Abstract
For carrying out the high-technological processes in heat power installations the fragile capillary-porous coatings up to a limiting condition of heat exchange surface were researched. The coatings made of metallic materials (copper and stainless steel) and of natural mineral media (quartz, granite and teschenit) were studied. A model of the nucleation of steam bubbles in the cells of the porous coatings was developed during vaporization of coolant from their explosive emergence, taking into account the development of the “dry” spots before the damage; also the dynamic angle was defined in the range of (74÷80) degrees. The limiting state of the medium according to the model of the bubbles is studied when solving the problem of thermal elasticity. During the destruction of the coating caused by only a compression a number of curves corresponding to a definite thickness of the coming-off coating particle were obtained. Intervals of the specific heat fluxes coming to steam bubbles are established. In these intervals there is a destruction of a porous coating and metal surfaces at the joint action of capillary and gravity potentials.
Highlights
IntroductionCarrying out high-heat-stressed processes is bound to emergence of the limiting state (before the damage) of the heated surface
Carrying out high-heat-stressed processes is bound to emergence of the limiting state of the heated surface
To determine the limit state of two-phase medium according to the model (Fig.1) it is considered the solution of thermal elasticity problem for natural capillary-porous structure material type and the steam-generating metallic surface
Summary
Carrying out high-heat-stressed processes is bound to emergence of the limiting state (before the damage) of the heated surface. Based on the above it is of interest to study the capillary-porous structure, produced of natural materials. Such surfaces are being used in large-scale production of power installations (labyrinth seals, gas turbine blades) [4,7,9]. Increasing the temperature of the coating for a very short period of time the resulting in a strong dynamic effect These effects become very significant and the compressive stresses reach their high values, often in several times higher than the compression strength of the material. It is necessary to consider these stresses when studying the mechanism of thermal damage of porous coatings. It is necessary to establish the type of stresses more quickly reaching their limits for the supplied heat fluxes
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