Scroll Wrap Research Articles

Modeling and analysis of a novel CPSC/CI combined profile for scroll compressors

The scroll profile design has become a research hotspot and plays a decisive role in scroll machines. However, the modeling process is complicated due to different expressions of peripheral and central profiles in most full meshing profile (FMPs). Moreover, systematic modeling and in-depth property investigation of scroll profile are still insufficient. Herein, this study simplifies scroll profile modeling by constructing a novel FMP that combines a cubic power series curve (CPSC) with a circular involute (CI) to improve the properties of scroll compressors. An analytical model of CPSC/CI scroll wraps is proposed using the orthogonal components approach and validated by numerical examples. Geometric models to calculate chamber volume and gas load action length, and gas load models, are established. The effects of the CPSC/CI on the scroll wrap tip, built-in volume ratio and gas load are investigated. The proposed CPSC/CI enhances scroll compressor's properties by providing favorable properties not only with wider range of variation in scroll wrap tip and built-in volume ratio but also smaller gas load vibrations due to its superior flexibility, compared to circular arc/CI. This study provides new possibilities for enhancing scroll compressor performance through the design of scroll wrap profile.

Geometric modeling and performance analysis of a combined algebraic spiral scroll compressor

This study proposed a combined algebraic spiral (CAS) scroll compressor with a profile that consists of two algebraic spirals with different parameters smoothly connected by a higher-order curve. The advantage lies in the ability of the ending algebraic spiral to regulate the stroke volume and wrap size, while the starting algebraic spiral can control the discharge volume and the center part of the wrap, thus improving the geometric performance of the scroll compressor. The research established the geometric model of CAS scroll wrap and conducted parametric studies. The results indicate that CAS scroll compressor exhibits the minimum discharge volume, maximum stroke volume, and compression ratio when both the discharge volume chamber and the stroke volume chamber are entirely constructed using the algebraic spiral. Moreover, it was observed that the radial leakage curve length decreases as the polar angle at the connection point increases. Under identical wrap diameters and adequate minimum wall thickness, a larger spiral coefficient may be chosen for the ending algebraic spiral in order to enhance geometric performance. Conversely, a smaller spiral coefficient and spiral index for the starting algebraic spiral can improve compression and reduce leakage. Moreover, in comparison to a single algebraic spiral scroll compressor with an equivalent wrap size, CAS scroll compressor exhibits a 20.62% decrease in discharge volume, a 31.62% rise in compression ratio, a 30.75% reduction in radial leakage curve length, and superior geometric performance when compared to other algebraic spiral scroll compressors.

Study on the contact and size of radial and flank leakage gaps of scrolls in a scroll compressor with CFD/CSM simulations

The leakage gaps in scroll compressors are crucial to the performance and the correction of scrolls to reduce these gaps needs a better understanding of the deformation and contact of scrolls under actual operating conditions. In this study, the Computational Fluid Dynamics model of the scroll compressor is established to obtain the temperature and pressure loads on scrolls. The comprehensive deformation of scrolls under loads and contact behaviors with given orbiting radii are calculated by Computational Structural Mechanics. Results show the significant space-time inhomogeneity of both flank and radial leakage gaps. Although the average flank leakage gap size can be reduced to a certain value if orbiting scroll operated under the ideal orbiting radius at the cost of the large radial contact force. The deformation unevenness and the contact of the scrolls retards the further decrease of flank leakage gaps. The radial leakage gap in specific scroll tips fluctuates during one cycle, but the more stable downward trend along the scroll wrap makes it easier to compensate the gap by gradually reducing the scroll height from outer to inner.

가변속 전동 스크롤 압축기의 스윙 부시 설계에 관한 연구

For a variable speed electric scroll compressor used for vehicle heat pump system, an eccentric bush combined with counterweight, so called swing bush, is widely used as a radial compliance device to control orbiting radius. Rotation radius of swing bush is a key design parameter in determining both sealing force magnitude exerted on the scroll wrap flank and restoring ability of the orbiting scroll back to its normal position after recess due to abnormal chamber pressure rise caused by the presence of refrigerant droplets, for instance. In this study, an analytical model for swing bush dynamics is presented and a way of optimum design is illustrated by a parametric study.

