Scroll Profile 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.

A Digital Image Method for Calculating the Working Chamber Volume of a Combined Profile Scroll Compressor

Background: The efficient and accurate calculation of working chamber volume can greatly contribute to the optimized design efficiency of the combined profile scroll compressor, but current papers and patents lack research on the method of calculating the working chamber volume of a combined profile scroll compressor. Objective: A method of using digital image processing is proposed to efficiently calculate the working chamber volume of a combined scroll compressor. Methods: This method discretizes and reconstructs the scroll profile that forms the working chamber into a coordinate sequence with equal involute angle intervals. By calculating the relationship between the coordinate sequence and the rotation angle, a general coordinate sequence that forms the working chamber profile is obtained. The real-time changes in the projection image of the working chamber during all the suction, compression and discharge processes can be accurately depicted. The digital image is processed to obtain the actual projection area of the working chamber, and thus, the volume of the working chamber is accurately calculated. Results: The digital image method can accurately calculate the volume change of the working chamber of the combined profile scroll compressor by selecting the appropriate involute angle interval and digital image size, with a mean relative error of less than 1%. At the beginning of suction and the end of discharge, the calculated volume has been found to have poor accuracy, with a maximum relative error higher than 10%. Conclusion: The digital image method has been found to have high accuracy, greatly reduce the difficulty of the analysis of the working chamber volume, and promote the design optimization of the combined profile scroll compressor, thus broadening the idea for the calculation method of the working chamber volume of the scroll compressor.

Study on a variable wall thickness profile of electric scroll compressor used for automobile air conditioner

Profile design plays an important role in improving the performance and reliability of scroll compressors. To expand design ideas of variable wall thickness profile (VWTP) of electric scroll compressor used for automobile air conditioner, a method to generate and modify VWTP is developed in this paper. The VWTP is generated according to the generalized profile theory and modified with symmetrical arc modification (SAM) and symmetrical arc plus line modification (SAPLM) at the central part. To make sure that the generated VWTP can form scroll profile, the generation conditions for coefficients of swing radius are discussed in detail. For the VWTP modified with SAM and SAPLM at the central part, a new way to classify scroll chambers and analyze the evolution of scroll chambers is proposed. Geometry analyses such as conjugate points on involute curves and arc segments, volume and its derivative with respect to orbiting angle are conducted as well. The generation and geometry analysis method of VWTP is validated through a design example of VWTP for electric scroll compressor with a displacement of 34 mL. The performance of the electric scroll compressor was tested through experiment and the results show that the cooling capacity can reach 7.5 kW and the COP can reach 3.0.

A review of the research status of scroll expander

In order to solve the problem of energy crisis and take the road of sustainable development, the development of renewable energy and recycling of low-grade waste heat have attracted more and more attention. As a new type of volumetric energy conversion device, scroll expander is wi dely used in Organic Rankine Cycle (ORC) waste heat recovery, because of its advantages such as small size and so on. Scroll profile is one of the main factors affecting scroll expander performance. Compared with the traditional constant section scroll profile with same suction volume, volume ratio and shell size, the new type of variable section scroll profile could reduce scroll tooth height, better mechanical properties and improve efficiency, therefore making it more suitable for working under complex operating conditions. In order to reduce the head invasion rate, airflow friction factor, the power loss at the air inlet, and improve the pneumatic power conversion efficiency, a new head correction method is proposed. Although R123, R134 and R245 are the most commonly used working medium in scroll fluid machinery, the selection of working medium in scroll expander is still a key problem. The overall performance of the scroll expander can be improved by designing different inlet shapes and positions or double-symmetrical exhaust ports. The radial leakage caused by axial clearance of scroll expander can be improved by developing new scroll profile to reduce the length of radial leakage line and optimizing the design of scroll top sealing mechanism. The tangential leakage caused by radial clearance can be improved by enhancing the manufacturing precision and installation accuracy of scroll plate and designing the radial variable mechanism. At present, fewer research has been carried out on the leakage of scroll expander. Therefore reducing the leakage loss to improve the performance of scroll expander is of great significance in the future research.

