Q1: Economy of an evaporator is influenced by the

ANS:D - both(b) & (c)

a) Steam pressure: The steam pressure used in an evaporator system affects the temperature at which the evaporation occurs. Higher steam pressures generally result in higher temperatures, which can increase the rate of evaporation and the overall efficiency of the system. However, higher steam pressures may also require more energy input, so there's a trade-off between increased evaporation rate and energy consumption. Optimizing the steam pressure is essential to achieve the desired level of efficiency and economy in the evaporator system. b) Feed temperature: The temperature of the feed entering the evaporator system influences its efficiency. A higher feed temperature can reduce the temperature difference between the feed and the heating medium, which in turn reduces the driving force for heat transfer and may decrease the energy consumption. However, excessively high feed temperatures can also lead to issues such as thermal degradation of the feed or scaling within the evaporator. Therefore, controlling the feed temperature within an optimal range is crucial for maximizing the efficiency and economy of the evaporator system. c) Number of effects: The number of effects in a multiple-effect evaporator system significantly impacts its economy. Each additional effect utilizes the latent heat of vaporization from the previous effect, leading to a cascading effect that reduces the energy consumption per unit of water evaporated. As a result, increasing the number of effects improves the overall efficiency and economy of the evaporator system. However, adding more effects also increases the capital and operating costs of the system, so there's a balance to be struck between the benefits of additional effects and the associated costs. In summary, while steam pressure and feed temperature play important roles in the efficiency of an evaporator system, the number of effects has a particularly significant impact on its economy due to the cascading heat utilization effect. Therefore, optimizing all these factors is essential to achieve the desired level of efficiency and economy in evaporator operations.