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General information about handling Danfoss OptymaTM condensing units

General information and practical tips for using Danfoss OptymaTM condensing units are given below. OptymaTM condensing units represent a complete range of units with hermetic Danfoss reciprocating compressors. The design of this series corresponds to the needs of the market. In general, to give an overview of the program, each subsection is divided into the different hermetic compressors mounted on the condensing units.

  1. Danfoss OptymaTM condensing units with the 1-cylinder compressors of the types TL, FR, NL, SC, SC-TWIN and GS: OptymaTM A01 and A04.
  2. Danfoss OptymaTM condensing units with the hermetic 1, 2 and 4 cylinder compressors of the types MTZ and NTZ: OptymaTM A02.

 

 

Furnishing

Danfoss OptymaTM condensing units are supplied with compressor and condenser mounted on rails or base plate. The electrical wiring is done with the help of terminal boxes. In addition, shut-off valves, soldering adapters, collectors, double pressure switches or mains cables with Schuko plugs can complete the scope of delivery. Please refer to the relevant technical Danfoss documentation or the valid price list for details and order numbers. Your local Danfoss sales office will be happy to help you with your selection.

 

 

Power supply and electrical equipment

A01 and A04 These condensing units are equipped with hermetic compressors and fans for 230V-1Ph-50Hz networks. The compressors are equipped with an HST starting device (compressor can start against pressure) consisting of a starting relay and a starting capacitor. These components can also be supplied as spare parts. The starting capacitor is designed for short switch-on cycles (1.7% ED).

In practice, this means that the compressors can be started up to 10 times per hour with a duty cycle of 6 seconds each. OptymaTM A02 condensing units These condensing units are equipped with hermetic compressors and fans for networks with: 400 V-3 Ph-50 Hz for compressors and fan(s) 400 V-3 Ph-50 Hz for compressors and 230 V-1 Ph- 50 Hz for fan(s) - the running capacitor(s) of the fans are mounted in the electrical switch box 230 V-3 Ph-50 Hz for compressors and 230 V-1 Ph-50 Hz for fan(s) - the running capacitor(s) are in electrical control box mounted 230V-1 Ph-50 Hz for compressors - the starting device (capacitor and relays) are mounted in the control box and 230 V-1 Ph-50 Hz for fan(s).

The starting current of the MTZ and NTZ three-phase compressors can be reduced by using a soft starter. CI-tronicTM soft start is recommended for this type of compressor. Depending on the compressor model and the soft starter, the starting current can be reduced by up to 40%. The mechanical stress that occurs during start-up is also reduced, which leads to an increase in the service life of the internal components. If you have any questions about the details of the CI-tronicTM, please contact your local Danfoss sales office.

The number of compressor starts is limited to 6 per hour under resistance starting. HP/LP pressure equalization is required prior to launch when using MCI-C.

 

 

Hermetic compressors

The fully hermetic compressors TL, FR, NL, SC, SC-TWIN and GS have a built-in winding protection switch. When the winding protection is activated, there may be a switch-off time (up to 45 minutes) due to heat accumulation in the motor.

The single-phase MTZ and NTZ compressors are internally protected, depending on temperature and current, by a bimetallic protector that controls the current in the main and auxiliary windings.

The three-phase compressors MTZ and NTZ are equipped with an internal motor protection against overcurrent and overtemperature. The motor protection is located in the star point of the windings and opens all 3 phases simultaneously via a bi-metal disk. After the compressor has switched off via the winding protection, it can take up to 3 hours to switch on again.

If the motor fails, you can use resistance measurement to determine whether the winding protection switch is switched off or whether the winding is broken.

 

 

condenser and fan

The highly effective condensers allow a wider range of applications at higher ambient temperatures. Depending on the capacity, one or two fans are used per condenser unit.

In addition, the fans can be expanded with a Danfoss Saginomiya fan speed controller, type RGE, for example. This allows good condensing control and reduces noise levels. The fans are equipped with self-lubricating bearings, so that many years of maintenance-free operation are guaranteed.

 

 

shut-off valves

provided with shut-off valves on the pressure side. The shut-off valves of the OptymaTM A01 and A04 condensing units are shut off when the spindle is turned clockwise towards the soldering socket. This frees the flow between the pressure gauge connector and the flared connection. If you turn the spindle counterclockwise to the rear stop, the pressure gauge port is shut off. The flow between the soldering piece and the flared connection is free. In the middle position, the flow through the three connections is free. The soldering adapters included help avoid flared connections and make the system hermetic. The shut-off valves of the OptymaTM A02 condensing units are mounted directly in the suction line and on the pressure side of the compressor and receiver. The shut-off valve on the suction side is provided with long straight pipe sockets,

 

 

collector

Liquid receivers are fitted as standard on condensing units for expansion valve operation.

The collectors from an internal volume of 3 l are equipped with Rotolock valves.

 

 

junction box

The OptymaTM A01 and A04 condensing units are electrically pre-wired and equipped with a junction box. This allows the power supply and additional electrical wiring to be connected quickly and easily

The connection box of the OptymaTM A02 condensing units is equipped with terminal blocks, both for the power supply and for the control circuits. The electrical wiring of all components (compressor, fan, PTC, pressure switch) are combined in this box. The electrical circuit diagram is located in the cover of the connection box. This junction box has protection class IP 54.

 

 

high pressure switch

The Danfoss condensing units can be ordered with a combined high and low pressure switch KP17W/B, switchable on the high pressure side. In this way, the pressure monitor or pressure limiter function can be activated. Condensing units that are not supplied with pressure switches from the factory must be fitted with a pressure switch on the high-pressure side in systems with thermostatic expansion valves in accordance with EN 378.

The collectors from an internal volume of 3 l are equipped with Rotolock valves.

The following settings are recommended:

(Observe the maximum permissible operating pressure of the additional components installed in the system.)

refrigerantlow pressure sidehigh pressure side

switch-off point (bar)switch-on point (bar)switch-on point (bar)switch-off point (bar)

R407212125

R404A/R507MBP1.20.52428

R404A/R507 LBP10.12428

R404A/R507 LBP10.12428

R134a1.20.41418

 

 

lineup

The Danfoss OptymaTM condensing units must be installed in a well-ventilated area. It must be ensured that there is sufficient fresh air available for the condenser on the intake side. It must also be ensured that there is no short-circuit flow between fresh air and exhaust air. The fan motor is connected in such a way that the air is drawn in the direction of the compressor via the condenser. For optimal operation of the condensing unit, the condenser must be cleaned regularly.

