Particle Loss in Splitters and Dilutors United Stales Environ mental Prulotlion Agency ------- Particle Loss in Splitters and Dilutors Assessment and Standards Division Office of Transportation and Air Quality U.S. Environmental Protection Agency Prepared for EPA by ICF Incorporated, LLC EPA Contract No. EP-C-16-020 Work Assignment No. 1-03 Acknowledgements Jacob Swanson, Adjunct Assistant Professor Department of Mechanical Engineering University of Minnesota David B. Kittelson, Professor F.B. Rowley Chair in Mechanical Engineering Director, Center for Diesel Research Department of Mechanical Engineering University of Minnesota John Gorman, Research Associate Department of Mechanical Engineering University of Minnesota NOTICE This technical report does not necessarily represent final EPA decisions or positions. It is intended to present technical analysis of issues using data that are currently available. The purpose in the release of such reports is to facilitate the exchange of technical information and to inform the public of technical developments. rnA United States EPA-420-R-21-005 Environrrntntal Prolotliun \/LI Agency January2021 ------- Contents Table of Figures 1 Table of Tables 2 Introduction 3 Executive summary of results 3 Methods - splitter measurements 5 Results - splitters 8 2-way splitter, V2 x 3/s 8 2-way splitter, 3/s x 3/s 11 4-way splitter, 3/s x 3/8X3/8X3/8 14 Methods - dilutor measurements 16 Results - dilutor measurements 18 Conclusions 21 Table of Figures Figure 1. Representative aircraft exhaust particle size distribution with a geometric mean diameter of 30 nm and geometric standard deviation of 1.8 3 Figure 2. Results from three flow split conditions for the 1/2" x 3/8" splitter. Each graph includes all experimental data, a best-fit line, and a theoretical line based on diffusion loss theory 4 Figure 3. Results from three dilutor operating conditions. Each graphs includes all experimental data, the AIR penetration requirements, and a best-fit line 4 Figure 4. Apparatus for splitter loss measurement with DOS 6 Figure 5. Apparatus for splitter loss measurement with silver particles 6 Figure 6. Photographs of experimental apparatus for splitter evaluation 7 Figure 7. Particle size distributions of each particle generation source 8 Figure 8. Flow split: 5 L/min and 5 L/min 8 Figure 9. Flow split: 8.5 L/min and 1.5 L/min 9 Figure 10. Flow split: 1.5 L/min and 8.5 L/min 9 Figure 11. Flow split: 12.5 L/min and 12.5 L/min 9 Figure 12. Flow split: 1.5 L/min and 23.5 L/min 10 Figure 13. Flow split: 23.5 L/min and 1.5 L/min 10 Figure 14. 1.5 L/min and 8.5 L/min split condition showing poor agreement between model and experimental results (compare to Figure 10) 11 Figure 15. 1.5 L/min and 23.5 L/min split condition showing poor agreement between model and experimental results (compare to Figure 12) 11 Figure 16. Flow split: 5 L/min and 5 L/min 12 Figure 17. Flow split: 1.5 L/min and 8.5 L/min 12 Figure 18. Flow split: 8.5 L/min and 1.5 L/min 12 Figure 19. Flow split: 12.5 L/min and 12.5 L/min 13 Figure 20. Flow split: 23.5 L/min and 1.5 L/min 13 Figure 21. Flow split: 1.5 L/min and 23.5 L/min 13 Figure 22. Flow split: 2.5, 2.5, 2.5, 2.5 L/min 14 Figure 23. Flow split: 1.5, 1.5, 1.5, 5.5 L/min 14 Figure 24. Flow split: 5.5, 1.5, 1.5, 1.5 L/min 15 1 ------- Figure 25. Flow split: 6.5, 6.5, 6.5, 6.5 L/min 15 Figure 26. Flow split: 1.5, 1.5, 1.5, 20.5 L/min 15 Figure 27. Flow split: 20.5, 1.5, 1.5, 1.5 L/min 16 Figure 28. Apparatus for dilutor loss measurement with DOS 16 Figure 29. Apparatus for dilutor loss measurement with silver particles 17 Figure 30. Apparatus for dilutor loss measurement with NaCl (salt) 17 Figure 31. Schematic of heated dilutor with temperature setpoints indicated 18 Figure 32. Picture of heated dilutor (insulation used but not shown so that heating can be more clearly seen) 18 Figure 33. Dilutor conditions: P = 2 bar, DR = 8.16 19 Figure 34. CFD results for P = 2 bar, DR = 8.55 