Internal Convection: Heat Transfer in Ducts and Channels

Question 1

Which of the following factors does NOT affect the Nusselt number in turbulent internal flow?

Accepted Answer

Entrance length

Answer

Reynolds number

Answer

Prandtl number

Answer

Channel geometry

Question 2

In a duct with constant wall temperature boundary condition, the thermal boundary layer:

Accepted Answer

Grows downstream

Answer

Shrinks downstream

Answer

Stays constant

Answer

Oscillates

Question 3

Which type of flow regime is characterized by irregular and unpredictable velocity fluctuations?

Accepted Answer

Turbulent

Answer

Laminar

Answer

Transitional

Answer

Viscous

Question 4

The hydrodynamic entrance length for internal convection is typically defined as:

Accepted Answer

The length required for the velocity profile to fully develop

Answer

The length required for the temperature profile to fully develop

Answer

The length required for the boundary layers to merge

Answer

There is no entrance length for internal convection

Question 5

In laminar flow within a duct, the Nusselt number is proportional to:

Accepted Answer

Prandtl number

Answer

Reynolds number

Answer

Grashof number

Answer

Peclet number

Question 6

Which of the following dimensionless parameters characterizes flow development in ducts?

Accepted Answer

Graetz number

Answer

Friction factor

Answer

Stanton number

Answer

Colburn factor

Question 7

Compared to laminar flow, the heat transfer coefficient for turbulent flow is generally:

Accepted Answer

Higher

Answer

Lower

Answer

Equal

Answer

Dependent on the Reynolds number

Question 8

In fully developed laminar flow within a duct, the velocity profile is:

Accepted Answer

Parabolic

Answer

Triangular

Answer

Rectangular

Answer

Exponential

Question 9

The entrance region in a duct is characterized by:

Accepted Answer

Developing velocity and temperature profiles

Answer

Fully developed velocity and temperature profiles

Answer

Uniform heat flux

Answer

Constant heat transfer coefficient

Question 10

In internal convection, which dimensionless number characterizes the ratio of viscous forces to inertial forces?

Accepted Answer

Reynolds number

Answer

Nusselt number

Answer

Prandtl number

Answer

Grashof number

Question 11

Laminar flow in a duct occurs when the Reynolds number is:

Accepted Answer

Below 2100

Answer

Between 2100 and 10,000

Answer

Above 10,000

Answer

Zero

Question 12

The Dittus-Boelter correlation is used to determine the Nusselt number for:

Accepted Answer

Turbulent flow in a circular duct

Answer

Laminar flow in a circular duct

Answer

Laminar flow in a non-circular duct

Answer

Turbulent flow in a non-circular duct

Question 13

The Graetz problem analyzes:

Accepted Answer

Heat transfer in a duct with developing flow

Answer

Heat transfer in a duct with constant surface temperature

Answer

Heat transfer in a duct with constant heat flux

Answer

Heat transfer in a duct with mixed boundary conditions

Question 14

The dimensionless parameter used to characterize the relative importance of forced convection to natural convection is the:

Accepted Answer

Grashof number

Answer

Reynold number

Answer

Prandtl number

Answer

Nusselt number

Question 15

In a duct with uniform heat flux boundary conditions, the temperature profile is:

Accepted Answer

Parabolic

Answer

Hyperbolic

Answer

Linear

Answer

Exponential

Question 16

The Prandtl number for water at room temperature is approximately:

Accepted Answer

7

Answer

1

Answer

100

Answer

10

Question 17

The Reynolds number for turbulent flow in a circular tube is:

Accepted Answer

Re > 2300

Answer

Re = 5000

Answer

Re = 1500

Answer

Re < 1000

Question 18

In developing internal convection, the local Nusselt number:

Accepted Answer

Varies along the tube length

Answer

Decreases uniformly

Answer

Is constant

Answer

Increases uniformly

Question 19

Which of the following correlations is used for forced convection in a circular tube with turbulent flow:

Accepted Answer

Dittus-Boelter correlation

Answer

Sieder and Tate correlation

Answer

Churchill and Bernstein correlation

Answer

Colburn correlation

Question 20

In internal natural convection, the Rayleigh number is:

Accepted Answer

A dimensionless number representing the ratio of buoyancy to viscous forces

Answer

A dimensionless number representing the ratio of pressure drop to viscous forces

Answer

A dimensionless number representing the ratio of heat transfer to viscous forces