In the 1900’s, the World Health Organization (WHO) attempted to bring a basic level of immunization to all people by launching the Expanded Program on Immunization (EPI). Immunization efforts in developing countries have been hampered by many problems including vaccine spoilage due to compromises in the thermal integrity of the vaccine container during transportation. This work focusses on the testing and design of a portable container made for multi-day transportation of vaccines transported by hiking. The final container performance is compared with a model developed from early container testing. The objective is to reduce vaccine spoilage that occurs as a result of failure due to heat exposure in remote cold chains in Southeast Asia.
Vaccines that experience a temperature excursion can spoil or become useless. To test containers for use in the jungles of Southeast Asia, a heated chamber was instrumented with a temperature monitoring system and was equipped with a heated mat. The net thermal resistance of common coolers, vacuum insulated containers, and coolers construct from industrial insulation materials was quantified using an ice melt test. A subset of the packages was selected to determine each package’s cold life, or ability to maintain the 2-8°C temperature range acceptable for the vaccine cold chain. A final container system, named the VACS C1, was designed, lab tested, and field tested.
The lumped capacitance energy balance was used as a method for modeling the design, and performance of the tested containers. For design of the VACS C1, package geometry was constrained, and the lumped capacitance model was used to optimize the geometry within the constraints. The energy balance was used to predict the performance of test containers and the VACS C1 in lab and field conditions.
Initial testing of consumer grade coolers showed that flexible coolers have lower thermal resistance values than hard shell containers. Testing of vacuum insulated coolers indicated that the cold life of a vacuum sealed container directly correlates to the container’s thermal resistance. Container cold life ranged from about 1.3 to 1.8 times the predicted cold life for a vacuum insulated container.
Field testing showed that the cold life of the VACS C1 was significantly improved from existing field containers. An initial field test resulted in a total a cold life that exceed 50 hours of mobile exterior exposure, while only using about 50% of the capable ice payload. Additionally, using the VACS C1 ice life as a conservative estimate of cold life, it was predicted that the VACS C1 is capable of outperforming comparable existing containers by 37%. The container also was predicted to outperform a heavier, less mobile container by as much as 15% (9.5 hours).
|Commitee:||Demko, Jonathan, Reynolds, Greg|
|School Location:||United States -- Texas, US|
|Source:||MAI 81/12(E), Masters Abstracts International|
|Subjects:||Mechanical engineering, Thermodynamics|
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