raw · papers · ingested 2026-06-27
V-groove effective absorptance and the matching emittance penalty (cavity physics)
Source: https://arxiv.org/pdf/2007.14347
Source: arXiv 2007.14347 (cavity blackbody absorbers) + Thermopedia “Solar Energy”; standard cavity optics. Credibility: Medium-high (preprint + reference encyclopedia + textbook physics). Confidence: high (well-established formula).
Key physics
- α_eff = 1 − (1−α)ⁿ, n = number of internal bounces (set by groove angle). Worked: α 0.90 → ~0.97 (2 bounces) → ~0.99 (3); α 0.85 → ~0.94 → ~0.997.
- So geometric trapping realistically adds only ~+0.05 to +0.10 absorptance over flat black paint, with diminishing returns above α≈0.9.
- The penalty: the same cavity geometry raises apparent IR emittance by the identical 1−ρⁿ mechanism — grooves increase absorptance AND thermal-emission loss together. Grooves are therefore not a replacement for a spectrally-selective coating (α≥0.95, ε≈0.05-0.10).
- Larger collector-level gains from V-corrugated absorbers (+10-36% efficiency in air/liquid collectors, e.g. ECM 2019: +15.8% optical) come mostly from increased surface area + convective heat transfer to the fluid, not absorptance.
Relevance
Bounds the absorber-side optical gain for geometric-blackness-solar-adsorption-bed-face: small (+0.05-0.10) and offset by an IR-emittance penalty — and the bigger reported gains are a heat-transfer effect (which loops back to bed transport), not light-trapping.