The working principle of the evaporator used in an under-counter ice machine is based on the fundamental thermodynamic concept of heat exchange and the phase transition of water from a liquid to a solid (freezing). The evaporator is a key component responsible for creating the conditions necessary to freeze water and produce ice. Here's a detailed explanation of how the evaporator works:

1. Introduction of Water: The ice-making process begins when water is introduced into the ice machine. This water can come from a connected water supply line or a manual water reservoir, depending on the machine's design.

2. Water Distribution: Once inside the ice machine, the water is evenly distributed over the surface of the evaporator. The evaporator typically consists of a metal plate, a set of tubes, or a specialized freezing surface designed to facilitate efficient heat exchange.

3. Temperature Reduction: The evaporator is maintained at a temperature well below the freezing point of water, often achieved by circulating a refrigerant, such as a gas or a liquid, through coils or pipes within or adjacent to the evaporator. This low temperature creates a cold environment that promotes the freezing of water.

4. Heat Transfer: As water flows over or through the evaporator, heat from the water is transferred to the evaporator's surface. This heat transfer process causes the water to lose thermal energy, causing it to cool down and eventually freeze.

5. Formation of Ice: As the heat is continually extracted from the water, it gradually reaches the freezing point (0°C or 32°F) and begins to solidify, forming ice. This ice forms as a layer on the evaporator's surface and continues to grow in thickness as more water flows over it.

6. Harvesting Cycle: Once the ice layer on the evaporator reaches the desired thickness, a harvest cycle is initiated. During this cycle, mechanisms within the ice machine release the newly formed ice from the evaporator's surface. The method of ice release can vary depending on the machine's design, such as using hot gas, hot water, or mechanical means.

7. Ice Discharge: The released ice falls or is scraped off the evaporator's surface and is collected in the machine's storage bin, which is typically located beneath the evaporator.

8. Continued Production: With the ice layer removed, the cycle repeats. Water is continuously introduced, frozen on the evaporator, harvested, and stored in the bin as long as the ice machine is operational.

The evaporator's ability to maintain a consistent low temperature and efficiently transfer heat from the water to the refrigerant is crucial for the successful production of ice. The design and efficiency of the evaporator, as well as the control of operational parameters, contribute to the quality, quantity, and speed of ice production in under-counter ice machines. Regular maintenance, including cleaning and descaling the evaporator, is essential to ensure optimal performance over time.