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There are many substances that must be kept cold in a hospital. Vaccines are the best known. For this reason, most health care facilities have at least one refrigerator. However, these cold boxes are typically concentrated in one part of the hospital, perhaps the blood bank. A subset of substances are sometimes needed on very short notice, far from the refrigerator. For example, oxytocin (used to contract the uterus after delivery) is unpredictably needed on short notice. Or, they may be required in very remote areas, where they must be carried by hand. Having no access to refrigeration, but knowing the need for the substances, many facilities simply leave a vial of the substance on the counter or exposed to heat and hope that it does not lose its potency. SpecificationsWhat is needed is a refrigerator of very small volume. It should be sufficient to store one days worth of the chemical (perhaps 5 ml) without the need for electricity or, preferably, any outside fuel. The cavity should be able to be maintained at about 10 degrees C for 12 hours. It could require shaking, cranking, solar, a hot piece of charcoal or any other non-electric fuel source. Costs should be below $100 in quantities of 500. Information on oxytocin is available in the attachments tab. |
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Numerous portable refrigerators make use of a thermoelectric cooler. Wikipedia does a good job defining the Peltier Cooler: "The effectiveness of the pump at moving the heat away from the cold side is totally dependent upon the amount of current provided and how well the heat from the hot side can be removed." A very crude equation describes this, given here (http://en.wikipedia.org/wiki/Thermoelectric_effect#Peltier_effect).
Unfortunately, as engineers, we know this isn't always the case, and so a better (but much more complicated) description of the cooler's effectiveness is given by multiple factors, many of which depend on the environment in which they operate. This may prove difficult in trying to optimize a system.
The equation (http://electronicdesign.com/Articles/Index.cfm?AD=1&ArticleID=6325) has many unknowns, many of which may be difficult in trying to elucidate from manufacturers we try to contact.
As a last resort of trying to understand these heat sinks, we can try and test several out, by using a method described in this paper (Methods and devices....PeltierConstantDetermination.pdf), which has been uploaded. But based on experience, it seems that most commercial coolers are very broad in their ability to cool in different environments. Understanding all this (something I don't have enough knowledge to do...yet), will be the next step in trying to build a fridge from scratch.
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