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Comparison of contours-map of (a) evaporation, (b) mass fraction and (c) SMD of the ethanol droplets at different angles of injections (see Table 2 for case description).
Source publication
This work presents the nanostructured coating formation using suspension thermal spraying through the HVOF torch. The nanostructured coating formation requires nanosize powder particles to be injected inside a thermal spray torch using liquid feedstock. The liquid feedstock needs to be atomized when injected into the high-velocity oxygen fuel (HVOF...
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... interesting effects of the droplets breakup and evaporation in the CC are witnessed after the angular injection (GTI) of feedstock (Fig. 5). The ethanol droplets convert into vapours, and maximum evap- oration is observed inside the CC middle region for 0°-15° angles of in- jection. For a 20° angle of injection, the droplets move towards the C-D nozzle throat region (Fig. 5a). As compared to 0° STI, the rate of evapo- ration is increased when droplets are injected at an ...
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... of the droplets breakup and evaporation in the CC are witnessed after the angular injection (GTI) of feedstock (Fig. 5). The ethanol droplets convert into vapours, and maximum evap- oration is observed inside the CC middle region for 0°-15° angles of in- jection. For a 20° angle of injection, the droplets move towards the C-D nozzle throat region (Fig. 5a). As compared to 0° STI, the rate of evapo- ration is increased when droplets are injected at an angle of 5° and 10° GTI. A small decrease in the maximum value of evaporation is observed for 15° and 20° angles of injection (Fig. 5a) while lower mass fractions of Table 2 for case description). liquid ethanol are observed in these cases ...
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... 0°-15° angles of in- jection. For a 20° angle of injection, the droplets move towards the C-D nozzle throat region (Fig. 5a). As compared to 0° STI, the rate of evapo- ration is increased when droplets are injected at an angle of 5° and 10° GTI. A small decrease in the maximum value of evaporation is observed for 15° and 20° angles of injection (Fig. 5a) while lower mass fractions of Table 2 for case description). liquid ethanol are observed in these cases (Fig. 5b), which confirms the overall enhancement in the rate of evaporation. Moreover, the elongat- ed evaporation regions are identified in Cases 2.4 and 2.5 as seen in Fig. 5a. This further proves that the overall evaporation of ...
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... (Fig. 5a). As compared to 0° STI, the rate of evapo- ration is increased when droplets are injected at an angle of 5° and 10° GTI. A small decrease in the maximum value of evaporation is observed for 15° and 20° angles of injection (Fig. 5a) while lower mass fractions of Table 2 for case description). liquid ethanol are observed in these cases (Fig. 5b), which confirms the overall enhancement in the rate of evaporation. Moreover, the elongat- ed evaporation regions are identified in Cases 2.4 and 2.5 as seen in Fig. 5a. This further proves that the overall evaporation of liquid droplets is augmented while the maximum value of 15.2 × 10 −7 and 20.4 × 10 −7 kg/s is illustrated in Cases ...
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... of evaporation is observed for 15° and 20° angles of injection (Fig. 5a) while lower mass fractions of Table 2 for case description). liquid ethanol are observed in these cases (Fig. 5b), which confirms the overall enhancement in the rate of evaporation. Moreover, the elongat- ed evaporation regions are identified in Cases 2.4 and 2.5 as seen in Fig. 5a. This further proves that the overall evaporation of liquid droplets is augmented while the maximum value of 15.2 × 10 −7 and 20.4 × 10 −7 kg/s is illustrated in Cases 2.4 and 2.5, respectively (Fig. 5a). Based on these results, it is found that increasing the angle of injec- tion intensifies the rate of evaporation of ethanol droplets ...
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... the overall enhancement in the rate of evaporation. Moreover, the elongat- ed evaporation regions are identified in Cases 2.4 and 2.5 as seen in Fig. 5a. This further proves that the overall evaporation of liquid droplets is augmented while the maximum value of 15.2 × 10 −7 and 20.4 × 10 −7 kg/s is illustrated in Cases 2.4 and 2.5, respectively (Fig. 5a). Based on these results, it is found that increasing the angle of injec- tion intensifies the rate of evaporation of ethanol droplets inside the ...
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... the droplet evaporation, the location of the highest mass frac- tion of ethanol is observed around the throat region for all angles of in- jection (Fig. 5b). After the non-premixed combustion of ethanol droplets with the oxygen residues, the T G increases inside and outside the torch, as shown previously in Fig. 5a. Gradually the mass fraction of ethanol decreases as the ethanol burns inside the torch. For 0°, 5° and 10° angles of injection, the ethanol cannot completely burn even after ...
