Extended Surfaces: Enhancing Heat Transfer in Mechanical Engineering

Question 1

Which type of extended surface is specifically designed to augment heat transfer from a cylindrical surface?

Accepted Answer

Annular fin

Answer

Pin fin

Answer

Plate fin

Answer

Integral fin

Question 2

The critical length of a fin is the length at which:

Accepted Answer

The fin becomes ineffective in enhancing heat transfer

Answer

The heat transfer rate reaches its maximum value

Answer

The temperature gradient along the fin becomes zero

Answer

The fin material experiences melting

Question 3

In a pin fin, the location where the heat transfer rate is highest is at the:

Accepted Answer

Base of the fin

Answer

Tip of the fin

Answer

Middle of the fin

Answer

Heat transfer rate is uniform along the fin

Question 4

The primary purpose of a heat sink is to:

Accepted Answer

Enhance heat transfer away from a surface

Answer

Reduce heat transfer away from a surface

Answer

Control the temperature of a surface

Answer

Improve the efficiency of a heat engine

Question 5

In an extended surface, which heat transfer mode is dominant?

Accepted Answer

A combination of convection and conduction

Answer

Convection

Answer

Conduction

Answer

Radiation

Question 6

Which analytical method is commonly used to solve for extended surface temperature distributions?

Accepted Answer

Method of separation of variables

Answer

Method of superposition

Answer

Numerical methods

Answer

Experimental methods

Question 7

What is the characteristic dimensionless parameter for extended surfaces?

Accepted Answer

Biot number

Answer

Nusselt number

Answer

Reynolds number

Answer

Prandtl number

Question 8

The primary purpose of extended surfaces is to:

Accepted Answer

Enhance heat transfer by increasing surface area

Answer

Reduce pressure drop

Answer

Improve fluid flow

Answer

Increase structural rigidity

Question 9

To evaluate the performance of an extended surface, which parameters are typically used?

Accepted Answer

Both effectiveness and fin efficiency

Answer

Effectiveness

Answer

Fin efficiency

Answer

Heat transfer rate

Question 10

In a fin with constant cross-sectional area, the heat transfer rate generally:

Accepted Answer

Is maximum at the base and gradually decreases towards the tip

Answer

Remains constant along the fin

Answer

Is minimum at the base and gradually increases towards the tip

Answer

Varies sinusoidally along the fin's length

Question 11

The effectiveness of a fin, denoted as η_f, is a dimensionless parameter that represents the ratio of:

Accepted Answer

Actual heat transfer rate to the maximum possible heat transfer rate

Answer

Maximum possible heat transfer rate to the actual heat transfer rate

Answer

Fin surface area to the base area

Answer

Fin length to the base diameter

Question 12

Which material is commonly preferred for high-performance heat sinks due to its excellent thermal conductivity?

Accepted Answer

Copper

Answer

Aluminum

Answer

Stainless steel

Answer

Plastic

Question 13

In the design of an extended surface, such as a fin or heat sink, which of the following parameters is typically NOT a primary consideration?

Accepted Answer

Aesthetics and visual appeal

Answer

Heat transfer rate enhancement

Answer

Pressure drop across the device

Answer

Cost of manufacturing and materials

Question 14

How does the thermal conductivity of the base surface affect the heat transfer performance of an extended surface?

Accepted Answer

Higher thermal conductivity of the base surface enhances heat transfer from the base to the extended surface.

Answer

Increased thermal conductivity of the base surface reduces heat loss from the extended surface to the surroundings.

Answer

Higher thermal conductivity of the base surface leads to an increase in the extended surface area.

Answer

The thermal conductivity of the base surface has no influence on the performance of the extended surface.

Question 15

Compare the advantages and disadvantages of using multiple extended surfaces in an application versus a single, larger extended surface.

Accepted Answer

Multiple extended surfaces provide a larger overall surface area for heat transfer, leading to higher heat transfer rates.

Accepted Answer

Using multiple extended surfaces can result in a more uniform temperature distribution, reducing thermal stresses.

Accepted Answer

Multiple extended surfaces are often easier to manufacture and assemble, potentially reducing production costs.

Answer

A single, larger extended surface is always more efficient and cost-effective than multiple smaller surfaces.

Question 16

How does the cross-sectional shape of an extended surface affect its heat transfer performance?

Accepted Answer

It significantly influences the surface area and thermal conductivity, impacting heat transfer effectiveness.

Answer

It has a negligible impact on heat transfer performance.

Answer

Only specific shapes, like circular or rectangular, significantly affect heat transfer effectiveness.

Question 17

Which of the following is NOT a type of extended surface?

Accepted Answer

Plane surface

Answer

Fin

Answer

Answer

Tube

Question 18

What is the main purpose of using extended surfaces in heat transfer?

Accepted Answer

To enhance heat dissipation by increasing surface area.

Answer

To increase heat transfer coefficient.

Answer

To reduce thermal resistance.

Answer

To improve fluid flow characteristics.

Question 19

What is fin effectiveness?

Accepted Answer

A measure of the heat transfer performance of a fin relative to an ideal fin without heat loss from the fin tip.

Answer

The ratio of the fin length to the fin thickness.

Answer

The ratio of the heat transfer coefficient at the fin base to the heat transfer coefficient at the fin tip.

Question 20

What is the condition for the optimal fin spacing in a fin array?

Accepted Answer

When the heat transfer rate per unit volume of the array is maximized.

Answer

When the fin efficiency is maximized.

Answer

When the pressure drop across the array is minimized.

Question 21

What is the primary purpose of a heat sink in an electronic device?

Accepted Answer

To dissipate heat generated by electronic components.

Answer

To increase the electrical conductivity of the device.

Answer

To improve the device's aesthetics

Question 22

Which of the following materials is commonly used for extended surfaces in heat exchangers?

Accepted Answer

Copper

Answer

Wood

Answer

Plastic

Answer

Rubber

Question 23

What is the effect of increasing the fin length on the heat transfer rate of an extended surface?

Accepted Answer

Increases heat transfer rate up to a certain point, after which it becomes less significant.

Answer

Decreases the heat transfer rate

Answer

Does not affect the heat transfer rate

Answer

Depends on the fluid temperature