Paraffin Layer Research Articles

Hydrophobic surface patterning with soft, wax-infused micro-stamps

HypothesisWaxy hydrocarbons diffuse freely in polydimethylsiloxane (PDMS), and this capability can be leveraged to generate inexpensive surface micropatterns that modify adhesion and wetting. ExperimentsPatterns are created by placing a waxy Parafilm sheet on the back of a PDMS stamp containing microscale surface features. When heated, the paraffin liquefies and diffuses through the stamp, creating a thin liquid layer on the micropatterned stamp surface; when placed in contact with a target surface, the layer solidifies and is retained on the target when the stamp is removed. Micropatterns were generated on different materials and surface topographies; pattern geometry was evaluated using optical profilometry and changes in wetting were evaluated using contact angle goniometry. Diffusion of paraffin through PDMS was evaluated using XPS. FindingsWax micropatterns have submicron lateral resolution and thickness ranging from 85 to 380 nm depending on contact time. By using XPS analysis to track paraffin diffusion within the PDMS stamp during this process, we estimate the diffusion coefficient to be 5.3 × 10−7 cm2/s at 65 °C. This means that the paraffin layer at the stamp surface replenishes in less than a second after stamping, so it can be used multiple times without re-inking to deposit complex, multi-layer paraffin patterns.

The Effect of a Liquid Cover on the Thermal Performance of a Salinity Gradient Solar Pond: An Experimental Study

Salinity Gradient Solar Ponds (SGSPs) offer the potential to capture and store solar energy for use in a range of domestic and industrial activities in regions with high solar insolation. However, the evaporation of water from these ponds is a significant problem that must be overcome for them to be deployed successfully. Thus, two ponds were constructed in the city of Nasiriya, Iraq. The two ponds were cylindrical with a diameter of 1.4 m and a total depth of 1.4 m. The water body in the two ponds was constructed with layer depths of 0.5, 0.75 and 0.1 m for the lower convective zone (LCZ), non-convective zone (NCZ) and the upper convective zone (UCZ) respectively. One of the two ponds was covered with a thin liquid paraffin layer (0.5 cm) to eliminate evaporation from the surface of the UCZ. The behavior of the standard SGSP and that of the covered pond with evaporation suppressed can be straightforwardly compared. The experimental units were run for six months from 1st of February to 31st of July 2019. It was shown in the first instance that by covering the pond with a thin layer of paraffin, that evaporation could be suppressed. The results showed that for the conventional SGSP, the temperature of the LCZ reached a maximum of ca. 76°C while in the covered pond the temperature of the LCZ was consistently lower than that in the uncovered pond by approximately 5–6°C. The results also indicated that the temperature of the UCZ in the covered pond was higher than that in the uncovered pond by about 10°C in the second half of the study period. However, it was noted that on rainy days the paraffin layer was swept away from the surface; and this could hinder the implementation of thin liquid cover in the large SGSP.

Solution of a mathematical model for the concentration of a hexane solution of technical paraffin to obtain its food modification

For pectin-containing film structures, which are used for the production of biodegradable packaging materials and are hydrophilic in nature, their paraffinization, i.e., applying a thin layer of molten food paraffin to the surface of the film for subsequent protection of packaged food products from moisture and sunlight, will reduce the influence of external factors, primarily moisture, To rationalize the convective preconcentration of a hexane solution, it is necessary to select such regime parameters that will allow not only the removal of hexane with toxic components dissolved in it from the object of study in a relatively simple apparatus, but also significantly reduce the time for the process within temperature restrictions. The latter condition, in view of the complexity of the empirical determination of the temperature distribution in a thin layer of the object of concentration, is advisable to implement by solving the system of equations for the transfer of thermal energy and mass in partial derivatives, however, we can restrict ourselves to one equation for the transfer of thermal energy, using empirical kinetic dependences that describe the removal of n-hexane from the composition. The aim of the study was to adapt paraffin to a hexane solution and solve the model of heat and mass transfer during its concentration in order to exclude the possibility of reducing its temperature below the value of possible preliminary crystallization. The model was implemented numerically by the finite difference method. As a result of the solution, the intensity of the temperature front advancement along the height of the film of the hexanoparaffin composition was found with varying the proportion of paraffin in the process of its concentration with convective supply of thermal energy to it, i.e., it was adapted to the resulting solution and a mathematical model of heat and mass transfer was solved during its concentration to eliminate the likelihood of a decrease in its temperature below the value of possible pre-crystallization. The data obtained do not conflict with the known results of other researchers and can be successfully used for operational calculation and design of the designated processes and units.

