Jet Surface Research Articles

Two-dimensional transient heat transfer model of moving quenching jet based on machine learning

The heat transfer model plays a significant role in improving the steel quality during quench cooling by water jet impingement. However, the available models are still incapable of accurately modeling the heat transfer process. In this work, we perform the multiple impingements of jet on high-temperature steel plate surface experimentally and reveal the effects of surface temperatures, jet velocity, moving speed, and equalization time on the heat transfer behaviors. Then, we propose a time-constrained surface heat flux calculation method to measure the transient heat flux more accurately. Even in the case of lower temperature measurement frequency and larger heat conduction delay, precise calculation results can also be predicted. Importantly, a machine learning method is employed to fit and analyze a large number of experimental data, the machine learning model can predict two-dimensional (2D) transient heat flux in the moving cooling process and the accuracy can be continuously reinforced with the increase of experimental data. Based on the well-trained machine learning model, a heat flux prediction software is developed and open access at GitHub. This work provides an accurate heat transfer model for numerical analysis and shows great application potential in the steel industry, and the results will help deepen the understanding of the heat transfer mechanism.

Effects of surface texturing and laminar plasma jet surface hardening on the tribological behaviors of GCr15 bearing steel

Surface texturing (ST) and laminar plasma jet (LPJ) surface hardening were applied to GCr15 bearing steel to improve its wear resistance. Ball-on-disk reciprocating tests were then conducted under dry and oil-lubricated conditions to investigate the tribological behaviors. Morphology and evolution of the frictional interfaces were analyzed by SEM images to reveal the anti-wear mechanism. Results show that LPJ surface hardening can remarkably reduce the wear of GCr15 bearing steel by increasing surface hardness and thus decreasing the actual contact. Whether ST can improve the wear of GCr15 bearing steel mainly depends on the evolutions of frictional interface and wear mechanisms, namely the competitive relationship of stress concentration with trap effect or hydrodynamic pressure effect under dry friction or oil-lubricated condition.

Characteristics of instantaneous flow structures of the surface jet over a submerged weir

This paper presents the results of a LES of turbulent surface jets over a submerged weir. The mean flow and turbulent structures are presented for both flat and deformed bed conditions. LES results with the scour hole reveal that the separated shear layer is extended by about three times, locating the reattachment point further downstream. In addition, the presence of the scour hole increases both total and maximum TKE and decreases near-bed TKE. Quantitatively, with the scour hole, the maximum near-bed TKE is decreased by 50%. It turns out that the area of high instantaneous bed shear stress does not match with that of high time-averaged bed shear stress, but does match well with that of the high near-bed TKE. The vortices generated by the weir propagate differently with and without the scour hole and shed light on the generating mechanism of a scour hole.

EXPERIMENTAL STUDIES OF OPERABILITY OF HARDENED CUTTING EDGES OF PARTS

The operability of machine and tool parts is often determined by the state of the working surface. It is on the surface that cracks arise, wear and corrosion processes begin. The presence of defects, the degree and depth of hardening, the level of residual internal stresses, the structure, the nature of the transition to the base material, most often determine the reliability and service life of parts and structures. Based on a critical review of hardening methods, it was found that one of the promising ones is the effect on the treated surface of a plasma jet of different power density. To ensure wear resistance of the working edges, the surface was treated with low-temperature plasma at an indirect arc plasmatron installation. The work investigated the phase and structural transformations after plasma coating on model samples of steel 65G, studied the structure and built microhardness profiles. Optimal parameters of plasma processing of articles are determined: distance from plasmatron - 30 mm, rotation speed - 10 s-1, heating time - 10 s. The established optimal modes of hardening treatment were used for plasma hardening using the example of an instrument (spiral drills made of steel grades R6M5, R6AM5 and 11R3AM3F2) under production conditions. For all types of drills, it was possible to obtain a hardened layer of 1-1.5 mm deep from the surface. According to the results of metallographic analysis, the microstructure of the hardened layer contained a white, non-etchable in acids zone with a high microhardness of up to 12000 MPa, the depth of which reached up to 0.4 mm; then there was a structure consisting of martensite and residual austenite with a microhardness of up to 9000 MPa. Tests of experimental drills for resistance, carried out in production conditions, showed an increase in their resource by 2 times compared to a tool that did not undergo plasma hardening, confirmed the possibility of multiple regrind within the hardened layer.

