Nozzle Heating Research Articles

Research on Adhesive Quality Control Based on Piezoelectric Dispensing Valve

Non-contact dispensing in the electronics packaging industry is becoming the most widespread dispensing method. The crucial research direction is to achieve accurate flow control for non-contact dispensing technology. However, the whole dispensing process contains fluid-solid coupling and its nonlinear and unstable flow, which makes it difficult to obtain an accurate prediction model for the quality of adhesive points. In this paper, based on the existing theory and the idea of minimum error backpropagation, we compare the experimental data with the theoretical value of adhesive point by subsequent experiments. Finally, a simple and effective adhesive point quality prediction model for non-Newtonian fluids in the dispensing process is obtained. The Taguchi method was used to prove that the maximum error between the predicted adhesive point quality and the experimental value is <10%, which is highly accurate. The Minitab software was used to analyze Taguchi's experimental data, and the sensitivity of dispensing quality to process parameters was ranked as follows: driving voltage > adhesive supply pressure > nozzle heating temperature; this study can be of guidance to the design of dispensing valve structure and dispensing process parameters, and to achieve high speed and high precision flow control.

A Simple Method for Generating Narrowly-dispersed Bioaerosols in Various Sizes

Biological warfare agents (BWAs) cause disease in humans, animals, and plants when purposefully dispersed in an area. To minimize contamination and personnel exposure and initiate early treatment, effective BWA detection or monitoring techniques are needed. Currently, bioaerosol detection or monitoring techniques are used for detecting BWA; however, these techniques have limitations, such as limited sensitivity. To improve the detection performance and develop novel techniques, an additional step in sample preparation, such as obtaining particles of various sizes, is needed. In this study, we investigated the simple and effective generation of bioaerosol particles using a custom-made inkjet aerosol generator (IJAG). Unlike previous inkjet aerosol generators, the operation conditions of the IJAG are fixed at a nozzle heating temperature of 140°C, a driver voltage of 150 V, a pulse width of 60 µs, and a frequency of 250 Hz. The only controlled factor was the concentration of bioaerosol models, including Bacillus globigii spores, ovalbumin, and polystyrene sphere latex. Our system generated bioaerosols with a diameter of 1–8 µm and a narrow distribution size. These results suggest that our IJAG system can achieve the simple and versatile generation of narrow-dispersed bioaerosols for a wide range of available materials. Our study can help improve the sensitivity of detection and monitoring systems for BWAs and bioaerosols.

Grey relational based Taguchi analysis on heat transfer performances of direct oil spray cooling system for electric vehicle driving motor

In the present study, the grey relational based Taguchi analysis is conducted to evaluate the effect of influential factors on heat transfer performances of direct oil spray cooling system for electric vehicle driving motor. The influence of spray flow characteristics considering three nozzle types of spiral, full-cone and hollow-cone, coolant temperature (CT), heating capacity (HC), flow rate (FR) and distance between nozzle spray and heating source (D) are evaluated on heat transfer performances of maximum temperature, temperature uniformity, maximum injection pressure, heat transfer coefficient, friction factor and Nusselt number. The Taguchi analysis evaluates the effect of influential factors in terms of mean, range, influence order, F-value and percentage contribution while the grey relational analysis evaluates the combined parameter of two performances in terms of grey relational grade (GRG). The decreasing influence order of factors is evaluated as FR>HC>CT>D with corresponding percentage contributions of 39.16%, 33.99%, 14.16% and 12.68% for GRG of heat transfer coefficient and spray power consumption and FR>HC>D>CT with corresponding percentage contributions of 86.02%, 7.98%, 3.54% and 2.46% for GRG of Nusselt number and friction factor. An efficient direct oil spray cooling system could be fabricated for electric vehicle driving motor based on qualitative and quantitative effects of various influential factors on its heat transfer performances.

Hydrogen Micro Jet Diffusion Combustion in a Coaxial Air Jet

In this paper the results of experimental studies of the combustion of a round microjet of hydrogen in a ring subsonic coaxial air jet are presented. It is shown that the combustion scenario for a subsonic hydrogen jet outflow is associated with the presence of a “bottleneck flame region” and nozzle heating, but the initial spherical shape of the flame region is transformed into a cylindrical one. It was found that the combustion of a round microjet of hydrogen in a satellite ring coaxial air jet at a supersonic outflow velocity is accompanied by the presence of supersonic cells.

