How does the clay cool the water?

The kind of clay made from unburnt clay has the ability to make the water inside become cooler . This is very popular in Central Asia and has many names: in Spain called "Alicaratxa", in Egypt called "Gâula" .

(Photo: culture)

The secret to the cooling effect of these scales is very simple: the water contained in the pot penetrates into the clay wall and slowly evaporates, and when it evaporates, it takes a portion of the heat from the jar and from the water in the jar .

However, the cooling effect here is not very large. It depends a lot of conditions. The hotter the air, the faster the water seeps out of the evaporator, the more cold the water inside the jar becomes. The cooling also depends on the humidity of the surrounding air: if the air has a lot of moisture, the evaporation process is very slow and the cold water is not much. In contrast, in dry air, evaporation occurs very quickly, causing the water to cool markedly. The faster the wind blows, the stronger the evaporation process and thus enhances the cooling effect (wind effect can also be seen when we wear wet clothes on hot days. When there is wind, we will feel cool, comfortable).

The temperature drop in the cheeses usually does not exceed 5 degrees Celsius. On hot days in Central Asia, when the thermometer is only 33 degrees Celsius, the water in the bowl is usually only 28 degrees C. Thus, the cooling effect This type of jar is of no benefit. But this type of jar holds cold water very well and people use it mainly for that purpose.

We can try to calculate how cold the water in "alicaratxa " is . For example, we have a container of 5 liters of water. Suppose that the water inside the jar has evaporated, losing 1/10 liter. In hot days 33 degrees Celsius, want to evaporate 1 liter of water (1 kg) to take about 580 calories, the water inside the jar has evaporated, losing 1 / 10kg, so it needs 58 calories. If all these 58 calories are supplied by the water in the water, the water temperature inside the jar will decrease by 58/5, which is approximately 12 degrees. But most of the heat needed for evaporation is taken from the city; on the other hand, the water is in medium size while cooling down while being heated by the hot air adjacent to the walls. Therefore, the water inside is only about half the number found above.

It is difficult to say, where it is more cold - to go out or in the shade. In the sun, the water evaporates faster, but at the same time, more heat is coming in. But most definitely is to stay in the shade, slightly windy.