Additional Pressure Loss Research Articles

Experimental and numerical study of the cooling characteristics of the double-walled cooling structure on integral support plate

The diffuser, rectifier, fuel injection rod, and flame holder in the afterburner are designed integrally, and a double-layer cooling structure is installed for the integral flame holder. Infrared thermography is employed to carry out the cooling efficiency test experiments under non-afterburner conditions, and the numerical simulation method is used to obtain the flow characteristics inside the integral afterburner. The effects of subtle geometrical parameter changes on the near-wall flow and wall-cooling effect are investigated. The results show that: The cooling air covers the film panel to form a film under the traction of the backflow vortex and spiral vortex behind the support plate, which provides effective cooling for the integral flame holder; the increase of the mass flow ratio will improve the cooling effectiveness of the double-wall, but it will cause additional pressure loss; impact spacing H has a small effect on the cooling effectiveness and relative pressure loss; reduced film aperture diameter df, increased aperture spacing S and aperture row angle β lead to a drop in the cooling capacity of the double-wall, whereas a reduced impact aperture diameter di leads to a certain degree of improvement in the cooling effectiveness of the double-wall.

ОПРЕДЕЛЕНИЕ ОПТИМАЛЬНЫХ ПАРАМЕТРОВ КАПЕЛЬНОЙ ЛЕНТЫ ДЛЯ МЕХАНИЗИРОВАННОЙ УКЛАДКИ

The introduction of drip irrigation systems in irrigated areas is impossible without the creation of special machines for laying drip tape. The advantage of in-soil laying of the tape is the absence of losses due to evaporation of irrigation water and the inadmissibility of its heating to temperatures dangerous for the plant in the hot season. To ensure high-quality laying of the drip tape in the soil, constant tension of the tape is required when the speed of the machine fluctuates or it suddenly stops. The absence of constant tension will lead to jamming of the tape in the laying pipe or its twisting, which will make further operation of the drip irrigation system impossible and will require repair work that requires additional labor costs. Constant tension of the tape ensures its precise location in the soil, which will eliminate additional pressure losses when the position of the tape changes during operation of the drip irrigation system. To maintain constant tension, a permanent brake is required. This creates additional tensile forces applied to the tape. The tape is also affected by the resistance of laying it in the soil. The research was aimed at establishing the numerical values of the forces acting on the drip tape to assess their impact. The most popular tapes on farms are those with a thickness of 0.15...0.25 mm due to their low cost. Research has established that for underground installation it is desirable to use a tape with a thickness of at least 0.2 mm. When using a tape with a thickness of 0.15 mm, tensile forces can lead to dangerous deformations of the tape, making it impossible to further use

Investigation on the effect of the leading angle of the strut on the stabilization characteristics of lifted jet flames

To achieve stable combustion within supersonic combustors, the strut-based mixing augmentation techniques are commonly employed. Large Eddy Simulations (LES) are employed to capture the intricate details of the combustion process in this study, focusing on the influence of shock waves induced by the leading edge of the strut and recirculation zones formed at the trailing edge on flame structure and stability. The effects of five struts with different leading edge angles on the stabilization characteristics of lifted jet flames were investigated, and a novel wedge-shaped strut was proposed. The results reveal that variations on the leading-edge angle of the struts lead to significant differences in the morphology of the jet flames. Under conditions permitting stable combustion, a strut with a 5° leading edge half-angle exhibits the highest combustion efficiency, though the combined effects of shock waves and recirculation zones in the 7° leading edge half-angle strut are also noteworthy. Based on these findings, a novel wedge-shaped strut design is introduced, which combines the characteristics of both strut types. The novel wedge-shaped strut achieves a combustion efficiency of 97 % at the slight cost of additional total pressure loss, providing a foundation for further optimization.