АВТОМАТИЧНА СИСТЕМА БЕЗПЕРЕРВНОГО КОНТРОЛЮ СТАНУ НАСАДКИ ДОМЕННОГО ПОВІТРОНАГРІВАЧА

The analysis of the existing methods for assessing the hot blast stove state, in particular its checkerwork was carried out. Based on the existing methods, the task of creating an automatic control system of the hot blast stove checkerwork state was set. The main operational parameters of the hot blast stove affecting the efficiency of its operation were selected. The structure of an automatic continuous control system of the hot blast stove state was developed, which includescontinuous monitoring of the differential pressure in the nozzle, the casing temperature various levels, and the composition of the exhaust gases. Selected modern automation equipment. Using adatabase of the values of the main technological parameters of the operation of a real hot blast stoves block, a regression dependence was built, allowing to calculate the efficiency of each of thehot blast stoves. It was found that the regression dependence also shows the "direction" and the degree of influence of each operating parameter on the heat engineering efficiency of the hot blaststove. The calculation of the efficiency for each hot blast stove was performed. A comparative analysis of the calculated efficiency with technological efficiency was carried out. It was shown thatthe calculated value practically coincides with the technological value. With the possibility of obtaining regression dependences of the efficiency and nozzle resistance on the main parameters characterizing the nozzle and blast heating, in real time it is possible to predict the dynamics of the hot blast stove state or to simulate various modes of operation of the unit. According to the results of the research, it is arguable that the developed control system can be successfully implemented and used in the blast furnace process.

An Experimental Investigation into Nozzle Vane Heating to Prevent Erosion in the Last Stages of Steam Turbines

The paper is devoted to an experimental investigation of nozzle vane heating in the last stage of a wet steam turbine. The investigation was performed at a steam-dynamic test facility whose circuit was connected to an operating cogeneration power station (TETs). The working fluid was steam from a heat extraction assembly of a steam turbine. To prepare a polydisperse wet steam flow specific for the last stages of steam turbines, a three-stage wetting system based on feedwater injection into the flow was used. The object of investigation is a flat vane cascade consisting of hollow vanes. The vane cavities are fed with superheated steam to provide heating. Experimental data are presented demonstrating that it is advisable to heat nozzle vanes: first, the economic characteristics are improved, and, second, erosion of the blades in the last stages decreases. This method can be used as an alternative to the internal moisture separation from the steam path. The experimental investigation yielded the effect of the temperature difference between the main flow and the heating steam on the amount of heat transferred to the main flow and on the steam conditions at the outlet from the heating chamber. It was found that condensation in the heating chamber decreased its outlet pressure. This should be considered in designing a similar active system to control erosion of rotor blades. The measured profile losses of kinetic energy downstream of the vane cascade for different temperature difference values are presented. The kinematic characteristics of the liquid phase downstream of the vane trailing edge are determined. Large temperature differences are found to have a negative effect on droplets and can reduce the erosion resistance of the blades as compared with profiles without any active erosion control methods.

Diffusion Combustion of a Hydrogen Microjet at Variations of its Velocity Profile and Orientation of the Nozzle in the Field of Gravitation

ABSTRACTExperimental data on diffusion combustion of round hydrogen microjets with a parabolic and a “top-hat” mean velocity profiles at the nozzle exit at different spatial orientation of the microjets are reported. Most of all, we are interested in the behavior of the so-called «bottleneck flame region» of the jet and its contribution to the diffusion combustion. As is found, in the cases of the jet velocity opposite and orthogonal to the direction of the gravitational force, the main features of combustion are practically the same. Otherwise, at the velocity vector matching the direction of the gravitational force, the combustion characteristics become much different. Combustion in the «bottleneck flame region» is found to be more stable at the parabolic profile while the stability of combustion is reduced at the top-hat velocity distribution at the nozzle exit. Then, the flame detachment occurs in the absence of the «bottleneck flame region» and the microjet combustion is terminated at a much higher velocity. An inversion of the dependence l/d = f(U0) is observed at the transition from the parabolic to the top-hat velocity profile of the jet. The ratio of the «bottleneck flame region» size (l) to the nozzle exit diameter (d) is l/d. The nozzle heating is shown to have a profound effect on the microjet combustion.