Broadband microwave absorber composed of sandwich structure with a lossless medium as the intermediate layer

A broadband microwave absorber with a sandwich structure has been designed, creatively taking lossless medium (paraffin or air) as the intermediate layer. The paraffin layer effectively adjusted the impedance of the absorber, especially at the high-frequency region, hence observably raising the upper limit of the effective absorption region from 14.5 GHz to 18 GHz. As a result, the effective absorption bandwidth (EAB, reflection loss less than −10 dB) is broadened to 10.1 GHz, covering the entire Ku band and the entire X band, with a total thickness of only 2.5 mm, among which the paraffin intermediate layer has a thickness of 0.8 mm. Based on Maxwell's equations, normalized Poynting vector and loss analysis are given, which reveals the paraffin layer can enhance the total loss, though paraffin is lossless. In addition, the intermediate paraffin layer can also be replaced with air or even vacuum, providing a new perspective for the design of a high-performance absorber with lighter weight.

Measurement of Oil Consumption by Turbine Flow Meters in Conditions of Wax Deposition

Commercial metering of oil is performed at almost all stages of the life cycle, from well production control to the transfer of the produced oil to the end customer. In most cases, special systems for measuring the quantity and quality of commercial oil (SIQO) are used for this. If such a system implements an indirect dynamic measurement method, then a turbine flow meter is most often a means of measuring volumetric flow. Its accuracy depends on many external factors, including wax deposits on the inner surface of the measuring pipeline and on the elements of the flow meter itself. The article investigates the influence of the thickness of the paraffin layer on the error value of the turbine flow meter. It is shown that the decrease in metrological reliability occurs mainly due to the appearance of a paraffin layer in the measuring line itself. It is proposed to determine the timing of the metrological characteristics verification by indirect parameters, in particular, by the change in pressure in the measuring line.

Heat transfer during solidification of PCM layers with inclusion of nano-powders

For heating a room, air flow heat exchanger with involving wavy PCM layers were employed in current study. FVM was incorporated to model current unsteady process and RT30 was utilized as base PCM which is mixed with alumina nano-powders. Cold turbulent air flow enters the channel with temperature of 12 oC. Liquid paraffin converts to solid phase and heat release from the layers. So, warm air exits the domain. Amplitude of paraffin layers and fraction of alumina have been scrutinized in results. Validation with experimental paper illustrates nice agreement of current modeling. Air reaches the heat from paraffin layers and its temperature increases. Rise of time decline the outlet temperature. Augment of amplitude has various influences on outlet temperature at various time stages. The longest process belong to case with pure paraffin and a=5mm which it takes 5.33hr to finish the process. When a=20mm, φ=0.04, the best discharging rate can be obtained and process takes 3.19hr to reach full solidification. Dispersing nano-powders makes freezing time to decrease about 5.49% when a=20mm. Employing greatest amplitude cause required time to reduce about 35.82% when φ=0.04.

Parametric investigation of a nanofluid-NEPCM based spectral splitting photovoltaic/thermal system

Photovoltaic cells can convert incoming sunlight within their responsive wavelength range into electricity. Unfortunately, the majority of the incident radiation is reflected, absorbed directly as heat, or indirectly converted to heat due to internal losses (i.e., ≥ 52.9%, even world-record efficiency cells). In concentrated photovoltaic systems, this added heat can further degrade the electrical conversion efficiency of the cells if it is not removed, resulting from an elevated operating temperature. Spectral splitters and absorptive filters can remove the unused portion of the solar spectrum before it is converted to heat in the photovoltaic cells and harvest this energy for active use in thermal applications. In this paper, an innovative concentrated photovoltaic/thermal system that utilizes a layered design containing an optical fluid and a phase change material was investigated as a new alternative absorptive filter. Five possible configurations of this filter were compared from energy, exergy, and energy storage perspectives. These layers consist of a phase change material (dotriacontane, a paraffin) layer and fluid channel layers (a glycerol fluid) with suspended Ag and/or Au nanoparticles. The optical properties of the nanofluid and the nano-enhanced phase change material (NEPCM) were modeled using Mie and Rayleigh scattering theories. The comparison showed that the configuration containing the nanofluid channel at the top of the nano-enhanced phase change material performs well in all aspects of energy, exergy, and energy storage. A parametric study was conducted to determine the effects of nanoparticles volume fraction, concentration ratio, mass flow rate, nanofluid thickness and phase change material thickness on PV/T system performance with this filter configuration. It was found that volume fractions lower than 0.3 × 10−5 and 0.2 × 10−5 for Ag and Au, respectively, provided the best system performance for the assumed geometric and operational conditions. At an optimal mass flow of 0.005 kg s−1 for the nanofluid, this design achieved a maximum exergetic efficiency of 24% for a concentration ratio of 30. The results also revealed that the nanofluid-NEPCM filter is not suitable for concentration ratios of less than 10. Overall, this study finds that nanofluid-NEPCM-based spectral splitter, in addition to successfully filtering radiation, can store energy efficiently.

