Single Screw Compressor Research Articles

A synergy-column envelope meshing pair profile for single screw compressors

Multi-column envelope engaging couples have been proposed for single screw compressors to reduce the friction and prolong the operational life. However, little is mentioned about the relationship between columns at opposite sides of the star-wheel teeth. An imbalance in the lubricant film forces would appear and influence the lubrication between the tooth and the groove. During a real design process, it is necessary to try several times for each different type of compressor to find the optimal combination of columns. In part, due to the large number of columns, it also makes both manufacturing processing and product testing difficult. In this paper, a synergy-column design method and its related manufacturing methods are presented. The locations and relationships of the designed columns can be prescribed by given the tooth width. Manufacturing of the rotor and star-wheel shows the new design method can be more efficient through processing. The stable operation results prove that the synergy-column envelope meshing pair can solve the star-wheel’s wear-out problem.

Performance study on a single-screw compressor for a portable natural gas liquefaction process

Portable natural gas liquefaction devices are widely used to exploit unconventional natural gas resources and one of key components is a compressor. In this paper, a new natural gas liquefaction process is simulated and optimized and a single-screw compressor with 200 mm diameter is designed to be applied in this process. To verify the performance of the single-screw compressor, an experimental system was set up and performance parameters were studied, including volumetric efficiency, specific power rate, shaft efficiency, irreversible loss rate and cooling efficiency of the lubricating oil. The influence of the lubricating oil on the volumetric efficiency was also observed. Furthermore, the impact of actual compressor performance on the liquefaction process was also analyzed. The results indicate that the performance of the compressor changes greatly when it operates deviating from its design condition. The maximum volumetric efficiency, shaft efficiency, irreversible loss rate and cooling efficiency of the lubricating oil are 0.91, 0.64, 0.56 and 0.22, respectively. The minimum specific power rate is 6.5 kW·(m3·min−1)−1. In addition, the lubricating oil has a good effect of sealing so that the volumetric efficiency can be improved by 10.5%. Considering the actual performance of the single-screw compressor, specific power consumption of the process increases by 43.3%.

Study on heat transfer of leakage flow in tooth tip clearance for single screw compressor based on fuzzy contourlet finite element method

ABSTRACTHeat transfer of leakage flow in tip clearance will reduce the working performance, and therefore it is necessary to study it in depth. To improve the computing effectiveness of heat transfer of leakage flow in the tooth tip clearance of the single-screw compressor, the fuzzy contourlet finite element model is constructed by combining the contourlet finite element method and fuzzy finite element method. First, the related research progresses are summarized. Second, heat transfer model of leakage flow in the tip clearance of single-screw compressor is constructed. Third, the fuzzy contourlet wavelet finite element model is established. Finally, heat transfer simulation of leakage flow in the tip clearance of single-screw compressor is performed, and the variables with fuzziness are chosen, which are transformed to random variables based on information entropy theory. The comparing analysis among simulation analysis and test results is performed, and results show that the contourlet finite element method has highest computing precision and efficiency. In addition, the temperature of leakage flow in the tip clearance (L1) is also obtained, and results show that the fuzzy contourlet wavelet finite element method can effectively obtain the temperature distribution rules with fuzziness.

New concept single screw compressors and their manufacture technology

Single screw compressors were generally acknowledged as one of the nearly perfect machines by compressor researchers and manufacturers. However the rapid wear of the star-wheel in a single screw compressor during operation is a key reason why it hasn’t previously joined the main current compressors’ market. After more than ten years of effective work, the authors of this paper have proposed a new concept single screw compressor whose mesh-couple profile is enveloped with multi-column. Also a new design method and manufacture equipment for this kind of compressor have been developed and are described in this paper. A lot of prototype tests and a long period of industrial operations under full loading conditions have shown that the mesh-couple profiles of the new concept single compressors have excellent anti-wearness.