Temperature-dependent dielectric and microwave absorption properties of silicon carbide fiber-reinforced oxide matrices composite

Simultaneous improvement of mechanical and microwave absorption properties of the composites at high temperatures still undergoes considerable challenges. We have investigated the high-temperature microwave absorbing properties of the silicon carbide fiber-reinforced oxide matrices (SiCf/mullite–SiO2) composite on the basis of our previous work. Results indicate that the complex permittivity increases from 8.19 − j5.09 to 16.39 − j9.83 at 10 GHz with the temperature rising from 200 to 600 °C. The SiCf/mullite–SiO2 composite has relatively high tanδ values indicating superior microwave attenuation ability. The reflection loss (RL) values of the composite increase with rising thickness. It can be noticed that the RL response curves of different thicknesses are basically consistent at 200 and 400 °C. In addition, the RL value of the composite is less than − 5 dB in the whole X band when the thickness is under 2.9 mm and the temperature is below 400 °C. The hybrid oxide matrices of mullite and SiO2 are beneficial to improve the dielectric properties, especially high-temperature microwave absorption properties of the SiC fiber-reinforced ceramic matrix composite. The superior microwave absorption properties indicate that the SiCf/mullite–SiO2 composite is a promising candidate in aircraft engine nozzle and aerodynamic heating parts of aircrafts at high temperatures.

Isothermal and heated subsonic jet noise using large eddy simulations on unstructured grids

Jet noise remains the major contributor to airplane noise at take-off. In the past half-century of research, sound generation mechanisms in supersonic jets have been extensively characterized, while the sound sources in subsonic jets are still to be clearly identified. For the last two decades, Large Eddy Simulations (LES) have become a major tool for investigating jet noise sources due to their ability to capture detailed information in turbulent flows and their moderate cost that allows industrial applications. However, many challenges still arise when dealing with complex nozzle geometries and heating effects in the jet core. In this paper, subsonic jets with or without nozzle geometry at Mach number of 0.9 and moderately high Reynolds numbers ranging from 2 × 105 to 1 × 106 are computed using LES, providing a base of validation for different nozzle configurations and operating conditions. In this work, the high-order unstructured LES solver AVBP is combined with Ffowcs Williams and Hawkings’ acoustic analogy on unstructured grids. The vortex pairing phenomenon is evidenced without properly triggering the turbulence in the jet at the nozzle exit. Hence, a non-geometrical tripping, where the firsts prism layers of the mesh at the nozzle wall are removed, is proposed and shown to be a successful method for triggering proper turbulence development in shear layers for the cases with nozzle. Moreover, it is more easily implemented because it does not require any geometrical modifications and it generates more natural turbulence than previous methods, leading the path to actual industrial dual-stream configurations. Both isothermal and heated jet flow cases are performed and validated with existing experimental data in terms of aerodynamics and acoustics, which demonstrates the capacity of an unstructured LES solver to correctly simulate both cold and heated jet noise phenomena.

Micronozzle Chocking under Diffusion Combustion of Hydrogen

The results of experimental investigations of the micronozzle-chocking phenomenon under diffusion combustion of a hydrogen microjet at a high outflow velocity in the case of ignition of hydrogen near the nozzle cut are presented. It is found that the cause of micronozzle chocking is the heating of the nozzle walls from the flame-neck region retained up to transonic velocities and preventing nozzle cooling and the passage of the hydrogen jet to the supersonic-flow velocity. It is shown that hydrogen ignition far from the nozzle cut with a developed hydrogen supersonic flow into the flooded space leads to the disappearance of the flameneck region, flame detachment from the nozzle cut, and, correspondingly, termination of the nozzle heating and the possibility of the microjet coming out at the supersonic-flow velocity for the hydrogen jet. It is established that the flame-neck region is a stabilizing factor for the subsonic combustion of a hydrogen microjet up to transonic velocities. In the second case, the presence of supersonic cells stabilizes the supersonic diffusion combustion of the hydrogen microjet.