Numerical Investigation on the Thermal Control of Lithium Batteries for Electric Cars Using Metal Foams and Phase Change Materials

Electric cars, in addition to representing an ecological solution for the serious problems of climate pollution due to the use of fossil fuels, can also represent a turning point in terms of renewal for the world economy with a product that in a short future will become a standard in all the advanced economies of the globe. One of the main problems of electric cars is given by the thermal control of their batteries, since, below and above a certain temperature range and also with the use of the air conditioning, they abruptly decrease the autonomy of the vehicle, creating inconvenience to the owners of such cars. The thermal control of lithium batteries for electric cars must therefore take into account both the problems of thermal increase due to the functioning of the battery itself, and the climatic conditions outside the vehicle which impact, if above a certain range, negatively on the performance of the automobile, decreasing both the autonomy and the battery life. In this study, an attempt is made to control both thermal aspects by trying to thermally isolate the battery from the vehicle’s external climate and by trying to control the temperature peaks due to the operation of the battery itself. For this purpose, in this study a two-dimensional model is considered to investigate numerically the thermal control of a lithium battery of a commercial electric car. The battery has the size of 8 cm x 31 cm x 67 cm and its capacity is equal to 232 Ah with 5.3 kWh. The thermal control is realized by means one internal layer of copper foam and paraffin, placed around the battery, and a more external paraffin layer. The external surfaces are cooled by an air flow. The governing equations are solved by finite volume method using the commercial code Ansys-Fluent. Different cases are simulated for different thickness of the two layers and air flow velocity. The results, carried out for metal foam with different PPIs and porosities, are given in terms of temperature and liquid fraction fields, heat transfer behaviors such as surface temperature profiles as a function of time and temperature distributions along the external surface of battery for the different cases.

Interfacial thermal conductance between multi-layer graphene sheets and solid/liquid octadecane: A molecular dynamics study

Mixtures of paraffin and carbon nanofillers have promising potential for thermal storage, as paraffin (the matrix) possesses high latent heat and the nanofillers compensate for the low thermal conductivity (TC) of paraffin. Understanding thermal transport in these materials is essential for practical applications, as weak thermal transport hinders fast charge/discharge of thermal energy. Here, we use non-equilibrium molecular dynamics (NEMD) simulations to study the interfacial thermal conductance (ITC) between graphene sheets and octadecane (C18H38) matrix under the limiting conditions of the sheets being parallel or perpendicular to the direction of the imposed heat flux. The results show that the systems containing thin graphene layers exhibit higher values of ITC. This study captures the asymptotic saturation of thermal conductance for the liquid phase of the perpendicular structure. Besides, given the greater number of structured layers of paraffin upon phase change, the ITC for the solid paraffin-graphene system is higher than the conductance of the liquid paraffin-graphene interface. We use the Pearson correlation coefficients of the vibrational power spectrum (VPS) of interfacing materials to explain the orders of magnitude variations of the observed ITC.

