An analogy between reaction and heat transfer

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Some of the simplifying assumptions that underlie the characteristic concepts of chemical engineering are identified and their impact is examined. Many of them are found to be obsolete. They remain in textbooks and perhaps in computer packages out of inertia and, in some instances, out of misdirected respect for those who conceived them. It is concluded that students, teachers, and industrial practitioners should question the continued validity of simplifying assumptions and of the viability of the concepts and expressions that incorporate them.

Section: Analogiesmentioning

confidence: 99%

An Evaluation of the Usual Simplifying Assumptions

Churchill¹

2012

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“…The principal idealizations, which are significant in a practical sense, were the neglect of the development of the flow and of the variation of the physical properties with temperature, composition, and pressure. With those values as a database, Churchill 38 discovered several generalities and derived several closed-form solutions, with only one empirical coefficient, for the enhancement of the heat transfer coefficient for forced convection. These two sets of results are for particular and somewhat idealized chemical conditions, primarily one firstorder, irreversible, equimolar reaction, but they provide guidelines for numerical and closed-form solutions for more complex reacting systems such as those encountered in radiantly stabilized combustion.…”

Section: The Operational Characteristics Of the Integrated Water Boilermentioning

confidence: 99%

Guidelines for Modeling Based on Experiences with Radiantly Stabilized Combustion

Churchill

2008

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Many processes of interest in chemical engineering are yet beyond the reach of a numerical solution in a practical sense. For such processes, creative modeling by means of idealizations and approximations and innovative methods of solution may be needed. Homogeneous combustion, because of extreme temperature gradients, developing flow, turbulent convection of momentum, energy, and species, thermal radiation, and a seemingly unlimited array of free-radical reactions, each with a complex and uncertain dependence on temperature, exemplifies such a process. Guidelines for such modeling have been identified from the accumulative experiences of a long sequence of research on one form of combustion, namely that stabilized primarily by thermal radiation.

“…Analogies for Waves. 88 devised an analogy between chemical reactions and external heat transfer in fully developed tubular flow. This expression differs radically in character from the classical ones for fluid flow and heat transfer in that it is for developing and interacting reaction and heat transfer, and in that it encompasses both the laminar and the turbulent regimes.…”

Section: Analogies Between Momentum and Energymentioning

confidence: 99%

Role of Universalities in Chemical Engineering

Churchill

2007

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Chemical engineering has survived and thrived for over 100 years, while many other branches of engineering have vanished or faded. This survival may be attributed to several factors, one of which is the more pervasive and effective utilization of universalities in the form of generalizations, simplifying concepts, and analogies. At the same time, many of the generalities, simplifying concepts, and analogies in current textbooks, handbooks, and even computer design packages are wrong or obsolete and should be deleted or noted to be only of historical interest. The radical changes that are currently afoot in chemical engineering and in the world in which it is now practiced can be expected to make many more obsolete or irrelevant, thereby creating a need and/or opportunity for the formulation of new ones. The origin and the past, present, and future role, if any, of the generalizations are examined in Parts I and II; that of the simplifying concepts are examined in Part III, and that of the analogies are examined in Part IV.