Simulation and experimental research on energy conversion efficiency of scroll expander for micro‐Compressed Air Energy Storage system

A scroll expander was applied to the Micro‐Compressed Air Energy Storage system, and its energy conversion efficiency was investigated. In order to study the variation mechanism of the volume, mass, pressure and temperature of the air in different chambers, the mathematical model of the expansion process was developed on the base of the geometric model, mass conservation equation, ideal gas equation and energy conservation equation. Then, the mathematical model was implemented in Matlab, and the simulated energy conversion efficiency defined as the ratio between the output shaft power of the scroll expander and the input compressed air power was obtained. Furthermore, a test system was built in order to validate the mathematical model and study the improvement of the energy conversion efficiency. The prototypes of the scroll expander with different cross‐sectional areas of the intake port or the discharge port were fabricated and tested in the experiments. Results show that the simulated torque and energy conversion efficiency agree well with the experimental results. Also, there is a small deviation between the expansion process and the ideal isentropic process due to the gas leakage, intake and discharge loss. In addition, the air supply pressure and the cross‐sectional area ratio of the discharge port to the intake port are two important parameters for the improvement of the energy conversion efficiency. The experiments show that the energy conversion efficiency varies from 23% to 36% at the air supply pressure of 0.35 to 0.65 MPa, indicating that it is proportional to the air supply pressure. It can also be concluded from the experiments that when the air pressure is higher than 0.45 MPa, the ideal ratio range can be determined as 0.6‐0.8. Copyright © 2013 John Wiley & Sons, Ltd.     

Non‐minimum phase switched systems: HOSM‐based fault detection and fault identification via Volterra integral equation

In this paper, the problem of continuous and discrete state estimation for a class of linear switched systems with additive faults is studied. The class of systems under study can contain non‐minimum phase zeroes in some of their ‘operating modes’. The conditions for exact reconstruction of the discrete state are given using structural properties of the switched system. The state space is decomposed into the strongly observable part, the non‐strongly observable part, and the unobservable part, to analyze the effect of the unknown inputs. State observers based on high‐order sliding mode to exactly estimate the strongly observable part and Luenberger‐like observers to estimate the remaining parts are proposed. For the case when the exact estimation of the state cannot be achieved, the ultimate bounds on the estimation errors are provided. The proposed strategy includes a high‐order sliding‐mode‐based fault detection and a fault identification scheme via the solution of a Volterra integral equation. The feasibility of the proposed method is illustrated by simulations. Copyright © 2013 John Wiley & Sons, Ltd.     

Nisin as a Food Preservative: Part 1: Physicochemical Properties,Antimicrobial Activity,and Main Uses

Nisin is a natural preservative for many food products. This bacteriocin is mainly used in dairy and meat products. Nisin inhibits pathogenic food borne bacteria such as Listeria monocytogenes and many other Gram-positive food spoilage microorganisms. Nisin can be used alone or in combination with other preservatives or also with several physical treatments. This paper reviews physicochemical and biological properties of nisin, the main factors affecting its antimicrobial effectiveness, and its food applications as an additive directly incorporated into food matrices.     

Production and characterization of phenolic compounds by flash pyrolysis of palmyra palm

New and renewable fuels are the major alternatives to conventional fossil fuels. Biomass in the form of agricultural residues is becoming popular among new renewable energy sources, especially given its wide potential and abundant usage. This study deals with the characterization of the pyrolysis oil obtained from palmyra palm fruit bunch (Borassus flabellifer) produced by flash pyrolysis in the maximum yield. The pyrolysis oil was analyzed to determine its elemental composition and heating value. The chemical composition of the pyrolysis oil and fractions was investigated using various chromatographic techniques such as Fourier transform infra-red (FTIR) spectroscopy, gas chromatography–mass spectroscopy (GC-MS), and ¹H NMR spectroscopy. The bio-oil product was presented as an environmentally friendly green biofuel candidate. The analytical results showed that the pyrolysis bio-oils were very complex mixtures of organic compounds and contained a lot of nitrogenated and oxygenated compounds such as, phenols, aliphatic hydrocarbons, pyridines, amines, ketones, and so on.     

Experimental investigation of the drying characteristics of a mixed mode natural convection solar crop dryer with back up heater

A mixed mode natural convection solar crop dryer with a backup heater was designed and constructed from locally available materials and used to dry freshly prepared pineapples under four drying Scenarios for drying to correspond to specified drying periods for four typical seasons in Ghana. The experiments were devised for the material moisture content to be monitored continuously till the desired moisture content of between +106% and 184% (d.b) was achieved. In solar heating mode of operation, results show that the thermal mass was capable of storing part of the absorbed solar energy but the quantities involved are insufficient to sustain night drying. It was possible to dry a batch of pineapples in each mode of operation. The dryer reduced the moisture content of pineapple slices from about; 924% to 106% in 19 h; 1049% to 184% in 10 h; 912% to 155% in 7 h; and 1049% to 144% (d.b) in 23 h, for drying in Scenarios 1, 2, 3 and 4, respectively. The average moisture pickup efficiency values obtained were 27%, 24%, 11%, and 32% for drying in Scenarios 1, 2, 3, and 4, respectively.     

手机与电视互动业务及技术实现

介绍了手机与电视互动的几种业务模式,分析了技术实现流程,对推广该业务的限制条件进行了分析,并对业务应用前景作出了预测.     

HFVB2445型高频筛模态分析与试验

针对HFVB2445型高频筛,利用有限元分析软件ANSYS Workbench对其进行模态分析,得到了6阶刚体模态和前4阶弹性模态的仿真频率和振型,并采用锤击法对其实体产品进行测量,得到了筛箱的试验模态频率和振型;将仿真模态与试验模态进行了逐一对比,验证了仿真结果与试验结果基本一致,确定了该高频筛的模态频率及振型特点,找到了筛箱的薄弱部位,为振动筛的动态特性优化设计提供了参考。     

建筑节能推广复杂性分析与管理研究

建筑节能推广是集成了技术、经济、管理、社会、环境、价值等多种要素的社会活动,建筑节能推广普及对于我国实施能源节约战略具有重要意义。运用复杂性科学的基本原理,从整体性、开放性、动态性、层次性和自组织性等方面对建筑节能推广进行复杂性分析与管理研究,提出了基于集成管理思想,包括推广管理对象、推广利益主体、推广目标、推广管理全过程和推广评价等系统要素的复杂性集成管理模式,并探讨了建筑节能推广管理模式中各要素的内容。     

Terminal voltage build-up and control of a DFIG based stand-alone wind energy conversion system

The paper presents the voltage build-up process and the terminal voltage control of a doubly-fed induction generator (DFIG) driven by a pitch controlled wind turbine for the supply of autonomous system without any auxiliary source. A control strategy for the complete system including voltage build-up phase is developed with a view to provide as well as possible the required power for load. Indirect stator flux-oriented vector control is proposed to keep the stator voltage constant by means of a back-to-back converter connected to the rotor side, while the management system is supported by the pitch angle and the load shedding controllers. A novel scheme for voltage build-up is presented, which requires no additional hardware support, and physical interpretation of how self-excitation can occur from residual magnetism in the machine core is examined. A reliable start-up process is accomplished by using an appropriate voltage reference ramp which enables minimizing energy loss during the starting. The proposed system is modeled and simulated using Matlab/Simulink software program to examine the dynamic characteristics of the system with proposed control strategy. Dynamic simulation results for different transient conditions demonstrate the effectiveness of the proposed control strategy.