A computationally efficient scroll compressor model for both single-phase and two-phase compression considering scroll wrap temperature distribution

A general scroll compressor model with high accuracy, fast simulation speed and good numerical robustness is proposed in this study. The governing ordinary differential equations derived from mass and energy conservation use pressure and specific enthalpy as state variables, which can be applied to both single-phase compression and two-phase compression. Both the governing equations for inner compression and the nonlinear equations for internal leakages are explicit in pressure and specific enthalpy to avoid severe numerical stiff problems. In addition, the detailed scroll wrap temperature distribution is calculated based on the proposed second order differential equation considering heat conduction and periodic heat convection. Validation against experimental data shows that cooling capacity errors are less than 3.5% and power consumption errors are less than 2.8% in non-injection and liquid injection conditions. Evaluation of model speed and robustness shows that the model has a convergence rate of 100% and an average calculation speed of 12.4 s per case in various conditions.

Impact of micro-grooves in scroll wrap tips on the performance of a trans-critical CO2 scroll compressor

Radial leakage was commonly regarded as the primary factor restricting the aero-thermodynamic performance of scroll compressors. In this paper, a passive flow control approach of micro-grooves in scroll wrap tip for the radial leakage in the scroll compressor was proposed, and its flow characteristics were numerically investigated. The impact of micro-grooves geometric parameters, such as groove number, depth, and partitions, on the flow control effect of the radial leakage was discussed, which was obtained by analyzing the evolution of the flow field and its influence on the performance of the scroll compressor. Results showed that the adoption of micro-grooves in scroll wrap tip yielded a significant limitation on the radial leakage, and geometrical parameters of the micro-grooves directly affected the flow control performance. Increasing groove numbers and partitions decreased the radial leakage effectively, while the leakage decreased first and then increased with the increase of the groove depth. The energy dissipation induced by the continuous throttling effect, jet expansion, and vortex in the groove cavity was the main flow control mechanism. The quadruple-grooves with the groove width of 0.5 mm and the groove depth of 100 μm were adopted in this study eventually. The volumetric and isentropic efficiency of the scroll compressor raised up 2.1 and 1.0 percentage point compared to the original case, respectively. Through reasonable working conditions and micro-grooves geometry, the aero-thermodynamic performance of the oil-free scroll compressor could be improved effectively by the scroll wrap tip with micro-grooves.

Geometric design and analysis of scroll compressors with a novel circular involute modified wrap

The scroll geometry in the central region of the scroll wrap plays a crucial role in determining the working performance of scroll compressors. In order to improve the comprehensive performance of scroll wraps, in this study, a novel circular involute modified wrap was put forward, in which the central and peripheral wrap profiles were connected by a circular involute in the central regions, so that a pair of fully smooth and correct meshing scroll wraps were generated. A geometric model of the involute modified wrap were proposed, and then equations of the wrap profiles and relations between geometric parameters were derived. Effects of geometric parameters on the shape and performance of the involute modified wrap were discussed in detail. Furthermore, the compression ratio of the involute modified wrap was studied by numerical simulation, and the deformation of the involute modified wrap produced by temperature load and pressure load was calculated, compared with the conventional circular arc modified wrap under the same geometric shape of scroll compressors. Study results demonstrate that the proposed involute modified wrap may simultaneously improve the compression ratio and the strength of wrap head for scroll compressors; in addition, the involute modified wrap is good for design flexibility, and therefore is superior to the circular arc modified wrap.

