Minimum Flow Rate Research Articles

The influence of workpiece speed on microhardness and residual stresses in vacuum-carburised 20MnCr5 steel using the single-piece flow method

To determine the impact of selected conditions of abrasive treatment on the value and distribution of microhardness and residual stresses in layers carburised by a continuous single-piece flow method. Reference pieces were low pressure carburised at 920°C and then heat-treated in a 4D Quench heat treatment chamber at a pressure of 7 bar and tempered at 190ºC for 3 hours. In the next stage, samples were ground at various vw piece speeds, introducing grinding fluid into the cutting zone using the WET spraying method or using the MQL method at a minimum flow rate. The distribution of microhardness and residual stresses generated in the technological outer layer of the pieces following heat and chemical treatment and the grinding process was measured. Results of the tests indicated that the vw piece speed and method used to supply cooling and lubricating fluid to the grinding zone had an impact on selected parameters of the technological outer layer of flat samples made of 20MnCr5 steel. The process of grinding using an electrocorundum grinding wheel results in a deterioration of residual stresses in the material. For each of the three analysed vw piece speeds, reduced changes in material microhardness prior to cutting occur in the outer layer of samples ground using GF supplied at a minimum flow rate using the MQL method. Environmental considerations and having to conform to increasingly stringent regulations related to environmental protection and employee safety motivate researchers and businesses to entirely eliminate or reduce the use of grinding fluids in the grinding process and, therefore, to optimise grinding technology. Modern manufacturing industry requires the grinding process, which follows heat and chemical treatment, to be performed with the highest possible efficiency. However, retaining high parameters of the technological outer layer in comparison to the sample material following vacuum carburisation (before grinding) is extremely difficult. An optimised configuration of parameters of the grinding process and method of supplying grinding fluids enables meeting the current and future high expectations of the industry in this regard. The tests have enabled us to determine the impact of the applied vw workpiece speed and method of supplying grinding fluid on microhardness and residual stresses. Generally speaking, grinding with an electrocorundum grinding wheel results in a deterioration of residual stresses. For both methods of supplying GF (WET and MQL), the distribution of microhardness in the material of the samples ground with the highest workpiece speed (18.0 m/min) indicated no significant differences with regard to the distribution of microhardness in the material of the samples following heat and chemical treatment.

CARD21: In Vitro Investigation Of The Timing Of The LVAD Pulsatility Event On Intraventricular Hemodynamics

Background: To reduce in-pump thrombosis and potentially improve left ventricular (LV) washout, pulsatility events (i.e., periodic LVAD speed modulation) have been introduced in 3rd generation LVADs. However, this pseudo-pulsatility of the centrifugal continuous flow pumps is not synchronized with native LV residual contractility. This study investigates the effect of timing of pulsatility events, with respect to LV pressure variations along the cardiac cycle, on intraventricular hemodynamics. Methods: Time-resolved stereo particle image velocimetry measurements were performed in a patient-derived quasirigid LV silicon model implanted with an LVAD. The residual LV contractility was modelled as a periodic variation in intraventricular pressure (IVP). Velocity fields in two orthogonal planes were measured for 7.5 cardiac cycles (including 3 occurrences of the pulsatility events, which happen every two seconds), for 3 LVAD speeds and 4 different synchronicities of pulsatility: at maximum/ minimum IVP and during increasing/decreasing IVP. Instantaneous measurements of the flowrate through the LVAD, with a time-resolution of 1 ms, were collected during the entire experiment. Ventricle stagnation index (VSI) was computed for each measurement plane and all experimental conditions studied. Results: Despite maintaining a constant average flowrate, the synchronicity of the LVAD pulsatility with the oscillatory IVP strongly influenced the flow rate waveforms, especially the peak and minimum instantaneous flow rates. A strong effect of the timing of pulsatility was also observed on intraventricular hemodynamics: pulsatility events taking place during decreasing IVP (diastole) resulted in higher VSI than other timing of pulsatility. Overall, these high resolution, instantaneous measurements of LVAD flow rate and pressure also highlighted the complex interrelations between LVAD speed, peripheral resistance, IVP and flow rate. Conclusion: This in vitro study elucidates the effect of LVAD pulsatility event synchronicity with the cardiac cycle on flowrate and LV flow patterns.

