Nowadays, many large and medium-sized cities use refrigerated trucks for the transportation of goods. Because the industry penetration rate is still low, there are still a large number of food, meat, fruits, vegetables, medicines, alcohol, etc. that deteriorate during the transportation process every year. Unnecessary losses. The vigorous promotion and application of Refrigerated truck trailers/dry van semi-trailer are of great significance for further integrating the refrigerated truck market, improving the status quo of my country’s refrigerated transportation industry, reducing the waste of perishable goods in transit, and ensuring food safety. Concerns from all walks of life.
Refrigerated truck trailers /dry van semi-trailer are closed van transport vehicles used to transport frozen or fresh-keeping goods. They have dedicated refrigeration transport vehicles equipped with refrigeration units and polyurethane insulation compartments. Commonly used to transport frozen food (freezer truck), dairy products (dairy truck), vegetables and fruits (fresh goods truck), vaccine drugs (vaccine truck), etc.
1. Refrigerated truck trailers /dry van semi-trailer insulation
Vehicles used to transport perishable food products must be well insulated to prevent the heat carrier from flowing through the vehicle bulkhead. The thermal insulation quality is measurable, and its thermal conductivity is U. The smaller the U factor, the better the insulation. The most commonly used material for insulation of refrigerated vehicles is foam plastics because of their low U-factor, lightweight, water-resistance, and no corrosion. During manufacturing, “in-place foaming” of plastics can obtain greater thermal insulation advantages. This process can block the cracks and gaps through which air may pass. The use of highly polished steel or aluminum skins can further improve the quality of insulation because they can reflect heat radiation from the sun or the road. There are also reflective paints for refrigerated vehicles. However, if the exterior of the vehicle is not kept clean, the reflection effect of any material will be reduced. If the door seal leaks, high-quality insulation is of little value. The door seal must be installed correctly and in good condition.
2. Refrigerated truck trailers /dry van semi-trailer air circulation
Air circulation is one of the most important factors in the protection of refrigerated and perishable food cargo. If the cooling air cannot circulate correctly to maintain the product temperature, the cooling capacity is meaningless. The air circulation cycle brings the heat of the product and the heat entering through the bulkhead, floor, and ceiling of the trailer to the refrigeration unit, and the refrigeration unit discharges this heat. Heating air can be circulated to protect fresh products from frostbite. In addition, in order to ensure the uniform temperature of all cargo, air circulation is also extremely important. There are two main methods of air circulation in refrigerated vehicles. The conventional method is top or top air supply. The second method is to supply air from the bottom. This method has been widely used in shipping containers for decades, but its application on highway trailers is very limited.
3. Refrigerated truck trailers /dry van semi-trailer top air supply
In trailers using top air supply, the following structural features are used to enhance air circulation and subsequent cargo temperature control. Use the air duct on the ceiling to guide the air from the fan to the rear of the trailer.
4. Refrigerated truck trailers /dry van semi-trailer body return air
High air flow floor, used to circulate air under the floor. A general trailer cooling fan needs a return air passage of 1,548 cm2 when running at 100 capacity. When the air circulation space under the product is insufficient due to the floor design, the product should be installed on a pallet or floor bracket. Ribbed side walls or partitions with a thickness of at least 3 cm to allow top airflow to descend to the sides of the cargo. This device can reduce heat conduction through the bulkhead or from the product. Up to 20% of the top airflow should flow down to the side walls. An integral partition wall is used to allow air to return to the refrigeration unit unhindered. If the air is blocked, the fan will rotate but not blow. Place the next wall at least 3 inches 8 cm from the front wall. There should be an open space of not less than 15 cm between the bottom of the floor and the bottom edge of the next wall. The top edge of the next wall should have an open area of 196 to 323 cm2 to mix the top and bottom air in the event of a loading error or movement of the goods, and to spend part of the return air to the thermostatic switch. In the open space at the bottom of the next wall, crash pads or vertical ribs should be installed to prevent cargo from blocking the air from the bottom of the next wall to the fan.
5. Refrigerated truck trailers /dry van semi-trailer air supply at the bottom of the body
A small number of road cold-field trailers and most of the shipping containers for overseas trade are bottom-vented. In this type of system, under a pressure of 0.37 to 0.73 kPa water column, the air is sent under the cargo at a flow rate of 85 to 142 cubic meters per second and then flows upward through the cargo. The air is above the top of the cargo and returns to the refrigeration unit through the top of the next wall.
6. Refrigerated truck trailers /dry van semi-trailer multi-temperature vehicles
In recent years, vehicles that use multi-temperature vehicles for food delivery operations have begun to gain ground, especially fast-food restaurants and independent grocers. Multi-temperature vehicles usually have three cargo compartments, each controlled at -18°C or lower, for cold and frozen food; about 2°C for refrigerated food, and about 13°C for freezing-sensitive products.
7. Refrigerated truck trailers /dry van semi-trailer body humidity
The correct humidity or moisture content in the air surrounding fresh fruits and vegetables can help maintain their quality during transportation. Most perishable garden products require a high relative humidity of 85 to 95% to avoid dehydration and keep the product fresh and crisp. The relative humidity mentioned here refers to the percentage of water vapor in the air relative to the saturation point of the air at a given temperature. In mechanically refrigerated vehicles, moisture continuously evaporates from the product and passes through the refrigeration coil to condense out of the circulating air. In the process of transportation, the goods have a certain amount of moisture loss, through the method of adding ice to the top or packaging. Thorough pre-cooling to reduce the temperature difference between the product and the surrounding air. Keep the refrigeration coil at a temperature that is only a few degrees below the required transportation temperature.