Convection Heat Transfer Quizzes | Heat Transfer | Mechanical Engineering

Question 1

The Nusselt number is a dimensionless parameter that characterizes the ratio of what?

Accepted Answer

Convective to conductive heat transfer

Answer

Heat transfer rate to surface area

Answer

Temperature difference to thermal conductivity

Answer

Boundary layer thickness to characteristic length

Question 2

Which parameter does NOT affect the convection heat transfer coefficient (h)?

Accepted Answer

Heat flux

Answer

Fluid velocity

Answer

Surface roughness

Answer

Fluid temperature

Question 3

Which of the following is not a type of convection heat transfer?

Accepted Answer

Condensation

Answer

Natural convection

Answer

Forced convection

Answer

Mixed convection

Question 4

In forced convection heat transfer, which factor primarily determines the convection heat transfer coefficient?

Accepted Answer

Fluid velocity

Answer

Fluid temperature

Answer

Surface roughness

Answer

Surface emissivity

Question 5

In forced convection, what is the main factor causing fluid movement?

Accepted Answer

External mechanical devices like pumps or fans

Answer

Differences in density due to gravity

Answer

Effects of surface tension

Answer

Electromagnetic forces

Question 6

Which heat transfer mechanism does NOT involve fluid motion?

Accepted Answer

Radiation

Answer

Natural Convection

Answer

Forced Convection

Answer

Mixed Convection

Question 7

Which mechanism is NOT involved in free convection heat transfer?

Accepted Answer

Conduction

Answer

Buoyancy forces

Answer

Viscous forces

Answer

Thermal expansion

Question 8

A fluid flowing over a heated surface causes the fluid to heat up. Which type of convection heat transfer is this?

Accepted Answer

Forced convection

Answer

Natural convection

Answer

Radiation

Answer

Mixed convection

Question 9

What dimensionless number compares inertial forces to viscous forces in fluid flow?

Accepted Answer

Reynolds Number

Answer

Nusselt Number

Answer

Prandtl Number

Answer

Grashof Number

Question 10

What is the primary mechanism responsible for convection heat transfer?

Accepted Answer

Advection

Answer

Diffusion

Answer

Thermal radiation

Answer

Conduction

Question 11

In forced convection heat transfer, the Nusselt number is a dimensionless parameter that relates the convective heat transfer coefficient to:

Accepted Answer

Fluid velocity and temperature gradient

Answer

Fluid density and specific heat

Answer

Surface area and fluid viscosity

Answer

Grashof and Rayleigh numbers

Question 12

In convection heat transfer, which equation is commonly used to determine the heat transfer rate between a fluid and a surface?

Accepted Answer

Newton's law of cooling

Answer

Fourier's law of conduction

Answer

Ohm's law

Answer

Stefan-Boltzmann law

Question 13

In forced convection, what causes the fluid to move?

Accepted Answer

External forces

Answer

Density differences

Answer

Temperature gradients

Answer

Diffusion

Question 14

In natural convection heat transfer, which dimensionless number is employed for characterization?

Accepted Answer

Grashof Number

Answer

Nusselt Number

Answer

Reynolds Number

Answer

Prandtl Number

Question 15

In a convection heat transfer boundary layer, which characteristic is associated with laminar flow?

Accepted Answer

Parabolic velocity profile

Answer

Constant thermal conductivity

Answer

High turbulence levels

Question 16

Which statement about free convection heat transfer is incorrect?

Accepted Answer

Free convection occurs when an external force causes fluid flow.

Answer

Free convection is driven by density variations caused by temperature differences.

Answer

Free convection heat transfer coefficients are typically lower than forced convection heat transfer coefficients.

Question 17

In free convection heat transfer, which dimensionless number represents the ratio of buoyancy forces to viscous forces?

Accepted Answer

Grashof number

Answer

Nusselt number

Answer

Reynolds number

Answer

Prandtl number

Question 18

In convection heat transfer, which dimensionless number is irrelevant?

Accepted Answer

Froude Number

Answer

Nusselt Number

Answer

Reynolds Number

Answer

Prandtl Number

Question 19

Which of the following is not a type of convection heat transfer?

Accepted Answer

Radiation

Answer

Natural convection

Answer

Forced convection

Answer

Mixed convection

Question 20

In forced convection heat transfer over a flat surface, how does the boundary layer thickness vary along the flow direction?

Accepted Answer

Increases

Answer

Decreases

Answer

Remains constant

Answer

Varies randomly

Question 21

In internal forced convection, which parameter has the strongest influence on the heat transfer coefficient for fully developed flow inside a circular tube?

Accepted Answer

Reynolds number

Answer

Tube length

Answer

Prandtl number

Question 22

Which factor is NOT involved in determining the Prandtl number?

Accepted Answer

Fluid velocity

Answer

Fluid viscosity

Answer

Fluid density

Answer

Fluid specific heat

Question 23

In natural convection heat transfer, what causes the fluid to move?

Accepted Answer

Temperature differences creating density variations

Answer

Applied external pressure

Answer

Wind currents

Answer

Magnetic fields

Question 24

Which factor does NOT affect the rate of convective heat transfer between a surface and a fluid?

