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Research Papers: Combustion and Reactive Flows

The Wall Heat Transfer Phenomenon of Premixed CH4/Air Catalytic Combustion in a Pt Coated Microtube

[+] Author and Article Information
Jing-yu Ran

e-mail: ranjy@cqu.edu.cn

Sheng Wu

e-mail: wusheng924@sohu.com

Key Laboratory of Low-grade
Energy Utilization Technologies
and Systems of the Ministry of Education,
Chongqing University,
Chongqing 400044, China

Lin Yang

Key Laboratory of Low-grade Energy
Utilization Technologies and
Systems of the Ministry of Education,
Chongqing University,
Chongqing 400044, China;
School of Computer Science
and Information Engineering,
Chongqing Technology and Business University,
Chongqing 400067, China
e-mail: ctbuyanglin@163.com

Li Zhang

Key Laboratory of Low-grade Energy
Utilization Technologies
and Systems of the Ministry of Education,
Chongqing University,
Chongqing 400044, China
e-mail: lizhang@cqu.edu.cn

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received October 11, 2011; final manuscript received August 18, 2013; published online November 7, 2013. Assoc. Editor: Wei Tong.

J. Heat Transfer 136(2), 021201 (Nov 07, 2013) (9 pages) Paper No: HT-11-1470; doi: 10.1115/1.4025429 History: Received October 11, 2011; Revised August 18, 2013

In this paper, a 2D model with detailed heterogeneous chemical mechanism has been employed to investigate the heat transfer phenomenon of premixed CH4/air catalytic combustion in a Pt coated microtube. Especially, the thermal processes such as coupled heat transfer between the internal surface of the microtube and the gas phase, thermal conduction along the solid structure, convection and radiation between the external surface and the environment are comprised in the simulation. The results show that the thermal conductivity of different solid wall materials dramatically affects the uniformity of temperature distribution of the catalytic surface. To maintain stable combustion in the microtube, the thermal conductivity should exceed 0.49 W/m/K at least and conductive walls (FeCr alloy and corundum ceramic) are more appropriate to manufacture microcombustors. The extremely small Biot number at the external surface indicates that convective heat transfer coefficient and emissivity to the environment are the key factors determining the heat loss of the microtube. The amount of heat loss influences the reaction rate and residence time of the mixtures in the microtube, which would affect the conversion of CH4. An increase of the wall thickness improves the heat transfer along the solid structure, also increases the total heat loss.

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References

Figures

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Fig. 1

Schematic of the microtube configuration

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Fig. 2

(a) Temperature distribution of the axis with different grid numbers and (b) comparison of temperature distribution of the axis and spatial mass fraction of CH4 with and without a homogeneous mechanism

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Fig. 3

Temperature distribution of the catalytic surface with different thermal conductivity

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Fig. 4

(a) Average temperature of the external surface with different wall thermal conductivity and (b) heat loss with different wall thermal conductivity

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Fig. 5

Average temperature and heat loss of the microtube with different convective heat transfer coefficient

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Fig. 6

Critical convective heat transfer coefficient with different inlet Re number

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Fig. 7

CH4 conversion at the exit of tube and the average velocity in the microtube with different convective heat transfer coefficient

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Fig. 8

Temperature distribution of the catalytic surface with different wall thickness

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Fig. 9

Heat loss from the external surface with different wall thickness

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Fig. 10

Heat loss of the microtube with different emissivity

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Fig. 11

The lowest inlet temperature with different emissivity

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