Screw Refrigeration Compressor Research Articles

Performance improvement of twin screw refrigeration compressors for chillers by modifying the suction arrangement

To improve the efficiency of the twin-screw refrigeration compressor at a high speed of about 3000 rpm, the suction arrangement was investigated in this paper. Several simplified CFD models of a twin-screw refrigeration compressor for chillers were established to parametrically analyze the influence of the suction delay, rotor wrap angle, and suction bearing distance. The parametric studies showed that the volumetric efficiency could be improved by 3 % by a suction delay of 18°, and more volumetric efficiency could be improved by shortening the length of it. The optimal delay angle was found to be linear with the rotational speed. Increasing the wrap angle from 300° to 330°, the volumetric efficiency decreased by 2–3 %, and the adiabatic efficiency increased by about 0.2 %. By increasing the distance between the suction bearings and the rotor end face from 5 mm to 80 mm, the isentropic efficiency increases by about 1.4 %. Based on the parametric studies, two modified machines were built and tested by experiments. Experimental results showed that the volumetric efficiency of machines #1 and #2 increased by 1.5 % at 3000 rpm. The isentropic efficiency of machine #2 increased by 0.78 % at 3000 rpm and 1.27 % at 3300 rpm.

HIGH PERFORMANCE TECHNOLOGIES USED IN FUSHENG SCREW COMPRESSORS 
 AUTHORS

In the context of negative changes occurring in the planets biosphere, such as pollution of the environment and the atmosphere, global warming, and depletion of energy resources, increasingly high criteria are imposed on manufacturers of refrigeration equipment, the most important of which are: (a) enhancement in the energy efficiency of refrigeration equipment; (b) decrease of material consumption of refrigeration units, and (c) use of clean and safe materials and refrigerants.
 The Taiwanese company, Fusheng, has been one of the world leaders in the production of screw refrigeration compressors for several decades. The experts at the company are always working to enhance the manufactured equipment and implement the most cutting-edge technologies.
 Recently, the most effective steps in this area have been the advancement and mastering of the manufacturing of special two-stage low-temperature screw compressors of the SRT series, as well as the production of compact screw compressors with an integrated BSR series oil separator with a variable compression ratio and semisealed screw refrigeration compressors with a volumetric capacity of 85 m3/h to 1946 m3/h
 The SRT compressor series consists of six types, with a first-stage volumetric capacity of 120759 m3/h and a second-stage volumetric capacity of 50300 m3/h

Experimental investigation on twin screw refrigeration compressor with different capacity control methods

Slide valve and variable-speed control are commonly used in twin screw refrigeration compressors independently to regulate the refrigerating capacity of the compressor. In this paper, the pressure fluctuation characteristics, noise characteristics, and thermodynamic performance of a twin screw refrigeration compressor with slide valve and variable-speed control at the same volume flow rate are tested and compared. The relationship among pressure fluctuation, noise characteristics, and thermodynamic performance is investigated, when the evaporating temperature and the condensing temperature are set to 6 °C and 36 °C, respectively. Results show that the compressor with variable-speed control has better comprehensive characteristics than that with slide valve. The noise of the compressor with variable-speed control is lower than that of the compressor with the slide valve and the reduction of noise reaches 10.52 dB(A) at the volume flow rate of 381.07 m3•h−1. The thermodynamic performance under part-load conditions of the compressor with variable-speed control is better than that of the compressor with slide valve. The improvement of COP and total efficiency reaches 33.57% and 38.16% at the volume flow rate of 381.07 m3•h−1.

Thermodynamic analysis of volume flow rate ratio on the performance of a NH3/CO2 cascade refrigeration system

NH3/CO2 cascade refrigeration system is the most potential and promising selection in low temperature applications. To meet the cooling demands of CRS at various working conditions, the capacity regulation of the screw refrigeration compressor is needed. This paper specifically studied the impacts volume flow rate ratio of high temperature cycle (HTC) and low temperature cycle (LTC) on the system performance. The simulation model of CRS including energy and exergy analysis was established. Based on the obtained results with the models, it can be found that there exists an optimum volume flow ratio that makes the maximum COP and exergy efficiency and the optimum volume flow ratio value is different under various working conditions. When the evaporation temperature is -55°C the optimum volume rate ratio is about 2.4 and corresponding maximum COP and exergy efficiency of CRS is 1.031 and 0.346, respectively. The optimum condensing temperature of LTC is -9.75°C. When the volume flow ratio is increasing, which means the motor frequency or rotational speed of HTC compressor increases while the rotational speed of LTC compressor is fixed, the optimum intermediate temperature decreases and the discharge temperature of HTC compressor increases proportionally. The cooling capacity could be enhanced by increasing the volume flow ratio. The obtained results are helpful for the screw refrigeration compressor regulation in CRS under various working conditions and cooling demands.

