Improved electrospray design for aerosol generation and flame propagation analysisJournal of Loss Prevention in the Process Industries

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Accepted 17 September 2015

Available online 21 September 2015

Keywords:

Aerosol apparatus, which impedes the development of optimal aerosol hazard mitigation measures. The focus of higher flash point liquids, its flammability can be drastically increased when it is operated under high pressure and temperature, which is common in the processes in industries. When a liquid is released under such circumstances, an aerosol/mist often forms.

Once an aerosol forms, its properties are significantly different from re, the probability due to the aerosol roup of high flash involved in many arch (FME&R) replosions in a tenFebo and Valiulis, 1996). Moreover, more than 200 incidents involving HTFs have been reported in the past 20 years (Huang et al., 2013b).

One industrial scenario for mist formation is superheated liquid flashovers, in which the liquid vaporizes, expands and cools down to form fine liquid droplets. Another scenario is a liquid stream breaks down into coarse droplets due to friction force between the liquid surface and air, as demonstrated in previous work (Krishna et al., 2003; Sukmarg et al., 2002). Although it is well known aerosols pose great threat to the process industries and have been * Corresponding author. Present address: 3122 TAMU, 246 BRWN, College Station, TX 77843-3122, USA.

Contents lists available at ScienceDirect

Journal of Loss Prevention w.

Journal of Loss Prevention in the Process Industries 38 (2015) 148e155E-mail address: mannan@tamu.edu (M.S. Mannan).liquid's flash point. A liquid is defined as flammable if the flash point of which is under 37.8 C as in NFPA 30 standard (National

Fire Protection Association, 2012), or under 60 C in GHS standard (United Nations, 2011). For flash points above these values, it is called “combustible liquid,” and attention to the liquid is usually less than that of a “flammable liquid.” However, the real hazard depends on the properties and the operating condition of liquid, not solely on the flash point. For combustible liquids including the ignition process and combustion. Furthermo of reaching an ignition source is also increased dispersion.

For example, heat transfer fluids (HTFs), a g point liquids widely used in industry, have been incidents. Factory Mutual Engineering and Rese ported there were 54 HTFs-related fires and ex year period and caused $150 million in loss (Fire and explosion hazards of a liquid are often classified by the the bulk liquid, the surface area will be much higher and evaporation rate will also increase dramatically, which would facilitateMist

Electrospray

Flammability

Flame speed 1. Introductionhttp://dx.doi.org/10.1016/j.jlp.2015.09.011 0950-4230/© 2015 Elsevier Ltd. All rights reserved.this study is development of an improved aerosol electrospray device for the generation of high quality aerosol data. The goal is achieved through higher nozzle packing, precise nozzle and mesh hole alignment and adding two ground meshes. In addition to a flat ground mesh, the utilization of a cylindrical ground mesh demonstrated improved confinement and guidance of droplets. Duratherm 600, heat transfer fluid, was examined to demonstrate the modified electrospray device capabilities as compared to previous design. Results show the modified electrospray can produce more uniform droplets, more even test chamber dispersion, smaller droplet size and higher concentration aerosol, which is essential to study aerosol flame propagation. Accordingly, the results of aerosol flame speed tests for the improved design were more reproducible. Moreover, it was found that a traditional propane pilot flame was unable to ignite the smaller aerosol droplet size due to the strong turbulence generated by the open flame.

However, by careful modification of the pilot flame length, the turbulence decreased dramatically and the small droplet size aerosol can be tested. © 2015 Elsevier Ltd. All rights reserved. the bulk liquid or vapor. Since the droplet size is much smaller thanReceived in revised form 17 September 2015Article history:

Received 8 June 2015

Although the hazards of aerosol fires and explosions have been studied for decades the data for aerosol flame propagation is still scarce. Additionally there is a lack of standard techniques and measurementImproved electrospray design for aeroso propagation analysis

Yan-Ru Lin, Hao Chen, Chad Mashuga, M. Sam Man

Mary Kay O'Connor Process Safety Center, Artie McFerrin Department of Chemical Engi

TX 77843-3122, USA a r t i c l e i n f o a b s t r a c t journal homepage: wwgeneration and flame an* ing, Texas A&M University System, College Station, in the Process Industries elsevier .com/locate/ j lp i.d. and 5.08  104 m o.d.) were assembled on a small metal plate, which is connected to a high voltage source (HV1). A metal mesh positioned right beneath the metal plate is connected to a second high voltage source (HV2) and serves as a relative ground. Ten 5.08  104 m i.d. plastic capillaries connect the syringes to the nozzles to transport the test fluid. The high voltages are generated by the function generators (Stanford Research System, DS-345) and then amplified to the desired levels by high voltage amplifiers (Trek

Inc. 610E). The voltage difference between HV1 and HV2 is maintained at several kilovolts to energize the test fluid. As liquid stream with sufficient electric conductivity passes through the nozzles, the liquid meniscus takes a conical shape (cone-jet) and fine droplets are generated.

In our aerosol flammability study, some desired physical properties are higher concentrations, small mean droplet size, monodispersed droplets, stable spray and even droplet dispersion in the test chamber. Attention to equipment details are required to achieve the desired aerosol conditions. First, every nozzle should be positioned at the center of the metal mesh hole to create a uniform electric field. If the electric field is not uniform, the resulting droplet size distribution will be poly-dispersed. The comparison between improved design and previous electrospray setup is shown in Fig. 2.