Predictive hybrid control of the supermarket refrigeration benchmark process

Predictive control is applied to a supermarket refrigeration process in which all actuators are on/off devices. This process has been proposed as a benchmark for the evaluation of hybrid control methods. It is shown that decentralized predictive control of display case temperatures, when combined with predictive control of suction manifold pressure, can greatly reduce or eliminate on/off compressor cycling. The strategy is scalable to large systems. Results are presented for an application involving 10 display cases and six compressors. Traditional hysteresis control causes synchronization of display case temperature oscillations. The proposed predictive approach includes desynchronization, which is shown to be necessary for minimization of compressor cycling. Finally, it is shown that the minimum possible number of compressor cycles can be estimated. This limit on control system performance is imposed by process design and operating conditions. It is also shown that the recommended predictive control strategy operates close to the minimum possible number of compressor cycles for the benchmark process.     

内置转子换热管强化传热数值模拟

为分析内置转子换热管的传热效果,建立光管和内置转子换热管的三维模型,对换热管内流场、温度场、压力场以及传热过程进行模拟,得到管内流体的阻力特性和传热特性.模拟结果表明:内置转子换热管内的三维流动比较复杂,转子与管壁之间缝隙内的流体有明显的环绕流动,切向速度和径向速度也增大到一定范围;相同雷诺数条件下,内置转子换热管压降...     

Cooling Load Density Optimization of an Irreversible Simple Brayton Refrigerator

The performance optimization of an irreversible simple Brayton refrigerator coupled to constant-temperature heat reservoirs is carried out by taking the cooling load density, i.e., the ratio of cooling load to the maximum specific volume in the cycle, as the optimization objective using finite-time thermodynamics (FTT) or entropy generation minimization (EGM) in this paper. The analytical formulae about the relations between cooling load density and pressure ratio, as well as between coefficient of performance (COP) and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers, and the irreversible compression and expansion losses in the compressor and expander. The influences of the effectiveness of the heat exchangers, the temperature ratio of the reservoirs, and the efficiencies of the compressor and expander on the cooling load density versus COP are provided by numerical examples. The cooling load density optimization is performed by searching the optimum pressure ratio of the compressor, and searching the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for the fixed total heat exchanger inventory. The influences of some design parameters, including the effectiveness of the heat exchangers between the working fluid and heat reservoirs, the efficiencies of compressor and expander, the temperature ratio of heat reservoirs, on the maximum cooling load density, the optimum heat conductance distribution and the optimum pressure ratio are provided by numerical examples. The refrigeration plant design with optimization leads to a smaller size including the compressor, expander, and the hot- and cold-side heat exchangers.     

Numerical simulation of two-phase flow in deformable porous media: Application to carbon dioxide storage in the subsurface

In this paper, conceptual modeling as well as numerical simulation of two-phase flow in deep, deformable geological formations induced by CO₂ injection are presented. The conceptual approach is based on balance equations for mass, momentum and energy completed by appropriate constitutive relations for the fluid phases as well as the solid matrix. Within the context of the primary effects under consideration, the fluid motion will be expressed by the extended Darcy's law for two phase flow. Additionally, constraint conditions for the partial saturations and the pressure fractions of carbon dioxide and brine are defined. To characterize the stress state in the solid matrix, the effective stress principle is applied. Furthermore, the interaction of fluid and solid phases is illustrated by constitutive models for capillary pressure, porosity and permeability as functions of saturation. Based on this conceptual model, a coupled system of nonlinear differential equations for two-phase flow in a deformable porous matrix (H²M model) is formulated. As the displacement vector acts as primary variable for the solid matrix, multiphase flow is simulated using both pressure/pressure or pressure/saturation formulations. An object-oriented finite element method is used to solve the multi-field problem numerically. The capabilities of the model and the numerical tools to treat complex processes during CO₂ sequestration are demonstrated on three benchmark examples: (1) a 1-D case to investigate the influence of variable fluid properties, (2) 2-D vertical axi-symmetric cross-section to study the interaction between hydraulic and deformation processes, and (3) 3-D to test the stability and computational costs of the H²M model for real applications.     

变频压缩式制冷系统的内模解耦控制策略

为了使变频压缩式制冷系统在变负荷情况下同时具备良好的稳定性和鲁棒性,并希望该类制冷系统的能效比COP得到进一步的提高,设计出了内模解耦控制策略.该策略采用基于内模结构的解耦控制方法增强系统鲁棒性,并利用最小过热度曲线实时修订过热度设定值为相应负荷下的最小稳定过热度值,使得压缩机功率减少,制冷量增加.仿真与实验结果表明,该控制策略下的变频压缩式制冷系统不仅避免了过热度震荡、响应迟缓等问题,而且具备了较强的抗扰性和鲁棒性,并进一步将COP值提高到5.8左右.     