 

 

weatherproof housing

Danfoss condensing units that are installed outdoors should be fitted with a protective roof or with a weatherproof housing. The scope of delivery optionally includes high-quality weatherproof housings. Please refer to the applicable price list for order numbers or contact your local Danfoss office.

The Danfoss condensing units can be ordered with a combined high and low pressure switch KP17W/B, switchable on the high pressure side. In this way, the pressure monitor or pressure limiter function can be activated. Condensing units that are not supplied with pressure switches from the factory must be fitted with a pressure switch on the high-pressure side in systems with thermostatic expansion valves in accordance with EN 378.

The collectors from an internal volume of 3 l are equipped with Rotolock valves.

 

 

Careful assembly

More and more commercial refrigeration and air conditioning systems are built with condensing units equipped with hermetic compressors. High demands are placed on the quality of the assembly work and the adjustment of such a refrigeration system.

 

 

impurities and foreign particles

Contamination and foreign particles are among the most common causes that negatively affect the reliability and lifespan of refrigeration systems. The following impurities can get into the system during assembly:

  1. Scale formation during soldering (oxidation)
  2. Flux residue from soldering
  3. moisture and foreign gases
  4. Chips and copper residue from deburring the pipes

Therefore, Danfoss recommends the following precautions:

  1. Only cleaned and dried copper pipes and components that meet the DIN 8964 standard are to be used.
  2. Danfoss offers you an extensive
  3. Moisture and foreign gases and a coordinated product range of the required automatic refrigeration. Please contact your local Danfoss office.

 

 

pipe laying

When laying the pipelines, the aim should be to keep the pipeline network as short and compact as possible. Low-lying areas (oil pockets) where oil can collect should be avoided

 

 

Condenser and evaporator are at the same height.

The suction side should be arranged with a slight fall towards the compressor. The maximum permissible distance between the condensing unit and the evaporator is 30 m. To ensure the oil return, the cross-sections listed above are recommended for the suction and liquid lines.

 suction lineliquid line

Outer diameter of copper pipe [mm]

tsp8th6

FR106

NL106

SC108th

SC TWIN1610

GS 211210

GS 341610

 

 

The condensing unit is located above the evaporator.

The target height difference between the condensing unit and the evaporator should not exceed 5 m. The pipeline length should not exceed 30 m. The suction lines are to be designed with double bends as oil traps downwards and upwards. This is done with a U-bend at the bottom and a P-bend at the top of the vertical riser. The maximum distance between the bends is 1 to 1.5 m. In order to ensure the oil return, the following cross-sections are recommended for the suction and liquid lines:

 suction lineliquid line

Outer diameter of copper pipe [mm]

tsp8th6

FR106

NL106

SC 12 and 15108th

All other SC compressors128th

SC TWIN1610

GS 211210

GS 341610

 

 

The condensing unit is located below the evaporator.

The desired height difference between the condensing unit and the evaporator is max. 5 m. The pipe length between the condensing unit and the evaporator should not exceed 30 m. The suction line is to be designed with double bends as an oil trap downwards and upwards. This is done with a U-bend at the bottom and a P-bend at the top of the vertical riser. The max. distance between the bends is 1 to 1.5 m. To ensure the oil return, the following cross-sections are recommended for the suction and liquid lines:

 suction lineliquid line

Outer diameter of copper pipe [mm]

tsp8th6

FR106

NL106

SC128th

SC TWIN1610

GS 211210

GS 341610

 

 

Piping of the condensing units

The connecting pipes should be flexible (jumping in three levels or with anti-vibration mounts). When laying the pipelines, the aim should be to keep the pipeline network as short and compact as possible.

 

 

Low-lying areas (oil pockets) where oil can collect should be avoided. Horizontal lines should be laid falling towards the compressor. In order to ensure oil return, the suction gas velocity in risers must be at least 8-12 m/s.

In the case of horizontal lines, the suction gas speed must not fall below 4 m/s. The vertical pipelines are to be designed with double bends as oil traps at the top and bottom. This is done with a U-bend at the bottom and a P-bend at the top of the vertical pipe. The maximum riser height is 4m unless a second U-bend is fitted.

 

 

If the evaporator is mounted above the condensing unit, it must be ensured that no liquid refrigerant gets into the compressor during the standstill phase. In order to avoid the formation of condensation water and an unintentional increase in suction gas overheating, the suction line must generally be insulated. The suction gas overheating is adjusted individually for the respective application. Further information can be found in the following chapter under “Max. permissible temperatures”.

 

 

leak test

The Danfoss condensing units are already tested for leaks with helium and provided with an inert gas filling at the factory and must therefore be evacuated with the system. In addition, the added refrigerant circuit must be checked for leaks with nitrogen. In this case, the suction and liquid valves of the condensing unit remain closed. The use of colored leak detectors will void the warranty.

 

 

soldering

The Danfoss condensing units are already tested for leaks with helium and provided with an inert gas filling at the factory and must therefore be evacuated with the system. In addition, the added refrigerant circuit must be checked for leaks with nitrogen. In this case, the suction and liquid valves of the condensing unit remain closed. The use of colored leak detectors will void the warranty.

 

 

protective gas

At the high brazing temperatures under the influence of atmospheric air, oxidation products (scale) are formed.

A protective gas must therefore flow through the system during soldering. Pass a gentle stream of dry inert gas through the pipes. This is usually dry nitrogen (N2).

Only start soldering when there is no longer any atmospheric air in the component in question. Start the work process with a powerful flow of protective gas, which you reduce to a minimum when you start soldering. This weak protective gas flow must be maintained throughout the entire soldering process.

Soldering is to be carried out under oxygen and gas with a soft flame. The solder should only be added when the melting temperature has been reached.

 

 

evacuation and filling

The vacuum pump should be able to extract the system pressure to approx. 0.67 mbar and work in two stages if possible.

Moisture, atmospheric air and inert gas should be removed.

If possible, two-sided evacuation from the suction and pressure side of the condensing unit should be provided.

Use the connections on the suction and liquid side stop valves.

 

 

A filling level or filling cylinder or, for smaller condensing units, a scale is used to fill the system. The refrigerant can be supplied as liquid to the liquid line if a charging valve is fitted. Otherwise, the refrigerant must be fed into the system in gaseous form via the suction shut-off valve while the compressor is running (break the vacuum beforehand).

Please note that the refrigerants R 404A/R 507 and R 407C are mixtures. Refrigerant manufacturers recommend that R 507 be charged in liquid or gaseous form, while R 404A and R 407C should be charged in liquid form. It is therefore recommended to top up R 404A/R 507 and R 407C as described using a filling valve.