CFD analysis of the influence of variable wall thickness on the aerodynamic performance of small scale ORC scroll expanders

This research paper presents a CFD analysis of small scale ORC scroll expanders using variable and constant wall thicknesses by providing back-to-back aerodynamic performance comparisons. The evaluation of the three-dimensional and transient CFD results shows that the shorter scroll profile length of the variable wall thickness design (VWD) generated lower average radial and axial gas forces. In addition, higher pressure gradients in between individual working chambers contributed to a higher peak of the tangential gas moment despite higher transient gas force and tangential gas moment variations. Moreover, the pressure trace analysis reveals that the expansion process was finished at a crank angle of 816° in VWD, compared to 996° in the constant wall thickness design (CWD). The studies of the static pressure distributions along the surface of the fixed scroll of the two geometries indicate that static pressure drops through local radial clearances were higher in VWD. However, a higher number of static pressure drops occurred in CWD. The expansion process of CWD was driven by lower pressure gradients resulting in a complete dissipation of the large-scale vortices in the expansion chambers of CWD at the crank angle of 672°, in contrast to 600° in the expansion chambers of VWD.

Compressor Profile Optimization Based on Hybrid Intelligent Algorithm

In order to improve the working characteristics of the scroll compressor, according to the scroll profile of the compressor, the energy efficiency ratio (EER) of the scroll compressor is taken as the objective function, and the number of scroll turns N and knots are determined based on the genetic annealing algorithm. The distance p, the height of the scroll body h, and the thickness of the scroll profile t are optimized. In the optimized solution set, three sets of optimized profile and initial profile are selected for theoretical calculation of thermodynamic characteristics and volume characteristics, and the specific influence of scroll compressor profile parameters on compressor characteristics is explored in detail, and compared with the unoptimized scroll. The initial parameters of the rotary compressor are compared with the theoretical performance. The results show that the pitch p has a significant effect on the energy efficiency ratio and discharge volume of the scroll compressor, and the number of scroll turns N has a significant effect on the characteristic of suction volume. Three kinds of optimized scroll profile parameters S2, S3, S4 are selected in the optimal solution set. Compared with the initial value S1, the working characteristics are improved. The energy efficiency ratio was increased by 38.10%, 42.58%, and 50.26%; the suction volume was increased by 66.1%, 82.3%, and 73.9%; the exhaust volume was increased by 21.1%, 29.6%, and 50%; the internal volume ratio was increased by 36.4%. 40.9%, 27.3%. It is proved that the use of genetic annealing algorithm achieves the purpose of improving the compressor's operating characteristics.

Internal Flow and Cavitation Analysis of Scroll Oil Pump by CFD Method

In this study, a three-dimensional model with actual clearances was established for a scroll oil pump, and the internal flow was simulated by the CFD method. The internal flows at different rotation angles were studied, and the cavitation and pressure pulsation in the scroll pump under different working conditions were analyzed. The results show that the flow in the two working chambers of the scroll pump is asymmetric due to its structural characteristics and motion mode. The high-pressure pulsation occurs in the working chamber during the end of the suction and the beginning of discharge. Under the action of high-pressure difference, there is a high-speed jet in the clearance between the orbiting and fixed scrolls, which causes a large area of cavitation downstream of the clearance. Under a low suction pressure, cavitation intensifies with the increase in rotating speed, which leads to a decrease in volumetric efficiency. It can effectively improve cavitation by increasing the suction pressure and volumetric efficiency of the pump. The pressure pulsation can be effectively improved by increasing the axial clearance and reducing the rotating speed. The method of reducing pressure pulsation by shortening the scroll profile is proposed.

Optimization of the tip profile of orbiting scroll in an asymmetry suction chamber scroll compressor

The scroll compressors with asymmetrical suction chamber have large discharge loss, as the pressure in outside chamber is far larger than the discharge pressure when the discharge process begins. It is necessary to optimize the scroll profile around the discharge port to reduce the discharge loss. The theoretical method is to redesign the tip profile to obtain the same volume ratio of outside working chamber with the inner working chamber. However, as it is difficult to predict the discharge loss through the flank gap in discharge chamber, the optimum design cannot be obtained. In this paper, we establish an optimization platform based on the CFD method. The profile of orbiting scroll tip is parametrized with CAD software, then the CFD calculation will be done and the performance parameters will be extracted. The MOST optimization algorithm is used to search the best performance parameters and control the parameterized value of scroll profile. After iterations, the best profile with the modification angle of 66.3° was obtained. Compared to the original model, the volumetric efficiency of the compressor increased by 4.11%; and the isentropic efficiency increased by 4.91%. Afterwards, the flow field are analysed to study the characteristics of the optimized scroll compressor. The results show that the backflow, the secondary vortex in discharge chamber and the discharge mass flow pulsation were reduced, which led to the decrease of the discharge loss and the improvement of the isentropic efficiency.