19 Figure 35. Dilutor conditions: P = 3 bar, DR = 8.4 20 Figure 36. Dilutor conditions: P = 4 bar, DR = 9.13 20 Figure 37. Dilutor conditions REPEAT: 2 bar, DR = 8.16 21 Table of Tables Table 1. Total penetration of "aircraft exhaust particles" through a 1/2" x 3/8" two-way splitter. Results are rounded to two significant figures 4 Table 2. Total penetration of "aircraft exhaust particles" through a Dekati DI-1000 dilutor. Results are rounded to two significant figures 5 Table 3. All experimental condition for splitter evaluations. Each condition was evaluated with a different aerosol (silver and DOS). All flowrates are given in standard conditions 5 2 ------- Introduction The EPA provided University of Minnesota researchers three "splitter" devices and a Dekati DI- 1000 dilutor for the purposes of 1) experimental characterization and 2) modeling of particle loss in each device. The UMN used three aerosol types (salt, silver, DOS) of various size ranges to challenge the splitters and dilutors to determine loss. Commercial computation fluid dynamics (CFD) software was used to model results. Executive summary of results The main body of the report describes the measurements and results in detail. This section summarizes all results and estimates the impact of losses in the context of an aircraft exhaust particle size distribution. A representative aircraft particle size distribution (Figure 1) was multiplied by representative solid particle penetration curves measured for the 1/2" x 3/8" two- way splitter operated at various flow split conditions and the Dekati DI-1000 dilutor operated at various pressures. Figure 2 shows results from the three flow split conditions considered in this analysis, two of which are the "extreme ends," including: 1) very low loss (equal split and high flow in each branch), 2) low loss (higher split ratio then in #1, low flow in one branch), and 2) low loss (very high split ratio, low flow in one branch). Figure 2 shows curves in red that are fits to all experimental data for each test condition. All data was used to provide the widest size range for the fit. The physics-based fit curve was based off the Gormley / Kennedy diffusion equations. The "theory" curve is described more later but in brief, it is the diffusion loss calculated using laminar flow diffusion loss equations and ignoring fluid effects (e.g. recirculating flow). Similarly, Figure 3 shows curves in red that are fits to all experimental data for three pressure conditions for the Dekati dilutor (2, 3, and 4 bar compressed air pressure). The experimental data includes data for the dilutor operated both "hot" and "cold." The dilutor "fits" were based off the same diffusion equation as the splitters multiplied by a constant*particle diameter that represents in effect of impaction, the mechanism responsible for particle loss for larger particles and higher velocities that are present in the dilutor. The Aerospace Information Report (AIR) minimum dilutor penetration requirements curve (from 15 to 100 nm) is shown for reference. Dp, nm Figure 1. Representative aircraft exhaust particle size distribution with a geometric mean diameter of 30 nm and geometric standard deviation of 1.8. 3 ------- 1.50 1.30 11.10 ro Id §0.90 CL 0.70 0.50 1/2x3/8 5 L/min and 5 L/min Theory 1.50 1.30 1110 1 0.90 0) CL 0.70 0.50 1/2 x 3/8 1.5 L/min and 3.5 L/min Theory - __ —¦' Fit All data 10 100 Dp, nm 1000 10 100 Dp, nm 1000 1.50 1.30 11.10 ro % §0.90 CL 0.70 0.50 1/2 x 3/8 1.5 L/min and 23.5 L/min Theory Fit All data" 1 10 Qpj pm 100 1000 Figure 2. Results from three flow split conditions for the 1/2" x 3/8" splitter. Each graph includes all experimental data, a best-fit line, and a theoretical line based on diffusion loss theory. 1.50 1.30 c -1.10 ro oj §0.90 CL 0.70 0.50 Dilutor 2 bar AIR penetration requirement ¦ All data 1.50 1.30 H.10 3 J j 0.90 0.70 0.50 Dilutor 3 bar Fit 5.. 