>v</sub> T<sub>v</sub>/p<sub>v</sub> h<sub>fg</sub>
B.	T<sub>v</sub> T<sub>sat</sub> = (2 /r p<sub>g</sub>) R<sub>v</sub> T<sub>v</sub><sup>2</sup>/p<sub>v</sub> h<sub>fg</sub>
C.	T<sub>v</sub> T<sub>sat</sub> = (2 /r p<sub>g</sub>) R<sub>v</sub> T<sub>v</sub><sup>2</sup>p<sub>v</sub> h<sub>fg</sub>
D.	T<sub>v</sub> T<sub>sat</sub> = (2 p<sub>g</sub>) R<sub>v</sub> T<sub>v</sub><sup>2</sup>/p<sub>v</sub> h<sub>fg</sub>
Answer» C. T<sub>v</sub> T<sub>sat</sub> = (2 /r p<sub>g</sub>) R<sub>v</sub> T<sub>v</sub><sup>2</sup>p<sub>v</sub> h<sub>fg</sub>

Discussion

9.	The milk while boiling in an open vessel spills out because of the ___________ phenomenon.
A.	Sub-cooled boiling
B.	Super-cooled boiling
C.	Sub-heated boiling
D.	Super-heated boiling
Answer» B. Super-cooled boiling

Discussion

Explore topic-wise MCQs in Heat Transfer Operations.

Avoiding the Critical heat flux is an engineering problem in heat transfer applications, such as nuclear reactors, where fuel plates must not be allowed to overheat. To cope with this, what measure can be taken?

Why does the heat flux decrease when the temperature increases way above the nucleate boiling point?

What is the term KL in the giver equation of Nusselt number for nucleate boiling heat transfer correlations? Nub = ( frac{( frac{q}{A})D_b}{(T_s-T_{sat})k_L} )

The Nusselt number for nucleate boiling is correctly represented by which equation?

The heat flux Q/A depends on the specific heat of the liquid Cf as which one of the following given?

Consider a situation when evaporation takes place at the liquid-vapour interface in which the heat transfer is mainly due to free convection then the Nusselt Number for the film follows which one of the following relation?

Spherical bubbles of diameter 3 mm are observed in the bubble boiling phase of water at 1 atmosphere pressure. Assuming pure water vapour is present inside the bubbles, calculate the temperature of that vapour.Given Surface tension = 73mN/m

What is the relation between the vapour temperature and the liquid temperature on nucleation for a bubble inside the fluid?

The milk while boiling in an open vessel spills out because of the ___________ phenomenon.

What is the term KL in the giver equation of Nusselt number for nucleate boiling heat transfer correlations?
Nu_b = ( frac{( frac{q}{A})D_b}{(T_s-T_{sat})k_L} )

The heat flux Q/A depends on the specific heat of the liquid C_f as which one of the following given?

Spherical bubbles of diameter 3 mm are observed in the bubble boiling phase of water at 1 atmosphere pressure. Assuming pure water vapour is present inside the bubbles, calculate the temperature of that vapour.
Given Surface tension = 73mN/m