QC-35 is a generic equivalent of Dowfrost HD, offering the
same quality material at a much better price.
QC-35 is manufactured and
sold by our sister company
Chemical.net. Did you know that Chemical.net is one of the few companies in
the country that offers heat transfer fluids in unlimited range of percentages,
from 20% through 100%? They also offer custom packaging and drop shipping. Need
it dyed? Yellow, pink, green, blue? They do it. Give them a call with any
questions! (888) 243 6425 or (215) 332 4000.
Standard materials can be
used with QC-35 Heat Transfer Fluid. Steel, cast iron, copper, brass,
solder, and plastic piping materials are all generally acceptable.
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
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
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
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
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
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.