Journal of Thermal and Fluid Science (JTFS)
Volume 7 · Issue 2 · August 2026 · pp 29-35
Research Article · Peer Reviewed
Received: May 12, 2026 · Accepted: July 30, 2026 · Published: August 11, 2026
DOI: 10.26706/jtfs.7.2.20260802
Open Access · CC BY 4.0

Optimization of a Carbon Black Combustion Chamber Inlet: A Tapered-Transition Redesign to Eliminate Dead and Recirculation Zones

Shrikant Vijay Pawar1*, Dr. Nitin Kardekar2

1 Research Scholar, Department of Mechanical Engineering, Sunrise University, Alwar, India.
2 Associate Professor, Department of Mechanical Engineering, JSPM NTC, Pune, India.

*Correspondence: shrikant1474@gmail.com

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Abstract

Wall-adjacent dead zones and recirculating flow are a common cause of poor performance in industrial combustion chambers and reactors, and are frequently traced to abrupt changes in flow-passage cross-section. This paper reports a comparative computational fluid dynamics (CFD) study evaluating a low-cost geometric remedy replacing a stepped inlet-to-chamber transition with a smoothly tapered one for a small-scale carbon black combustion chamber–reactor unit in which such dead and recirculation zones had been identified. Two three-dimensional geometries, differing only in the profile of the inlet transition, were evaluated under identical operating conditions: an air-fuel mixture entering at 0.079 kg/s and 1350°C, secondary air totaling 0.2156 kg/s at 250°C admitted through two ports, and an operating pressure of 101325 Pa. The original (stepped) geometry was meshed with approximately 3.9 million cells and exhibited extended near-wall dead zones and organized toroidal recirculation cells at the entry of the air-fuel mixture into the combustion chamber. The modified (tapered) geometry, meshed with approximately 3.65 million cells under an equivalent near-wall resolution strategy, drastically reduced the extent of these dead zones and eliminated the recirculation entirely, as confirmed by both local velocity contours and velocity vector analysis, while leaving the secondary-air choke velocity unchanged at 89.43 m/s. The reactor-outlet static and total pressures increased only marginally in the tapered design, from 201.05 Pa to 207 Pa and from 295.85 Pa to 299 Pa respectively a negligible penalty for the flow-uniformity gain achieved. These results demonstrate that a purely geometric, low-cost modification of the inlet transition is sufficient to resolve the principal adverse flow features of the reactor, and the tapered design is recommended for adoption ahead of physical prototyping.

Keywords

computational fluid dynamics design optimization combustion chamber carbon black reactor recirculation zone dead zone tapered inlet comparative CFD study

References

  1. "Separation control and efficiency improvement in a 2D diffuser by means of contoured cavities," International Journal of Heat and Fluid Flow, 2013.
  2. "Turbulent flow with separation in an asymmetric diffuser," validation study of separation, recirculation, and reattachment prediction in a divergent duct.
  3. H. Xing et al., "Optimization study of the dump diffuser in gas turbine to reduce pressure loss," International Journal of Aerospace Engineering, 2018.
  4. F. C. Lockwood and J. E. Niekerk, "Parametric study of a carbon black oil furnace," Combustion and Flame, vol. 103, pp. 76–90, 1995.
  5. K. Ono, K. Dewa, Y. Matsukawa, Y. Saito, Y. Matsushita, H. Aoki, K. Era, and T. Aoki, "Influence of furnace temperature and residence time on configurations of carbon black," Chemical Engineering Journal, vols. 200–202, pp. 541–548, 2012.
  6. T. Chagas, R. Serfaty, and A. G. Barreto Jr., "Modeling the Carbon Black Production in Enclosed FSP Reactor," Journal of Fluid Flow, Heat and Mass Transfer, vol. 9, 2022.
  7. M. Ahmadi Motlagh and S. H. Hashemabadi, "Estimation of temperature and residence time of carbon black oil furnace industrial reactors," 2006.
  8. F. R. Menter, "Zonal two equation k-ω turbulence models for aerodynamic flows," AIAA Paper 93-2906, 1993.
  9. F. R. Menter, "Two-equation eddy-viscosity turbulence models for engineering applications," AIAA Journal, vol. 32, no. 8, pp. 1598–1605, 1994.
  10. F. R. Menter, M. Kuntz, and R. Langtry, "Ten years of industrial experience with the SST turbulence model," Turbulence, Heat and Mass Transfer, vol. 4, pp. 625–632, 2003.
  11. K. C. Patil and S. James, "Evaluation of RANS-based turbulence models for isothermal flow in a realistic can-type gas turbine combustor application," arXiv:2312.14459, 2023.
  12. H. K. Versteeg and W. Malalasekera, An Introduction to Computational Fluid Dynamics: The Finite Volume Method, 2nd ed. Harlow, U.K.: Pearson Education Limited, 2007.
  13. B. E. Launder and D. B. Spalding, "The numerical computation of turbulent flows," Computer Methods in Applied Mechanics and Engineering, vol. 3, no. 2, pp. 269–289, 1974.
  14. P. J. Roache, "Perspective: A method for uniform reporting of grid refinement studies," Journal of Fluids Engineering, vol. 116, no. 3, pp. 405–413, 1994.
  15. I. B. Celik et al., "Procedure for estimation and reporting of uncertainty due to discretization in CFD applications," Journal of Fluids Engineering, vol. 130, no. 7, 078001, 2008.
  16. D. C. Wilcox, Turbulence Modeling for CFD, 3rd ed. La Cañada, CA: DCW Industries, 2006.
  17. S. V. Patankar, Numerical Heat Transfer and Fluid Flow. Washington, DC: Hemisphere Publishing Corporation, 1980.
  18. F. Morsch, J. Weber, and J. Kruis, "Simulation of particulates in a carbon black reactor," Journal of Nanoparticle Research, vol. 6, pp. 613–626, 2004.
  19. J.-B. Donnet, Carbon Black: Science and Technology, 2nd ed. New York: Marcel Dekker, 1992, pp. 1–64.
  20. "Effect of Area Ratio on Flow Separation in Annular Diffuser," CFD study of inlet swirl and area ratio effects on diffuser wall flow reversal, 2019.