The evaporator is an integral part of the ice machine’s operation. It produces ice by absorbing both sensible and latent heat from the water as it passes over its outer surface. The sensible heat absorbed by the evaporator will reduce the water from its initial inlet temperature to its freezing point. The higher the inlet water temperature, the more sensible heat must be removed from the water and the longer the freeze cycle. The latent heat removed causes the water to change state, thus producing ice.
The amount of latent heat removed from the water on each batch of ice is relatively constant. It is related to the mass of the water used to produce the ice. Each ice machine manufacturer has its own distinctive evaporator design, from its basic construction to how water flows over its surface to the shape of the ice produced. Understanding the various designs of evaporators and how the ice is formed will aid any technician in troubleshooting these machines.
There are two basic styles of evaporators in current use today. The most popular style is an evaporator oriented in the vertical position, where the water flows either down both sides or down just one side. The less common style is one in which the evaporator is mounted horizontally and the water is sprayed or pumped up into its cells. As water is sprayed up into the cells of the evaporator, some of it will freeze onto the surface.
Examining the evaporator during the freeze cycle can aid a technician in identifying many common problems associated with these machines. How the ice is formed or not formed on the evaporator can allow a technician to easily determine several common problems. For example, a slab of ice that is lopsided — heavy on one end and light on the other — is usually an indication of a refrigeration issue, such as a low refrigerant charge, or an issue with its metering device.
Several ice machine designs produce ice cubes that are held together to form a slab of ice, which breaks apart into cubes as it falls into the ice bin. The production of an ice slab is necessary to facilitate removal of the ice from the evaporator during the harvest cycle. The weight of the entire slab helps to pull all the ice from the evaporator. A properly formed slab will form an ice bridge to hold the individual cubes together. Many ice machine manufacturers recommend a 1/8-inch bridge thickness for a properly formed slab.
Observing how the ice is formed on an evaporator is definitely beneficial when servicing ice machines. It is generally a good practice to watch the machine for two complete cycles while troubleshooting. Most problems will surface within this time. If the ice machine is adequately producing ice for two complete cycles, chances are it will continue to produce ice in a normal fashion.
Publication date: 12/3/2018