Investigation of the Structure of Waves Generated by a $\delta$-perturbation of the Surface of a Capillary Jet

The wave capillary flow of the surface of an inviscid capillary jet, initiated by a single $\delta$-perturbation of its surface, is studied. It is shown that the wave pattern has a complex structure. The perturbation generates both fast traveling damped waves and a structure of nonpropagating exponentially growing waves. The structure of self-similar traveling waves is investigated. It is shown that there are three independent families of such self-similar solutions. The characteristics of the structure of nonpropagating exponentially growing waves are calculated. The characteristic time of formation of such a structure is determined.

Water jet impingement onto a hot steel plate

The research studies the interaction between subcooled small diameter water jet and thick steel heater at different surface temperatures, liquid velocities and jet angles. Although the heater surface temperature exceeded the Leidenfrost temperature and reached 340oC, the liquid, according to visual observations, wetted the surface. Geometrical characteristics of the heater surface wetted area and jet deflection angles were measured. It was hypothesised that jet deflection from the surface, accompanied by finely dispersed drops generation, occurs when thermal boundary layer, which develops in the liquid near the heater surface, reaches the liquid's outer surface. The preliminary measurements seem to confirm the hypothesis Keywords: Free-surface jet, quenching, jet impingement boiling, liquid film, Leidenfrost temperature.

Вскипание жидкой пленки при столкновении водяной струи с нагретой стальной поверхностью

The research studies the interaction between subcooled small diameter water jet and thick steel heater at different surface temperatures, liquid velocities and jet angles. Although the heater surface temperature exceeded the Leidenfrost temperature and reached 340℃, the liquid, according to visual observations, wetted the surface. Geometrical characteristics of the heater surface wetted area and jet deflection angles were measured. It was hypothesised that jet deflection from the surface, accompanied by finely dispersed drops generation, occurs when thermal boundary layer, which develops in the liquid near the heater surface, reaches the liquid's outer surface. The preliminary measurements seem to confirm the hypothesis.

Analytical Models for Determining the Propagation of Rectangular Surface Jets for Fishway Attraction Flow

The present paper evaluates suitability of two analytical models to determine the propagation of rectangular surface jets as a tool to design fishway attraction flow. It focuses on rectangular orifices of vertical slot fishways with aspect ratios (width-to-height) for W/H < 1. Both models were rewritten to match boundary conditions for fishways because they were initially derived for horizontal orifices. As the basis for the evaluation, the output of the analytical models to RANS simulations for 12 geometries 1/16 <= W/H <= 4 is compared. Applied analytical equations for half-lengths for cases W/H >= 4 are within 5 % of RANS modeling results for all cases. The location of centerline transition locations from analytical models also agree reasonably well with RANS modeling. The findings support efficient design of optimum attraction flow propagation using simple, rapid analytical approaches.

EVALUATION OF THE BOTTOM SURFACE WATER JET IMPINGEMENT COOLING RATE USING MODIFIED RUN-OUT TABLE

Evaluation of Temperature-Time Profiles by the Lumped Thermal Mass analysis method for bottom surface jet impingement cooling system was carried out. This was done by controlled accelerated cooling using a modified run-out table (ROT). The evaluation was with variant pipe diameters of 10mm - 40mm by a single water jet, having impingement gaps in the range of 55mm - 95mm and controlled sub-cooled to a range of 150oC – 110oC. The results revealed that the cooling rate was faster at an impingement gap of 95mm in all the pipe diameters. This was evident from the plot of temperature-time, with a gap of 95mm showing 1.93oC/s and 3.24oC/s at diameters of 10mm and 40mm respectively. This evidently revealed that at any given pipe diameter the cooling rate is higher at a higher impingement gap for bottom surface controlled cooling. This is also suggested by the calculated heat transfer coefficient that shows an increase with the increase in pipe diameter and impingement gap for an increase in cooling rate. Therefore, for bottom surface jet impingement cooling, a higher impingement gap for any pipe diameter will give a better cooling rate for the steel austempering process.