دراسة عددية لتعزيز انتقال الحرارة للتدفق المضطرب في ال نابيب المدملة

The importance of heat transfer enhancement has gained greater significance in many engineering applications, and a great amount of effort has been devoted to the use different techniques to improve the thermal performance of flowing fluids in pipes. Dimpled tubes were used for this purpose in this study. In this investigation, the heat transfer-flow characteristics of turbulent flow in dimpled tubes subjected to uniform heat flux are numerically investigated. The rate of heat transfer, friction factor, and performance evaluation criterion were determined for various designs of dimpled tubes and compared with smooth tubes. The considered cases are conducted in the Reynolds number range of 3000 to 12,000. The ANSYS Fluent R19 is used for this purpose. The Reynolds-averaged Navier-Stokes equations(RANS) are used to model the governing flow equations. The realizable k-ε turbulence model is used with enhanced wall conditionsto simulate turbulent flow adjacent to the inner wall surface. The results revealed that the rate of heat exchange in dimpled tubes higher than that of smooth ones. but with additional pressure loss. Moreover, the heat transfer performance of the staggered arrangement is higher than the inline arrangement by 17 %. Also, the performance evaluation criteria (PEC) increases with the increasing in dimples diameter, and decreases with increasing in relative pitch spacing, the maximum enhancement reaches 31% for d = 5 mm, and relative pitch spacing S/D = 2 at Re = 4000.

Research on dynamicflow rate self-sensing in control valves

In the field of control valves of nuclear energy, the measurement and control of the flow rate are widely concerned. Applying the traditional differential pressure flowmeter to directly measure the flow rate of the control valve would lead to unnecessary pressure drop, excessive energy consumption of the pump and high cost, and the obtained flow rate is mainly steady flow rate. In this paper, a self-sensing method of the dynamic flow rate of the control valve is proposed with the advantages of no flowmeter, no need to add moving parts. The original control valve in the pipeline system is used to measure the flow rate, which would not cause additional pressure and energy loss. The self-sensing model of the dynamic flow rate of the control valve is established, and the measurement of the dynamic flow rate is converted into the measurement of the dynamic pressure. The feasibility of the self-sensing model is verified by the experiment on the flow measurement experimental platform. The self-sensing performance of the dynamic flow rate under valve's various working conditions is sufficiently analyzed. Moreover, the self-sensing model is modified and optimized based on the Isight platform. The results show that by introducing the correction coefficient, the maximum relative error after optimization between the self-sensing flow rate and set value is reduced from 11% to 6% under the random movement condition of the valve plug, which enhances the self-sensing ability of the dynamic flow rate.

Investigation of a thermomechanical improved tangential fan geometry

In convection-dominated thermoprocessing plants, the current state of the art is to use centrifugal and axial fans in conjunction with flow straighteners to ensure a homogeneous inflow of the fluid and thus a homogeneous temperature distribution. However, flow straighteners lead to an additional pressure loss in the system that must be overcome. Tangential fans can deliver a homogeneous volume flow over the entire width of the fan even without flow straighteners. Therefore, they offer a possibility to increase the energy efficiency of these systems. Based on this motivation, the possibilities of increasing the thermomechanical long-term stability of tangential fans are being evaluated as part of a current research and development project. To this end, the effects of design changes on the generated flow and the mechanical loads are being investigated with the help of FEM and CFD simulations. The aim is to design a tangential fan that can withstand the mechanical and dynamic loads and deliver a consistently high and homogenous fluid flow at the same time. A geometry based on the results of the simulations was manufactured as a functional sample. This sample was investigated at the hot test stand of the IOB and is compared to a reference tangential fan.

