TRANSPORT REFRIGERATION


While Globalization has made the relative distance between two regions of the world vastly smaller, the physical separation of these same regions is still a very important reality. Phone calls, emails, and videos can be transmitted in fractions of seconds to all corners of the globe, but physical objects such as a bushel of grapes, a drug or a bodily organ cannot. It takes time and coordination to efficiently move a shipment and every delay can cost money and in some cases may even cost lives. To ensure that cargo does not become damaged or compromised throughout this process, businesses in the pharmaceutical, medical and food industries are relying more and more on the cold chain technology.
Road transport refrigeration equipment are required to operate reliably in much harsher environments than stationary refrigeration equipment. Due to the wide range of operating conditions and constraints imposed by available space and weight, transport refrigeration equipment has lower efficiencies than stationary systems.

The majority of refrigerated road transportation is conducted with semitrailer insulated rigid boxes. Many factors are considered in the design of the envelope of a refrigerated transportation unit: extremes of exterior weather conditions, desired interior conditions, insulation properties, infiltration of air and moisture, trade-offs between construction cost and operating costs and physical deterioration from shocks and vibrations.
The most common refrigeration system in use for refrigerated food transport applications today is the vapour compression system. Mechanical refrigeration with the vapour compression cycle offers a wide range of options for compressor drive methods. The choice may be based on duty required, weight, noise requirements, maintenance requirements, installation cost, environmental considerations and fuel taxation.

The most common drive systems for refrigerated transport vapour compression systems are

Vehicle alternator unit: with this method which is commonly used in small delivery vans, the vehicle engine crankshaft drives an upgraded single alternator and a 70 Ah battery. The alternator charges the vehicle battery which feeds a small refrigeration system with 12 V dc supply. The system can also be driven with a 230V mains electric supply during standby.

Direct belt drive: with this system, which is used in the majority of van-sized vehicles, the compressor of the refrigeration unit is directly driven from the vehicle engine through a belt.

Auxiliary alternator unit: This system uses a dedicated large alternator driven by a belt from the main traction engine, generating power to drive an electric motor in the refrigeration unit. Fan motors for the heat exchangers and the control system are also fed from the alternator output.

Auxiliary Diesel Unit: This system uses an engine built into the refrigeration unit which can be powered by diesel.

Source & Image Courtesy: Grimsby, ASME

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