Early-winter North Atlantic low-level jet latitude biases in climate models: implications for simulated regional atmosphere-ocean linkages

Climate model biases in the North Atlantic (NA) low-level tropospheric westerly jet are a major impediment to reliably representing variability of the NA climate system and its wider influence, in particular over western Europe. A major aspect of the biases is the occurrence of a prominent early-winter equatorward jet bias in Coupled Model Inter-comparison Project Phase 5 (CMIP5) models that has implications for NA atmosphere-ocean coupling. Here we assess whether this bias is reduced in the new CMIP6 models and assess implications for model representation of NA atmosphere-ocean linkages, in particular over the sub-polar gyre (SPG) region. Historical simulations from the CMIP5 and CMIP6 model datasets were compared against reanalysis data over the period 1861–2005. The results show that the early-winter equatorward bias remains present in CMIP6 models, although with an approximately one-fifth reduction compared to CMIP5. The equatorward bias is mainly associated with a weaker-than-observed frequency of poleward excursions of the jet to its northern position. A potential explanation is provided through the identification of a strong link between NA jet latitude bias and systematically too-weak model-simulated low-level baroclinicity over eastern North America in early-winter. CMIP models with larger equatorward jet biases exhibit weaker correlations between temporal variability in speed of the jet and sea surface conditions (sea surface temperatures and turbulent heat fluxes) over the SPG. The results imply that the early-winter equatorward bias in jet latitude in CMIP models could partially explain other known biases, such as the weaker-than-observed seasonal-decadal predictability of the NA climate system.

Influence of Orography Upon Summertime Low‐Level Jet Dust Emission in the Central and Western Sahara

AbstractLow‐level jets (LLJs) drive frequent emission of mineral dust in the central and western Sahara in boreal summer. A major hotspot for this process is central Algeria, northern Mali and Mauritania, through which blow the dry near‐surface northeasterly Harmattan winds, with a peak in dust emission around the low‐lying Tidihelt region. North African orography is thought to contribute to the strength of the LLJ over the Bodele dust source in Chad, but its influence on erosivity over summertime source regions remains unquantified. In this paper, the contribution of central Saharan orography to the strength of Harmattan LLJs and associated dust emission frequency is tested. An idealized simulation with flattened Hoggar mountains is compared with a control using the Met Office Unified Model at 12 km horizontal resolution. In the absence of the Hoggar mountains, dust emission frequency estimated using an empirical relationship with surface wind speeds is found to decline across the entire northeasterly “LLJ alley,” including by 31% in the Tidihelt where composited jet surface winds drop from 9.0 to 7.3 m s−1 under a more easterly regime. The mountains are linked to a low‐level leeward geopotential height perturbation, with a northern limb reinforcing northeasterlies through the Tidihelt. Dome‐shaped elevated heating situated over the Hoggar mountains explains the difference between the simulated wind fields in the two experiments. These findings suggest that central Saharan orography plays an important role in sustaining erosive dusty conditions during boreal summer.

