EXP 1-1 Review of Studies

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Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results

PSAs produce a fine spray which makes them favourite in many industrial, chemical and agricultural applications of sprays in flowing environments. The increased interphase area allows high rates of mixing and evaporation. Atomiser type and size, its arrangement at cross-flowing air and the range of flow velocities were chosen here with regard to the wide range of such applications of PSA sprays under flow conditions, which appear in combustion engines, gas scrubbing or agricultural spraying.
The PSAs are widely explored under still laboratory conditions [10]. The interaction of the liquid film and the spray with the cross-flow is a complex phenomenon, and only a few studies cover this topic. Sprays exposed to cross-flow conditions exhibit differently: the penetration lowers, spray shape changes, and break-up length reduces [37].
Lynch et. al. al [39] investigated PSA in a cross-flow of heated air. The flow velocity ranged from 7 to 30 m/s with a cross-flow $Tu$ of 6 – 7%. Bi-modal size behaviour of the droplets was observed due to different drag forces acting on small and large droplets [40]. Prakash et al. [38] investigated the primary break-up of PSA in cross-flow and found the different character of the break-up of windward and leeward sheets. Lee et al. [37] investigated the break-up distance of PSA in cross-flow and also reported different break-up distance for each side of the liquid film. For the bag break-up type, the authors observed a tri-modal droplet size distribution. These differences found by both teams might result from the fact that each side of the sheet features a different angle with the cross-flow direction. The windward side then exhibits greater $u_{r}$ than the leeward side, which modifies the magnitude of the forces acting on the sheet in Equation (9) and causes different $We_{r}$. Deshpande et al. [41] studied PSA spray in cross-flow numerically. At higher cross-flow velocities, droplets were entrained from the windward side and interacted with the leeward side droplets. In [37], the conversion of the kinetic energy of air to the compressive force $F_{p}$ acting on the liquid film was suggested. This force not only affects $l_{b}$ but may also change the spray cone angle ($SCA$) and tilts the entire liquid film. Zhang et al. [42] found that a smaller $SCA$ improves the penetration of the liquid into the cross-flow and significantly affects the flow field around the atomiser. Wang et al. [43] observed the best mixing of droplets with cross-flow for $SCA$ between 60 and 90°.
The spray trajectory in cross-flow is mainly governed by the factors of $q$ and $We_{a}$ [44]. The droplet break-up in cross-flow depends on flow velocity and $Tu$ [45], [46]. In dense sprays like these from PSAs, droplet collisions are frequent, and the ambient flow intensifies that. Santolaya et al. [47] studied under still laboratory conditions the effect of droplet collisions on the axial droplet distribution in PSA spray. No studies on droplet collisions in PSA spray under cross-flow were found. Though one can hypothesise, based on [47], that the cross-flow increases the droplet collision rate. The knowledge of spray and gas interaction is crucial for finding out the effect of the flow on droplet size and trajectories, evaporation and cooling down rates to determine and reduce the blown-away fraction and others. It is necessary to evaluate the performance and suitability of the spray for these applications. It allows for nozzle improvements which result in more efficient and stable combustion, lower fuel consumption and lower emission production [48] [49], lower droplet drift in agriculture sprays [50] and increased capture efficiency in Venturi scrubbers [33].
The experiments that are time-consuming and costly can be replaced by numerical modelling, which just needs to be validated first by sufficiently extensive and good-quality experimental data under the flow conditions. So far available CFD modelling predominantly addressed PSA in still ambient conditions. Here are the available cases of PSA with the ambient flow. Deshpande et al. [41] used Lagrangian–Eulerian point parcel treatment of the spray in OpenFOAM for computational analysis of hollow cone liquid injection into cross-flow. They, using the drag force, classified the spray into the near and far field spray region. Zhang et al. [42] employed a Scale-Adaptive numerical Simulation to investigate the flow field structure of hollow cone spray injected into cross-flow. The atomisation was modelled by Linear instability analysis and Taylor analogy break-up theory. Sun et al. [51] compared different models for heat and mass transfer for a spray in cross-flow and found different effects on droplet evaporation. Dikshit et al. [52] simulated the pressure atomiser for small-scale GT applications. The study was mainly devoted to the understanding of secondary droplet break-up.
Most of the studies of the PSA spray in the cross-flow solely used high-speed imaging. It is limited in image resolution, where smaller droplets are not captured and dense flows are hardly resolved. Other drawbacks stem from difficulties with the extraction of numerical data, time-consuming manual analysis and challenges with automated analyses. These problems are precluded by optical diagnostic methods such as PDA.
The controlled airflow is provided by wind tunnels. There are a lot of their designs utilising different kinds of flows to simulate the working conditions of atomisers [53] [54]. Some wind tunnels simulate only ambient airflow, while others simulate airflow at varied pressure, temperature or combination of both these factors [55] [56] [57].

