Optical methods for studying the dynamics of heat and mass transfer in capillary-porous structures

The operation of power units at boiler-turbine parameters beyond standard supercritical levels necessitates highly intensive cooling systems. This study focuses on development and investigation of a boiling coolant system for advanced steam turbines operating under these extreme conditions. A capillary-porous cooling system, designed for the hollow section of nozzle blades and operating on a heat pipe principle enhanced with an additional mass potential, is presented. Experimental setups were developed to optically investigate the dynamics of vapor and liquid phase formation. The research employed holographic interferometry using an LG-38 helium-neon laser-based interferometer to study vapor generation. Process visualization was achieved through high-speed cinematography with an SKS-1M camera, supplemented by photography and filming using Zenit and RFK-5M still cameras, and Krasnogorsk and Kiev-16C movie cameras. The initial stage of vapor bubble nucleation and the subsequent dynamics of growth and collapse within the capillary-porous structure were examined. The ability to partition the total energy during bubble nucleation was identified as a critical factor for combating erosion and cavitation. The paper presents chronograms and holographic interferograms of heat transfer processes for various mesh structures, thermal loads, and liquid excess levels, including calculations of internal boiling characteristics and liquid droplet ejection. An emergency scenario was simulated by reducing the coolant flow to a minimum. The proposed cooling system is applicable to the design of new turbine configurations for ultrasupercritical operations. A key finding of interest is the relationship between the limiting state of the capillary-porous coating and the heat transfer crisis during regime shifts, which paves the way for developing real-time diagnostic systems for these structures.

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