• DETERMINATION OF GEYSER EVENTS IN A THERMOSYPHON WORKING WITH GRAPHENE OXIDE NANOFLUID

    Machines. Technologies. Materials., Vol. 13 (2019), Issue 2, pg(s) 74-77

    Two-phase closed thermosyphons are efficient passive devices with potential for using in many heat transfer applications. One of the boiling regimes that may occur is the geyser boiling. It is a repetitive irregular process of pushing liquid without its previous evaporation in the direction of condenser. Although it does not affect time-averaged thermal performance of the device, it causes additional mechanical load and shortens the life-time of the device. Unfortunately, geysering is not well investigated, thus no precise definition exists. This paper focuses on the process of data reduction that leads to geyser boiling detection. It may be applied for various working fluids and operating conditions. Two parameters are crucial for recognizing geyser events from the background noise (pressure variations followed by the geyser): the minimum amplitude of pressure increase and waiting period between ensuing events. We compared two working fluids: water and graphene oxide nanofluid. In general, with increase of heat flux the frequency of geysers increases and their amplitude decreases.

  • INFLUENCE OF CARBON NANOTUBES AND GRAPHENE ON THERMAL AND ELECTROMAGNETIC PROPERTIES OF PLA NANOCOMPOSITES

    Machines. Technologies. Materials., Vol. 12 (2018), Issue 12, pg(s) 510-513

    This work investigate electromagnetic and thermal properties of poly(lactic) acid-based composites with graphene nanoplates (GNP) and multiwalled carbon nanotubes (MWCNTs), produced by solution blending method. It was found that the MWCNT carbon nanotubes are an effective filler for both absorption and reflection of electromagnetic waves in the GHz and THz frequency domains. The higher aspect ratio of carbon nanotubes, compared to industrial MWCNT, is the cause of better electromagnetic characteristics of nanocomposites prepared by solution blending method (SB). The DSC analysis of the samples shows that the glass transition is around 60oC, followed by cold crystallization with enthalpy and melting temperature around 150oC. The TGA analysis show, that the thermal stability of PLA polymer is improved by addition of 6% MWCNTs and GNP.

  • INVESTIGATION OF RHEOLOGICAL AND SURFACE PROPERTIES OF POLY(LACTIC)ACID POLYMER / CARBON NANOFILLER NANOCOMPOSITES AND THEIR FUTURE APPLICATIONS

    Industry 4.0, Vol. 4 (2019), Issue 1, pg(s) 19-23

    The recent subject of great research challenge and one of the most active area of research for well in materials science include the development of nanofiller reinforced polymer materials for additive manufacturing application. The dispersion of nanofiller in polymer matrix is a critical issue not only for control of processing but also for pre-defined properties. Quantitative analysis of extent of dispersion of nanofiller by measuring the rheological and surface characteristics of polymer nanocomposites has great technical importance for improving processing conditions, as well as for understanding the fundamental characteristics of materials at the nanoscale. The incorporation of nanofiller graphene into polymers is a promising approach to impart certain electrical and magnetic properties, mechanical reinforcement and high thermal conductivity to the resulting material. Rheological and surface properties of the poly(lactic) acid (PLA) based nanocomposites incorporating 0-9 wt.%. graphene nanoplates (GNPs) were investigated in the present work and a new strategy to tune such properties of PLA matrix by varying filler content is proposed.

  • MATHEMATICAL MODELLING OF TECHNOLOGICAL PROCESSES AND SYSTEMS

    A VARIATIONAL SOLUTION OF THE SCHRÖDINGER EQUATIONS IN AN INHOMOGENEOUS СOULOMB FIELD

    Mathematical Modeling, Vol. 1 (2017), Issue 3, pg(s) 131-133

    The present work is devoted to computer modeling of the emission processes from the surface of graphene. The pivotal obstacle for emission is a model of the unperturbed emission surface. The hydrogen-like atom model is one of the useful approaches describing the states of the emission surface. In [1] this model was used considering ion screening in the Brandt model [2]. To calculate the ground state of the electron, we used the variational solution of the Schrodinger equation, based on the minimization of the potential energy of an electron in the field of a homogeneous ion. However, the field of the screened singly ionized carbon atom in the Brandt model is not homogeneous. Therefore, it was shown in [3] that it is possible to obtain a binding energy error of up to 40% when using only the external screening parameter without taking into account the inhomogeneity. In this paper, we consider the effect of the ion screening parameter in the Brandt model λ and the algorithm for determining it by minimizing the total energy of the electron interaction in s state in two parameters: the effective ion charge and the ion screening parameter. The obtained solution of the Schrödinger equation is used to calculate the ground state of a hydrogen-like carbon atom in a graphene lattice at zero temperature and is compared with the results of [2, 4].

  • TECHNOLOGIES

    GRAPHENE SUPPORTED CATALYST FOR ENHANCED BIOMASS HYDROLYSIS

    Machines. Technologies. Materials., Vol. 11 (2017), Issue 6, pg(s) 287-290

    The present work reports on a new silicotungstic acid catalyst supported on graphene (HSiW/G). The deposition was performed by sonochemical method proven as an effective technique for the synthesis of the supported catalysts. The catalyst (HSiW/G) was characterized using a variety of physico-chemical methods as TEM, HR SEM, DLS, FTIR and Raman spectroscopy. Homogeneous distribution of HSiW on the surface of graphene was demonstrated. Hydrolysis of biomass for the production of glucose was studied. The hydrolysis of glycogen was performed with a HSiW/G catalyst by hydrothermal treatment. The yield of glucose (65 wt%) obtained was about 8 times higher than that obtained with the same amount of bare HSiW. Stability of the HSiW/graphene even after 3 repeated uses was confirmed. The mechanism of enhancement of the catalytic activity was discussed in terms of a special interaction between the graphene support and HSiW and also the appearance of hydrophobic cavities on the surface of graphene.

  • GRAPHENE: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 3 (2017), Issue 1, pg(s) 6-9

    Graphene (GR), a single-atom-thick sheet of hexagonally arrayed sp2-bonded carbon atoms, is close to become the next disruptive technology, replacing some of the currently used materials and leading to new markets. The contribution will focus on the production, characteristics, and current and prospective applications of this new carbon nanomaterial. Combustion synthesis (CS) is proposed as a novel approach to produce GR-related nanomaterial.

  • GRAPHENE-BASED HYBRID NANOMATERIALS FOR ELECTROCHEMICAL BIOSENSORS

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 1 (2015), Issue 3, pg(s) 25-28

    Nanomaterials can be combined or modified with other materials allowing the development of a great variety of composite nanomaterials and nanohybrids with new structural and functional characteristics. This article aims to show the advantages of hybrid nanomaterials as transduction, amplification and labeling elements for the construction of electrochemical biosensing platforms. Special attention will be paid to the used of graphene-based hybrid nanomaterials for biosensing.