Reservoir Characterization of a Tight Gas Field Using New Modified Type Curves for Production Data Analysis—A Case Study from Ordos Basin

Using data from 56 tight gas wells from the study field (Y field) in the Ordos basin of China, this paper presents performance-based reservoir characterization of the study field from production data and geophysical data. Post-fracturing evaluation is realized by applying our new modified production decline type curves for fractured wells. Compared to traditional type curves, our newly proposed modified dimensionless type curves help identify field data diagnostics for various flow regimes of fractured wells and also facilitate the curve matching process with real data to obtain fruitful and crucial reservoir and fractured well information, including key parameters such as reservoir flowing capacity (kh), well productivity, fracture length, drainage area and original gas in place. This paper intends to promote the extensive application of this new technique. With the support of the reservoir information provided by production decline analysis using our modified type curves, the commercial flow units are delineated in terms of interrelated porosity-permeability of sandstone based on pore throat aperture crossplotting and corresponding flow unit productivity. Furthermore, two crossplots of well logging interpreted porosity versus resistivity are constructed, suggesting their good correlated relationships with relative flow unit productivity and initial gas abundance in place, respectively. The two crossplots enable qualitative evaluation of formation penetrated by well, which makes them very useful and practical as wireline logging is basically available for every well. The well production routine is also analyzed systematically by considering a well’s inflow performance, tubing performance and minimal liquid-carrying gas flow rate to investigate if a gas well is producing at optimal conditions or if a measure should be taken to improve the well’s production. Through analysis of the Y field, this study introduces an integrated workflow with the support of the new modified type curves to effectively help understand the reservoir characteristics and the flow behaviors of the tight gas field. The key takeaway from this study is that the new modified dimensionless production decline curves in terms of qDM vs. tDM can be applied in field practice to achieve a systematically comparable understanding of the performance of MHFHWs globally.

DETERMINATION OF THE MINIMUM GAS FLOW RATE REQUIRED FOR COMPLETE REMOVAL OF CONDENSATE FROM THE WELL IN GAS-CONDENSATE WELLS

The article provides a brief analysis of the determination of the minimum gas flow rate required for complete removal of condensate from the wellbore in gas condensate wells. In gas wells, water collects in the wellbore as a result of condensation of produced water and steamed water entering the wellbore together with the well product. In gas condensate wells, gas condensate from the formation is added to it. Thus, part of the filters of gas and gas condensate wells is filled with liquid, which ultimately reduces the flow rate of these wells. At the beginning of the development and operation of gas and gas condensate fields, the amount of liquid (water) and condensate in the gas is low, and due to high formation pressure in the first period of this field, raised to the surface. Over time, the velocity of the well product in the gas condensate wells gradually decreases, and as the amount of water and condensate entering the reservoir increases, the fluid accumulates in the well as the reservoir cannot be fully lifted by its own energy. This creates a counter-pressure on the bottom of the well and affects the formation, which closes with a liquid column in the filter section of the well, which significantly reduces the flow rate of the well, and in some cases leads to a complete shutdown of the well. Various methods have been developed and are still being used to prevent this and to ensure the efficient operation of gas and gas condensate. Keywords: layer waters, condensation, gas condensate, filter, layer pressure, well bottom.

Second law analysis on an elliptical twisted tube for a heat exchanger

This works presents a second law analysis on a heat exchanger tube configurated as circular smoot tube (CST), elliptical smooth tube (EST) and elliptical twisted tube (ETT) with different aspect ratios and pitch lengths. The ETTs were configurated with different aspect ratio (AR) of 1.5 and 2.0 and twist pitch length (PL) of 50, 100 and 200 mm. The hydraulic diameter was kept as constant for all cases, since the results are influenced by the change in hydraulic diameter. CFD analyzes were run to perform the second law analysis of the considered cases. The analyzes were carried out by considering that the thermo-physical properties of the water fluid change depending on the temperature. Besides, the analyzes were carried out under steady state condition and turbulent flow condition which corresponds to Reynolds number ranging from approximately 4000 to 27,000. The results are evaluated and discussed in terms of the thermal, the frictional and the total entropy generation, the Bejan number, the entropy generation number, the exergy destruction and the second law efficiency. It is resulted that the increase in AR and the decrease in PL for the ETTs show better the second law efficiency. As a result, in the case of ETT_AR=2.0_PL=50 at the minimum mass flow rate considered in the study, the highest second law efficiency is obtained as 0.45, which corresponds to a value greater than 80% in the case of CST.