Construction and Analysis of Variable Wall Thickness Profile of Double Scroll Teeth of Scroll Compressor

Based on the changing trend of the geometric parameters of the scroll profile of the involute of circle with variable radii, a new type of double scroll teeth profile of scroll compressor composed of involute of circle with variable radii is constructed. The construction process of the baseline is discussed, and the baseline equations are deduced. According to the principle of normal equidistance, the geometric model of variable wall thickness double scroll teeth is established, and the suction volume, tooth thickness, and scroll area of double scroll teeth are compared with those of the double scroll teeth composed of ordinary involute of circle. The results show that: compared with ordinary double scroll teeth with constant thickness, the scroll diameter when two scrolls mesh is reduced and the revolutions of orbiting scroll required in the working process are reduced and it is easy to select better scroll profile through adjusting the changing coefficient of the base circle radius k, which provides a reference for scroll machinery using environment-friendly working fluids.

Structure Design and Performance Test of CO2 Scroll Compressor for Heat Pump

Scroll profile design and shell strength design are important in the development of CO2 scroll compressors for heat pumps. In order to meet the multi-operating conditions of the heat pump, the non-clearance profile correction method and the clearance profile correction method are analysed, and the clearance profile correction method was adopted to complete the profile design. The safety factor design method was compared with the reliability design method, and the shell of the CO2 scroll compressor for heat pump was designed based on the reliability design method. The test results show that the scroll tooth with clearance correction method meets the design requirements of heating capacity of 4.8kW±10%, the energy efficiency ratio is not less than 4.6, and the shell structure with 99.38% reliability can meet the structural safety requirements.

Dynamic modelling and experimental validation of scroll expander for small scale power generation system

This work presents a detailed and generic dynamic modelling and simulation method of scroll expander for small scale power generation system. The geometric models of the scroll were built step by step, including the scroll involute, scroll dimensions, chamber areas and volumes, the scroll profile modifications and so on. The valve model, internal leakage model, motion equation, heat transfer equation and energy balance equation were combined with the geometric models to complete the scroll expander modelling. A mathematic model of a direct current generator or an experimentally determined correlation of generated power against rotational speed of the used generator was integrated to the expander model as the power output unit. To enhance the adaptability of the current model, an overall dynamic friction coefficient of the scroll expander and the generator was innovatively proposed and introduced as one of the key parameters in the present study. The accurate value of this coefficient should be experimentally determined for a specific expander – generator system; with the knowledge of such a parameter, the mechanical friction loss can be accurately and easily calculated in the simulation study. The present modelling and simulation method have been validated by several sets of experimental results based on different scroll expanders studied by different researchers, and the corresponding overall dynamic friction coefficient was found in the order of magnitude of 10−3Nms.

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.

Numerical Control Machining of Scroll with Variable Thickness

With the development of scroll technology, the requirements of more efficient and more accurate processing method for scroll compressor parts become more urgent. This paper proposes a method to improve the machining effect of scroll compressor. The approach is based on 3-point arc approximation method which divides combined profile of scroll wrap into subparagraph arcs that can be interpolated on CNC System. This approach simplifies the programming process and improves the curve fitting effect. The results indicate that the fitting error is in the predetermined range, and the interpolation points of cutter center track are significantly less than those based on CAD/CAM software. The method presented in this paper is of significance to the NC machining of novel precise scroll profile.

Numerical modelling of temperature distribution for orbiting scroll wrap in an air scroll compressor

The heat transfer of orbiting scroll wrap in an air scroll compressor under steady operation is simplified as a two-dimensional heat conduction problem with periodic moving convection boundary conditions. The heat conduction equation and the equivalent initial condition are obtained in a body-fitted coordinates system constructed by the normal angle and the normal component of the scroll profile. To solve the numerical temperature model with the discrete form based on the control volume method, a new iteration method was developed. The numerical analysis cases involving two orbiting scroll wraps, thin and thick scroll wraps, show that the temperature is uniform along scroll wrap thickness, and can therefore be represented by the mid-area temperature of the scroll wrap. The temperature increases linearly with the increasing normal angle and involute angle. The temperature is almost invariable with the orbiting angle and so that can be considered to be steady in engineering practice.