制冷仿真实训系统

针对目前制冷企业技能培训的教学手段落后与制冷企业自动化管理水平普遍较低的现象。开发了制冷仿真软件1．0。该文首先阐明了软件的功能定位，并对开发工具MCGS的特点与运行机理作了讨论；通过制冷压缩机仿真模型的建立。重点分析了制冷仿真系统的建模方法——以各个设备为对象、对于不同的蒸发系统以热平衡和质平衡为主线，建立系统数学模型；对各个对象的传质与传热基理，在不违背制冷工艺变化规律的前提下，作恰当地较大简化，在此基础上使系统能动态地仿真其变化规律；最后对软件的各部分组成与功能作了介绍。     

双转子涡喷发动机气动性能优化控制研究

航空发动机的控制规律作用巨大,它决定了发动机能否获得设定的稳态工作下性能指标,同时保证工作过程中的压气机和涡轮的气动稳定性;双转子涡喷发动机气动性能优化控制的目的就是有效地挖掘发动机的使用潜力;研究方法采用部件特性法对发动机进行稳态建模,并针对某双转子涡喷发动机的稳态模型进行三种不同稳态控制规律下的仿真,得到发动机性能参数的不同变化趋势,并对其进行了详细的分析;结果表明:保持低压转子转速不变的情况下,随着压气机进口总温的增加,高压转子转速上升,涡轮前温度升高,发动机推力增加;保持涡轮前温度不变的情况下,随着压气机进口总温的升高,低压压气机气动负荷变重,低压转子转速降低;高压转子转速也下降,但是下降幅度很小;燃油流量增加;保持高压转子转速不变的情况下,随着压气机进口总温的升高,燃油流量有一定的增加,低压转子转速有所降低;推力受多重因素的影响,推力值变化趋势较为复杂。     

Output pressure and efficiency of electrokinetic pumping of non-Newtonian fluids

Theoretical expressions of the flow rate, output pressure and thermodynamic efficiency of electrokinetic pumping of non-Newtonian fluids through cylindrical and slit microchannels are reported. Calculations are carried out in the framework of continuum fluid mechanics. The constitutive model of Ostwald-de Waele (power law) is used to express the fluid shear stress in terms of the velocity gradient. The resulting equations of flow rate and electric current are nonlinear functions of the electric potential and pressure gradients. The fact that the microstructure of non-Newtonian fluids is altered at solid–liquid interfaces is taken into account. In the case of fluids with wall depletion, both the output pressure and efficiency are found to be several times higher than that obtained with simple electrolytes under the same experimental conditions. Apart from potential applications in electrokinetic pumps, these predictions are of interest for the design of microfluidic devices that manipulate non-Newtonian fluids such as polymer solutions and colloidal suspensions. From a more fundamental point of view, the paper discusses a relevant example of nonlinear electrokinetics.     

Accelerating Liquid Simulation With an Improved Data-Driven Method

In physics-based liquid simulation for graphics applications, pressure projection consumes a significant amount of computational time and is frequently the bottleneck of the computational efficiency. How to rapidly apply the pressure projection and at the same time how to accurately capture the liquid geometry are always among the most popular topics in the current research trend in liquid simulations. In this paper, we incorporate an artificial neural network into the simulation pipeline for handling the tricky projection step for liquid animation. Compared with the previous neural-network-based works for gas flows, this paper advocates new advances in the composition of representative features as well as the loss functions in order to facilitate fluid simulation with free-surface boundary. Specifically, we choose both the velocity and the level-set function as the additional representation of the fluid states, which allows not only the motion but also the boundary position to be considered in the neural network solver. Meanwhile, we use the divergence error in the loss function to further emulate the lifelike behaviours of liquid. With these arrangements, our method could greatly accelerate the pressure projection step in liquid simulation, while maintaining fairly convincing visual results. Additionally, our neutral network performs well when being applied to new scene synthesis even with varied boundaries or scales.     

Fuzzy-Bayesian network for refrigeration compressor performance prediction and test time reduction

A typical characteristic of refrigeration compressor performance tests is their long duration. A reduction in the time periods related to this activity can be achieved using unsteady-state data analysis. This paper presents an original approach to predicting compressor performance using Bayesian networks and a hybrid Fuzzy-Bayesian network. All analysis was performed using real test data.     

基于半导体制冷器件的小型温度控制系统

本文介绍了基于半导体制冷器件的小型温度控制系统的设计思想以及实现方法。重点研究了半导体制冷器件的基本原理、系统构成、以及PID控制方法的单片机（SCM）实现。系统经实际测试,温度可在-2．5℃到60℃范围内设定,设定精度0．1℃,超调量不超过2℃,稳定后最大波动0．5℃以下。采用此方法设计的小型温度控制系统摒弃了传统使用压缩机的制冷技术而采用半导体制冷器件,因而具有控制灵活,控制精度高的优点,并显著降低了成本。能够满足生物、医学以及一些工业领域对小型恒温箱的要求,具有一定的推广应用价值和市场前景。     

MathCAD2001在复杂流体流动计算中的应用

在流体流动计算中经常会遇到求解非线性方程或非线性方程组等复杂的数学问题,使用传统的手工计算或计算机编程计算都是不方便的。本文开发了使用MathCAD2001解决复杂的流体流动计算问题的方法。首先对流体流动过程进行分析, 得出需要求解的数学模型。然后在MathCAD2001中选择适当的求解函数进行求解。该方法过程简便、概念清楚、使用方便, 便于教师课堂教学使用。     

