多孔竖板辐射供暖室内温度分布数值模拟研究

针对提出的新型多孔辐射竖板结构,通过CFD软件对不同结构及运行参数下辐射竖板换热进行模拟,并与实验测试结果对比,验证数值计算模型的正确性.结果表明:竖板表面温度、热流密度受供水温度影响明显,供水温度升高10℃,竖板表面温度升高3℃左右,热流密度增加13 W/m2.室内空气温度水平方向分布均匀,垂直方向室内空气温度在垂直...     

干式地板辐射供冷结合置换通风复合式系统实验研究

本文针对干式地板辐射供冷结合置换通风复合式系统进行了实验研究,测量了从系统开启到关闭的室内温度、地板表面温度、围护结构表面温度等参数,分析了系统运行过程中地板表面温度、距地面0.1 m处空气露点温度和湿度、系统换热量、温度场和湿度场以及热舒适性变化.结果表明:置换通风系统的引入可有效地避免地面结露;系统稳定运行时,室内空气温度在竖直方向分布均匀;辐射换热量占总换热量的27.8%;水系统提供的辐射换热量有限,系统稳定时,热舒适性较差,这是由于系统供水温度偏高引起的,可通过降低供水温度得到改进.     

电加热辐射地板传热特性的实验研究

本文利用组合式电热辐射板实验研究了电加热地板采暖辐射板内的传热特性。研究结果表明:辐射板的结构材料及其物性参数对表面温度分布和采暖能耗具有重要的影响。即使在实验条件下加热板内各层温度,使其呈周期性波动,但室内地板表面温度分布仍然非常均匀。在辐射板的热量损失中,通过辐射板下表面的损失热量接近辐射板全部的热量损失。     

基于不同管径毛细管辐射顶板供冷性能模拟

建立三维毛细管辐射供冷顶板传热模型,利用CFD方法对不同毛细管管径下辐射顶板流动及传热进行数值模拟求解,以获取辐射顶板的供冷量及辐射表面温度分布状况。数值模拟得到的供冷量与ASHRAE手册中辐射供冷顶棚的传热理论计算结果相符,相对误差小于15%。数值研究表明,当毛细管管径在3~5mm的范围时,辐射顶板能保证良好的供冷性能,辐射表面温度分布均匀;管径大于5mm或者小于2mm,辐射板供冷量明显减少,辐射表面温度分布越不均匀。     

内嵌管式辐射地板传热简化模型研究

本文建立了考虑绝热层向下传热的内嵌管式辐射地板传热的简化计算模型,并获取了其解析解。同时对该地板辐射传热进行了数值模拟,计算结果可作为评价解析解准确性的参考标准。计算结果表明,不考虑绝热层向下传热的地板表面温度及热流解析解结果与数值模拟结果有很大的差异;考虑绝热层向下传热的地板表面温度及热流解析解结果与数值模拟结果比较吻合,温度平均误差为0.22℃,热流平均相对误差为3.2%。     

辐射地板供冷量及表面温度分布的简化计算方法

辐射地板的供冷量、表面温度分布的均匀性和表面最低温度是研究者以及工程人员重点关注的三个问题。通过求解导热方程,得出辐射地板热阻的解析表达式,提出一种辐射地板供冷量、表面温度分布的简化计算方法。在实际应用中,可通过公式便捷地计算出辐射地板供冷性能相关的主要参数。     

冷风侵入下的大空间地板辐射采暖效果实测分析

为研究寒冷地区冷风侵入下的大空间地板辐射采暖效果,对某中小型高铁站候车厅空气温度、地板表面温度、地板制热量等参量进行了实测。经分析得到以下结论:冷风侵入下候车厅空气温度和地面温度均较低且空间分布不均匀,空气平均温度为16. 1～18. 9℃,地面平均温度为17. 4～21. 4℃,地面最大温差可超过12℃;冷风侵入下室内空气温度和非加热表面温度降低较快,而地面温度降低缓慢,因此两者之间的温差增大,这导致了地板总制热量的骤增,闭站期间地板制热量为40～60 W/m~2,运营期间局部最大可增大到120～130 W/m~2。结果表明,冷风作用下地板辐射采暖效果较差,候车厅舒适度范围为-0. 53～-1. 2;同时人员也会感受到由于吹风感和较低的地板表面温度引起的局部热不舒适。     

