With increase in the mass velocity of the gas, the rate of drying during the constant rate period __________ , if the conduction and radiation through the solid are negligible.

ANS:A - increases

With an increase in the mass velocity of the gas during the constant rate period of drying, and assuming conduction and radiation through the solid are negligible, the rate of drying generally increases. Explanation:

• During the constant rate period of drying, the rate of moisture removal from the solid material is primarily controlled by the rate of mass transfer of moisture from the interior of the solid to the surface.
• Increasing the mass velocity of the drying gas results in higher convective heat and mass transfer rates at the solid-gas interface.
• Higher mass velocity enhances the boundary layer thinning effect, reducing the thickness of the stagnant gas film adjacent to the solid surface. This thinning of the boundary layer promotes faster mass transfer of moisture from the solid to the gas phase.
• As a result, the rate of drying increases with an increase in the mass velocity of the gas, allowing for more rapid removal of moisture from the solid material.
• However, it's important to note that this relationship may be influenced by various factors such as the properties of the drying gas, the characteristics of the solid material, and the design of the drying system.