Intertube Spacing Research Articles

A numerical and experimental study of breakdown of falling film on horizontal circular tubes

Falling film horizontal tube heat exchangers are used in several industrial applications such as sea water desalination, multi effect distillation, chemical industries, ocean thermal energy conversion systems and refrigeration. Different flow patterns that occur during falling film evaporation on an array of horizontal tubes are droplet, droplet-columnar, columnar, columnar-sheet and sheet modes. From the heat transfer point of view, a sheet mode (continuous falling film spanning the intertube space) is the most desirable falling-film mode. Falling film breakdown leads to the occurrence of dry patches on tubes which cause heat transfer deterioration. In the present study, falling film breakdown on horizontal tubes under adiabatic condition has been investigated both numerically and experimentally. The study focuses on the influence of tube pitch to diameter ratio on the threshold film Reynolds number required to maintain continuous falling film. Results indicate that the threshold film Reynolds number increases with the increase in the pitch to diameter ratio for a given diameter of the tube. The study also shows that as the number of tubes in the column increases, the threshold film Reynolds number required to maintain continuous film over all the tubes increases. The study highlights the need for correlations for the column-sheet mode transition that take into account the effect of number of horizontal tubes in a vertical array.

ОЦЕНКА ЦЕЛЕСООБРАЗНОСТИ ИСПОЛЬЗОВАНИЯ ВОЗДУШНЫХ КОНДЕНСАТОРОВ С ДВИГАТЕЛЕМ СТИРЛИНГА В РЕКТИФИКАЦИОННЫХ УСТАНОВКАХ

Air cooling devices in which fans pumped the flow of atmospheric air have become widespread in industry. Many times, the energy cost of driving fans is less than the cost of water cooling, which includes the cost of both lifting water from reservoirs and moving water during circulating water supply. Also, most of the water losses are because of its evaporation. Using air cooling devices allows significant savings in cooling water, simplifies cleaning of the outer surface of heat exchange pipes. Currently, Stirling engines can contribute to global energy transformation, they are used as heat energy converters and can and can use any heat sources, the authors of the article propose a method for vapor condensation in rectification plants, where a Stirling engine is used as a fan drive and an estimated calculation method has been created. A schematic diagram of an upgraded rectification plant is presented. In the entire range of studies, under sufficiently favorable weather, the heat flow from steam in the proposed condenser with a Stirling engine can exceed 100 kW, which allows up to 300 tons of water per day to be withdrawn from the circulating water supply and will save over 15 kW of electricity. Studies have shown that the total heat flow does not depend on the efficiency of the Stirling engine, the energy of the condensing steam is spent on heating the air passing through the inter-tube space. With an increase in the power of the Stirling engine, an increase in thermal, heat transfer coefficient and minimum heat transfer surface area is observed.

The method of calculating the parameters of a heat exchanger with porous inserts based on the obtained criterion equation

The issues of improving the efficiency of heat exchange equipment are relevant. Heat exchange equipment is used in various industries. Porous metals have proven themselves well when used in heat exchange systems of gas turbine and rocket engines, laser mirror systems, nuclear reactors and other similar systems to increase the efficiency of heat exchange. The use of porous structures is effective due to a significant increase in the heat exchange area. The paper presents the results of experimental and theoretical studies of the efficiency of using porous aluminum inserts in the construction of a shell-and-tube heat exchanger. The efficiency of using porous aluminum inserts in the construction of a shell-and-tube heat exchanger has been experimentally shown. A similarity equation is obtained for calculating the Nusselt criterion, which makes it possible to find the heat transfer coefficient, and as a consequence, heat transfer for the coolant flowing through porous inserts in the inter-tube space of the heat exchanger. A cluster model was used to calculate the heat exchange area from the side of the coolant flowing through the pairs. The correspondence of the obtained calculation formula with the results of the experimental work is shown. A method of thermal calculation of a heat exchanger with porous aluminum inserts using a cluster model and the obtained criterion equation for calculating the heat transfer coefficient is proposed. The conclusion is made about the expediency of using porous metals in heat exchange structures.

Building-Block Size Mediates Microporous Annealed Particle Hydrogel Tube Microenvironment Following Spinal Cord Injury.

