This Excel spreadsheet series is drawn from an article by David Clough that appeared in AIChE's CEP Magazine. Share your tips, on Engage!ĭo you have some tips of your own about spreadsheets? If you're a member, I'd love you to share them on AIChE Engage. Clough, the author of this series, and combines two of AIChE’s most popular spreadsheet courses, Spreadsheet Problem-Solving for Chemical Engineers and Excel VBA Programming for Chemical Engineers. If you know you want to delve even deeper than this blog series – or if our Excel tips leave you hungry for more – be sure to check out AIChE’s virtual combo course on spreadsheet problem solving and VBA programming.
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And if you want a full crash course instead of just helpful tips, you should check out the AIChE Academy's " Spreadsheet Problem-Solving for Chemical Engineers," where these tips come from, and also check out the other Excel courses available through the AIChE Academy at Want more Excel tips for chemical engineers? If you're just joining us, check out the entire series. Below is a spreadsheet that arranges this calculation, with the underlying formulas, which follow beneath the spreadsheet. Therefore, a simple, analytical solution is not available. Notice that in order to compute f M, we need a value of f M for the right-hand side of Eq. As a simple example, we can use the Colebrook equation relating the Moody friction factor ( f M), Reynolds number ( Re), pipe inside diameter ( D i), and pipe roughness (ε) for turbulent flow: I suggest taking advantage of Excel’s Iterative Solver to converge circular calculations. For cases of nonconvergence, numerical methods are available, notably that of Wegstein, that may force convergence. It is possible in some cases to reformulate this problem mathematically to eliminate the circular calculation, but that leaves the scheme in an unnatural format that is more difficult to manage and understand.Ĭircular calculations that use a simple substitution method do not always converge, but in chemical engineering problem-solving they commonly do converge. The strategy for solving such calculations is to specify a starting value and then “recycle” the value calculated later until the loop converges. In such a situation, a value is needed to continue the calculation, but that value is calculated later in the scheme. In a more general sense, many process calculations, when laid out in logical sequence, involve circular calculations. A process with a recycle stream involves a circular calculation that cannot proceed automatically because of its iterative nature. One of the main reasons chemical engineers became attracted to spreadsheets was for their ability to carry out flowsheet calculations. Do you have some tips of your own about spreadsheets? If you're a member, I'd love you to share them on AIChE Engage.