A Passive Phase-Change Vaccine Carrier Sized for 72 Hours at 43 °C: Design and Thermal Model

Design study (simulated, not measured) of a passive vaccine cold-chain carrier that holds a 6 kg payload within 2-8 degC for at least 72 h at a constant 43 degC ambient (WHO PQS hot-zone condition) with no electricity. A two-node enthalpy thermal model sizes 8.0 kg of 5 degC phase-change material behind a hybrid wall of 20 mm vacuum insulation panel plus 30 mm polyurethane foam: computed hold time is 88.4 h to the 8 degC limit and 93.3 h to 10 degC, the payload never falls below 4.23 degC under refrigerator conditioning of the coolant, and the estimated parts cost is US $254.53 at stated unit prices. Freeze risk under freezer misuse is quantified. Includes model code and full results.