Spinal cord injury (SCI) is a life-altering event, which often results in loss of sensory and motor function below the level of trauma. Biomaterial therapies have been widely investigated in SCI to promote directional regeneration but are often limited by their pre-constructed size and shape. Herein, the design parameters of microporous annealed particles (MAPs) are investigated with tubular geometries that conform to the injury and direct axons across the defect to support functional recovery. MAP tubes prepared from 20-, 40-, and 60-micron polyethylene glycol (PEG) beads are generated and implanted in a T9-10 murine hemisection model of SCI. Tubes attenuate glial and fibrotic scarring, increase innate immune cell density, and reduce inflammatory phenotypes in a bead size-dependent manner. Tubes composed of 60-micron beads increase the cell density of the chronic macrophage response, while neutrophil infiltration and phenotypes do not deviate from those seen in controls. At 8 weeks postinjury, implantation of tubes composed of 60-micron beads results in enhanced locomotor function, robust axonal ingrowth, and remyelination through both lumens and the inter-tube space. Collectively, these studies demonstrate the importance of bead size in MAP construction and highlight PEG tubes as a biomaterial therapy to promote regeneration and functional recovery in SCI.

УДОСКОНАЛЕННЯ КОНСТРУКЦІЇ ВОДООХОЛОДЖУВАНИХ ПАНЕЛЕЙ ДУГОВИХ СТАЛЕПЛАВИЛЬНИХ ПЕЧЕЙ ЛИВАРНОГО КЛАСУ

The article outlines the importance of the foundry industry and the role of arc steelmaking furnaces (ASFs) in it. It was noted that water-cooled panels in EAFs are key elements that ensure the structural integrity and safety of furnaces by removing excess heat during steelmaking. An analysis of literature sources has revealed that there are certain issues that characterize the imperfections of certain structural parts of modern water-cooled panels, such as insufficient cooling efficiency, corrosion, and leaks, which lead to a decrease in the performance of the BF and an increase in energy consumption. These factors have been analyzed and some optimization ways have been identified to improve overall efficiency and durability. The article emphasizes that modern technologies can reduce the consumption of energy and refractory materials by reducing the capacity of the steelmaking bath and optimizing the heat balance. Particular emphasis is placed on the potential for modernizing water-cooled panels to improve the efficiency of the steelmaking process. The paper reveals the mechanism of operation of water-cooled chipboard panels as a spatial system of steel tubes connected by means of transition elements and placed with different densities and a layer of thermal insulation material in the intertube space. This determined the need to improve the design of the panels by optimizing their spatial structure to ensure a more efficient heat transfer process. Improving the energy efficiency of chipboard means reducing heat energy losses, which, among other things, ensures more stable operation during melting, reduces component wear and extends the service life of water-cooled panels. The design of the water-cooled panels has been improved by varying the distance between the axes of the water-cooled tubes depending on their diameter and spatial location. This design makes it possible to optimize the layer of heat-insulating material and minimize unproductive heat loss. Failure to comply with the calculated value of the pipe spacing can lead to increased heat loss. The calculations and graphical dependencies demonstrate the efficiency of heat flow distribution and minimization of heat losses. The new design reduces heat loss by 45% and improves the performance of water-cooled panels.

ДОСЛІДЖЕННЯ ЕФЕКТИВНОСТІ ТЕПЛООБМІННОГО ПРОЦЕСУ В ОХОЛОДЖУВАЧІ ТУРБІННОГО МАСТИЛА МО-2 В ЗАЛЕЖНОСТІ ВІД СХЕМИ РОЗТАШУВАННЯ ТРУБОК У ТРУБНИХ ҐРАТАХ

