Let’s talk heat transfer liquids and systems
Heat is essential to mankind’s well-being. It is also an essential component for all types of industrial processes, including aging, annealing, bonding, cooking, curing, distilling, drying, melting, reacting, and softening. Some specific applications are petroleum refining, pharmaceuticals, asphalt for use on roads, roofing tar, making felt and linoleum, bakeries, candy making, cardboard box manufacture, chemicals, dairies, food processing, furniture manufacture production, plastic extruding, molding and laminating, rubber curing, resin and varnish production, textile processing and finishing, and vegetable oil processing. The list keeps growing…and so does the use of Viking pumps to handle heat transfer liquids (HTLs).
Old and new methods
Up until World War II, the primary methods of providing heat for such processes were either through direct fire or indirect transfer via vapor. These methods, however, could not keep up with modern processing requirements for higher temperatures and safety regulations; as well as business demands to do things faster, better, and cheaper. Nowadays, the method of choice is an indirect transfer system with a liquid that provides:
- Even heat
- Quick temperature response
- Efficient heat transfer
This solution also has the following advantages:
- Non-corrosive to common materials of construction
- Stable over the operating range
- Easy to pump and seal
- A pour point below ambient temperatures
- A vapor pressure below atmospheric at 700°F
Commonly used liquids
While there are several liquids (or mixtures) suited for indirect heat transfer systems, the major HTLs are modified terphenyls, diphenyl-diphenyl oxide mixtures, mineral oils, and polyalkylene glycols. Each of these have different physical properties and should be selected based on their maximum recommended operating temperature, vapor pressure, boiling point, etc.
Heat transfer systems
We define the main function a heat transfer system as follows: to deliver heat, in the form of a hot liquid, in varying amounts, at a precise temperature, from a heat source to a "user" incorporated in the system.
Heat transfer systems vary widely in size, from self-contained packages taking up only a few cubic feet of space and delivering a few thousand BTUs with a liquid flow rate of from 5 to 10 GPM, to systems the size of a small power plant with several million BTU heat transfer rate with flows in the 10,000 GPM and up range. Regardless of size, most systems in use today include the following items: heater, heat user(s), expansion tank, controls, piping, and the pump. Some include additional items, such as heat exchangers, storage tanks, etc.
Large versus small systems
For the larger systems (120 GPM circulation and up), centrifugal pumps are generally used. Large systems are normally designed for a given application; thus, the various pieces of equipment, including the pump, can be selected for a specific set of conditions. Some larger systems incorporate an additional positive displacement pump in their start-up cycle to bring the system up to a temperature where the viscosity is low enough, so that the centrifugal can handle it easily.
For smaller systems, furnished as a packaged unit by fabricators, a positive displacement rotary pump is often used, since it can:
- Maintain a relatively constant flow rate with varying head or discharge pressures
- Be used with systems intended for a variety of services, liquids, and pressures
- Vary flow rate by simply changing the speed (Note: Most pumps are either gear reducer or V-belt driven; to change the flow rate, you must change the reducer ratio or the sheave size.)
- Be used for cold starts (Depending on the particular liquid and the ambient temperature, viscosity may get up to 5,000 SSU.)
- Reverse flow through the pump by reversing direction of rotation (This facilitates draining the system or removing the oil from a user during a changeover, e.g., changing dies.)
- Provide longer seal life and reduced seal problems due to slower shaft speed
Selecting a heavy-duty pump
Normally being tied in with processing or production of some kind, the duty cycle of an HTL system often runs from 40 hours per week to continuous service. Therefore, good, reliable, conservatively designed equipment is a must!
To fulfill the long service life expected, we recommend only heavy-duty pumps. That would include our Viking Series 4124A with U1700 cartridge seal. And for temperatures up to 350°F, we recommend the Series 4195 pump with Viton seal. These models are shown below. (Refer to the Viking Pump Catalog for more details.)
Optimizing pump operation
- The following practices will help ensure optimal operation of your HTL system and long service life of the pump:
- System pressure should be kept as low as possible and still achieve the necessary heat delivery rate.
- The liquid side of the system should be kept as clean as possible.
- Samples of the liquid should be analyzed periodically to be sure that there is no deterioration of the liquid. (Liquid suppliers will often conduct this analysis as a customer service.)
ABOUT VIKING PUMP
Viking Pump® is a global leader in positive displacement pumping solutions. With 100+ years of application experience solving their customers’ needs daily, Viking Pump offers internal gear pump, external gear pump, and vane pump solutions. Additionally, accessories, parts and kits round out the offerings to support customers full systems and keep the liquid flowing. Viking pumps are distributed globally through factory trained stocking distributors. Find one near you by visiting vikingpump.com/contact