Phase Change Heat Transfer Materials and Methodology
Reclaiming Terpene Losses
By: Clancy Callaghan, Mechanical Engineer
This paper considers two methods used to condense terpenes and other Volatile Organic Compounds (VOC’s) from vapor to liquid in an effort to reclaim or “trap” them.
Condensing terpene vapors to liquid can be achieved by removing heat from the terpene molecules until they change phase from vapor to liquid (i.e. reach their Dew Point).
To remove heat from the molecules it is necessary to transfer the heat to another material. This task becomes more challenging when under vacuum which requires even colder temperatures than it would otherwise.
An additional obstacle to consider, is the chemical-compatibility of the materials used in-contact with the VOC’s. When trapping terpenes it is crucial that we preserve their natural unadulterated properties. The substances being collected are highly sought after, valuable, and frequently used for medical purposes.
There are three modes of heat transfer to consider; convection, conduction, and radiation.
Convection is not an option when operating at vacuum pressures since there are so few molecules there is no opportunity for organized flow.
Most cold traps and cold fingers have large cylindrical shapes that rely on radiation as the principle mode of heat transfer. This is due mainly to the manufacturing restrictions involved with using glass as the condensing surface. Glass is classified as an insulator and internal surfaces rarely attain advertised temperatures. The idea of the large cylindrical vessel is that the vapor will spend more time in the larger volume, and lose heat during this time via radiation. Because the vessels are typically large and smooth geometric shapes the molecules rarely engage any surface and therefore conduction plays a minimal role in heat transfer.
The CF-1000 relies on conduction as the principle mode of heat transfer, and then radiation as secondary. Because the unit’s condenser is made from high grade aluminum, which is 145 times more thermally conductive than glass, its surface reaches its low condensing temperature much faster than glass. Aluminum can retain a more uniform temperature that can quickly and continuously remove heat.
The CF-1000’s condenser also has a dynamic flow design that "confuses" the vapor particles, forcing the molecules to make maximum contact with the sub-zero surfaces until they lose enough energy to condense. Each time a molecule makes contact with a surface, some of its energy/heat is directly absorbed to the surrounding surface via conduction.
In addition to removing heat from the terpenes via conduction, the CF-1000 also removes heat from the molecules by absorbing the emission of electromagnetic waves (i.e. thermal radiation).
To take harvesting terpenes a step further, the CF-1000’s aluminum condenser surface is coated with a thin Teflon film that offers two distinct advantages over glass cold traps; its hydrophobic and chemical properties.
The hydrophobic or “non stick” properties of Teflon assist the accumulated liquid terpenes down to the terpene collection chamber at the bottom of the unit. The specialized hydrophobic coating is also more chemically inert than glass and is the coating of choice for medical equipment across the board.