Effective cooling of the turbine oil is important for the reliability and optimal operation of the turbogenerator. The oil is used for lubrication and cooling of the support and radial bearings of the turbine, bearings of the generator and reducer, gears and splined rollers. It is also used as a hydraulic fluid in the hydraulic turbine start-up system. For reliable and safe operation of the system, it is necessary to maintain the correct temperature of the lubricant. Research is aimed at studying the influence of the layout of the heat exchange tubes in the tube grids on the cooling efficiency of the TP-22 turbine oil. With the help of the SolidWorks software complex, a geometric model of the MO-2 turbine oil cooler was created with three schemes for the placement of heat exchange tubes in tube grids: corridor, radial and checkerboard. Adhering to the parameters of the technical characteristics of this cooler, the nominal parameters of temperatures and consumption of coolants (cooling water and turbine lubricant TP-22) were chosen. The result of the calculations were the temperature fields of the coolants and the trajectories of the movement of lubricant particles in the intertube space of the cooler. When creating a geometric model and further research, the main technical characteristics of the shell-and-tube horizontal cooler MO2 were adopted, namely: the temperature of the turbine oil at the inlet is 45°С, the nominal flow rate of the oil is 3.1 m3/h, the temperature of the water at the inlet is 20°С, the nominal flow rate water - 15 m3/h. The conducted computer modeling made it possible to investigate the influence of the layout of the heat exchange tubes in the tube grids on the cooling efficiency of the turbine lubricant in the MO-2 shell-and-tube cooler. It was shown that the most effective, among the studied schemes, is the checkerboard arrangement of heat exchange tubes in tube grids. This scheme makes it possible to reduce the consumption of cooling water, relative to the nominal one, which will allow the use of water pumps of lower power.

PRIMARY OIL REFINING AND HEAT EXCHANGER APPARATUS

Different technological processes are applied in the field of modern oil refining. Each of the processes in turn is implemented by many technological schemes and methods. In petroleum refining and chemical production, these technological processes provide the basis for many simple processes. In this way, the learning of the processes is facilitated. They process oil and its products by applying various processes. Oil refining and its main organic synthesis plants are composed of a collection of various technological processes and general plant farms. Depending on the number and quality of the products received from the factories, great attention is paid to the supply of hardware and equipment. It is through these equipment and devices that technological processes are carried out. Heat exchangers are among the most commonly used devices in the oil refining industry. The most common type of heat exchangers are shell-and-tube heat exchangers. Shell and tube heat exchangers are technological in the oil and gas industry pretreatment to improve properties and reduce viscosity of streams stages are widely used. Distribution of shell-and-tube heat exchanger design reliability and due to the variety of types and versions to work in a wide range of temperature, pressure and corrosive environment. At the current stage of production development, an important trend is increasing the efficiency of the used technological equipment, ensuring high energy efficiency in relation to heat exchange equipment. Flat cross-sections of different configurations are used to organize the cross current in the inter-tube space of the heat exchanger and to increase the cooling speed. The presence of such partitions significantly complicates the flow pattern of the cooling liquid, and is reliable for the flow around the tube bundle. Currently used methods of heat exchanger heat calculation based on criterion dependencies do not take into account all characteristics of the flow. Keywords: Boiler, reactor, heater, furnace, filter, air cooler, electrodehydrator, gasoline, diesel, catalyst, injector, pump, piping, hot flow, cold flow.

Методика расчета витых теплообменников, применяемых для термической обработки инструментов горного оборудования

