FINITE ELEMENT ANALYSIS OF UNFASTENED COLD-FORMED STEEL CHANNEL SECTIONS WITH WEB HOLES UNDER END-TWO-FLANGE LOADING AT ELEVATED TEMPERATURES

This paper presents the results of a finite element investigation on cold-formed steel (CFS) channel sections with circular web holes under end-two-flange (ETF) loading condition and subjected to elevated temperatures. The stress strain curve for G250 CFS with 1.95 mm thickness at elevated temperatures was taken from Kankanamge and Mahendran and the temperatures were considered up to 700 oC. To analyse the effect of web hole size and bearing length on the strength of such sections at elevated temperatures, a parametric study involving a total of 288 FE models was performed. The parametric study results were then used to assess the applicability of the strength reduction factor equation presented by Uzzaman et al. for CFS channel-sections with web holes under ETF loading from ambient temperature to elevated temperatures. It is shown that the reduction factor equation is safe and reliable at elevated temperatures.

REACTIONS OF HYDROXIBENZOIC ACIDS WITH 2-AMIDINOPROPAN-2-PEROXYL IN ACID MEDIA

Методом хемилюминесценции определена реакционная способность гидроксибензойных кислот при взаимодействии с 2-амидинопропан-2-пероксильными радикалами, генерированными при термическом распаде азоинициатора 2,2ʹ-азобис(2-амидинопропан) дигидрохлорида в фосфатном буфере при рН=2. Установлена зависимость между антирадикальной активностью и молекулярными дескрипторами кислот, связанными с механизмом их антирадикального действия, в виде полуэмпирического линейного однофакторного уравнения. Полученная связь «дескриптор-активность» может быть основой для прогнозирования антирадикальных свойств фенолокислот и подобных им структур в водных средах. The reactivity of hydroxybenzoic acids in the reaction with 2-amidinopropane-2-peroxyl radicals generated by thermal decomposition of azoinitiator 2,2ʹ-azobis(2-amidinopropane)dihydrochloride in phosphate buffer at pH=2 was determined using chemiluminescence method. The relationship between the molecular acid descriptors, associated with the mechanism of their antiradical action, and antiradical activity in the form of a semi-empirical linear one-factor equation was established. The obtained «descriptor-activity» relationship can be used as a basis for predicting the antiradical properties of phenolic acids and similar structures in aqueous media.

The Quest for the Ideal Darcy-Weisbach Friction Factor Equation from the Perspective of a Building Services Engineer

The calculation of the friction factor involved in the Darcy-Weisbach equation has a key role in the accurate assessment of distributed head losses. For the turbulent flow regime, this friction factor was mathematically expressed in the form of the Colebrook-White (C-W) equation, widely accepted by engineers and scientists. Nevertheless, the C-W equation is an implicit one and must be solved using numerical methods. This is a major disadvantage for the average engineer, who always prefers an explicit equation which could be easily integrated into his familiar spreadsheet environment. The present paper is investigating some of the most used explicit alternatives to the C-W equation, with respect to several case scenarios taken from typical Building Services hydraulic calculations.

Friction factor calculation for turbulent flow in annulus with temperature effects

Purpose The purpose of this paper is to present a new friction factor equation for practical use, including fluid temperature, pipe diameter ratio and inner pipe rotation effects. Design/methodology/approach A friction factor relationship is developed by applying Buckingham’s Theorem of dimensional analysis. Then, the formula is calibrated using experimental data conducted at Izmir Katip Celebi University flow loop. Moreover, the effects of fluid temperature, inner pipe rotation and pipe diameter ratio on friction factor are investigated experimentally. Findings Satisfactory agreements are obtained between proposed formula and experiments. The experimental results indicate that major variable parameters affecting friction factor is Reynolds number. Pipe rotation has negligible effect on friction factor at high Reynolds number. Prandtl number is one of the important parameters affecting the friction factor. Moreover, as the pipe diameter ratio is decreased, friction factor increases. Originality/value Determining fluid behavior of fluids under high temperature is especially important for deep wells during drilling. Temperature drastically changes fluid properties and flow characteristics in wells. These changes have a remarkable effect on pressure losses. However, since the temperature is considered constant in the calculation of the pressure loss, problems can be encountered in most systems. Friction factor is one of the important parameters for determining pressure loss in closed conduits. The originality of this work is to propose a new friction factor equation for practical use, including fluid temperature, pipe diameter ratio and inner pipe rotation effects.