Q1: In evaporators, lowering the feed temperature

ANS:C - both (a) and (b).

In evaporators, lowering the feed temperature generally increases the heating area required and reduces the economy. Lowering the feed temperature increases the temperature difference between the feed and the heating medium, which in turn increases the heat transfer area required to achieve the desired rate of evaporation. Additionally, lower feed temperatures often require more energy input to achieve the desired level of evaporation, reducing the overall energy efficiency or economy of the evaporator system. So, the correct option is: both (a) and (b). a) Increasing the heating area required: When the feed temperature is lowered in an evaporator, it results in a smaller temperature difference between the feed and the heating medium. As a consequence, the rate of heat transfer between the heating medium and the feed is reduced. To compensate for this decrease in heat transfer rate and maintain the desired evaporation rate, a larger heating area is needed. This is because a larger heating surface area allows for more efficient heat transfer, ensuring that sufficient heat is transferred to evaporate the desired amount of liquid. b) Reducing the economy: The economy of an evaporator refers to its efficiency in terms of energy consumption. Lowering the feed temperature often requires more energy input to achieve the desired level of evaporation. This increased energy consumption reduces the overall efficiency or economy of the evaporator system. Additionally, the need for a larger heating area, as explained in point (a), can lead to higher capital and operational costs, further reducing the economic efficiency of the evaporator. In summary, lowering the feed temperature in an evaporator increases the heating area required due to reduced heat transfer rates and decreases the economy due to increased energy consumption and potentially higher costs associated with a larger heating area.