Component essential to the refrigeration system’s operation.
Continuing with the presentation of the refrigeration system’s basic components, which began with the compressor in issue 114, let’s talk about condensers.
The condenser is a heat exchanger, and as the name implies, has the function to dissipate to the refrigeration system’s external environment the heat absorbed in the evaporator and generated by the compression process.
Proper functioning of the refrigeration system depends on the proper performance of its cooling elements, which are always assembled in this order: compressor, condenser, filter drier, expansion device (capillary tube or expansion valve), evaporator and closing the cycle, the compressor again.
Improper selection of the condenser can have negative consequences for the cooling system and the compressor.
When the condenser is too small, there is loss of cooling capacity and the system doesn’t reach the desired temperatures, since the heat exchanger isn’t able to dissipate to the external environment all the heat absorbed in the evaporator and generated during the compression process.
As a result, there is a pressure increase on the high side and for the compressor to ensure compression, extra effort is generated on the motor (increasing current), bearings and shaft. So, energy consumption and the temperature increases in the motor, which may trigger the thermal protector or, in some cases, may cause valve plate rupture and charring due to the high discharge pressure and temperature (high side).
It’s worth remembering that the condenser must be regularly monitored and maintained, removing, periodically or whenever necessary, dust or dirt accumulated during use. A dirty condenser will increase energy consumption and lose heat exchange capacity, thereby reducing cooling capacity.
Heat exchange mechanism and condensation process
During the compression process, the refrigerant temperature and pressure naturally increases. For cooling to continue, it’s necessary that this refrigerant gas cools and condenses, turning back into liquid.
The heat exchange mechanism between the refrigerant and the condenser occurs by passing air, cooler, around the condenser tubes, warmer, causing the air to absorb heat by the convection process.
Static condensation (natural convection process) is mainly applied in refrigerators, mini-fridges, freezers and other household appliances.
While forced condensation (forced convection process) uses a micro-fan, whose main advantage is the increased ability to exchange heat by movement of forced air by the fan on the condenser. This process is usually applied to light commercial systems that require greater cooling capacity, such as beverage displays, chilled or refrigerated islands, ice machines, etc.
Once the heat exchange mechanism is understood, the refrigerant condensation process can be divided into three parts which are sequential:
1. Cooling the superheated gas to the condensing temperature
This process is characterized by the heat exchange with the external environment through the condenser which results in lowering the refrigerant fluid temperature. During compression, the temperatures at the compressor outlet in the discharge tubing can reach levels around 100°C in some cases. In order for condensation to occur, it’s necessary to cool the gas to its condensation temperature, which varies according to the discharge pressure. The higher the discharge pressure, the higher the condensation temperature. From the moment the refrigerant fluid reaches such a temperature, it starts the condensation process.
2. Refrigerant fluid condensation
During the condensation process the fluid is at the saturation temperature related to the discharge pressure. At this point, all the refrigerant heat exchange with the environment results in gas condensation, becoming liquid. This process releases large amounts of heat to the environment, and is central to the cooling system. When all the gas becomes liquid, a new phase starts in the condensation process, which is the sub-cooling of the refrigerant.
3. Refrigerant sub-cooling
After the condensation process, the liquid continues exchanging heat with the environment. But now the exchange generates a temperature change of the liquid, causing it to cool. This exchange is carried out until the moment when the refrigerant passes through the filter drier and enters the expansion device (capillary tube or expansion valve).