Noise control of a two-stage screw refrigeration compressor

Twin-screw compressors are widely used in refrigeration systems, but typically suffer from severe vibration and noise due to pulsing gas flow during operation. Gas pulsation is the main noise excitation source of screw compressors, presenting significant fundamental harmonic characteristics. This study examined noise control technologies for screw refrigeration compressor designs, such as acoustic wave interference, gas–solid resonance, and perforated muffler. Based on the structure characteristics and noise spectrum characteristics of a single-machine two-stage screw refrigeration compressor, several noise reduction measures were tested, including a half-wavelength tube, Helmholtz resonator, and multi-cavity series muffler. The experimental results show that after optimization, the noise measured on the exhaust side was reduced from 85.3 dB(A) to 81.9 dB(A) under the rated conditions of −25 °C evaporating temperature and 50 °C condensing temperature. At a constant 50 °C condensation temperature, the noise on the exhaust side of the compressor decreased from 93.7 dB(A) to 85.9 dB(A), an improvement of 7.8 dB(A), at 0 °C evaporation temperature. At an evaporation temperature of 5 °C, the noise on the exhaust side of the compressor decreased from 95.6 dB(A) to 86.5 dB(A), an improvement of 9.1 dB(A), indicating effective optimization under variable working conditions.

Heat transfer simulation in cavity of twin screw compressor under coupling of clearance leakage-heat by utilizing fuzzy beamlet finite element model

In order to optimize structure of twin screw compressor, and improve the working efficiency of twin screw refrigeration compressor, the heat transfer rules of cavity in twin screw refrigeration should be obtained correctly. Because the coupling of clearance leakage flow and heat transfer has a significant effect on heat transfer of cavity medium of twin screw refrigeration compressor, the heat transfer model of cavity medium under clearance leakage-heat coupling is constructed. To promote the computation accuracy and efficiency, the fuzzy beamlet finite element model is constructed by considering fuzzy affecting parameters and taking beamlet transform as interpolating function of element. The heat transfer laws of medium in cavity are obtained based on the theoretical an experimental analysis. Based on the simulation results, the computation error of fuzzy beamlet finite element method has least computation error and diversity than the other two methods for comparison, and the running time of fuzzy beamlet finite element method is least. Heat transfer analysis of medium in cavity under three conditions is carried out, and results show that temperature of cavity medium of twin screw refrigeration compressor is highest when the clearance leakage-heat coupling is considered and agrees better with reality; therefore, the proposed method has higher computing precision and efficiency than selected numerical methods according to computing results and running time. The impact of different clearances on heat transfer of medium in cavity is analyzed based on fuzzy beamlet finite element method, results show that the temperature of cavity medium increases accordingly as tooth top clearance, clearance between teeth, suction end clearance and exhaust end clearance increase, and the suction end clearance and exhaust end clearance have less effect on temperature of cavity medium.

Theoretical study on heat transfer characteristics of single screw refrigeration compressor with Multicolumn envelope meshing pair

In single screw refrigeration compressor (SSRC), the heat transfer has always been a key issue that affects its performance. However, the theoretical research on heat transfer characteristics of SSRC with Multicolumn Envelope Meshing Pair (MEMP) has not been carried out yet. Therefore, in this paper, a geometric model of heat transfer area and a theoretical calculation model describing the heat transfer process of the SSRC with MEMP are established to predict the heat transfer characteristics. The presented model is verified as a powerful tool for heat transfer characteristics analysis by the experimental results. With the validated models, heat transfer characteristics of the SSRC with MEMP under different operating parameters were researched and the effect of operating parameters on the heat transfer characteristics has been analyzed. All of these works can provide the basis for the later optimization design of heat transfer performance for the SSRC.