Simulation of the Deformation and Contact of Scrolls in the Scroll Compressor

The control of the clearances in a scroll compressor is crucial to ensure the reliability and efficiency of compressor, especially for the compressors without radial compliance mechanism. In this study, the fluid-solid-thermal simulation is conducted to get the temperature field, the pressure load distribution on scroll wraps. Then, the influences of the temperature, pressure and the inertial force on the deformation of scroll wraps are investigated. On these bases, the variation of gap size and potential contact between scroll wraps is analysed under various orbiting radii. It is shown that the deformation caused by temperature is more significant than the pressure and inertial force. The contact occurs even though orbiting follows the theoretical orbiting radius due to the positive radial deformation of scroll wrap and negative radial deformation of inner wall of fixed scroll.

Leakage and friction characteristics at sliding surface of tip seal in scroll compressors

• Simultaneous measurement of leakage and friction at tip seal was conducted. • The influence of several parameters on seal effect and friction was clarified. • The influences of several parameters on seal effect and friction were generalized. • Lubrication condition at the tip seal based on the Stribeck curve was clarified. A tip seal is applied to prevent a radial leakage at a tip of scroll wrap in scroll compressors. When the tip seal is pressed hard against a base plate of the scroll, the radial leakage will decrease, while friction at the tip seal will increase. There is a trade-off between the leakage and the friction. It is needed to clarify the relationship between the leakage and the friction at the tip seal to optimize a scroll compressor design. In this study, a test apparatus which could evaluate the leakage and the friction at sliding surface of the tip seal simultaneously was developed. The influence of several parameters, such as upstream pressure, length and width of the tip seal, oil supply rate, rotational speed and oil viscosity, on the seal effect and the friction was examined with the test apparatus, and the influences of these parameters were generalized.

Design Method of Offsetting the Orbiting Scroll and Its Influence on the Self-Rotation Characteristics of the Orbiting Scroll

In order to reduce the diameter of compressor casing of the automotive scroll compressor, the orbiting scroll is sometimes offset along a certain direction. This paper summarizes the method of offsetting the orbiting scroll, and analyses the influence of the offset amount on the self-rotation characteristics of the orbiting scroll. The theoretical calculation results show that a larger offset amount is beneficial to increase the stroke volume, however it is easy to make the orbiting scroll rotate around its driving center in the negative direction which would cause an impact on the scroll wrap and the anti-rotation mechanism. At last, this paper affords some advices in how to offset the orbiting scroll.

전동식 스크롤 압축기의 축 방향 순응 기능 향상에 대한 연구

For an electric scroll compressor used for automobile air conditioning, a way of improving the axial compliance mechanism has been suggested, and an analytical study has been performed to demonstrate improved performance. For this improvement, a back pressure hole is suggested to be made, at the location such that it is to be exposed to central high pressure compression chambers, while limiting exposure time by partially covering the hole inlet with fixed scroll wrap tip. In this way, back pressure build-up time was significantly shortened, with no drawback in mass flow rate, compared to the conventional back pressure hole mechanism.

Analyses of Deformation and Stress of Oil-free Scroll Compressor Scroll

The solid model of orbiting and fixed scroll is created by the Solidworks The deformation and stress of scrolls under gas force, temperature field, inertia force and the coupling field are analyzed using the Ansys software. The deformation for different thickness and height scroll tooth is investigated. The laws of deformation and stress for scrolls are gotten. The research results indicate that the stress and deformation of orbiting scroll are mainly affected by the temperature field. The maximum deformation occurs in the tooth head of scroll wrap because of the largest gas forces and the highest temperature in the tooth head of scroll wrap. The maximum stress is located in the end of the tooth, and the maximum stress of the coupling field is not the sum of loads. The scroll tooth is higher, and the deformation is bigger. The scroll tooth is thicker, and the deformation is smaller.