Abstract 13623: In Silico Comparison of Pressure Head Loss for Outflow Variations of a Novel LVAD Accessory Compared to Generic LVAD Pump Outflow

Introduction: Left ventricular assist device (LVAD) implantation is a treatment option for end-stage heart failure, requiring a sternotomy. A novel accessory, redirecting the outflow via the left ventricular apex into the ascending aorta, allows for LVAD implantation via left thoracotomy. Pressure distribution within accessory designs is unknown. Our goal was to compare three different outflow designs with a generic LVAD outflow (Control) to optimize the accessory’s outflow design. Hypothesis: We hypothesize that the LVAD accessory leads to higher pressure head loss than Control and that there are relevant differences among varied designs. Methods: Volume models of the LVAD accessory variations (A–C) and Control were created using computer aided design. Computational fluid dynamics (CFD) was used to simulate blood flow through the accessories and generic outflows. A verification study was performed to optimize numerical parameters. Pressure head loss (mmHg) was calculated for each outflow while changing the LVAD flow rate continuously (2–7 L/min). Pressure loss was compared by mean differences (MD). Results: Pressure head loss increased with higher LVAD flow rate among all groups. Addressing the accessories’ outflow designs, Design B revealed the lowest increase in pressure loss revealing a mean slope of 2.3 mmHg/L/min compared to 4.6 and 3.0 for Design A and C. Referring to a flow rate of 5.5 L/min, a common flow rate among clinical LVAD patients, and comparing pressure head loss with Control, we found an additional pressure loss of 15.5, 6.4 and 8.3 mmHg in Design A, B and C, respectively. Conclusion: There is a trade off between fitting the outflow design to the cardiac geometry and the pressure head loss. Continued optimization of the LVAD accessory could allow minimally invasive LVAD implantation with minimal changes in LVAD performance. Potential compromise between improved design and performance renders CFD an important tool for medical device development.

Effect of Vortex Generator Placement and Nanofluids on Channel Flow Heat Transfer

In this research, an attempt has been made to enhance the heat transfer for a plate-fin heat exchanger with the new arrangement of classic delta winglets used for vortex generators and compared the same with the existing literature. The computational domains are developed by dislocating delta winglets from their original position, so there is no additional pressure loss with flow geometry. All the flow domains are analyzed by computing the 3D Reynolds averaged Navier–Stokes equations using ANSYS Fluent. Two different working fluids are considered one is water and nanofluids (water with Aluminum oxide). Heat transfer characteristics are analyzed for different placements of winglets for both water and nanofluids. The plate-fin heat exchanger’s performance has been optimized with the optimum location of winglets and nanofluids from the analysis of numerical results. For the case of 0% nanofluids at 300 Reynolds number, Case 3 Nusselt number has been increased by 23.2% with a decrease in pressure drop of 17.7% with the dislocation of one winglet. It represents the enhancement of heat transfer.

ON THE ISSUE OF TRANSPORTATION OF LIQUEFIED CARBON DIOXIDE

Link for citation: Vanchugov I.M., Rezanov K.S., Shestakov R.A. On the issue of transportation of liquefied carbon dioxide. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 8, рр. 190-209. In Rus. The relevance of the study is caused by the need to capture and utilize one of the main types of greenhouse gases – carbon dioxide (CO2). This need is primarily related to the ever-increasing CO2 emissions, three quarters of which are accounted for by the combustion of various fuels. The main aim is to analyze and systematize international methods for calculating the pipeline transport of liquefied carbon dioxide (LCO2) to determine differences in numerical results, including factors taken into account and not taken into account in the methods under consideration, as well as to analyze water transport type as an alternative to pipeline transport. Objects: liquefied carbon dioxide, a pipeline for transporting LCO2. Methods: numerical modeling of LCO2 pipeline transport according to international methods to estimate the required diameter capable of providing a given pumping flow rate, analysis of the results obtained. Results. The authors have carried out a review of existing methods for calculating LCO2 pipelines, carried out numerical modeling and analysis of the results were, during which it was revealed that most models ignore the influence of impurities, which, however, affect the technological parameters of operation and modeling of LCO2 pipelines, which will lead to inaccuracies in their design and operation. In addition, it was found that the fluid velocity in the pipeline is calculated according to the parameters in the initial section, which corresponds to its minimum value in the pipeline, and is assumed to be equal to it throughout the pipeline without taking into account the expansion of LCO2 from changes in temperature and pressure along its length and, consequently, without taking into account additional pressure losses and changes in other technological parameters that they can directly affect the operational safety and economic efficiency of the designed or operated LCO2 pipeline. It should also be noted that the diameter determination equations depending on the length of the pipeline are not suitable for estimating the optimal diameter of the pipeline. As for alternatives to pipeline transport, first of all, it is worth noting the possibility of transportation by tankers over long distances or the possibility of using LCO2 to increase the flow rate of deposits on the shelf and in hard-to-reach places of the coastal zone.

