## 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:

$R=C1+C2ln[T2−t2U]$

(15-522)

where:
C1 = 3.1679
C2 = 3.7948
2. The area ratio is:

$AFA=C3(R)C4$

(15-523)

where
C3 = 1.2557
C4 = 1.0031
3. The face velocity of air, FV, ft/min.

$FV=C5($

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