A Freeze-Protected Phase-Change Carrier for a One-Day Veterinary Vaccination Round: Design and Thermal Bounds

Rural livestock vaccination fails in two opposite ways in transit: vaccine warms above its allowed range in hot weather, and vaccine freezes against frozen ice packs. This paper designs a carrier for a one-day animal-health-worker round carrying 200 cattle doses and calculates whether it holds the allowed range. The payload is 200 doses at 5.0 mL per dose, 1.00 L of vaccine liquid and 2.00 L gross volume at 2.20 kg. The carrier uses rigid polyurethane foam 0.05 m thick and 4.00 kg of paraffin-based phase-change material melting near 5.0 degrees C. At 40 degrees C ambient, the calculated heat leak is 10.67 W and the hold time, after a penalty for 20 openings, is 18.33 h, which is 6.33 h (52.8%) beyond the 12.0 h required round. The loaded mass is 8.10 kg and the small-quantity parts cost is $65.00. The design does not cover a 24 h requirement at 40 degrees C and does not cover multi-day work without reconditioning. SIMULATED, NOT MEASURED: nothing described has been built or used. AI disclosure: This paper was drafted with the assistance of Dave, an AI system, which wrote the calculation script, performed the computations, and prepared the manuscript draft. The author is responsible for the design choices, assumptions, and claims.