Refrigerated trucks are van-type special transport vehicles equipped with insulation structure and refrigeration devices for refrigerated transportation.
● Classification of refrigerated trucks
Refrigerated trucks are actually called refrigerated and insulated vehicles, which are divided into two categories: refrigerated trucks and insulated vehicles.
Insulated vehicles refer to vehicles with insulated compartments suitable for short-distance insulated transportation.
Refrigerated trucks refer to vehicles with insulated compartments and refrigeration devices.
According to the refrigeration method of the refrigeration device, there are mechanical refrigerated trucks, frozen plate refrigerated trucks, liquid nitrogen refrigerated trucks, dry ice refrigerated trucks, ice refrigerated trucks, etc. Among them, mechanical refrigerated trucks are the main models of refrigerated trucks
Classified by chassis carrying capacity: micro refrigerated trucks, small refrigerated trucks, medium refrigerated trucks, and large refrigerated trucks.
Classified by compartment type: bread refrigerated trucks, van refrigerated trucks, and semi-trailer refrigerated trucks.
● Composition of refrigerated trucks
Refrigerated trucks are mainly composed of automobile chassis, heat-insulated compartments, refrigeration units, temperature recorders in the compartments and other components. For vehicles with special requirements, such as meat hook trucks, optional parts such as meat hooks, waist rails, aluminum alloy rails, ventilation slots, etc. can be installed.
Refrigerated truck compartment: generally composed of polyurethane materials, fiberglass, color steel plates, stainless steel, etc. The production technologies include: “sandwich” board bonding type (commonly used) for piece-by-piece assembly, injection foaming type for piece-by-piece assembly, integral skeleton injection foaming type, vacuum adsorption type pasting, etc.
Refrigerated truck refrigeration unit: Refrigeration units are divided into non-independent refrigeration units and independent refrigeration units. Domestic units and imported units, etc. General models use external refrigeration machines, and a few micro refrigerated trucks use built-in refrigeration machines. For refrigerated trucks with lower temperature requirements, built-in cold plates in the compartment can be used (the function is equivalent to evaporators).
● Refrigeration principle of refrigerated trucks
There are many ways to refrigerate refrigerated trucks. The following 5 are the more common refrigeration methods:
1. Water ice and salt ice refrigeration: Water ice refrigeration equipment requires less investment and low operating costs, but the heat absorption per unit mass of ordinary water (salt) ice is small, the cooling in the car is limited, and the salt ice will pollute the environment and food after melting, corrode the car and the goods and get damp,
Therefore, water (salt) ice refrigeration is mainly used for refrigerated transportation of aquatic products such as fish.
2. Dry ice refrigeration: The device is simple, the investment and operating costs are low, it is easy to use, and the goods will not get damp. The CO2 gas produced by the sublimation of dry ice can inhibit the reproduction of microorganisms, slow down fat oxidation, and weaken the respiration of fruits and vegetables. However, the sublimation of dry ice is easy to cause frost, and excessive CO2 gas will cause refrigerated fruits, vegetables and other refrigerated objects to have difficulty breathing and necrosis. In addition, the temperature in the compartment is difficult to adjust, the cost of dry ice is high, and the consumption is large, so it is rarely used in practice.
3. Cold plate refrigeration: The device itself is heavy and large in size, occupying a certain volume of the car, and the cold plate can only work continuously for 8~15 hours after being filled once. Therefore, cold plate refrigeration is suitable for medium and short-distance transportation of medium and light refrigerated vehicles. In recent years, with the increasing prominence of energy and environmental pollution issues, the application of cold plate refrigeration has developed rapidly and has become a refrigeration method second only to mechanical refrigeration.
4. Liquid nitrogen refrigeration: The device has a simple structure, reliable operation, no noise and pollution; liquid nitrogen has a large refrigeration capacity and rapid refrigeration, which is suitable for quick freezing. Liquid nitrogen vaporization will not make the compartment damp, and nitrogen is good for food preservation and prevention of dry consumption. In addition, liquid nitrogen refrigeration has accurate temperature control (plus or minus two degrees). However, liquid nitrogen is expensive and needs to be filled frequently, so its promotion is subject to certain restrictions. Similarly,
other low-temperature vaporized liquid gases can also be used as refrigerants, such as liquid carbon dinitride.
5. Mechanical refrigeration: Mechanical refrigeration methods include vapor compression, absorption, vapor injection, etc. At present, vapor compression is the most widely used. The compression refrigeration unit is mainly composed of a compressor, a condenser, a throttle valve (or expansion valve) and an evaporator.