Accepted Answer

Ambient pressure

Answer

Fluid velocity

Answer

Surface roughness

Answer

Fluid viscosity

Question 25

Which of the following factors would hinder heat transfer in a forced convection scenario?

Accepted Answer

Lower fluid viscosity

Answer

Higher fluid velocity

Answer

Larger surface area

Answer

Greater temperature difference

Question 26

In convection heat transfer, which fluid property determines its resistance to flow when a force is applied?

Accepted Answer

Viscosity

Answer

Density

Answer

Thermal conductivity

Answer

Specific heat capacity

Question 27

In free convection heat transfer, which non-dimensional number expresses the ratio of viscous forces to buoyancy forces acting on a fluid?

Accepted Answer

Grashof Number

Answer

Reynolds Number

Answer

Prandtl Number

Answer

Nusselt Number

Question 28

Question: Describe the physical mechanisms that drive convection heat transfer in fluids. Explain how these mechanisms facilitate the transfer of thermal energy.

Accepted Answer

Convection heat transfer is driven by temperature differences within the fluid, resulting in buoyancy-driven fluid motion.

Answer

Option 1: Convection heat transfer occurs solely due to the diffusion of thermal energy within the fluid.

Question 29

Which of the following factors does not affect the heat transfer coefficient for mixed convection?

Accepted Answer

Surface roughness

Answer

Grashof number

Answer

Reynolds number

Answer

Prandtl number

Question 30

Condensation is a phase change process that occurs when a vapor transforms into a liquid. What is the driving force for condensation?

Accepted Answer

Temperature difference

Answer

Pressure difference

Answer

Concentration difference

Answer

Electrical potential difference

Question 31

The heat transfer coefficient for condensation on a vertical surface is typically:

Accepted Answer

Much higher than for natural convection

Answer

Slightly higher than for natural convection

Answer

About the same as for natural convection

Answer

Lower than for natural convection

Question 32

How does turbulence promote enhanced convection heat transfer?

Accepted Answer

Decreases boundary layer thickness and increases fluid mixing.

Answer

Increases fluid heat capacity.

Answer

Increases boundary layer thickness and decreases fluid mixing.

Question 33

Which of the following is NOT an experimental technique used to measure the convective heat transfer coefficient?

Accepted Answer

Computational fluid dynamics (CFD)

Answer

Surface thermocouple method

Answer

Heat flux sensor method

Answer

Optical measurement techniques

Question 34

Which of the following is NOT a type of convection heat transfer?

Accepted Answer

Radiation heat transfer

Answer

Forced convection

Answer

Free convection

Answer

Mixed convection

Question 35

In mixed convection heat transfer, how do the Grashof number (Gr) and Reynolds number (Re) determine the flow regime?

Accepted Answer

When Gr >> Re^2, the flow becomes laminar and buoyancy-driven.

Accepted Answer

When Re >> Gr^2, the flow becomes turbulent and momentum-driven.

Answer

The flow is always laminar regardless of Gr and Re values.

Answer

The flow is always turbulent regardless of Gr and Re values.

Question 36

In a heat exchanger, how does increasing the heat transfer surface area affect its ability to transfer heat?

Accepted Answer

Increases heat transfer rate

Answer

Decreases heat transfer rate

Answer

No effect on heat transfer rate

Question 37

Laminar flow in a pipe exhibits a parabolic velocity profile. What is the ratio of the maximum velocity to the average velocity for laminar flow in a pipe?

Accepted Answer

2.0

Answer

1.5

Answer

3.0

Answer

4.0

Question 38

The Nusselt number characterizes:

Accepted Answer

The ratio of convective to conductive heat transfer

Answer

The rate of heat transfer by convection

Answer

The thickness of the boundary layer

Answer

The temperature difference between the surface and the fluid

Question 39

Which parameter does NOT affect the convective heat transfer coefficient in circular pipe flow?

Accepted Answer

Surface roughness

Answer

Reynolds number

Answer

Prandtl number

Answer

Fluid viscosity

Question 40

Which type of convection heat transfer involves buoyancy-driven fluid motion?

Accepted Answer

Natural convection

Answer

Forced convection

Answer

Mixed convection

Answer

Condensation convection

Question 41

The boundary layer is characterized by:

Accepted Answer

Significant fluid velocity gradients

Answer

Zero fluid velocity

Answer

Constant fluid velocity

Answer

Constant fluid temperature

Question 42

Which common application utilizes natural convection heat transfer?

Accepted Answer

Heating a room with a radiator

Answer

Cooling electronic components

Answer

Boiling water in a kettle

Answer

Transferring heat in a nuclear reactor

Question 43

Where is the local heat transfer coefficient typically highest for fluid flowing over a heated surface?

Accepted Answer

Near the leading edge of the surface

Answer

Near the trailing edge of the surface

Answer

At the midpoint of the surface

Answer

Independent of the location on the surface

Question 44

Which technique is ineffective for enhancing heat transfer in convection?

