Analysis of hyperbolic cooling towers with local imperfections

Two methods to analyse hyperbolic cooling towers with local imperfections are presented. One method relies on the finite element technique. For this a specialized finite-element program, which can model any arbitrary imperfections while retaining the advantage offered by the basically axisymmetric nature of the shell, was developed. The other method is an approximate procedure, which may be implemented with a purely axisymmetric analysis capability. The two methods are compared through numerical studies. A cooling tower shell with a bulge-type imperfection is examined under dead load and wind load conditions. It is concluded that the finite-element model presented is effective for the analysis of such shells, while the equivalent-load method may be adequate for some cases. Also, it is shown that both meridional and circumferential stress resultants may be radically influenced by a small bulge imperfection.     

Finite element techniques for the analysis of cooling tower shells with geometric imperfections

Two finite element methods for analysing geometrically imperfect cooling tower shells are presented. In the first the geometry of the imperfection is modelled by the elements; in the second the imperfection is represented by an equivalent load on the shell. Axisymmetric and general shell elements have been considered.Results are given which show that the first approximation to the equivalent load is sufficiently accurate and that it is possible to represent local imperfections by axisymmetric imperfections which require less computation. It is also shown that axisymmetric elements should be used wherever possible, because of their greater efficiency, following the geometry of an axisymmetric imperfection but representing local imperfections by equivalent loads.     

An assessment of the role of geometric imperfections in the collapse of the fiddlers ferry cooling tower

The B2 cooling tower at Fiddlers Ferry Power Station collapsed during a gale in January 1984. It was known that this tower contained a roughly axisymmetric bulge just above the ring beam which had been present since the time of construction. This paper describes various finite element analysis that were carried out to assess the effect of this geometrical imperfection on the stresses in the tower. It is shown that the bulge would have caused vertical cracks to develop and the subsequent propagation of both horizontal and vertical cracks would have ultimately lead to the collapse of the tower.     

冷却塔冷却过程模拟计算

分析了冷却塔的传热传质过程,考虑了冷却塔蒸发水带走的热量,推导出该过程的数学模型。认为利用该模型计算简单,省时,计算结果与经典的Ｓｕｔｈｅｒｌａｎｄ数值比较,误差为５％。     

冷却塔的噪声控制研究

根据某高档住宅小区冷却塔辐射噪声的测量数据,应用有限元分析方法分析了冷却塔的声场分布云图,分析了冷却塔的主要噪声来源和频带特性。分别从吸声、消声和隔声三个方面制订噪声控制的方案,所有降噪设施不但考虑防尘、防潮,而且满足设备相应的风量和温度要求,噪声控制取得了良好的效果。     

冷却塔比焓采集的研究

提出以比焓作为换热设备信息化设计的参数采集单位,以冷却塔为例分析了比焓采集误差与物理传感器测量误差之间的关系,得出物理传感器的选择依据,给出了比焓采集系统的设计要则。     

Measurement of the geometric initial imperfections in diaphragms

A method, using a new surveying technique, is used for the measurement of the geometric initial imperfections in box girder diaphragms. The method, accurate to ±0·1 mm, may be used on diaphragms contained in a box girder where contact with the surface of the diaphragm is difficult or impossible or inadvisable due to the presence of strain gauges.     

冷却塔供冷系统设计方法

介绍了冷却塔免费供冷的原理,通过对工程设计中的一些方法和概念进行分析,提出开式冷却塔加板式换热器是冬季冷却塔供冷较实用的形式,探讨了冬季内区采用较高空调供水温度的可行性、冷却塔冬季性能曲线、冷却塔供冷与冷水机组供冷工况切换点的取值、水泵的选取、冷水机组选用等问题.给出了冷却塔系统设计实例.     

如何正确选用封闭式冷却塔

认为在回收利用某些民用空调及工业制冷的排热时，使用封闭式冷却塔比传统的使用开敞式冷却塔加热交换器或空调器更经济，而且运行操作更简便易行。比较了几种形式冷却塔的特点并简述了其热交换原理、结构和应用条件。     

逆流式冷却塔的噪声治理

根据逆流式冷却塔辐射噪声的实测频谱图,分析了冷却塔的主要噪声来源和频谱特征.分别从吸声、消声和隔声等方面制定了降噪方案,取得了良好的降噪效果.     

Measurement and assessment of geometric imperfections in thin-walled panels

Thin-walled members may be subject to performance limitations arising through local or distortional buckling of slender elements comprising the cross-section of the member, or overall buckling of the member. The effects of structural instability may be aggravated by the presence of geometric imperfections in these elements. An investigation is presented into methods of measuring and assessing geometric imperfections in cold-rolled thin-walled steel panels. These methods can be used to characterise the geometry of prismatic thin-walled members that exhibit performance sensitivity due to geometric imperfections. The measurement procedures investigated include close-range photogrammetry, precise optical levelling, and the use of a co-ordinate measurement machine. The assessment procedure comprises a least-squares spectral decomposition of the measurements to characterise the imperfections existent in the panels under investigation, and estimates of the precision of the derived Fourier coefficients are used to inter-compare the three measurement procedures. The investigation has demonstrated that statistically significant imperfections may exist in thin-walled members at short and medium wavelengths, leading to a reduction in the load carrying capacity. Both optical levelling and the co-ordinate measurement machine technique can yield desirable results, but for high precision work, use of the co-ordinate measurement machine is recommended.     