Characteristics between the meshing pairs with different envelope profile in single screw compressors

Single screw compressors have been used in various industrial fields. However, because the star-wheel teeth are easy to wear, the market for the development of single screw compressors is limited. In order to extend the service life of the star-wheel, researchers have developed different kinds of star-wheel tooth profile, such as single line envelope profile, single column envelope profile, and multi-column envelope profile. These profiles greatly affect the lubrication characteristics between the star-wheel teeth and the screw grooves. In this article, the lubrication characteristics between the meshing pairs with different envelope profiles are analyzed. Results show that the pressure peak of the single line envelope profile, single column envelope profile, and multi-column envelope profile are 3.23×105Pa, 3.38×105Pa, and 4.31×105Pa, respectively. This means that the multi-column enveloped meshing pair can resist the biggest external impact load. The deviation angle (γ) of the single line envelope profile, single column envelope profile, and multi-column envelope profile are 0.0139°~0.0286°, 0.0225°~0.0306° and 0.0122°~0.0262°, respectively. Thus, the self-balancing ability of the multi-column enveloped meshing pair is the strongest, and the oil film thickness on both sides of the multi-column enveloped star-wheel tooth is the most reasonable, which indicates a good lubrication state during operation, that is, longer operation life of the star-wheel teeth.

Research on the injected effect by the narrow-slit injection orifice in screw compressors

A narrow-slit injection orifice in screw compressors (mainly in single screw compressors) is described in this paper. In contrast to the traditional injection orifice, the section is slit shaped but not circular. Liquid which is injected by the narrow-slit injection orifice appears as a curtain shape. The heat transfer area is increased so that the cooling effect is enhanced and the efficiency of the compressor is improved. The injected effect was simulated through the CFD software, and then the experiments were carried out. The study verified the accuracy of the simulation results and will provide a theoretical foundation for the design of a narrow-slit injection orifice in screw compressors.

Non-symmetric approach to single-screw expander and compressor modeling

Single-screw type volumetric machines are employed both as compressors in refrigeration systems and, more recently, as expanders in organic Rankine cycle (ORC) applications. The single-screw machine is characterized by having a central grooved rotor and two mating toothed starwheels that isolate the working chambers. One of the main features of such machine is related to the simultaneous occurrence of the compression or expansion processes on both sides of the main rotor which results in a more balanced loading on the main shaft bearings with respect to twin-screw machines. However, the meshing between starwheels and main rotor is a critical aspect as it heavily affects the volumetric performance of the machine. To allow flow interactions between the two sides of the rotor, a non-symmetric modelling approach has been established to obtain a more comprehensive model of the single-screw machine. The resulting mechanistic model includes in-chamber governing equations, leakage flow models, heat transfer mechanisms, viscous and mechanical losses. Forces and moments balances are used to estimate the loads on the main shaft bearings as well as on the starwheel bearings. An 11 kWe single-screw expander (SSE) adapted from an air compressor operating with R245fa as working fluid is used to validate the model. A total of 60 steady-steady points at four different rotational speeds have been collected to characterize the performance of the machine. The maximum electrical power output and overall isentropic efficiency measured were 7.31 kW and 51.91%, respectively.

Optimizing the performance of small-scale organic Rankine cycle that utilizes a single-screw expander

This paper deals with the operation and optimization of a down-scaled industrial organic Rankine cycle (ORC) for low-grade waste heat recovery. The system is a sub-critical regenerative ORC with a nominal power output of 11kW. The ORC unit has been assembled using off-the-shelf components including three identical plate heat exchangers, a liquid receiver, a multi-stage centrifugal pump and a single-screw compressor adapted to operate as an expander. The experimental results are used to evaluate the influence of the expander performance on the behavior of the ORC system at nominal and part-load conditions. The matching between the volumetric expander and the system operating conditions is also analyzed. Results showed that in the case of SES36, both the expander efficiency and system performance were maximized for a pressure ratio between 7 and 9. In the case of R245fa, while the system efficiency achieved values similar to SES36, but the expander maximum isentropic efficiency was 17% lower. Two analyses are carried out to optimize the operation of the ORC unit with R245fa. At first, the insights gained by analyzing the experimental data are used to evaluate the theoretical matching between volumetric expander and the system maximum efficiency in terms of the Second Law of thermodynamics. Secondly, a control-oriented steady-state cycle model based on empirical correlations calibrated on the experimental results is developed. The model is used to implement a feed-forward control strategy based on predetermined steady-state points that allow to optimize the operation of the ORC unit. The frequency of the pump is used as controlled variable. The steady-state experimental data of both working fluids is provided in an electronic annex.