Introduction. In modern conditions (depletion of deposits, complication of development conditions, the application of sanctions on the import of equipment, etc.), a special role is played by increasing the resource of equipment used in the mining industry, including processing drilling impact-rotary tools. One of these methods is cryogenic processing of machining tools, as a result of which the hardness and wear resistance of the cutting tool increase several times. For the production of cryogenic substances such as nitrogen, oxygen, methane, etc. in the liquid state, a method is proposed based on the use of adsorption-cryogenic technology implemented through the use of heat exchangers, the development of calculation methods of which is the subject of this article. The purpose of the research is to develop a methodology for calculating heat exchangers used as cold sources for cryogenic surface treatment of mining equipment tools in order to harden it. Research methods. The analysis of the current state of development of technical and technological solutions in the field of development and construction of heat exchangers was carried out through the use of such informal methods as: expert, morphological and factographic. To optimize the modeling calculations of the a priori selected configuration of the heat exchange surface, the method of uniform (blind) search was used. Research results and discussion: 1. In the course of the conducted research, the results of the analysis of the current state of development of technical and technological solutions in the field of development and construction of heat exchangers were obtained. 2. A method for calculating twisted heat exchangers has been developed. 3. It is determined that the presented method of calculating heat exchangers used as cold sources for cryogenic surface treatment of mining equipment tools in order to harden them allows optimization of modeling calculations a priori of the selected configuration of the heat exchange surface. 4. It is established that: heat exchangers with finned pipes should be used when the ratio of the heat transfer coefficient of the flow inside the pipes to the corresponding coefficient in the inter–tube space is 3 ...5 times greater. 5. The use of finned pipes in heat exchangers makes it possible to increase the area of the outer surface of the pipes due to finning, thereby improving the thermal characteristics of heat exchangers, while reducing its weight and size characteristics. 6. It has been revealed that heat exchangers with dense winding are less efficient compared to devices with sparse winding, and heat exchangers with smooth pipes should be used in cases of proximity of the values of the heat transfer coefficient of flows in the tube and inter-tube space. Resume: 1. The analysis of the current state of development of technical and technological solutions in the field of development and construction of heat exchangers was carried out. 2. A method has been developed for calculating heat exchangers used as cold sources for cryogenic surface treatment of mining equipment tools in order to harden them. 3. The developed method of calculating heat exchangers can be used to design heat exchangers consisting of pipes with different surface geometries that are wound onto the core in a spiral, used both in the extractive industries and in the engineering, chemical, oil and gas, rocket and space industries. The further development of the research topic is the optimization of the operating parameters of the heat exchanger according to the criterion of energy efficiency.

INTENSIFICATION OF HEAT TRANSFER IN HEAT EXCHANGE EQUIPMENT DURING CONDENSATION OF WATER VAPOR AFTER STEAM TURBINE INSTALLATIONS IN NUCLEAR POWER.

The determining parameter that characterizes the intensity of heat transfer in heat exchange equipment is the heat transfer coefficient, the value of which depends on the thermal resistances occurring in the corresponding equipment. Thus, in the heat exchanger-condenser of a steam turbine installation of a nuclear power station, this is the thermal resistance during heat transfer of cooling water in heat exchange tubes and during heat transfer of water vapor condensing in the intertube space. The value of the heat transfer coefficient also depends on the geometric and thermophysical characteristics of the heat heat exchange tubes, on the contamination of the cooling water, on the presence of air in the condensing vapors. According to the proposed scheme of the experimental setup of the "pipe in a pipe" type, calculations of the heat transfer coefficient were performed when using an external transparent glass pipe and an internal metal pipe, which was treated from the outside with a water-repellent coating that provides dropwise condensation of water vapor, as well as without treatment for film condensation. Contamination of the cooling water and the presence of air in the water vapor in both cases of condensation should be the same and as minimal as possible. The analysis of the results of the calculations allows us to draw the following conclusions: the change in the state of the outer surface of the heat exchange tubes increases the heat transfer coefficient during condensation of water vapor almost three times, which ensures an increase in the efficiency of heat transfer (more than 10%), and accordingly allows to reduce the working surface of the heat exchange equipment, which is especially relevant in modern conditions of operation of power equipment, when there is a need for emergency reconstruction of partially destroyed heat exchange equipment. Bibl. 11, Fig. 2.

ОЦЕНКА ЭФФЕКТИВНОСТИ СЕПАРАТОРА С СООСНО РАСПОЛОЖЕННЫМИ ТРУБАМИ ПРИОБЕСПЫЛИВАНИИ ГАЗОВЫХ ВЫБРОСОВ ПРИ РАЗЛИЧНОМ УГЛЕ РАСКРЫТИЯ ПРЯМОУГОЛЬНЫХ ЩЕЛЕЙ

