Articles about thermal fluid systems often start with a variation of the statement that “thermal fluid systems typically require little ongoing maintenance for the first few years of operation” and then go on to extol the various advantages of indirect thermal-fluid process heating over competitive heating methods, such as direct heat, steam and so on. The corollary to that statement, however, is that by the time there is a problem, the operating personnel that were trained on the system have moved on, been excessed or promoted. As a result, when things do go wrong, the guessing begins. And, unless there is an obvious cause like a geyser from the expansion-tank vent or a pump that sounds like it’s moving ball bearings, someone will likely blame the thermal fluid for the problem. There are several problems that seem to occur with some frequency. This article reviews a number of real examples and describes how the symptoms can be misinterpreted. The suspected fluid properties and the testing procedures necessary to determine which of the fluid properties (if any) is responsible for the problem are examined. Finally, recommended corrective actions are proposed. 

The following is an example, Illustrate Fluid can not be real culprit to reduce throughput in a continuous convection oven.

EXAMPLE:  A poultry processor was experiencing reduced throughput in a continuous convection oven. The heater and pumps were checked for problems, and all temperature and pressure sensors were replaced. Someone suggested cleaning the heat-transfer fluid system. Since the fluid had been in service for a number of years, it was assumed to have degraded and formed blockages in the coils because the temperature drop across the heat exchanger was much lower than when the unit was new. The fact that the fluid had been tested routinely and found to be in good condition was totally ignored in the evaluation. Management personnel wanted to clean the system and then change the heat transfer fluid. A lube-oil additivetype cleaner was added to the system with the expectation that the problem would be solved. When there was no progress, a thermal-fluid sample kit was requested along with a request to estimate the cost of replacement fluid. Once again the viscosity of the sample was found to be well within the normal range. The plant manager was very disappointed with the results showing that the fluid was not the problem, because he had to send the maintenance staff back in to keep looking for the real culprit. Eventually it was discovered that an air damper inside the oven had a broken weld that allowed it to flip up into the air stream, effectively blocking the coils. Throughput was reduced because insufficient heat was getting to that section of the oven.