Improving surface wettability and adhesion property of polytetrafluoroethylene by atmospheric-pressure ammonia water-mixed plasma treatment

Polytetrafluoroethylene (PTFE) has excellent properties and has been widely used in various fields. However, the PTFE surfaces have relatively poor wettability and adhesive property, which restrains their widespread applications. Although atmospheric-pressure plasma jets have been employed to treat the PTFE surfaces, hydrophilization effect and processing efficiency still need to be further improved. In this paper, we propose to add ammonia water into the working gas of the atmospheric-pressure plasma jets to better modify the PTFE surfaces. The influences of ammonia water contents on surface wettability and adhesive property of the PTFE surfaces were investigated by water contact angle (WCA) measurement and peel strength experiments, respectively. When the ammonia water-mixed ratio was 1%, a WCA of ∼19° was obtained after 120 s plasma treatment, which was much lower than that treated by pure helium plasma jet (∼29°) and untreated surface (∼101°). In addition, the adhesive property was also well improved by the ammonia water-mixed plasma jets: peel strength of the sample treated by the ammonia water-mixed plasma jet was respectively 119 N/m and 446 N/m larger than that of the sample treated by pure helium plasma jet and the untreated sample.

Numerical Investigation of a Rectangular Jet Exhausting over a Flat Plate with Periodic Surface Deformations at the Trailing Edge

Multiple competing factors are forcing aircraft designers to reconsider the underwing engine pod configuration typically seen on most modern commercial aircraft. One notable concern is increasing environmental regulations on noise emitted by aircraft. In an attempt to satisfy these constraints while maintaining or improving vehicle performance, engineers have been experimenting with some innovative aircraft designs which place the engines above the wings or embedded in the fuselage. In one configuration, a blended wing concept vehicle utilizes rectangular jet exhaust ports exiting from above the wing ahead of the trailing edge. While intuitively one would think that this design would reduce the noise levels transmitted to the ground due to the shielding provided by the wing, experimental studies have shown that this design can actually increase noise levels due to interactions of the jet exhaust with the aft wing surface and flat trailing edge. In this work, we take another look at this rectangular exhaust port configuration with some notional modifications to the geometry of the trailing edge to determine if the emitted noise levels due to jet interactions can be reduced with respect to a baseline configuration. We consider various horizontal and vertical offsets of the jet exit with respect to a flat plate standing in for the aft wing surface. We then introduce a series of sinusoidal deformations to the trailing edge of the plate of varying amplitude and wave number. Our results show that the emitted sound levels due to the jet–surface interactions can be significantly altered by the proposed geometry modifications. While sound levels remained fairly consistent over many configurations, there were some that showed both increased and decreased sound levels in specific directions. We present results here for the simulated configurations which showed the greatest decrease in overall sound levels with respect to the baseline. These results provide strong indications that such geometry modifications can potentially be tailored to optimize for further reductions in sound levels.

Rapid surface preparation for three-dimensional characterization of defect and microstructure of metal additive manufacturing using electrochemical jet

Process-induced volume defects and unsuitable microstructure have inhibited the effective quality assurance of parts manufactured by selective laser melting (SLM). Elucidating the complex interaction between the process, defect/microstructure, and performance is of critical importance. In this work, we have developed and demonstrated the capabilities of an electrochemical jet surface processing (EJSP) method to easily and effectively uncover defects and unveil the crystal microstructure and fusion mechanism in SLM parts of SUS316L and AlSi10Mg respectively. Experiments show that the EJSP method is highly effective in localized three-dimensional microstructural unveiling which eliminates the need for conventional sample preparation by polishing, and internal defects and retained fusion signatures at multiple layers are readily identified within seconds. Furthermore, EJSP unveils three-dimensional structural information at both micro- and nano-scale to facilitate crystallography and phase analysis. This unique approach has high potential to significantly improve qualification methods of SLM parts, which benefits in-depth research of microstructure characteristics and their formation mechanism in the SLM process with high efficiency and low cost.

Study of the salinity and pH dilution pattern of discharged brine of the Konarak desalination plant into the Chabahar bay: a case study

This research aims to study the salinity and pH dilution pattern of discharged brine of the Konarak desalination plant into the Chabahar bay, their relation on coastal environment, and type of its brine discharge. Due to the shallow water depth of the coast and type of brine discharge, evaluating the salinity and pH was done with a sampling of surface seawater. The type of brine disposal is a direct surface discharge of negatively buoyant flow in the coastal environment of Chabahar bay. The brine discharge mechanism is a shore-attached surface jet, which is most likely influenced by the cross-flow deflection, dynamic shoreline interaction, and more minor by bottom attachment factors. The laboratory simulations using actual brine and seawater and either satellite pictures support the finding dilution pattern. The zone of initial dilution is under 50 m which, in the long run, can affect the quality of water of intake seawater pool of the plant.

