Computer analysis,design and simulation of horizontal ground heat exchangers

This paper presents a new computerized procedure for dealing with the design of horizontal ground heat exchangers (HGHE). The computer program is based on the transient model of coupled nonlinear partial differential equations governing heat and mass flow in soils. The model is two-dimensional and delineates the operation of ground heat storage with the HGHE and such phenomena as freezing/thawing and drying/rewetting of soil moisture. Comprehensive climatological data, such as ambient temperature, solar radiation, wind velocity, rainfall, snowfall, snow characterstics, and water vapour pressure is used to simulate conditions at the ground surface over any required length of time. The package can be applied to any geographical location by changing climatic and soil data input. The designer has the possibility of selecting any of 12 types of soils from sand to clay, 12 commercial heat pumps, nine different configurations of the HGHE, 16 plastic pipes for ground coils, and 13 ground coil fluids. The program, however, does not calculate the length of the HGHE but it evaluates the thermodynamic performance of a ground heat pump system and provides comprehensive data on thermal and hydraulic conditions in ground heat storage. The length of the ground heat exchanger is obtained from a line source theory model or from site dimensions and pipe spacing. Computed results for ground heat exchanger operation correlate fairly well with experimental data. Simulation of temperature and moisture content in the ground for natural conditions (no heat extraction/deposition) showed a fair agreement with field data. The entire computer program is user-friendly, interactive, menu-driven, and written in FORTRAN 77.     

Determination of the total concentration and speciation of Al(III) in tea infusions

The aluminium species in different tea infusions were investigated, by determining their stability constants and concentration. This was done for some particular samples using a simple experimental method based on the sorption of aluminium on the strongly sorbing resin Chelex 100, by a batch procedure. From the thermodynamic information obtained it is possible to calculate the concentration of the different species, and in particular that of the free metal ion, which is very important for evaluating the adsorption of aluminium on biological membranes. It was found that aluminium in the tea infusions here considered is present at high total concentration, approximately 0.1 mM, but mainly linked to strong complexes, for instance with side reaction coefficient higher than 10(5.11) at pH 3.95 in one case (tea 1). This could be the reason for the low toxicity of aluminium in tea. These strong complexes were not dissociated even in the presence of Chelex 100. In this case only a limiting value of the reaction coefficient could be evaluated. The presence of the very strong complexes was found in all the tea sample here considered. In two of the considered samples (one black and one green tea) a part of Al(III) was linked to less strong complexes, for example with a reaction coefficient 10(4.14) (tea 2, pH 4.20). The presence in the considered tea infusions of other substances able to complex aluminium was also detected, by the well known ligand titration procedure, at concentration ranging from 0.65 to 3.37 mM in three tea infusions, and at somewhat higher concentration in the case of the ready drink, which was also considered for comparison.     

Potential of ground heat source systems

This paper presents a historical background of ground source heat pump technology, followed by a review of its current shortcomings. Based on these observations the author assesses the R&D needs and recommendations for future research.     

ECO布局中的电源线/地线网络局部SOR分析方法

供电电压直接决定芯片性能,在IC设计的各个阶段考虑供电电压约束具有重要的意义.受制于电源线/地线(P/G)网络分析的高复杂性,尽管供电电压已成为布图规划设计中的一个设计约束,但目前在布局设计中还未考虑供电电压约束.有别于ICCG,SOR等经典的全局分析算法,提出了一种局部的连续过松弛方法(SORPECO),并在ECO布局过程中对P/G网电压约束进行高效的分析.基于前一个布局的P/G网电压分布,针对ECO试探布局中某些轻微设计变动,SORPECO只需对这些设计变动的局部变化周边区域进行松弛,以更新P/G网电压分布.受益于P/G网络分析的局部性,SORPECO拥有局部、高效和高精度等优点.实验结果表明,与通常用于布图规划的传统高效的ICCG算法相比,SORPECO不仅精度损耗几乎可以忽略(最大误差0.062%),而且可以加速2个数量级.     

水泥土搅拌桩加固软土地基实例分析

本通过工程实例说明，位于稳定水位以下的土体采用水泥土搅拌桩进行加固应优先采用干法作业，而不宜采用湿法作业。     

地电位升高对通信设备的影响及其防护

针对电力通信系统运行特点,着重对电力系统接地故障引起的地电位升高及其对通信设备的影响进行了分析,提出了相应的保护措施,并介绍了两种保护装置。     

实用运算放大器网络中的虚地性质

本文提出用一个理想电压控制电流源(VCCS)并接于嵌在一个倒相放大器电路中的实际运算放大器(OP.amp)输入端,虚地性质(VGP)可以扩展到使用的运算放大器单位增益带宽那样高的频率.文中给出用真正运算放大器的VCCS的实用电路.用互补变换法可得出非倒相放大电路图.     

低温高压自动脱落冷氦连接器研制

主要介绍了冷氦连接器的研制与试验,以及研制中的技术难点及解决途径。此连接器的研制,解决了低温,高压下多路连接密封问题,隔热和绝热问题以及射前脱落问题,为ＣＺ－３Ａ三级冷氦增压系统得到实施提供了一个必不可少的关键设备。     

Analysis of the energy performance of a ground source heat pump system after five years of operation

GeoCool plant was the result of a EU project whose main purpose was to adapt ground coupled heat pump technology to cooling dominated areas. The execution of this experimental plant was completed at the end of year 2004, starting on February 2005 the regular operation of the air conditioning system. Since then, GeoCool facility has been monitored by a network of sensors characterizing its most relevant parameters. Several aspects of the performance and behaviour of the system during its first operational year were presented on a previous paper. This paper presents the energy performance measurements of GeoCool ground coupled heat pump system acquired during five years of operation as well as the evolution of the return water temperature from the ground as a representative of the ground temperature. The analysis of the experimental results shows that the system energy performance is maintained through the years with no appreciable impact on ground thermal response.