Heatsink may not be the best description for the heaters. They are composed of formed alumina silicate and have grooves for the nichrome wire. On the side that does not connect with the vessel, there is also a layer of some mettalic alloy with fins, but in practice the entire unit is covered in insulation, so it's ability to act as a heatsink in practice is minimal.
We are shipped different vessels periodically, as our work by nature is experimental.
In the past, we were using off the shelf PLCs manufactured by a company called Eurotherm with basic PID capabilities. There was a separate controller for each set of 6 that would control the others, but these only gave us the ability to put in a set point and a ramp to reach that set point and did not have the ability to program in an entire run with the hold time and ramp down. These, as well, used the pause method for syncing together.
The solenoids we use are manufactured by Albright and are sometimes called contactors.