Unsteady Leakage Flow Through Axial Clearance of an ORC Scroll Expander

As the scroll-type expander (STE) becomes an attractive expansion device for small-scale organic Rankine systems, performance enhancement of STE could achieve a further improvement of the energy efficiency of ORC system. The gas leakages through the axial and radial clearances have a great effect on the overall performance of STE. The present work proposed a three-dimensional numerical technique available for modeling the radial leakage flows through the axial clearances at the tip and root of scroll wrap. The radial leakage flow patterns of both axial clearances are investigated. Asymmetrical distribution of the radial leakage flow through the axial clearances at both sides of working chambers are revealed. Leakage flow difference between the top and bottom axial leakage clearances is comparatively discussed. The effects of radial leakage on the flow fields in the working chambers are also analyzed. The results show the radial leakage flows occur at the axial clearances of both the scroll segments between asymmetrical working chambers and those between symmetrical working chambers. Radial leakage flows through the top and bottom axial clearances are approximately symmetrical about the meshing line. Pressure distribution in the axial clearance passage is uneven along the scroll involute direction, especially in the axial clearance passages between asymmetric chambers. Pressure distortion occurs in the downstream of the axial clearance passage between asymmetric working chambers nearby the mesh point of the scroll wraps. Radial leakage flow leads to the secondary vortex flows and non-uniform pressure distributions in the working chambers.

Design and testing of an algebraic scroll expander for power generation from a waste heat recovery system

A scroll expander was designed, fabricated, and tested as a power converting device in a waste heat recovery system fitted to the cooling system of internal combustion engine. An algebraic spiral was adopted as the base curve for the scroll wrap profile for the compact scroll design. A reduction of approximately 13.2% was accomplished in the scroll diameter, compared to conventional involute scroll. Additionally, numerical analysis on the expander performance showed that the performance of the designed algebraic scroll expander was about the same as that of a conventional scroll expander. The fabricated prototype was tested in a R134a Rankine cycle with a heat source of 20 kW. For the operating conditions of 20–26 bar and 90–93℃ at the expander inlet and 8–9 bar at the outlet, the expander produced a shaft power of 0.6–0.7 kW at an operating speed range of 1500–2000 r/min. This corresponded to an expander efficiency of 40–45%. The volumetric efficiency also increased as the expander speed increased, reaching to 80% at 2000 r/min. Furthermore, compared to the numerical simulation results, the mechanical efficiency from the test data was found to be considerably low as much as 30%.

Analysis and numerical simulation of a novel gas–liquid multiphase scroll pump

This paper presents analysis of a novel multiphase scroll pump to transport gas–liquid two-phase mixtures, in which each compression chamber has a flank clearance which forms a pressure unloading gap connected to the discharge port. Therefore, this multiphase scroll pump has the function of unloading gas–liquid mixture pressure automatically during the compression process, so the frequently occurring problem of liquid slugging in displacement multiphase pumps is solved. Hence, safety and reliability are improved. In this paper the working process model of the presented multiphase scroll pump is discussed; and equations of fluid motion and geometry of scroll wrap profiles are given. Grid generation and numerical methods are discussed, and numerical simulation of the working process for a multiphase scroll pump is conducted using the commercial CFD software package Fluent, with results suggesting key parameter values for design of multiphase scroll pumps.

히트 펌프용 비대칭 스크롤 압축기의 가스 인젝션 포트 설계

For an asymmetric scroll compressor for heat pump application, a numerical simulation was carried out to investigate the effects of injection port design on the compressor`s performance under gas injection. To validate the simulation, the numerical results were compared with experimental results obtained from a scroll compressor with a base injection port design. There was good agreement between simulation and experimental results, with around a 1% difference in the injection mass flow rate when the injection pressure was below for the heating mode. Various injection port angular positions were numerically tested to yield better injection performance. The largest improvement in heating capacity was obtained at angles of and inward from the scroll wrap end angle for low-temperature and standard heating conditions, respectively, while the maximum COP improvement was at and , respectively. A considerable improvement in cooling capacity was also found at the injection port angle of .