Hydraulic characteristics of countercurrent jets on adverse-sloped beds

Abstract The counter-current jet (CCJ) acts like a reverse surface jet layer covering the free jump surface and has potential applications in the energy dissipation of hydraulic engineering. The present study investigated the hydraulic characteristics of CCJs on adverse-sloped beds. The results showed that, compared to the horizontal bed, the slope didn't increase the energy dissipation rate of CCJ but reduced the return flow length and upstream depth. The velocity distribution along the depth was divided into the boundary layer region, mixing region, and reverse surface jet region. The velocity distribution in the boundary layer region and the mixing region was similar to the classical wall jet. The jet Froude number and the bed slope had no significant effect on the turbulence intensity distribution and turbulence kinetic energy (TKE) distribution of CCJ. The distribution of TKE was similar to that of a submerged jump. The maximum absolute turbulence intensity appeared at exactly half of the maximum velocity. The maximum TKE appeared at the mixing region. Besides, empirical formulas for estimating length scales and maximum velocity attenuation are proposed. The results could provide a reference for the potential application of CCJ in energy dissipation in hydraulic engineering.

Surface coating on aluminum substrate with polymeric guanidine derivative to protect jet fuel tanks from microbial contamination

Antimicrobial coatings can act as an effective barrier to microbial growth and colonization in jet fuel tanks, which can effectively avoid the safety problems and economic losses. In this study, we initially synthesized an antimicrobial and water-insoluble complex, poly (hexamethylene guanidine) hydrochloride-sodium stearate (PHMG-SS), and its minimum inhibitory concentrations (MICs) were measured as 0.25 g/L, 0.25 g/L, 0.25 g/Land 0.5 g/L against Escherichia coli , Staphylococcus aureus , Bacillus subtilis and Yarrowia lipolytica , respectively; then, PHMG-SS was facilely coated onto the surface of aluminum substrate by the aid of a green linker, polyvinyl butyral (PVB). The PHMG-SS-coated aluminum exhibited a powerful microbicidal activity against the above four microorganisms , and provided a greater than 99.999% (5 log) reduction in viable counts of experimental microorganisms within 30 min through contact. In addition, the antimicrobial performance could still be observed after 7 d of ultraviolet radiation or soaking in jet fuel. Furthermore, the antimicrobial mechanism was investigated and concluded as damaging the microbicidal morphologies and suppressing the activity of respiratory chain dehydrogenase . Finally, PHMG-SS-coated aluminum was evaluated as interior surface of jet fuel tanks to protect jet fuel, and the experimental results showed that PHMG-SS-coated aluminum achieved a greater than 99.9999% (6 log) reduction in viable counts of a mixed suspension of Escherichia coli , Staphylococcus aureus , Bacillus subtilis and Yarrowia lipolytica within 30 min. The outputs from this work represent a highly versatile approach to build an antimicrobial barrier to protect jet fuel from microbial contamination, and such approach is also worthy of wide application to treat other surfaces. • The antimicrobial coating and the coating technology were environmental-friendly and could be applied on a large scale. • The developed antimicrobial coating exhibited desirable biocidal efficacy without detectable PHMG leaching. • The antimicrobial aluminum sheet could quickly kill the mixed microorganisms and exhibited desirable UV resistance. • The antimicrobial aluminum sheet showed the potential to protect jet fuel tanks from microbial contamination.

