A numerical study on heat transfer enhancement and design of a heat exchanger with porous media in continuous hydrothermal flow synthesis system

doi:10.1016/j.cjche.2017.01.015

Abstract

Abstract: The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis (CHFS) system to enhance the heat transfer and minimize the required length of the heat exchanger. For this purpose, numerous numerical simulations are performed to investigate performance of the system with porous media. First, the numerical simulation for the heat exchanger in CHFS system is validated by experimental data. Then, porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness, based on the minimum required length of the heat exchanger. Finally, by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate, the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed. The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%. The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness. Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.

Key words: Continuous hydrothermal flow synthesis, Heat exchanger, Heat transfer enhancement, Porous media, Numerical simulation

摘要： The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis (CHFS) system to enhance the heat transfer and minimize the required length of the heat exchanger. For this purpose, numerous numerical simulations are performed to investigate performance of the system with porous media. First, the numerical simulation for the heat exchanger in CHFS system is validated by experimental data. Then, porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness, based on the minimum required length of the heat exchanger. Finally, by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate, the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed. The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40% and reduces the required length of the heat exchanger by approximately 35%. The results also illustrate that the most proper thickness of the porous media is approximately equal to 90% of the product tube's thickness. Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.

关键词: Continuous hydrothermal flow synthesis, Heat exchanger, Heat transfer enhancement, Porous media, Numerical simulation

Pedram Karimi Pour-Fard, Ebrahim Afshari, Masoud Ziaei-Rad, Shahed Taghian-Dehaghani. A numerical study on heat transfer enhancement and design of a heat exchanger with porous media in continuous hydrothermal flow synthesis system[J]. , 2017, 25(10): 1352-1359.

