Selection Guide · 2026-10-20
Low-Temp Secondary Refrigerant Selection: Brine vs Glycol
Evaluate secondary refrigerants for -20°C to -60°C chemical reactors across viscosity, thermal conductivity, corrosion, and energy efficiency.
Key takeaways
- Between -20°C and -40°C, conventional ethylene glycol viscosity surges (34.3 mPa·s at -20°C), significantly increasing pumping power and transitioning flow toward laminar regimes.
- Potassium formate-based coolants like Eurotherm NF operate down to -60°C with kinematic viscosity of ~25 mm²/s at -40°C and thermal conductivity of ~0.50 W/(m·K), reducing heat exchanger sizing and pump load.
- Calcium chloride brines present severe pitting and stress corrosion cracking risks on carbon steel and austenitic stainless steels; inhibited glycols and organic salts offer safer metallurgy protection.
- For cryogenic duties below -60°C, water-based solutions reach freezing limits, requiring synthetic hydrocarbons like Eurotherm 100 operable down to -115°C under closed nitrogen-blanketed loops.
Core Engineering Criteria for Indirect Industrial Cooling
In fine chemical synthesis, pharmaceutical intermediate crystallization, and controlled thermal loops, jacketed reactors and cooling coils rely heavily on secondary refrigeration fluids. As the thermal transfer medium between central chillers and process vessels, the thermo-physical properties of the secondary refrigerant directly dictate chiller evaporator temperatures, overall heat transfer coefficients, and continuous pumping energy consumption.
Engineering evaluations center on five decisive parameters: operational temperature limits and pour points, low-temperature kinematic viscosity, thermal conductivity combined with specific heat, metallurgy compatibility, and operational environmental safety. Because liquid properties vary drastically at sub-zero temperatures, misjudging viscosity curves or corrosion mechanisms often leads to poor batch cooling curves, high parasitic pumping loads, or pipe failure.
Technical Parameter and Performance Comparison
Inorganic brines such as calcium chloride feature low upfront fluid cost but impose severe pitting corrosion threats on carbon steel and austenitic stainless steel piping. Formulated ethylene glycol solutions are widely accessible, yet their sharp viscosity escalation at sub-zero levels increases pumping hydraulic resistance. Engineered organic salt formulations and dedicated synthetic hydrocarbons solve these bottlenecks across challenging thermal bands.
The table below compares key engineering parameters across standard and engineered secondary refrigerants to assist plant engineers in fluid selection:
| Product / Medium | Chemical Chemistry | Operating Range (°C) | Low-Temp Viscosity | Thermal Conductivity / Cp | Metallurgy & Corrosion Risk | System Suitability |
|---|---|---|---|---|---|---|
| Eurotherm NF | Water-based potassium formate | -60 to 115 | 25 mm²/s (@ -40°C) | Thermal cond. ≈ 0.50 W/(m·K) | Mild on common alloys; biodegradable | Open or closed loops (rec. ≤ 110°C) |
| Eurotherm MEG | Ethylene glycol + inhibitors | -40 to 110 | 34.3 mPa·s (@ -20°C) | Moderate thermal conductivity | Inhibitor pack protects multi-metal loops | Open or closed loops (rec. ≤ 110°C) |
| Eurotherm BF | Water-based organic salt | -35 to 110 | 28 mm²/s (@ -40°C) | Cp ≈ 2.6 kJ/(kg·K), Cond. ≈ 0.49 W/(m·K) | Non-corrosive to copper and carbon steel | Open or closed loops (rec. ≤ 110°C) |
| Eurotherm 100 | Synthetic hydrocarbon | -115 to 175 | 0.721 mm²/s (@ 40°C; pumpable at -115°C) | Excellent heat transfer at high velocity | Non-corrosive; check seal elastomer swell | Closed systems only (nitrogen/inert seal) |
| Calcium Chloride Brine | Aqueous inorganic salt | -30 to 50 (conc. dependent) | Moderate viscosity at low temp | Good thermal conductivity | High pitting risk on carbon and stainless steel | Common in open baths; high corrosion risk |
| Dowtherm SR-1 (Public Data) | Inhibited ethylene glycol | -40 to 120 | Viscosity climbs steeply below -10°C | Moderate thermal conductivity | Formulated corrosion inhibitor package | Closed and selected open systems |
Navigating -20°C to -60°C: Viscosity, Flow Regimes, and Pumping Power
As secondary fluid temperature drops from 0°C down past -20°C, viscosity becomes the predominant barrier to thermal and hydraulic efficiency. Glycol solutions such as Eurotherm MEG have dynamic viscosities of 5.38 mPa·s at 20°C, but this figure reaches 34.3 mPa·s at -20°C. Elevated viscosity causes internal pipe flow to shift from turbulent to transitional or laminar regimes, dropping film heat transfer coefficients and forcing circulation pumps to fight higher pressure drops.