Influence of Temperature on Wax Deposit on Corrosion of Crude Oil Pipeline

The paper aims to study the effect of temperature on wax deposition on corrosion of crude oil pipeline at different flow rate with time. The waxy crude oil sample is pumped into the design and fabricated experimental flow-loop set up under different operating conditions. The effect of temperature on corrosion at different flow rate of wax deposition during the corrosion inhibition were studied at flow rate of 10.21, 20.37, 30.45, 40.28 and 50.70 L/min and time at 3, 6, 9, 12, 15 and 18 min while keeping temperature constant for each of the experimental run at 15, 20, 25, 30 and 35°C, to determine the corrosion rate against time. The results showed that at flow rate of 10.21 L/min and time 18 min at constant temperature of 15°C, the corrosion rate is 0.11 mpy. At flow rate of 10.21 L/min and time 18 min at constant temperature of 20°C, the corrosion rate is 0.08 mpy. At flow rate of 10.21 L/min and time 18 min at constant temperature of 25°C, the, corrosion rate is 0.12 mpy. Based on the results, a significant reduction of corrosion rates and excellent corrosion protection is achieved while others provided only moderate or negligible protection to the crude oil pipeline. However, the wax layer becomes thicker with time, if the temperature stays below the WAT for extended period of time and can in the long run, cause partial or total blockage of the pipe. Hence, as the deposition of the paraffin wax increases the corrosion rate decrease. The paraffin wax film presence on the surface promotes a significant reduction of general corrosion rates on the pipeline, although localized corrosion was observed due to loss of integrity of the paraffin layer. It means that deposition of paraffin wax inhibit corrosion and also give protection to the pipeline layer. Finally, due to the long chain paraffin layer being physically removed from the surface most of the corrosion protection has been lost during the periods of increased flow rate or temperature.

СТРУКТУРА КАНАЛА ПЛЮМА, ФОРМИРУЮЩЕГОСЯ В ПЛОСКОМ СЛОЕ (МОДЕЛИРОВАНИЕ ПЛЮМА В ЗОНЕ СУБДУКЦИИ)

Experimental studies of a plume forming in a flat paraffin layer above a local heat source are presented. The experiments were performed on an installation with a transparent front wall. The flat payer is inclined two degrees with respect to the gravity vector. The thermal power transferred from the plume conduit under conditions of stationary thermal conduction is determined. The structure of the plume conduit and the structure of free-convective flows are determined for different plume thermal power values. Free-convection flows along the conduit height are cellular ones. The cellular structure occurs due to unstable stratification along the height of the plume conduit. The ascending flow in the plume conduit is a localized jet stream; the descending flow exists along the perimeter of the conduit. The cell boundaries correspond to narrowings of the plume conduit, formed due to cooling of the descending flow to a temperature close to the melting point. The cell parameters are determined for different values of relative thermal power (Ka criterion).The free-convection flow structure in the cells of the plume conduit is elucidated. The modes of reaching the surface for plumes forming in a flat layer are determined in relation to Ka criterion. When the relative power Ka exceeds 1.14, the model plume reaches the surface with the formation of a mushroom-shaped head. This case may correspond to plumes responsible for the formation of batholiths in the Andean subduction zone. Experiments have shown that the structure of the plume conduit in a flat layer corresponds to the plume structure formed in a solid massif above a local heat source. Distinctions in the thermal and hydrodynamic structure for a flat layer are observed due to the solid surfaces bounding the layer.

Modulating electromagnetic interference shielding performance of ultra-lightweight composite foams through shape memory function

High-performance electromagnetic interference shielding (EMI) materials are desirable in aerospace, military and mobile electronics applications. However, fabrication of smart and ultra-lightweight EMI shielding materials with adjustable EMI shielding performance through an energy-efficient and environmental-friendly process is still challenging. Herein, we demonstrate using a conductive biomass-derived d-glucaric acid-chitosan/single-walled carbon nanotube (SWNT/GA-chitosan) polymer composite layer and a crystallized paraffin layer to fabricate ultra-lightweight polyurethane foams with shape memory and adjustable EMI shielding functions, of which the shape change via external stimulus enables the foams to adjust EMI shielding efficiency autonomously. The foam coated with synthesized conductive composite layers shows an exceptional EMI shielding effectiveness of 56 dB at an ultra-low density of 0.03 g/cm3 with only 0.171 vol% SWNT. The foam also exhibits ultra-high durability over 2000 compression-recovery cycles. Furthermore, introduction of paraffin layer as a reversible network results in shape memory foams with high fixity ratio >95% and recovery ratio >90%. These foams exhibit a wide range of adjustable EMI shielding efficiency from 18 dB to 30 dB by controlling their macroscopic shape from compression. Such smart foams with shape memory and adjustable EMI shielding functions fabricated by an environmental-friendly strategy represent a promising material candidate for the wide applications of EMI shielding.

