Hydrofluoroolefin (HFO) Refrigerants and Their Compatibility with Lubricants
Refrigeration systems, being the heart of various cooling and freezing applications, play a vital role in various industries, such as food and beverages, pharmaceuticals, and many more. Refrigeration systems use refrigerants, which are the cornerstone of heat transfer processes to lower temperatures. With increasing environmental concerns and the necessity for a more sustainable solution, refrigerants like hydrofluoroolefin (HFO) are gaining traction.
HFOs, a type of non-chlorine based refrigerants, have similar performance and properties to other popular refrigerants like CFCs and HCFCs but have a more desirable environmental footprint due to their relatively short atmospheric lifetime and global warming potential (GWP) being significantly lower (0.02-19, for example, pentane). Their miscibility with lubricants is crucial, as a suitable lubricant must have the ability to reduce wear and tear of compressor parts, minimize pressure increase during startup, and optimize compressor efficiency.
Which Type of Lubricants are HFO Refrigerants Miscible In?
As mentioned earlier, compatibility of HFOs with lubricants is key to optimizing the performance and lifespan of refrigeration systems. Studies have shown that aluminum-based synthetic ester lubricants, also known as polyalphaolefin (PAO), have excellent miscibility with HFOs (Table 1).
| Lubricant Type | HFO Compatibility |
|---|---|
| Aluminum-based Synthetic Ester Lubricant (PAO) | (Yes)** |
| Ceramic Lubricants | (Possibly, depending on manufacturer’s claim) |
| Oils with ester group | ( Limited miscibility, requires investigation of each oil) |
| Oils with aminated group | (Limited compatibility, may corrode some components) |
Noteworthy Insights
• PAO has exceptional high-performance qualities, high viscosity index (1000-2000), excellent thermal stability (300°F), and maintains a neutral pH, thus preventing contamination and corrosion concerns.
• Ceramic lubricants, particularly silicon nitride-based oils, demonstrate some miscibility with HFOs due to the non-reactive and high-temperature-tolerant properties of their ceramics.
• Oils with an ester group in their molecular structure often display a moderate level of miscibility with HFOs; however, additional investigations should be conducted as individual results may vary (compatibility can depend on oil structure, composition, and chemical properties).
• Oils with aminated groups, which tend to undergo reactions with amines, should not be utilized as they pose risk of corrosion to compressor parts.
Additionally, another important consideration regarding lubricants and HFOs is the potential occurrence of lubricant degradation in presence of HFO’s, often due to excessive thermal stability, chemical structure and pH levels. Furthermore, research is still focused on evaluating the effects on performance of various HFO’s blended with different PAO structures and ratios
Best Practices for Design and Optimization
When dealing with HFO refrigerant-lubricant combination:
- Optimal compatibility, through testing specific PAO blends with an HFO, should guide design considerations.
- Maintain an environment with minimal acidity levels and controlled moisture (<3ppm) in system water and oil channels to preserve lubricant compatibility and effectiveness.
- Minimize equipment wear by considering thermal stresses, and apply sufficient static and dynamic mechanical testing and evaluation for selected materials under the intended condition
• Implementing such a proactive approach can improve reliability and minimize downtime throughout the lifetime of the refrigerator or chilling equipment.
This understanding can aid in:
- Enhancing reliability, as well-prepared for any possible occurrences with performance.
- Better efficiency, more proficient functioning contributes.
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Note:
• Table, graphs or illustrations used.
Incorporating and building an understanding of both these compatibility factors, can yield excellent results, like for an optimal lubricating properties HFO and optimal heat transport efficiency of it by well-selected HFO Refrigerants, ensuring enhanced safety standards for equipment lifetime while further contributing to Environmental Preservation.
In conclusion the optimal matching of HFO and synthetic ester Lubricants for optimal System Function in refrigeration.
Table References:
https://www.wur.nl/media/exportsites/wur/en/Publicaties/ rapport_r_k_p_h_a_v_f_t_v_j_7.pdf
By studying specific lubricant materials (particularly PAO lubricants and their various types, blending, and PAO) for their reaction properties on the basis HFO molecular structure and conditions which a Lubricant works to an HFO cooling or HFO cooling technology equipment that it may influence
A further examination study by exploring different chemical aspects with diverse materials is currently on research.
By making reference this, and an updated look on new products.
Further investigation into novel techniques by applying PAO on hydrofluoro-olefins in more aspects
research ongoing about in some projects.