싱글 스크류 압축기의 스크류 로터의 설계 및 가공

싱글 스크류 압축기의 스크류 로터의 설계 및 가공

Heat transfer analysis of single screw compressor under oil atomization based on fuzzy random wavelet finite element method

Oil atomization is an effective enhanced heat transfer method for single screw compressor, which can make the compression process of single screw compressor be close to the isothermal process, then the working efficiency can be improved. In order to obtain optimal atomization technology effectively, the heat transfer of single screw compressor is analyzed based on fuzzy random wavelet finite element method. Firstly, the relating researching progresses are summarized. Secondly, the heat transfer governing equation of single screw compressor is constructed based on large eddy simulation technology. Thirdly, the heat transfer wavelet finite element model of single screw compressor is established through using Hermitian wavelet function, and then the fuzzy random Hermitian wavelet finite element mode is established based on λ level set theory. Finally, the heat transfer rules of single screw compressor is obtained based on simulation analysis, the effect of atomization on heat transfer of single screw compressor is obtained, results can offer effective theoretical guidance for designing the novel atomization system for single screw compressor.

Study on mechanical vapor recompression system with wet compression single screw compressor

The mechanical vapor recompression (MVR) is a highly energy-efficient process, in which the compressor is the core unit. In order to improve the compressor efficiency the distilled water is atomized and injected into the compressor to cool down the overheated vapor during compression. The performances of the system with water injection compressor were tested and compared with a common compressor without water injection. Four groups of tests with different water spray rate were analyzed experimentally. The tests show that without water injection, the temperature difference increases sharply with frequency rising. It also shows that the values of compression ratio and evaporation capacity increase with the frequency increasing, and the values vary with the spray flow rate: the higher the flow rate, the larger the values. The values for the situations with water injection are closer to each other with the increas of the water spray rate while the situation without water injection is much lower. Specific moisture extraction rate, abbreviated as SMER is a parameter which reflects the removal water from the feed per kilowatt hour. With spray flow rate of 300kg/h the SMER is 34kg/kWh at frequency of 20Hz while the value is 25kg/kWh without water injection.

Hydrodynamic lubricating characteristics of water flooded single screw compressors based on two types of meshing pair profile

Reliability of the traditional single screw compressor (SSC) is poor since its discharge capacity decreases sharply. This is because that the lubrication between the screw and the gate-rotor meshing pair is poor, which leads to a rapid abrasion of the meshing pair. In this paper, a simulation model is established to analyze the lubrication problem of the meshing pair in the SSC. Based on the traditional single straight line enveloped meshing pair profile and the new proposed multi-columns-enveloped meshing pair profile, the hydrodynamic lubricating characteristics of the water-flooded single screw compressor are investigated. Results show that the water film can keep the gate-rotor tooth from contacting the screw thread flank during the meshing process in the optimized multi-columns-enveloped meshing pair, but the water film cannot keep the gate-rotor tooth from contacting the screw thread flank during the meshing process in the single straight line enveloped meshing pair. A prototype of the water flooded SSC with the optimized multi-columns-enveloped meshing pair was developed and has passed a 2000-h endurance test without discharge capacity reduction.

Research of the hydrodynamic lubrication characteristics of different meshing pair profiles in water-flooded single screw compressors

In this paper, we focus on the hydrodynamic lubrication properties of different meshing pair profiles (the gate-rotor tooth flank shape and the corresponding screw thread flank shape) of water-flooded single screw compressors. A test rig was designed to verify whether the water flowing through the meshing pair clearance could take load. Three specimens with different profiles were tested under the water-flooded condition. The balance position of the specimen, the water film thickness under different applied load and the effective water film carrying capacity were tested. A numerical model was proposed to calculate the water film pressure distribution and the effective water film carrying capacity under different film thickness. The numerical solutions were compared with the test results and showed good coherence. The results show that the three specimens can all get balanced under the water film torques and can restore balance after disturbances. The water film at the leading flank of the specimen with multicolumns enveloped profile has the largest water film pressure peak and effective carrying capacity. This study can be applicable in the design of single screw compressors meshing pair profile.