Characteristicsx and suppression of NVH in twin screw refrigeration compressors

Characteristics of NVH (Noise, vibration and harshness) in twin screw refrigeration compressors, mainly caused by mechanical vibration and turbulent gas flow, are discussed in detail. According to the different generation mechanism, suppression methods of mechanical NVH and hydrodynamic NVH are proposed, respectively. Mechanical NVH is related to rotor profile, bearings, lubricating conditions and maching precision, while hydrodynamic NVH is inevitable and severe for all positive displacement compressors due to gas compression and turbulent flow. Concluded from three cases of NVH suppression for semi-hermetic twin screw refrigeration compressors, half-wave method based on acoustic interference theory, pulsation damper evolving from Helmholtz resonator and broadband perforated tube silencer are effective paths to alleviate hydrodynamic NVH in twin screw refrigeration compressors without bringing in extra energy losses.

CFD Simulation and Experimental Study of Working Process of Screw Refrigeration Compressor with R134a

Twin-screw refrigeration compressors have been widely used in many industry applications due to their unique advantages. The performance of twin-screw refrigeration compressors is generally predicted by one-dimensional numerical simulation or empirical methods; however, the above methods cannot obtain the distribution of the fluid pressure field and temperature field inside the compressor. In this paper, a three-dimensional model was established based on the experimental twin-screw refrigeration compressor. The internal flow field of the twin-screw compressor was simulated by computational fluid dynamics (CFD) software using structured dynamic grid technology. The flow and thermodynamic characteristics of the fluid inside the compressor were analyzed. The distribution of the internal pressure field, temperature field, and velocity field in the compressor were obtained. Comparing the P-θ indicator diagram and the performance parameters of the compressor with the experimental results, it was found that the results of the three-dimensional numerical simulation were consistent with the experimental data. The maximum error was up to 2.578% on the adiabatic efficiency at the partial load working condition. The accuracy of the 3D numerical simulation of the screw compressors was validated and a new method for predicting the performance of twin-screw refrigeration compressors was presented that will be helpful in their design.

Theoretical study on wear characteristics of single screw refrigeration compressor with multicolumn envelope meshing pair

In single screw refrigeration compressor (SSRC), the wear of meshing pair has always been a key issue that restricts its development. In order to solve this problem, a Multicolumn Envelope Meshing Pair (MEMP) was proposed. However, the theoretical research on wear resistance of MEMP has not been carried out yet. Therefore, in this paper, a theoretical calculation model describing the influence of the MEMP profile parameters on wear characteristics of the SSRC with MEMP is established to predict the wear resistance. The presented model is verified as a powerful tool for wear characteristics analysis by the experimental results. With the validated model, the effect of MEMP profile parameters on the wear characteristics of SSRC has been analyzed. Optimization analysis shows that in the design stage more envelope columns with a larger center distance and larger envelope column diameter should be chosen for the MEMP to get a better wear resistance.

Theoretical research and optimization analysis for the injection process of the single screw refrigeration compressor

In single screw refrigeration compressor (SSRC), the liquid refrigerant injected into the working chamber is used to reduce the exhaust gas temperature and improve the compressor performance. In this paper, a new calculation model of the injection process considering internal compression, leakage and heat transfer is presented based on the meshing principle of the meshing pair and the working mechanism of the SSRC with injection. By this model, the actual capacity and injection quality can be obtained using the calculated effective injection area. The influence of the structural parameters such as the initial position and the injection-hole diameter to the characteristics of the injection process and the thermodynamic properties of the SSRC are analyzed. Through the comparison of the injection process with different structural parameters, optimization analysis of the structural parameters can be obtained. All of this work can provide the basis for the later optimization design of the injection process.

Performance investigation of a pressure pulsation dampener applied in the discharge chamber of a twin screw refrigeration compressor

Intermittent gas flow generates pressure oscillations in the twin-screw refrigeration compressor that cause serious problems such as structural vibration and noise. In order to reduce the amplitude of this pressure pulsation, a pressure pulsation dampener (PPD) applied in the discharge chamber of a twin screw refrigeration compressor was proposed based on the theory of Helmholtz resonator. A mathematical model was developed to design an optimal PPD by incorporating the R134-oil mixture sound speed model and the pressure pulsation simulation model. A comprehensive experimental study was then performed to validate the model and evaluate the effect of key parameters such as oil flow rate and cavity volume on attenuation performance of the PPD. Vibrational characteristics of the compressor equipped with and without the PPD were also measured and compared. Under the design frequency of 250 Hz, the vibrational acceleration of compressor under-chassis reduced by 36.2% to 41.1% when the compressor was fitted with the proposed PPD.

