8.8.1 Thermal/hydraulic design of a flashing drain cooler
The temperature of the feedwater leaving the heater for a specified temperature difference is found by performing a heat balance over the drain cooler (Fig 3.62 (c)).
The temperatures required to complete the diagram shown in Fig 3.62 (b) are now available. Assuming that all the condensate flows through the drain cooler tubenest, then the tubenest will have the same number of tubes as the LP heaters in the feed system. The overall diameter will also be the same. The LMTD calculation is shown in Fig 3.62 (b). The heat transfer surface is then found using the same method as for a normal LP heater.