Variation of (a) total heat transfer surface area, and (b) steam economy with pressure in the last effect at various vapor bleeding configurations e) Effect of pressure in the last effect on steam economy for different bleeding configurations Steam economy is the number of kilograms of water vaporized from all the effects per kilogram of steam use (Chantasiriwan, 2017). Pressure in the last effect is related to the steam requirement of the system, as discussed above. An increase in pressure in the last effect increases steam requirement of the system as the system is trying to compensate for the lost overall temperature difference driving force. Also, an increase in steam requirement, decreases steam economy of the system. The variation of steam economy with pressure in the last effect is presented in Figure 12 (b) where different bleeding configurations are compared. Increasing pressure in the last effect decreases the steam economy of the system as shown in Figure 12 (b). With incorporation of vapor bleeding, steam economy of the system is restored and improved more. Again, simulation results show that, bleeding by a combination of E1&E3gives the highest steam economy in the system as compared to other bleeding configurations. Furthermore, bleed E3 and bleed E4show similar results of steam economy in the system. Similarly, bleed E1 and a combination of E2&E4 give same results. Therefore, for the five-effect evaporator system, with a concern to improve its performance, vapor bleeding is the method to use as it reduces steam consumption and improves steam economy of the system as shown in Figure 12(b). With a well selected and implemented bleeding configuration such as combination of E 1 &E 3 the system performance is highly improved than using other configurations.