An important task in dedusting gas emissions at chemical industry enterprises is to achieve high efficiency. A complex of devices is used for this. Large particles are removed from gases in coarse cleaning devices. Fine particles are removed from gases in fine cleaning devices. However, fine filters are quickly clogged, which leads to an increase in hydraulic resistance and, in some cases, to a decrease in efficiency. An urgent task is to increase their service life and increase efficiency. For this purpose, the paper proposes the design of a separator with coaxially arranged pipes, which is proposed to be installed in front of fine filters. The aim of this work is to numerically investigate the effect of the angle of opening of rectangular slits on the efficiency and hydraulic resistance of a separator with coaxially arranged pipes. The article presents the design of the separator. The principle of operation is described. During numerical calculations, the inlet velocity of the gas flow was set at the inlet of the device, which varied from 3 to 10 m/s, and the mass flow rate of particles was 5 g/s. The particle density varied from 1000 to 3000 kg/m3. The particle diameter varied from 1 to 15 microns. The opening angle of the slits varied from 16 to 24 °. During the calculations, the following main conclusions were made: the structure of vortices in the inter-tube space determines the degree of efficiency of a separator with coaxially arranged pipes, with the angle of opening of rectangular slits α = 20 °, the maximum separation efficiency of fine particles up to 10 microns in size from a dusty stream is equal to an average of 40.3%, the separation efficiency of fine particles from a dusty stream is achieved. the flow rate increases with an increase in the input gas velocity and particle density, because they are easier to dislodge from the swirling gas, the pressure loss in the separator with coaxially arranged pipes is no more than 626 Pa.

Energy-efficient vacuum evaporation units for concentration in the dairy industry

The application of various types of evaporation plants for concentration of solutions was analyzed. It was noted that the most promising for thickening dairy products are film-type vacuum-evaporation units with mechanical compression of secondary steam. The heating chamber of the evaporator is made in the form of a vertical shell-and-tube heat exchanger with the supply of heating steam into the intertube space and with the downward movement of product solutions in the vertical boiling tubes. Based on the analysis of known studies on hydrodynamics and heat exchange of film processes (condensation, film heating and evaporation and steam separation), a conclusion was made about the lack of data for calculating pressure losses in the steam circuit of the evaporator with sufficient accuracy. To solve this problem, improved methods of calculating the hydraulic resistance of the intertube steam path of the heating chamber and the two-phase flow of the product film and secondary steam in evaporative boiling tubes have been developed using the published results of hydrodynamic resistance research. Pressure losses for the movement of secondary steam in the lower chamber of the evaporator include losses for acceleration of the steam released from the falling film of the product. It is shown that the hydraulic depression of the movement of steam in the intertube space of the heating chamber, depending on the type of scheme, can be from 2.3% to 77% compared to the working temperature pressure of the heating surfaces. The four-way flow scheme of the heating steam used in the design of the vacuum-evaporation unit ensures a reduction of hydraulic losses by up to 15%. A technical and economic analysis of the costs of operating a vacuum-evaporation unit with a productivity of 10 t/h of vaporized steam was performed, according to which the lowest reduced costs were established at a temperature drop of 5˚C on the compressor. The results of the research were used in the development of structures and the manufacture of vacuum-evaporation units with mechanical and mixed (mechanical and thermal) compression at PrJSC "Kalyniv Machine-Building Plant" (Kalynivka, Vinnytsia Region). 10 vacuum evaporation units with a capacity of 5 to 20 t/h of evaporated moisture were manufactured and put into operation.

ЭКСПЕРИМЕНТАЛЬНОЕ ОПРЕДЕЛЕНИЕ ГИДРАВЛИЧЕСКОГО СОПРОТИВЛЕНИЯ УПРОЩЕННОЙ МОДЕЛИ МУЛЬТИВИХРЕВОГО КЛАССИФИКАТОРА С СООСНО РАСПОЛОЖЕННЫМИ ТРУБАМИ

An important task in the production of fine bulk material based on silica gel is to obtain a narrow fraction of the powder of the required dispersion. Existing devices, due to the required dispersion of bulk powder, technological and other parameters, do not always allow this to be done. The paper considers various classifiers. Their disadvantages for carrying out fractionation of bulk material based on silica gel at the Salavat Catalyst Plant are shown. The authors of the work proposed the design of a multi-vortex classifier for obtaining powder in size from 10 to 40 microns. The aim of this work is to obtain an experimental dependence of the hydraulic resistance of a simplified model of a multi-vortex classifier on the average velocity of the gas flow. 3 simplified models of the multi-vortex classifier are presented. The scheme of the experimental setup is presented. The method of conducting experiments is described. Based on the work carried out, the following conclusions were drawn. 1) Pressure losses in simplified models of a multi-vortex classifier range from 6 to 670.5 Pa at an input average gas flow velocity of 4.1 to 23.6 m/s. 2) The maximum hydraulic resistance corresponds to the first model with the largest number of local resistances - rectangular slots. 3) The equations of hydraulic resistance and coefficients of hydraulic resistance from the average velocity of the gas flow are obtained for 3 models of the multi-vortex classifier. 4) It is qualitatively obtained that there is a critical equivalent diameter of the inter-tube space, reflecting the beginning of the destruction of the vortex structure in the multi-vortex classifier. This factor leads to an increase in the hydraulic resistance of the device.

