Counter-convection vapor control system

A vapor phase processing system comprising:

• a vessel containing a processing vapor zone and a central opening in the top walls of the vessel by which a work product is introduced into and removed from the processing vapor and through which the vapor produced by the processing vapor zone tends to flow upwardly by convection;
• first means centrally disposed within the vessel above the processing vapor zone and spaced from the confronting vessel side walls and including one or more inner walls defining a central vertical channel in the vessel in communication with the vessel opening, and one or more outer surfaces spaced from the confronting vessel side walls and defining with the vessel top walls a peripheral space substantially not in communication with the opening;
• and
• second means associated with said first means for establishing a temperature differential within the vessel above the processing vapor zone to cause a flow which is upward in the peripheral space and downward in the central channel, said downward flow providing a counter-convection flow which opposes the upward convection flow of the vapor from the vapor zone through the vapor channel and toward the vessel opening.

In a vapor phase processing system of the type wherein an open top tank has therein a preselected process fluid in both liquid phase and vapor phase, and wherein said fluid in vapor phase tends to flow out of the open top of the tank by convection through a central spatial region of said tank in a first upward direction;

• vapor phase control apparatus for preventing the exit of said fluid in said vapor phase through the open top, comprising:
• first means for producing a flow of said fluid in said vapor phase in a second direction generally parallel to said first direction and through a peripheral spatial region between the walls of said tank and said central spatial region;
• and
• second means cooperative with said first means for diverting the flow of said fluid in said vapor phase in said second direction to a flow in a third direction generally opposite said first direction and through said central spatial region of said tank;
• whereby a downward counter-flow of said fluid in said vapor phase is produced which opposes the upward flow of said fluid in said vapor phase to prevent the exit of said fluid in said vapor phase from the open top of the tank.