If the amount of refrigerant to be charged is unknown, charging will continue until bubbles no longer appear in the sight glass. Constant monitoring of the condensing and suction gas temperature is necessary to ensure normal operating temperatures.

Please observe the following procedure for evacuating and filling the OptymaTM A01 and A04 condensing units: For evacuation, both outer hoses are connected to a manifold and the condensing unit is evacuated with the shut-off valves open - the spindle in the middle position.

After evacuation, both hoses (pressure and suction side) are connected to the manifold. Only then is the vacuum pump switched off.

The refrigerant bottle is connected to the center connection of the manifold and the filler neck is briefly vented. The corresponding valve of the manifold is opened and the system is filled via the pressure gauge connection of the suction shut-off valve with the max. permissible refrigerant charge when the compressor is in operation.

 

 

Please note the following recommendation for evacuation and filling

It is recommended to carry out the evacuation as described below:

1. The condensing unit service valves must be closed.

2. After the leak search, a two-sided evacuation should be carried out with a vacuum pump to 0.67 mbar (abs.). It is recommended to use clutch lines with the largest possible passage and to connect them to the service valves.

3. As soon as the vacuum of 0.67 bar (abs.) is reached, the system is disconnected from the vacuum pump. The system pressure must not increase during the next 30 minutes. If the pressure rises quickly, the valve is leaking. A new leak search and evacuation (from 1) must be carried out. If the pressure increases slowly, this indicates that moisture is present. In this case, you should evacuate again (from 3).

4. Open the service valves on the condensing unit and break the vacuum with dry nitrogen. Repeat process 2 and 3.

 

 

General note:

The compressor should not be switched on until the vacuum is broken. When the compressor is operated with a vacuum in the compressor housing, there is a risk of voltage flashover in the motor winding.

 

 

Exceeding the max. permissible operational fill quantity and outdoor installation

Protective measures must be taken if the refrigerant is filled in excess of the max.

Refer to the Danfoss compressor technical information and/or installation instructions for the maximum allowable operating charge levels. If you have any questions, your responsible sales office will be happy to advise you.

The use of a crankcase heater offers a quick and easy solution to prevent refrigerant migration during downtimes.

 

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Higher energy efficiency - an imperative from the current sustainability megatrend.

According to the International Energy Agency (IEA), electricity demand will increase by up to more than 60% in the current decade, depending on the region (see Figure 1).

 

Figure 1: Electricity demand outlook for selected regions/countries in the Stated Policies Scenario, 2019-2030 (IEA, 2020).

 

The reasons for this are the electrification of mobility and the use of more and more electrical appliances such as air conditioners and heat pumps. Last, but not least, the conversion of various industries such as the chemical or steel industry to new processes that intend to use hydrogen as an energy source or starting material also plays a role. After all, hydrogen is produced by means of hydrolysis with the use of electric power.

All these changes are leading to competition for electricity as a resource. Even with rapid expansion of generation capacities, the result is likely to be rising electricity prices and also rising CO2 emissions, since a large proportion of the global electricity mix is still based on fossil fuels.

The latter is toxic for climate change, the former a challenge for the profitability of energy-intensive companies such as refrigeration plant operators, whose operating costs are largely caused by their electricity consumption.

How can both negative effects be avoided or at least mitigated? The answer lies in increasing the energy efficiency of companies and, consequently, of your plants. There are several ways to achieve this.

One of them is the acquisition of new, technologically advanced equipment. However, not every company can afford capital-intensive investments. Another option is retrofitting existing plants. This also includes exchanging the lubricants used. In fact, increases in energy efficiency of several percent can be achieved by using precision-fit, high-performance synthetic lubricants instead of mineral oil-based lubricants.

This type of upgrade is also an option for refrigeration systems or in the case of refrigeration compressors.

 

How can energy savings be realized in refrigeration systems with the help of lubricants and application knowledge?

Lubricants have a number of functions in a tribological system (see also Fundamentals of lubrication technology). In refrigeration compressors, these include reducing friction as well as removing heat from heat-stressed areas. In screw compressors in particular, the lubricant also performs a sealing function by closing the gap between the two rotors in the compression chamber, thus preventing the refrigerant from flowing back from the high-pressure side to the low-pressure side. In addition, the tendency to evaporate as well as the change in viscosity over a longer period of time plays a major role in the energy efficiency of a compressor system. Above all, a lubricant's tendency to evaporate and its resistance to aging determine the formation of residues and thus the cleanliness of a system. That a clean system runs more efficiently than a dirty one is self-explanatory. In short, the better a lubricant performs the functions listed, the higher the energy efficiency of a refrigeration system in the end.

The lubricants themselves differ significantly in the dimensions of base oil, additives and viscosity. Even within these dimensions, there are considerable differences in quality. In other words, even the same type of base oil, for example, hides different qualities that ultimately determine the performance of the lubricant used. Further information on the different base oil types can be found in the article Basics of Lubricating Oils. LINK

Basically, it can be stated that synthetic high-performance lubricants are superior to mineral oil-based products. Nevertheless, it is important to select the right high-performance lubricant with care to avoid problems with seals or with compatibility with the previously used lubricant.

 

Proof of energy savings by means of measurements

Synthetic high-performance lubricants differ not only in their superior performance, for example, compared with mineral oil-based products, but also in their much higher price. Nevertheless, their use is generally worthwhile not only from an environmental point of view but also from an economic one.

However, an estimate of the energy and cost savings is not always sufficient for a well-founded investment decision. Especially not if a changeover to a high-performance lubricant is appropriate as a measure to increase energy efficiency as part of a monitoring audit of an ISO 50001 certification. Concrete proof of increased energy efficiency by means of measurements can then help.

There are different approaches how to prove the increased energy efficiency of the equipment and thus also the energy savings. A common mistake here is the assumption that a quick glance at the electricity meter is enough. This is, of course, only a snapshot that merely represents the current electricity consumption in an unknown operating state.

Precisely to prevent such errors, there are standards that define how increase in energy efficiency is to be measured in order to be able to make a reliable statement at the end regarding the savings achieved. The best-known standards include the following:

- the International Performance Measurement and Verification Protocol

- the ISO 50015

Both standards are very similar in content and, among other things, point out that verification of energy savings is not possible or meaningful without considering the influencing factors (influence on the energy consumption of a system).

Klüber Lubrication therefore not only offers its customers expertise when it comes to selecting the right lubricant, but also carries out corresponding measurements according to international standards on the customer's plant if required as part of the "KlüberEnergy" service program (see Figure 2). The measured results are subsequently presented transparently in a report.