Numerical Study of Vortex Flow in a Classifier with Coaxial Tubes

Centrifugal air classifiers are one of the most used separation devices in particle technology. The study aims to obtain a detailed description of the bulk material classification mechanism in the developed centrifugal classifier. The classifier design and the mechanism of the stable vortex structure formation in the inter-tube space of the device are described. Velocities within and between the vortices are studied to identify regions with inverse flows, which serve as transport channels for particles. The computational fluid dynamics modeling results indicate three channels with negative or near-zero axial velocities: between the vortices, near the outer wall of the internal tube, and the inner wall of the external tube. The selectivity of the device decreases when transport channels are disrupted due to flow mixing, which is caused by the height shifting of the vortex centers.

Macrophage-like Cells Are Responsive to Titania Nanotube Intertube Spacing-An In Vitro Study.

With the introduction of a new interdisciplinary field, osteoimmunology, today, it is well acknowledged that biomaterial-induced inflammation is modulated by immune cells, primarily macrophages, and can be controlled by nanotopographical cues. Recent studies have investigated the effect of surface properties in modulating the immune reaction, and literature data indicate that various surface cues can dictate both the immune response and bone tissue repair. In this context, the purpose of the present study was to investigate the effects of titanium dioxide nanotube (TNT) interspacing on the response of the macrophage-like cell line RAW 264.7. The cells were maintained in contact with the surfaces of flat titanium (Ti) and anodic TNTs with an intertube spacing of 20 nm (TNT20) and 80 nm (TNT80), under standard or pro-inflammatory conditions. The results revealed that nanotube interspacing can influence macrophage response in terms of cell survival and proliferation, cellular morphology and polarization, cytokine/chemokine expression, and foreign body reaction. While the nanostructured topography did not tune the macrophages’ differentiation into osteoclasts, this behavior was significantly reduced as compared to flat Ti surface. Overall, this study provides a new insight into how nanotubes’ morphological features, particularly intertube spacing, could affect macrophage behavior.

Excellent piezoresistivity of composites made from networked carbon nanotubes and polydimethylsiloxane: An intertube barrier driven strain sensing

Composites made from multi-walled carbon nanotubes and polydimethylsiloxane exhibit an excellent piezoresistivity at elastic limits where strain sensitivity reaches 0.93–0.96 and resistance changes due to stretching and compressing matches with loading histograms. Resistance change becomes pulse-like as the samples are bent and/or twisted, attributed to the rapid increase in intertube spacing. Straining induces movements and segmentations of tube aggregates with tube mobility ranging at 0.1–90 nm/s. Intertube barrier driven sensing mechanism is viscoelasticity related and is therefore interpreted on the basis of spring-dashpot models.

Heat Exchange in Staggered Threaded Pipe Banks with Similar Developed Surface Patterns under Natural Draft Conditions

Helical pipes with similar developed surface patterns efficiently operate under forced convection conditions. The available literature describes their essential advantages over the tubes of a round-ribbed profile and the possibility of their application as a heat-exchanging section for the air-cooling unit. However, the peculiarities of the operation of such units require checking an opportunity for the use of helical pipes with similar developed surface patterns under natural draft conditions. The purpose of the research is to get new data on the flow structure in the intertube space of the staggered banks of such pipes under natural draft conditions. These data are required for the in-depth analysis of the appropriateness of the use of such pipes for “dry” air cooling systems. The methods of investigation included the use of the academic licensed software package ANSYS Student for numerical computations. It was established that the heat exchange in ribbed pipes under natural draft conditions is specified first of all by the parameters of the staggered bank (longitudinal and transversal pitches of the arrangement of pipes in the bank) and the geometric parameters of the pipes, in particular the pitch between the humps and the dents on the tube surface that form its helical surface. Design ratios were suggested for the determination of the averaged heat exchange in the staggered banks of the single-thread helical pipes with similar developed surface patterns. It was shown that the pitch characteristics of the banks have the greatest effect on the similarity equation. A preliminary validation was carried out for the methods adopted for the design of helical pipes and the known methods used for the computation of the staggered banks of smooth cylindrical pipes. The obtained research data can be used for the evaluation of the intensification of the heat exchange and for the flow analysis in order to increase the efficiency of the heat-exchange equipment.

