In the journal “modelist-Konstruktor” has repeatedly published materials on the makeshift “fridges” where to store your products use natural cold which in the middle zone of our country, not to mention its North, more than enough. In all of these devices when too much frost, the optimum temperature is maintained by heating the food. The sensors used for this are very different, but for some reason, nobody comes to use the effect of phase transformation. In short, a physical phenomenon accompanying the freezing and melting of water.
As you know, when water freezes it increases its volume, and it can be used to drive various mechanisms. I want to offer readers several devices which successfully works this effect.
The switch electrically. It can be used in insulated foam boxes, which often set on the balcony or outside the window. At the bottom of this “fridge” fits the heater — for example, medical heat pad. On top of it is second bottom, aluminum tray, which are perishable products. Here is placed and a temperature sensor. It is a hermetic container of flexible material (e.g., polyethylene) filled with water. It is desirable that this vessel had the shape of a parallelepiped in such sometimes Packed shampoos, or lotions.
The bottle is a rigid frame, on the wall of which are mounted normally open contacts or, better, limit microswitch. When the water in the bottle freeze, its thickness will increase and the wall of the vessel will compress the contacts including heated pan. Move the side walls can reach 10 mm when the cross-section of the bottle is about 30X70 mm. After turning on the heated the ice melts, the vessel takes the same form and the heater is turned off.