Numerical investigations on an improved micro-cylindrical combustor with rectangular rib for enhancing heat transfer

Zuo, Wei; Jiaqiang, E; Liu, Haili; Xin, Zhao; Zhang, Zhiqing

doi:10.1016/j.apenergy.2016.10.009

Cited by 104 publications

(17 citation statements)

References 53 publications

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“…However, the latter one has little influence on the combustion process, and therefore is neglected [33,34]. Furthermore, the effect of the pressure diffusion is not considered because of the small magnitude [35,36]. As for the settings of the Fluent model, the NO x model provides the capability to model thermal, prompt, and fuel NO x formation, as well as NO x consumption due to re-burning in combustion systems.…”

Section: D Computational Modelmentioning

confidence: 99%

NO emission performance assessment on a perforated plate-implemented premixed ammonia-oxygen micro-combustion system

Cai

Becker

Cao

et al. 2021

Chemical Engineering Journal

101

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The present work examines the NO x emission characteristics of a premixed micro-combustion system with a perforated plate implemented. For this, a three-dimensional (3D) computational model involving a detailed chemical-kinetic mechanism for ammonia-oxygen combustion in the micro-combustor is developed. The model is first validated with the experimental measurements available in the literature before conducting comprehensive analyses. It is found that implementing a perforated plate in the micro-combustion system creates a flow recirculation zone downstream characterized by a low flame temperature and combustion speed. Meanwhile, the conjugate heat transfer between the combustion products and the inner combustor walls is shown to play a key role in the NO generation by relocating the flame in the axial direction and thus changing the chemical reaction rate. Furthermore, the preferential diffusion caused by the variation in the mass diffusivity of different species and the two-dimensionality flow is identified to vary significantly in comparison with the case in the absence of the perforated plate, especially in the vicinity of the recirculation zone. This diffusion effect results in the considerable drop in the N/O atomic ratio, primarily due to the reduction and increase of O 2 and H 2 O, together with less available N 2 , and consequently affecting the NO generation rate. This work confirms that the flow field, the conjugate heat transfer as well as the preferential diffusion effect could be regarded as the potential mechanisms leading to the NO x emission variation in the recirculation zones. Nomenclature 3Dthree-dimensional specific heat of species, CO carbon monoxide CO 2 carbon dioxide CH 4

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Section: D Computational Modelmentioning

confidence: 99%

NO emission performance assessment on a perforated plate-implemented premixed ammonia-oxygen micro-combustion system

Cai

Becker

Cao

et al. 2021

Chemical Engineering Journal

101

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“…Thus, the mean wall temperature improved apparently. Zuo et al enhanced the temperature of wall and uniformity of temperature by developing a micro‐combustor with decreasing wall thickness, 23 constructing micro‐elliptical tube combustors, 24 designing micro‐combustors with rectangular rib 25 and counter‐flow double‐channel micro‐combustors 26 . Additionally, Ni et al 27 studied further on the number of ribs in micro‐combustor, and it showed that the outer wall temperature of two ribs was higher than one ribs under whatever inlet velocity.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigations on the emitter power and energy conversion efficiency improvement of micro‐cylindrical combustor by an internal spiral fin for micro‐thermophotovoltaic systems

Zhao

Yan

et al. 2021

Int J Energy Res

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Aiming at improving the energy output and energy conversion efficiency of thermophotovoltaic systems, a micro-combustor with high and uniform outer wall temperature is desirable. Therefore, the micro-cylindrical combustor with a novel micro-spiral fin is proposed to improve the thermal performance. The effect of inlet velocities of premixed hydrogen/air, the critical design parameters of the spiral fin length (L) and the spiral fin pitch (W) on the thermal performance of the micro-cylindrical combustor are numerically investigated.Results show that micro-spiral fin is beneficial to improve the outer wall temperature value and uniformity, which can significantly increase the emitter power and energy conversion efficiency of micro-cylindrical combustor. However, the improvement of thermal performance is at the cost of higher pressure loss. Furthermore, compared with all the investigated geometrical models, the micro-cylindrical combustor with spiral fin length at the size of 14 mm and spiral fin pitch at the size of 2.355 mm obtains the best comprehensive heat transfer performance.

