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Characterization of Aerated-Liquid Jets Using Simultaneous X-Ray Radiography and X-Ray Fluorescence Measurements
| Content Provider | Semantic Scholar |
|---|---|
| Author | Carter, Campbell D. |
| Copyright Year | 2014 |
| Abstract | The aerated-liquid jet is a capable injection scheme to provide favorable plume penetration and droplet size for efficient combustion in high-speed air-breathing propulsion systems. In the past, structures of aerated-liquid jets were characterized by liquid-only measurements, resulting in an incomplete understanding of the two-phase flows within the near field of spray plumes. In the present study, near-field structures of aerated-liquid jets discharged from specially contoured exit adaptors into a quiescent environment were explored, using simultaneous X-ray radiography for liquid phase measurement and X-ray fluorescence for gas phase measurement. Water and argon were used as the injectant and aerating gas, respectively. The test matrix includes variations in liquid flow rate, injection angle, exit orifice size, adaptor contour, and aerating configuration. It was found that liquid and aerating gas exhibit different plume characteristics, even for the injection condition with vigorous mixing schemes to generate a uniform two-phase mixture inside the injector prior to the final injection. The gas plume stays along the injector axis and is narrower than the liquid plume, especially at the downstream locations for well-dispersed sprays. The potential mechanisms for the separation of liquid and gas plumes were proposed in this study. It was also found that the liquid mass distribution within the aerated-liquid jets injected at a small injection angle is highly asymmetric. A significant amount of the liquid is distributed on the obtuse side of the spray plume. With a sufficiently high injection pressure, it was also found that the aerated-liquid jet injected from a small orifice can actually generate a wide spray plume with a reduced plume density and plume velocity. The spray plume with a coannular liquid distribution profile may not be desired in actual applications, due to its narrow plume width and nonuniform liquid mass distribution. For the present designs of the inside-out aerated-liquid injector (wherein the aerating tube is immersed in the liquid flow), it was found that similar spray structures can be generated at the same injection conditions. ILASS Americas, 26 Annual Conference on Liquid Atomization and Spray Systems, Portland, Oregon, May 18-21, 2014 __________________________________________ * Corresponding author, Kuocheng.Lin.ctr@us.af.mil INTRODUCTION Among the candidate injection schemes inside the liquid-fueled high-speed air-breathing propulsion systems, liquid aeration has been a plausible approach to enhance liquid atomization in a high-speed crossflow environment. By preparing a two-phase mixture inside the injector with a small amount of gas to mix with the liquid fuel, the resulting aerated-liquid jet is capable of generating a well-dispersed plume for effective mixing with the ambient air and therefore for efficient combustion. This approach can save the precious time and space required for the breakup of liquid column. It has been shown that the liquid aeration technique can generate a spray that penetrates well into the flow and produces a large fuel plume containing a large number of small droplets. Recently, the near-field structures of aerated-liquid jets have been explored with various X-ray diagnostics, such as X-ray phase contrast imaging (PCI) and X-ray radiography. The studies with X-ray PCI show that an aerated-liquid jet with a modest aeration level can quickly disperse droplets and ligaments within the near field of the spray. Droplet diameter, bubble diameter, and bubble film thickness within the periphery of the spray were measured form the X-ray PCI images. The line-of-sight feature of PCI, however, prevents droplet size measurement and liquid mass distribution characterization within the dense core region. The studies with X-ray radiography characterize liquid mass distributions within the near fields of aerated-liquids with quantitative measurements. Liquid-based plume properties, such as averaged density, velocity, and momentum flux, were readily derived from the X-ray radiography data sets. In these studies, structures of aerating gas within the aeratedliquid jets were not measured. The objective of the present study is to expand the study of Lin et al. by simultaneously measuring liquid and gas phases within the plumes of aerated-liquid jets, using X-ray radiography and X-ray fluorescence, respectively. Mass distribution profiles for both liquid and gas, along with the averaged plume properties, were then compared to identify the effects of liquid flow rate, adaptor contour, injection angle, orifice size, and aerating configurations. EXPERIMENTAL METHODS The experiment was conducted at the 7-BM beamline of the Advanced Photon Source (APS) at Argonne National Laboratory. Water and argon were supplied into the aerated-liquid injector at desired flow rates to form a two-phase mixture inside the injector before discharge