Post Harvest Unit Operations

• Factors Governing Air-Screen Grain Cleaner Capacity:
• An air-screen grain cleaner separates impurities based on aerodynamic drag (aspirator air duct) and particle dimensions (screens):
• Grain bed depth: Governs screen stratification and air passage.
• Size of screen surface: Width and length define total active screening area ($m^2$).
• Feeding mechanism: Ensures uniform, non-pulsing curtain flow across the full screen width.
• Percentage opening area of screen: Dictates open perforation fraction through which clean grain passes.
• Conclusion: Capacity depends on (A), (B), (C) and (D) (Option 3).

Correct option: (3) (A), (B), (C) and (D).

• Keller and Karmeli Drip Emission Uniformity Formula:
• The field emission uniformity ($EU$) of a drip/trickle irrigation subunit is given by:

where:

• $C_v$ is the manufacturer's coefficient of emitter variation
• $n$ is the number of emitters per plant/emission point
• $q_n$ is the average of the lowest quarter (25%) of emitter flow rates
• $\bar{q}$ is the average flow rate of all sampled emitters
• Conclusion: Matches Option 2.

Correct option: (2) 100(1.0 =) 127Cy, da

• Leaching Requirement (LR) in Salinity Management:
• The Leaching Requirement ($LR$) is the fraction of applied irrigation water that must pass through the crop root zone to prevent soil salinity from exceeding a specified threshold:

where:

• $D_d$ = depth of drainage water percolating below root zone
• $D_i$ = depth of applied irrigation water
• $EC_{iw}$ = electrical conductivity of the irrigation water
• $EC_{dw}$ = electrical conductivity of drainage water at bottom of root zone
• Conclusion: Option 1.

Correct option: (1) Option 1