Optimization analysis of the motor cooling method in semi-closed single screw refrigeration compressor

Semi-closed single screw refrigeration compressors (SSRC) are widely used in refrigeration and air conditioning systems owing to the advantages of simple structure, balanced forces on the rotor, high volumetric efficiency and so on. In semi-closed SSRCs, motor is often cooled by suction gas or injected refrigerant liquid. Motor cooling method will changes the suction gas temperature, this to a certain extent, is an important factor influencing the thermal dynamic performance of a compressor. Thus the effects of motor cooling method on the performance of the compressor must be studied. In this paper mathematical models of motor cooling process by using these two methods were established. Influences of motor cooling parameters such as suction gas temperature, suction gas quantity, temperature of the injected refrigerant liquid and quantity of the injected refrigerant liquid on the thermal dynamic performance of the compressor were analyzed. The performances of the compressor using these two kinds of motor cooling methods were compared. The motor cooling capacity of the injected refrigerant liquid is proved to be better than the suction gas. All analysis results obtained can be useful for optimum design of the motor cooling process to improve the efficiency and the energy efficiency of the compressor.

Influence of Oil Injection System on Efficiency of Speed-Controlled Screw Refrigeration Compressor

The problems of enhancing the efficiency of screw refrigeration compressors with speed control of refrigeration output are studied. Based on a mathematical model developed, it is demonstrated that compressor efficiency depends a great deal on the operation of the oil injection system. When an oil injection system that ensures optimal compressor operation under fixed conditions is chosen, change in operation conditions does not cause significant loss of efficiency. At the same time, if the oil injection system is non-optimal, change in operation conditions does not enhance compressor efficiency. This means that the configuration of the oil injection system determines the level of compressor efficiency, which remains practically unchanged if the operation conditions are changed.

Effects of lubricating oil on the performance of a semi-hermetic twin screw refrigeration compressor

Lubricating oil is often employed in a twin-screw refrigeration compressor for lubricating bearings, sealing leakage paths, cooling refrigerant gas and regulating capacity. In this paper, the effect of lubricating oil on the performance of a semi-hermetic twin-screw refrigeration compressor is investigated. A mathematical model is established and a comprehensive experimental investigation is performed for this purpose. The model is validated using experimental data and then used to investigate the effect on compressor performance of lubricating oil supplied to the suction and discharge end bearings, and returned to the suction pipe. The results show that the compressor performance is reduced as the compensation oil injection flow rate increases in the suction pipe. However, as the compensation oil injection position moves from the suction pipe to a proper compression chamber position, the compressor efficiencies increase as the oil flow rate increases. The results also show that the compressor performance decreases as the oil flow rate increases at the suction end bearing. But the effect on the compressor performance of the lubricating oil supplied to the discharge end bearing depends on the oil temperature. Low temperature oil supplied to the discharge end bearing increases the compressor performance, while high temperature oil lowers the compressor performance. These analyses provide useful information for optimizing lubricating oil distribution to maximize energy efficiency in semi-hermetic twin screw refrigeration compressors.

Research of thermal dynamic characteristics for variable load single screw refrigeration compressor with different capacity control mechanism

In the single screw refrigeration compressor (SSRC), the capacity control mechanism is normally employed to meet the actual required cooling capacity under different load conditions. In this paper, theoretical calculation models describing the working process of the SSRC with the single slide valve capacity control mechanism (SVCCM) and SSRC with the frequency conversion regulatingmechanism (FCRM) are established to research the thermal dynamic characteristics for variable load SSRC under part-load conditions. Experimental investigation on a SSRC under part-load conditions is also carried out to verify the theoretical calculation models. By using these validated models, the thermodynamic performances and dynamic characteristics of the SSRC with different capacity control mechanism under part-load conditions have been analyzed and compared. Through the comparison, the economical efficiency andreliability of the SSRC with different capacity control mechanism were obtained. All of these works can provide the basis for the later optimization design for the variable load single screw refrigeration compressor.

