How can refrigerators keep cold for a long time?

I believe that as long as you pay attention to the supercooled chain, you've heard about this kind of heat preservation container. The main function of the cold preservation container is to refrigerate low-temperature goods. The temperature range is roughly: 2 ~ 8 ℃. The main effect is to refrigerate and keep fresh. The function of the refrigerator is understood. Then how does the cold preservation container achieve long-term cold preservation?

There are two kinds of refrigerators in the market. One is active refrigeration, which needs to be plugged in for refrigeration. For example, the car refrigerator, the other is passive refrigeration, which can keep cold for a long time without plug-in. The specific principle of their cooling is as follows:

1. The working principle of the refrigerated box that needs to be plugged in is to change the refrigerant state in a closed system by means of the compressor, use the liquid volatilization to absorb heat (similar to the principle that alcohol is sprinkled on the body and quickly volatilization will feel cool), and then use the evaporator of the closed system to conduct heat exchange with the surrounding environment for refrigeration and maintenance, of course, there are other auxiliary equipment, such as circulation. Air motor, etc.

2. The principle of refrigerators that do not need plug-in refrigeration is mainly to use dry ice or ice bag ice box to cool the surrounding environment by changing the heat absorption of the material state. This kind of refrigeration does not need power supply in the distribution process. Its refrigeration is not limited by the transportation conditions and region, and the distribution is flexible (different from the previous one: the ice bag ice box for refrigeration is prepared in advance, so that After use, it needs to be charged and cooled by the refrigeration equipment again, and then it can be used. The last refrigeration method can be recycled, as long as there is electricity, it can be used all the time).