 

Figure 2: KlüberEnergy overview (own illustration)

 

The KlüberEnergy Service Program has already achieved energy savings on several refrigeration plants. For example, a reduction in energy consumption of more than 3% or around 28 MWh per year was achieved and verified on a refrigeration compressor of an Italian food manufacturer. Together with the cost savings resulting from the longer service life of the Klüber Lubrication lubricant, the savings add up to more than EUR 4,300 per year with a payback period of only 4 months. The absolute savings will now be maximized by converting all refrigeration compressors to Klüber Lubrication's lubricant.

 

Author

Alexander Leis New Business Development Manager Energy Efficiency Klüber Lubrication München SE & Co. KG

 

Sources:

IEA, Electricity demand outlook in selected regions/countries in the Stated Policies Scenario, 2019-2030, IEA, Paris https://www.iea.org/data-and-statistics/charts/electricity-demand-outlook-in-selected-regions-countries-in-the-stated-policies-scenario-2019-2030

 

Do you have any questions or need consulting?

Klüber Lubrication can look back on more than 90 years of experience in the fields of friction optimisation and specialty lubricants. We will be pleased to provide personal advice for your specific requirements regarding refrigeration compressor oils.

This is how you can reach us: Stefan Zuber Global Business Team Compressors Phone: +49-89-78 76 502 Email: Stefan.Zuber@klueber.com

Website: www.klueber.de

Editor and copyright: Klüber Lubrication München SE & Co. KG Reprints, total or inpart, are permitted only prior consultation with Klüber Lubrication München SE & Co. KG and if source is indicated and voucher copy is forwarded. The data in this document is based on our general experience and knowledge at the time of publication and is intended to give information of possible applications to a reader with technical experience. It constitutes neither an assurance of product properties nor does it release the user from the obligation of performing preliminary tests with the selected product. It constitutes neither an assurance of product properties nor a guarantee of the suitability of the product for a specific application. They do not release the user from from the obligation of performing preliminary field tests with the product selected for a specific application. All data are guide values which depend on the lubricant's composition, the intended use and the application method. The technical values of lubricants change depending on the mechanical, dynamical, chemical and thermal loads, time and pressure. These changes may affect the function of a component. We recommend contacting us to discuss your specific application. Products from Klüber Lubrication are continually improved. Therefore, Klüber Lubrication reserves the right to change all the technical data in this document at any time without notice.

Klüber Lubrication München SE & Co. KG - Geisenhausenerstraße 7 - 81379 München Deutschland Munich District Court, HRA 46624

 

 

Sources

Alexander Leis New Business Development Manager Energy Efficiency Klüber Lubrication München SE & Co. KG

 

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In the first two parts of this training, we wrote about the basics of tribology and of lubricating oils. In this part, we want to provide information on the basics of lubricating greases. You are going to learn what a lubricating grease actually is, what types of greases there are, and what kind of benefits they offer in practice.

 

 

What is a lubricating grease?

Lubricating greases are compounds which effectively reduce mechanical friction and wear, provided a suitable quality is chosen. From a chemical perspective, these compounds are made up of a lubricating oil, a thickener and additives. Greases are an ideal choice where a friction point is to be effectively protected for as long as possible. Besides providing optimum lubrication, they also shield the component from external influences such as splash water, air humidity and dirt, depending on the individual ambient conditions.

Depending on the individual requirements of a specific application, you may choose between high-temperature, low-temperature, high-speed or heavy-load greases, or those certified as H1.

 

 

What is the composition of a lubricating grease?

Depending on the intended use and field of application, the formulation of a lubricating grease comprises the following ingredients:

 

 

Which base oils are most commonly used for making greases?

  1. Mineral oil (paraffinic or naphtenic) (MIN)
  2. Polyalphaolefins (PAOs)
  3. Ester oils (E)
  4. Polyalkylene glycols (PAG)
  5. Silicone oils
  6. Perfluoropolyether oils (PFPE)

 

 

What is a thickener?

Thickeners are substances increasing the consistency (nature and degree of internal cohesion) of a grease. A differentiation is made between metal soap greases and soap-free greases.

 

 

What is the function and what are the tasks of a thickener?

  1. It retains the oil to give the grease its texture.
  2. It continuously releases oil, providing the friction point with lubricant.
  3. It contributes to building up a lubricant film.
  4. It seals the friction point, shielding it against dirt and moisture.

 

 

What types of thickener are there for greases?

 

 

What is a lithium grease?

Lithium greases are made by neutralising a 12-hydroxy stearic acid lithium hydroxide in an oil. Lithium soap greases are often used as multipurpose lubricants. Lithium soap shows the best behaviour of all simple soaps and is used in many applications.

 

 

What is an aluminium complex soap grease?

Aluminium complex soap greases show very good resistance to water and good pumpability. They are often used for the lubrication of components and machines in the food-processing industry.

 

 

What is a barium complex soap grease?

Barium complex soap greases contain as thickener mixtures of various, mostly organic acids saponified with barium hydroxide. Greases of this type show good resistance to water and steam, good anticorrosive characteristics, a high load-carrying capacity and have a high drop point. They are suitable for both low and high temperatures and are frequently used in high-speed rolling bearings.

 

 

What is a calcium complex soap grease?

Calcium complex soap greases contain as thickener mixtures of various, mostly organic acids saponified with calcium hydroxide. These greases have good anticorrosive characteristics, are resistant to water and show a high load-carrying capacity.

 

 

What is lithium complex soap grease?

Lithium complex soap greases are enhanced lithium soap greases offering better stability and high-temperature characteristics. As thickener, mixtures of various, mostly organic acids saponified with lithium hydroxide are used.

 

 

What is a sodium complex soap grease?

Sodium complex soap greases contain as thickener mixtures of various, mostly organic acids saponified with sodium hydroxide. Greases of this type show good emulsifying behaviour. They are mostly used as fluid greases in gearboxes.

 

 

What is a bentonite grease?

Bentonite greases show good high-temperature behaviour. They have no drop point. Depending on the base oil type, they show good low-temperature behaviour.

 

 

What is a polyurea grease?

Polyurea are used as grease thickeners that do not form ash. Greases with polyurea thickeners are used for high-end greases with a high drop point.

 

 

What is a PTFE (polytetrafluoroethylene) grease?

PTFE greases are used for very demanding technical requirements. They have a wide service temperature range, are resistant to aggressive media, have a high load-carrying capacity. PTFE also offers emergency running properties. Typically, a PFPE (perfluorinated polyether) oil or silicone oil is used as a base oil for PTFE greases.

 

 

Which thickeners are intermiscible?