逆流式冷却塔的性能系数

利用Werkel理论,针对没有填料层的淋水式冷却塔内的热湿交换情况.建立了淋水式冷却塔内水与空气热湿交换的能量方程.推导出冷却塔的COP表达式;并用数值法计算了某运行工况下冷却塔的COP,通过实验得出该冷却塔的性能曲线,并据此曲线回归出了该冷却塔COP的经验表达式。     

基于热工性能分析的闭式冷却塔能量调节

通过对闭式冷却塔的热工性能分析,得出在一定工况条件下,闭式冷却塔冷却能力的主要影响因素为管内介质的流量和温度、喷淋水量和喷淋水温以及空气流量.同时针对不同影响因素给出了相应的能量调节方式.     

冷却塔的噪声治理研究与实践

结合工程实例,分析了集中空调系统冷却塔噪声超标的原因,给出降低噪声的措施,计算了各消声措施的噪声衰减量。实测结果表明,消声效果良好。     

Probabilistic analysis of secant piles with random geometric imperfections

The failure to achieve minimum design overlap between secant piles compromises the ability of a structure to perform as designed, resulting in water leakage or even ground collapse. To establish a more realistic simulation and provide guidelines for designing a safe and cost-effective secant-pile wall, a three-dimensional model of a secant pile, considering the geometric imperfections of the diameter and direction of the borehole, is introduced. An ultrasonic cross-hole test was performed during the construction of secant piles in a launching shaft in Beijing, China. Based on the test results, the statistical characteristics of the pile diameters and orientation parameters were obtained. By taking the pile diameter D, inclination angle β, and azimuth angle α as random variables, Monte Carlo simulations were performed to discuss the influence of different design parameters on the probability density functions of the overlap of secant piles. The obtained results show that the randomness of the inclination angle and pile diameter can be well described by a normal distribution, whereas the azimuth angle is more consistent with a uniform distribution. The integrity of the secant-pile wall can be overestimated without considering the uncertainty of geometric imperfections. The failure of the secant-pile wall increases substantially with increasing spatial variability in drilling inclination and diameter. A design flowchart for pile spacing under the target safety level is proposed to help engineers design a safe and economical pile wall.     

空调系统中冷却塔的节能

指出对空调系统中的风机、水泵等的耗能就给予与制冷机组同样的重视,系统节能应整体考虑。分析了冷却塔出水温度对系统性能的影响,举例说明了不同工况的能耗对比。     

The effect of geometric imperfections on the vibrations of anisotropic cylindrical shells

Analytical–numerical models to analyse the flexural vibration behaviour of anisotropic cylindrical shells are presented. The two models (denoted as Level-1 and Level-2 Analysis) have different levels of complexity and can be used to study the influence of important parameters, such as geometric imperfections, static loading, and boundary conditions. A specific anisotropic shell is used in the calculations in this paper. The influence of the imperfection shape and amplitude on the natural frequency is investigated for this shell via both the Level-1 and the Level-2 Analysis. Imperfections with the shape of the “lowest vibration mode” give a decrease of the natural frequency with increasing imperfection amplitude. The results of the Level-2 Analysis for the effect of imperfections on the natural frequency are in reasonable agreement with Finite Element calculations.     

并联冷却塔一种管道设计方案的探讨

工程中并联冷却塔常采用在冷却塔进水管设置电动阀与冷却水泵联动、出水管不设置电动阀、各并联塔之间设置平衡管的方案。这种设计方案符合设计规范和技术措施的规定,但运行时当部分冷却塔的进水管水阀关闭后,常会出现开启的冷却塔持续溢流、而关闭的冷却塔持续补水的现象。通过一个案例的计算分析,研究出现该现象的原因,并提出改进建议。     

封闭式冷却塔供冷系统气象条件分析

在阐述封闭式冷却塔供冷技术原理及系统形式的基础上,探讨了封闭式冷却塔供冷与空气湿球温度的关系,分析了封闭式冷却塔供冷技术的节能效果。根据山东省某市全年8760h逐时实测气象数据,统计出了空气湿球温度在各区间出现的频率及累计频率,结果表明,一年中空气湿球温度小于等于10℃的时间达4208h。这对于全年运行的空调系统而言,节能潜力巨大。     

The fate of chlorine in recirculating cooling towers Field results

Chlorine and chloramines are volatile compounds which are stripped (“flashed off”) from recirculating cooling water systems by the large volumes of air which flow through the water in the cooling tower. The fraction of a volatile gas, such as hypochlorous acid (HOCl), which is removed by stripping is determined by Henry's constant H for that gas: H = X_G/X_L, where X_G is the mole fraction of the gas in the air and X_L is the mole fraction of the gas in the water. We have measured H for HOCl, OCl⁻, NH₃, NH₂Cl, NHCl₂ and NCl₃ at 20 and 40°C. We found H = 0.076 for HOCl, compared to 0.71 for NH₃, at 20°C. At 40°C, H was about 2.5-fold larger for HOCl. This means that 10–15% of the HOCl is stripped from cooling water on each passage through a typical cooling tower. The measured flashoff of free available chlorine (HOCl + OCl⁻) was markedly pH-sensitive with a pK of 7.5, exactly as expected if HOCl is volatile but OCl⁻ is not. The data permit a quantitative understanding of the fate of chlorine in cooling systems. The values of H at 40°C for NH₂Cl, NHCl₂ and NCl₃ were 1.28, 3.76 and 1067. This means that all of the chloramines are quickly stripped in a cooling tower.