Investigate on structure for transparent anti-icing surfaces

The ice-phobic and transparent surface based on the distinctive structure of a coating material has been investigated. Moth eye structure fabricated on the quartz substrate was covered with a flat paraffin layer to isolate it in a cold and humid environment. Paraffin wax was chosen as the coating material due to low thermal conductivity, easy coating, and original water repellency. The paraffin layer only stayed on the top of the nanostructure, separated it from the outside environment to obstruct heat energy being transferred to the cold substrate, and prevented the wetting transition, which was observed regularly on the rough surface. The uncountable number of air blocks trapped inside the nanostructure also contributed to delayed heat transfer, leading to an increase in the freezing time of the attached water droplet. The anti-icing performance was evaluated in terms of adhesion strength, freezing time, and freezing rain sustainability. The nanostructure coated sample was compared with barely coated and superhydrophobic nanostructure surface and demonstrated a preeminent performance.

Moth-Eye Mimicking Solid Slippery Glass Surface with Icephobicity, Transparency, and Self-Healing

Slippery liquid-infused porous surfaces (SLIPSs) have been actively studied to improve the limitations of superhydrophobic (SHP) surfaces, especially the defects of the nonwetting chemical coating layer and the weak mechanical robustness of surface micro/nanostructures. However, the SLIPSs also have several drawbacks including volatilization and leakage of lubricant caused by long-term usage. In this study, we suggest the use of icephobic, highly transparent, and self-healing solid slippery surface to overcome the limitations of both surfaces (SLIPS and SHP) by combining specific biomimetic morphology and intrinsic properties of paraffin wax. A moth-eye mimicking nanopillar structure was prepared instead of a porous structure and was coated with solid paraffin wax for water repellence. Moth-eye structures enable high surface transparency based on antireflective effect, and the paraffin layer can recover from damage due to sunlight exposure. Furthermore, the paraffin coating on the nanopillars provides an air trap, resulting in a low heat transfer rate, increasing freezing time and reducing adhesion strength between the ice droplet and the surface. The heat transfer model was also calculated to elucidate the effects of the nanopillar height and paraffin layer thickness. The antireflection and freezing time of the surfaces are enhanced with increase in nanopillar height. The paraffin layer slightly deteriorates the transmittance but enhances the icephobicity. The solar cell efficiency using a biomimetic solid slippery surface is higher than that of bare glass due to the antireflective effect. This integrated biomimetic solid slippery surface is multifunctional due to its self-cleaning, anti-icing, antireflection, and self-healing properties and may replace SLIPS and SHP surfaces.

RESEARCH OF AMPLITUDE-FREQUENCY CHARACTERISTICS OF CLEANING AND DIAGNOSTIC DEVICES MOTION NOISES IN PIPELINES

Background The main criterion for the safe operation of pipelines during cleaning and in-line diagnostics is the non-stop movement of the device (projectile) from the launch chamber to the reception chamber. Stopping or jamming a projectile in the area between the launch and reception cameras is an emergency. Therefore, when passing shells through the pipeline, it is necessary to constantly monitor their movement and periodically record the passage time of the shell at the control points from the moment it is launched until it arrives at the final site, i.e. accompany throughout the pipeline. When projectiles of any design move in the pipeline, the cuffs and / or disks of the projectile rub against the inner wall, at which acoustic waves are generated. These waves propagate both along the wall of the pipeline, and along the pumped liquid in both directions. The acoustic method for controlling the movement of shells in the pipeline is one of the effective ways to control the movement and can provide the greatest detection range of the projectile. Aims and Objectives Investigation of the amplitude-frequency characteristics of the noise of the cleaning and diagnostic devices (shells) in pipelines with the aim of developing a technical device for monitoring their movement and recording travel time at control points. Results The largest amplitude of the noise of movement of the in-tube projectile is observed in the frequency range from 20-40 to 4000-5000 Hz, and the frequency varies from 5-10 to 8000-10000 Hz. The amplitude of the noise largely depends on the distance between the moving projectile and the installation location of the acoustic sensor. When the projectile passes through the transverse welds of the pipeline, a short-term surge in the amplitude of the noise of the projectile movement occurs. The noise amplitude is inversely related to the thickness of the paraffin layer in the oil pipeline and the magnitude of its change from the thickness of the paraffin is insignificant. The influence of the material of the cuffs/disks of the projectile on the amplitude of the acoustic signal is also insignificant

