Неисчерпаемые проблемы теплообмена

Abstract

The article considers the heat transfer problems studied by the researchers of the MPEI Department of Engineering Thermal Physics (DETP) during the last five years. Modes involving low-frequency temperature pulsations have been revealed during heat transfer with liquid metals under the conditions of turbulence being suppressed by magnetic field; these pulsations, which are caused by thermo-gravity convection, present potential danger for the liquid metal cooling systems used in nuclear power engineering and in nuclear fusion installations. The facilities available at the joint laboratory of the Joint Institute for High Temperatures (JIHT) of the Russian Academy of Sciences and the Moscow Power Engineering Institute, which was established on the JIHT territory, have opened the possibilities for studying magnetic hydrodynamics and heat transfer for combinations of parameters close to the conditions under which real liquid metal-cooled systems operate. Numerical investigations of heat transfer, including direct numerical simulation (DNS) of single-phase turbulent flows or processes in heterogeneous systems, are used as an efficient tool for studying the mechanisms governing the relevant phenomena. Along with this, they open the possibility to solve applied problems, also within the framework of commercial agreements. Numerical techniques were used to optimize the metal hydride-based hydrogen cleaning and compressing systems and to study the fluid dynamics and heat transfer in air-cooled condensers. The processes taking place in the experimental section of an air-cooled condenser were for the first time simulated in the conjugated statement with taking into account the performance characteristics of gas removal devices. Solution of the natural convection problem in large-scale closed volumes at high Rayleigh numbers is an example of successful combined application of approximate analytical and numerical analysis methods. Hydrodynamics and heat transfer in two-phase media are widely studied at the Department. A few series of experiments on condensation of ethanol and water vapor mixtures with the mass fraction of alcohol ranging 0.8 to 16% on the surface of horizontal and vertical tubes have been conducted. It has been shown that the heat transfer intensity for such mixtures can increase by more than a factor of 4 as compared with condensation of pure steam. The specific features pertinent to boiling in microchannels on a smooth surface and on a surface microstructured by depositing nanoparticles have been studied. For annular two-phase flows, droplet entrainment and deposition models have been developed, and equations for predicting the distribution of droplets between the liquid film and flow core have been proposed. Comprehensive investigations of film boiling for subcooled liquid have been carried out. A unique array of experimental data on the cooling conditions of high-temperature spheres made of three different metals in four different liquids at pressures ranging from 0.1 to 1.0 MPa in a wide range of subcooling values has been created. A hypothesis about the conditions under which an intensive heat transfer mode may appear during film boiling of subcooled liquid, in which the heat transfer intensity is 20 to 30 times higher than it is during saturated film boiling. Experimental and theoretical investigations of sonoluminescence and hydroluminescence accompanying cavitation in liquids are conducted. Work is underway on developing methods for simulating macroscopically permeable phase interface boundaries in numerically solving heat and mass transfer problems under the conditions of phase transformations.