局部火灾中火焰辐射对顶棚升温影响的研究

基于绝缘表面温度(AST)原理,将辐射角系数对热量传递的影响计入绝缘表面温度,建立局部火灾中顶棚表面受火焰辐射影响程度的评价标准,确定火焰辐射影响范围。采用FDS,设置两个火灾场景对热量传递进行数值模拟,研究表明:在同一时刻,绝缘表面温度与烟气温度差值小于绝缘表面温度的1%时,可忽略火源辐射影响。如果用顶棚临界高度和辐射半径定量描述火焰辐射区,则当顶棚高度大于临界高度时,火焰辐射对顶棚的升温影响可以忽略;当顶棚高度小于等于临界高度时,火焰辐射对顶棚升温的影响存在一个辐射半径,位于该辐射半径内的顶棚表面,其升温将会受到火焰辐射的影响。     

冷风侵入对候车厅地板辐射采暖的影响研究

地板辐射采暖以其舒适性高,节能环保的特点而在中小型高铁站中广泛采用,成为候车厅冬季主要的采暖方式。地面温度对维持室内热环境至关重要,而地板采暖的辐射换热比例直接决定房间的表面温度,继而决定室内的舒适度情况。对寒冷地区5个中小型高铁站进行调研,总结了候车厅的主要类型及其地面温度的分布规律,证实了冷风侵入的不利影响。之后利用实测验证的CFD模型,对不同冷风侵入速度下辐射地板的辐射换热比例进行了量化分析。最终基于CFD模拟的结果,分析了冷风侵入下地板表面对流换热系数的变化,并与ASHRAE手册推荐的自然对流换热系数计算公式及文献中引用较多的机械通风条件下混合对流换热系数计算公式得到的结果进行对比,说明了冷风影响下,地板表面复合换热特性的变化。最终结果表明,当入口处风速从0. 05 m/s增大至0. 9 m/s时,辐射地板的辐射换热比例将从67%下降到39%,低于辐射采暖地板规定的最小辐射换热比例;而受冷风侵入和地板表面温度、室内温度的共同作用,辐射地板表面的对流换热系数将随入口处风速的增大而增大,当风速从0. 05 m/s增大至0. 5m/s时,对流换热系数从3. 1 W/(m~2·K)增大至3. 5 W/(m~2·K),当风速大于0. 5 m/s后,对流换热系数有所减小并趋于常值(3. 4 W/(m~2·K))。这一结果说明,现行计算方法中将地板表面边界条件中的对流换热系数及当量辐射换热系数取为定值的做法并不可取,有必要对冷风侵入条件下辐射地板表面传热特性的变化慎重考虑。为设计阶段量化冷风影响,合理确定供暖系统设计参数提供了参考和依据。     

基于沟槽结构的充液式辐射板供冷性能实验研究

本文设计了1种新型沟槽结构充液式冷辐射板,并开展了辐射板供冷性能的实验研究。实验结果表明:沟槽结构及内部充液设计,可强化冷水与辐射板表面间的换热,显著提高辐射板表面温度分布的均匀性,消除局部低温,从而实现较好的热舒适性。在实验小室室温为27~34℃,冷水供水温度为15~17℃,供水流量为0.1~0.2 L/s时,本辐射板单位面积供冷量可达260~720 W/m2。实验工况下辐射板表面温度较为均匀,最大温差为2.9℃,辐射板下部垂直方向上温度梯度小于3℃/m。     

Decomposition of 2-naphthalenesulfonate in aqueous solution by ozonation with UV radiation

