June 22, 2008
June 22, 2008
June 25, 2008
13.1388.1 - 13.1388.18
Visual Basic Software for Design and Performance Problems Introduction
Most chemical engineering textbooks still show graphical solutions for certain routine design calculations. The Moody plot for friction factors, which is based on experimental data, and the corresponding plots for flow past submerged objects are examples. However, in recent years, curve fits for these have yielded equations that are at least as accurate as reading a graph. Graphs of the Kremser and Colburn equations for separations in dilute systems are another example; although, these equations were derived in order to construct the plots. For heat exchangers, the log-mean-temperature-difference (LMTD) correction factor is generally read from a graph since most textbooks do not provide the appropriate equations, even though the graphs are obtained from these equations.
If the equations are used, it is possible to obtain the information found on the graph and to do design and performance calculations more accurately by means of a computer program. In this paper, we describe Visual Basic for Applications (VBA) programs written for the following design problems: flow in pipes, flow past submerged objects (including packed and fluidized beds), separation in dilute systems, and heat exchangers. The programs not only find the parameters usually obtained from a graph (friction factor, drag coefficient, absorption or stripping factor, LMTD correction factor) but they also perform routine design and performance calculations. The definitions used here are that a design calculation is used to determine the size of a unit with a given input and a desired output, and a performance calculation is used to determine the output of a unit with a given input and a given size.
These programs are not meant to replace process simulators; they are meant to be teaching tools that are more accessible to students than process simulators.
Description of Programs
Table 1 summarizes the programs that will be available for demonstration. Additional details of each program follow.
Separation in Dilute Systems
The relationships used are the Kremser equation1
y A,out − y* , out A 1− A = (1) y A,in − y* ,out A 1 − A N +1
if A = 1
y A,out − y* , out A 1 = (2) y A,in − y* , out A N +1
Brak, N., & Shaeiwitz, J., & Turton, R. (2008, June), Visual Basic Software For Design And Performance Problems Paper presented at 2008 Annual Conference & Exposition, Pittsburgh, Pennsylvania. https://peer.asee.org/3156
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