How can I choose between Unistats and open bath circulators?

Unistats are technologically advanced circulators from Huber.  Open bath units are a more traditional design.

Generally, Unistats are recommended for more demanding reactor applications (e.g. rapid cooling/heating required, large exothermic reaction to control, large vessel volume, or very low/high temperatures required), while bath units are a lower cost alternative for less demanding reactor applications.  (Of course, if you want to put objects into a bath rather than temperature control a jacketed reactor, you will need a bath unit!)

Some key differences between the Unistats and baths are as follows:

Huber Unistats

• Small internal volume – faster temperature change possible, as less oil in the circulator to heat/cool.
• Plate heat exchangers compared to coil heat exchangers – more efficient heat transfer, so again, faster heating/cooling.
• Thermal fluid (oil) isn’t exposed to air at very high or low temperatures – longer lifetime of oil, and can use it at a wider temperature range than in open baths.
• Integrated expansion tank to allow for oil expansion under heating and contraction under cooling.  Additional expansion tank can be added for further space for drain-down of a reactor.
• Have Pilot ONE controllers with the highest level (E-grade) of software – ‘Professional’.
• Cannot use water-glycol as thermal fluid (only oil).
• Higher cost.

• Slower heating/cooling per kW as larger internal volume so more oil to be heated/cooled (the temperature change you want in the vessel’s jacket must take place for the oil in the bath too) and coil heat exchanger used rather than plate heat exchanger.
• The bath is open to atmosphere (oxygen and water vapour).  At high temperatures, oil (if used as thermal fluid) can be degraded through its reaction with the air, and vapours are given off (which smell).  At low temperatures, moisture absorbed into the thermal fluid means ice can form on the refrigerator coil and ice crystals can form in the fluid.
• Lower maximum temperature of oils – should not be used above flash point.
• No expansion tank; take care not to overflow bath.
• Huber open baths may have only a basic controller.  Huber bath units with a Pilot ONE controller have the lowest level (E-grade) of software as standard – ‘Basic’.
• Can use water-glycol as thermal fluid, as an alternative to oil.
• Lower cost.
• N.B. Some issues can be minimised and performance improved by purchasing a displacement insert and/or a software upgrade – please see separate FAQ entries for more information.  Please note, these options are not available for all models.