What is the main difference between mass flow and funnel flow?

In mass flow, the entire contents of the bin move during discharge, ensuring first-in-first-out flow. In funnel flow, a flow channel forms above the outlet with stagnant material at the periphery (Clause 4).

How do I calculate the pressure on the vertical silo wall?

Use Janssen's theory (Clause 8), where vertical pressure is a function of depth, and horizontal pressure is the vertical pressure multiplied by the Janssen ratio 'K'.

How do I determine the minimum outlet size for a mass flow bin?

The minimum outlet dimension must be large enough to prevent the formation of a stable cohesive arch. It is calculated using Jenike's theory based on the material's critical stress for arching (σ_cr) and flow factor (Clause 6.3).

What causes 'switch' pressure?

During the onset of flow in a mass flow bin, the stress field shifts, causing a localized high-pressure zone near the transition from the vertical section to the hopper. This must be considered in the structural design (Clause 8.4).

IS 9178

: 2000

Criteria for Design of Steel Bins for Storage of Bulk Materials, Part 2: Design Criteria

CurrentSpecializedCode of PracticeBIMStructural Engineering · Structural Engineering and Structural Sections

Download PDF BIS Portal Google

This standard provides criteria for the structural design of steel bins for storing bulk materials, focusing on achieving desired flow patterns. It outlines the design methodology for both mass flow bins, where all material moves during discharge, and funnel flow bins, where a channel forms within stagnant material. The code details the application of Janssen's and Jenike's theories to calculate material pressures and determine hopper geometry.

Criteria for Design of Steel Bins for Storage of Bulk Materials, Part 2: Design Criteria

Quick Reference Values

Janssen's pressure ratio 'K' (typical)0.4 to 0.6

Mass Flow Hopper Angle Condition (Conical)α < f(wall friction angle)

Funnel Flow Hopper Angle Condition (Conical)α > f(wall friction angle, internal friction angle)

Minimum recommended bin outlet size300 mm

Minimum plate thickness for bins5 mm (for walls), 6 mm (for hoppers)

Key Formulas

Janssen's Vertical Pressure: pv = (γD / 4μ') * [1 - exp(-4μ'Kh/D)]

Janssen's Horizontal Pressure: ph = K * pv

Jenike's Critical Outlet Dimension (Arching): B = H(α) * σ_cr / γ

Walker's Initial Pressure at Transition: p_hi = γ * R_h * [ (tan²(45+δ/2)) / (tanα + tanφ') ]

Practical Notes

Accurate measurement of the bulk material's properties (like angle of internal friction, wall friction angle, and bulk density) via laboratory testing is critical for a safe and functional design; using assumed values is highly discouraged.

Mass flow design avoids many flow problems like 'ratholing' but results in higher wall loads, particularly a 'switch' pressure at the cylinder-hopper transition, which must be accounted for.

Funnel flow is simpler and imposes lower loads but is only suitable for coarse, free-flowing, non-degrading materials where first-in-first-out flow is not required.