This study investigates the ozonation of 2-naphthalenesulfonate (2-NS) combined with ultraviolet (UV) radiation. Naphthalenesulfonic acids are of importance as dye intermediates for the dye and textile auxiliary industries. Its derivatives, such as 2-NS, have been found in rivers and tannery effluents causing pollution problems. Thus, the 2-NS is of concern for the aquatic pollution control especially in the surface and waste waters. Ozonation combined with UV radiation is employed for the removal of 2-NS in the aqueous solution. Semibatch ozonation experiments were proceeded under different reaction conditions to study the effects of ozone dosage and UV radiation on the oxidation of 2-NS. The concentrations of 2-NS and sulfate are analyzed at specified time intervals to elucidate the decomposition of 2-NS. In addition, values of pH and oxidation reduction potential are continuously measured in the course of experiments. Total organic carbon is chosen as a mineralization index of the ozonation of 2-NS. The mineralization of 2-NS via the ozonation is remarkably enhanced by the UV radiation. These results can provide useful information for the proper removal of 2-NS in the aqueous solution by the ozonation with UV radiation.     

Modellierung von kurzwelliger solarer Strahlung bei der hygrothermischen Bauteilsimulation – numerische Lösung und analytischer Ansatz

Modelling of shortwave solar radiation within the hygrothermal simulation of building envelope parts – numerical solution and analytical approach. This article presents a model for the determination of shortwave solar radiation on building envelope parts, which is – based on measured weather data of direct and diffuse solar radiation on a horizontal surface – suitable to be integrated in computercodes for hygrothermal building part simulation. Therewith, firstly a well‐rounded concept has been worked out, which allows to calculate the radiation flux on any orientated and sloped wall or roof construction at any location taking into account the self‐shading. Furthermore, there is presented an analytical approach for the same problem that is suitable to perform sensitivity analyses with in an easy way. At the end of the article, an example calculation of a wall construction orientated into different directions is presented.     

混凝土坝-基岩地震动力相互作用时域有限元分析

混凝土坝地震响应分析是坝工安全评估的关键一步。坝与基岩动力相互作用对混凝土坝地震响应具有重要影响。因此,建立一个可考虑坝与基岩动力相互作用影响的数值分析方法是十分必要的。给出了分析混凝土坝–基岩系统地震响应的时域有限元法。在时域有限元分析中,地震波的输入以及地基辐射阻尼的模拟常常是2个十分重要的课题。基于柱面波动方程提出了能同时实现地震动输入和模拟地基辐射阻尼的方法,这种方法非常简单有效,几个数值算例验证了方法的精度和有效性。最后,对混凝土重力坝地震响应进行了数值分析,结果表明无限地基辐射阻尼的影响是显著的。     

Human biokinetic data and a new compartmental model of zirconium--a tracer study with enriched stable isotopes

Biokinetic models describing the uptake, distribution and excretion of trace elements are an essential tool in nutrition, toxicology, or internal dosimetry of radionuclides. Zirconium, especially its radioisotope ⁹⁵Zr, is relevant to radiation protection due to its production in uranium fission and neutron activation of nuclear fuel cladding material. We present a comprehensive set of human data from a tracer study with stable isotopes of zirconium. The data are used to refine a biokinetic model of zirconium.Six female and seven male healthy adult volunteers participated in the study. It includes 16 complete double tracer investigations with oral ingestion and intravenous injection, and seven supplemental investigations. Tracer concentrations were measured in blood plasma and urine collected up to 100 d after tracer administration. The four data sets (two chemical tracer forms in plasma and urine) each encompass 105-240 measured concentration values above detection limits.Total fractional absorption of ingested zirconium was found to be 0.001 for zirconium in citrate-buffered drinking solution and 0.007 for zirconium oxalate solution.Biokinetic models were developed based on the linear first-order kinetic compartmental model approach used by the International Commission on Radiological Protection (ICRP). The main differences of the optimized systemic model of zirconium to the current ICRP model are (1) recycling into the transfer compartment made necessary by the observed tracer clearance from plasma, (2) different parameters related to fractional absorption for each form of the ingested tracer, and (3) a physiologically based excretion pathway to urine.The study considerably expands the knowledge on the biokinetics of zirconium, which was until now dominated by data from animal studies. The proposed systemic model improves the existing ICRP model, yet is based on the same principles and fits well into the ICRP radiation protection approach.     

