Figure 2-4.—Single-pass SW/DW heat exchanger with double-tube sheets.
Figure 2-5.—Two-pass SW/DW heat exchanger with single-tube sheets.
Double-tube sheets are used at both ends of a tube
bundle. A void space between the sheets prevents
contamination of the distilled water and permits the
monitoring of water loss due to tube leakage. You
should be on the lookout to detect leakage at the
“telltale drains,” which indicates a failure of a tube
joint. The type of water leaking out indicates whether
the failure is in the primary or secondary system. The
telltale drains should never be plugged or capped off.
A leak in one of the tubes shows up as a loss of
water in the secondary side of the liquid-cooling sys-
tem, because it operates at a higher pressure than the
primary side. This is intentional, as it ensures that the
distilled water is not contaminated with seawater
when a leak develops in a heat exchanger.
A double-pass heat exchanger is generally used
when there is limitation on the installation of the heat
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