1.50 1.30 c ¦S 1.10 ro OJ §0.90 CL 0.70 0.50 Dilutor 4 bar AIR penetration requirement 10 100 Dp, nm 1000 10 100 Dp, nm 1000 10 100 Dp, nm 1000 Figure 3. Results from three dilutor operating conditions. Each graphs includes all experimental data, the AIR penetration requirements, and a best-fit line. To determine overall "splitter" results, the representative aircraft exhaust particle number size distribution was multiplied by each splitter penetration curve fit shown in Figure 2. The result gives the total number penetration shown in Table 1. The particle number size distribution was also weighted by diameter cubed to represent a volume (or mass) distribution. This distribution was also multiplied by each penetration curve fit to give a total "mass penetration" as seen in the right column of Table 1. Overall, losses are very low. The total number penetration is about 98% when the flowrate is around 1.5 L/min and closer to 99% when the flowrate is higher - regardless of the split. The uncertainty of these numbers has not been rigorously determined but it is approximately ± 1%. Results show that in splitters, loss is dominated by diffusion, not impaction, regardless of flowrate and split condition. One consequence of this is that the mass penetration - which is impacted by larger particles that diffuse less - is nearly unity for all conditions. As seen in the main results section, the penetration data for the 3/8" x 3/8" two-way splitter and the 3/8" x 3/8" x 3/8" x 3/8" four-way splitter were substantially similar to these results and the conclusions here are representative for all splitters evaluated. Table 1. Total penetration of "aircraft exhaust particles" through a 1/2" x 3/8" two-way splitter. Results are rounded to two significant figures. Split condition Number Mass 5 L/min and 5 L/min 0.99 1.0 1.5 L/min and 8.5 L/min 0.98 1.0 1.5 L/min and 23.5 L/min 0.98 1.0 To determine overall "dilutor" results, the representative aircraft exhaust particle number size distribution was multiplied by each dilutor penetration curve fit shown in Figure 3. The result 4 ------- gives the total number penetrations shown in Table 2. Experimental data clearly shows more larger sized particles are lost in the dilutor compared to the splitters. The total "mass penetrations" were calculated in the same way as described with the splitters. Overall, number penetrations were about 88% for all operating conditions. Because some particles were lost due to impaction in the dilutor, the mass penetration was lower - around 85%. Table 2. Total penetration of "aircraft exhaust particles" through a Dekati DI-1000 dilutor. Results are rounded to two significant figures. Operating pressure condition Number Mass 2 bar 0.88 0.86 3 bar 0.88 0.84 4 bar 0.88 0.86 Methods - splitter measurements EPA provided UMN stainless steel splitters with the following inlet / outlet configuration: 1)1/2" x 3/8" (2-way), 2) 3/8" x 3/8" (2-way), and 3) 3/8" x 3/8" x 3/8" x 3/8" (4-way). Dimensions listed are tube outer diameters. The flow split geometry met AIR requirements. As shown in Table 3, splitters were evaluated with different flowrate and splits to evaluate particle loss for different conditions. Table 3. All experimental condition for splitter evaluations. Each condition was evaluated with a different aerosol (silver and DOS). All flowrates are given in standard conditions. Flow conditions Total flowrate, L/min flow split, L/min 2-way (3/8 x 3/8) 10 1.5/8.5 2-way (3/8 x 3/8) 10 5/5 2-way (3/8 x 3/8) 25 1.5/24 2-way (3/8 x 3/8) 25 12.5/12.5 2-way (1/2 x 3/8) 10 1.5/8.5 2-way (1/2 x 3/8) 10 5/5 2-way (1/2 x 3/8) 25 1.5/23.5 2-way (1/2 x 3/8) 25 12.5/12.5 4-way 10 1.5/1.5/1.5/5.5 4-way 10 2.5/2.5/2.5/2.5 4-way 25 1.5/1.5/1.5/20.5 4-way 25 6.25/6.25/6.25/6.25 Figure 4 shows the apparatus to generate semi-volatile nanoparticles that atomizes a solution of isopropyl alcohol and dioctyl sebecate (DOS). DOS is a high molecular weight organic liquid. The atomized particles pass through a diffusion drier to remove the isopropyl