Detection of salts of 2,4-D in aqueous solution by laser raman spectroscopy

Laser Raman spectroscopy is used to detect a salt of a herbicide, 2,4-dichlorophenoxy acetic acid, in water solution at concentrations as low as 500 ppm. The Raman spectrum of the powder is substantially different from the spectrum of the pollutant in aqueous solution. The spectrum of the potassium and sodium salts are the same for the powder or aqueous solution. Five strong bands exist in aqueous solution, and four of these bands are detectable at concentrations as low as 500 ppm. A plausible assignment to group frequencies for some of the Raman bands is given.All spectra were excited with a 50 mW He-Ne gas laser at 6328 Å. Lower concentrations should be detectable with a more powerful laser at a higher frequency because: (1) the intensity of the scattered radiation is proportional to the product of the intensity of the electric field perturbing the molecule and the fourth power of the scattered frequency; (2) the attenuation coefficient of water is less; (3) the photocathode used is more efficient at higher frequencies and (4) the monochromator grating used is blazed at 5000 Å. The resonance Raman effect is discussed as a possible method for the detection and identification of small optimal concentrations of pollutant in water.     

Summer-performance of inclined roof solar chimney for natural ventilation

Effect of inclination of absorber on the airflow rate has been investigated in a solar induced ventilation system using Roof Solar Chimney (RSC) concept. During summer months, due to the higher altitude of sun, absorber at small inclination with the horizontal plane captures more solar radiation, but suffers with reduction in the stack height. Results of the developed solution show that optimum absorber inclination varies from 40° to 60° depending upon the latitude of place. At Jaipur (India) 45° is found to be optimum for obtaining maximum rate of ventilation. At this inclination, the rate of ventilation is about 10% higher as compared to 60° and 30° inclinations. Experimental investigations show good agreement with the theoretical results. Roof Solar chimney of this size can easily be mounted on residential buildings for enhancing natural ventilation.     

Solar and UV photodecomposition of 2,3,7,8-tetrachloro dibenzo-p-dioxin in the environment

Photodegradation of 2,3,7,8-tetrachloro dibenzo-p-dioxin can be achieved in field soils, and on any other material contaminated by this substance providing a layer of a substance consisting of a hydrogen donor is added followed by irradiation by sunlight or high-pressure mercury lamps. A suitable layer is obtained by spraying surfaces with a 1 : 1 xylene-ethyl oleate solution into which TCDD dissolves. Photodecomposition rate is affected by the intensity of radiation, the medium upon which 2,3,7,8-tetrachloro dibenzo-p-dioxin is dispersed and temperature. Radiations from high-pressure mercury lamps can be used to decontaminate both indoors and outdoors of buildings, while natural summer solar radiation has been found to be effective in the decontamination of floors, walls and soil. Decontamination occurs to a certain extent also beneath the soil surface.     

极端热湿地区围护结构热湿耦合传递模型

极端热湿地区常年高温多雨,为了准确预测围护结构内的温度和湿度分布,模拟高温、高湿和高太阳辐射对围护结构的影响,建立了适用于极端热湿地区的围护结构热湿耦合传递模型,在边界条件中加入太阳辐射和雨水负荷对传热传湿的影响,考虑了随材料含湿量不断变化的材料物性参数。为了求解模型,提出了基于计算机软件COMSOL的模型求解方法,利用MATLAB计算方程组不断变化的系数,并确定了软件容差和网格的设置条件:相对容差推荐设定在0.001,绝对容差设定为0.000 1,网格按极细化划分。通过对比HAMSTAD标准实例验证了模型的准确性。     

敞开式太阳能集热/再生器的理论模型及性能分析

对敞开式太阳能集热再生器建立理论解析模型,理论求解发现溶液在常温下再生时存在一个最佳单位面积流量使单位面积蒸发率最大。溶液入口温度和室外风速是决定最佳流量值的2个最重要参数,溶液浓度和太阳辐射强度对最大蒸发率影响最明显。当溶液出口温度低于入口温度时,最佳流量不存在,溶液流量越大再生效果越好。当室外风速为2m/s时,溶液再生蒸发率最大。文章全面揭示了影响敞开式集热/再生器性能的各项因素。