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... the droplet evaporation, the location of the highest mass frac- tion of ethanol is observed around the throat region for all angles of in- jection (Fig. 5b). After the non-premixed combustion of ethanol droplets with the oxygen residues, the T G increases inside and outside the torch, as shown previously in Fig. 5a. Gradually the mass fraction of ethanol decreases as the ethanol burns inside the torch. For 0°, 5° and 10° angles of injection, the ethanol cannot completely burn even after the barrel exit, and it leaves the torch without prior combustion (Fig. 5b). The reason for this delay in ethanol combustion for smaller an- gular injection is ...
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... with the oxygen residues, the T G increases inside and outside the torch, as shown previously in Fig. 5a. Gradually the mass fraction of ethanol decreases as the ethanol burns inside the torch. For 0°, 5° and 10° angles of injection, the ethanol cannot completely burn even after the barrel exit, and it leaves the torch without prior combustion (Fig. 5b). The reason for this delay in ethanol combustion for smaller an- gular injection is the incomplete evaporation of ethanol droplets within the CC and the barrel sections. While with 15° and 20° angles of injec- tion the droplets completely burn and disappear near the barrel exit. Moreover, at larger angles of injection of 15° and 20°, ...
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... Fig. 5c the values of Sauter Mean Diameter (SMD) of the ethanol droplets are shown. This figure clearly shows the variation in the angle of injection and its effects on the dispersion of droplets inside the CC. In all cases, the SMD decreases gradually from the initial size of 150 μm due to droplets fragmentation inside the HVSFS torch. About ...
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... with the CC walls. Thus, to protect the CC walls from droplets impingement while improving the overall flow physics, the angle of in- jection of 15° can be a good choice. As seen and analysed, at 15° angular injection the droplets do not strike the CC walls, and can breakup and evaporate completely within the core combustion region (section-I) (Fig. 5a-c). Also, this delivers extra thermal and kinetic energy to the HVSFS flame (as seen in Fig. ...
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... can also be seen in Fig. 9a that the value of the spray-half-angle is quite small, consequently, the droplets cannot inject into the core of the combustion zone. Hence, the lower rate of evaporation is observed for the ETI when compared to the GTI (shown previously in Fig. 5a). The two red zones in Fig. 9b (for Case 3.3), demonstrate that the overall evaporation is augmented when GLR is increased. It is proved from Case 3.3 (Fig. 9c) that less ethanol is left in the barrel section, and it is completely evaporated and was burned before the torch exit. While in Cases 3.1 and 3.2, some ethanol discharges ...
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Citations
... A promising technique to efficiently burn high viscosity fuels is the combustion using effervescent atomizers [8][9][10]. The advantages of these systems over other types of injector systems, such as pressure atomizers, are related to the larger exit orifices, reduced injection pressures and lower gas flow requirements, allowing the production of a fine spray [8,11]. A finer spray enhances the total surface area of the fuel, which allows for better air-to-fuel mixing, heat and mass transfer. ...
... The author have concluded that the SMD decreases in the regions closer to the spray nozzle (both axially and radially), while in regions further downstream this trend is the complete opposite. Mahrukh et al. [11] studied the effects of effervescent atomization of the liquid feedstock on gas and droplet dynamics, vaporization rate, and secondary breakup in a high-velocity suspension flame spray process (HVSFS). The authors concluded that the effervescent-type injection improves the gas and droplet dynamics inside the HVSFS torch as it performs better than the surface-type injection. ...
... Also, there are no studies evaluating the combined effect of the air flow and spray patterns on combustion performance and CO emission. Literature focuses mostly on the influence of the atomization parameters (GLR, fuel and air pressure, etc) on the characterization of the spray (particles distribution, particles size, injection profile, injection velocity, etc) [9][10][11]13,[16][17][18][19][20]. Some authors include the swirl as a variable on the process, but without factual evidence on combustion performance [21]. ...
... Due to the pressure difference between the suction chamber and the secondary flow, the secondary fluid can be entrained in the primary flow in the form of small droplets or bubbles [17]. The phenomenon of spray pulsating exists in all nozzles [18,19]. For two-phase flow atomization, there are obvious fluctuations in the gas-liquid flow coefficient in the vicinity of the nozzle due to the gas phase. ...
