8.8.2 Thermal/hydraulic design of a water-to-water drain cooler
The temperature out of the drain cooler is found by a heat balance over the drain cooler as shown in Fig 3.62; however, in this case the drains flow is treated as hot water.
The heat transfer coefficient is calculated as for an HP or LP internal drain cooler, using the temperatures indicated in Fig 3.62 (e).
The tubenest will have the same number of tubes as the first LP heater for full condensate flow, and will have the same shell diameter as the LP heaters.
The baffle pitch is determined by the need to maintain the velocity of the water across the tubes to give the needed heat transfer coefficient.
The drain cooler actually used depends on the manufacturer's assessment of the most cost effective type for a particular installation.