Experimental study on diffusion combustion of high-speed hydrogen round microjets

Abstract Experimental data on the phenomenon of nozzle choking at diffusion combustion of a high-speed hydrogen microjet at its ignition close to the nozzle are presented. As is found, such a phenomenon is due to the nozzle heating by the «bottleneck flame region» which is generated at the origin of microjet. This flow region persists up to transonic velocities of the microjet preventing from cooling of the nozzle and the transition to supersonic speed. In the case of hydrogen ignition far from the nozzle exit in supersonic conditions, the «bottleneck flame region» is suppressed, the flame becomes detached from the nozzle which is no longer heated so that the supersonic range is attained. The subsonic combustion of hydrogen microjet is stabilized by the «bottleneck flame region» while the supersonic one becomes more stable at the generation of shock cells. The results of the present study provide new details on the combustion of hydrogen microjets and could by useful for the operation of different burners.

Effects of fuel inlet boundary condition on aromatic species formation in coflow diffusion flames

In a number of previous numerical studies, the fuel inlet velocity boundary conditions (BC) of coflow diffusion flames were specified at the exit of the fuel nozzle with a parabolic velocity profile. Such choices were based on the assumption that the flow inside the vertical fuel tube is fully developed and the buoyancy has negligible impact on the fuel flow at the nozzle exit. These assumptions, however, might not hold in practical experiments. This study demonstrates it is necessary to account for the effect of inlet BC location to accurately predict the nozzle exit velocity profile as well as the velocity, temperature profiles downstream, which are prerequisites for meaningful polycyclic aromatic hydrocarbon (PAH) and soot prediction in coflow diffusion flames. In particular, laboratory-scale laminar coflow diffusion flames at atmospheric pressure have been studied computationally with a focus on the effects of the fuel inlet velocity profile on PAH formation. Two sets of simulations were conducted which differ in the location specified for the fuel inlet boundary. In the first case, the fuel inlet boundary was specified at the nozzle exit while in the second case it was specified at a distance of 7 cm upstream of the nozzle exit. Parabolic velocity profiles were specified for both cases. In each set of simulations, flames with three different fuels (methane, ethylene and propane) were tested. Detailed high-temperature reaction mechanisms accounting for the formation of aromatic species were employed. The results showed that the fuel inlet BC location notably influence the predicted flow/temperature field and the resultant PAH concentration. Moreover, the effects become more notable with lower fuel stream velocities. It was also found that for propane with a density larger than air, recirculation zones were formed near the nozzle exit which exerted an additional influence on the flow development and temperature field as well as PAH formation. In addition, the effects of nozzle heating on flow development and PAH formation were also investigated.

Integrated 3D printing and corona poling process of PVDF piezoelectric films for pressure sensor application

This paper presents a novel process to fabricate piezoelectric films from polyvinylidene fluoride (PVDF) polymer using integrated fused deposition modeling (FDM) 3D printing and corona poling technique. Corona poling is one of many effective poling processes that has received attention to activate PVDF as a piezoelectric responsive material. The corona poling process occurs when a PVDF polymer is exposed to a high electric field created and controlled through an electrically charged needle and a grid electrode under heating environment. FDM 3D printing has seen extensive progress in fabricating thermoplastic materials and structures, including PVDF. However, post processing techniques such as poling is needed to align the dipoles in order to gain piezoelectric properties. To further simplify the piezoelectric sensors and structures fabrication process, this paper proposes an integrated 3D printing process with corona poling to fabricate piezoelectric PVDF sensors without post poling process. This proposed process, named ‘Integrated 3D Printing and Corona poling process’ (IPC), uses the 3D printer’s nozzle and heating bed as anode and cathode, respectively, to create poling electric fields in a controlled heating environment. The nozzle travels along the programmed path with fixed distance between nozzle tip and sample’s top surface. Simultaneously, the electric field between the nozzle and bottom heating pad promotes the alignment of dipole moment of PVDF molecular chains. The crystalline phase transformation and output current generated by printed samples under different electric fields in this process were characterized by a Fourier transform infrared spectroscopy and through fatigue load frame. It is demonstrated that piezoelectric PVDF films with enhanced β-phase percentage can be fabricated using the IPC process. In addition, mechanical properties of printed PVDF was investigated by tensile testing. It is expected to expand the use of additive manufacturing to fabricate piezoelectric PVDF-based devices for applications such as sensing and energy harvesting.