Study on Scroll Profile Design Using Involute of Elliptic for Scroll Compressor

The scroll compressor has the conjugate motion of meshing by the fixed scroll and the planet scroll. Several kinds of geometrical curves can be adopted to form the scroll compressor profile such as involute of circle with variable and constant radius, algebraic spiral, and so on, to improve the performance of scroll compressor. This study proposes a new scroll profile design using elliptic involute and two-envelope method to create a new conjugate meshing scroll of variable cross section. The curve of the scroll section on both sides can be specified as an arbitrary mathematical function. First, the base scroll swept out by the central base circle. Next, the base circle translation path envelope of the planet scroll is moved by the basic involute curve. The base circle translation path envelope is the first envelope. The second envelope generated by the planet scroll conjugate profile is the fixed scroll. By using two-envelope method, the variety of conjugate scroll can be produce with the cross section and symmetrical variables for parametric design.

Optimum design of scroll profiles created from involute of circle with variable radii by using finite element analysis

A design procedure, combining the geometry of the scroll profiles constructed from an involute of circle with variable radii into the CAE, has been developed. Thermal and structural analyses by means of the finite element method have been investigated in this study. When compared to the conventional scroll profile with the same suction volume, volume ratio and housing size, this new design confirms the smaller radial and axial deformations, and with better rigidity by carrying out the parametric studies. The reduction in the radial deformation of the scroll wrap is far larger than that in the axial deformation because of the lower wrap height and the wrap becomes thicker at the center as it decreases from the inside outwards. The increasing orbiting radius and the decreasing wrap volume also compromise each other to make an acceptable little increment in centrifugal force of the orbiting scroll. One of the studied cases has been recommended as the optimum solution towards the specified design objective and constraints.

Analysis of Geometric Characteristics of Scroll Compression Chamber for Scroll Fluid Machine

Based on the general geometrical model of scroll compression chamber for scroll fluid machine, the geometric characteristics of scroll compression chamber, such as width, length, volume, and comprehensive curvature radius at the mesh point, and their variation as well are comprehensively analyzed. It is shown by the analysis that among all of the geometric characteristics, the width variation is the most complicated one; the comprehensive variation of the width together with the length can be used to determine the deformation processes of the chamber. The variability of its length, volume, and comprehensive curvature radius at meshing points should be taken as its basic deformation characteristics. For a scroll compression chamber with involute of circle, its deformation efficiency is higher and dynamic stability is excellent. At the same time, the scroll wrap with involute of circle is easy to fabricate and the profile with involute of circle is used widely for the major part of the scroll profile.

FEM Analysis of Scrolls with Single Profile and Hybrid Profile

A new method to design hybrid scroll profile is introduced. The finite element analysis models for hybrid profile and single profile scrolls are established respectively. The stress and deformation of these two kinds of scrolls are analyzed by finite element method under the combined action of temperature load and gas load in the process of one revolution of crank shaft. The analysis data show that the stress and deformation of hybrid-profile scroll are similar to that of involute-profile scroll. Furthermore, the length of baseline of hybrid profile reduces approximately 27.32% with respect to that of involute profile. The results of this study are helpful in the design of scroll compressor with hybrid scroll profile.

FEM Analysis of Scrolls with Single Profile and Hybrid Profile

A new method to design hybrid scroll profile is introduced. The finite element analysis models for hybrid profile and single profile scrolls are established respectively. The stress and deformation of these two kinds of scrolls are analyzed by finite element method under the combined action of temperature load and gas load in the process of one revolution of crank shaft. The analysis data show that the stress and deformation of hybrid-profile scroll are similar to that of involute-profile scroll. Furthermore, the length of baseline of hybrid profile reduces approximately 27.32% with respect to that of involute profile. The results of this study are helpful in the design of scroll compressor with hybrid scroll profile.

A Study on Synthesis Design and Optimization Analysis on Scroll Profiles for Scroll Vacuum Pump

The scroll profile plays a very important role in the design of a scroll vacuum pump in oil filter. Therefore, a geometric general form of the scrolls based on Whewell equation was developed in this study. The general planar curve form of the scrolls was specified using the Whewell equation, which consists of three segments and it is easy to analyze and optimize. The analysis reveals that the general model can contain most scrolls based on circle. A general design and multi-objective optimization process for the profile of scroll vacuum pumps was proposed. The design and optimization process was developed based on geometric and multi-objective considerations. The Nondominated Sorting Genetic Algorithm was applied to this multi-objective optimization question. The finite element method/FEM is the kernel of the approach. The scroll components work in a high pressure and high temperature environment, which results in the deformation of the scroll wall. The FEM and optimization can evaluate the deformation due to the cutting force and compensate accordingly.