The fluid that circulates between the seals is called barrier fluid if it is higher than stuffing box pressure. It is called buffer fluid if it is lower than stuffing box pressure. Insulated piping coming from the top of the gland to the convection tank, and finned piping coming out of the tank will aid convection if heat removal is a problem. A pumping ring can be installed between the seals for those instances where natural convection is not sufficient to remove the heat being generated between the faces. This is very necessary when oil is used as the barrier fluid.
Oil has a low specific heat and poor conductivity, making it a poor choice as a barrier fluid.
Most of the newer cartridge dual seals come equipped with a built in pumping ring. Introducing the fluid between the seals, from an external source. Be sure to bring the fluid in at the bottom of the gland and out the top to prevent an air pocket from forming in the gland. You should be aware that a stationary version is also available from any of the major seal companies. Two way balance is always desirable in any dual seal application to allow you the option of using either a high or low pressure barrier fluid and to prevent the seal faces from opening if either the system or the barrier fluid pressure fluctuates.