Oil-free Compressor Research Articles

Research on oil-free hermetic refrigeration scroll compressor

A prototype of the oil-free hermetic scroll compressor for the application of the refrigeration system of the aviation devices was constructed. The performance of this prototype oil-free scroll compressor was simulated using a thermodynamic model, and was measured. And it was concluded that the prototype oil-free scroll compressor is useful for the refrigeration system of the aviation devices. The simulated results were consistent with the measured ones within less than 10 per cent of the mean deviation. When the evaporating and condensing temperatures were 5 and 55°C, respectively, the volumetric efficiency, discharge temperature, and coefficient of performance were 0.61, 135°C, and 1.45, respectively. The prototype oil-free scroll compressor had been operating reliably for more than 200 h under 85.7 per cent duty cycle and 20 h for 100 per cent duty cycle.

Twin screw oil-free wet compressor for compression–absorption cycle

The performance of a twin screw compressor operating under wet (two-phase) compression conditions in an ammonia–water compression absorption heat pump cycle is investigated both theoretically and experimentally. The paper reports on the influence of the location of liquid intake or, depending what applies, injection angle and mass flow rate of the injected liquid on compressor performance. Labyrinth seals separate the oil-free process side from oil lubricated bearing housing. Labyrinth seals leakage is modelled and its impact on performance is theoretically and experimentally investigated. The need for liquid injection from the discharge side to obtain acceptable performance is discussed based on experimental results.

Research on oil-free air scroll compressor with high speed in 30 kW fuel cell

To supply the clean compressed air to a fuel cell system, an oil-free compressor is needed. The working process of the oil-free air scroll compressor and its cooling feature are discussed in this paper. A prototype, delivering 100 m 3/h and having a speed of 5000 rpm, is researched. The water from the fuel cell system is used as the lubricant of the bearings and the moving parts of the compressor. The prototype of the oil-free air scroll compressor has been designed, fabricated and tested, and the performances are satisfactory. Whatever material the scroll parts are constructed of, for example, aluminum alloy or titanium alloy, the trend of the compressor delivery with rotary speed is similar. However, the power consumption varies with the materials and the surface coating of the scroll parts because different materials and surface coating have different friction coefficients.

A new closed-loop cryosurgical device for endometrial ablation

A new cryosurgical device was developed in an attempt to overcome problems of current systems. It incorporates a mixed-fluid J-T stage, thereby reducing working pressure. This allows incorporation of an oil-free compressor to circulate the mixture and eliminates the need for coolant replenishment. The compressor console is small and portable, with a footprint of 3.5 square feet. Probe surface temperatures of −90 to −110°C are achieved. Working pressures are reduced 3- to 10-fold over existing devices (300–350 p.s.i.). In a live goat study, liver ice balls 3.7 cm in diameter were created in 10 minutes. In an extirpated uterus, in a 37°C water bath, tissue ice balls ranging from 29.1 to 35.4 mm were created in 6 minutes and tissue was destroyed to depths of 6 to 12 mm. This cryosurgical system is suitable for endometrial ablation.

The Design, Selection, and Application of Oil-Free Screw Compressors for Fuel Gas Service

Fuel gas compressors installed in cogeneration systems must be highly reliable and efficient machines. The screw compressor can usually be designed to meet most of the gas flow rates and pressure conditions generally required for such installations. To an ever-increasing degree, alternative sources are being found for the fuel gas supply, such as coke-oven gas, blast-furnace gas, flare gas, landfill gas, and synthesis gas from coal gasification or from pyrolysis. A feature of the oil-free screw compressor when such gases are being considered is the isolation of the gas compression space from the bearing and gear lubrication system by using positive shaft seals. This ensures that the process gas cannot be contaminated by the lubricating oil, and that there is no risk of loss of lubricant viscosity by gas solution in the oil. This feature enables the compressed gas to contain relatively high levels of particulate contamination without danger of “sludge” formation, and also permits the injection of water or liquid solvents into the compression space, to reduce the temperature rise due to the heat of compression, or to “wash” any particulate matter through the compressor.

Analysis of Internal Clearance of Oil-Free Screw Compressor and Its Application to Performance Simulation.