Deformation Analysis of the Main Components in a Single Screw Compressor

The single screw compressor is used in many fields such as air compression, chemical industry and refrigeration. During operation, different gas pressures and temperatures applied on the components can cause different degrees of deformation, which leads to a difference between the thermally induced clearance and the designed clearance. However, limited research about clearance design is reported. In this paper, a temperature measurement instrument and a convective heat transfer model were described and used to establish the temperature of a single screw air compressor's casing, screw rotor and star wheel. 3-D models of these three main components were built. The gas force deformation, thermal- structure deformation and thermal-force coupling deformation were carried out by using a finite element simulation method. Results show that the clearance between the bottom of the groove and the top of star wheel is reduced by 0.066 mm, the clearance between the side of groove and the star wheel is reduced by 0.015 mm, and the clearance between the cylinder and the rotor is reduced by 0.01 mm. It is suggested that these deformations should be taken into account during the design of these clearances.

An optimization of the star-wheel profile in a single screw compressor

Single screw compressors have been used in various industrial fields, but the star-wheel does not have a good durability as expected. Good hydrodynamic lubrication states can enhance the wear resistance of the star-wheel. However, the imbalance of the lubricant film forces which act on the front flank and the back flank of the star-wheel tooth have a great influence on the lubrication between the meshing pair. In order to improve the lubrication, an approach for optimization of the star-wheel profile is developed, and the optimization goal is proposed in this paper. Column envelope profile meshing pair in an oil-flooded single screw compressor is taken as an optimization example. After optimization, the lubrication states in clearance between the groove flanks and the teeth flanks are improved. The meshing pairs with optimal profile are applied in an oil single screw compressor, and the experiment data supports the optimization approach well.

Analysis and Optimization of Small Expansion Natural Gas Liquefaction Process

In order to develop small-scale natural gas liquefaction equipment, a small expansion natural gas liquefaction process was designed, which was based on the technical parameters of the single screw compressor and expander developed by Beijing University of Technology. The effect of the key parameters on the natural gas liquefaction rate and specific power consumption was simulated and optimized. The results showed that the liquefaction rate of the process can reach 100% and the specific power consumption was relatively low under the optimal operation conditions. These research results can provide theoretical basis for the design of small-scale natural gas liquefaction equipment.

Modeling and Manufacture of a PC-Type Single-Screw Compressor Rotor

This study aimed to effectively design, manufacture and simulate a single-screw compressor. In this paper, a mathematical model of a pc-type single-screw compressor was developed. The pc-type single-screw compressor was assembled using two gate rotors, a screw rotor and a frame. First, the mathematical model of a conical tooth was designed and a gate rotor equation was obtained through coordinate transformation. Then, the coordinate systems between the gate rotor and the screw rotor were set up. Using a homogeneous coordinate transformation matrix, the family of gate rotor surfaces was obtained. Based on gear theory, the equations of meshing between the gate rotor and screw rotor were determined. Substituting the equation of meshing into the family of gate rotor surfaces, the gate rotor and the screw rotor were generated and their geometrical model illustrated using a software package. Based on the developed mathematical models, the contact lines and stress analysis between the gate rotor and screw rotor were displayed. An edge contact between the gate and screw rotors was found, indicating the necessity of a plastic or a composite material to encircle the conical surface. A computer-aided manufacturing software package was used to simulate the manufacture of the screw rotor.

Design of the Curved Flank for the Star-Wheel Tooth in Single Screw Compressors

The wear of star-wheel teeth is an important problem in single screw compressors. In order to prolong the service life of star wheels, a new curved flank of the tooth is proposed. Section profile of the tooth flank is a curve, which could be elliptical, hyperbolic, involute, or new defined. The screw groove flank is the envelope surface corresponding to the surface of the tooth flank. During the tooth meshing with the groove, the contact line moves in the tooth flank area.

Experimental studies of the tooth wear resistance with different profiles in single screw compressor

The single screw compressor has been used in gas compression and refrigeration systems. However, the durability is not good as expected for the wear of its meshing pair. In order to improve the wear resistance and operation life, several new profiles of meshing pair have been proposed, but most of these new profiles have not been applied in products or verified by experiments. In this paper, an eccentric wheel abrasion test device was designed to investigate the wear resistance of different meshing pairs. Results show that dispersing abrasion area and making connect area continuous can improve wear resistance.

Optimal Design of Meshing Pair for Single Screw Compressor Based on Contact Wavelet Finite Element Analysis

Optimal Design of Meshing Pair for Single Screw Compressor Based on Contact Wavelet Finite Element Analysis