alcohol. An Air Vac Engineering dilutor is used to create a vacuum to pull the sample flow through the system as well as increase the total flowrate. The diluted flow is pulled through the splitter under test by an Alicat 5 ------- vacuum mass flow controller. A TSI SMPS (with long column DMA and 3025 CPC) measures the particle size distribution upstream and downstream of the splitter. Upstream and downstream sample lines were identical in length and geometry. For "salt" particle measurements, the DOS solution was replaced by a solution of NaCl in deionized water. All other components of the apparatus were the same. Silica gel diffusion dryer ' ^ Vent Flow controllers 2-way splitter 1000 ppm dioctyl sebecate (DOS) in n-propanol JL f I iDilutor 3-way valve -KX- ~° SMPS 1 fll Ai- Bi_ ~° T-. Figure 4. Apparatus for splitter loss measurement with DOS Figure 5 shows the apparatus to generate silver nanoparticles using an evaporation/condensation technique. The furnace temperature was 1050°C and the flowrate through the furnace was 1.5 L/min. An Air Vac Engineering dilutor is used to create a vacuum to pull the sample silver particle flow through the furnace as well as increase the total flowrate. The diluted flow is pulled through the splitter under test by an Alicat vacuum mass flow controller. A TSI SMPS (with long column and 3025 CPC) measures the particle size distribution upstream and downstream of the splitter. Upstream and downstream sample lines were identical in length and geometry. T-. Figure 5. Apparatus for splitter loss measurement with silver particles. Figure 6 is a photograph showing both of the particle generation apparatuses and the mass flow control system. 6 ------- Figure 6. Photographs of experimental apparatus for splitter evaluation. Figure 7 is a graph of the typical size distributions produced by each technique. Particle loss in each splitter was determined by measuring the penetration of particles for each condition. Penetration based on three repeat measurements was calculated as the ratio of these concentrations and error bars are calculated based on the standard deviation. Preliminary work showed number of scans (between three and nine scans) did not affect the calculation of penetration. For all results, loss was measured in the flow split listed first. E.g., a result labeled "8.5 L/min and 1.5 L/min" means that the measurements were made in the 8.5 L/min branch. "Theory" curves are calculated based on diffusion loss from the Gormley / Kennedy equations (Diffusion from a Stream Flowing through a Cylindrical Tube P. G. Gormley and M. Kennedy, Proceedings of the Royal Irish Academy. Section A: Mathematical and Physical Sciences, 52, 1948 - 1950, 163-169) using the length / appropriate flowrate of the splitter. Data is corrected for diffusion loss in the few inches of tubing connecting upstream and downstream sampling system. This correction is on the order of 1%. Commercial CFD software was used to model the results. Details of the computer modeling, including boundary conditions, mesh information, and software settings is not yet available. 7 ------- 1.E+08 1.E+07 o 05 CL £1.E+06 CD 0 _l 1 1.E+05 1.E+04 1 10 _ 100 1000 Dp, nm Figure 7. Particle size distributions of each particle generation source Results - splitters 2-way splitter, % x 3/s Figure 8 through Figure 13 shows the experimental and modeled particle loss results for the 2- way splitter with 1/2" inlet and 3/8" outlet diameters. The silver, DOS, and salt particles have overlapping size ranges. For all cases where the flow split branch is 1.5 L/min, there is a clear increase in particle loss for small sizes (<10 nm). For all cases, there is no indication of any loss for particles >100 nm, indicating that particle impaction is not a loss mechanism in the splitters. CFD results show regions of flow recirculation in the splitters for all cases, which apparently impacts loss more in the low flowrate cases. In all cases, the modeled results