Clearance between male and female rotors and that between the rotors and casing of an oil-free screw compressor in operation are calculated. Surface displacement vectors of both rotors due to, for example, thermal deformation, profile errors, and deviation of the center distance, are converted to such that the clearance between the rotors changes assuming that the rotor surface is approximated by a plane in the vicinity of the calculating point and that the normal line of the plane does not change direction before or after the displacements. The calculation is applied to a computer simulation for predicting air compressor performance. Change in volumetric efficiency related to suction air temperature was calculated and the results agreed well with experimental ones.

Analysis of a hybrid compression—absorption cycle using lithium bromide and water as the working fluid

Hybrid refrigeration cycles which combine a mechanical compressor and an absorption cycle in such a way that they share a single evaporator were analysed. The motivation for the investigation of hybrid cycles was the need to more efficiently utilize the output of an internal combustion engine. The hybrid cycles make efficient use of both the work and the heat output of an engine. Performance calculations are reported for a promising cycle which utilizes LiBr-H 2O as the working fluid. For this working fluid, the refrigerant is water. Owing to the potential sensitivity of the absorption cycle components to oil contamination, the cycle was analysed assuming an oil-free steam compressor (screw design). Although oil-free steam compressors are available, they are used only sparingly in the industry. The capital cost for such a compressor is very high and the isentropic efficiency of the available units is low. This combination of high cost and low performance results in poor economics for the hybrid cycle based on the available technology. However, the cycle has significant potential from a thermodynamic viewpoint and it provides an incentive for compressor manufacturers to refine the oil-free steam compression technology.

A 3He purification system based on a new method using ultrathin polymer tubes

A new 3He purification system has been developed for use with an ion source of a cyclotron. The method of purification is based on the principle of gas diffusion through an ultrathin polymer layer. The essentials of this system are two modules consisting of many thin polymer tubes. Two oil-free diaphragm compressors pressurize the contaminated gas to the modules through which purified 3He seeps out, and force it onto the ion source for recycling continuously. The gas compositions at several points of the system are investigated with a quadrupole mass analyzer. The total system is capable of supplying 3He with almost constant purity of more than 99% in all operating time for 3He ion acceleration at the cyclotron. The system was initially charged with 61 3He to keep the flow rate of 2 cm 3/min at standard temperature and pressure (STP) for a three-days operation. Neither periodic attention to the system nor regeneration of the modules was required in many continuous four- or five-days runs.

Les hélico compresseurs ou compresseurs à vis

In the first part of the paper the patenting of the helical compressor at the end of the last century by a Swedish engineer as a type of air and gas blower, modified some 50 years later by another Swedish engineer as an air and gas compressor, is discussed. Decade by decade, the machine was developed by the Swedish firm SRM and by their licenced manufacturers machining the screw compressor in Sweden, Germany, France, Scotland, etc. At the present time this type of compressor seems to be fully developed and occupies a first class position in the range of positive displacement machines. Recently, a new type of screw compressor has been patented by a French engineer, this machine having only one main rotor and two small satellites, compared with the early type which had only two main rotors. These two types of compressors are now competing on the refrigeration market all over the world. In the second part of the paper, all the improvements made during the 50 yeats of development are examined in detail. In the beginning, the screw compressor was designed as an oil free compressor and was not very well adapted to the refrigerating plants, this type of oil free compressor still being used for the compression of pure gases. The first improvement was the oil injected screw compressor allowing the machine to support high compression ratios and large pressure differences and some time later, to be fitted with a sliding valve for the purpose of volume adaptation. One other modification to the profile of the rotors results in greater compressor efficiency allowing it to work with higher compression ratios; for example, in the case of low temperatures such as are used for the freezing of food products. This is not a good solution for saving energy, and the performance has been improved by creating a complementary orifice designed as a superfeed port. This increases the global efficiency of the whole circuit with a screw compressor. The same improvements were carried out on the mono rotor screw compressors and now the two types of compressors are competing with the same auxiliaries imposed by the special lubrication of this type of machine. Some comparisons are made with reciprocating and centrifugal compressors.