Accepted Answer

Using a high-viscosity fluid

Answer

Enlarging the surface area of the heat transfer surface

Answer

Introducing turbulence into the flow

Answer

Swirling the flow

Question 45

In selecting a heat transfer correlation for convection heat transfer calculations, which factors are most critical to consider?

Accepted Answer

Flow geometry and fluid properties

Answer

Heat transfer mode and fluid properties

Answer

Flow geometry and heat transfer mode

Answer

Fluid properties and heat transfer mode

Question 46

Which of the following is NOT a recognized mode of convection heat transfer?

Accepted Answer

Radiation convection

Answer

Forced convection

Answer

Natural convection

Answer

Mixed convection

Question 47

Indicate the dimensionless group that characterizes forced convection:

Accepted Answer

Reynolds number

Answer

Nusselt number

Answer

Grashof number

Answer

Prandtl number

Question 48

Which of the following is NOT a viable technique to enhance convection heat transfer?

Accepted Answer

Reducing fluid velocity

Answer

Increasing surface area

Answer

Using fins or extended surfaces

Answer

Adding turbulence promoters

Question 49

The Rayleigh number is a dimensionless group primarily used to characterize:

Accepted Answer

Natural convection

Answer

Forced convection

Answer

Mixed convection

Answer

Condensation

Question 50

In natural convection heat transfer, how does the Grashof number influence buoyancy-driven flow and heat transfer rates?

Accepted Answer

A higher Grashof number typically indicates stronger buoyancy forces and increased heat transfer rates.

Answer

The Grashof number has no effect on buoyancy-driven flow.

Answer

The Grashof number only affects the flow pattern, not heat transfer rates.

Answer

The Grashof number is only relevant to forced convection heat transfer.

Question 51

Which of the following is NOT a challenge associated with numerical simulations of turbulent convection heat transfer?

Accepted Answer

Straightforward implementation and accurate results

Answer

High computational cost due to complex flow dynamics

Answer

Uncertainties from turbulence models

Answer

Determining convergence criteria for stability and accuracy

Question 52

The Nusselt number is a dimensionless parameter used to characterize what aspect of convection heat transfer?

Accepted Answer

Convection heat transfer coefficient

Answer

Thermal conductivity

Answer

Specific heat capacity

Answer

Fluid density

Question 53

In a forced convection heat transfer scenario, the heat transfer coefficient:

Accepted Answer

Increases with increasing fluid velocity

Answer

Is independent of fluid velocity

Answer

Decreases with increasing fluid velocity

Answer

Is constant for a given fluid and surface

Question 54

In natural convection heat transfer, the driving force is:

Accepted Answer

Density gradient

Answer

Pressure gradient

Answer

Temperature gradient

Answer

Velocity gradient

Question 55

In mixed convection heat transfer, the heat transfer coefficient:

Accepted Answer

Can be influenced by both forced and natural convection

Answer

Is always higher than in forced convection

Answer

Is always higher than in natural convection

Answer

Is independent of both forced and natural convection

Question 56

The Graetz number is a dimensionless parameter used to characterize:

Accepted Answer

Entrance region length in pipe flow

Answer

Thermal boundary layer thickness

Answer

Nusselt number

Answer

Prandtl number

Question 57

Which of the following factors does NOT affect the heat transfer coefficient in convection?

Accepted Answer

Presence of a magnetic field

Answer

Fluid properties

Answer

Surface geometry

Answer

Flow conditions

Question 58

In free convection, heat transfer occurs primarily due to:

Accepted Answer

Differences in density caused by temperature variations

Answer

Pressure gradients

Answer

Gravitational forces alone

Answer

External forces

Question 59

Which equation accurately represents Newton's law of cooling for forced convection?

Accepted Answer

Q = hA(T_s - T_∞)

Answer

Q = σAε(T_s^4 - T_∞^4)

Answer

Q = h(T_s - T_∞)/(L/k)

Answer

Q = kA(dT/dx)

Question 60

The Nusselt number (Nu) is a dimensionless parameter that characterizes:

Accepted Answer

The ratio of convective heat transfer to conductive heat transfer

Answer

The ratio of heat transfer rate to temperature difference

Answer

The ratio of surface area to volume

Answer

The ratio of fluid velocity to surface temperature

Question 61

Which factors primarily influence the convective heat transfer coefficient (h)?

Accepted Answer

Fluid properties, flow conditions, and surface geometry

Answer

Surface roughness alone

Answer

Fluid temperature alone

Question 62

Which of the following examples best represents a situation involving natural convection heat transfer?

Accepted Answer

Air rising from a heated surface

Answer

Heat transfer through a vacuum

Answer

Forced air cooling of an electronic device

Answer

Condensation on a cold window

Question 63

The Grashof number (Gr) is a dimensionless parameter primarily used to characterize:

Accepted Answer

Natural convection heat transfer

Answer

Forced convection heat transfer

Answer

Fluid flow

Answer

Radiative heat transfer

Question 64

For convection heat transfer problems, the boundary condition q'' = constant represents:

Accepted Answer

A constant heat flux at the surface

Answer

Zero temperature gradient at the surface

Answer

Zero second derivative of temperature at the surface

Answer

A constant surface temperature