Development of Solar Accumulating Drying Equipment Based on the Theoretical Studies of Solar Energy Accumulation

The process of heating a dewatered object in an infrared solar drying plant (with paraffin on the bottom) with solar energy storage is considered. To solve this problem, it is assumed that the heat capacity of paraffin exceeds the heat capacity of the dehydrated object. Infrared rays fall on the upper layer, and heat exchange takes place due to heat and mass transfer with the surface air located between the metal plate and the object to be dehydrated. The equations of thermal conductivity for a dewatered object are given, its relationship at the phase interface is determined using the equality of temperature and heat flow. For an exposure of overheating with a period of 6.5 h, the time of passage of the phase boundary in accordance with the law of motion of the spreading (hardening), was determined according to the formula of ξ = α √6,5 h ≅ 12 h.The optimal thickness of the accumulating paraffin layer was ascertained. On the basis of the theoretical studies, experiments were conducted to study the temperature field of various heataccumulating materials in the laboratory of Tashkent State Technical University. It was found that of all heat-accumulating materials, paraffin has the best heat retention ability when its thickness is of 2–4 cm. The optimal variant of a solar accumulator drying plant with a heat accumulator, viz. paraffin has been designed. In particular, 2–4 cm of paraffin layer with a mass of 50 kg with a corresponding flat surface in terms of specific heat of evaporation is 2400 kJ/kg. The specific melting value of paraffin (150 kJ/kg) allows additional evaporation of 5.8 l of moisture when drying objects. The proposed solar accumulator drying plant can be used for dehydration of medicinal herbs.

Ultralow-Voltage-Driven Smart Control of Diverse Drop's Anisotropic Sliding by in Situ Switching Joule Heat on Paraffin-Infused Microgrooved Slippery Surface.

Stimuli-responsive anisotropic slippery surfaces (ASSs) have demonstrated intriguing performance in manipulating the behaviors of some liquids. However, most present methods have been limited to conductive droplets, certain specific conductive platforms, and higher manipulation temperature that greatly hinder its practical applications. Here, an electric-responsive paraffin-infused ASS (ER-PIASS) composed of paraffin, microgrooved PDMS, and flexible embedded silver nanowire heater is reported. Owing to the fast electric-response of ER-PIASS, smart control between anisotropic sliding and pinning for diverse liquids can be realized by remotely loading and discharging electric-stimuli. The underlying mechanism is that the generated Joule heat melts the solidified paraffin to slide a pinning droplet once an electric-trigger is loaded due to the formation of a slippery air/liquid/liquid/solid system. Once the voltage is discharged, the liquefied paraffin would rapidly solidify to stick to a slipping droplet because of the recovery of a frictional air/liquid/solid system. Additionally, the effect of the groove's height (h), spacing between two adjacent grooves (d), and thickness of the paraffin layer on the anisotropic degree was quantitatively studied and an optimized value of 75° is thus harvested. Through tuning the recipe of the hybrid lubricant, the responsive voltage and temperature for ER-PIASS can be dramatically decreased to ultralow figures of 2.0 V and 34.2 °C. By taking advantage of this ultralow-voltage-driven biocompatible ER-PIASS, we enable the anisotropic smart control of cell culture medium and yeast droplets for their directional coalesce, growth, and fission. We believe that such stimuli-responsive surfaces will be promising candidates for manipulating droplets' directional sliding behavior and further bloom the studies of flexible microfluidics devices.

A numerical model to investigate non-gray photothermal characteristics of paraffin-containing glazed windows

Most of numerical methods developed for the photothermal transfer researches of the paraffin-containing glazed windows adopt the gray-body model, in which the spectrum properties of glass and paraffin are generally not taken into account, even though scholars are aware of the fact that glass and paraffin are spectrum selective. Therefore, in this work, a one-dimensional photothermal model that accounts phase dependent thermophysical properties and spectrum dependent optical properties was developed based on the finite difference method, which is utilized to study the heat transfer through the glazed units incorporating paraffin. The results of the established model including non-gray characteristics of glass and paraffin with different spectrum bands were compared with the experimental results in terms of transmittance and temperature. It was observed that 4-band spectrum can accurately simulate the heat transfer process. Then, the photothermal performance of the double-layer glazed windows was studied with the verified model for different melting temperatures of paraffin under summer conditions and paraffin layer thicknesses under both summer and winter conditions, and the transmitted energy from the window units for the considered parameters was quantified. The results showed that inappropriate selection of melting temperature or paraffin layer thickness may defeat the purpose of energy saving. For the studied climatic conditions, the photothermal performance of the paraffin-containing glazed window is better when the melting point of paraffin was 18–26 °C, and the recommended paraffin layer thicknesses is 6–12 mm considering the transmitted energy.

