How to select heaters in thermoregulating units design

A new video on our Tempco YouTube channel is about the selection of electric heaters in thermoregulating units.
The range of Tempco’s Treg thermoregulating units enables to regulate the temperature of fluids employed in industrial processes, in a wide temperature range from -20° C up to +300°C. Depending on the temperature level required, the units work using different thermal fluids, such as glycol water, diathermic oil or silicon oils.

Electric heaters are employed to heat up the water or the oil, aimed to work as thermal vectors when other heat sources are not available, such as steam.

Their function is very delicate, as they have often to heat up fluids with significant thermal capacities, but at the same time they have to preserve to fluid to be heated. At this purpose, there are some critical temperature limits for the fluid that must not be surpassed. The value to consider is the surface temperature of the heater at its contact with the fluid.

Diathermic oil requires in particular lower surface temperatures of the heater, in order to avoid the cracking of the oil itself. When carbonized, the deteriorated oil creates a coating on the heater surface, lowering its thermal conductivity and heating efficiency, also leading to collateral effects such as the burn or short circuit of the heater.

Heaters must thus be sized according to a very low specific heat, that is watts dissipated by cm2, using specific charts during the design of thermoregulating units, in order to maintain heater’s surface temperature within the values allowed for the fluid employed. Temperature sensors are thus integrated inside the heaters, in direct contact with the external surface of the heating element checking its surface temperature, limiting the functioning when design limits are exceeded.

Heaters can have different shapes and be made in several materials, such as carbon steel, copper and stainless steel, according to the kind of fluid they are supposed to work with. In our Treg thermoregulating units we employ custom made cored heaters, with very low surface temperatures and specific heat.

A low specific heat requires a greater surface, meaning bigger heaters and higher costs in order to achieve the temperature needed. Nevertheless this measure ensure a longer service life for the heater, and therefore a longer service life of the thermoregulating unit, resulting in important savings in the long term.