Major components in these systems consist of the heater, heat exchanger, vented expansion tank, and circulating pump. The expansion tank need not have inert gas applied in these types of systems in order to keep positive pressure on the circulating pump. Pressurized liquid phase systems using both hot oils and synthetics are similar in design to non-pressurized systems except that inert gas is applied through the expansion tank when the required operating temperature of the heat transfer fluid is above its boiling range. The inert gas also acts as a buffer in the expansion tank between the hot fluid surface and the atmosphere, eliminating fluid oxidation. A simple vapor phase system can be designed using hydrostatic pressure to gravity return the condensate from the user to the vaporizer, eliminating the need for a condensate pump.
More complex systems require a flash tank, condensate return tank, and a condensate return pump.
The disadvantage of the added capital equipment cost and the complexity of vapor phase systems is offset by the increased BTUs delivered per pound of vapor versus liquid, and increased temperature control at the user- important in heat sensitive processes. Criteria For Selecting The Best Fluid Chemistry. If a existing system or a system on the design board is a vapor phase system and requires a high temperature fluid, the fluid options are extremely limited. Only a handful of high temperature vapor phase synthetic fluids are available from different heat transfer fluid manufacturers. Hot oils cannot be used in the vapor phase.