Influence of a Variable in Time Heat Transfer Coefficient on Stresses in Model of Power Plant Components

Abstract

The paper discusses the issue of the modelling of strains and stresses resulting from heating and cooling processes of components in power plants. The main purpose of the work is to determine the mechanical behavior of power plant components operating under mechanical and thermal loading. The finite element method (FEM) has been used to evaluate the temperature and stresses changes in components as a function of time. Temperature fields in the components of power plants are dependent, among parameters, on variable heat-transfer conditions between components and the fluid medium, that may change its condition, flowing inside them. For this reason, an evaluation of the temperature field and the consequent stress fields requires the use of heat-transfer coefficients as time-dependent variables and techniques for determining appropriate values for these coefficients should be used. The methodology that combines computer modelling of the temperature fields with its measurements performed at selected points of the pipelines may be used in this case. The graphs of stress changes as a function of time have been determined for the chosen plant components. The influence of the heat transfer conditions on the temperature fields and mechanical behavior of components in question have been discussed.

Modelowanie wpływu parametrów eksploatacyjnych na stan naprężenia rur grubościennych w kotłach o parametrach nadkrytycznych

“…W rzeczywistych warunkach podczas uruchamiania bloku występują chwilowe gwałtowne zmiany temperatury uwarunkowane procedurą włączania poszczegól-nych elementów instalacji, związane z działaniem systemu sterowania. Pojawiają się wówczas oscylacje temperatury pary [1][2][3][4][5]. Szybkość zmian temperatury pary w krótkich przedziałach czasu może osiągać znaczne wartości.…”

“…W dalszej kolejności należy wziąć pod uwagę eksperymentalnie wyznaczone właści-wości zmęczeniowe rozpatrywanego materiału, a w szczególności wpływ temperatury na przebieg cyklicznych procesów odkształcania i trwałość w warunkach zmęczenia cieplno-mechanicznego [7][8][9][10][11]. Należy również rozpatrzeć wpływ zmienności współczynnika przejmowania ciepła w zależności od parametrów pary i czasu na rozkłady temperatury w rozpatrywanych elementach [4,5]. Zagadnienia te będą przedmiotem kolejnych analiz.…”

Impact of Heat Transfer on Transient Stress Fields in Power Plant Boiler Components

“…In the technical literature on the fatigue of the materials of power equipment components, one can find studies on the analysis of temperature fields and thermal stresses caused by changes in the operating parameters of these devices [5][6][7][8][9][10][11][12][13]. There are considered examples of elements for which data on time-varying mechanical and thermal loads were available.…”

“…The heat transfer coefficient on the surface of the considered elements was determined on the basis of variable parameters of the medium flowing through them, including temperature and flow rate, using computer programs, including computational fluid dynamics (CFD) methods [7][8][9][10]. Earlier works by the authors also used methods of matching the heat transfer coefficient to the results of local temperature measurements in order to obtain consistency of the calculated temperature distributions and the measurement results [11,12]. However, there are no extensive studies devoted to the verification of the obtained calculation results on the basis of the results of tests in industrial conditions.…”

Heat Transfer in the Components of Power Boilers and Related Technological and Endurance Problems

“…These studies include analyses of the operating conditions of individual components of energy equipment, the determination of the fatigue characteristics of materials used for operations at elevated temperatures, and analyses of temperature fields and stresses caused by time-varying loads [4][5][6]. These complementary issues are components of the methodology for assessing the durability of equipment elements, in which the variable temperature field is the cause of time-varying thermal stresses.…”