Sensitivity analysis of a comprehensive model for a miniature-scale linear compressor for electronics cooling

A comprehensive model of a linear compressor for electronics cooling was previously presented by Bradshaw et al. (2011). The current study expands upon this work by first developing methods for predicting the resonant frequency of a linear compressor and for controlling its piston stroke. Key parameters governing compressor performance – leakage gap, eccentricity, and piston geometry – are explored using a sensitivity analysis. It is demonstrated that for optimum performance, the leakage gap and frictional parameters should be minimized. In addition, the ratio of piston stroke to diameter should not exceed a value of one to minimize friction and leakage losses, but should be large enough to preclude the need for an oversized motor. An improved linear compressor design is proposed for an electronics cooling application, with a predicted cooling capacity of 200 W a cylindrical compressor package size of diameter 50.3 mm and length 102 mm.     

An experimental and numerical study on an inherent capacity modulated linear compressor for home refrigerators

Linear compressors are built based on a free piston system and usually require stroke controllers, since the piston movement is sensitive to the ambient temperature. This paper presents a novel design method for an inherent capacity modulated linear compressor that uses R600a for application in household refrigerators. The compressor is capable of modulating its capacity independently, and this feature secures stable and efficient operation without requiring stroke controllers. Electrical parameters are designed to deliver inherent capacity modulation in accordance with cooling demand variation. Mechanical parameters are tuned to establish an efficient resonance system. A numerical model was developed and a prototype compressor was constructed. The prototype compressor was evaluated over a condensing temperature range of 15-50 °C, which corresponds to an ambient temperature range of 5-43 °C. The simulation results show that the cooling capacity was inherently modulated from 55 to 90% over the ambient temperature range, and the inherent modulation is confirmed 70-90% by the experiment.     

A novel linear electromagnetic-drive oil-free refrigeration compressor using R134a

A new type of oil-free moving magnet linear compressor with clearance seals and flexure springs has been designed for incorporation into a vapour compression refrigeration system with compact heat exchangers for applications such as electronics cooling. A linear compressor prototype was built with a maximum stroke of 14 mm and a piston diameter of 19 mm. An experimental apparatus was built to measure the compressor efficiencies and coefficient of performance (COP) of a refrigeration system with the linear compressor, using R134a. The resonant frequency for each operating condition was predicted using the discharge pressure, suction pressure and stroke. Refrigeration measurements were conducted for different strokes under each pressure ratio with a fixed condenser outlet temperature of 50 °C and evaporator temperature ranging from 6 °C to 27 °C. The results show that the COPs are around 3.0 for tests with a pressure ratio of 2.5 (evaporator temperature of 20 °C).     

A review of linear compressors for refrigeration

Linear compressor has no crank mechanism compared with conventional reciprocating compressor. This allows higher efficiency, oil-free operation, lower cost and smaller size when linear compressors are used for vapour compression refrigeration (VCR) system. Typically, a linear compressor consists of a linear motor (connected to a piston) and suspension springs, operated at resonant frequency. This paper presents a review of linear compressors for refrigeration system. Different designs and modelling of linear compressors for both domestic refrigeration and electronics cooling (miniature VCR system) are discussed. Key characteristics of linear compressor are also described, including motor type, compressor loss, piston sensing and control, piston drift and resonance. The challenges associated with the linear compressors are also discussed to provide a comprehensive review of the technology for research and development in future.     

A comprehensive model of a novel rotating spool compressor

A comprehensive simulation model of a novel rotating spool compressor is presented. The spool compressor provides a new rotary compression mechanism with easily manufactured components. A detailed analytical geometry model of the spool compressor is presented, which includes the geometry of the vane. This geometry model is included in an overall comprehensive compressor model that includes sub-models for friction, leakage, and heat transfer. The results of the comprehensive model were validated using experimental data from a prototype compressor. The prototype compressor has an overall displacement of 23.9 cm³, and was operated using R410A as the working fluid. The model predicts the volumetric efficiency, discharge temperature, and shaft power of the prototype compressor to within 3.13% MAE, 16.5 K and ?13.2 W average deviation, respectively. The trends and spread in the data indicate that additional effort should be focused on the operation of the active sealing elements within the compressor.     

Linear compressors for electronics cooling: Energy recovery and its benefits

A comprehensive model of a linear compressor for electronics cooling was previously presented by Bradshaw et al. (2011) then enhanced and used for a sensitivity analysis of the leakage gap, eccentricity, and piston geometry by Bradshaw et al. (2013). The current work utilizes the previously developed model to explore the energy recovery characteristics of a linear compressor as compared to those of a reciprocating compressor. The impact of dead (clearance) volume on both a linear and reciprocating compressor is analyzed. In contrast to a reciprocating compressor the overall isentropic efficiency of the linear compressor remains relatively unaffected by an increase in dead volume up to a certain point. This behavior is attributed to the ability of the linear compressor to recapture the energy of the compressed gas during the expansion process. This characteristic behavior allows a linear compressor to be used for efficient capacity control from roughly 35–100%.     

