The basic components of a refrigeration unit on a refrigerated truck include the compressor, condenser, expansion valve, evaporator, and the control system. Here’s a breakdown of each component’s role:
1. Compressor:
The compressor is the central part of the refrigeration system, often referred to as the “main unit.” Its main functions are:
- Absorbing refrigerant vapor from the evaporator to maintain a low evaporation pressure within the evaporator.
- Increasing the pressure of the low-pressure, low-temperature refrigerant vapor by compressing it into high-pressure, high-temperature superheated vapor, enabling it to condense under warmer conditions (e.g., around 35°C in summer).
- Circulating and moving refrigerant through the system to complete the refrigeration cycle.
2. Condenser:
The condenser allows the refrigerant to release heat and convert back into a liquid. Condensers are classified based on the cooling medium:
- Water-cooled condensers: Use water to absorb the heat released by the refrigerant. The cooling water can either be single-use or recirculated. Types include vertical, horizontal, and shell-and-tube condensers.
- Air-cooled condensers (also known as fan-cooled): In these, the refrigerant’s heat is dissipated by air, which can be either naturally circulated or forced using a fan. These condensers are commonly used in locations where water supply is limited.
- Water-air cooled condensers: These systems use both water and air for cooling, but rely primarily on water evaporation on the surface of the heat exchange tubes to absorb a large amount of heat (latent heat of vaporization). The air accelerates the evaporation by carrying away the water vapor. These systems are suitable for dry regions with low water supply.
- Evaporative condensers: This type relies on a secondary refrigerant system where one refrigerant evaporates to cool the primary refrigerant, causing it to condense. This is commonly used in cascade refrigeration systems.
3. Expansion Valve:
The expansion valve performs a throttling function, reducing the pressure of the high-pressure liquid refrigerant coming from the condenser. As the refrigerant passes through the valve, its pressure drops, leading to partial vaporization and a decrease in temperature. This low-pressure, low-temperature vapor-liquid mixture enters the evaporator for further cooling.
4. Evaporator:
The evaporator is a heat exchanger where the refrigerant, now at low pressure and temperature, absorbs heat from the refrigerated space or from a secondary cooling medium (air, water, brine, etc.). As the refrigerant evaporates, it removes heat from the surrounding environment, achieving the refrigeration effect.
Each of these components works together to maintain the proper temperature inside the refrigerated truck, ensuring the safe transport of perishable goods.