Experimental study of the effectiveness of water-air suspension to prevent an explosion

For many countries where mining facilities exist, the importance of the mining sector is steadily increasing. Also, the mining sector is central to the global economy. However, the environment is adversely affected by explosions of finely dispersed coal dust and methane-air mixture in the mine. Dust deposited on the surface of the mine workings is as dangerous as hovering dust. The use of a water suspension system is effective for reducing the concentration of coal dust because dispersion increases. To ensure technological and environmental safety during combustion, release, mixing and distribution of gas impurities in the atmosphere (including in multiply connected areas with complex terrain or in closed spaces), an adequate mathematical description of the processes of creating and maintaining multiphase dispersed structures is required. The creation of such a mathematical model is possible only using the system of unsteady Navier–Stokes equations for compressible gas. For the practical implementation of this mathematical model, experimental studies are needed, which will confirm the possibility to create a water suspension with the necessary dispersion, the area of irrigated surface and at the required distance by the atomizer. The maximum range (in the extreme drops) of the jet was measured from the projection of the atomizer barrel onto the test site using pre-installed beacons. The size of the water droplets was determined by sampling from a stream on small glass slides coated with a thin layer of paraffin. Glass slides were photographed under a microscope and the diameter of the drop was determined using software. It was established experimentally that spraying a liquid with a mass flow rate of 1.0 l/s through square cells measuring 150 μm ensures the formation of a stable water-air dispersed suspension at a distance of 10 m. This is the most effective range where a stable air-dispersed air curtain was formed. By numerical simulation, it was established that the presence of water droplets provides not only complete deposition of coal dust, but also an additional decrease in the overpressure and temperature of the high-temperature cloud of the combustion products of the methane-air mixture. This is due to the transition of the liquid phase to the vapor state. From the analysis of the simulation results it can be seen that the effectiveness of water curtains decreases when extinguishing explosions of only methane-air mixture (that is, without participation in the explosion of coal dust).

TYPES AND STATISTICAL DATA ANALYSIS OF SCRAPE CRYSTALLIZERS FAILURES IN OIL DEWAXER UNITS

The efficiency and performance of the oil dewaxing unit depends not only on the physicochemical properties of the raw materials, but also on the equipment’s performance. Maintaining equipment in working condition and preventing premature failures are basic principles in operating equip- ment. Since complex equipment is used for crystallization processes, increasing reliability is important for the oil refining industry. Considered scraper crystallizer is a pipe in pipe heat exchanger with internal scraper devices. The advantages of this equipment are the developed heat exchange surface, continuous operation mode, ease of regulation of the operating mode, the possibility of the process with minor supercooling of the separating mixture. Crystallizers are horizontal pipe-in-pipe heat exchangers. The inner tube is equipped with a rotating shaft with metal scrapers to remove the paraffin layer from the pipe walls. The solution of the dewaxed raw material is pumped through the internal tubes, and the refrigerant (ammonia, propane, ethane or cold filtrate) is countercurrent through the annular space. Practice shows that the repair of a scraper crystallizer of the «pipe in pipe» type is a complex process that requires substantial expenses, both for capital and for physical strength of workers. Repair schedule complicates equipment failures due to premature wear of components. The failure of one crystallizer reduces the installation load by 10-15 %, which in turn affects the final production of oils. This article describes the principle of operation and the types of failures to the components of the scraper crystallizer; analysis of the replacement of worn parts, failures of crystallizers, and examples of worn parts. As a result of analyzing the data of parts replacement during of scraper crystal- lizers repairs collected over many years of operation, it was concluded that the most susceptible to wear of the crystallizers’ parts are scrapers and tee bearings, the premature wear of which is in most cases are root causes of the equipment failure.