Psychrometric Behavior during Adiabatic Drying:

• In an adiabatic drying process, unsaturated air passes over a moist bed with no net heat exchange with the surroundings. Sensible heat from the drying air provides the latent heat needed for water evaporation from the crop.
• As sensible heat is consumed, the dry bulb temperature (DBT) drops along a constant wet bulb temperature / constant enthalpy line.
• The evaporated moisture enters the air stream, directly increasing the humidity ratio (specific humidity, $W$).
• Because humidity ratio increases, the partial pressure of water vapour ($p_v$) increases proportionately: $p_v = \frac{W \cdot P}{0.622 + W}$.
• Simultaneously, lower temperature reduces saturation vapor pressure ($p_s$), so relative humidity ($\text{RH} = p_v / p_s$) increases markedly.

Working Principle of the LSU (Louisiana State University) Dryer:

• Assertion (A) is True: The LSU dryer is the standard commercial continuous flow-mixing type grain dryer, specifically designed for paddy to eliminate moisture gradients across the grain bed.
• Reason (R) is True: The vertical drying column contains alternating rows of inverted V-shaped sheet metal ducts (air ports). Grain descends slowly by gravity between these ports from feed to discharge, while hot air is introduced through inlet ports and exhausts through alternating exhaust ports.
• Explanation: The staggered placement of these inverted V-shaped ducts splits and deflects the descending grain stream constantly, forcing thorough mixing while air flows across the grain layers. Hence, Reason (R) correctly explains Assertion (A).

Thermodynamics of Freeze Drying (Lyophilization):

• Principle: Freeze drying (lyophilization) is a dehydration method where product moisture is first completely frozen into solid ice below its final eutectic / glass transition temperature.
• Sublimation: The frozen product is then subjected to deep vacuum below the triple point of water ($611.7\text{ Pa}$, $0.01^\circ\text{C}$) while supplying gentle heat. Under these thermodynamic conditions, ice sublimes directly into water vapour without entering the liquid state ($S \to V$).
• Comparison: Individual quick freezing (IQF) rapidly freezes particulate food into discrete items without removing water, whereas freezing simply lowers temperature below freezing.

The LSU dryer is a continuous-flow, baffle-type (mixing type) column dryer specifically designed for cereal grains, particularly paddy (C) and pulses (A). It provides uniform drying without over-heating grain kernels, preventing head rice breakage. It is not suitable for perishables like marine products or fruits/vegetables. Option analysis: (A) Marine products cannot be dried in column baffle dryers. (B) Fruits/vegetables require tray/tunnel dryers. (C) (A) and (C) only (pulses and paddy) are suitable granular crops. (D) Marine products are unsuitable.