References

37 S. Lee, W. Kim, and W. Yoon, Journal of Mechanical Science and Technology 24 (2), 559 (2010).
38 R. Surya Prakash, H. Gadgil, and B. N. Raghunandan, International Journal of Multiphase Flow 66, 79 (2014).
39 A. Lynch, R. G. Batchelor, B. Kiel, J. Miller, J. Gord, and M. F. Reeder, 21 (8), 625 (2011).
40 R. L. C. Flemmer and C. L. Banks, Powder Technology 48 (3), 217 (1986).
41 S. Deshpande, Atomization and Sprays 21 (2011).
42 H. Zhang, H. Zhang, and B. Bai, Heat Transfer Engineering, 1 (2021).
43 W. Wang, H. Zhang, Z. Zhao, Q. Zheng, and B. Bai, Computers & Fluids 154, 216 (2017).
44 A. R. Karagozian, Physics of Fluids 26 (10), 101303 (2014).
45 R. Clift, J. Grace, and M. Weber, 1978 (unpublished).
46 O. Diemuodeke and I. Sher, Turbulence Induced Droplet Break-up. (2013).
47 J. L. Santolaya, J. A. Garcia, E. Calvo, and L. M. Cerecedo, International Journal of Multiphase Flow 56, 160 (2013).
48 J. Kim, R. Reitz, and S. Park, Proceedings of The Institution of Mechanical Engineers Part D-journal of Automobile Engineering - PROC INST MECH ENG D-J AUTO 224, 1113 (2010).
49 M. Boutazakhti, M. Thomson, and M. Lightstone, COMBUSTION SCIENCE AND TECHNOLOGY 163, 211 (2001).
50 M. Wenneker, Zande, and J. van de Zande, Agricultural Engineering International X (2008) May (2008).
51 H. Sun, B. Bai, and H. Zhang, Heat Transfer Engineering 35 (6-8), 664 (2014).
52 S. Dikshit, D. Kulshreshtha, and S. Channiwala, Numerical simulation of Pressure Swirl Atomizer for Small Scale Gas Turbine Combustion Chamber. (2017).
53 M. Arifuzzaman and M. Mashud, IOSR Journal of Engineering 02, 83 (2012).
54 K. Alfred Sunny, N. Manoj Kumar, H. Mona, and R. Rai, International Journal of Earth Sciences and Engineering 10, 18 (2017).
55 M. Guo, K. Nishida, Y. Ogata, C. Wu, and Q. Fan, Fuel 206, 401 (2017).
56 M. Eslamian, A. Amighi, and N. Ashgriz, AIAA Journal 52, 1374 (2014).
57 K. Bunce, J. Lee, and D. Santavicca, in 44th AIAA Aerospace Sciences Meeting and Exhibit (American Institute of Aeronautics and Astronautics, 2006).

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Contributed by: Ondrej Cejpek, Milan Maly, Ondrej Hajek, Jan Jedelsky — Brno University of Technology

Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results

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