Q1: A solid material shows case hardening properties while drying. Which of the following should be controlled to control the drying process ?

ANS:D - Temperature of the solid

To control the drying process and prevent case hardening in a solid material, it's essential to manage the drying conditions effectively. The factors that influence case hardening during drying include the rate of moisture removal from the surface of the material and the internal moisture gradient within the solid. Controlling the temperature of the solid is crucial to prevent case hardening. If the temperature of the solid material is too high during drying, it can lead to rapid moisture evaporation from the surface, forming a crust or skin that inhibits further moisture migration from the interior. This phenomenon can result in case hardening, where the outer layer becomes hardened while moisture remains trapped inside, leading to uneven drying and potential quality issues. Therefore, by controlling the temperature of the solid material during drying, you can help ensure that moisture removal occurs evenly throughout the material, minimizing the risk of case hardening. While controlling the flow rate of inlet air, relative humidity of outlet air, and humidity of inlet air can also influence the drying process, they may have less direct impact on case hardening compared to temperature control. However, optimizing these factors in conjunction with temperature control can further enhance the efficiency and effectiveness of the drying process.