Criteria for use of groundwater as renewable energy source in geothermal heat pump systems for building heating/cooling purposes

Environmental protection measures are conducted directly by the use of renewable energy sources. The energy development of cities in Europe is aimed at the sustainable use of renewable energy sources in order to achieve the substitution of fossil fuels and the reduction of the hazardous gas emission into the atmosphere. Geothermal resources of medium and low enthalpy in Europe being used for obtaining heat energy are providing about 6600 MW_t, currently having the growth trend of 50 MW_t annually. The use of geothermal low enthalpy, namely of subgeothermal groundwater resources, has even higher annual growth rate, and if such a trend is kept till the year 2010, the produced energy will amount about 8000 MW_t. Criteria of the groundwater use as a hydrogeothermal energy resource in heat pumps are complex, and they deal with aspects of incoming temperatures and groundwater quantities. The precise limit temperature of groundwater that would separate the direct use of geothermal energy (only by the use of heat exchangers), and indirectly by the use of a heat pump has not been determined in the professional and scientific practice of Serbia so far. Taking into account that relatively small number of new flat is being built in Serbia nowadays, if we want to save energy it is necessary to carry out the energy reconstruction of the existing flats whose number is estimated to be more than 2.8 million. By the application of subgeothermal energy and the use of heat pumps, energy consumption would be significantly reduced.     

压簧圈多工位级进模设计

分析了压簧圈的结构工艺,给出了排样设计及模具结构,详述了自动送料机构、浮动导料装置、浮顶装置及模具的工作过程。该模具结构合理、可靠,对同类零件的模具设计具有一定的参考价值。     

基于有限元的汽车曲轴锻件空洞闭合研究

空洞是大型锻件内部的一种常见缺陷,为了提高锻件的性能,必须将其消除.基于有限元软件分别选取高径比、摩擦系数、空洞尺寸、温度、锻件尺寸等因素对空洞的闭合过程进行了模拟.结果表明:影响空洞闭合的主要因素为高径比、温度及摩擦系数.这在很大程度上深化了对空洞闭合的认识.     

MECHANISM OF DENDRITE FORMATION FROM A STREAM OF SUBMICRON AEROSOL IN THE PRESENCE OF EXTERNAL ELECTRIC FIELD

In the present work we extend the model of dendrite formation to the case of submicron unipolar charged particles, where the main transport mechanism in convective Brownian diffusion and electrical effects due to the presence of charges on the particles and electric field around cylindrical collector.

We present solutions for the case of slip flow around the fiber and free molecular flow around particles.     

Preliminary investigation of a transcritical CO2 heat pump driven by a solar‐powered CO2 Rankine cycle

In this paper, a transcritical carbon dioxide heat pump system driven by solar‐owered CO₂ Rankine cycle is proposed for simultaneous heating and cooling applications. Based on the first and second laws of thermodynamics, a theoretical analysis on the performance characteristic is carried out for this solar‐powered heat pump cycle using CO₂ as working fluid. Further, the effects of the governing parameters on the performance such as coefficient of performance (COP) and the system exergy destruction rate are investigated numerically. With the simulation results, it is found that, the cooling COP for the transcritical CO₂ heat pump syatem is somewhat above 0.3 and the heating COP is above 0.9. It is also concluded that, the performance of the combined transcritical CO₂ heat pump system can be significantly improved based on the optimized governing parameters, such as solar radiation, solar collector efficient area, the heat transfer area and the inlet water temperature of heat exchange components, and the CO₂ flow rate of two sub‐cycles. Where, the cooling capacity, heating capacity, and exergy destruction rate are found to increase with solar radiation, but the COPs of combined system are decreased with it. Furthermore, in terms of improvement in COPs and reduction in system exergy destruction at the same time, it is more effective to employ a large heat transfer area of heat exchange components in the combined heat pump system. Copyright © 2012 John Wiley & Sons, Ltd.     

大容量机组低、中压凝结水系统运行特性对比分析

针对目前大容量高参数机组所具有的低压和中压凝结水系统在除氧器滑压运行的特点进行了管路特性的确定,并通过低压系统中工频凝结泵与变频凝升泵串联运行,以及中压系统中凝结泵变频运行的调节特性分析,给出了为保证系统设备所需最低压力和水泵最低转速的限制下两种系统更加合理的运行方式;以典型的300MW亚临界同容量机组为例进行能耗比较,为现行的低压凝结水系统是否有必要进行节能改造提供了可参考的理论依据.     

湖水源热泵系统排热工况下散点排水对湖体温度场的影响

采用流体计算软件建立三维湖体模型，模拟设计日下湖体自然水温，用实测水温进行修正作为初始条件；根据别墅群全年逐时负荷的模拟结果，采用动态取排水温和水量作为边界条件；以典型气象年数据为基础，通过用户自定函数输入水面换热边界；分别对某别墅群水库水源热泵系统的排放水管网采用与雨水排水管网相结合的散点排水以及采用传统的集中排水方式进行了动态数值模拟，得到供冷季逐时排热工况下湖体温度场的分布情况，分散排水优势明显。分析模拟结果表明：集中排水方案水体周温升0.33 ℃，分散排水方案水体周温升0.16 ℃；水体水道狭长体积有限的区域在连续排水的情况下，有明显热累积现象。连续运行条件下，散点排水取水口水温的模拟结果表明：7~10月，位于常年水位4.6 m水深下的取水口取水温度在27~23.5 ℃之间，可实现热泵系统高效运行。     

砼泵主油缸换向平稳性差的故障机理分析

该文在对混凝土输送泵主油缸结构、串接方式进行分析的基础上,从理论上对主油缸换向平稳性差的故障原因和故障机理进行了研究分析.所取得的分析结论对指导人们现场快速诊断类似故障具有积极意义.     

Design,experimental investigation and multi-objective optimization of a small-scale radial compressor for heat pump applications

The main driver for small scale turbomachinery in domestic heat pumps is the potential for reaching higher efficiencies than volumetric compressors currently used and the potential for making the compressor oil-free, bearing a considerable advantage in the design of advanced multi-stage heat pump cycles. An appropriate turbocompressor for driving domestic heat pumps with a high temperature lift requires the ability to operate on a wide range of pressure ratios and mass flows, confronting the designer with the necessity of a compromise between range and efficiency. The present publication shows a possible way to deal with that difficulty, by coupling an appropriate modeling tool to a multi-objective optimizer. The optimizer manages to fit the compressor design into the possible specifications field while keeping the high efficiency on a wide operational range. The 1D-tool used for the compressor stage modeling has been validated by experimentally testing an initial impeller design. The excellent experimental results, the agreement with the model and the linking of the model to a multi-objective optimizer will allow to design radial compressor stages managing to fit the wide operational range of domestic heat pumps while keeping the high efficiency level.