A two-phase flow ejector is an important part of a water mist fire suppression system, and these devices have become a popular research topic in recent years. This paper proposes a supersonic ejector that aims to improve the efficiency of water mist fire suppression systems. The effects of ejector geometric parameters on the entrainment ratio (ER) were explored. The effects of primary flow pressure (PP) on the mixing process and flow phenomena were studied by a high-speed camera. The experimental results show that the ER first increases and then decreases with increasing PP. ER increases with increasing ejector area ratio (AR). The PP corresponding to the maximum ER of ejectors with a different nozzle exit position (NXP) is 3.6 bar. The ejector with an NXP of +1 and AR of 6 demonstrate the best performance, and the ER of this ejector reaches 36.29. The spray half-cone angle of the ejector increases with increasing ER, reaching a maximum value of 7.07°. The unstable atomization half-cone angle is mainly due to a two-phase flow pulsating phenomenon. The pulsation period is 10 ms. In the present study, a general rule that provides a reference for ejector design and selection was obtained through experiments.
... Tabbara et al. [1] looked at injecting water droplets into the combustion chamber, to investigate the effect the initial droplet diameter has on the evaporation rate. Mahrukh et al. [2][3][4] . looked at the effect different axial injection types, models for suspension properties and the effect of an atomization model on the droplet breakup and evaporation rates. ...
... Surface area C 1 Calibration constant (9.352 ×10 −7 w. m −2 ) C 2 Calibration constant ( To determine the temperature of particles within SHVOF thermal spray it is necessary to determine the particle heat transfer coefficient. Traditionally in SHVOF thermal spray modelling the analysis on the heat transfer coefficient is computed from the Ranz-Marshall [11] correlation for the Nusselt number. ...
... Kavanau et al. [14] derived the heat transfer coefficient of spherical particles within the slip flow regime and derived a Nusselt number correlation for application to particles within a rarefied gas flow. Kavanau provided an alternative Nusselt correlation that accounts for the effect of rarefaction on the Nusselt number, which is given by Eq. (5) in the modelling section (2) . The correlation proposed by Kavanau et al. asymptotically approaches the value predicted by Sauer et al. [15] for free molecular flow for large Kn [16] . ...
Suspension high velocity oxy fuel thermal spray is a system characterized by supersonic velocities and length scales of particles of the order of nm-μm. As the effects of rarefication become significant the assumptions within the continuum models begin to collapse, the effects of rarefication can be evaluated through the flow Knudsen number. Modifications to the numerical modelling must be made to incorporate the effects of rarefaction. This study looks to include the effects of rarefication into the computational fluid dynamics (CFD) models for the suspension high velocity oxy-fuel (SHVOF) thermal spray process. A model for the heat transfer coefficient that take into account the Knudsen and Mach number effects is employed. Finally, the Ranz-Marshall correlation for the Nusselt number is compared to the Kavanau correlation and a compressible Nusselt number correlation. The model is validated through comparisons of particle temperatures which are obtained from two colour pyrometry measurements using a commercially available Accuraspray 4.0 diagnostic system. This study shows that there is a significant improvement in the prediction of inflight particle temperatures when accounting for the effects of compressibility and the effects of rarefication on the Nusselt number.
... Propane gas is used as fuel. 34 First, the operating conditions for the CH-2000 HVOF gun are set as displayed in Table 1. The flame at these conditions reached a supersonic state, and visible shock diamonds are observed in the flame jet. ...
The nanoparticles’ coating are generated via Solution-Precursor High-Velocity Oxygen Fuel Spray (SP-HVOF) process. The Zirconium nitrate pentahydrate precursor was used with varied solute concentrations, solvents types and injection nozzles for analysing the effects over the nanoparticles’ coating formation. The solvents types are pure water, water-ethanol mixture, and pure ethanol while injection types are plain-orifice, angular- and effervescent injections. Various nanoparticles’ size distribution and morphologies are analysed for varied salt concentrations, solvent types, and injection nozzles by using the Scanning Electron Microscopy (SEM) of sprayed substrates. The particles at low salt concentration showed spherical morphology with narrow size distribution; while at higher concentrations irregular shaped agglomerated and large particles are observed. Moreover, the mixtures of aqueous-organic and pure organic-based solvents are preferred to improve the SP-HVOF process efficiency to generate small size and homogeneous nanoparticles. Towards the variation in injection nozzles, when different types of injection nozzles are tested the effervescent-type atomization nozzle has produced the best quality nanoparticles.
