Temperature control systems for autoclavable fermentors

For the temperature control of autoclavable fermentors, a double jacket integrated into a heating circuit is usually used, or an electric heating mat is placed around the single-walled glass vessel in combination with a cooling finger in the reactor vessel.

Both systems have their advantages and disadvantages.

Double jacket vessel with heating circuit

A glass double jacket vessel allows a gentle heat transfer due to the large heat exchange surface; steep temperature gradients, which can have an unfavourable effect on the cultivated organisms, are avoided. At the same time, the full view of the reactor is maintained through the uncovered double glass wall.

If, however, the double-walled vessel is autoclaved together with the medium (full sterilization), long heating and cooling times in the autoclave must be accepted, which can often lead to an intolerable change in the chemical composition of the nutrient medium.

An autoclavable reactor vessel with double jacket is therefore particularly suitable for cell culture applications that require gentle heating and cooling on the one hand and are where vessels are usually sterilized empty in the autoclave on the other hand, since the culture media for cell culture generally do not tolerate thermal sterilization at all.

Single wall vessel with heating mat and cooling finger

A glass vessel without a double jacket, which is heated with a heating mat and cooled with a cooling finger, can be sterilized together with the medium in a much shorter time in an autoclave, and the quality of the medium is significantly less impaired. This variant is also the most cost-effective. On the other hand, the use of a heating mat in combination with a cooling finger results in a smaller exchange surface for heating and cooling in particular and thus a less gentle heat transfer. Furthermore, the electric heating mat considerably impairs the view into the glass reactor.

Single-wall vessel with perfused baffles as heat exchanger and with heating circuit

Bioengineering AG offers a third solution for autoclavable glass fermentors, which combines various advantages especially for the cultivation of microorganisms. A glass vessel without a double jacket is equipped with hollow, perfused baffles that are connected to the heating circuit of the control column. The single-walled vessel enables short heating and cooling times during full sterilization in the autoclave. The hollow baffles inside the reactor vessel provide a heat transfer evenly distributed over a large surface. Heating and especially cooling and adjusting at a new temperature take considerably less time than with the other solutions. This is because, on the one hand, there is good heat transfer due to the large surface area of the steel wall of all four baffles and, on the other hand, because the total volume of the heating circuit is considerably smaller than with the double wall solution. At the same time, the full view of the glass wall into the reactor vessel is maintained, unimpeded by a heating jacket.

This solution without a heating jacket but with hollow baffles through which heating or cooling water flows has proven to be the best system for microbial applications in which the medium is to be sterilized together with the fermentor in an autoclave.