into a quiescent environment. The water spray was placed in the path of a focused X-ray beam. The schematic in Fig. 1 illustrates the overall setup. The aerated-liquid jet was vertically discharged into a collecting bucket with a small opening on the cap to prevent stray droplets from entering the beam path. In addition, the distance between the nozzle exit and the bucket cap was kept around 15 mm, in order to avoid splashing. Both the aerated-liquid injector and the collecting bucket were rigidly mounted on a traversing table, which provided movement normal to the X-ray beam. Aerated-Liquid Injectors A critical component of the liquid aeration system is the mixing chamber used to create the two-phase mixture upstream of the spray nozzle. Two types of aerated-liquid injector mixing chamber designs were tested in the present study, as illustrated in Fig. 2. The outside-in aerating configuration (Fig. 2(a)) features a liquid flow at the core of the mixing chamber with the aerating gas discharged through aerating orifices from an annular passage to create a two-phase mixture upstream of the injector orifice. This injector design has been extensively utilized in previous studies. It has an internal diameter of 2.0 mm in the mixing chamber. The inside-out aerating configuration (Fig. 2(b)) features an aerating tube immersed in the liquid flow to deliver the aerating gas through specially-designed aerating orifices to create the two-phase mixture. In the present study, three internal diameters of 0.165” (4.2 mm), 0.188” (4.8 mm), and 0.208” (5.3 mm) were selected for the mixing chambers to accommodate the aerating tube, which has a fixed outside diameter of 0.125” (3.2 mm). It is of interest to explore the effects of the annular gap (between the aerating tube and the injector wall inside the mixing chamber) on the structures of aerated-liquid jets. Adaptors Two groups of exchangeable adaptors were tested. Theses adaptors can be integrated with the injector bodies of both aerating configurations, in order to further modulate the two-phase mixture before discharge. Group A adaptors were designed to explore the effects of internal contour on the structure of aerated-liquid jets and have been utilized in previous studies. Figure 3 shows the internal contours of these adapters. Each of the six Group A adaptor has an exit or throat diameter of D=1.0 mm (note that the throat diameter is given the subscript “2” in Fig 3). Two adaptor lengths of 2.5 mm (L/D=2.5) and 10.0 mm (L/D=10) were tested to explore the effects of passage length and contour curvature on spray structure. Group B adaptors feature variations in injection angle and exit orifice size, as illustrated in Fig. 4. Table 1 lists the critical dimensions for in the five Group B adaptors. The configuration with a straight passage and a constant L/D of 10 was selected for these adaptors. For those adaptors with an injection angle less than 90 , the final passage length, L, is measured from the axis at the orifice exit plane to the adaptor seat or the tip of the injector body. For an adaptor with a small exit orifice, the physical adaptor length is reduced accordingly. Aerating Tubes Two aerating tubes with prescribed aerating orifices placements were selected to mate with the inside-out aerated-liquid injectors. Each aerating tube has an outside diameter of 0.125” (3.2 mm), an internal diameter of 0.085” (2.2 mm), and a sealed tip. Figure 5 shows the distribution patterns of the aerating orifices on the aerating tubes. The Case #4 pattern features 12 aerating orifices distributed in 6 rows. Each row has two aerating orifices. The location of the aerating orifice is offset by 90 between rows. Each aerating orifice has a diameter of D = 0.025” (0.64 mm). For the Case #6 aerating tube, a total of 8 aerating orifices are closely distributed in two rows. The location of the aerating orifice is offset by 45 between rows. Each aerating orifice has a diameter of D = 0.030” (0.76 mm). In the present designs, the total cross-sectional area of the aerating orifices for each aerating tube is approximately the same as the cross-sectional area of the aerating tube. Selection of these two aerating tubes for the experiment at the Argonne National Laboratory was based on the bench testing of 6 different aerating tube designs with variations in aerating orifice diameter, number, and distribution pattern. It was concluded that both Case #4 and Case #6 designs are capable of delivering steady and uniform aerated-liquid jets, based on visual observations of spray steadiness and uniformity for the intended test conditions. The actual quality of the aerated-liquid jets from available combinations of aerating tubes and inside-out injectors will be determined by the X-ray measurements. Aerating Gas Unlike the use of nitrogen as the aerating gas in previous studies, argon was selected as the aerating gas in the present study, in order to generate X-ray fluorescence signals for gas phase detection. For the study of the aerated-liquid je |
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| Alternate Webpage(s) | http://www.ilass.org/2/conferencepapers/10_2014.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
