Portable refrigeration unit

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 loose its potency.

Specifications

What 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.

Setup The refrigeration team constructed two zeer pots on September 14, 2008. A large and small pot was created with ceramics from Home Depot; there were concerns that the pots may not have been porous enough in their walls. The bottoms, on the other hand, had quarter-sized holes in them for water drainage. The team did their best to seal the holes with painters tape and duct tape. Some water was still leaking as the 14-hour temperature testing began. The tests were performed in the Teer basement labs overnight. These labs are kept fairly cool so the team decided to shine two 100W, incandescent, reflector-equipped lamps on them through the testing to encourage evaporation. 20mL of water were placed in each pot and their temperature measured every five minutes via a LoggerPro device. A control water sample of ~200mL was placed under the lamps as well as a probe to measure the air temperature.

Preliminary Results At hour four, it was observed that water leaking from the large pot had soaked the dangling t-shirt covering completely. There were also yellowish rings forming above the sand on each pot; possible proof of some evaporation.

Data Just after shaking off the screensaver the morning after data-collection, the laptop taking the temperature data went to a blue screen. The attached LoggerPro file, zeer_test1.cmbl, shows the initial data point (which was autosaved) and the final temperature data, roughly 17 hours after the test began. The actual collected data can be visualized with an asymptotic rise in temperature over a four hour period from the initial to the final data point (the data was briefly seen before the computer crashed).

need info from Toni as to which Ti belongs to which probe

Conclusions The pots in test one showed no cooling effect. T1 seemed to be somewhat insulated from the heating effects but none of the probes showed a drop in temperatures. In all likelihood, this is due to the loss of water through the bottom of the pot. Incidentally, the leaking water didn't really do much for cooling the pot. Sand in both pots was dry to the touch. By the test's end, the leaking water was gone and the cloth coverings had dried. It was qualitatively observed to be somewhat warm in the large pot, difficult to tell in the small one.

Improvements

• employ clay as a hole-plugger
• attempt to keep the recorded data...maybe set up an autosave routine?
• use a covered pot with no water or no sand as control