Systematic Safety Evaluation of Cold Plasma-Activated Liquid in Rabbits

Plasma-activated liquid (PAL) can effectively and selectively kill various types of cancer cells both in superficial and deeper tumors. As a promising novel approach to oncotherapy, the safety of PAL is essential in the clinic but has not been thoroughly assessed. In myeloma and blood tumors, the pathogenesis is in the bone marrow cavity. We have therefore evaluated the safety of PAL in New Zealand rabbits by intra-bone marrow injection, and provide a basis of further clinical research and application of PALs. In this study, both a plasma jet and plasma surface were used to treat saline solution, phosphate-buffered solution, and cell culture medium, to produce PAL. Then, oscillograms and optical emission spectra were evaluated to characterize the plasma discharge. Acute toxicity tests and safety evaluation studies were conducted by intra-bone marrow injection of PAL into New Zealand rabbits, while control rabbits received saline only. Body weight, vital organ coefficient, organ appearance, organ histopathology, blood cell and hemoglobin parameters, and blood biochemical indicators were tested on the 30th day after injection. We found that there was no mortality or loss of mobility throughout the experimental period. Acute toxicity tests showed that there were no PAL-related side effects in rabbits receiving the maximum dose of 700 μL PAL. PAL treatments did not affect body weight, organ coefficient, organ appearance, organ histopathology, or blood biochemical indicators. However, the percentage of lymphocytes decreased while the percentage of neutrophil granulocytes increased compared with the control group. In summary, our results indicate that PAL can be safely injected into bone marrow of New Zealand rabbits without significant toxicity.

Numerical Optimization of Drying Energy Consumption from Multiple Jets Impinging on a Moving Curved Surface

Due to the increasing energy cost, the efficiency of the industrial dryer as the energy-intensive processes should be improved. The designer should optimize the design parameters of industrial drying equipment to achieve the minimum drying energy consumption. SST k-ω turbulence model is used to simulate a real geometry for industrial drying applications. For the optimization of the impinging round jet, the specific drying energy consumption is set as the objective function to be minimized. The jet to surface distance, jet to jet spacing, jet inlet velocity, jet angle, and surface velocity are chosen as the design parameters. The SHERPA search algorithm is used to search for the optimal point from the weighted sum of all objectives method. One correlation is developed and validated for the specific drying energy consumption. It is found that the SST k-ω turbulence model succeeded with reasonable accuracy in reproducing the experimental results. The minimum specific energy consumption correlates with high values of the jet to jet spacing, jet angle, and surface velocity and low values of the nozzle to surface distance and jet inlet velocity. The agreement in the prediction of the specific drying energy consumption between the numerical simulation and correlation is found to be reasonable and all the data points deviate from the correlation by less than 7%.

Numerical investigation on noise reduction of rotor blade-vortex interaction using blade surface jet blowing

The effects of blade surface jet blowing on the reduction of rotor blade-vortex interaction (BVI) noise are investigated using the compressible Reynolds-averaged Navier-Stokes equations and the Ffowcs Williams-Hawkings equations. A detailed analysis of the accuracy of the Weighted Essentially Non-Oscillatory (WENO) scheme and Monotone Upstream-Centered Scheme for Conservation Laws for simulating the flow field and predicting the BVI noise is performed using a two-bladed scaled AH-1 helicopter main rotor undergoing BVI as the baseline case. Additionally, a grid convergence study is conducted. The BVI noise is accurately predicted using the fifth-order WENO scheme and high-resolution grid system (the prediction errors of the peak sound pressure are less than 4%). Surface boundary conditions are introduced to model the effect of jet blowing on the blade surface on the flow control of the baseline case. Blade surface blowing is analyzed near the trailing edge and the leading edge near the rotor tip. The results show that blowing near the blade trailing edge is effective for BVI mitigation by altering the tip vortex strength and increasing the blade-vortex miss distance. The sound pressure level is reduced by 2.6 dB, and the peak amplitude is attenuated by more than 30%, with a 9.8% loss in rotor thrust. Therefore, blowing near the trailing edge may be considered a promising approach for active BVI noise control.