Using an energized oxygen micro-jet for improved graphene etching by focused electron beam

We report on an improved Focused Electron Beam Induced Etching (FEBIE) process, which exploits heated oxygen delivery via a continuous supersonic micro-jet resulting in faster graphene patterning and better etch feature definition. Positioning a micro-jet in close proximity to a graphene surface with minimal jet spreading due to a continuous regime of gas flow at the exit of the 10 μm inner diameter capillary allows for focused exposure of the surface to reactive oxygen at high mass flux and impingement energy of a supersonic gas stream localized to a small etching area exposed to electron beam. These unique benefits of focused supersonic oxygen delivery to the surface enable a dramatic increase in the etch rate of graphene with no parasitic carbon “halo” deposition due to secondary electrons from backscattered electrons (BSE) in the area surrounding the etched regions. Increase of jet temperature via local nozzle heating provides means for enhancing kinetic energy of impinging oxygen molecules, which further speed up the etch, thus minimizing the beam exposure time and required electron dose, before parasitic carbon film deposition due to BSE mediated decomposition of adsorbed hydrocarbon contaminants has a measurable impact on quality of graphene etched features. Interplay of different physical mechanisms underlying an oxygen micro-jet assisted FEBIE process is discussed with support from experimental observations.

3D Microporous Scaffolds Manufactured via Combination of Fused Filament Fabrication and Direct Laser Writing Ablation

A 3D printing fused filament fabrication (FFF) approach has been implemented for the creation of microstructures having an internal 3D microstructure geometry. These objects were produced without any sacrificial structures or additional support materials, just by precisely tuning the nozzle heating, fan cooling and translation velocity parameters. The manufactured microporous structures out of polylactic acid (PLA) had fully controllable porosity (20%–60%) and consisted of desired volume pores (~0.056 μm3). The prepared scaffolds showed biocompatibility and were suitable for the primary stem cell growth. In addition, direct laser writing (DLW) ablation was employed to modify the surfaces of the PLA structures, drill holes, as well as shape the outer geometries of the created objects. The proposed combination of FFF printing with DLW offers successful fabrication of 3D microporous structures with functionalization capabilities, such as the modification of surfaces, the generation of grooves and microholes and cutting out precisely shaped structures (micro-arrows, micro-gears). The produced structures could serve as biomedical templates for cell culturing, as well as biodegradable implants for tissue engineering. The additional micro-architecture is important in connection with the cell types used for the intention of cell growing. Moreover, we show that surface roughness can be modified at the nanoscale by immersion into an acetone bath, thus increasing the hydrophilicity. The approach is not limited to biomedical applications, it could be employed for the manufacturing of bioresorbable 3D microfluidic and micromechanic structures.

Fuel density effect on near nozzle flow field in small laminar coflow diffusion flames

Flow characteristics in small coflow diffusion flames were investigated with a particular focus on the near-nozzle region and on the buoyancy force exerted on fuels with densities lighter and heavier than air (methane, ethylene, propane, and n-butane). The flow-fields were visualized through the trajectories of seed particles. The particle image velocimetry technique was also adopted for quantitative velocity field measurements. The results showed that the buoyancy force exerted on the fuel as well as on burnt gas significantly distorted the near-nozzle flow-fields. In the fuels with densities heavier than air, recirculation zones were formed very close to the nozzle, emphasizing the importance of the relative density of the fuel to that of the air on the flow-field. Nozzle heating influenced the near-nozzle flow-field particularly among lighter fuels (methane and ethylene). Numerical simulations were also conducted, focusing specifically on the effect of specifying inlet boundary conditions for fuel. The results showed that a fuel inlet boundary with a fully developed velocity profile for cases with long tubes should be specified inside the fuel tube to permit satisfactory prediction of the flow-field. The calculated temperature fields also indicated the importance of the selection of the location of the inlet boundary, especially in testing various combustion models that include soot in small coflow diffusion flames.