Influence of vortical flow induced by a wall-mounted short cylinder with a streamlined front side on a horizontal air–solid two-phase flow

To induce large oscillations of air flow and suspend particles easily near the particle supply point in a low air velocity region of horizontal air-solid two-phase flow, a short cylinder model with a streamlined front side (refer to streamlined model) is proposed and is fixed on the bottom or top of the pipe in front of the particle feed. The streamlined front side of the model is designed to reduce the flow resistance, and the rectangular rear section of the model generates wake vortical flow so as to induce large airflow oscillation. The test tube consists of a horizontal pipe having an inner diameter of 80 mm and a length of 5 m. Spherical polyethylene particles with an average diameter of 2.3 mm and density of 978 kg/m3 were used as the test solid particles. Average air velocities and particle mass flow rates ranged from 9 to 16 m/s and 0.11 to 0.51 kg/s, respectively. Compared with the non-model air-solid two-phase flow, the streamlined model has reduced the pressure drop, critical and minimum conveying air velocities, power consumption, and additional pressure drop. This model achieved the highest reduction rate with a minimum air velocity of approximately 6% and an additional pressure loss of approximately 37.5%. According to particle image velocimetry measurement of air-solid two-phase flow, the time-averaged particle velocity and fluctuating particle velocity generated by the streamlined model are larger than those in the non-model flow, so even low air velocities can easily convey particles.

Additional pressure loss coefficient of pneumatic conveying of moist-mixed materials for shotcrete based on CFD-DEM method

A systematic study of pressure loss through four common pipeline forms for pneumatic conveying of moist-mixed materials for shotcrete (horizontal straight pipes, vertical pipes, horizontal elbow, and vertical upward elbow) was conducted using CFD-DEM coupling. On-site experiments were conducted to verify the accuracy of the simulation. The research results showed that solid-gas ratio and moist-mixed materials for shotcrete have an influence on pipeline pressure loss. Furthermore, coefficients for additional pressure loss in horizontal and vertical pipes, and an equivalent horizontal length for both types of bends were established. Additionally, the spatial position and velocity of particles were examined under four conditions. The findings of this study have implications for the design and pressure loss estimation of pneumatic conveying pipelines for moist-mixed materials for shotcrete.

Numerical analysis and experiments on heat transfer and flow structures in rotating three-pass serpentine channels with ribs, guide vanes and trailing bleed holes

Numerical and experimental studies are conducted on heat transfer and pressure loss in a three-pass serpentine channel with trailing bleed holes. The guide vanes' effects in the smooth and ribbed channels are studied comparatively. Based on the hydraulic diameter and inlet velocity, the Reynolds number ranges from Re = 14,000 to Re = 100,000, and the rotation number ranges from Ro = 0 to Ro = 0.1. Through the numerical simulations, the rib configuration in serpentine channels influences the guide vane's flow control effects. Applying the guide vanes in the ribbed serpentine channel's tip bend region enhances the flow impingement and advection, increasing the total Nusselt number in the blade-tip region by about 25%, and this region's heat transfer uniformity is improved as well under non-rotating and rotating conditions without additional pressure loss penalty in the channel. Moreover, it is a promising method to improve the turning flow structures and enhance heat transfer further in the ribbed serpentine channel by applying the tandem guide vane in the tip bend region. Both the numerical computations and experiments show only slightly higher and more uniform heat transfer in the second and third passages after applying the guide vanes in the bend regions under non-rotating and rotating conditions. The experiments indicate that the rotation effects show a more appreciable influence on the heat transfer enhancement values along the serpentine channel than the channel Reynolds numbers. The heat transfer differences between the leading and trailing sides are 15.4%, 14.0%, and 21.3% in the three passages, respectively, at Re = 14,000 and Ro = 0.1, referring to the averaged Nusselt number in each passage. The CFD results demonstrate that the rotation significantly improves the heat transfer in the third passage by promoting more radial outflow through the tip hole, reducing the flow rates through the lateral bleed holes by about 13.2%.

