Refrigerated trucks, commonly called reefers, are the heroes of the cold chain, ensuring that perishable goods such as fresh produce, dairy products, and pharmaceuticals arrive at their destination in optimal condition. In this article, Holdwell walks you through how refrigerated trucks work to control temperature and ensure that temperature-sensitive goods are transported safely and efficiently.
How Do Refrigerated Truck Work？
At the heart of every truck refrigeration unit is a complex process known as the refrigeration cycle. This cycle involves the coordinated work of four major components: the compressor, condenser, expansion valve, and evaporator. Understanding this cycle process is key to mastering how these units maintain precise temperatures in mobile environments.
Compressor:
The compressor acts as the "pump" of the refrigeration system. There are several types of compressors used in truck refrigeration units, including reciprocating, scroll, and screw compressors. Each type has its own advantages in terms of efficiency, reliability, and capacity. Regardless of the type, the main function of the compressor is the same: to increase the pressure and temperature of the refrigerant gas in preparation for the heat exchange process.
Condenser:
The condenser is usually located on the outside of the refrigeration unit, usually at the front of the trailer. It consists of a series of coils or tubes, usually made of copper or aluminum, with fins to increase the surface area. As the hot refrigerant passes through these coils, an external fan blows air over them, promoting heat dissipation. The efficiency of the condenser is critical because it determines how effectively the system removes heat from the refrigeration cycle.
Expansion valve:
Commonly referred to as the system's "throttle valve," the expansion valve plays a key role in regulating the refrigerant flow and creating the necessary pressure drop. The sudden drop in pressure causes the refrigerant to expand and cool rapidly. Modern refrigeration units may use thermostatic expansion valves or electronic expansion valves, which can more precisely control the refrigerant flow based on system needs.
Evaporator:
The evaporator is strategically placed within the cargo hold to maximize cooling efficiency. It is typically designed with a large surface area to facilitate the absorption of heat from the surrounding air. Factors such as airflow patterns, frost accumulation, and ease of maintenance all influence the design of the evaporator. Some systems may employ multiple evaporators or specially shaped units to ensure even cooling throughout the cargo hold.
How the Refrigeration Cycle Works?
1. The process begins with the compressor, which pressurizes the refrigerant gas, significantly increasing its temperature and pressure.
2. This hot, high-pressure refrigerant then travels to the condenser. Here, it releases heat to the outside environment, cools, and condenses into a liquid state.
3. The cooled, high-pressure liquid refrigerant then passes through the expansion valve. This component acts as a pressure relief, converting the refrigerant into a low-pressure cool mist.
4. This cool mist enters the evaporator located within the cargo area. As it passes through the evaporator coils, it absorbs heat from the surrounding air, effectively cooling the space.
5. Having absorbed heat from the cargo area, the refrigerant, now warmer and back to a gaseous state, returns to the compressor to begin the cycle all over again.
This continuous process enables the refrigeration unit to maintain a constant temperature within the trailer regardless of external conditions.
Working together through carefully coordinated processes, these components enable truck refrigeration units to maintain precise temperatures in challenging mobile environments. This level of temperature control is critical to maintaining the quality and safety of temperature-sensitive cargo during transportation.
Silent Guardian - Insulation
While the refrigeration system is at the heart of temperature control, insulation plays an equally important role as a silent guardian against heat intrusion. A well-sealed, well-insulated cargo area is essential to minimize heat transfer, thereby reducing the workload of the refrigeration system and increasing overall efficiency.
Materials Used:
Modern refrigerated trucks feature a variety of high-performance insulation materials:
High-density foam: Offers excellent heat resistance and is lightweight.
Fiberglass: Offers good insulation and is moisture-resistant.
Composite panels: Combines durability with superior insulation properties.
These materials are often combined to form a multi-layer insulation system that maximizes thermal efficiency. The thickness and quality of the insulation can significantly impact a truck's ability to maintain temperature, especially over long hauls or in extreme weather conditions.
Directional Cooling: Air Circulation Systems
Maintaining uniform temperatures throughout the cargo area is essential to maintaining product quality. An effective air circulation system ensures even temperature distribution and prevents hot or cold spots from forming.
By working together in a carefully orchestrated process, these components enable truck refrigeration units to maintain precise temperatures in challenging mobile environments. This level of temperature control is essential for preserving the quality and safety of temperature-sensitive goods during transport.
