raw · papers · ingested 2026-06-19
SAAR: Solar Ammonia Absorption Refrigerator (Senior Design Project)
Source: Zotero local PDF: storage/PGB9NQSI/Solar Ammonia Absorption Refrigerator Seni - Jacob Buehn.pdf
Read from local Zotero full-text PDF (group 5183627 / Joule Heist).
Key findings
- Goal: maintain 2-8 °C for temperature-sensitive vaccines/medicines for a 24-36 hour period in rural/off-grid conditions, operable in ambient climates up to 35-50 °C; targeted unit cost ~$300 (actual build materials totaled $251.57). Deliverable is open-source (unpatented) manufacturing plans.
- Working pair is calcium chloride / ammonia (CaCl2-NH3), an intermittent adsorption process. Target operating envelope: low side 20-30 °C, high side 90-140 °C, operating pressure 8-14 bar. Design max operating pressure 14 bar (203 psi) with a 2:1 safety factor, hydrostatic test to 28 bar.
- Working-pair decision matrix compared water-ammonia (high side 10-13 bar @ 90-100 °C), lithium bromide-water, carbon-methanol (needs vacuum; 2-5 bar @ 90-110 °C), and CaCl2-ammonia (no water vaporization, no vacuum/leveling needed, but corrosive to aluminum/brass/copper and subject to heat crystallization). CaCl2-NH3 selected.
- Reaction enthalpy used: 78 kJ/mol; assumed molar ratio NH3:CaCl2 = 8:1 total, 6:1 working. Generator cage volume 301.59 in³; charge sized to 4.404 lb anhydrous CaCl2 + 5.41 lb liquid ammonia (276.17 in³ total).
- Market benchmarks: Crosley IcyBall (1927, water-ammonia, ~250 psi, ~24 h cooling of 4 cu ft); S.T.E.V.E.N. ($510, ~10 lb ice/day); ISAAC (Energy Concepts, double-intermittent ammonia-water, 35 lb ice/day from 37 ft collector at $11,000, up to 150 lb/day from 125 ft collector at $17,000).
- Ammonia (R-717) property data: molecular weight 17.03 g/mol, boiling point -33.5 °C, latent heat of vaporization 1371.2 kJ/kg, critical point 132.4 °C / 112.8 bar, vapor pressure 8.88 bar at 21 °C, auto-ignition 630 °C.
- Material compatibility for ammonia: carbon steel, stainless steel, aluminum, PTFE, PCTFE, nylon, PP, EPDM, butyl rubber satisfactory; brass and copper NOT recommended; Viton/silicone/PVDF/nitrile degrade.
- Solar heating options evaluated: Scheffler reflector, Fresnel concentrator lens (md60, 42” focal length), and parabolic reflector; plus alternative low-grade heat (campfire, propane, kerosene, wood) for cloudy days. Generator uses perforated diffuser tubes to minimize adsorption stratification; vessel follows ASME BPVC Section II / EN 13445-2 design intent.