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Research Papers

The Interplay of Heat Transfer and Endothermic Chemistry Within a Ceramic Microchannel Reactor

[+] Author and Article Information
Danielle M. Murphy, Margarite Parker

Department of Mechanical Engineering,
Colorado School of Mines,
1500 Illinois Street,
Golden, CO 80401

Neal P. Sullivan

Department of Mechanical Engineering,
Colorado School of Mines,
1500 Illinois Street,
Golden, CO 80401
e-mail: nsulliva@mines.edu

1Corresponding author.

Manuscript received August 16, 2013; final manuscript received November 27, 2013; published online February 26, 2014. Assoc. Editor: Ranganathan Kumar.

J. Thermal Sci. Eng. Appl 6(3), 031007 (Feb 26, 2014) (7 pages) Paper No: TSEA-13-1139; doi: 10.1115/1.4026296 History: Received August 16, 2013; Revised November 27, 2013

Ceramic microchannel heat-exchanger and reactor technology is capable of achieving high performance while operating under high-temperature, corrosive, and/or oxidative environments. This work describes two computational fluid dynamics (CFD) modeling studies which examine the coupling of heat transfer and endothermic methane-steam-reforming chemistry within a ceramic microchannel reactor. These modeling tools are then applied to improve microchannel-reactor design and performance. Within the reactor, methane is converted to syngas through steam reforming; the thermal requirements for this endothermic chemistry are provided by heat transfer from hot-inert gas on adjacent layers. Fluid flow, heat transfer, and complex elementary surface chemistry are all simulated using the ANSYS FLUENT models. CFD studies reveal the substantial chemical contribution of reforming on thermal gradients across and within the reactor. Improved control of the reforming temperature is also discovered through stack-design analysis, where an odd number of inert-gas layers are found to create more-uniform reactive wall temperatures. Model results provide insight on the interplay of conjugate heat transfer and chemical kinetics in reactor design.

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Figures

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Fig. 1

(a) Photograph of microchannel heat exchanger/reactor. (b) Exploded illustration showing hot inert (red) and cold reactive (blue) gas-flow paths in a counterflow configuration. Magnified section highlights lamination points required for hermetic sealing during fabrication. (Reprinted with permission from Murphy et al., 2013, International Journal of Hydrogen Energy, 38, pp. 8741–8750. Copyright 2013 Elsevier [16].)

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Fig. 2

Geometrically simplified four-layer model geometry (with dimensions)

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Fig. 3

(a) 2D temperature field down the center length of reactive channel 1; (b) net heat of reaction on the reactive surface within reactive channel 1; (c) 2D temperature field down the center length of inert channel 1. In all figures, the width (x direction) is magnified by a factor of five.

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Fig. 4

Temperature profiles in the vertical (y) direction located at (a) z = 17.9 mm; and (b) z = 53.7 mm. Transverse position is held constant in the center of the reactor at x = 2.3 mm.

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Fig. 5

Geometrically simplified model geometry for the five-layer design (with dimensions)

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Fig. 6

Average wall temperatures in the four- and five-layer designs as a function of axial position z within the reactive channels

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Fig. 7

Microchannel-reactor model results comparing performance of four- and five-layer designs. Experimental results for four-layer reactor are shown as symbols. (a) Temperature of exhaust streams, (b) product mole fractions, and (c) methane conversion, hydrogen yield, and carbon monoxide selectivity as a function of GHSV.

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Fig. 8

Model-predicted thermal and mole-fraction fields: (a) reactive-side gas temperature, (b) mole fraction of CH4, and (c) mole fraction of H2 as a function of channel width (x) and axial position (z) down the center of reactive channel two for the 50,000 h−1 GHSV case. The x-axis is scaled by a factor of 5 relative to the z-axis.

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