In LiBr absorption refrigeration systems, the production of cooling mainly relies on the evaporation and heat absorption of refrigerant water under vacuum conditions. Unlike conventional vapor-compression refrigeration systems, LiBr absorption chillers do not rely on mechanical compressors to compress the refrigerant. Instead, they utilize the physical property that water can evaporate at lower temperatures when the surrounding pressure is reduced. By making use of this phenomenon, the system is able to achieve refrigeration through the heat absorbed during the evaporation process.

Under normal atmospheric pressure, water is widely known to boil at 100 °C. However, the boiling point of water is not constant and varies depending on the surrounding pressure. When the system pressure decreases, the resistance that liquid molecules must overcome in order to transform into vapor becomes smaller. As a result, water can evaporate or even boil at significantly lower temperatures. Under high-vacuum conditions, the evaporation temperature of water can drop dramatically. For example, when the pressure is reduced to approximately 1 kPa, water can evaporate at a temperature close to 5 °C. This characteristic provides the fundamental physical basis for absorption refrigeration technology.

Inside the evaporator of a LiBr absorption chiller, the system is maintained under a high-vacuum environment by means of vacuum-maintaining or purging devices. The pressure within the evaporator is therefore much lower than atmospheric pressure. In this environment, water, which serves as the refrigerant, is sprayed evenly over the surface of the evaporator tube bundle. When the sprayed refrigerant water contacts the tube surface, part of the water rapidly evaporates because of the low pressure inside the evaporator.

During the evaporation process, water must absorb a large amount of energy in order to change from the liquid phase to the vapor phase. This energy is known as latent heat of vaporization. Because water has a very high latent heat of vaporization, even a relatively small amount of evaporation can absorb a significant amount of heat. This heat absorption is the key mechanism that enables the refrigeration process.

The heat absorbed during evaporation mainly comes from the chilled water flowing inside the evaporator tubes. The chilled water carries heat from air-conditioning systems or industrial processes into the evaporator. As the refrigerant water outside the tubes evaporates, it continuously absorbs heat from the chilled water inside the tubes, causing the temperature of the chilled water to decrease. The cooled chilled water is then circulated back to air-conditioning terminals or industrial equipment, where it provides cooling for air or process applications. In this way, the system delivers the required cooling capacity to the external system.

The water vapor generated in the evaporator subsequently flows into the absorber, where it is rapidly absorbed by the concentrated LiBr solution. LiBr has a strong affinity for water vapor, meaning that its solution can effectively absorb water vapor. Once the vapor is absorbed, the pressure within the evaporator remains at a low level, allowing the evaporation process to continue. If the vapor produced in the evaporator were not removed or absorbed in time, the internal pressure would gradually rise, reducing the evaporation rate of the refrigerant water and ultimately affecting the cooling performance of the chiller. Therefore, the continuous absorption of water vapor by the solution plays an essential role in maintaining the low-pressure environment required for evaporation.

Through the combined processes of evaporation, heat absorption, vapor absorption, and vacuum maintenance, the LiBr absorption chiller is able to sustain a continuous refrigeration cycle. In essence, this type of refrigeration system makes use of the property that water can evaporate at low temperatures under vacuum conditions while absorbing a large amount of heat. By continuously removing heat from the chilled water, the system produces the desired cooling effect. Because this technology operates smoothly and can utilize heat sources such as steam, hot water, or industrial waste heat, LiBr absorption chillers are widely used in large central air-conditioning systems and various industrial cooling applications.