529. Gaskets for joining glass devices to high vacuum pumping systems: G A Gusev and A I Kurilko, Electronic Technology, Scient-Techn Collect, Technology and Organisation of Production, No 3, 1971, 33–37 ( in Russian)

A small closed-cycle liquefier and cryostat, liquefying He3 by Joule-Thomson expansion, is described. Its characteristics, operation, and performance are discussed. The JT expansion takes place from pressures of 4 atm abs or less at flow rates up to 14 litres (s t p) min−1. The closed cycle character of the circulation is maintained by use of an oil-free diaphragm compressor. The coefficient of liquefaction at an input pressure of 4 atm is about 59%, which at the maximum flow of 14 litres (s t p)−1 corresponds to a refrigerative capacity at 3·2 K of 230 mW. When used as a cryostat, the liquid He3 chamber has a capacity of 40 cm3 and this can be filled in a few minutes. Using a built-in adsorption pump, temperatures down to 0·25 K can be maintained for periods up to 50 hours under conditions of minimal refrigerative loading. Using the quantitative results obtained with this liquefier, deductions are made regarding the inversion curve of He3 and a design has been made for a cryostat covering the temperature range 0·25 K and upwards, which does not require any liquid refrigerants, such as liquid nitrogen, liquid hydrogen, or liquid helium.

A closed-cycle Joule-Thomson liquefier and cryostat for He 3

A small closed-cycle liquefier and cryostat, liquefying He 3 by Joule-Thomson expansion, is described. Its characteristics, operation, and performance are discussed. The JT expansion takes place from pressures of 4 atm abs or less at flow rates up to 14 litres (s t p) min −1. The closed cycle character of the circulation is maintained by use of an oil-free diaphragm compressor. The coefficient of liquefaction at an input pressure of 4 atm is about 59%, which at the maximum flow of 14 litres (s t p) −1 corresponds to a refrigerative capacity at 3·2 K of 230 mW. When used as a cryostat, the liquid He 3 chamber has a capacity of 40 cm 3 and this can be filled in a few minutes. Using a built-in adsorption pump, temperatures down to 0·25 K can be maintained for periods up to 50 hours under conditions of minimal refrigerative loading. Using the quantitative results obtained with this liquefier, deductions are made regarding the inversion curve of He 3 and a design has been made for a cryostat covering the temperature range 0·25 K and upwards, which does not require any liquid refrigerants, such as liquid nitrogen, liquid hydrogen, or liquid helium.

Paper 19: The Oil-Free Screw Compressor

The initial development of oil-free screw compressors took place during the 1940s and 1950s. The research work carried out demonstrated that the compressor had a number of highly desirable features, many of which were not obtainable from existing compressor types. In addition, it was determined that the operating range of pressure and volume for which the compressor proved most suitable was effectively between the ranges of reciprocating and aerodynamic compressors. This paper discusses the principles used in designing a range of high-performance, oil-free screw compressors incorporating the knowledge learnt from earlier development work. The effect of operating conditions on performance is described and the limiting parameters identified. Certain effects of multi-staging are described, and a short description given of developments in screw compressors other than those that are oil free.

A low temperature plant for the production of heavy water

A plant for the production of heavy water, which was erected by Sulzer Brothers for Emser Werke AG. at Domat/Ems, Switzerland, is described. The raw material is natural water which first undergoes seven-fold deuterium enrichment in three electrolysis stages. The gaseous mixture of hydrogen and deuterium produced by electrolytic dissociation is cooled to --251 ts C. The liquid then goes to a Kuhn rectifying column, where the exchange processes taking place at 22 ts K result in 400-fold deuterium enrichment. The product of the column is burned with oxygen and then passed to a second Kuhn column in which the D/sub 2/O concentration is brought up to 99.8%. The plant at Ems employs oil-free labyrinth-piston compressors and highspeed expansion turbines for hydrogen. High vacuum is used to insulate all heat exchangers, turbines, and control units. (auth)

Oilfree Compressors

It is frequently essential to secure supplies of oilfree compressed gases and the normal type of compressor, with piston lubrication, cannot be employed. Oilfree compressors may also have to be used where there is danger of explosions due to lubricating oil mist, and still another instance where oilfree compressors must be used is in cases where the gases being compressed would have a chemical action on the lubricating oil if it were present.