The PCM will typically freeze at a couple of degrees below 5°C, say at 1°C. Even if frozen at below 0°C, it will very quickly reach its phase change temperature — the temperature at which it changes phase from liquid to solid or vice versa – of 5°C. It will continue to be at this temperature, till it melts completely.
Hence the insulated boxes can contain a 5°C PCM pack instead of the 0°C gel pack. The temperature of the product will never go below 2°C and not exceed 8°C, till the entire PCM melts. Quantities of PCM to be used can be calculated based on the ambient temperatures during transport and type of insulation. Similarly, PCMs have been designed to change phase at -23°C (instead of dry ice at below -40°C) and at 21°C (instead of using just cold water at 21°C which holds only specific heat).
Thermal Batteries for Vaccine Safety
These thermal batteries are a great way to ensure the safety of vaccines. From the perspective of logistics industry, usage of PCM reduces the overall volume of coolants required, providing a reduction in volumetric weight by 30 per cent, while making the overall shipment lighter and portable.
This happens because the PCMs work on the principle of latent heat, which is typically higher than the specific heat of water. Thus, lower amounts of PCM are required to store the same amount of energy that water would store on the principle of specific heat.
Administration Control and Regulation
The second but equally important method to control vaccine wastage is governmental controls and regulations. With focus on patient health and a mission to eradicate diseases, guidelines on good distribution practices are being mandated and constantly updated by international bodies that require the temperature control logistics to be compliant to these regulations. The European Union has made it mandatory that controlled room temperature transport requiring vaccines and pharma products should never cross 25°C during its entire logistic supply chain. This means Indian companies that export to Europe or if their cargo transits through Europe will need to begin using a 22°C PCM.
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