Abstract
Modeling of the low heat conductive low-porous capillary porous coatings and metal (copper, stainless steel) surfaces (base layer) was studied. Heat and mass transfer in the porous coatings moved with excessive liquid due to the combined action of capillary and mass forces. The dynamics of vapor bubble was described along with their heat-dynamic properties, which were observed by the optic research methods. Finding solution for the thermoelasticity allowed to reveal the influence of the specific heat flow and heat tension of compression and stretching depending on time of supply and sizes of pulled particles at the time of the system limit state as to "porous coating - base layer". The theory was confirmed by the trial, which was observed by camcorder SKS-1М.
Highlights
Modeling of thermal stresses destroying the porous coating of heat-exchange surfaces of power plants
Тепловые потоки подсчитывались от времени взрывообразного появления первого зародыша (10-8 с) до времени разрушения материалов (102 - 103 с), т.е. от времени релаксации до времени, описывающего микропроцесс
Modeling of capillary porous coatings and analogy of the processes taking place in them allow to reveal the mechanism of heat transfer at vaporization of liquids, to establish the zones of fatigue cracks occurrence and development in the centers of steam embryo activation, to study natural and artificial porous coatings applied to metal fences up to the onset of the ultimate state of materials
Summary
Times for a developed surface than for a conventional surface with a specific heat flow up to 1×104. Α – linear expansion factor; Е – Young's modulus (elasticity modulus); ν – Poisson ratio (lateral contraction); If we are given the limit values of tension (σlim.tens.) and compression (σlim.comp.) stresses for coating and metal, we obtain the dependence of the heat flux (q) required for destruction, based on the time of supply (τ) and the depth of penetration (δ). It is spent to maintain the nucleating center with a radius of Rkr and prevents it from collapsing (q reaches up to 108 W/m2) At this time interval, a thermodynamic equilibrium is established for the transition from microprocesses (microparticles and clusters with sizes of (10-7÷10-8) m (nanoparticles) of separate (single) individual bubbles to processes described by the behavior of a large number of bubbles, using integrated characteristics (q, α, ΔT, ΔP, w), where α, ΔT, ΔP, w is average values of heat transfer coefficients, temperature and hydro-gas dynamic pressures and flow velocity.
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