References

[1] J.A. Darr, M. Poliakoff, New directions in inorganic and metal-organic. Coordination chemistry in supercritical fluids, Chem. Rev. 99(1999) 495-541.
[2] T. Adschiri, K. Kanazawa, Rapid and continuous hydrothermal synthesis of boehmite particles in sub and supercritical water, J. Am. Ceram. Soc. 75(1992) 2615-2618.
[3] S. Moussiere, P. Joussot-Dubien, Modeling of heat transfer and hydrodynamic with two kinetics approaches during supercritical water oxidation process, J. Supercrit. Fluids 43(2007) 324-332.
[4] A.E. Scheidegger, The Physics of Flow Through Porous Media, Univ. Toronto Press, 1974.
[5] M. Kaviany, Principles of Heat Transfer in Porous Media, Springer, 1995.
[6] A. Aimable, H. Muhr, Continuous hydrothermal synthesis of inorganic nano powders in supercritical water:Towards a better control of the process, Powder Technol. 190(2009) 99-106.
[7] M.D. Bermejo, M.J. Cocero, Supercritical water oxidation:A technical review, AIChE. J. 52(2006) 3933-3951.
[8] E. Lester, P. Blood, Reaction engineering:The supercritical water hydrothermal synthesis of nano-particles, J. Supercrit. Fluids 37(2006) 209-214.
[9] M. Vesna, J. Christopher, K. Suela, Imaging the continuous hydrothermal flow synthesis of nano-particulate CeO₂ at different supercritical water temperatures using in situ angle-dispersive diffraction, J. Supercrit. Fluids 87(2015) 118-128.
[10] K. Brett, F. Veruscha, Critical process parameters and their interactions on the continuous hydrothermal synthesis of ironoxide nanoparticles, Chem. Eng. J. 281(2015) 312-321.
[11] E. Sherif, E.M. Hosam, Synthesis and surface modification of nanophosphorousbased flame retardant agent by continuous flow hydrothermal synthesis, Particuology 22(2015) 82-88.
[12] F.W. Dittus, L.M.K. Boelter, Heat transfer in automobile radiators of the tubular type, Univ. Calif. Publ. Eng. 2(1930) 443-461.
[13] E.A. Krasnoshchekov, B.S. Petukhov, V.S. Protopopov, An investigation of heat transfer to fluids flowing in pipes under supercritical conditions, Proceedings of the Second International Heat Transfer Conference, University of Colorado, Boulder, USA 1961, pp. 569-578.
[14] J.D. Jackson, W.B. Hall, Forced convection heat transfer to fluids at supercritical pressure, Turbulent Forced Convection in Channels and Bundles, vol. 2, Hemisphere Publishing Corporation, New York 1979, pp. 563-611.
[15] M.J. Watts, C.T. Chou, Mixed convection heat transfer to supercritical pressure water, Proceedings of the 7th International Heat Transfer Conference, Munchen, Germany 1982, pp. 495-500.
[16] N. Zhou, A. Krishnan, F. Vogel, A computational model for supercritical water oxidation of organic toxic wastes, Adv. Environ. Res. 4(2000) 79-95.
[17] J. Licht, M. Anderson, M. Corradini, Heat transfer to water at supercritical pressures in a circular and square annular flow geometry, Int. J. Heat Fluid Flow 29(2008) 156-166.
[18] Y.M. Cai, J.T. Christopher, Numerical modelling of hydrothermal fluid flow and heat transfer in a tubular heat exchanger under near critical conditions, J. Supercrit. Fluids 57(2011) 236-246.
[19] Y.M. Cai, J. Jing, Z. Yang, Z. Xue, Simulation for scale-up of a confined jet mixer for continuous hydrothermal flow synthesis of nanomaterials, J. Supercrit. Fluids 58(2015) 211-222.
[20] J. Gheorghe, The influence of the porous media permeability on the unsteady conjugate forced convection heat transfer from a porous sphere embedded in a porous medium, Int. J. Heat Mass Transf. 77(2014) 1124-1132.
[21] R. Fumei, Zh. Wenhuan, Sh. Baochang, Numerical study of heat transfer enhancement in a pipe filled with porous media by axisymmetric TLB model based on GPU, Int. J. Heat Mass Transf. 70(2014) 1040-1049.
[22] J. Wajs, D. Mikielewicz, Influence of metallic porous microlayer on pressure drop and heat transfer of stainless steel plate heat exchanger, Appl. Therm. Eng. 93(2015) 1337-1346.
[23] G.C. Bourantas, E.D. Skouras, V.C. Loukopoulos, Heat transfer and natural convection of nanofluids in porous media, Eur. J. Mech. B Fluids 43(2014) 45-56.
[24] W. Lin, B. Sundén, J. Yuan, A performance analysis of porous graphite foam heat exchangers in vehicles, Appl. Therm. Eng. 50(2013) 1201-1210.
[25] W. Wang, J. Guo, S. Zhang, J. Yang, X. Ding, X. Zhan, Numerical study on hydrodynamic characteristics of plate-fin heat exchanger using porous media approach, Comput. Chem. Eng. 61(2014) 30-37.
[26] D.C. Wilcox, Turbulent Modeling for CFD, Second ed. DCW Industries, California, 1994.
[27] W.P. Jones, B.E. Launder, The prediction of laminarization with a two-equation model of turbulence, Int. J. Heat Mass Transf. 15(1972) 301-314.
[28] C. Somerton, P. Wood, Effect of walls in modeling flow through porous media, J. Hydraul. Eng. 114(1988) 1431-1448.
[29] D.A. Nield, A. Bejan, Convection in Porous Media, Third edition Springer, 2006.
[30] C. Wang, Zh. Guo, D. Zhang, S. Qiu, W. Tian, Y. Wu, G. Su, Transient behavior of the sodium-potassium alloy heat pipe in passive residual heat removal system of molten salt reactor, Prog. Clear Energy 68(2013) 142-152.
[31] http://www.ansys.com/Products/Simulation+Technology/Fluid+Dynamics/Fluid+Dynamics+Products/ANSYS+Fluent.
[32] H. Xu, L. Gong, S. Huang, M. Xu, Flow and heat transfer characteristics of nanofluid flowing through porous media, Int. J. Heat Mass Transf. 83(2014) 399-407.