冷却塔塔筒温度效应特征和计算公式

Features and formula for thermal effects on hyperbolic cooling towers

为深入理解温度效应对冷却塔塔筒的作用机理,以某大型冷却塔为例,在温度荷载介绍和温度效应计算的基础上,对温度作用下的内力和变形进行了系统分析.研究发现:塔筒的内外温差可以分解为系统温度作用和对称温度梯度作用,结构在前者作用下可发生自由变形,故一般无内力效应,而后者仅产生弯矩作用而无轴力和变形.有限元计算中,2014版《工业循环水冷却设计规范》的夏温分布模式会在向阳面与背阴面的分界线附近存在较为显著的子午向轴力和平面内剪力,而这在2003版规范的夏温效应中是没有的.同时,根据冷却塔结构特点以及温度对壳体结构的作用机理,提出了塔筒温度作用下的弯矩计算公式.这不仅提供了无需有限元计算即可准确获得温度效应的方法,也从理论上解释了弯矩环向分布特征.

The study was initiated for further understanding of the mechanism of thermal effects on hyperbolic cooling towers(HCTs).A comprehensive study on a representative HCT was presented about the internal forces and deformation under thermal effects,following the systematic introduction on the thermal actions and thermal effects calculations.It was found that the specified temperature gradient across the tower shell could be regarded as the combination of global temperature variation and symmetrical temperature gradient.The tower shell could deform freely under the former global temperature variation and usually there are no internal forces in the shell.On the contrary,the latter symmetrical temperature gradient gives birth to only moments in the shell but no axial forces or deformation.In finite element calculation,the specified temperature gradient for summer condition would bring remarkable meridian axial force and in-plane shear force around the boundary of sunshine and shadow according to the Code for Design of Cooling for Industrial Recirculating Water of edition 2014,which are nonexistent according to the code in its edition 2003.Moreover,a simple and practical formula was proposed for the moment calculation in tower shell,based on the structural behavior and mechanism of thermal effects on shell structures.The formula not only provides a new method to get the accurate moment in tower shell under thermal action besides FEM calculation,but also explains the consistency between the latitude distributions of temperature gradient and moment.