What Is Duplex Pipe?
A duplex pipe is a type of tubing that consists of concentric inner and outer tubes of different diameters. This dual-tube design safeguards against flow loss from inner tube damage and facilitates the heat exchange between liquids and gases flowing within the inner tube. Certain designs allow for absorbing external air fluctuations by securing the inner and outer tubes in distinct manners.
Applications of Duplex Pipe
1. Environmental Preservation Applications
The outer tube is designed to protect the inner tube from damage and fluid loss, thereby preventing environmental contamination.
2. Heat Exchanger Applications
Duplex pipes are commonly used in heat exchangers, facilitating heat transfer between the gas or liquid in the inner tube and the fluid in the outer tube. Their design minimizes fluid clogging and allows for a compact configuration by coiling the tubes. Duplex pipes support both parallel and counter flow, with enhanced performance achievable by adding fins to the inner or outer surfaces of the tubes. In refrigeration cycle heat exchangers, fins are often added to the waterside to improve heat transfer efficiency significantly.
3. Double-Piping Applications
An everyday use is in bathtub hot water systems, where hot water circulates between the heater and the tub through the gap between the pipes. This design is also employed in the air supply and exhaust for FF heaters, using the outer pipe for intake and the inner pipe for exhaust, demonstrating its utility in wall penetrations and HVAC ducts.
4. Double-Wall Construction Applications
The duplex pipe’s double-wall configuration, with no space between the tightly sealed inner and outer tubes, is ideal for environments with differing corrosion conditions between the tubes. This construction is utilized in thermal power condensers, as well as heat exchangers in refining and petrochemical plants, combining materials like carbon steel, brass, and stainless steel for cost efficiency and corrosion resistance.
5. Medical Applications
Duplex pipes are utilized in medical tracheostomies for both inhalation and exhalation processes.
6. Civil Engineering Applications
These pipes are employed to transport two different chemicals that combine at the endpoint to condition-specific soil areas.
Principle of Duplex Pipe
The features and capabilities of duplex pipes vary with the material combination of the inner and outer tubes. Utilizing materials with high heat conductivity for both tubes enables their use as efficient heat exchangers. Transparent outer tubes allow quick detection of inner tube issues, while strong, clear materials can prevent cracks and leaks. Such combinations are particularly valuable in applications requiring high reliability, like automotive piping. Transparent materials also facilitate constant monitoring of the water level within the pipes, and nozzle-shaped ends enable applications such as sprayers.
Other Information on Duplex Pipe
1. Hazardous Substances Designation
Substances such as cadmium, cyanide compounds, organic phosphorus compounds like parathion, lead, hexavalent chromium compounds, arsenic, mercury and its compounds, polychlorinated biphenyls, and trichloroethylene fall under the category of hazardous substances.
2. Use of Duplex Pipe
Duplex pipes offer a straightforward and cost-effective solution for complying with these regulations. Their use in hazardous substance piping allows for visual inspection and immediate detection of leaks, especially when the outer tube is transparent. This applies to the pipe’s main body, as well as fittings, flanges, valves, and pumps through which hazardous substances flow.