The following table serves for rough guidance. For a reliable determination of oil miscibility, it is always recommendable to have corresponding tests conducted at the lubricant manufacturer.

 

 

What does the NLGI grade mean for a lubricating grease?

Lubricating greases are characterised by classifying them into NLGI (National Lubricating Grease Institute( consistency grades according to DIN 51818.

 

This classification is based on the measured penetration of a standardised cone into the grease acc. to DIN ISO 2137. Since it is not possible to manufacture a grease with always the exactly same consistency, each NLGI grade has a permissible penetration range of approx. 30 units (1 unit = 0.1 mm penetration depth). The next grade follows at an interval of 15 units.

 

 

What benefits do lubricating greases offer?

  1. Less complex component/machine design (sealing)
  2. Long service life with low maintenance
  3. In many cases for-life lubrication
  4. Low consumption
  5. Better sealing due to grease

 

 

Do you wish to acquire more in-depth knowledge of the subjects tribology, lubrication technology and lubricants?

Then the trainings offered by Klüber Lubrication might be an option for you. Twice to three times per year, we offer two-day trainings in Munich. Alternatively, you can order individual trainings tailored to your needs on the subject of "lubrication and lubricants" to be held on your premises.

 

 

Do you have any questions or need consulting?

Klüber Lubrication can look back on more than 90 years of experience in the fields of friction optimisation and specialty lubricants. We will be pleased to provide personal advice for your specific requirements regarding refrigeration compressor oils.

This is how you can reach us:Stefan ZuberGlobal Business Team Compressors Phone: +49-89-78 76 502 Email: Stefan.Zuber@klueber.com

Website: www.klueber.de

Editor and copyright: Klüber Lubrication München SE & Co. KGReprints, total or inpart, are permitted only prior consultation with Klüber Lubrication München SE & Co. KG and if source is indicated and voucher copy is forwarded. The data in this document is based on our general experience and knowledge at the time of publication and is intended to give information of possible applications to a reader with technical experience. It constitutes neither an assurance of product properties nor does it release the user from the obligation of performing preliminary tests with the selected product. It constitutes neither an assurance of product properties nor a guarantee of the suitability of the product for a specific application. They do not release the user from from the obligation of performing preliminary field tests with the product selected for a specific application. All data are guide values which depend on the lubricant's composition, the intended use and the application method. The technical values of lubricants change depending on the mechanical, dynamical, chemical and thermal loads, time and pressure. These changes may affect the function of a component. We recommend contacting us to discuss your specific application. Products from Klüber Lubrication are continually improved. Therefore, Klüber Lubrication reserves the right to change all the technical data in this document at any time without notice.

Klüber Lubrication München SE & Co. KG - Geisenhausenerstraße 7 - 81379 München Deutschland Munich District Court, HRA 46624

 

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In the first part of our training Basics of lubrication technology, we wrote about friction and wear as well as the various types of lubricants. In this part, we want to provide information on the basics of lubricating oils. It is to give you an overview of what lubricating oils are, what their structure and composition is, what types of oils there are and what benefits and drawbacks each one of them have.

 

 

What is a lubricating oil?

Lubricating oils are fluid media which act as intermediate substances depending on the frictional condition of the friction point, and normally assume the function of a design element. They are one of the most important types of lubricants and are also vital components when making lubricating greases.

"Oils" are fluid organic compounds, which have to meet various quality requirements depending on their intended use. Which requirements a lubricant must meet depends on the specific application.

  1. Reduction of friction
  2. Reduction of wear
  3. Reduction of energy losses
  4. Increase of service life using synthetic oils
  5. In line with food law
  6. Readily biodegradable
  7. Corrosion protection
  8. Heat transfer medium
  9. Coolant of heat dissipation medium
  10. Reduction of maintenance costs

 

 

What is the composition of a lubricating oil?

Depending on the intended use and field of application, the formulation of a lubricating oil comprises the following ingredients:

 

 

What is viscosity?

The viscosity is a measure for the thickness of a fluid. Viscosity is also referred to as the internal friction of a fluid. The higher the viscosity, the less capable of flowing is the fluid (e.g. honey). The lower the viscosity, the thinner is the fluid, i.e. capable of flowing quicker under the same conditions (e.g. water). The viscosity of an oil changes as a function of temperature. At low temperatures, oils become more viscous, at elevated temperatures they become thinner. Engine and vehicle gear oils are classified acc. to SAE classes, industrial oils acc. to ISO viscosity grades (ISO VG).

 

 

Which ISO viscosity grades (ISO VG) are there?

According to DIN 51519 there are 18 different viscosity grades. Every viscosity grade is determined for a temperature of 40°C (V40).

 

 

Viscosities and their uses in practice

  1. Low viscosity oils (ISO VG 2 - 100):

These are used as penetration oils, rust dissolvers, hydraulic oils, compressor and vacuum pump oils or low-temperature oils for components like chains, bearings and gears.

  1. Medium-viscosity oils (ISO VG 150 - 460):

These are used as gear and chain oils in industry.

  1. High-viscosity oils (ISO VG 680 - 1500):

These are used as adhesive oils for low-speed open drives and gears or for chain lubrication.

 

 

What are the most common industrial base oil types?

  1. Mineral oil (paraffinic, naphtenic and aromatic) (MIN)
  2. Polyalphaolefins (PAOs)
  3. Ester oils (E)
  4. Polyalkylene glycols (PAG)
  5. Silicone oils
  6. Perfluoropolyether oils (PFPE)

 

 

What is a mineral oil?

Mineral oil is made from crude oil by means of distillation and refining. It consists of hydrocarbon compounds. Depending on the molecular composition, we classify them into paraffinic, naphtenic and aromatic mineral oils.

 

There are applications where an inexpensive mineral oil can be a wise choice. It should generally be noted, though, that a high-performance synthetic oils is often economically more viable in the long term.

 

 

Price ranges of mineral vs. synthetic oils

 

 

What is a polyalphaolefin oil?

Polyalphaolefins are synthetic hydrocarbons (SHC) made from ethylen as the starting material. For this reason they are often referred to as "synthetic mineral oils". Polyalphaolefins consist of iso-paraffins with varying numbers of hydrocarbon side chains of the same length.

 

 

What is an ester oil?

Ester oils are synthetic lubricants. Esters are chemical compounds originating primarily from the reaction of acids (mostly organic/fatty acids) and ethanol, going along with the removal of water.

 

 

What is a polyalkylen glycol oil?

Polyalkylen glycols, also known as polyglycols, are polymerised ethylen oxide or propylen oxide entities or combinations thereof started by addition to an ethanol. For their solubility in water, the ethylen oxide content is what matters most.