Optimization of electrostatically actuated miniature compressors for electronics cooling

This paper explores the feasibility of using electrostatically actuated diaphragm compressors in a miniature-scale refrigeration system for electronics cooling. A previously developed experimentally validated analytical model for the diaphragm compressor is used in conjunction with an optimization approach to determine the required dimensions for the compressor. The analysis reveals that the pressure rise and volume flow rate required for the electronics cooling application are not achieved using a single compressor because of material property limitations. A three-dimensional array of compressors is proposed instead with which the cooling requirements and the size restrictions for electronics cooling applications may be simultaneously satisfied.     

无油线性压缩机的频率特性和活塞偏移特性研究

针对线性压缩机随工况和热负荷变化而引起共振频率和活塞中心位置偏移量改变的问题,建立了关于压缩机共振频率的线性等效模型和傅里叶变换计算模型.两种模型用来预测线性压缩机的共振频率,后者同时用来计算活塞中心位置偏移量,模型中考虑了不同行程、不同排气压力对共振频率的影响以及不同行程、不同排气压力和不同运行频率对活塞中心位置偏移...     

Piston position sensing and control in a linear compressor using a search coil

Linear compressors with clearance seals are well established for cryocoolers using either a Stirling cycle or pulse tube. However, both piston stroke and piston offset require detection and control in valved compressors. In order to manufacture linear compressor in large scale, then a simple, robust, and cheap control system is required with a minimum of sensors and actuators. This work introduces an approach to sensing the position of the piston using a search coil. The piston stroke is detected by calculating the peak-to-peak flux linkage in relation to the measured drive voltage and current. The piston offset is proportional to an integrated modulus of the back electromotive force (emf) of the search coil. Two PID (proportional-integral-derivative) controllers were developed to control the piston stroke by adjusting the drive voltage and a solenoid valve and bleed flow to control the piston offset. Experimental results validate the proposed compressor control technique.     

Analysis on the stirling-type pulse tube refrigerator in consideration of dynamics of linear compressor

This paper describes the performance analysis of Stirling-type pulse tube refrigerator (PTR) in conjunction with the dynamics of the accompanied linear compressor. The dynamic behavior of the piston in the linear compressor is directly influenced by the load condition of the PTR. In this paper, the dynamic equation of the piston is simultaneously solved with the thermo-hydraulic governing equations of the PTR using linear analysis model and the performance of the PTR is predicted with the accompanied thermal losses. The developed analysis code is verified with the experimental results. The effect of the inertance tube length which plays an important role in the PTR is also specifically investigated from the experimental and simulation results. It clearly shows the effect of the flow impedance of the inertance tube on the dynamic response of the piston as well as the cooling performance of the PTR.     

Testing and modelling of an automotive wobble plate compressor

Wobble plate compressors are well used in air conditioning for high-class automobiles. They allow continuous control by automatic adjustment of the piston stroke, to keep the low pressure above a certain limit. Here an externally controlled wobble plate compressor is analyzed experimentally through its isentropic and volumetric effectivenesses and control characteristics. Compressor effectivenesses depend mainly on the compressor speed and pressure ratio: there is obtained, for example, isentropic and volumetric effectivenesses of 0.65 and 0.8 for a pressure ratio of 4 at 1000 rpm and 0.4 and 0.35 for the same pressure ratio at 4000 rpm. This degradation is attributed to the increasing of the supply pressure drop. The “lubricant” (oil + dissolved refrigerant) mass flow rate is obtained by minimization of the residuals of the thermal balances on the compressor, condenser and evaporator. Here an important oil-flow circulation is obtained: between 9.5% and 12.5% of the refrigerant flow rate. A special displacement sensor is used to measure instantaneous piston stroke and to relate it to overall compressor performance. This measurement is then compared with the results obtained with a semi-empirical model, which is able to predict, in part load, the compressor displacement. The model predicts the displacement ratio with deviations that vary between −14.5% and +8.1%.     

基于COMSOL的线性压缩机动力学仿真与实验验证

为了提出一种有效且简易的线性压缩机设计和优化方案,本文针对一款商用Cryo S 100小型斯特林制冷机,推导出其动磁式线性压缩机中气体阻尼力和气体弹簧力的表达式,并采用COMSOL软件将压缩机动力模型和电磁模型相耦合,建立了联合仿真模型,模拟了不同负载下压缩机的动力特性,模拟结果与SAGE相吻合.通过空载下对线性压缩机...     

