From Supply Chain Management Encyclopedia
Russian: Изотермические вагоны
Classification and General Characteristics of Refrigerated Vans
One of the conditions for the delivery of perishable goods - to maintain the desired temperature in the cargo area of the transport module at the same level. Therefore, transport modules that satisfy this requirement, called isothermal.
The relative constancy of temperature in the cargo area of the transport module is achieved by passive (insulation enclosing surfaces) and active (endogenous or cold engine) means. Using only passive means characteristic of wagons- thermoses and containers-thermoses. For perishable goods that require strict compliance with the temperature conditions, use of active means - refrigerated trucks and refrigerated containers.
Isothermal cars are classified by the number of attributes. By appointment for their shared purpose wagons divided into the transport of a wide range of perishable goods and into special created for the transportation of certain types of products. Universal and special wagons for the isothermal method of cooling divided by the cars with the engine cooling (refrigerated); cars, refrigerated ready-made refrigerants (water ice, ice-salt mixtures, dry ice, liquid nitrogen) and wagons- thermoses that have no heating and cooling devices. In the future, perhaps, the use of cars, cooled by thermoelectric batteries. By the number of wagons in one unit refrigerated rolling stock (CPF) was isolated refrigerated section (five wagons and three wagons) and autonomous refrigerated wagons with office space (ARW-E).
Isothermal wagon made a four welded metal body length of 21 meters and maximum allowed speed of 120 km / h. As the power system refrigerator vans used diesel generator sets (central or individual). Cargo room in refrigerator van fitted with cooling and heating systems of forced ventilation and air circulation, devices for air and cargo monitoring. As an insulating material for the enclosing structures of the cargo spaces are used microporous rubber and other insulation materials.
In the five-van refrigerated sections all elements of refrigeration and heating plants get their energy from the main diesel power. The railways of Russia and the CIS operate two types of five-van refrigerator sections of the plant construction Dessau (Germany) and Bryansk Engineering Plant, as well as self-contained refrigerated van built with Dessau factory premises (ARW-E).
Requirements for Isothermal Wagons
Isothermal wagon are to satisfy the following requirements:
- Ability to maintain the cargo area of optimum temperature and humidity, regardless of external conditions
- Ensuring adequate circulation and ventilation in the cargo area
- Providing cooling of fruits and vegetables in the process of transporting
- High thermal characteristics walling
- Possibility of full automation of the equipment and temperature control
- Rreliability and simplicity of its service
- Exclusion of air infiltration
- The effective use of in-service
- Ability the traffic at speeds up to 150 km / h, including in the composition of passenger trains.
Requirements for Insulation Materials
Strict requirements are applied to insulation materials enclosures isothermal wagons.
High-quality insulating material shall be: - Low thermal conductivity ( ) - Low density (ρ <250 kg/m3) - Low hygroscopicity (moisture absorption increases λ) and water vapor permeability - Frost and fire – resistant - The lack of smell - Cheapness, etc.
The air is the one of the best heat insulator, it meets all the requirements (λ = 0,023 W / (m K), ρ = 1,29 kg/m3). The layer of still air is found in many structures, such as double glazing windows of vans. Heat insulating materials tend to make porous, which reduces their density and thermal conductivity.
By their building insulation materials can be divided into hard (plates, sheets), flexible (mats, sheets, ropes, harnesses), loose (balls, grains), fiber (absorbent cotton), powder. Thermal insulation materials are mainly inorganic origin:
- Aerated concrete (λ = 0,082 W / (m K), ρ = 280 kg/m3) - a frozen mixture of grout and soap suds;
- Mineral wool (λ = 0,056 W / (m K), ρ = 150 kg/m3) - fibrous material derived from silicate melts;
- Glass fiber (λ = 0,05 W / (m K), ρ = 100 kg/m3) - derived from the same material that glass made;
- Foam polystyrene (λ = 0,05 W / (m K), ρ = 25 kg/m3) - the product of sintering pellets of polystyrene beads;
- Penopolivinilhlorid (λ = 0,035 W / (m K), ρ = 70 kg/m3);
- Polyurethane foam (λ = 0,025 W / (m K), ρ = 20 kg/m3), etc.
Among the organic insulating materials the microporous rubber (λ =0,05 W / (m K), ρ = 15 kg/m3) - hardened foamed urea-weight resin, are widely used in refrigerator vans.
Heat Transfer Coefficient
Thermal insulation of isothermal vans usually have layered. The most important characteristic is their heat-transfer coefficient k. Its value than greater than more intense heat penetrates through the fence and removed from the interior and exterior of surfaces. K value characteristic of refrigerator vans and thermoses. For the known structural operation conditions value k = 0,27 ... 0,35 W / m2 parameters is determined by the laws of heat transfer.