appear to be in close agreement with the experimental results. Good agreement between model and experiment was not the case initially, as discussed in the next section. Results from Figure 8, Figure 10, and Figure 12 were averaged and analyzed further in the "executive summary of results" section. Figure 8. Flow split: 5 L/min and 5 L/min. 8 ------- 1.50 1.30 ; no CL 0.90 0.70 0.50 1000 Dp, nm Figure 11. Flow split: 12.5 L/min and 12.5 L/min 9 ------- 1 10 100 1000 °? Dp, nm ¦ Figure 12. Flow split: 1.5 L/min and 23.5 L/min 1.50 1.30 | 1.10 "ro oj S. 0.90 0.70 0.50 1 Modeling issues Figure 14 and Figure 15 show selected sample results from the initial modeling efforts. In each example, the model result does not closely match the experimental or theoretical calculation. It was determined that the size of the computational solution domain had an effect on some of the results that included larger recirculation zones. All of the cases that appeared to have the truncated recirculation zone were "re-run" with a larger solution domain. These re-run simulations gave much better agreement in all cases. 10 ------- 1.50 ¦ 1.10 q_ 0.90 0.70 0.50 1000 10 100 Dp, nm Figure 14. 1.5 L/min and 8.5 L/min split condition showing poor agreement between model with truncated solution domain and experimental results (compare to Figure 10). 1.50 1.30 £ 1.10 a! 0.90 0.70 0.50 Til DOS Salt Theory Silver ! s Model I 10 100 Dp, nm 1000 ¦ 0.00 ImsMl Figure 15. 1.5 L/min and 23.5 L/min split condition showing poor agreement between model with truncated solution domain and experimental results (compare to Figure 12). 2-way splitter, 3/s x 3/s Figure 16 through Figure 21 shows the experimental and modeled particle loss results for the 2- way splitter with 3/8" inlet and outlet diameters. These results show very similar trends as compared to the 1/2" x 3/8" splitter results with regards to increased diffusion loss for 1.5 L/min cases and close agreement between modeled results and theory. 11 ------- I I 2.50 I 2 00 0.00 (m sA-t] 1000 Dp, nm Figure 17. Flow split: 1.5 L/min and 8.5 L/min I ¦ 0.00 ImsM] 1000 Dp, nm Figure 18. Flow split: 8.5 L/min and 1.5 L/min 12 ------- Model jjjjy. Salt Theory ^ DOS Silver T I 6.67 I 5.72 1 0.00 (msA-il »> f 10 100 1000 Dp, nm Figure 19. Flow split: 12.5 L/min and 12.5 L/min 10 100 1000 Dp, nm Figure 20. Flow split: 23.5 L/min and 1.5 L/min 1.50 1.30 ; no CL 0.90 0.70 0.50 1000 Dp, nm Figure 21. Flow split: 1.5 L/min and 23.5 L/min 13 ------- 4-way splitter, 3/s x 3/s x 3/s x 3/s Figure 22 through Figure 27 shows the experimental and modeled particle loss results for the 4- way splitter. These results show very similar trends as compared to both the 1/2" x 3/8" splitter and 3/8" x 3/8" splitter results with regards to increased diffusion loss for 1.5 L/min cases and close agreement between modeled results and theory. 1.50 1.30 j 1.10 £ 0.90 0.70 0.50 10 100 1000 Dp, nm Figure 22. Flow split: 2.5, 2.5, 2.5, 2.5 L/min 1.50 1.30 i 1.10 a. 0.90 0.70 0.50 Salt Theory 1000 10 100 Dp, nm Figure 23. Flow split: 1.5, 1.5, 1.5, 5.5 L/min 14 ------- 1.50 1.30 | 1.10 cl 0.90 0.70 0.50 Salt Model Theory Silver 10 100 1000 Dp, nm Figure 24. Flow split: 5.5, 1.5, 1.5, 1.50 1.30 ; no cl 0.90 0.70 0.50 10 100 1000 Dp, nm Figure 25. Flow split: 6.5, 6.5, 6.5, 6.5 L/min 1.50 1.30 ; no q1 0.90 0.70 0.50 10 100 Dp, nm 1000 Figure 26. Flow split: 1.5, 1.5, 1.5, 20.5 L/min 15 ------- Methods - dilutor measurements Dekati provided UMN a DI-1000 dilutor on loan. The particle generation methods were described previously and just briefly mentioned here. Figure 28 shows the apparatus to generate semi-volatile nanoparticles that atomizes a solution of isopropyl alcohol and DOS. Figure 29 shows the apparatus to generate silver nanoparticles using an evaporation/condensation technique. Figure 30 shows the apparatus to generate larger salt (NaCl) particles that atomizes a salt / water solution. Particle loss in the dilutor was determined by