Heat and mass transfer coefficients in catalytic monoliths

Gupta, Nikunj; Balakotaiah, Vemuri

doi:10.1016/s0009-2509(01)00134-8

Cited by 129 publications

(93 citation statements)

References 12 publications

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“…This minimum is always found when the inlet temperature of the gas is below the temperature of the side walls. In literature [13], a minimum value for the Nusselt number has also been observed when heat transport is influenced by the wall heat conduction. It is reported that at low Gz h , the Nu t and Nu sb are approximately equal to the value for the situation when the side walls have the same temperature as the inlet temperature.…”

Section: Nusselt Correlation For Laminar Flowmentioning

confidence: 98%

Heat and mass transfer in a square microchannel with asymmetric heating

Male

Croon

Tiggelaar³

et al. 2004

International Journal of Heat and Mass Transfer

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This paper describes the heat and mass transfer in a square microchannel that is heated from one side. This microchannel represents a reaction channel in a microreactor that is used to study the kinetics of the catalytic partial oxidation of methane. The microchannel is contained in a silicon wafer and is covered by a thin silicon sheet. At the top side of this sheet, heating elements are present which mimic the heat that is produced as a result of the exothermic chemical reaction. Correlations for Nusselt and Sherwood numbers as a function of the Graetz number are derived for laminar and plug flow conditions. These correlations describe the heat and mass transport at the covering top sheet of the microchannel as well as at its side and bottom walls. By means of computational fluid dynamic simulations, the laminar flow is studied. To determine an approximate laminar flow Nusselt correlation, the heat transport was solved analytically for plug flow conditions to describe the influence of changes in the thermal boundaries of the system. The laminar flow case is experimentally validated by measuring the actual temperature distribution in a 500 lm square, 3 cm long, microchannel that is covered by a 1 lm and by a 1.9 lm thick silicon sheet with heating elements and temperature sensors on top. The Nusselt and Sherwood correlations can be used to readily quantify the heat and mass transport to support kinetic studies of catalytic reactions in this type of microreactor.

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Section: Nusselt Correlation For Laminar Flowmentioning

confidence: 98%

Heat and mass transfer in a square microchannel with asymmetric heating

Male

Croon

Tiggelaar³

et al. 2004

International Journal of Heat and Mass Transfer

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“…Among them, only three are of interest to chemical engineers: (1) constant temperature asymptote Nu T,ϱ , where both circumferentially and axially uniform wall temperature is specified; (2) constant flux asymptote of the first kind, Nu H 1 ,ϱ , where circumferentially constant wall temperature and axially constant wall flux are specified; and (3) constant flux asymptote of the second kind, Nu H 2 ,ϱ , where both axially and circumferentially uniform wall fluxes are specified. It is a well known fact that, for a straight circular channel with wall reactions, the asymptotic Sherwood numbers are bounded by constant flux and constant concentration (temperature) asymptotes and vary smoothly from one to the other as the local Damkö hler number s 2 varies from 0 to ϱ (Gupta and Balakotaiah, 2001;Tronconi and Forzatti, 1992). It will be shown here that the presence of a washcoat around the circular flow areas does not alter the asymptotes but shifts the transition regime between them.…”

Section: Introductionmentioning

confidence: 69%

“…Nevertheless, in the mass transfer controlled regime, Nu ϱ reaches the constant temperature asymptote of the flow geometry as the asymptotic Sherwood number. It should be pointed that the accurate values for the asymptotic Sherwood or Nusselt numbers in the kinetic regime are needed to predict the light-off or ignition point accurately, as shown by Gupta and Balakotaiah (2001).…”

Section: Discussionmentioning

confidence: 99%

“…It is a well-known fact that the asymptotic Sherwood number for circular or parallel-plate duct with wall reaction (that is, with negligible washcoat diffusional limitations), varies from constant flux (Sh H,ϱ ) to constant concentration (Sh T,ϱ ) asymptote as s 2 varies from 0 to ϱ (Gupta and Balakotaiah, 2001;Tronconi and Forzatti, 1992). For these geometries, the constant flux asymptotes of first (Sh H 1 ,ϱ ) and second (Sh H 2 ,ϱ ) kind are the same because of the 1-D diffusion in the transverse direction, whereas they differ from each other for channels with other geometries, such as square, triangle, and so forth, where transverse diffusion is 2-D. Table 1 lists the values for the asymptotic Sherwood or Nusselt numbers for some commonly used channel geometries.…”

Section: Analytical Solutions (For Linear Kinetics)mentioning

confidence: 99%

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Mass‐transfer coefficients in washcoated monoliths

Bhattacharya¹,

Harold²,

Balakotaiah³

2004

AIChE Journal

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“…Likewise, the numerical error that arises in the calculation of Sherwood and Nusselt numbers near ignition/extinction points, attributed to the Gibbs phenomenon, has not been recognized in the literature except for some recent work (Gupta and Balakotaiah, 2001). As shown by Gupta and Balakotaiah (2001) both the 1-D two-phase and the 2-D/3-D models that do not include solid conduction are index infinity differentialalgebraic systems and the standard method of solution (discretization in the transverse direction and integration in the axial direction) gives only one of these solutions and even this one solution has significant error near the ignition point, attributed to the Gibbs phenomenon.…”

Section: Introductionmentioning

confidence: 99%