Brief description

A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact.

Use / Function

Refrigeration and Air Conditioning: Transferring heat from a cooled space to the outside environment. See Mechanical Refrigeration.
Power Plants: Condensing steam back into water or preheating water for a Boiler.
Internal Combustion Engines: Removing excess heat from the engine block via a radiator. See Internal Combustion Engine.
Chemical Processing: Controlling the temperature of chemical reactions.
Distillation: Cooling vapors to condense them back into liquid. See Distillation.

Operating principle

Heat exchangers work by providing a large surface area for heat to move from a hotter fluid to a cooler one, typically through a conductive material like metal.

Conduction: Heat moves through the walls of the tubes or plates separating the fluids.
Convection: Heat is carried away from the surface by the flow of the fluids.
Flow Patterns:
- Parallel Flow: Both fluids move in the same direction.
- Counter-Flow: Fluids move in opposite directions (most efficient for heat transfer).
- Cross-Flow: Fluids move perpendicular to each other (common in radiators).

How to create it

1. Shell and Tube (Most common industrial type)

Construct a large outer cylinder (the shell).
Place a bundle of smaller tubes inside the shell.
One fluid flows through the tubes, while the other flows around them inside the shell.

2. Plate Heat Exchanger

Stack several thin metal plates with spaces between them.
Fluids flow through alternating spaces, allowing for a massive surface area in a compact volume.

3. Finned Tube (Radiator style)

Attach thin metal fins to the outside of a pipe.
As fluid flows through the pipe, a fan or natural air current blows across the fins, rapidly removing heat.

Materials needed

Highly Conductive Metals: Copper and Aluminum are best for heat transfer.
Corrosion-Resistant Metals: Steel or Stainless Steel for high pressure or corrosive fluids.
Seals and Gaskets: To prevent leaks between the two fluid paths.

Variants and improvements

Radiator: A specific type of heat exchanger designed to cool a liquid using air.
Condenser: Designed to change a gas into a liquid by removing heat.
Evaporator: Designed to change a liquid into a gas by adding heat.

Limits and risks

Fouling: Accumulation of scale, rust, or biological matter on the surfaces, which reduces efficiency.
Corrosion: Fluids can eat away at the metal walls, leading to leaks and mixing.
Thermal Stress: Rapid temperature changes can cause the metal to expand or contract, potentially cracking the structure.
Pressure Drop: Pushing fluid through narrow tubes or spaces requires significant pumping power.