Liquid cooling vs hybrid cooling for fast charging lithium-ion batteries: A comparative numerical study

Lithium-ion batteries (LIBs) rely on efficient thermal management systems for their safe and reliable operation. Issues like overheating of LIBs due to excessive heat generation, thermal runaway and thermal propagation are still a challenge for engineers. To address the challenge, numerous cooling methods viz. liquid cooling, air cooling, cooling using phase change materials (PCMs), hybrid cooling (i.e., combining liquid and PCM cooling), etc., have been proposed by different authors in the past. Though all the above methods are best suited for LIBs under normal charging/discharging operations, their suitability for cooling fast charging LIBs remains unexplored. In general, the heat generation and risks due to thermal runaway in LIBs are relatively more during fast charging than normal charging. As regards hybrid cooling employing PCMs, the method is yet to be benchmarked, as PCMs themselves suffer from low thermal conductivity issues that may affect their overall thermal performance. The present work is an attempt to address the above-stated aspects. Detailed 3D numerical simulations on three different design configurations (D1-D3) of a prismatic LIB module consisting of four 10 Ah batteries fast charged at 8C rate are reported herein. Two different cooling methods viz. (i) liquid cooling employing a dielectric liquid coolant (STO-50) and (ii) hybrid cooling combining liquid dielectric and a PCM (RT35) are investigated, and their performances compared. The results reveal interesting facts on the ability of liquid cooling (D2) over hybrid cooling (D3) for fast charging LIBs. Parametric studies show that the coolant flow direction (horizontal/vertical) and thermal conductivity of the PCM (kpcm) have a profound influence on the cooling obtained compared to PCM’s melting temperature (Tm) and latent heat (λ). It is concluded that PCM based hybrid cooling is not suitable for cooling LIBs under fast charging unless kpcm is enhanced to 1 W/mK or above. A minimum coolant flow rate of 2 lpm is needed to limit the battery temperatures to 40 °C or below for the module under fast charging conditions. An increase in PCMs latent heat from 160 to 200 kJ/kg has no significant influence on the cooling achieved.

Local heat exchanger network optimization of industrial coal-to-olefin process based on hot direct feed/discharge strategy

• Local HEN is optimized based on the proposed hot direct feed/discharge strategy. • The sensible heat replaces 6.0 MW provided by the latent heat of steam originally. • An increment of 3.09 M$/y can be achieved corresponding to 0.6 Mt/y olefins. Chemical process comprises multiple units that are linked together through process streams. Though it has the advantages of operation independence and flexibility, it will lead to considerable energy consumption and equipment investment. Existing studies have placed more stress on the heat integration and steam reduction for single unit. However, it is rarely optimized for the linking stream. In this study, local heat exchanger network was optimized based on the proposed hot direct feed/discharge strategy. On the whole, the heat integration consists of the integrations in the hot direct feed/discharge region and the downstream process. This strategy was capable of regulating the temperature distribution and improving the freedom of energy comprehensive optimization. The heat integration for downstream process was re-optimized under the principle of minimum steam consumption, where minimum steam flowrate was determined using the latent heat and the sensible heat of steam simultaneously. As revealed from the results, the optimal design decreased hot utility and cold utility by 32.24 MW and 29.14 MW. The steam condensate contributed 6.0 MW heat, which was provided by the latent heat of steam originally. Furthermore, as demonstrated from techno-economic analysis, an annual increment of 3.09 M$ benefit was achieved in a 0.6 Mt/y coal-to-olefins (CTO) process.

Buffer effect of turbine rim cavity on hot gas ingestion

The rotor disc in the gas turbine creates a pump effect that entrains the fluid near it to radially outward. The hot gas in the mainstream enters the stator–rotor wheel space to maintain mass balance, leading to gas ingestion. The mechanism of the gas ingestion, and the spoiling effect of purge flow on mainstream, and the formation and transform mechanism of the source and core fluid regions in rotor–stator system are revealed in this research. In addition, a radial–radial–axial clearance rim seal (RRACS) is proposed to form a new stator–stator cavity to buff the ingestion flow. Numerical results show that the minimum mass flow rate for seal of the RRACS is 15.76% of the standard axial clearance rim seal.

