Heat exchanger

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Typically, heat exchangers are used to allow heat from liquids or gases to pass to other liquids or gases, without the two coming into direct contact. Essentially they transfer the heat without transferring the fluid that carries the heat.

Heat exchanges are often used as part of heating, cooling or heat recovery systems.

Heat exchange devices can be used in a number of processes, including:

• Air conditioning systems.
• Radiators.
• Refrigeration.
• Heat pumps.
• Heat recovery ventilation.
• Waste water treatment.
• Nuclear and power plants.
• Machinery and engines.
• Specialist energy-saving devices such as energy-efficient showers.

The two most common types of heat exchangers are the 'shell and tube' and 'plate' or 'fin':

• In shell and tube heat exchangers, one fluid flows through a series of metal tubes within a sealed unit while another fluid passes between the tubes. The two fluids can flow in the same direction which is called parallel flow, in opposite directions, known as counter flow or counter current, or they can flow at right angles, known as cross flow.
• Plate or fin heat exchangers consist of metal fins with large surface areas that air passes around. This more open construction can allow easier inspection, cleaning and disassembly. This system is often used for chilled beams or integrated service modules.

Variations on these basic types include; plate heat exchangers, double pipe heat exchangers, pillow heat exchangers and so on.

Earth-to-air heat exchangers draw ventilation supply air through buried ducts or tubes. As the temperature of the ground below 3m is practically constant, it substantially reduces ambient air temperature fluctuations and can provide space conditioning throughout the year, with the incoming air being heated in the winter and cooled in the summer.

The appropriate heat exchanger can be selected by consideration of:

• Space availability.
• The heat carrying mediums.
• Fluid flow capacity.
• Pressure limits.
• Temperature ranges.
• Thermal performance requirements.
• Requirements for maintenance and repair.

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[edit] Related articles on Designing Buildings Wiki

• Absorption heat pump.
• Air conditioning.
• Air source heat pumps.
• Chilled beams.
• Coefficient of Performance CoP.
• Earth-to-air heat exchangers.
• Geothermal pile foundations.
• Ground energy options.
• Ground source heat pumps.
• Heat pump.
• Heat recovery.
• Integrated service module.
• Refrigeration.
• Thermal labyrinths.
• Water source heat pumps.