Car refrigerators have been sold for a long time, but they are not taken seriously by everyone - it painfully looks like a toy. To admit, and we became curious what they are capable of.
For the test we took a 15-liter Coleman car refrigerator, known to us as one of the best, and another 15-liter isothermal container obtained from the same refrigerator when replacing the top cover, a 20-liter isothermal bag and a couple of cold batteries 10-liter "face value". The role of the main measuring device was entrusted to a two-liter plastic bottle of water and a thermometer immersed inside.
Let's start by checking the fridge. We put in it a measuring capacitance with an initial temperature of + 20 ° C and wait for the results. After 2 hours, the temperature drops by 6 ° C, after 8 hours after the start of the procedure, it reaches + 8 ° C, and after a day it stops at + 3 ° C (curve 1 in the figure). Well, not bad at all. An ordinary household refrigerator, taken for comparison, cooled the two-liter capacity a little slower, but went into the gap if necessary to perform a larger amount of work.
The difference between a car refrigerator and a household refrigerator - in the absence of refrigerant - car refrigerators use the Peltier thermoelectric effect (see ЗР, 1999, No. 6, p. 52). Their convenience also lies in the fact that thermoelectric modules have the property of reverse. Therefore, most of these refrigerators can switch to the "heaters" mode, for example, to warm up lunch. Such a warm-up can take two to three hours, but it is still better than nothing.
Now let's turn to isothermal containers and bags. For their effective work, in addition to the cargo you are interested in, you should put a couple of cold accumulators from the freezer. These are small plastic briquettes with saline, which has a high heat capacity. Being well frozen, batteries are able to resist up to 15 hours the heating of products stored in an isothermal container or bag. This is evidenced by the location of the inflection points of curves 2 and 3 in the figure. The curves show the capabilities of the container (curve 2) or bags (curve 3) to store pre-chilled products. It is curious that in the case of the container, the temperature of the water in the measuring bottle dropped by half a degree in the first 4 hours and only then crawled up monotonously - the batteries frozen to -18 ° C said their word. Thus, after 10 hours, the temperature of the cargo in the container rose only by one degree, after 20 hours - by 6 ° C, reaching + 11 ° C, and only after 44 hours it was equalized with atmospheric (see curve 2).
The ability to maintain life-giving coolness is highly dependent on the degree of loading of the container. Expressed scientifically - from the total heat capacity of the cargo in the container. The bag keeps cold a little worse. In it, with batteries in 5 hours, the temperature rises by a degree, after ten hours - by three degrees, after 20 hours - by 11 ° C, reaching + 18 ° C. But this is not bad at all. The same two-liter, wrapped in five layers of the newspaper, completely warms up to atmospheric temperature in 12 hours (curve 4), and left in the fresh air - in 8 hours (curve 5).
It remains only to determine the cost of products. A refrigerator will pull about $ 130-150, an insulated container - $ 30, a bag - $ 20, and one cold battery will cost $ 1.