Removing cuttings from inclined and horizontal wells: Numerical analysis of the required drilling fluid rheology and flow rate

Inclined and horizontal wells are prone to the accumulation of drilling cuttings. Determination of the optimal drilling parameters that facilitate cuttings removal is a key problem. Existing experimental, theoretical and field-based empirical analyses of the hole cleaning problem have failed to fully reveal the processes of cuttings transport, settlement, and accumulation concerning drilling string rotation in large annuli with high-density non-Newtonian drilling fluids. In this study, a coupled computational fluid dynamics-discrete element method (CFD-DEM) simulation model of the interaction between cuttings and drilling fluid was established. This allows the influences of well inclination, drill pipe rotational rate, flow rate, fluid density, and rheological properties on hole cleaning efficiency to be analyzed. A multi-parameter correlation equation between wellbore cleaning efficiency and wellbore size, inclination angle, drill string eccentricity, drill string rotational speed, rate of penetration, cuttings size, flow rate, and fluid density was obtained using dimensional analysis and multivariate nonlinear regression of simulation data. Finally, with consideration of wellbore cleaning characteristics, formation pressure bearing capacity, and pump condition constraints, the proposed multi-parameter correlation model was used to provide optimal wellbore cleaning parameters. The cleaning efficiency of horizontal wells is lowest in the inclined section. Hole cleaning efficiency increases significantly with drill pipe rotational rate, flow rate, and 6 RPM Fann dial reading. The proposed model can correlate hole cleaning efficiency with the 6 RPM Fann dial reading of drilling fluid and flow rate. At a given hole cleaning efficiency, the required minimum flow rate decreases with increases in the 6 RPM Fann dial reading. Similarly, the required minimum 6 RPM Fann dial reading decreases with increases in flow rate. The models and design layout proposed in this paper provide a new approach to solving hole cleaning parameter design problems in highly inclined and horizontal wells.

Modeling the Semivariogram of Climatic Scenario around Rivers by Using Stream Network Mapping and Hydrological Indicator

Precipitation erosivity propels detrimental hydrological happenings with substantial eco-friendly and socio-economic influences. The conception of the precipitation-vegetation interface is very vital for implementing acclimatization and mitigation techniques for terrestrial bionetworks. Numerous investigations have reconnoitered the spatial correlation of precipitation-vegetation context along the season-precipitation quantity gradient. Here, comprehensive scrutiny of spatio-temporal patterns of climatology-vegetation response to seasonal variability incongruities in River Ikpoba, southern Nigeria, using principal component scrutiny (PCS), semivariogram, cross-validation statistics, spatial distribution mapping, and hydrological indicators for multi-source climatic datasets for pre-impact flow (1913–1966) and post-impact flow (1967–2022). PCS outcomes reveal seven PCs whose eigenvalues were greater than one were hauled out of the twenty-five variables. The River Ikpoba water quality variables displayed a moderately strong rate of spatial reliance, which made it possible to create the spatial distribution map for the carefully chosen water quality variables. Results from further scrutiny of the river Ikpoba flow duration curve show the highest flow rate value between 900–1000cms for the month of October. The post-impact flow's highest value was 65cms in 2008, whereas the pre-impact flow was 64cms. Likewise, 90 days’ minimum highest flow rate was 250cms, 30 days was 1180cms, 7 days was 105cms, and 1 day was 105cms. Whereas the maximum for 1 day was 7200cms, 3 days’ value was 6400cms and 7 days' was 4500cms. This indicates that as the day progressed, the flow rate was increasing for a consecutive 30 days at a low flow rate, but at 90 days it declined. As the day progresses, the values for the maximum value decrease. Doi: 10.28991/HEF-2022-03-01-02 Full Text: PDF

Influence of Peripherally Inserted Central Catheters With Proximal Valves on Red Blood Cell Hemolysis During Transfusion.

