A thermal immersion circulator is an electrically powered device that circulates and heats a warm fluid kept at an accurate and stable temperature. It is used in process, environmental, microbiological, hazardous waste, and other laboratories. Since the late twentieth century they have also been used for sous vide food cooking (prolonged cooking of food in sealed packages in a water bath at lower temperatures than usually used for cooking).
A thermal immersion circulator comprises a circulator pump (a mechanism to move the fluid), a heating element immersed in the fluid, an accurate temperature probe, and control circuitry which compares the measured temperature with the desired value and supplies power to the heater as required to stabilise the temperature.
It has been recommended that second-hand laboratory circulators should not be used for food, or in a kitchen, due to the risk of contamination, as chemical residues cannot be completely removed. A food-grade, rather than laboratory, circulator is advised, even if unused.