Theoretical and experimental study on thermodynamic performance of single screw refrigeration compressor with Multicolumn Envelope Meshing Pair

In single screw refrigeration compressor (SSRC), the Multicolumn Envelope Meshing Pair (MEMP) was proposed to reduce the wearof the meshing pair. However, the application of this new type meshing pair will change the thermodynamicperformance of SSRC. It is necessary to research the thermodynamicperformance of the SSRC with MEMP to evaluate the value of the proposed MEMP. In this paper, a theoretical calculation model describing the working process of the SSRC with MEMP is established to predict the thermodynamicperformance of the SSRC. Experimental investigations on the performance of a SSRC with MEMP under different conditions are also carried out to verify the theoretical calculation model. Obtained results show that the theoretical calculation results are in good agreement with the experimental ones, which means that the presented theoretical calculation model is a powerful tool for performance analysis of the SSRC with MEMP. With the validated model, thermodynamicperformances of the SSRC with MEMP have been analyzed. The SSRC with MEMP is proved to have high volume displacement and volumetric efficiency butneeds slightlymore shaft power. The maximum increment of shaft power and volumetric efficiency of SSRC with MEMP is 5.06% and 3.7% respectively in all working conditions.

A semi-empirical method for assessing the performance of an open-drive screw refrigeration compressor

A semi-empirical modeling procedure for twin-screw compressor performance simulation is proposed in this paper. In detail, the compression process is split into a number of stages, taking into account fluid leakages, heat transfers as well as heat and power losses. Compared to the simplified models reported in technical literature for other positive-displacement units, a different formulation for ambient heat loss is proposed, while mechanical power losses are modeled according to torque losses depending on both load and viscous friction effects. The proposed model applies to open-drive compressors, so three specific units for refrigeration applications with medium-high evaporation temperature are selected as the test cases for model tuning and validation, based on manufacturer's catalog data. After the identification of eight parameters, the model is able to compute the mass flow rate, the shaft power and the fluid discharge temperature, as well as volumetric and compressor efficiencies and ambient heat losses.Contrary to geometric models, the semi-empirical procedure proposed in this study does not take the presence of lubricating oil into account, as (i) oil injection with no external cooling results in a thermal neutral process; (ii) the compression work for the oil is negligible in comparison with the one required by the refrigerant fluid; and (iii) even injecting oil at a lower temperature, no considerable saving in refrigerant specific work can be achieved. Actually, this hypothesis does not significantly affect the output of the model. As a matter of fact, referring to the first test case with the larger displacement volume and to the identification of the eight model parameters based on eight convenient data points, the mass flow rate delivered by the compressor is predicted with a maximum error up to 2.44%, and the shaft power is predicted with an even limited error, except for few points with the lowest and highest pressure ratios, where the shaft power is under-estimated by 5%. Moreover, fluid temperature at the compressor exhaust is calculated with an error within ±1 K for pressure ratios up to 7.5. Similarly interesting results are achieved for the other two test case compressors, with absolute values of the errors in mass flow rate and shaft power predictions always less than 3% and 5% respectively.Finally, further considerations on the actual possibility of generalizing the model to semi-hermetic units are suggested.

Research of leakage characteristics of single screw refrigeration compressors with the Multicolumn Envelope Meshing Pair

The Multicolumn Envelope Meshing Pair (MEMP) was proposed and has been applied for the single screw refrigeration compressor (SSRC) to reduce the wear of the meshing pair. However, the geometric model shows its changed shape of the leakage paths compared with the existing straight line envelope meshing pair (LEMP). It is necessary to research the leakage characteristics of the SSRC with MEMP and LEMP, to evaluate the value of the proposed MEMP. In this paper, the geometric model of the leakage paths between star-wheel and screw rotor is established. A two-phase leakage mathematical model for gas-oil flow is presented to predict the gas leakage rate of the SSRC with MEMP. The experiments of the performance of a SSRC with MEMP were conducted to verify the leakage mathematical model. Obtained results show the leakage of the SSRC with MEMP is a little bit smaller than that of the SSRC with LEMP.

Research on operating characteristics of single slide valve capacity control mechanism of the single screw refrigeration compressor

In the single screw refrigeration compressor (SSRC), the single slide valve capacity control mechanism (SVCCM) is the functional component used to achieve capacity control under different load conditions with cooperation of screw rotor and housing. In this paper, a new calculation model considering internal compression and leakage is presented to research the capacity control process and built-in volume ratio control process. By this model, the actual capacity and built-in volume ratio at different slide valve work locations can be determined using the calculated by-pass area and discharge area. The influences of structural parameters of the slide valve to the control characteristics of the capacity control process and the thermodynamic properties of the compressor are analyzed. Through the comparison of the capacity control process and the built-in volume ratio control process, the axial displacements of the slide valve required in the capacity control and in the built-in volume ratio control were obtained. All of this work can provide the basis for the later optimization design for the slide valve.