How do you calculate the homogeneity index?

1. Definition

Homogeneous moisture distribution is crucial for preventing moisture stratification in subsequent building components and enabling short wetting distances.

Assessing the homogeneity of vapour introduction poses no difficulty once the underlying principles are understood. The finer the steam is metered and the more widely it is distributed across the available air cross-section, the better the steam injection. The number and arrangement of the steam distributors, as well as the type, number and spatial distribution of the steam nozzles, play a decisive role.

According to VDI 6022 Part 1, steam-air humidifiers must be operated in such a way as to prevent condensation forming in the air ducts. For this reason, the humidification section must be sufficiently dimensioned and a homogeneous distribution of moisture across the air cross-section must be ensured.

The homogeneity index is very well suited for the quick and clear assessment of homogeneous steam distribution in steam distribution registers.

Air cross-section: ALuft [m²]

Steam distributor: nDV [pcs]

Steam outlet: nDA [single- or double-sided]

Number of nozzles: nDÜSEN [pcs]

Humidification capacity: mDAMPF [kg/h]

Homogeneity index: HINX

[dimensionless parameter]

HINX = (A_AIR * n_DV * n_DA * n_NOZZLES) / m_STEAM

2. Example

Homogeneous moisture distribution is crucial for preventing moisture stratification in subsequent components and enabling short humidification runs.

System 1:Esco DR73-A5.10-8 (with 20 nozzles per nozzle block and steam outlet on both sides)

Steam output: 100 kg/h

Air cross-section:4 m²

Number of nozzles: 100

HINX = (4 * 5 * 2 * 100) / 100 = 40

System 2:Alternative type (2 nozzle bars and 90 nozzles with steam outlet on one side)

HINX = (4 * 2 * 1 * 90) / 100 = 7.2