Tuesday, June 7, 2011
Phase Change Material as a safe substitute for Dry ice
Dry ice is generally used as a refrigerant for packaging and transporting food, pharmaceutical products and biological samples that are needed to be kept frozen. Dry ice is generally considered non toxic with an enthalpy of sublimation equal to 57 1 kJ/Kg which makes it a very effective coolant. Dry ice however is very dangerous if not handled with care. It's sublimation produces carbon dioxide vapors which is harmful in high concentrations and directly enhances carbon emissions. Direct contact with dry ice can freeze cells and give effects similar to burns. Phase Change Materials like PCM23N provide an advantage over using dry ice.
Inorganic phase change materials like PCM23N provide a safe renewable material which changes phase between solid-liquid and assures a temperature control in the range of -25°C to -15°C. Products like Phase Change Material PCM23N are intended to store & transport products at temperatures below -15°C as an alternative to Dry-Ice. Inorganic salt hydrates are non hazardous, non toxic, non flammable, reusable with stability of 1000s of cycles..
Phase Change Materials provide an advantage over using dry ice for applications where a temperature control of below -15°C is needed. Handling is comparatively safer as the ice pack is not as cold as -80°C (dry ice), the coolant changes phase between solid to liquid and is contained in a rigid bottles which makes them reusable. Phase Change Materials like PCM23N have been tested to remain stable for 3000 cycles, it requires much lesser energy to freeze these ice packs as compared to the energy required to freeze CO2 and finally, during use, Phase Change Material based Ice-Packs do not release any harmful gases. The insulated shippers can be sealed airtight with no need of additional ventilation and can be shipped by air as a safe products.
Molded EPS Insulated shippers with 2" wall thickness are generally used for shipping frozen products with dry ice as coolant. As these boxes cannot be sealed air tight for the fear of explosion, the heat gain increases and the sublimation of dry ice is quick. The air gaps make it difficult to calculate the heat gain of the insulated shipped and generally the quantity of dry ice used is more than required. This makes the shipper heavier, increases the shipping weight and the shipping cost, products that need to be in the range of -20°C to -15°C could be exposed to much lower temperatures and a wider a range -80°C to -10°C.
We tested a small 1.5" molded shipper 12" x 9" x 9" to keep the temperature below -15°C for 24Hrs if exposed to ISTA 7D winter and summer profiles. Knowing the ISTA 7D profiles we were able to estimate the heat gain within the box for both situations and calculate the number of savEnrg™ Ice-Packs required to sink this heat while maintaining the temperature. The pack-out performed as per requirement in the very first attempt as the calculation and performance were precise.
Test results for 24Hr Summer profiles:
The test profile is depicted in blue and the temperature within the insulated shipper is depicted in orange. The ice pack was frozen for 24hr at -30°C. Eight packs with a total weight of 4.5Kg of coolant can be seen to start changing phase at -20°C and this temperature remains stable even during the spikes in ambient temperature profile of 24hrs.
Test results for 24Hr Winter profiles:
The test profile is depicted in blue and the temperature within the insulated shipper is depicted in orange. The ice pack was frozen for 24hr at -30°C. Four packs with a total weight of 2.2Kg of coolant can be seen to start changing phase at -20°C and this temperature remains stable even during the spikes in ambient temperature profile of 24hrs.
The performance was found very predictable and mathematical simulations for any insulated shipper can be executed to estimate the quantity of cooling material required prior to using laboratory time. The rigid bottles are easy to handle and can be strategically positioned within the shipper for uniform temperature distribution. Some parts of the shipper can experience higher heat or cold stress as compared to other parts, knowing this, the bottles can be easily positioned
Phase Change Material based Ice-Packs give the advantage to save energy while freezing and reusing. During transportation there is no release of carbon dioxide and no danger of the any explosions due to pressure.