A Modified Model to Predict Liquid Loading in Horizontal Gas Wells

Abstract Liquid loading is inevitable during mature gas-well production, leading the liquids to accumulate at the bottomhole and additional pressure loss. Accurately predicting the liquid-loading initiation is crucial to gas-well production optimization. Significant efforts have been made to model liquid-loading behavior. However, few mechanistic models are capable of easily and accurately tackling the complicated non-uniform liquid-film distribution in the slanted section of horizontal wells. Based on liquid-film inversion, this study developed a simple and comprehensive model to calculate liquid-loading initiation for horizontal gas wells. First, the models for film thickness and critical velocity in the vertical pipe are developed. Then, considering the effect of inclination and velocity difference in liquid-film thickness and liquid-holdup distribution between vertical and inclined pipes, the relationship in vertical and inclined pipes between liquid holdup, liquid-film thickness, and angle correction term is established based on the liquid-holdup correlation for horizontal and inclined pipes described in the empirical model developed by Beggs and Brill, so that the thickness of the film and the corresponding critical velocity at any inclination can be calculated. Finally, the new modified model has been evaluated against both experimental and field-measured data set. In comparison to the Luo et al.’s model, the proposed model has been proven to be simple, accurate, and well-performed in predicting the liquid-accumulation initiation in horizontal wells.

Modeling of solids particle diversion to promote uniform growth of multiple hydraulic fractures

Solid particulate additives are sometimes used to promote the uniform growth of multiple hydraulic fractures in horizontal oil and gas wells. The principle is that solid particulates block, accumulate, and form larger porous plugging zones preferentially at entrances of fracture taking in the most fluid volume. These porous zones create fluid flow resistance or additional pressure loss; thereby, inhibiting the growth of these dominant fractures and diverting fluid to suppressed fractures. While this technology is promising, governing design parameters and ramifications of placing solids diverters inside the fracture remain unclear. This paper models the propagation of multi-fractures with diverter pressure losses induced by the porous plugging zones. The resulting non-linear hydraulic fracturing problem is solved numerically with an Implicit Level Set Algorithm (ILSA) for each time step and the mechanisms of diversion are illustrated by comparing and contrasting cases with and without particle diverter. In both cases, during the fluid ramp-up period (pumping rate gradually increases from 0 to fracturing rate (QT)), the injection can be equally distributed among fractures before the stress interference affects the fluid allocation (Phase I). Then, stress interference starts to partition more fluid into outer fractures and suppress the growth of the middle fracture (Phase II). Once the perforation friction loss is sufficient to counteract the stress interaction, injection begins to shift to the middle fracture, but still gives a significantly non-uniform fracture growth (Phase III). At this point, solid diverter particles are introduced, leading to three additional phases of growth. Phase IV introduces solid diverters to the treatment at a reduced pumping rate. Particles bridge, accumulate and create porous plugging zones at the flow entrance. A higher pressure drop in outer fractures diverts injection fluids to the middle fracture. Phase V resumes the treatment rate to QT without diverter. The increased pump rate in turn increases the pressure drop in outer fractures and diverts more fluids to the middle fracture. This results in a rapid extension velocity for the middle fracture, enabling it to have the chance to catch up with the longer outer fractures (in Phase VI). This process is controlled by the interplay among stress interference, perforation friction loss, and diverting pressure drop. These simulations demonstrate that a model-based optimization could improve the effectiveness of the diverter technology and promote a uniform multi-fracture growth.

