recirculation

Recirculation is the process of circulating a portion of a system's output back into its input, creating a loop. This feedback can be used to control temperature, concentration, flow, or quality of the material being processed.

In engineering and process systems, recirculation enhances mixing, improves heat transfer, and stabilizes conditions. It can reduce fuel or water consumption by reusing energy or resources, but it can also concentrate contaminants if not properly filtered.

In heating, ventilation, and air conditioning (HVAC), recirculated indoor air is mixed with outdoor air to maintain temperature and air quality more efficiently. Filters and sensors limit pollutants and adjust outdoor air proportion.

Automotive exhaust gas recirculation (EGR) sends a portion of exhaust gas back into the intake to lower combustion temperatures and reduce nitrogen oxide emissions.

Recirculating aquaculture systems (RAS) treat and reuse water through filtration, biofiltration, disinfection, and aeration, enabling high-density fish production with reduced water use.

In medicine and biology, enterohepatic or gastrointestinal recirculation describes the cycling of substances such as bile acids, drugs, or nutrients between organs via the blood and digestive tract. In hemodialysis, recirculation can refer to a problem where dialyzed blood returns to the circuit, lowering efficiency.

Safety and design considerations include ensuring adequate filtration, preventing stagnation, maintaining appropriate pressure, and monitoring for contamination or buildup of byproducts.