Effect of the Control of Polymer Flow in the Vicinity of Spinning Nozzle on Mechanical Properties of Poly(ethylene terephthalate) Fibers

Abstract In the melt spinning of PET, effects of the variation of flow behavior in the vicinity of spinning nozzle on the mechanical properties of as-spun fibers and drawn fibers were investigated. The variation of flow behavior was introduced by the change of spinning nozzle diameter and by the irradiation of CO2 laser to the spin-line at a position immediately below the spinneret. The curve representing the correlation between strength and elongation at break of as-spun fibers shifted toward the upper-right direction by the applications of small diameter nozzle and laser irradiation, indicating that the toughness of as-spun fibers was improved. The two-stage continuous drawing of as-spun fibers with various draw ratios revealed that the correlation between strength and elongation of drawn fibers also shifted toward the upper-right direction by the application of small diameter nozzle and laser irradiation. In other words, improved toughness in the as-spun fibers was preserved in the drawn fibers. Accordingly, by the drawing of the as-spun fibers prepared by the combination of small-diameter nozzle and laser irradiation, high-strength and high-toughness PET fibers with the tensile strength of 1.68 GPa (12.1 cN/dtex) and the elongation at break of 9.1% was obtained. Numerical simulation of the melt spinning process incorporating the effects of nozzle diameter variation and laser irradiation heating indicated that the maximum Deborah number in the spin-line decreased by the applications of small diameter nozzle and laser irradiation heating. Accordingly, it was speculated that the variation of the state of molecular entanglement caused by the difference of polymer flow in the melt spinning process has significant effect on the mechanical properties of resultant fibers.

Steady-state N2O decomposition on Pt and Rh surfaces using a free-jet molecular-beam excited by nozzle heating

Steady‐state N2O decomposition reaction on polycrystalline Pt and Rh surfaces has been studied using a supersonic free‐jet molecular beam (2.1 × 1018 molecules/cm2 s). The energy of the incident N2O beam was controlled by a nozzle heating technique in conjunction with a seeding technique. The decomposition rate shows both translational and vibrational energy dependence on the Pt surface. However, there is also the surface temperature dependence of the decomposition rate even varying the incident beam energy, indicating precursor‐mediated dissociation of N2O on the Pt surface. On the other hand, no energy dependence was observed on the Rh surface, suggesting that the decomposition dynamics are different between Pt and Rh surfaces.

Disturbance growth triggered by steady heating of a jet’s nozzle exit boundary layer

Experiments were conducted to investigate how heating only the nozzle exit boundary layer of an axisymmetric jet, with an unheated potential core, affects disturbance growth in the initial shear layer. The exit boundary layer had a minimum density ratio of 0.74, was laminar, and had a constant momentum thickness (θ) for all levels of nozzle heating used in this study. The fluctuating velocity (u′) and temperature (t′) in the exit boundary layer increased monotonically with increasing nozzle temperature. Low-amplitude acoustic excitation produced a more rapid growth of coherent velocity fluctuations for the heated case than for the unheated.

Arc heater nozzle heating test with hydrogen combustion products

A single-edge expansion test nozzle was tested in the Large Core Arc Tunnel of the McDonnell Douglas Corporation Aeromechanics Laboratory to obtain hypersonic vehicle flight-level nozzle heating data by using water to simulate hydrogen combustion products. The test objectives were to expand the data base for nozzle thermal design and computer code validation. A total of 34 runs were made for 15- and 25-deg nozzle ramp angles and water content of zero and 15 mol%. Six gauges each of heat flux and pressure were installed along the centerline of the nozzle ramp surface and one each at an off-centerline location. The fixed lower cowl was instrumented with two pressure gauges. Higher water injection rates produced higher heating rates, as did a higher enthalpy and lower ramp angle. Test data compared favorably with BARTZ and BLIMPK88 code predictions with equilibrium chemistry.