Q C-35 can also be used with aluminum at temperatures below 250º F.  At temperatures above 250º F, use of aluminum is not recommended because the inhibitors do not fully protect the aluminum components in the system.  Galvanized steel is not recommended in most cases because the zinc could react with the inhibitor in glycols, causing precipitation of components and release of hydrogen gas, particularly above 100º F.

Centrifugal pumps are commonly used with solutions of QC-35.  Reciprocating pumps are necessary where fluids must be pumped at high head pressures.  Pumps can be made of ordinary steel since the fluids are inhibited.  Piping valves and fittings can also be of ordinary steel.

Typically the same type of pump packing or mechanical seal used for water may be used with solutions of QC-35.  Packing and seal manufacturers should be consulted for materials appropriate to your application and operating temperature.  Solutions of QC-35 are also generally compatible with most plastics and elastomers.

 Bypass filters are recommended for removal of foreign solids.  Filters made of non-absorbent cotton, fiber, or cellulose-type media have been used successfully.

Using dissimilar metals in a system is not recommended because it may result in galvanic corrosion.  This type of corrosion can occur in electrolytic solutions when dissimilar metals (referencing the galvanic series) are in contact with or near each other.  (An example of dissimilar metals would be aluminum directly connected to copper.)  Solutions of QC-35 are better than plain water, but neither could fully protect against galvanic corrosion of dissimilar metals electrically coupled in a system.

Effective temperature range

QC-35 inhibited glycol has an effective operating temperature range of –28ºF to 250º F.

At temperatures below their lowest points, the fluids increased viscosities (>200 centipoise) can make them impractical to use without larger pumps.

At the upper end of the operating range, a maximum bulk temperature of 250º F is recommended, with film temperatures not to exceed 300º F.  Above these temperatures two factors present problems.  First, as with any water-based system, vapor pressure will increase rapidly above 300º F.  Smooth operating without localized boiling or “vapor lock” becomes difficult despite maintaining pressure on the system.

Second, thermal degradation of the fluid is a problem.  Glycol oxidation occurs in the presence of air at any temperature.  The higher the temperature, the faster the oxidation.  To minimize the oxidation rate, a closed system is recommended wherever possible.  At temperatures above 150º F, nitrogen padding is also recommended.  Although the fluids can tolerate brief exposures at temperatures up to 350º F, oxidation and degradation of both glycol and inhibitor become excessive with extended exposure above 300º F.

It should be noted that within the recommended operating range, film temperature at the wall of the heat exchanger should be no more than 25º F to 50º F higher than bulk temperature.  This helps to assure long fluid life.

Flammability

When mixed with water, QC-35 is not flammable and has no measurable flash point (Pensky-Martens Closed Cup) in concentrations up to 80% glycol.  QC-35 inhibited glycol to which no water has been added, has a flash point of 214º F and a fire point of 220º F (Cleveland Open Cup).

Film coefficients of inhibited glycols and water

QC-35 has heat transfer properties different from those of plain water.  These glycol solutions typically have lower film coefficients under equivalent flow conditions.  This may affect the design and operation of your system, depending on factors such as the heat transfer coefficient of the material being heated or cooled.   

Regulatory status regarding the use of inhibited glycols in food-related applications

Solutions of QC-35 are widely used in the food industry in immersion freezing, refrigeration coil defrosting, as secondary coolants in beverage processing and other applications.  We do not recommend the material be as a direct food additive.  However, its low toxicity, odor, and taste make it suitable for various food processing applications.  As with any fluid used in food processing, good manufacturing and handling procedures are required.

The active ingredient in QC-35, propylene glycol has been approved by United States Department of Agriculture (U.S.D.A.) for both defrosting refrigeration coils and for immersion freezing of wrapped meats, poultry, and meat products in plants operated under Federal Meat Inspection.

The Food and Drug Administration (F.D.A.) approves individual chemicals only, not proprietary products (trade names).  The two ingredients in QC-35 heat transfer fluid are generally recognized as safe by the Food and Drug Administration as a food additive under Part 182 of the Food Additive Regulations.  The regulation for propylene glycol is 21 CFR184.1666, for dipotassium phosphate, 182.6285.  The propylene glycol and dipotassium phosphate in QC-35 meet the requirements of these regulations.

Efficiency versus concentration

To obtain peak heat transfer efficiency while providing full freeze-protection, avoid using excess concentrations of QC-35 in water.  Generally, when the fluid is used either for freeze-protection or in secondary cooling applications, the concentration required would have a freeze point about 5º F lower than the lowest anticipated temperature.  For burst-protection, when slush or ice crystals in the fluid is not a problem, slightly lower (~5-10%) concentrations can be adequate.  Rarely is it necessary to use concentrations higher than 50-55% glycol in water.  The less glycol used, the higher the relative heat transfer efficiency of the solution.

For optimum corrosion protection, the minimum concentration of QC-35 in water should be 30%.  If operating at lower concentrations is desired, consult your technical representative for information relating to inhibitor adjustment.

Expansion Factor

Like all fluids, solutions containing QC-35 inhibited glycol expand as the temperature increases.  Expansion tanks should be sized to allow about 4% greater expansion than for plan water in the same temperature range. 

Also note that as temperatures drop below the freeze point of a glycol solution, ice crystals begin to form.  This causes the solution to expand and the slush will flow to available expansion volume.  The lower the temperature, the greater the expansion.  However, when it gets cold enough so that glycol crystals form, the volume of the solution will then begin to contract.  At very low temperature the entire mass freezes solid.