The Pusa bin is a low-cost, moisture-proof grain storage structure developed by the Indian Agricultural Research Institute (IARI). It is designed primarily for small-scale farmers to store grains safely, with a standard capacity typically ranging between 2 to 4 tons depending on the specific model and dimensions.

During the constant drying rate period, the surface of the food is fully saturated with moisture, maintaining a water activity of 1. Once the critical moisture content is reached, the surface can no longer be kept fully wet by internal moisture migration, causing the water activity at the surface to drop below 1 as the falling rate period begins.

Sensible cooling involves reducing the dry-bulb temperature of air without changing its moisture content. Since the saturation vapor pressure of air decreases as temperature drops, the relative humidity, which is the ratio of actual vapor pressure to saturation vapor pressure, must increase.

Thermal radiation, often referred to as infrared radiation, occupies the electromagnetic spectrum range between visible light and microwaves. The wavelength range is approximately 0.1 micrometers to 100 micrometers, which corresponds to 10^-7 to 10^-4 meters. This radiation is emitted by all matter with a temperature above absolute zero and is a primary mode of heat transfer in agricultural drying and environmental processes.

The Henderson equation is a widely used empirical model in agricultural engineering to describe the relationship between the equilibrium moisture content of agricultural products and the relative humidity of the surrounding air. It is particularly useful for designing grain drying and storage systems, as it helps predict how moisture will move between the product and the environment.

Proper aeration is essential for maintaining grain quality. A perforation rate of approximately 15% in aeration ducts is generally recommended to ensure uniform airflow distribution through the grain bulk while maintaining the structural integrity of the ductwork and preventing excessive pressure drops.

The formula to convert moisture content from wet basis (Mw) to dry basis (Md) is Md = Mw / (1 - Mw). Given Mw = 0.20, the calculation is 0.20 / (1 - 0.20) = 0.20 / 0.80 = 0.25, which equals 25%.

The Morai is a traditional storage structure used in various parts of India, specifically designed with an inverted truncated cone shape. This design helps in protecting stored grains from moisture and pests by elevating the storage area and allowing for better ventilation and drainage around the base.

Proper storage management requires that bags be stacked evenly, ideally against supporting walls to maintain structural integrity. To prevent collapse, ensure worker safety, and minimize damage to the grain, the standard industry practice is to limit the height of a stack to no more than 20 bags. Exceeding this height increases the risk of instability and can lead to excessive pressure on the bottom layers, potentially damaging the stored product.

In deep bed drying systems, the airflow rate must be sufficient to remove moisture without causing excessive energy consumption or uneven drying. A range of 2.9 to 3.9 cubic meters per minute per ton is generally recommended to ensure efficient moisture removal throughout the grain depth.