Reasons for Reduced Moisture Resistance of Sulfur-Extended Asphalt Concrete

The paper presents the results of a study of the mechanism for reducing the moisture resistance of sulfur-extended asphalt concrete. It is shown that a decrease in moisture resistance occurs due to the occurrence of chemical and physical processes. At the same time, it was found that during the manufacture of sulfur-bitumen composites, toxic gases H2S and SO2 are formed, which are capable of interacting with a mineral filler, as well as the interaction of sulfur with a mineral powder with the formation of sulfur-containing water-soluble salts, the extraction of which leads to a decrease in the moisture resistance of sulfur-bitumen materials. The change in the rate of leaching of these substances from the composite is due to the physical process caused by the crystallization of sulfur and the formation of a capillary structure, which significantly increases the rate of leaching of calcium and magnesium salts, which are products of dissolution or hydrolytic decomposition of water-soluble products of the interaction of sulfur, H2S and SO2 gases with calcium and magnesium carbonates. The intensity of chemical and physical processes intensifies with an increase in the amount of sulfur in sulfur-bitumen materials.

Skin microbiome dysbiosis in leprosy cases

<p>The human skin possesses a microenvironment conducive to the growth of the skin microbiome, which plays in many physiological functions in cutaneous immunity homeostasis and maturation. The microbiome composition depends on many variables, such as endogenous (host condition) or exogenous (environmental) factors and topographic location. Host-skin microbes’ interaction can be mutualism or pathogenicity. Dysbiosis or alteration in skin microbiota is associated with various dermatological diseases, including leprosy. Dysbiosis is driven by the alteration of the microbial communities themselves or due to the intrinsic features of the host. Leprosy is a chronic granulomatous disease caused by <em>Mycobacterium leprae</em> targeting the nerves and skin, leading to loss of sensation on the skin, with or without dermatologic lesions, and correlated with long term consequences, such as deformities or disability. Microvascular dysfunction and significant alterations in capillary structure due to invasion of <em>M. leprae</em> lead to altered hydration levels of the skin caused by disruption of blood flow; which changes the resident microbial community structure. The skin microbiome composition differences in leprosy patient’s skin lesions were observed; skin microbial diversity in the leprosy patients was lower than in healthy individuals. The diversity reduction was observed in freshly diagnosis leprosy patients, those at various stages of MDT, and post-MDT; indicated that both the interaction between skin microbial community and<strong> </strong><em>M. leprae</em> or the ongoing therapeutic regimen impacted the skin microbiome variation. </p><p> </p>

Research of the process of obtaining capillary-porous materials from metal powders for heat pipes

Heat pipes are designed to effective removing heat from heating elements and reducing the temperature of various devices. Heat pipes with capillary porous structures are designed to operate under conditions of unfavorable gravity forces. Their main advantages are their high heat transfer capacity, as well as the ability to retain the coolant in a capillary-porous structure under dynamic power loads. The purpose of this work is to study the process of obtaining capillary-porous materials from metal powders for heat pipes with increased efficiency of using the vibration molding method. The article substantiates the relevance of creating heat pipes from metal powders. The information about the influence of the contact angle, surface tension and capillary pressure on the heat transfer capacity of a heat pipe is provided. It is shown that for the efficient operation of the heat pipe it is necessary to create such a capillary structure of the porous material, which could simultaneously provide a high speed of movement of the coolant and its rise to a given height. The above requirements can be satisfied by creating a capillary structure using powder metallurgy methods by optimizing the distribution of pore sizes. In this case, the most promising method seems to be the method of molding when applying a vibration to a mold with a powder. It is possible to obtain the required pore distribution in this way by choosing the correct particle size, shape and vibration parameters. This makes it possible to ensure the packing of particles in size, which affects their packing density, pore size, tortuosity and length of pore channels. The distribution of the maximum pore sizes over the thickness of the samples obtained from powders of various granulometric composition with the use of vibration has been investigated. As a result, a process was developed for obtaining capillary structures by the method of vibration molding of metal powders, depending on the size of the powder particles, the amplitude and frequency of vibration. It is shown that this method can provide a given pore distribution of the capillary structure for heat pipes, which makes it possible to increase their heat transfer capacity.

Heat transfer intensity at water boiling on the surface of a capillary structure under sub-atmospheric pressure

This paper considers the effect of structural parameters and saturation pressure on the intensity of heat transfer from boiling on porous structures made of copper metal fibers. The study involved changing the structural and geometric characteristics of porous samples and saturation pressure. The study regime parameters were chosen based on the conditions of operation of steam chambers, namely the horizontal orientation of the work area, the capillary transport of the heat carrier to the work area. It was determined that reducing saturation pressure from 0.1 MPa to 0.012 MPa leads to a reduction in heat transfer by 15‒20 % depending on the parameters of porous structures. This pattern has been explained in this paper by the increased detachable diameters of steam bubbles that thus overlap part of the capillary structure's vaporization area, which leads to a decrease in the values of the discharged heat flux at the same temperature gradient values. The influence of values of the porosity and diameters of fibers, which the samples of a capillary structure were made from, was ambiguous. The parameter chosen for generalizing the data obtained was an effective diameter of the samples' pores, which is a more general characteristic. The generalization of the experimental data has demonstrated that the efficiency of heat transfer increases with an increase in the effective diameter of pores in the examined range from 20 to 90 µm. Estimation dependences have been built to determine the intensity of heat transfer under sub-atmospheric pressures for metal-fibrous porous structures at a deviation of up to ±30 %. It turned out that the resulting dependences could be used to determine the intensity of heat transfer by the examined powder structures under the sub-atmospheric pressure conditions. Applying these dependences would make it easier to design thermal stabilization systems based on steam chambers.

