Low-cost load shedding-resilient medicine storage with phase-change material theoretical heat Transfer evaluation of a design concept

Résumé

Diabetes mellitus is one of the most common non-communicable diseases; approximately 0.72 million people in South Africa require insulin treatment. Insulin—a hormone peptide drug— is temperature sensitive and undergoes thermal fibrillation when exposed to temperature above manufacturers' recommendations. Most insulin formations must be stored at 2°C - 8°C in a refrigerator when unopened to maintain its potency and to keep insulin within manufacturers' suggested expiry date. However, one of the unforeseen consequences of frequent power outages in South Africa—and many other developing nations—is thermal denaturation of insulin within household refrigerators caused by frequent power outages. In addition, users cannot tell if insulin has reduced pharmacological action. This publication presents a preliminary design for an in-refrigerator medicine storage container utilising phase-change material to stabilise the temperature of insulin or other medications during power outages, and to provide a visual indicator if a melting event has occurred, even if refrigeration has subsequently been restored, to alert the user that their insulin may have expired. It is found that the principal variables of interest to determine the time to melting are the thickness of the layer of phase-change material in the unit's walls, and the degree of insulation of the outer shell surrounding the phase-change material. It is also determined that asymmetric insulation parameters for the inner and outer surfaces of the container's walls are a crucial design feature for usability, permitting an initial freezing time that is more rapid than the melting time. The current design has been found to be unable to meet all usability criteria, primarily due to an unacceptably long freezing time, regardless of the values of the available parameters. It is therefore concluded that design revisions are required to meet all usability criteria

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