The aim of this study was to verify the occurrence of hemolysis after infusion of packed red blood cells (PRBCs) in 12 peripherally inserted central catheters (PICCs) with a proximal valve, according to size and infusion rate. This was an experimental in vitro study performed under laboratory-controlled conditions, and the sample was composed of 12 PICCs with proximal valves (3F and 4F catheter). Twelve type A+ aliquots from 10 PRBCs were analyzed preinfusion and postinfusion according to PICC size and infusion rate. Hemolysis markers, total hemoglobin (g/dL), hematocrit (%), free hemoglobin (g/dL), potassium (mmol/L), lactate dehydrogenase (U/L), and rate of hemolysis (%) were studied. Data were analyzed using analysis of variance and Bonferroni multiple comparison tests. After the infusions in 3F PICCs, an increase was seen in rate of hemolysis (P = .003) and free hemoglobin (P = .014), in addition to a reduction in total hemoglobin (P = .002), with significant influence of minimum and maximum flow rates on the rate of hemolysis. The study finding indicated that the smaller catheter size and the infusion rate influenced variations in some hemolysis markers, but the alterations observed in the hemolysis markers would not contraindicate the infusion of PRBCs by 3F and 4F PICCs with proximal valves.

Novel Operating Mode of a Fluidic Oscillator

Abstract Fluidic oscillators show promise for use in aerodynamic flow control applications, with many studies reporting oscillation frequencies in the 1–10 kHz range. Spyropoulos, “A Sonic Oscillator,” introduced a “sonic” oscillator whose oscillation frequency depends on the inlet flow rate. The purpose of this paper is to demonstrate the existence of a second mode of operation (mode II) for such an oscillator, with a separate physical mechanism to the traditional, flow rate-dependent mode (mode I). Mode II is shown to be a back-pressure-driven oscillation that is largely independent of flow rate once instigated. This is explained by a stationary wave formed along the outlet paths, and occurs when conditions on the degree of back pressure and the weakening of the Coandă attachment strength are met. For a fixed device geometry, the conditions reduce to a minimum flow rate threshold so that the combination of high flow rate and constant oscillation frequency could make mode II an attractive flow control solution in an industrial context where minimizing device size is often critical.

Finite Volume Method Modeling of Heat Transfer in Acoustic Enclosure for Machinery.

This paper deals with the problem of heat accumulation in acoustic enclosures. Increased noise levels at production sites or manufacturing lines force the application of acoustic enclosures. Effective noise reduction due to enclosures often comes with the additional thermal insulation of the device, which in many cases causes a strong increase in the device operation temperature. This paper presents the methodology of thermal phenomena numerical modeling based on the potential influence of acoustic enclosures on the increase in device operation temperature. The proposed model consists of an original acoustic enclosure concept design, and the numerical modeling is based on the computational fluid dynamics FVM (finite volume method) conducted in Ansys Fluent. The research comprised a set of simulations at different air flow rates of 52.5 m3/h, 105 m3/h, 210 m3/h and 420 m3/h at the enclosure inlet. The analysis carried out on the basis of flow paths and temperature distribution plots inside the enclosure led to the conclusion that the expected, analytically calculated minimum volumetric flow rate is not sufficient to effectively cool the investigated device to the required temperature of 26 °C, and higher air flow rates should be applied. Simulation results indicated that the numerical tools can be useful in the prediction of the heat exchange process, as well as in the selection of an appropriate source and location of cooling.

Generation of Ions from Aqueous Taylor Cones near the Minimum Flow Rate: "True Nanoelectrospray" without Narrow Capillary.