КАВИТАЦИОННЫЕ РАЗРУШЕНИЯ В ЖИДКОСТНОКОЛЬЦЕВЫХ ВАКУУМНАСОСАХ

The relevance of studying the parameters of operation of liquid ring vacuum pumps and the development of new designs is due to their demand in the agro-industrial complex. The paper provides a description of the cavitation phenomena that occur during the operation of a liquid ring vacuum pump. Cavitation degrades pump performance and can often cause failure. It can occur due to: low barometric pressure; large vacuum suction height; high temperature of the pumped liquid; additional pressure loss in the pump impeller. To identify the possibility of cavitation in a liquid ring vacuum pump, a cavitation characteristic is compiled. It is based on testing the pump at a constant flow rate of the working fluid and the speed of the impeller, performed on a special installation, the scheme of which is presented in the article. Cavitation phenomena in a liquid ring vacuum pump with water occur at a vacuum above 90%. For a single-stage liquid ring vacuum pump, this value corresponds to a vacuum range of 20-10 kPa, for a two-stage one - 10-1 kPa. A photo of the impeller blades of a liquid ring vacuum pump exposed to cavitation is presented. The formula for calculating the cavitation coefficient, which characterizes the cavitation reserve, is given. Its value depends on the design of the considered pump and the operating conditions of its operation and can be determined empirically. Practical recommendations are offered to prevent the occurrence of cavitation phenomena: decrease in water temperature; improving the accuracy of model selection; equipping the pump with an air ejector; use as a working fluid with a low content of saturated steam; production of the impeller from materials with increased anti-cavitation properties

OPERATION FEATURES OF AN ULTRASONIC FLOW TRANSDUCER WITH A COMPLEX TRAJECTORY OF THE MEASURING PATH

To measure the flowrate of fuel and energy resources, different methods are used, which determine the range of measuring instruments. Instruments based on ultrasonic measurement methods are widely used in measurement practice due to the provision of high accuracy, a wide range of measured flowrates, the absence of additional pressure losses and the design simplicity. Such instruments are easily integrated into automated readout systems for collecting and transmitting information. The asymmetry of the measured medium flow is a significant problem in the use of single-channel ultrasonic meters. This issue is successfully solved by using multi-channel flow transducers.
 The disadvantages of multi-channel ultrasonic flow transducers include a significant complication of the hydraulic channel design, the need to use more complex mathematical algorithms for processing the obtained output signal. This requires the use of high performance electronic elements, first of all microprocessors.
 The use of a transducer with multiple reflection of one measuring beam from the wall of the measuring path acts as an alternative to multi-channel measurement.
 The aim of the work is to create a mathematical model of an ultrasonic flow transducer with a complex measuring path trajectory. For research, a scheme with sounding along three chords was chosen, which implements the time-pulse measurement method, it provides for determining the flow rate by the difference in the time of passage of the measuring path along the flow and against it. In this case, the projections of the chords on the cross section of the measuring section create an equilateral triangle. An analytical expression for the conversion response is obtained for the case of several beam reflections in different planes.
 The authors reproduced the hydraulic part of the investigated flow transducer using simulation modeling implemented on the basis of the finite element method. Transducer’s operation simulation in the range of measured flow rates in the conditions of an ideally formed profile of the gas flow velocity in the transducer inlet cross-section has been carried out. The results obtained confirmed the absence of influence of the measuring circuit elements (beam reflectors) on the flow profile and the measuring beam trajectory.

Numerical study on a novel device for hydrogen mixing enhancement in a scramjet engine: Coaxial injector

The mixing process between the fuel and air is very important for the efficient operation of the scramjet engine, and it has attracted an increasing attention all over the world. In this work, the coaxial injector was developed and investigated by means of the three-dimensional Reynolds-averaged Navier-Stokes equations coupled with the SST k-ω turbulence model, and the numerical approaches were validated against the non-dimensional experimental streamwise velocities in four different streamwise positions on the symmetry plane. Further, the influence of the jet-to-crossflow pressure ratio for the hydrogen and air is evaluated numerically as well. The obtained results show that the mixing process induced by the coaxial injector is conducted more quickly, and it is a promising mixing enhancement device for the scramjet engine. The smallest value of the mixing length for the cases studied in the current study is 1.69. It brings nearly no additional total pressure loss when compared with the single injector, and the jet-to-crossflow pressure ratio has only a small impact on the total pressure recovery coefficient.