Finite Element Analysis of the Influence of Different Loads and Structures on the Stress of the Scroll Wrap

In order to research the comprehensive influence of gas-thermal-solid and the cooling fin on the deformation and stress of scrolls, the 3D models of orbiting and fixed scrolls are created. On the basis of finite element method(FEM) and indirect coupling method, the deformation and stress of orbiting scroll, fixed scroll and assembly of scrolls are investigated under the conditions of forced by gas force and thermal-solid coupling. The calculation results show that the maximum deformation occurs in the top of scroll teeth head and the maximum stress occurs in the bottom of the scroll teeth head when the orbiting scroll and fixed scroll are analyzed separately. The deformation and stress of the fixed scroll are slightly larger than the orbiting scroll. Temperature load has a greater effect on the deformation and stress of orbiting and fixed scroll. The deformation of scrolls decreases due to the mutual interference and restriction after the assembly. The suitable assembly clearance is got by the analysis of the maximum deformation and stress variation trend of the scrolls under the conditions of different axial and radial clearance. The comparative analysis of the cooling fin affect on deformation of the scroll teeth is carried out. The investigation results show that cooling fin can reduce the deformation of the scroll tooth and increase the reliability of operation.

Modeling of Top Scroll Profile Using Equidistant-Curve Approach for a Scroll Compressor

Scroll profile plays a key role in determining the performance of a scroll compressor. In this study geometric and dynamic characteristics of the scroll profile are analyzed to investigate the influence of its geometric continuity on property of a scroll compressor. Firstly, scroll profiles are created to redesign the geometry of scroll wrap by using the equidistant-curve approach on the basis of a generation line consisting of involute of circle and circular arc. Subsequently, the geometric and dynamic models of the scroll compressor are established. These models are related to parameters of the generation line of scroll profile and rotation angle of a moving scroll. Lastly, some simulation examples of second-order continuity (SOC) scroll profile are compared with first-order continuity (FOC) scroll profiles and some important conclusions are obtained. Results show that SOC scroll profile is superior to FOC profile in terms of volume ratio, stability of gas force, and possible leakage loss in a scroll compressor.

스크롤 컴프레서 팁실의 마찰특성

Division of Convergence Technology Engineering, Chonbuk National University(Received September 12, 2014; Revised October 31, 2014; Accepted November 2, 2014)Abstract − The basic elements in a rotary-type scroll compressor are two identical spiral scrolls containingrefrigerant gas. The pressure variations in the compression pockets of a scroll compressor change the forces act-ing on the orbiting scroll, and these forces affect the dynamic behavior of the compression mechanism parts. Toachieve high efficiency, using a self-sealing mechanism as a tip seal mechanism is very effective. Tip seals,which are placed on top of the scroll wraps, accomplish thrust sealing. This study calculates the friction forcebetween the tip seal and the side plate of a scroll compressor using the numerical model considered in the Reynoldsequation. The calculated friction force is verified by an experiment using a pin-on-disk apparatus. A hydraulic servovalve that controls the pressure of the oil hydraulic cylinder applies the normal load for the test, and a DC servomotor controls the sliding velocity of the disk. The friction force and normal load are measured by the force sensorsattached to the supporting parts. The results show that the theoretical and experimental results are similar and thatthe friction is influenced by the viscosity of the oil and the sliding velocity of the scroll.Keywords −friction (마찰), scroll compressor (스크롤 압축기), scroll wrap (스크롤 랩), spiral scroll (나선 스크롤),tip seal(팁실)

Experimental study and CFD approach for scroll type expander used in low-temperature organic Rankine cycle

This study focuses on experimental test of scroll type expanders in low-temperature organic Rankine cycle (ORC) system. In this circuit, lubricant has been mixed with R245fa as working fluid. In this experiment, two scroll expanders with different built-in volume ratio have been experimentally tested. Main test parameters considered are the pressure difference and the rotational speed of the expanders. It is found that the expander performance could be significantly improved when bigger built-in volume ratio is used. However the internal leakage and friction loss are vital factors to influence expander performance. The maximum shaft power output by expander of 1.77 kW and deliver electricity by generator of 1.375 kW. A Computational Fluid Dynamics approach (CFD) has been employed for preliminary investigation on the thermal-hydraulic behavior of the scroll type expanders. The simulation result shows that unbalance pressure distribution were occurred in the expander by means of top scroll wrap has been modified.