 

 

What is a silicone oil?

Silicone oils are polymerised siloxanes with organic side chains. They are made by means of chemical synthesis, with silicon being their main component. Due to their excellent penetration and spreading behaviour, they are used as sliding agents, defoaming agents, sealing and hydraulic fluids, or as high-end lubricants. Silicone oils are clear, colourless, neutral in odour and taste and non-toxic.

 

 

What is a perfluorinated polyether oil?

Perfluorinated polyether oils are synthetic oils made up of carbon, fluorine and oxygen. They are used where stresses are extreme (e.g. at very high temperatures and pressure) and are resistant to most aggressive media.

 

 

Which base oils are intermiscible?

The following table serves for rough guidance. For a reliable determination of oil miscibility, we would in any case recommend to have corresponding tests conducted at the lubricant manufacturer.

 

 

 

What are additives?

Additives are soluble substances added to an oil to enhance its chemical and physical characteristics.

 

 

What additives might be added to industrial oils?

 

 

What are solid lubricants?

Solid lubricants are minute particles and flakes that are added to lubricating oils, greases and pastes. They smoothly slide against one another, thereby reducing friction. The most common solid lubricants are graphite, MoS2, ceramics and PTFE.

 

 

What are the characteristics of additives and solid lubricants?

 

 

Do you wish to acquire more in-depth knowledge of the subjects tribology, lubrication technology and lubricants?

Then the trainings offered by Klüber Lubrication might be an option for you. Twice to three times per year, we offer two-day trainings in Munich. Alternatively, you can order individual trainings tailored to your needs on the subject of "lubrication and lubricants" to be held on your premises.

 

 

Do you have any questions or need consulting?

Klüber Lubrication can look back on more than 90 years of experience in the fields of friction optimisation and specialty lubricants. We will be pleased to provide personal advice for your specific requirements regarding refrigeration compressor oils.

This is how you can reach us:Stefan ZuberGlobal Business Team Compressors Phone: +49-89-78 76 502 Email: Stefan.Zuber@klueber.com

Website: www.klueber.de

Editor and copyright: Klüber Lubrication München SE & Co. KGReprints, total or inpart, are permitted only prior consultation with Klüber Lubrication München SE & Co. KG and if source is indicated and voucher copy is forwarded. The data in this document is based on our general experience and knowledge at the time of publication and is intended to give information of possible applications to a reader with technical experience. It constitutes neither an assurance of product properties nor does it release the user from the obligation of performing preliminary tests with the selected product. It constitutes neither an assurance of product properties nor a guarantee of the suitability of the product for a specific application. They do not release the user from from the obligation of performing preliminary field tests with the product selected for a specific application. All data are guide values which depend on the lubricant's composition, the intended use and the application method. The technical values of lubricants change depending on the mechanical, dynamical, chemical and thermal loads, time and pressure. These changes may affect the function of a component. We recommend contacting us to discuss your specific application. Products from Klüber Lubrication are continually improved. Therefore, Klüber Lubrication reserves the right to change all the technical data in this document at any time without notice.

Klüber Lubrication München SE & Co. KG - Geisenhausenerstraße 7 - 81379 München Deutschland Munich District Court, HRA 46624

 

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What is tribology

"Tribology is a branch of science and engineering dealing with the interaction of surfaces moving relative to one another. It addresses the entire field of friction, wear and lubrication, and includes interaction between boundary surfaces of solid bodies as well as those of solid bodies, fluids and gases". (Definition acc. to former DIN 50323)

 

 

What does a tribo-system look like?

 

 

How is friction generated and how can it be prevented

Whenever surfaces adhere to one another, slide or roll against one another, friction is generated. The forces acting between the surfaces are referred to as friction forces. The most important cause of friction forces lies with the surface condition of the friction bodies. Friction forces always act against motion, impeding or preventing it.

On rough surfaces, large forces are required to move the bodies relative to one another. On smooth surfaces, small forces are sufficient. In practice, friction cannot be eliminated completely. Even on extremely smooth surfaces, some, albeit very low, friction will occur. Friction causes abrasion/wear.

A fluid, i.e. a lubricant, interposed between the contact surfaces of the friction bodies will have a smoothening effect. The fluid penetrates into the microscopically small valleys of the surface. A fluid layer separating the friction bodies forms. This is what we call lubrication. The fluid separating layer is referred to as lubricant.

Using the right lubricant contributes to separating the friction bodies and minimising wear. This leads to longer service life of the component, less energy consumption to move it and hence lower costs.

 

 

What types of friction are there?

 

Sliding friction is a type of dynamic friction between bodies sliding against one another (brake, plain bearing, piston in cylinder.

Rolling friction is also movement friction . The bodies that roll on each other theoretically touch each other in a point or line shape (point contact: sphere; line contact: cylinder). The normal forces cause elastic deformation at the contact point. When surface contact occurs, sliding occurs in the edge zones, which is referred to as deformation-related micro-sliding.

Rolling friction is another type of dynamic friction. The bodies rolling against one another theoretically have point or linear contact (point contact: ball; linear contact: cylinder). The normal forces cause elastic deformation at the contact zone. As the surfaces come into contact, sliding occurs on the edge of the contact zone, which is referred to as micro-sliding due to deformation.

Combined rolling and sliding friction may occur at the same time in the relative motion of two friction bodies in contact to one another.

Boring friction occurs between two bodies where one body rotates about an axis perpendicular to the contact point surface of the other body.

 

 

What friction conditions are there?

The friction condition has a major influence on the friction and wear behaviour in the components' contact zones. We distinguish between the following three friction conditions: boundary friction, mixed friction and fluid friction.

 

 

The Stribeck curve describes the characteristic of the friction force as a function of the friction speed under hydrodynamic lubrication. Hydrodynamic lubrication means that lubricant enters the lubrication gap due to the relative motion of two contact surfaces. The pressure of the lubricant causes separation of the two contact surfaces.

 

In boundary layer lubrication, the lubricant penetrates into the solid body, forming a reaction layer. The load then acts on the friction bodies' roughness peaks.

In mixed lubrication, the load acts partly on the lubricant film and partly on the roughness peaks touching each other.

In full-fluid lubrication, it is the lubricant which fully bears the load. The contact surfaces are completely separated.

 

 

What types of lubricant are there?

Lubricating oils

Lubricating oils are the most widely used technical lubricants. They reduce friction causing noise and, in particular, wear. Oils also help to dissipate heat.

Lubricating greases

Lubricating greases are lubricants made up of an oil, a thickener and various additives.

