Heat Exchangers MCQs

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Questions and Answers

What is the major mode of heat transfer in a double pipe heat exchanger?

Convection

Both convection and conduction (correct)

Radiation

Conduction

When is a double pipe heat exchanger commonly used?

When space is limited

When a large heat transfer area is required

When a small heat transfer area is sufficient (correct)

When the budget is low

What type of flow arrangement is characterized by hot and cold fluids entering at opposite ends of a heat exchanger?

Cross-flow

Counter-flow (correct)

Parallel-flow

Multiple-flow

What is the purpose of logarithmic mean temperature difference in a heat exchanger?

To find the temperature driving force for heat transfer Signup and view all the answers

What is the definition of the heat transfer coefficient?

Heat transferred per unit area per kelvin Signup and view all the answers

Why is counter-flow direction preferred over parallel flow in a double pipe heat exchanger?

It ensures a constant wall temperature Signup and view all the answers

What happens when the logarithmic mean temperature difference is zero?

No further heat transfer is possible Signup and view all the answers

Which flow arrangement is characterized by both hot and cold fluids entering and leaving the heat exchanger at the same end?

Co-current flow Signup and view all the answers

Which of the following statements accurately describes the heat transfer coefficient on the gas side of a double pipe heat exchanger?

The gas side has a low heat transfer coefficient because of its low density and viscosity. Signup and view all the answers

What is the primary reason for using extended fins on the gas side of a double pipe heat exchanger?

To increase the surface area for heat transfer. Signup and view all the answers

What is the relationship between the logarithmic mean temperature difference (LMTD) and the heat transfer rate in a double pipe heat exchanger?

The heat transfer rate is directly proportional to the LMTD. Signup and view all the answers

Which of the following scenarios would result in a zero LMTD in a double pipe heat exchanger?

When the hot and cold fluids have equal inlet temperatures. Signup and view all the answers

What is the primary function of the separating wall in a double pipe heat exchanger?

To act as a heat transfer medium between the hot and cold fluids. Signup and view all the answers

In a double pipe heat exchanger, what type of heat transfer occurs between the fluid and the wall of the pipe?

Conduction and convection. Signup and view all the answers

What is the main difference between co-current and counter-current flow in a double pipe heat exchanger?

The direction of flow of the hot and cold fluids. Signup and view all the answers

Which of the following is NOT a benefit of using a double pipe heat exchanger?

Suitable for high-pressure applications. Signup and view all the answers

Study Notes

Heat Transfer in Double Pipe Heat Exchangers

Major mean of heat transfer in a double pipe heat exchanger is convection and conduction.
Double pipe heat exchangers are used when heat transfer area required is very low.

Flow Arrangements in Heat Exchangers

Hot and cold fluids enter at the same end of a heat exchanger, which is the definition of parallel-flow.
In co-current flow, both hot and cold streams enter the heat exchanger at one end, and leave at the opposite end.
In counter-current flow, the streams enter at opposite ends of the heat exchanger.

Logarithmic Mean Temperature Difference (LMTD)

LMTD is used to determine the temperature driving force for heat transfer in flow systems.
When LMTD is zero, no further heat transfer is possible.

Heat Transfer Coefficient

Heat transfer coefficient is defined as heat transferred per unit area per kelvin.

Convection and Conduction in Double Pipe Heat Exchangers

Convection occurs when fluid is in a constant uniform motion inside the pipes, which increases the overall bulk temperature of the fluid.
Conduction occurs when the separating wall carries heat from the hot fluid to the cold fluid through conduction.

Advantages of Counter-Flow Direction

Counter-flow direction is better for the application of constant wall temperature in double pipe heat exchanger compared to co-current flow direction, as it experiences varying temperatures.

Characteristics of Double Pipe Heat Exchangers

Double pipe heat exchangers are used when heat transfer area required is very low.
They occupy a small area and are inexpensive.

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Description

Multiple choice questions on heat exchangers, including types, heat transfer methods, and flow arrangements. Test your knowledge on heat exchangers and their applications.