External Convection Heat Transfer: Quizzes and Practice Questions

Question 1

In external convective heat transfer, which dimensionless parameter measures the relative importance of buoyancy forces?

Accepted Answer

Grashof number

Answer

Reynolds number

Answer

Prandtl number

Answer

Nusselt number

Question 2

For laminar flow over a cylinder, the Nusselt number depends on:

Accepted Answer

Reynolds number, Prandtl number, and cylinder diameter

Answer

Reynolds number and Prandtl number only

Answer

Prandtl number and cylinder diameter only

Answer

Reynolds number only

Question 3

Which flow regime is characterized by a turbulent boundary layer and a laminar core?

Accepted Answer

Transitional

Answer

Laminar

Answer

Turbulent

Answer

Fully developed

Question 4

Which of the following does NOT influence the convective heat transfer coefficient?

Accepted Answer

Material of the surface

Answer

Fluid properties

Answer

Surface roughness

Answer

Flow velocity

Question 5

In natural convection, which dimensionless parameter quantifies the influence of buoyancy forces relative to other forces?

Accepted Answer

Grashof number

Answer

Nusselt number

Answer

Prandtl number

Question 6

When a fluid flows over a surface, the layer of fluid near the surface exhibits:

Accepted Answer

A non-zero velocity gradient

Answer

Zero velocity gradient

Answer

Fluctuating velocity

Answer

Reverse flow

Question 7

The heat transfer coefficient represents:

Accepted Answer

Combined resistance of fluid and surface to heat transfer

Answer

Fluid's resistance to heat transfer only

Answer

Surface's resistance to heat transfer only

Answer

Fluid's ability to store heat

Question 8

The dimensionless parameter that signifies the ratio of viscous to thermal diffusion effects is:

Accepted Answer

Prandtl number

Answer

Reynolds number

Answer

Nusselt number

Answer

Grashof number

Question 9

Select the option that does NOT represent a type of external convection:

Accepted Answer

Internal convection

Answer

Forced convection

Answer

Natural convection

Answer

Mixed convection

Question 10

The Nusselt number represents the dimensionless ratio of:

Accepted Answer

Convective heat transfer to conductive heat transfer

Answer

Conductive heat transfer to convective heat transfer

Answer

Boundary layer thickness to characteristic length

Answer

Characteristic length to boundary layer thickness

Question 11

In natural convection, heat transfer is driven by:

Accepted Answer

Density difference

Answer

Temperature difference

Answer

Pressure difference

Answer

Velocity difference

Question 12

Which of the following is not a key dimensionless parameter used in external convection analysis?

Accepted Answer

Euler number

Answer

Reynolds number

Answer

Prandtl number

Answer

Grashof number

Question 13

Which of the following is a key factor influencing the external convection heat transfer coefficient for natural convection?

Accepted Answer

Gravitational acceleration

Answer

Fluid viscosity

Answer

Surface roughness

Answer

Flow velocity

Question 14

Consider a fluid flowing over an inclined flat plate. Which of the following factors will NOT affect the external convection heat transfer coefficient?

Accepted Answer

Surface temperature

Answer

Plate inclination angle

Answer

Fluid velocity

Answer

Fluid density

Question 15

The boundary layer thickness for external convection over a moving surface is generally:

Accepted Answer

Larger than that for a stationary surface

Answer

Smaller than that for a stationary surface

Answer

Independent of surface movement

Answer

Dependent on the direction of surface movement

Question 16

In forced convection heat transfer, the heat transfer coefficient is primarily influenced by:

Accepted Answer

Fluid velocity and properties

Answer

Surface geometry and roughness

Answer

Natural convection currents

Answer

Radiation exchange

Question 17

Consider a fluid flowing over a flat plate. What type of boundary layer regime is typically observed at the leading edge of the plate?

Accepted Answer

Laminar boundary layer

Answer

Transitional boundary layer

Answer

Turbulent boundary layer

Answer

Mixed convection boundary layer

Question 18

How does surface roughness generally affect the heat transfer coefficient in external convection?

Accepted Answer

Increases the heat transfer coefficient

Answer

Decreases the heat transfer coefficient

Answer

Has no significant effect on the heat transfer coefficient

Answer

The effect depends on the type of fluid and flow regime

Question 19

Consider two identical surfaces at different temperatures exposed to the same fluid. Which surface will experience a higher rate of convective heat transfer?

Accepted Answer

The surface with the higher temperature

Answer

The surface with the lower temperature

Answer

Both surfaces will experience the same rate of heat transfer

Answer

The rate of heat transfer cannot be determined without additional information

Question 20

Which of the following factors does NOT influence the critical Reynolds number for transition from laminar to turbulent flow in external convection?

Accepted Answer

Heat flux

Answer

Fluid velocity

Answer

Fluid properties

Answer

Surface geometry

Question 21

What is the primary significance of the Prandtl number in external convection heat transfer?

Accepted Answer

It influences the relative thickness of the velocity and thermal boundary layers

Answer

It represents the ratio of momentum diffusivity to thermal diffusivity

Answer

It determines the critical Reynolds number for transition to turbulence

Answer

It affects the shape of the temperature profile

Question 22

In forced convection heat transfer, the convective heat transfer coefficient (h) is primarily governed by which dimensionless parameter?

Accepted Answer

Reynolds number (Re)

Answer

Nusselt number (Nu)

Answer

Prandtl number (Pr)

Answer

Grashof number (Gr)

Question 23

For a given fluid flow and surface geometry, which of the following actions will result in a higher convective heat transfer rate?

Accepted Answer

Increasing the flow velocity

Answer

Increasing the fluid viscosity

Answer

Increasing the surface roughness

Answer

Decreasing the surface area

Question 24

In natural convection heat transfer, the Nusselt number (Nu) is primarily governed by which dimensionless parameter?

Accepted Answer

Grashof number (Gr)

Answer

Reynolds number (Re)

Answer

Nusselt number (Nu)

Answer

Prandtl number (Pr)

Question 25

The presence of a favorable pressure gradient in the flow direction during forced convection typically leads to:

Accepted Answer

Increased heat transfer rate

Answer

Decreased heat transfer rate

Answer

No change in heat transfer rate

Answer

Flow separation

Question 26

The governing equation for external convection heat transfer is:

Accepted Answer

Newton's law of cooling

Answer

Fourier's law of heat conduction

Answer

Stefan-Boltzmann law

Answer

Poisson's ratio

Question 27

For forced convection over a flat plate, a commonly used heat transfer correlation is the:

Accepted Answer

Dittus-Boelter equation

Answer

McAdams correlation

Answer

Chilton-Colburn analogy

Answer

Petukhov-Popov correlation