Definition
The diameter of water droplets leaving a nozzle in an adiabatic humidifier (microns, μm); a design parameter that directly drives evaporation time, wetting risk and hygiene safety.
Detailed Explanation
Droplet size is the single numerical indicator of atomisation quality. Unit: micron (μm); 1 μm = 0.001 mm. Adiabatic humidification bands: 5–15 μm "fine mist" (high-pressure misting, ultrasonic), 15–30 μm "medium" (mid-pressure), 30–80 μm "coarse" (low-pressure spray, wetting risk). Measurement: laser diffraction (Malvern Spraytec, Sympatec) for field validation. Manufacturers report D50 (median droplet) and DV90 (largest 10%).
Why It Matters
Droplet size drives three critical parameters: (1) EVAPORATION TIME — scales with droplet diameter squared (d² law); 10 μm ≈ 0.2 s, 30 μm ≈ 2 s, 100 μm ≈ 25 s. Faster evaporation → shorter absorption distance → more compact duct design. (2) WETTING RISK — above 50 μm droplets fall under gravity (terminal velocity ≈ 0.25–0.3 m/s @ 100 μm); landing on duct walls or floors causes hygiene problems, corrosion, slip hazard. (3) HYGIENE — fine mist (< 15 μm) is respirable with the air; if contaminated, Legionella risk. That is why fine-mist systems mandate RO + UV pre-treatment.
Practical Example
A print hall in Istanbul chose an evaporative humidifier (Neptronic SKV, cellulose pad — no droplet size, evaporation happens on the media surface). Standard hygiene class, 22°C / 55% RH. The alternative was a high-pressure misting system (SKH) with D50 = 12 μm, DV90 = 22 μm. Absorption distance 0.8 m, in-duct humidification stable ±3% RH. RO + UV pre-treatment added €4,500. Outcome: SKV gives simpler hygiene (no aerosol is released into the air) + lower capex; SKH gives more flexible placement + adiabatic cooling. The customer picked SKV because hygiene risk is lower.
Engineering Note
Droplet size is read from the manufacturer spec but must be field-validated by laser sizing (especially for hygiene-critical sites). Manufacturer tolerance is typically ±20%; field validation should sit within ±5%. If DV90 > 50 μm is measured, pump pressure has dropped or nozzles have worn — maintenance is triggered. At high RH (>70%) and low temperature (<15°C), even fine droplets do not evaporate; in those conditions evaporative is not recommended and the design should shift to steam.
NKT Application Link
For this application NKT – Nem Kontrol Teknolojileri supplies the Neptronic SKH high-pressure atomisation system and the Neptronic SKV evaporative humidifier. Unit-selection support is based on space conditions, humidification load and the feed-water analysis; technical service and spare parts are provided. Design and installation of water treatment, as well as engineering design, installation and commissioning, remain within the scope of the facility's designer, contractor and water-treatment specialist.