Lubricating pastes

Lubricating pastes have a basic makeup similar to that of greases, however with a higher content of solid matter (e.g. MoS 2 , graphite, copper, PTFE, ceramic)

Bonded coatings

Bonded coatings, or anti-friction coatings form a uniform, dry and friction-reducing lubricant layer on various materials and components. A bonded coating has a composition similar to that of a coloured paint, however instead of the coloured pigments it contains one or several solid lubricants.

Lubricating waxes

Lubricating waxes are no solid lubricants in the proper sense. However, they form a dry and adhesive layer on the surface to ensure reliable lubrication while reducing boundary and mixed friction. They consist of high-molecular synthetic hydrocarbons, additives and oil (mineral oil, synthetic hydrocarbon). From a specific temperature upwards, waxes become fluid. The melting point depends on the constituents and the composition of the wax.

Corrosion protection agents

Corrosion protection agents are substances that protect metal and other materials against undesirable decomposition (corrosion) processes. Corrosion occurs, among other things, when a material comes into contact with water.

 

 

What are the effects of lubricants?

 

 

Why are lubricants so important for the success of your company?

Matching specialty lubricants help reduce unplanned downtime caused by friction and wear, extend the maintenance intervals in machines and installations, reduce costs (e.g. operating costs, maintenance and repair costs), thereby increasing the profitability of your enterprise.

 

 

Do you wish to acquire more in-depth knowledge of the subjects tribology, lubrication technology and lubricants?

Then the trainings offered by Klüber Lubrication might be an option for you. Twice to three times per year, we offer two-day trainings in Munich. Alternatively, you can order individual trainings tailored to your needs on the subject of "lubrication and lubricants" to be held on your premises.

 

 

Do you have any questions or need consulting?

Klüber Lubrication can look back on more than 90 years of experience in the fields of friction optimisation and specialty lubricants. We will be pleased to provide personal advice for your specific requirements regarding refrigeration compressor oils.

This is how you can reach us:Stefan ZuberGlobal Business Team Compressors Phone: +49-89-78 76 502 Email: Stefan.Zuber@klueber.com

Website: www.klueber.de

Editor and copyright: Klüber Lubrication München SE & Co. KGReprints, total or inpart, are permitted only prior consultation with Klüber Lubrication München SE & Co. KG and if source is indicated and voucher copy is forwarded. The data in this document is based on our general experience and knowledge at the time of publication and is intended to give information of possible applications to a reader with technical experience. It constitutes neither an assurance of product properties nor does it release the user from the obligation of performing preliminary tests with the selected product. It constitutes neither an assurance of product properties nor a guarantee of the suitability of the product for a specific application. They do not release the user from from the obligation of performing preliminary field tests with the product selected for a specific application. All data are guide values which depend on the lubricant's composition, the intended use and the application method. The technical values of lubricants change depending on the mechanical, dynamical, chemical and thermal loads, time and pressure. These changes may affect the function of a component. We recommend contacting us to discuss your specific application. Products from Klüber Lubrication are continually improved. Therefore, Klüber Lubrication reserves the right to change all the technical data in this document at any time without notice.

Klüber Lubrication München SE & Co. KG - Geisenhausenerstraße 7 - 81379 München Deutschland Munich District Court, HRA 46624

 

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HFO / HFKW-blends as alternatives to HFKWs

The decision on the use of " low GWP" refrigerant 1234yf in vehicle air conditioning systems and the development of alternatives for other mobile applications and stationary systems has meanwhile initiated.

Primary objectives are the formulation of mixtures with significantly reduced GWP with similar thermodynamic properties as the HFKWs used today.

The basic components for this are the refrigerants R1234yf and R1234ze (E), which belong to the group of hydro-fluoro-olefins (HFO) with chemical double bond. They are characterized as preferred candidates in the sum of their characteristics. However, both refrigerants are flammable ( safety group A2L ). In addition, the volumetric cooling capacity is relatively low; it is approximately at R134a level for R1234yf and even more than 20% lower for R1234ze (E).

The list of other potential refrigerants from the HFO group is relatively long. However, there are only a few substances that meet the high requirements regarding thermodynamic properties, flammability, toxicity, chemical stability, compatibility with materials and lubricants. These include, for example, low-pressure refrigerants such as R1336mzz (Z) and R1233zd (E), which are primarily an option for liquid chillers with large turbocompressors or can be used with positive displacement compressors in high-temperature applications. R1233zd (E) has a (very) low ozone depletion potential (ODP). Upon release into the atmosphere, however, a rapid disintegration of the molecule occurs.

On the other hand, no suitable candidates with similar volumetric cooling capacity as R22 / R407C, R404A / R507A and R410A are currently in prospect for commercial application. Direct alternatives for these refrigerants with significantly lower GWPs must therefore be "formulated" as a mixture of R1234yf and / or R1234ze (E) with HFKW refrigerants, possibly even small amounts of hydrocarbons or CO2.

However, due to the properties of the HFKW refrigerants suitable as mixture components, flammability and GWP are diametrically related. In other words, mixtures as alternatives to R22 / R407C with a GWP

For R134a alternatives , the situation is more favorable. Due to the already relatively low GWP of R134a, a mixture with R1234yf and / or R1234ze (E) makes it possible to formulate non-flammable refrigerants with GWP approx. 600.

So currently two development directions are pursued:

  • Non-flammable HFKW alternatives (mixtures) with GWP values ​​according to the previously mentioned limits - Safety group A1. These refrigerants can then be used in terms of safety requirements in the same way as currently used HFKWs.
  • Flammable HFKW alternatives (mixtures) with GWP values ​​below any possible limits mentioned above - according to safety group A2L (for flame retardant refrigerants).

This group of refrigerants will then be subject to, among other things, fill quantity restrictions according to the future valid specifications for A2L refrigerants.

Non-flammable R134a alternatives

As previously mentioned, the starting point for developing non-combustible blends is most favorable for R134a alternatives. GWP values ​​of approx. 600 can be reached here. This is less than half compared to R134a (GWP100 = 1430). In addition, such mixture variants may have azeotropic properties, they can therefore be applied as single-component refrigerant.

For some time now, a blend developed by Chemours called Opteon ® XP-10 has been used on a larger scale in real plants. The results available so far are promising.

This also applies to a Honeywell-offered R134a alternative called Solstice N-13, which, however, differs in the mixture composition. Meanwhile, the refrigerants are listed in the ASHRAE nomenclature under R513A (Chemours) and R450A (Honeywell). The same category also includes the blends ARM-42 (ARKEMA) and R456A (Mexichem AC5X).

