raw · notes · ingested 2026-07-02
DIY adsorbent-bed fabrication — sorbent choice, activation, packing, conductivity (research note)
confidence: high
Source: https://www.sciencedirect.com/science/article/abs/pii/S0140700719301124
Consolidates: silica-gel/Al-foam study (S0140700719301124), consolidated carbon/ENG papers, activation/degradation data (zeolite 13X), compact-bed particle/thickness optima. Credibility: High (peer-reviewed sources; consolidated).
Sorbent choice
- Silica gel 0.5–1.5 mm — low-temp water systems. Coconut-shell activated carbon — methanol/ammonia. Zeolite 13X/4A — higher uptake, higher regen temp.
Activation / drying (mandatory before charging)
- Silica gel: 60–85 °C (domestic oven). Zeolite 13X: ~150 °C, tolerant to 250–350 °C — but over-baking degrades (13X loses 31/51/68% capacity / 5000 cycles at 150/200/250 °C).
- Silica/water: degas ~150 °C under vacuum 8–12 h with intermittent evacuation. Desorbing under vacuum lowers the needed temp.
Packing & HX contact
- Pack granules against corrugated fins; coat-first-then-pack (glue/crystallize first layer to metal, loose granules on top) removes contact resistance while keeping permeability. PVA/PVAc binder.
Conductivity boosts
- Open-cell aluminium foam bonded to the tube, packed with silica gel — cheapest buildable boost (~+50% adsorption rate).
- Graphite flakes (carbon+ENG → 6.75–7.45 W/mK vs ~0.1–0.3 loose) — but more graphite lowers permeability (heat-vs-mass tradeoff).
Bed dimensions
- Bed ~5 mm thick, grain sub-mm (~0.26 mm optimal), ~5 mm vapor channels. Both heat- and mass-transfer resistance scale with thickness². Loading ~2.8 kg silica/module; ~24–26 kg/adsorber for a few kW. Avoid dust fouling.