A Phase-Change Cold Box for the Last Mile Without a Grid: Computed Sizing, Hold Times, and Recharge for the +4 °C Cargo Class

Passive phase-change cold box for produce and vaccines on the last leg without grid power in transit. A paraffin PCM melting at 5 C is selected by computation, sized against a computed heat-leak budget for a 100 mm EPS box, with hold times at 30/35/40 C ambient, recharge requirements, and a same-arithmetic comparison against plain ice. All results are SIMULATED, NOT MEASURED.