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Solid-state cooling with caloric materials (Takeuchi & Sandeman, Physics Today)
Source: https://physicstoday.aip.org/features/solid-state-cooling-with-caloric-materials
Source: Physics Today 68(12), 2015 — Ichiro Takeuchi & Karl Sandeman. DOI 10.1063/PT.3.3022. Credibility: High (flagship feature by field leaders). Confidence: high.
The unifying frame
- Caloric cooling = a solid refrigerant whose entropy changes reversibly under a field: magnetic (magnetocaloric), electric (electrocaloric), uniaxial stress (elastocaloric), hydrostatic pressure (barocaloric). All characterized by isothermal ΔS and adiabatic ΔT_ad near a ferroic phase transition. No compressor, no high-GWP refrigerant.
- ΔT_ad by class: magnetocaloric ~3 K (1 T, Gd); electrocaloric ~0.003-2.5 K; elastocaloric ~17 K (NiTi) — largest single-field ΔT_ad. Entropy: magnetocaloric ~10-15 J/(K·kg) at 1 T; elastocaloric 10-80 J/(K·kg).
- Multicaloric = combining ≥2 fields for cross-coupled gains beyond the sum (e.g. Ni-Mn-In: +200% cyclic effect when 55 MPa stress added to 1.9 T).
The economic bar
- Vapor-compression COP ≈ 3.6; Carnot limit ≈ 28.8 for a 10 K lift at 298 K. Complete caloric systems must reach COP ≥ 4 to compete — “remains to be seen how price-competitive complete systems will be.”
- Driving-force costs: magnetocaloric needs ~1 T (expensive rare-earth magnets); elastocaloric ~400 MPa (tension)/600 MPa (compression); electrocaloric 100-1000 kV/cm. Hysteresis in first-order transitions dissipates energy every cycle and drives fatigue.
Relevance
The keystone synthesis for solid-state-cooling: defines the caloric family, the shared thermodynamics, and the COP-4 economic threshold every solid-state route must clear.