In contrast, potassium formate aqueous solutions such as Eurotherm NF exhibit a kinematic viscosity of only about 25 mm²/s at -40°C while maintaining thermal conductivity near 0.50 W/(m·K). In cryogenic reactor cooling down to -60°C, maintaining lower dynamic drag preserves turbulent mixing inside reactor jackets, which stabilizes wall temperature profiles and reduces auxiliary power consumption.
Pipe Corrosion, Open vs. Closed Loops, and Environmental Compliance
System life-cycle costs are governed far more by asset corrosion and down-time maintenance than by initial fluid fill expenses. Traditional calcium chloride brines in atmospheric, oxygen-rich environments attack carbon steel aggressive pitting. Furthermore, chloride ions disrupt passivated chromium oxide layers on 304 and 316L stainless steel, triggering localized pitting and stress corrosion cracking.
Formulated glycol fluids such as Eurotherm MEG and Eurotherm DF integrate corrosion inhibitors to suppress electrochemical reactions on pipe walls. Similarly, organic carboxylate salt coolants like Eurotherm BF and Eurotherm NF deliver broad compatibility across carbon steel, copper, and alloys, while remaining non-flammable and biodegradable for tight plant safety requirements.
Engineering Selection Paths for Chemical and Pharma Reactors
For processes operating between 0°C and -20°C, inhibited ethylene glycol solutions (such as Eurotherm MEG) offer practical stability and favorable operating economy. When toxicity guidelines or non-glycol compliance dictates alternative chemistry, organic salt solutions like Eurotherm BF provide an effective, non-hazardous profile.
For deeper cooling between -20°C and -60°C, low-viscosity organic salt coolants (Eurotherm NF) minimize jacket thermal lag and keep pumping energy within budget. If chemical synthesis requires ultra-low temperatures from -60°C down to -115°C, aqueous phases freeze solid, demanding low-pour-point synthetic hydrocarbons (such as Eurotherm 100) running inside closed, nitrogen-blanketed loops.
Engineering teams can simulate specific process duties using the Chemie Fluid Selection Tool (https://calculator.szchemie.com.cn/select) or the Chemie AI Selection Assistant (https://calculator.szchemie.com.cn/ai) to verify physical data and pump requirements under precise operating conditions.
FAQ
Why is calcium chloride brine discouraged in modern stainless steel chemical reactors?
Calcium chloride contains free chloride ions that break down the passive oxide film on austenitic stainless steels (such as 304 and 316L), leading to pitting, crevice corrosion, and stress corrosion cracking at weld zones. Inhibited organic salts and formulated glycols offer far safer metallurgy compatibility.
What challenges arise when running ethylene glycol coolants near -30°C?
At -30°C, aqueous ethylene glycol viscosity rises steeply, which causes fluid flow in heat exchanger channels to drop into laminar regimes. This degrades heat transfer rates and causes high differential pressures across circulation pumps. Low-viscosity organic salt coolants like Eurotherm NF maintain superior fluidity at these temperatures.
Can a potassium formate fluid like Eurotherm NF replace ethylene glycol in an existing system?
Yes, but the system must be completely drained, flushed, and cleaned before refilling. Mixing glycol and formate-based coolants directly can compromise corrosion inhibitor systems or cause precipitation. Engineering evaluation of system seals, valves, and metallurgy is recommended prior to conversion.
Can synthetic hydrocarbon fluids like Eurotherm 100 be used in open cold-bath circuits?
No. Synthetic hydrocarbons such as Eurotherm 100 have a closed-cup flash point of -7°C and are volatile. They must be operated exclusively in closed circulation systems equipped with nitrogen blanketing or cold-oil expansion seals to prevent air ingress and maintain explosion-proof safety standards.
Sources
Product data are typical laboratory values for reference only; please confirm with a Chemie engineer.