Study of Free-Convective Heat Exchange of Air-Coolable Finned Tube Bundles Intensified by Exhaust Shaft

The results of experimental studies of free-convective heat transfer of single-, double- and four-row bundles of finned tubes without and with an exhaust shaft are presented. It is shown that the inter-tube spacing significantly affects the energy efficiency of the bundle. The optimum inter-tube spacing is 61 mm for single-row, about 70 mm for double-row, and over 70 mm for four-row bundles. With increase of the number of rows in the bundle the specific capacity of the bundle increases, but the rate of its increase decreases. The specific heat capacity of a single-row bundle with an inter-tube spacing of 58 mm is higher than with an inter-tube spacing of 64 mm. The specific heat capacity of two- and four-row bundles is less at low exhaust shaft heights, but it is more when the relative shaft height is more than 0.14 and 0.26, respectively. The heat transfer of the bundles can be increased (more than threefold) using optimal ratio of the outlet section of the shaft and the flow capacity of the tube.

Evaluation of interactions of multi-walled carbon nanotubes with benzoic acid and its 2-halogeno derivatives and their cytotoxicity

In this study, interactions of multi-walled carbon nanotubes (MWCNTs) with benzoic acid and 2-halogeno (F−, Cl− and Br−) derivatives were investigated. In addition, these compounds were determined to be cytotoxic on Primary Peripheral Blood Mononuclear cells. Adsorption percentages of MWCNTs exposed to these acids at the same concentration for 24 hours were calculated. Raman spectroscopy, Fourier Transform Infrared Spectrocsopy (FT-IR) and Scanning Electron Microscope (SEM) techniques were used to determine the chemical and physical changes caused by acid species on the structure of MWCNTs. As a result of the investigations, it was determined that 2-bromobenzoic acid (BrBA) was adsorbed most favorably by the structure. The structure adsorbed the benzoic acid derivatives better than benzoic acid (BA). The least defect occurred in the sample subjected to BrBA. It was found that there was no correlation between absorption rates and defect occurrences in the structure. SEM results indicate aggregation, tube curl, and filling in inter-tube spaces in samples where absorption is intense. In FT-IR spectra of all structures obtained, the characteristic vibration band related to MWCNTs, and C = O stretching vibration band of the benzoic acid and its derivatives were observed around 1450 and 1680 cm−1, respectively.

Mathematical modeling of geothermal energy from a well extraction

The authors of the article examine the possibility of extracting geothermal energy to the Earth’s surface using the circulation of a heat carrier – water. For this purpose, an oil well is operated that is already suspended and is no longer used for its original purpose. A system of heat and mass transfer equations describing heat distribution in the ground around the well and in the coolant is presented. A mathematical model is developed for calculating the heat flow amount from the ground to the well distribution depending on time, thermal parameters and soil temperature; the temperature field in the near-well space calculation determining the parameters of the heating system transporting heat energy from the well to the surface is performed; the optimal period of well operation by the potential of non-reduced temperature is determined; the temperature field recovery time in the near-well space required for subsequent operation is calculated. Various well depths, geothermal gradient, and water injection rates are considered. For the first time, the relationship between ground temperature and liquid temperature in the inter-tube space and in the inner tube is considered simultaneously.

Simulation of optimal exploitation of production wells in northern oil and gas fields

In this paper a new model of the propagation of thermal fields in frozen soil from production wells in the northern oil and gas fields is considered. The proposed model takes into account the most significant thermal insulation characteristics of wells, including the intertube space. The developed complex of programs and the performed numerical simulatons allow to significantly reduce the area of the projected well pads of the oil and gas field by reducing the predicted radius of thawing of frozen soil from functioning wells and choosing the optimal mode of the operation during 30 years.