Generating ultrafine charged droplets using electrospray is crucial for attaining high ionization efficiency for mass spectrometry. The size of the precursor charged droplets depends on the spray flow rate, and conventional wisdom holds that an electrospray of a nL/min flow rate (nanoelectrospray) is only possible using narrow capillaries with an inner diameter of ∼1 μm or smaller. Here, the electrospray of aqueous solutions with high electric conductivities generated from a large off-line capillary of 0.4 mm i.d. has been performed using a high-pressure ion source. The electric discharge is avoided by operating the ion source at 2.5 bar gauge pressure. The highly stable Taylor cone can be tuned to a near-hydrostatic state that exhibits the "true nanoelectrospray" properties, i.e., high salt tolerance and minimal ion suppression. The Q1/2 scaling law describing the electrospray current I and flow rate Q is found to be valid down to the nanoflow regime under a condition that is free of electric discharge. For a given solution, the flow rate and the size of the initial droplets and ionization species can be controlled with the spray current as the indicator for the instantaneous flow rate without changing the emitter capillary of different sizes. In regard to the application, the nanoelectrospray with a large micropipette tip is easy to use, free of clogging when dealing with viscous and high-salt buffer solutions, and with reduced surface interaction with the emitter inner surface. An acquisition of very clean mass spectra of proteins from concentrated solutions of nonvolatile salts such as phosphate-buffered saline is demonstrated.

Application of palm oil mill waste to enhance biogas upgrading and hornwort cultivation

The potential of oil palm ash (OPA) to enhance H2S and CO2 removal from biogas by scrubbing with maturation pond effluent (MPE), and further the treatment of biogas scrubber effluent (BSE) by Ceratophyllum demersum L. (hornwort) cultivation were investigated in this study. The results show that OPA + MPE solution with pH 9.3 and alkalinity 7525 mg CaCO3/L was obtained with 0.7 kg/L OPA loading. A pilot scale scrubber was used to study the effects of absorbent flow rates of 60–210 L/h on upgrading to 300 L/h field biogas stream. At 210 L/h, the CO2 removal efficiencies were 33% and 53% for MPE and OPA + MPE, respectively. To approach 100% H2S removal efficiency, the minimum flow rates were 120 L/h for MPE and 90 L/h for OPA + MPE. 50–150 g wet weight of hornwort in 30 L diluted POME were loaded to investigate appropriate initial hornwort loading level for hornwort cultivation. The highest specific growth rate of 0.045 day−1 with biomass production of 3.8 g/day were obtained with a 50 g initial loading. Among the wastewaters (MPE, OPA + MPE, and BSE) treatment using hornwort cultivation, the highest 0.035 day−1 specific growth rate and 2.6 g/day biomass production of hornwort were obtained in diluted BSE cultivation, and in 3 weeks of cultivation. COD, nitrate, phosphate, and alkalinity decreased by 76%, 76%, 55%, and 5%, respectively. The Eco-Efficiency concept for palm oil mill waste utilization proposed in this study has a high potential for enhanced biogas upgrading by using OPA + MPE, and hornwort is a good candidate for BSE post-treatment integrated with biomass production.

Effect of flow rate on the performance of Biosand Filter

Lack of access to safe drinking water is an issue in some areas where centralized water treatment is not possible, the biosand filter (BSF) one of several such point-of-use technologies is available. This study was conducted in Côte d’Ivoire to evaluate the effect of flow rate on the performance of the BSF. Three biosand filter (BSF) built in Poly vinyl chloride was used to investigate the effect of three flow rates (1.95 L/d in BSF1; 3.9 L/d in BSF2 and 7.8 L/d in BSF3) for 91 days. Each BSF was filled with 15 cm of gravel, 90 cm of sand and 40 cm of supernatant water. Physical and chemical parameters were analyzed in raw water and filtered water with standards methods. The results showed that the percentage removal of TSS approximately the same for all filters. Ammonium concentrations ranged from 37 to 170 μg.L-1, 110 to 190 μg.L-1 and 150 to 278 μg.L-1 for filtered waters of BSF1, BSF2 and BSF3, respectively. Nitrite concentrations in filtered waters of BSF1 (2 - 33 μg.L-1) were less than those of BSF2 (5 - 45 μg.L-1) and BSF3 (7 - 49.5 μg.L-1). Nitrate concentrations in filtered waters of BSF2 (1.9 to 4 mg.L-1) and BSF3 (1.6 to 4.2 mg.L-1) were higher than those of BSF1 (0.6 to 2.3 mg.L-1). Chemical Oxygen Demand removal efficiency for BSF3 (68.2 ± 9.5%) was lower compared to BSF2 (82.6 ± 3.8%) and BSF1 (93.7 ± 2.8%). The flow rate has an influence only on the removal of ammonium, nitrite, nitrate and Chemical Oxygen Demand. The best treatment results were obtained with the minimum flow rate (1.95 L/d).

