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Next generation lubrication research system
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The direct oil injection system in traditional lubrication systems for screw compressors introduces high losses due to friction induced by oil churning. The friction work also create a temperature build-up in the bearings, because of this are larger bearing clearances needed to achieve reasonable bearing life. This type of lubrication system is also expensive to manufacture since several of the components in the lubrication system have moving parts, such as pumps and oil level regulators. The purpose with this project is therefore to start the developing process for the next generation screw compressor. It will focus on increasing the oil lubrication system efficiency and therefore increase the total compressor efficiency and reduce cost of manufacturing. This first study is carried around an oil-mist lubrication system, if successful this will almost eliminate the problems with oil churning and therefore minimize friction. Reduced bearing clearances are also achieved since the increased efficiency overcomes the temperature build-up within the bearing. The power loss reduction due to oil churning in today's machines would be decreased from 8-12 kW to 3-4 kW. This corresponds to a saving of 650MWh over the life of the machine or 45.000USD with current US energy prices. A simpler design will also decrease the costs of manufacturing since it does not require any moving. The cost of the lubrication system today can approach 20% of the total system cost (80.000SEK of a 400.000SEK refrigeration unit). The oil-mist system is tested and operated in a real compressor environment that is designed to achieve all pressure and temperature that a real oil- mist system has to operate in. The final performance of this new lubrication system is evaluated with a bearing test stand built to simulate the axial and radial forces generated on real compressor bearings. The performance is given by measuring the variation in oil film thickness that is achieved from each running condition. The creation of oil-mist is done with a simple vortex head design that atomises the liquid oil into a fine vapour, the oil particles produced are in-between 0.5-1 mm in diameter. Pressure gradients are used both over the vortex to create the mist and to transport the mist to and through the bearings. The oil-mist is directed and sprayed onto the bearings with reclassifier heads, the reclassifiers control the oil-mist flow and therefore the oil film thickness that are generated on the bearing surfaces. The amount of oil necessary to lubricate an entire compressor is very low, less then 20 litres is enough for one entire year of running for a mid-size system. The oil-mist system is compact and has no moving parts, this results in a low-cost design in mass production. However, there is one problem for future applications, the bearings packages at the out-let side of the compressor already works at the highest system pressure and it is therefore not possible to drive the mist through the bearings since no pressure gradient exists. The high-pressure bearings must therefore be built-in so that a pressure gradient is created over these bearings and as a consequence a small efficiency drop is induced on compressor system. The concept with oil-mist in refrigeration applications works and the task ahead is to test the oil-mist system with different configurations together with the bearing test stand before a final evaluation of this system can be made. There are many main problems to solve before inexpensive and efficient system can be introduced, but the results so far are encouraging and with further developments is a compact and inexpensive lubrication unit in terms of operational and manufacturing costs possible.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Oil-mist lubrication, compressor systems, efficiency
Keyword [sv]
URN: urn:nbn:se:ltu:diva-43339ISRN: LTU-EX--01/233--SELocal ID: 13892489-b3c0-47dc-9e46-8227cb704b4bOAI: diva2:1016570
Subject / course
Student thesis, at least 30 credits
Educational program
Mechanical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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