冰箱直线压缩机不稳定波动的机理分析

直线压缩机冰箱制冷系统的实验研究显示,在初始启动调节后供电参数保持不变过程中,直线压缩机出现了不稳定波动现象。最大的行程波动率约为3.8%,输入功的波动率约为21.3%,波动周期约为220 s。通过建立的直线压缩机动态仿真模型,对该不稳定现象进行解耦分析,结果表明：吸气压力的波动对直线压缩机行程的影响较大,排气压力的波动对其影响很小,但行程的波动对排气压力有一定的影响。直线压缩机启动过程中行程的反复调节引起了排气压力出现较大的波动,经过一段稳定运行后,该波动传递到直线压缩机的吸气端,从而引起了所述的不稳定波动。     

Study on Self-Sensor of Linear Moving Magnet Compressor's Piston Stroke

The mathematic model of the self-sensor was established by analyzing the moving magnet linear motor of linear compressor, and the measurement method of piston stroke was achieved. The piston stroke can be calculated by measuring the voltage and current of the linear motor coil. The self-sensor's circuit parameters were influenced by the parameters of the linear motor. For studying the performance of the self-sensor under the driving modes of variable-voltage control and variable time of flow control, piston stroke measurement and control software based on LabVIEW was designed, and the experimental study was carried out. The results show that using the linear motor as self-sensor is effective. Although the self-sensor has nonlinear problems at end of stroke and the electromagnetic interference, the steady-state error of self-sensor can be reduced by means of the better filter circuit and more accurately correcting the end of the piston stroke. So, this self-sensor can be satisfactorily employed with linear compressor.      

Modeling of a semi-hermetic CO2 reciprocating compressor including lubrication submodels for piston rings and bearings

A comprehensive model for a semi-hermetic CO₂ reciprocating compressor is presented. This comprehensive model is composed of three main sub-models simulating the geometry and kinematics, the compression process, and frictional power loss. Valve and leakage sub-models are included in the compression process model. The frictional power loss model includes the friction at the bearings and between the piston ring and cylinder wall. The predicted results of the comprehensive model are validated using external compressor performance measurements of compressor input power and mass flow rate. The mass flow rate and compressor input power are predicted to within 4.03% and 6.43% mean absolute error, respectively, compared to the experimental datum. Additionally, a parametric study is presented which investigates compressor performance as a function of the stroke-to-bore ratio.     

Development of a high efficiency refrigeration compressor

In order to improve the energy efficiency ratio of small reciprocating hermetic compressors the following factors are investigated: clearance volume, bore and stroke, rod length ratio, geometric dimensions of a piston and valves and superheat of suction gas.A prototype machine is developed based on this investigation. The reliability of this new type of compressor is confirmed and its energy efficiency ratio reaches 3.02 J W⁻¹ s⁻¹, which is 25% higher than the average value of our current machines.     

滚动转子式压缩机性能参数通用计算模型

探讨了滚动转子式压缩机容积效率、功率因子、制冷量、运行电流等几个主要性能参数的通用计算模型.依据压缩机厂商提供的大量不同系列压缩机的实验数据,运用麦夸特算法拟合求解各性能参数相关系数,总结出精度高、通用性好的性能关联式.对不同性能参数,以及单一性能参数的不同公式形式进行分析对比,结果表明,由该方法所建立的模型能够准确地描述变工况下滚动转子式压缩机性能参数,可作为滚动转子式压缩机性能参数计算的理想关联式.     

Opposed piston linear compressor driven two-stage Stirling Cryocooler for cooling of IR sensors in space application

A two-stage Stirling Cryocooler has been developed and tested for cooling IR sensors in space application. The concept uses an opposed piston linear compressor to drive the two-stage Stirling expander. The configuration used a moving coil linear motor for the compressor as well as for the expander unit. Electrical phase difference of 80 degrees was maintained between the voltage waveforms supplied to the compressor motor and expander motor. The piston and displacer surface were coated with Rulon an anti-friction material to ensure oil less operation of the unit. The present article discusses analysis results, features of the cryocooler and experimental tests conducted on the developed unit. The two-stages of Cryo-cylinder and the expander units were manufactured from a single piece to ensure precise alignment between the two-stages. Flexure bearings were used to suspend the piston and displacer about its mean position. The objective of the work was to develop a two-stage Stirling cryocooler with 2 W at 120 K and 0.5 W at 60 K cooling capacity for the two-stages and input power of less than 120 W. The Cryocooler achieved a minimum temperature of 40.7 K at stage 2.     

直线压缩机喷射补气特性分析

本文针对直线压缩机的喷射补气特性开展研究,基于直线压缩机电磁学模型、动力学模型和小孔进气模型,建立了喷射补气式直线压缩机及压缩腔仿真模型并进行了实验验证,研究了补气压力和参数调节对压缩机运行参数的影响。结果表明：喷射补气使吸气阀滞后开启和提前关闭,低压吸气量减小,排气量增大。在吸气压力为62.5 kPa、排气压力为765 kPa条件下,补气压力为200 kPa时,吸气量降低61%,排气量提升50%;补气压力为400 kPa时,低压无吸气,排气量相比于200 kPa补气时提升60%。给定供电参数条件下,喷射补气使自由活塞行程、偏移量与余隙容积增大,固有频率有一定的提高;定余隙容积运行时,随着补气压力的提升,气体力等效刚度和等效阻尼均增大。固定频率下,行程增大时吸气量随之增大,而补气流量达一定值后基本保持不变;频率调节时,压缩机在固有频率附近吸、补气量存在最大值,驱动频率较高时补气对吸气量的降低影响减弱。