新型节能空调控制系统的研制

地源热泵作为一种新型的高效节能空调系统,在实际的运行中,特别是多机组运行时,应该充分考虑主机和各个水泵的运行耗能问题。重点阐述了地源热泵空调控制系统的硬件实现、分区分时段控制及双机组运行的控制策略。实际运行证明,此控制系统很好地实现了对水泵和机组的节能控制。     

Optimization of cylindrical composite flywheel rotors for energy storage

The use of flywheel rotors for energy storage presents several advantages, including fast response time, high efficiency and long cycle lifetime. Also, the fact that the technology poses few environmental risks makes it an attractive solution for energy storage. However, widespread application of tailorable circumferentially wound composite flywheel rotors is hampered by the relatively low energy density that these rotors have been able to achieve. This contributes to high capital cost, which currently makes the flywheels prohibitively expensive for many applications. With the materials that are currently available, there seems to be ample room for improvement in the energy density achieved by composite flywheel rotors. To this aim, some of the design methods that have previously been proposed are herein studied, and our findings suggest that the manner in which the optimization problem is formulated is crucial to the design of high energy density flywheels. A new problem formulation is proposed, which is shown to lead to notable improvements in certain cases. By making use of the proposed problem formulation, flywheel rotors can be designed to consistently achieve high energy density relative to the materials that are made available. This can contribute towards lowering the cost of flywheel systems, and making flywheel energy storage viable for a wider range of applications.     

专家规则与PID复合控制在压缩机系统中的应用

针对串并联螺杆压缩机系统中的模型难以建立、能量滑阀的不确定性和时间滞后等问题,为解决压缩机吸排气压力在各种负荷变化时稳定性和快速性的矛盾问题,该文提出了一种专家规则与PID控制算法结合的控制方案,运用MATLAB对系统中控制回路进行仿真.仿真和实际运行结果表明,专家规则与PID复合控制策略在螺杆压缩机控制系统中取得良好效果,在负荷变化时,压力的超调量小、过渡时间适合且最终稳定.压缩机吸排气压力的稳定控制对于节约能量、提高制冷机效率和保证核聚变装置实验正常运行具有重要意义.     

大型制冷压缩机防喘振控制

介绍了大型制冷压缩机的新型计算机防喘振控制方案,并根据流体力学原理对该方案进行了分析。投用后,既保证了该压缩机的平稳操作,又降低了能耗。     

TOUGH+CO2: A multiphase fluid-flow simulator for CO2 geologic sequestration in saline aquifers

TOUGH+CO₂ is a new simulator for modeling of CO₂ geologic sequestration in saline aquifers. It is a member of TOUGH+, the successor to the TOUGH2 family of codes for multicomponent, multiphase fluid and heat flow simulation. The code accounts for heat and up to 3 mass components, which are partitioned into three possible phases. In the code, the thermodynamics and thermophysical properties of H₂O-NaCl-CO₂ mixtures are determined based on system status and subdivided into six different phase combinations. By solving coupled mass and heat balance equations, TOUGH+CO₂ can model non-isothermal or isothermal CO₂ injection, phase behavior and flow of fluids and heat under typical conditions of temperature, pressure and salinity in CO₂ geologic storage projects. The code takes into account effects of salt precipitation on porosity and permeability changes, and the wettability phenomena. The new simulator inherits all capabilities of TOUGH2 in handling fractured media and using unstructured meshes for complex simulation domains. The code adds additional relative permeability and capillary pressure functions. The FORTRAN 95 OOP architecture and other new language features have been extensively used to enhance memory use and computing efficiency. In addition, a domain decomposition approach has been implemented for parallel simulation. All these features lead to increased computational efficiency, and allow applicability of the code to multi-core/processor parallel computing platforms with excellent scalability.     

A valved responsive hydrogel microdispensing device with integrated pressure source

Stimulus responsive hydrogels provide the actuation pressure required for both valving and dispensing functions in the device presented. The microdispensing device uses an array of responsive hydrogels to deform a flexible membrane above a fluid reservoir chamber. When the microvalve is open, the deformation of the membrane reduces the volume of the reservoir chamber and pushes fluid through the microvalve. When the microvalve is closed, the expanding hydrogel array generates a storable pressure source that will result in fluid dispensing once the microvalve is opened. Experiments determined the pressure generated by this device to be 35 kPa. The device has a stroke volume of 45 /spl mu/L, and is able to hold the pressure for over 24 h.     

LMI‐based stability analysis of linear hybrid systems with application to switched control of a refrigeration process

We consider continuous‐time switched linear systems associated with linear state reset during mode switches, which are called linear hybrid systems and can be commonly found in switched control systems via bumpless transfer during controller switches. We use a multiple Lyapunov functions approach to develop constructive tools for stability analysis of linear hybrid systems. In particular, we derive a linear‐matrix‐inequalities based procedure to compute upper bounds of dwell time for uniform global exponential stability in linear hybrid systems, and we apply it to a refrigeration process that is regulated by several switched proportional‐integral controllers via bumpless transfer. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society