The presence of free water in a heat transfer system can cause volatility problems such as two-phase flow, pump cavitation and excessive pressurization, especially during system startups. Acids usually are formed in heat transfer fluid from contamination from material outside the system. Acids usually are formed in heat transfer fluid from contamination from material outside the system. Acid number increase usually is associated with open vent expansion tank operation, heat transfer fluid oxidation or heat transfer fluid degradation, producing weak acids. Process material containing oxidizing agents can contribute strong or weak acids.
Acids are harmful in two ways.
First, acids tend to accelerate the molecular breakdown of the heat transfer fluid. Secondly, they tend to form insoluble solids that accelerate mechanical deterioration of seals, valves, pumps, etc. Most heat transfer fluids have an initial total acid number at 0.00 to 0.10. Coke and sludge can adversely affect a system's heat transfer efficiency by heat transfer surface fouling. High and Low Boilers High and low boilers are formed when heat transfer fluids are heated to a high temperature and certain molecular bonds begin to break or thermally degrade.