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ERIC Number: EJ829435
Record Type: Journal
Publication Date: 2007
Pages: 5
Abstractor: As Provided
Reference Count: 0
ISSN: ISSN-0009-2479
The Devil's in the Delta
Luyben, William L.
Chemical Engineering Education, v41 n1 p19-23 Win 2007
Students frequently confuse and incorrectly apply the several "deltas" that are used in chemical engineering. The deltas come in three different flavors: "out minus in", "big minus little" and "now versus then." The first applies to a change in a stream property as the stream flows through a process. For example, the "[delta]H" in an energy balance around a unit is the difference between the enthalpies of the streams leaving and the enthalpies of the streams entering. The second delta is a driving force difference. In heat transfer, it is "hot temperature minus cold temperature." In mass transfer, it is "large chemical potential minus small chemical potential." The chemical potentials can be partial pressures, molar or mass concentrations, mole fractions or activities. The third delta indicates the change in a variable with time. For example, in a batch reactor the [delta]CA means the change in concentration of component A over some time period between t = t1 and t = t2. The delta in time is [delta]t = t2 - t1. Although the distinctions among these various deltas and their appropriate application should be obvious and fundamental, students frequently use the wrong delta. This note is intended to provide a friendly suggestion to professors that they remind their students of the need to be careful in applying deltas. (Contains 3 figures.)
Chemical Engineering Education, Chemical Engineering Division of ASEE. P.O. Box 142097, Gainesville FL 32614. Tel: 352-392-0861; Fax: 352-392-0861; e-mail:; Website:
Publication Type: Journal Articles; Reports - Descriptive
Education Level: Higher Education
Audience: Students; Teachers
Language: English
Sponsor: N/A
Authoring Institution: N/A