## Rating Method for Air-Cooled Exchangers

The rating methods for air-cooled exchangers are outlined by Cook [386] and Ganapathy [387]. Here, the preliminary design of air coolers is based upon correlations, tables and graphs presented by Smith [106] and Brown [388] and fitted to a series of equations developed by Blackwell [381].

### The Equations

1. The number of tube rows, R is:

$R={C}_{1}+{C}_{2}\mathrm{ln}\left[\frac{{T}_{2}-{t}_{2}}{U}\right]$

(15-522)

where:

C

_{1}= 3.1679C

_{2}= 3.79482. The area ratio is:

$\frac{A}{FA}={C}_{3}{\left(R\right)}^{{C}_{4}}$

(15-523)

where

C

_{3}= 1.2557C

_{4}= 1.00313. The face velocity of air, FV, ft/min.

$FV={C}_{5}{(}^{}$

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