The formation of ice in a refrigerator's freezer, even without the presence of visible water particles, is due to a process called "frost formation" or "frost buildup." This phenomenon occurs in refrigerators and freezers as a result of the following factors:
Moisture in the air: Even if you don't see any water particles, the air contains some level of moisture or humidity. This moisture is present in the form of water vapor, which is invisible to the naked eye. When you open the refrigerator or freezer door, warm and humid air from the surroundings enters the appliance.
Cooling process: Refrigerators and freezers work by removing heat from the enclosed space. When the warm and humid air from the outside comes into contact with the cold surfaces inside the freezer, the air cools down rapidly.
Condensation: As the air cools, its ability to hold moisture decreases. When the cooling air reaches its "dew point" temperature, it can no longer retain all the water vapor, and condensation occurs. The excess moisture in the air condenses on the cold surfaces of the freezer, forming tiny water droplets.
Freezing: Once the water droplets condense on the freezer's surfaces, they can freeze quickly due to the extremely low temperatures inside the freezer. Over time, these frozen water droplets accumulate and form ice.
Subsequent cycles: Each time you open and close the refrigerator or freezer door, more warm and humid air enters, and the cycle of condensation and freezing repeats, leading to a gradual buildup of ice.
To prevent excessive frost buildup, modern refrigerators are equipped with a defrosting system that periodically melts the ice and removes the water. This process helps maintain the efficiency of the appliance and prevents ice from interfering with the proper functioning of the freezer. Some refrigerators also have a self-defrosting feature that automatically removes the frost buildup at regular intervals.