calculating the penetration of particles for each condition. Penetration based on three repeat measurements was calculated as the ratio of these concentrations and error bars are calculated based on the standard deviation. The dilution ratio of the dilutor was determined by measuring the sample inlet flowrate with a Gilibrator and the outlet flowrate with a mass flow meter accurate to within 1% of measured flowrate. The measured dilution ratio was within 10% of manufacturer specifications. For some measurements, the dilutor was heated according to the schematic show in Figure 31. Figure 32 shows a photograph of the heated dilutor. Silica gel diffusion dryer ^ Vent 1000 ppm dioctyl sebecate (DOS) in n-propanol Figure 28. Apparatus for dilutor loss measurement with DOS 16 ------- Silver Filter Furnace . ^ Q Flow controller Figure 29. Apparatus for dilutor loss measurement with silver particles Diffusion dryer 0.008 v/v salt (NaCI) in water 3-way valve -KX— 23.5 L/min ~o SMPS ~ Figure 30. Apparatus for dilutor loss measurement with NaCI (salt) 17 ------- Heated Active heating T=333K Figure 31. Schematic of heated dilutor with temperature setpoints indicated. Figure 32. Picture of heated dilutor (insulation used but not shown so that heating can be more clearly seen) Results - dilutor measurements Figure 33 through Figure 37 shows the particle loss measurement results. Figure 33 contains modeled particle loss results based on the CFD results shown in Figure 34. It is believed that the model result does not perfectly match the experimental measurement because of the solution domain effect that was discussed with the splitter results. Work is ongoing to "re-run" cases with a larger solution domain. 18 ------- 1.50 1.30 .2 1/1° I "S a. 0.90 0.70 0.50 Silver Model * DOS 10 100 Dp, nm Figure 33. Dilutor conditions: P = 2 bar, DR = 8.16 1000 <5> ^ ¦!* # Vetoctty |m s*-1J Figure 34. CFD results for P = 2 bar, DR = 8.55 19 ------- 1.50 1.30 o1-10 TO s_ 0 £. 0.90 0.70 0.50 Silver 10 100 Dp, nm Figure 35. Dilutor conditions: P = 3 bar, DR = 8.4 1000 1.50 1.30 J1"10 TO "S q! 0.90 0.70 0.50 1 10 100 Dp, nm Figure 36. Dilutor conditions: P = 4 bar, DR = 9.13 1000 On different days, an entire set of conditions (silver, DOS and salt particles) was run for the dilutor with 2 bar inlet pressure. The results are shown in Figure 37. Particle loss trends are qualitatively reproduced quite well. 20 ------- 1.50 Testl Test2 1.30 §1.10 cl 0.90 0.70 0.50 10 100 1000 1 10 100 1000 Dp, nm Dp, nm Figure 37. Dilutor conditions REPEAT: 2 bar, DR = 8.16 Conclusions Particle loss in splitters is very low (< 2%) - regardless of flow split ratio and flowrate. Although other loss mechanisms (inertial, etc.) are included in the modeling work, diffusion is the only mechanism producing any significant loss. As such, particle loss increases when the flowrate in the splitter decreases. For example, the number penetration is about 98% when the flowrate is around 1.5 L/min and closer to 99% when the flowrate is 5 L/min. In nearly all cases, particle loss in splitters determined experimentally was slightly higher than calculations considering diffusion theory (and not any fluid mechanics effects). This suggests that particle loss in the fluid recirculation zones resulting from the flow split is an additional loss mechanism. Dilutor measurements showed the number penetration of representative "aircraft exhaust particles" through the dilutor was on the order of 90%. Slightly less mass penetrates because of some inertial loss in the dilutor at larger sizes. Loss increased with decreasing particle size (<20 nm) and with increasing particle size (>50 nm) with the least amount of loss occurring at an intermediate size of - 40 nm. There was no significant difference between loss measured with the dilutor "hot" or "cold." Agreement between experimental and CFD particle loss for the 2 bar case was reasonable but not as close as with the splitter measurements. 21 ------- |