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“…Zuo et al. 48 numerically investigated the combustion of H 2 –air mixture in a micro cylindrical combustion chamber with and without a rectangular rib. Numerical results showed that by adding a rectangular rib, the heat transfer between the combustor inner wall and the burned mixture is enhanced.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigations on the liftoff velocity of H₂-air premixed combustion in a micro-cylindrical combustor with gradually changed section area

Naeemi

Hashemi

2020

Proceedings of the Institution of Mechanical Engineers, Part C:

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Sustaining and stabilizing flames are crucial issues in micro-combustion. In some micro-electro-mechanical systems such as the micro-thermophotovoltaic system, the flame should be formed in the combustion chamber, not outside it (combustion without liftoff). So, study of the liftoff phenomenon is important and vital in these systems. The aim of this study is to evaluate effect of changing combustor section area on the critical liftoff velocity in a micro-cylindrical combustor. For this purpose, the critical liftoff velocities are numerically identified for four combustor configurations (convergent, divergent, convergent-divergent and divergent-convergent combustion chamber). Premixed mixture of hydrogen-air has been used as reactants for the current investigation. Turbulence model implemented in this paper is RNG k-epsilon and combustion reaction was modeled with 10 species and 21 steps scheme using Eddy Dissipation Concept model. Two non-dimensional numbers d1/d2 (inlet to outlet diameter ratio) and d1/d3 (inlet to throat diameter ratio) are defined. For d1/d2 > 1.0, the combustion chamber is convergent, otherwise it is divergent. When d1/d3 > 1.0, the micro combustor is convergent-divergent and for d1/d3 < 1.0, the micro combustor is divergent-convergent. The results indicate that with increasing d1/d2, the liftoff occurs in a lower inlet flow velocity. With varying d1/d3, from 0.71 (2.0/2.8) to 1.0 (2.0/2.0), the liftoff velocity is reduced. Based on the numerical results, it can be said that the use of convergent and convergent-divergent combustion chamber decreases liftoff velocity. Meanwhile, the combustor with diverging and diverging-converging structure can enhance liftoff velocity. In the same condition, critical liftoff velocity of divergent-convergent micro combustor is the highest among all cases and this configuration is appropriate for Micro Electro-Mechanical Systems that work with high inlet velocity.

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Numerical investigations on an improved micro-cylindrical combustor with rectangular rib for enhancing heat transfer

Cited by 104 publications

References 53 publications

NO emission performance assessment on a perforated plate-implemented premixed ammonia-oxygen micro-combustion system

NO emission performance assessment on a perforated plate-implemented premixed ammonia-oxygen micro-combustion system

Numerical investigations on the emitter power and energy conversion efficiency improvement of micro‐cylindrical combustor by an internal spiral fin for micro‐thermophotovoltaic systems

Numerical investigations on the liftoff velocity of H₂-air premixed combustion in a micro-cylindrical combustor with gradually changed section area

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Numerical investigations on an improved micro-cylindrical combustor with rectangular rib for enhancing heat transfer

Cited by 104 publications

References 53 publications

NO emission performance assessment on a perforated plate-implemented premixed ammonia-oxygen micro-combustion system

NO emission performance assessment on a perforated plate-implemented premixed ammonia-oxygen micro-combustion system

Numerical investigations on the emitter power and energy conversion efficiency improvement of micro‐cylindrical combustor by an internal spiral fin for micro‐thermophotovoltaic systems

Numerical investigations on the liftoff velocity of H2-air premixed combustion in a micro-cylindrical combustor with gradually changed section area

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Numerical investigations on the liftoff velocity of H₂-air premixed combustion in a micro-cylindrical combustor with gradually changed section area