Effect of jet schemes of the double-nozzle strut injector on mixing efficiency of air and hydrogen for a scramjet combustor

This work presents the numerical analysis of the DLR scramjet combustor for different jet schemes of the double-nozzle injector, namely the various injection directions, injection angles, and nozzle spacings. After comparing various jet schemes, it is found that the optimal jet scheme for the double-nozzle strut is to set the angle of 60° for the inward injection direction and the nozzle spacing of 3 mm. Furthermore, the mixing efficiency of the optimal jet scheme is investigated at different Mach numbers. The current research focuses on the mixing mechanism of air and hydrogen by analyzing the flow structures in the strut's wake region. It is observed that the double-nozzle configuration increases the number of vortexes behind the strut and creates a recirculation zone between the two jet streams. The mixing efficiency of the scramjet combustor improves significantly with an increase in the injection angle, but the spacing and direction of the double-nozzle have little effect on the mixing efficiency. It is found that the additional total pressure loss generated by the double-nozzle configuration can be negligible. In addition, the results show that the mixing efficiency of the optimal jet scheme for the double-nozzle is improved more significantly at low Mach numbers (e.g., Ma = 2 and 3).

Features of the calculation of air leaks through the mined-out space of coal mines

The movement of air leaks through the goaf of coal mines can lead to gas contamination of workings with the formation of local and layer accumulations of methane. This increases the likelihood of explosive situations. Therefore, an important factor is the ventilation scheme used in the excavation area. The process of gas flow through a goaf is an understudied issue. This is due to the difficulty of conducting direct measurements inside the object under study. In many works, when studying the movement of air leaks through the mined-out space, the linear Darcy filtration law is used. However, the influence of inertia forces can lead to additional gas pressure losses and, accordingly, to deviations from the classical law. Therefore, it is advisable to use the law of two-term filtration. The purpose of the work is to study the patterns of movement of air leaks through the mined-out space, taking into account its filtration parameters and the current ventilation scheme. The article presents the results of calculating the speeds of air leaks and the trajectories of streamlines in the mined-out space with direct-flow and return ventilation schemes. The Darcy formula and the Forchheimer formula were used in the calculations. It has been established that with a two-term filtration law, the values of the result-ing air leakage rates are less than with a linear law. This is due to pressure losses as a result of inertial forces. It has been established that with a direct-flow ventilation scheme, the rates of air leakage in the longwall increase exponentially along the goaf boundary in the direction of the ventilation flow and quadratic ally increase deep into the goaf to a certain maximum located at a distance of about half the length of the longwall. At the same time, in the case of the return-flow ventilation scheme, the rates of air leaks in the longwall have maxima at the boundary of the goaf and decrease linearly towards the center of the longwall, and in the goaf at a distance of up to three meters from the longwall, their quadratic decrease occurs. The results obtained make it possible to reduce the gas contamination of workings by choosing rational schemes and ventilation modes.

Rheological properties of wood polymer composites at high shear rates – Evaluation of additional pressure losses as a result of inlet effects

The study presents the results of rheological tests of wood polymer composites (WPC) on a polypropylene matrix. The influence of the filler on the additional pressure losses as a result of entrance effects has been analysed. The tests were carried out with the use of a capillary rheometer and a rheological head at the values of apparent share rate up to 101 860 s−1.The influence of the Bagley corrections on the apparent viscosity curve defined for the tested composites was determined. In the case of rheological tests at low shear rates, omit the additional pressure losses does not significantly affect the determined rheological properties. It was observed that with the increase of the filler content and shearing rate, the value of pressure losses significantly increases. It is necessary to consider the values of pressure losses in rheological measurements of rheological properties of WPC with the use of capillary rheometers.