Engineering Properties

Understanding the engineering properties of cereals, pulses, and oilseeds is crucial for designing and operating post-harvest technology (PHT) equipment. These properties influence the efficiency of operations like cleaning, grading, drying, storage, and transportation.

Physical Properties

i) Size and Shape:

• Shape: Refers to the geometrical form of the grain (e.g., spherical, oval, cylindrical).
• Size: Described by dimensions such as length, width, and thickness.
• Applications in PHT Equipment Design: Influences the design of sieves and screens in seed graders. Determines the free-flowing or bridging tendencies, affecting the design of hoppers and conveyors. Sphericity and equivalent diameters are used to describe the shape for optimizing storage bins and dryers.

ii) Porosity:

• Defined as the percentage of void space not occupied by grains in a bulk mass.
• Applications: Important for designing drying and aeration systems. Affects airflow resistance in storage structures.

iii) Coefficient of Friction:

• Ratio between the force of friction and the normal force on the grain’s surface.
• Applications: Used in the design of storage bins, hoppers, chutes, and conveying systems to ensure smooth flow.

iv) Angle of Repose:

• The natural slope angle formed when grains fall freely on a horizontal surface.
• Applications: Influences the design of storage bins and hoppers to prevent clogging and ensure smooth discharge.

Thermal Properties

i) Specific Heat (Cp): The amount of heat required to raise the temperature of a unit mass by 1°C. Applications: Crucial for designing heating, cooling, drying, and freezing equipment. Affects the energy requirements in thermal processing.

ii) Thermal Conductivity: The amount of heat flowing through a unit thickness over a unit area per unit time for a unit temperature difference. Applications: Important in the design of heat exchangers and drying equipment. Influences heat transfer calculations in storage and processing units.

3. Aero and Hydrodynamic Properties

i) Terminal Velocity: The air velocity at which a particle remains suspended in a vertical pipe. Applications: Essential for designing pneumatic separation and conveying systems. Influences the design of air classifiers and fluidized bed dryers.

4. Applications in PHT Equipment Design and Operation

i) Cleaning and Grading Equipment:

• Shape and Size: Utilized in screen separators, aspirators, and indent cylinder separators for efficient grading.
• Terminal Velocity: Applied in pneumatic separators for removing lighter impurities.

ii) Drying and Storage Systems:

• Porosity and Thermal Properties: Aid in designing efficient drying and aeration systems.
• Specific Heat and Thermal Conductivity: Used in calculating energy requirements for drying and cooling.

iii) Conveying and Handling Equipment:

• Coefficient of Friction and Angle of Repose: Important for designing augers, belt conveyors, and bucket elevators.
• Shape and Size: Influence the design of hoppers and chutes for preventing clogging.

5. General Principles of Food Plant Equipment Design

1. Perform the intended function efficiently.
2. Easy to clean and maintain hygiene.
3. Sturdy and durable with minimal repair needs.
4. Economical in operation.
5. Quick dismantling and reassembling for cleaning.
6. Use of inert, non-absorbing, and non-corrosive materials for food contact surfaces.
7. Elimination of dead-end areas and crevices to avoid contamination.
8. Avoidance of toxic metals like lead and cadmium.
9. Easy access to parts for cleaning and inspection.

6. Key Considerations for Equipment Design

• Use smooth, continuous surfaces to prevent microbial growth.
• Ensure rounded junctions for easy cleaning.
• Employ sanitary-type valves and fittings.
• Design for easy disassembly and maintenance.
• Prevent contamination from lubricants or condensates.