Effects of Water in Synthetic Lubricant Systems and Clathrate Formation: A Literature Search and Review

Abstract

EXECUTIVE SUMMARYMoisture is a universal contaminant of refrigeration systems, and a scientific understanding of the effects of water in these systems is needed for their proper design, efficient operation, and reliable service. The effects of water on chlorofluorocarbons and mineral oil have been extensively studied. In these non-polar systems with low solubility for water, moisture levels are usually controlled to twenty five parts per million or less to avoid free water and the associated corrosion of metals, compatibility problems with polymeric materials, and possible ice formation in expansion valves, capillary tubes, or evaporators. The phase-out of chlorofluorocarbon/mineral oil systems and the introduction of alternative hydrofluorocarbon (HFC) refrigerants and their compatible synthetic lubricants have once more raised concerns about the effects of water on the stability of refrigeration systems. The HFC/synthetic lubricant systems are polar and have good solubility for moisture, thus present reduced risk of free water with its associated problems. The current common practice of equipment manufacturers is to allow moisture levels of 50-100 parts per million (ppm) or less in new equipment with HFC and synthetic lubricants. However, service practices are not well controlled and may lead to high levels of water in the refrigeration system. Because of the different types of synthetic lubricants and system designs encountered in the refrigeration and airconditioning industry, initial investigations into the effects of excess water with the HFC/synthetic lubricant working fluids are limited, proprietary, or of a screening nature.There has not been a reported in-depth study of the effects of moisture on the long-term stability of the HFC/synthetic lubricant systems. Such a study would assist the equipment manufacturers in defining allowable maximum limits of water concentration for ii satisfactory long-term operation of the HFC/synthetic lubricant systems, and evaluating potential difficulties associated with the presence of excessive water.Under ARTI 21-CR Project 610-50035-01, Spauschus Associates, Inc. has compiled and critically evaluated the current state of knowledge of the effects of water on the stability of HFC/synthetic lubricant systems to identify key areas requiring further investigation. An extensive literature search was conducted and a confidential survey was prepared and sent to compressor, lubricant, desiccant and filter-drier manufacturers to determine the industry specifications on the amount of water allowable in the HFC/synthetic lubricant systems. Following are highlights from the extensive literature review and analysis of the survey:• Clathrate hydrates, first discovered in 1810, are solid solutions formed when water molecules are linked through hydrogen bonding creating cavities that can enclose various guest molecules also know as hydrate formers. The formation, nucleation, growth, decomposition, structures, properties, and thermodynamic phase equilibria have been reported for a num...

Physical, chemical, and lubricant properties of Brassicaceae oil

“…Van Gerpen et al stated that two problems can be generated by water, (i) the corrosion of engine fuel system components, caused by the formation of acidic compounds through the action of water on triglycerides and (ii) possible microbial growth that eventually produces sludge and slimes, which may plug filters. In general, long‐chain fatty acids perform as the boundary lubricants and this performance can be modified by water vapor and consequently increases the friction and wear . In this research, water content of the pressed oil samples was measured using Karl Firsher water titration (ASTM method D6304).…”