Heat transfer in capillary-porous natural coatings

Relevance. Study of heat exchange processes in capillary-porous natural coatings created by thermal spraying of powders during their application with a thermal tool. Quartzite, granite, teshenite, tuff and marble rocks are chosen as natural materials. A thermal tool with spin detonation jet was created and the technology of powder production by a new method was developed.

Methods. The thermo-tool due to the automatic device allows controlling the mode of coating creation by changing the burner power and torch length. The displacement scheme of tool feeding and the methodology of experimentation were developed. Powders were prepared in special molds from the system of conjugate elliptical surfaces and different eccentricity. The technology increases the powder yield of (0÷2)×10^-3 m class and increases the degree of powder hardening. The combustor was afterburning on the coating with oxidizer excess coefficient 0.6 ÷ 0.8, specific loads increased up to six times and amounted to (2÷15)×10⁶ W/m². The ductile rocks were subjected to melting.

Results. The transverse velocity of the ignition section of the spin detonation plume was close to the detonation velocity and twice the speed of sound in the jet. The thermal stress limit region for the coatings while maintaining superheat of (20÷75) K was superior to boiling in thin films, large volume, and heat pipes. Studies by holographic interferometry showed that the point of reference is the residual deformation defined by a network of small cracks that do not disappear when the thermal load is removed.

Conclusion. A nonlinear particle displacement curve was found, and detonation spraying reduces powder particle fracture along the interfaces of unmelted particles. The natural material provides high erosion resistance of the coating. The joint methods of investigation by means of holography, highspeed filming and analytical solution allow to specify the mechanism of coating creation and to obtain calculated values of heat fluxes and stresses.

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