With these options, cooling capacity, power requirements and pressure levels are similar to R134a. This also allows components and system technology to be adopted. Only minor changes, such as overheating adjustment of the expansion valves, are required. Suitable lubricants are polyol ester oils, which, however, have to fulfill special requirements, for example when using additives.

Particularly favorable perspectives arise in supermarket applications in the standard refrigeration area in cascade with CO 2 for deep freezing. Likewise in liquid chillers with larger refrigerant charges, where operation with flammable or toxic refrigerants would require extensive safety measures.

Alternatives for R22 / R407C, R404A / R507A and R410A

Since the available HFO molecules (R1234yf and R1234ze) have a significantly lower volumetric cooling capacity than the above-mentioned HFKW refrigerants, relatively large proportions of HFKWs with high volumetric cooling capacity have to be mixed for the respective alternatives. The potential candidate list is quite limited, including R32 with the benefit of a relatively low GWP of 675.

 

Potential Blend Components for Low GWP Alternatives

 

With kind permission of Bitzer Kühlmaschinenbau GmbH 

Source: Bitzer Refrigerant Report 19 

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Viscosity describes the flowability / toughness of liquids. It is the measure of the internal friction of a liquid. The viscosity is also a temperature-dependent variable.

The higher the viscosity, the thicker the liquid. The lower the viscosity, the thinner the liquid.

The particles of viscous liquids are stronger or weaker bound together and thus immobile or movable.

In the simple model the viscosity is shown as follows. Two parallel plates are filled with a liquid. The bottom plate is fixed and the top is moved constantly. To maintain the movement, a force is required. This force is proportional to the area A of the plates, the velocity v of the movement and the resistance of the liquid. In addition, the force is inversely proportional to the thickness s of the liquid layer.

 

lights

 

The proportionality factor is the viscosity

Immediately on the plates, the liquid adheres and moves with the same speed. In the process, the layers lying further inward slide past each other at different speeds in the direction of the stationary plate. In the simplest case, the speed decreases linearly from the moving plate to the resting plate.

If the viscosity is independent of the speed, it is a Newtonian fluid with a linear velocity profile.

 

There are two types of viscosity: kinematic and dynamic. However, they are directly related.

 

dynamic viscosity:

 η = p • ν (and = rho • nu) in N • s / m 2

The dynamic viscosity of liquids depends on the flow state, temperature and pressure.

 

kinematic viscosity:

n = n / p (n = est / rho) in m 2  / s

The kinematic viscosity describes the ratio of the dynamic viscosity [η] and the density [ρ] of the liquid.

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Refrigeration Oils

The main task of a refrigerating machine oil is the lubrication of machine parts, the sealing inside the compressor as well as the dissipation of heat generated in the lubrication gap.

To ensure the safe operation of a refrigeration system, a favorable solubility behavior between lubricating oil and refrigerant is required. The refrigeration oil must not falter (even at low temperatures), and after the compression should be a quick separation of oil and refrigerant.

Inadequate solubility of the refrigerating machine oil impairs the oil return, too high a solubility can lead to a drop below the minimum viscosity required for compressor lubrication.

Critical to the selection is the behavior of a refrigeration oil - in mixture with the refrigerant - in certain temperature ranges, in which the mixture can disintegrate into oil-rich and oil-poor phases. One calls such a process a miscibility gap.

Advantageous therefore refrigerating oils that form a homogeneous phase with the refrigerant over a large temperature and concentration range.

After initial problems with the conversion of older plants to the new replacement refrigerants, a large number of refrigeration oils are now available for use with halogenated HFC refrigerants and other refrigerants for a wide variety of requirements. According to their chemical compositions, refrigerator oils can be assigned to the following five groups.

 

Mineral oils (M)

 

are hydrocarbon compounds and are derived from petroleum or coal. Most mixtures of this group belong chemically to the alkanes (paraffins, which are simply saturated hydrocarbons). Today, these refrigerant oils find their application in hermetic compressors. In semi-hermetic and open compressors, they were displaced by synthetic and semi-synthetic refrigerant oils *. Paraffinic mineral oils are used as refrigeration oils in turbo-compressors because of their good viscosity-temperature behavior. For lower temperatures, they are not suitable because they tend to paraffin precipitates under such conditions, which can lead to clogging of the expansion valve.

Naphthenic mineral oils contain the bicyclic aromatic hydrocarbon naphthalene and are dewaxed. These refrigerant oils can also be used in the low temperature range. An advantage of these refrigerant oils is the good solubility in HFC refrigerants.

 

Alkylbenzenes (AB)

 

are produced on a large scale catalytically from petroleum. They are not chemically very reactive and are mainly used as solvents. Certain compounds of this class can be used as refrigeration oils. They have a very good solubility in HFC refrigerants and are distinguished from mineral oils also by a low tendency to foaming (when starting compressors).

 

Polyalpha Olefins (PAO)

 

also known as poly-α-olefins, are highly specialized synthetic refrigeration oils developed for the use of HFC, NH3 and CO2 applications. Because of their good viscosity-temperature ratio, they are used primarily in screw compressors. They have a high thermal stability and a good cold flow property even at lower temperatures. However, the solubility in CFC refrigerants is not satisfactory.

 

Polyolester Oils (POE)

 

They are often used in conjunction with HFC refrigerants and HFC refrigerant blends because of their good solubility with these refrigerants. Occurring miscibility gaps are generally not critical. Polyol ester oils are hygroscopic and easily absorb water, which can also cause it to decompose. The cause of this behavior is the chemical origin of these oils, they are made from alcohol and an organic acid with elimination of water.

Moisture must be avoided in the refrigeration cycle as it can lead to acid formation in addition to other negative effects. If this is the case, the cause is usually the decomposition of the polyol ester oil.

 

Polyglykole (PAG)

 

Also called polyalkylene glycols, characterized by a low viscosity reduction at low temperatures and high thermal stability. The disadvantage is their very high water absorption capacity. Another disadvantage is the incompatibility of these oils with many materials, which must therefore be subjected to a special test before use.

PAG oils are mainly used in conjunction with R 134a in automotive air conditioning compressors and NH3 refrigeration systems.

 

* "Synthetic and semi-synthetic oils" are petroleum finninates to which synthetically produced hydrocarbons are added. This results in molecular structures that are not found in nature.

 

 

Source: Reisner, Klaus; Reisner, Timo

Expertise Refrigeration An introduction to education and training with tasks and solutions

6th, revised and expanded edition 2016 ISBN 978-3-8007-4098-7, e-book: ISBN 978-3-8007-4099-4

VDE VERLAG GmbH, Berlin - Offenbach

 
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