Interaction of Chemical Reactions and Transport. 1. An Overview

Abstract

Chemical reactions, fluid mechanics, heat transfer, and mass transfer have both direct and indirect interactions. The direct ones, which are examined here, involve the effects of the fundamental mechanisms of reaction and transport on one another. The indirect ones, which arise from combined reactors, heat exchangers, and separators, are to be examined separately. Although most of the direct interactions have been recognized for decades, the investigations of such phenomena experimentally, theoretically, and numerically are very limited in number and scope. Furthermore, they are scarcely mentioned in textbooks on either chemical reaction engineering or transport. They could readily be incorporated in the software for computer-aided process design but have not, possibly because of the significant added complexity but more likely because of a lack of recognition of their importance or even their existence. In a supplementary investigation, selective numerical calculations have shown that, although the interactions between reaction and transport are of second order in magnitude in some applications, they are critical in others. Accordingly, in another supplementary investigation, new concepts, generalizations, and asymptotes have been devised to encompass these interactions and thereby abet their inclusion in future textbooks and software.

Pressure Loss and Transfer Rates in Microstructured Devices with Chemical Reactions

“…Each reaction and mixer/reactor has to be treated in more detail for safe and efficient operation. In his review paper, Churchill [35] gave a more detailed picture of the interaction of chemical reactions and transport processes.…”

The Interaction of Reactions and Transport Part II: Combined Reactors and Exchangers

“…This anomaly was eventually explained by the enhancement of the convective heat transfer coefficient by the heat of reaction associated with combustion as discussed by Churchill (2005). This anomaly was eventually explained by the enhancement of the convective heat transfer coefficient by the heat of reaction associated with combustion as discussed by Churchill (2005).…”

“…These several fundamental interactions are examined in a prior manuscript (Churchill, 2005). Owing to the non-linear dependence of the rate of reaction on temperature, as exemplified by the Arrhenius equation, and the non-linear dependence on concentration for all but first-order reactions, the turbulent fluctuations in temperature result in increases in the rates of reaction, and those in composition result in a decreases relative to that based on the time-mean values of temperature and composition.…”

An analogy between reaction and heat transfer

“…The step that proved absolutely crucial to what follows was the prior derivation by Churchill 8 of an exact solution in closed form for a very idealized process of flow, reaction, and heat transfer-that is, fully developed convection in fully developed laminar flow through a round tube with a volumetrically uniform rate of reaction, a uniform heat flux density through the wall, and radial conduction of heat, but no radial diffusion of species. A volumetrically uniform rate of reaction might be rationalized on the basis of asymptotically small perturbations in the composition attributed to the reaction and in the temperature attributed to the combination of the heat of reaction and the imposed heat flux.…”