Design solutions for gravity-independent heat pipes

Heat pipes with mesh wicks were designed (working liquid – water, envelope – copper tube). Wicks from the mesh of various weaves (plain, twill, leno and looped) with improved hydrophilic properties and secondary capillary structure were developed. Heat pipes are gravity-independent, adapted to work in various conditions of orientation and localization, and provide the transfer of high heat flux powers (up to 25 W/cm2 ). The peculiar properties of the developed heat pipes in contrast to the traditional heat pipes (with powder wicks) are: high performance characteristics, resistance to deep freezing; vibrostability.

Experimental research of capillary structure technologies for heat pipes

This paper presents an experimental study on three different capillary structure technologies of heat pipes for application in the thermal management of electronic packaging. The first capillary structure is that of axial grooves manufactured by wire electrical discharge machining (wire-EDM). The sintering process with copper powder produced the second heat pipe. Finally, a hybrid heat pipe was made by the combination of the two previous methods. The heat pipes were produced using copper tubes with an outer diameter of 9.45 mm and a length of 200 mm, and were tested horizontally at increasing heat loads varying from 5 to 35 W. The working fluid used was distilled water. The experimental results showed that all capillary structures for heat pipes worked successfully, so the studied manufacturing methods are suitable. Nonetheless, the hybrid heat pipe is the best, due to the lowest thermal resistance presented.

Investigating permeability of metal felt capillary structures of heat pipes for cooling electronics

The paper presents the experimental results on the permeability of metal felt capillary-porous structures with a fiber diameter of 10—50 μm at porosity values from 57% to 90% when the fluid filtration occurs along the felt plane. It is determined that the permeability depends on the geometric parameters of the capillary structure (fiber diameter), porosity and direction of fluid filtration. In previous permeability studies, no attention was paid to the direction of fluid movement in the capillary structure. It was believed that the metal felt structure is isotropic and the permeability was studied for cross-fiber filtration. In reality, unlike regular capillary structures (powder), metal felt structures are anisotropic and their characteristics depend on the direction of fluid filtration. In heat pipes, the capillary structure fibers are mostly positioned parallel to the axis of the pipe, and thus the fluid moves from the condensation zone to the evaporation zone along the fibers. It was shown that at a porosity of 55—70%, the value of permeability does not depend on the direction of filtration. In the porosity range from 70% to 90%, error can exceed 50%. In this porosity range, the permeability value at cross-fiber filtration significantly exceeds the permeability value at longitudinal filtration. This proves that the calculation relations for determining the permeability coefficients of metal felt capillary-porous structures obtained for cross-fiber filtration cannot be used to calculate heat pipes. Analyzing the results and processing the obtained experimental data allowed proposing an empirical dependence that generalizes the data with an error of up to 20% in the whole range of the studied porosity values. The research results can be used to design heat pipes with maximum heat transfer characteristics for cooling electronics.

Development of Thinned Aluminum Flat Heat Pipe Through Inclined Wall and Press Process

Heat pipes, commonly used for heat dissipation and thermal management in small electronic and communication devices, are regarded as an excellent solution. Heat pipes must be in surface rather than line contact to be applied to the module and system-level heat dissipation package. As such, a round copper heat pipe is transformed into a plate-like shape through a secondary press process. In this study, an extrusion structure is designed to be sloped to solve the difficulty of making it relatively thin compared with the large area of the plate structure. Specifically, substantial partitions separating the working fluid flow space in the plate-type heat pipe are designed to be inclined at 45 deg, and the extruded envelope is developed to obtain the desired total thickness through the secondary press process. The capillary structure is inserted and positioned within the envelope prior to the secondary press process. In this study, an aluminum flat heat pipe (AFHP) with 0.95 mm total thickness, 150 mm total length, and a capillary structure with braided or carbon wire bundles added thereto was designed and manufactured. Performance test results indicated that the heat transfer performance of the AFHP with inclined wall did not show any deterioration characteristic compared with the AFHP with a normal vertical wall. The isothermal characteristics and heat transfer rate of the AFHP with Cu braid wick were superior to those of AFHP with a simple rectangular groove wick. By contrast, when the carbon wire bundle is added in the Cu braid, the isothermal characteristic was enhanced twice, and the heat transfer rate was 15.5 W by improving approximately 42% under the conditions that inclination angle is −90 deg and the evaporator temperature does not exceed 110 °C.