Thermal spray, being a cost- and time-efficient process, is used extensively in industrial and engineering sections for mass production of desired coating structures, allowing to deposit a wide range of materials on various substrates. Conventionally, powder feedstocks are used in plasma and high-velocity oxy-fuel (HVOF) thermal spray that has limitations such as limited feedstock particle size (10-100 µm), clogging and limited options for coating materials. Liquid feedstocks, in the form of suspensions or precursor solutions could potentially resolve these issues by allowing nano- and submicron particles to be deposited, where unlike dry feedstock, the liquid medium helps in reducing the friction and avoiding the clogging. Also, liquid feedstocks, especially precursor solutions, provide the opportunity to deposit a wide range of coating materials with better control over coating microstructure, material composition and stoichiometry by varying the properties of the feedstock. Despite benefits, liquid feedstock has its own complexities, such as complex feedstock preparation, thermo-physical reactions during interaction with the energy source and gases. Therefore, it becomes essential to understand how different suspension and solution precursor feedstock properties affect the coating microstructures and properties. This review paper covers a detailed discussion on the role of different process parameters such as feedstock properties, injection methods, different torches and surface properties, affecting the coating quality and performance and related recent developments and challenges are discussed. This would be beneficial in optimizing the spray parameters to obtain coatings with desired microstructures. The later part of the review focuses on the economic aspect of the suspension/solution precursor-based plasma and HVOF spray methods and their various applications.
In the high velocity oxygen fuel (HVOF) spray process, coating properties are sensitive to the characteristics of in-flight particles, which are mainly determined by process parameters. Obtaining a comprehensive multi-physical model or analysis of the HVOF process remains challenging because of the complex chemical and thermodynamic reactions that occur during the deposition procedure. This study proposes to develop a robust methodology via the artificial neural networks (ANN) to solve this problem for the HVOF sprayed coatings under different operating parameters. Two ANN models were developed and implemented to predict coating’s performances (microhardness, porosity and wear rate) and to analyze the influence of operating parameters (stand-off distance, oxygen flow rate, and fuel flow rate) while considering the intermediate variables (temperature and velocity of in-flight particles). A detailed procedure for creating and optimizing these two ANN models is presented in this work, which encodes the implicitly physical phenomena governing the HVOF process. Results show that the developed implicit models can satisfy the prediction requirements and clarify the interrelationships between the spraying conditions, behaviors of in-flight particles, and the final coating performances, resulting in providing better control of the HVOF sprayed coatings.
Purpose
This paper presents the application of grey modeling for thermal spray processing parameter analysis in less data environment.
Design/methodology/approach
Based on processing knowledge, key processing parameters of thermal spray process are analyzed and preselected. Then, linear and non-linear grey modeling models are integrated to mine the relationships between different processing parameters.
Findings
Model A reveals the linear correlation between the HVOF process parameters and the characterization of particle in-flight with average relative errors of 9.230 percent and 5.483 percent for velocity and temperature.
Research limitations/implications
The prediction accuracies of coatings properties vary, which means that there exists more complex non-linear relationship between the identified input parameters and coating results, or more unexpected factors (e.g. factors from material side) should be further investigated.
Practical implications
According to the modeling case in this paper, method has potential to deal with other diverse modeling problems in different industrial applications where challenge to collecting large quantity of data sets exists.
Originality/value
It is the first time to apply grey modeling for thermal spray processing where complicated relationships among processing parameters exist. The modeling results show reasonable results to experiment and existing processing knowledge.
The study focuses on experimental characterization of the primary atomization associated with an effervescent atomizer. Unlike the existing designs available in the literature that inject air perpendicular to the liquid flow direction, the present atomizer design utilizes co-flowing air configuration. In doing so, the aerodynamic shear at the liquid-gas interface create instability and enhance the subsequent jet breakup. Both integrated and intrinsic properties of the liquid jet were extracted by utilizing high-speed flow visualization techniques. The integrated property consists of breakup length, while the intrinsic property involves primary and intermediate breakup frequencies. The primary instability is characterized by low-frequency sinusoidal mode, whereas the intermediate instability consists of high-frequency dilatational mode. Dimensionless plots of these parameters with Weber number ratio leads to a better collapse of data, thereby generates appropriate universal functions. The combined diagram of frequencies converge with increasing relative velocity. This may be due to the dominance of energy consuming sinusoidal wave as the aerodynamic shear increases.
Suspension high velocity oxy-fuel thermal spray typically utilizes axial injections of suspension into the combustion chamber. There are certain cases where the oxygen-sensitive nanoparticles benefit from a reduction in the time and temperature spent in the gas flow. Therefore, a radial injection outside of the nozzle can enable deposition of oxygen-sensitive nanomaterials. This study investigated the effect of the suspension flow rate, angle of injection and the injector diameter on the in-flight particle conditions. The combustion reaction is modeled using the eddy dissipation concept model with a robust reaction mechanism and compared to the current approach within the literature. This approach has not been employed within SHVOF thermal spray and provides a robust treatment of the reaction mechanisms. The suspension was modeled using a two-way coupled discrete particle model. Experimental observations were obtained using high-speed imaging, and observations of the liquid jet were compared to the numerical values.