On the hydrodynamic focusing for producing microemulsions via tip streaming

In this work we study experimentally and numerically the stability of hydrodynamic focusing to produce microemulsions. The jetting regime was produced experimentally for the lowest outer viscosity, while microdripping was obtained for the highest outer viscosity. The liquid ejection for small capillary numbers stabilizes as the distance between the feeding capillary and the focusing orifice decreases. The comparison between confined selective withdrawal and stretched flow focusing for the largest outer viscosity shows that confined selective withdrawal significantly enhances the stability of the microdripping mode, which entails a significant reduction of the minimum value of the droplet diameter. When surfactants are dissolved in the inner liquid at sufficiently large concentrations, we observe a significant decrease in both the minimum flow rate leading to tip streaming and the droplet diameter. The surfactant monolayer stabilizes the meniscus and promotes the transition from microdripping to jetting. The global stability analysis shows that jetting via tip streaming becomes unstable due to the growth of an oscillatory perturbation. The unstable perturbation affects the tapering meniscus for the lowest outer viscosity, which explains why the meniscus oscillates in the experiments. The critical flow rate ratio is accurately predicted by the global stability analysis in most of the experiments with the lowest outer viscosity. For the highest outer viscosity, the global stability analysis correctly predicts the microdripping mode and allows one to calculate the droplet emission frequency in that mode.

Оценка пропуска минимальных расходов воды сооружениями дюкерного типа мелиоративных систем

Issues related to the design and hydraulic calculation of the transit part of a closed tubular water supply structure of the siphon type is considered. The operating conditions of the siphon with rectangular pipes in the transition mode are evaluated, in which the entrance section of the pipes of the culvert structure experiences increased hydrodynamic loads, often leading to certain destructions. The siphon design was modeled with two breaks along the length with a smooth inlet head and without a head. During the experiments, the absence of infl uence of the inlet head of the tubular HTS on the length of the free-flow section was noted. It has been established that the conditions of formation and features of the hydraulic operation of the siphon in the transient mode are largely determined by its design features. With the flooding of the inlet head, the flow of air into the pipe is hindered and a transition mode of the second type is formed with a slight fluctuation of the water level in the upper pool. The dependence of the location of the point of separation of the flow with a decrease in the passing water flow rate on its value is revealed, which made it possible to obtain a graph of the dependence of the relative length of the non-pressure end section on the square root of the Froude number. A comparison was made with the results of studies by other authors, which showed an increase in the relative length in tubular HTS of the siphon type in sections with reverse slopes at the same Froude numbers. Recommendations are given on the methodology for carrying out hydraulic calculation of tubular structures of the siphon type with minimal flow rates.

Experimental Study on Cooling Efficiency of Hypersonic Optical Window

The cooling effectiveness of optical window influences the imaging quality of hypersonic vehicles. This study focuses on the supersonic film cooling efficiency on the optical window of a blunt cone in hypersonic flow. The experiments were conducted in a gun tunnel equipped with a Mach 8 nozzle providing a total pressure and temperature of 9 MPa and 900 K respectively. Three tangential 2D nozzles with different combinations of slot heights and Mach numbers were designed to detect the film cooling length under different injection pressures. The heat flux on window surface was measured by Thin Film Gauges and the flow field was monitored by schlieren technique. When the jet pressure matched the mainstream, the window was completely cooled, and the minimum mass flow rate was achieved when the slot height was 5mm and the jet Mach number was 2.5. If the pressure ratio of jet continues to increase, the heat flux density could be furtherly reduced, but the cooling efficiency of unit coolant mass flow decreased significantly. The data correlation results showed that the cooling efficiency presented a nonlinear relationship of second order polynomial with (x/Sh)λ-0.8 , and the effective cooling length of film was positively correlated with the cooling mass flow ratio (λ) and slot height of the nozzle. Besides, the increase of jet pressure resulted in thickening the mixing layer, which enhanced the heat insulation effect and reduced the heat flux as a result.

On the Minimum and Maximum Flowrate of Electrospraying: A Practical Approach, Based on Fundamentals, for Design Purposes

On the Minimum and Maximum Flowrate of Electrospraying: A Practical Approach, Based on Fundamentals, for Design Purposes