Skeletal heat conductivity of porous metal fiber materials

The influence of a number of physical characteristics and parameters of metallic fiber materials on their thermal conductivity is studied in this work. Such porous materials are intended, among other things, for their effective use in two-phase heat transfer devices (heat pipes). The use of heat pipes in aircraft and space vehicles provides a number of thermophysical advantages. In particular, heat pipes significantly expand the possibilities of air cooling of heat-loaded technical devices. The thermal conductivity of capillary-porous materials-structures, which are important elements of heat pipes, significantly affects the intensity of two-phase heat transfer inside heat pipes. Frame thermal conductivity is equivalent to the thermal conductivity of materials that are conditionally continuous medium. Studies of the influence of structural characteristics of porous materials, such as porosity and parameters (dimensions) of discrete particles-fibers (fractions of the studied materials), were performed using special experimental equipment created at the I.M. Frantsevich Institute for Problems of Materials Science of the National Academy of Sciences of Ukraine (Kyiv). Porous metal structures (coatings) made of copper, nickel, and steel fibers (MPM) were investigated under conditions similar to those for space heat pipes. The porosity values ​​of the prototypes of materials were in the range of 40 to 93%. The research results showed that the following physical characteristics of capillary structures, such as values ​​of thermal conductivity of metallic materials (fiber fractions), the porosity of capillary-porous metal materials (structures), significantly affect the value of thermal conductivity of porous materials. The dimensions of discrete particles-fibers also affect in a certain way the value of the MBM thermal conductivity but to a lesser degree. The results obtained in this work are summarized in the form of empirical dependencies – formulas, providing engineering calculations of the thermal conductivity values ​​of metal fiber materials. The research results are intended for practical application in aviation and spacecraft apparatus engineering. In particular, the presented results are necessary for the development and creation of effective heat pipes with metal fiber capillary structures.

The study of the destruction of heat-resistant chamotte concrete during its sharp heating and cooling

The article investigates the destruction of heat-resistant chamotte concrete of various classes: low-cement and medium-cement with the addition of quartz sand (to increase alkaline resistance) and with the addition of metal fiber (to reduce cracking) after exposure to thermal shock. Two methods for determining the heat resistance of concrete were used, in which the destruction of the material was evaluated using ultrasound using the method of a water-cooled plate and the method of one-sided heating-cooling. Studies conducted using the method of unilateral heating-cooling, revealed the formation of macrocracks in samples of low cement concrete. This method turned out to be more sensitive when evaluating concrete destruction.