Throughout the life of your organization you have developed rules, processes and procedures, implemented to help avoid the pitfalls and pratfalls you’ve encountered along the way. These rules are clear, vital, and mandatory – until they aren’t…
In our first two segments in this series, we discussed the importance of controlling your fluid dispensing process at the point of application and set down the rules for the implementation of a proper “temperature control envelope” at your point of dispense (click here if you missed either of them or would like to review). In this segment, we’ll examine those situations where, in addition to the point of application, temperature control is required in other areas of your process to combat system-generated issues.
In any fluid dispensing system, controlling fluid temperature at the point of application is always a requirement. The temperature-viscosity relationship is intractable, and its influence on the dispensing outcome is unwaveringly based in physics, so the rule always holds true. But, like any rule, followed blindly, it can lead you to believe you have solved all of your temperature-based problems. Sometimes, your system needs more.
Central Supply Systems
The fact is that some fluid dispensing systems are really a combination of multiple systems or stages, each with their own unique requirements that must be addressed. The most common is found when you have multiple dispensing locations across a factory – all supplied by a central distribution system. In these instances, your distribution system presents a separate set of issues and therefore requires you to take a different approach.
Often these distribution systems convey the fluid over long distances at elevated pressures and/or flow rates. This requires the pumping stages to add a great deal of energy into the system – and the addition of energy to a fluid always manifests itself as heat.
Some central supply systems recirculate. This is common for “suspensions” or fluids where the solids can settle out if left to sit for any length of time. Paints and coatings are typical examples. Recirculation agitates these fluids, keeping the solids in suspension, but on each additional pass through the pumping stage, the fluid picks up more heat. Unfortunately, fluids of this type can be damaged by this heat build-up; therefore, measures must be taken to protect these delicate fluids from damage that can cause them to perform poorly, even when passed to the best of dispensing systems.
Even distribution systems that do not recirculate – often called “dead-end” systems – can be negatively affected by changes in temperature. While these systems generally do not create the heat build-up encountered in recirculating systems, their performance can be seriously affected by variations in ambient temperature.
Often, these systems are used to convey high-viscosity fluids like sealers or adhesives, which have very steep viscosity vs. temperature curves. As a result, the changes in viscosity caused by relatively small changes in temperature can have a large impact on the pressure drop over the length of the system. Even when placed at the point of application, most regulators have a well-defined range of input pressures over which they can maintain a given output, and if this range is exceeded by the varying pressure drop produced by normal daily or seasonal ambient temperature variations, even the best of dispensing systems will perform erratically.
Another interesting phenomenon is that the low thermal conductivities of viscous fluids often result in a lag between the normal ambient temperature cycles and the temperature of the fluid reaching critical pressure drop points. This causes the problems to appear “out-of-sync” with the ambient cycle, thus masking it from consideration as a root-cause.
The Overlooked Parameter
Clearly, temperature is a critical parameter in the control of any fluid dispensing system, but one that is often overlooked. The key to success is the careful thermal analysis of all points in each dispensing system, over time, to assure that the fluid is both well-protected and properly controlled.