Containers make it possible to transport all kinds of goods. However, if you have to transport temperature-sensitive or perishable goods, traditional boxes may not be helpful to you. It would be nice to have a reefer container to hold your goods. What if we told you? It’s called a reefer container.
Refrigerated containers play a vital role in the COVID-19 pandemic. As countries go into lockdown, reefer containers allow food, medicine, and vaccines to be delivered wherever they are needed. Refrigerated trucks are designed to transport this temperature-sensitive cargo and are undoubtedly one of the most critical container types.
Special reefer container mainly refers to a special container used to load special cargo. As an essential means of transporting food, its materials have special requirements. Because for the internal structure of the box, there are requirements for odorless, non-toxic, mildew proof, anti-corrosion, and other performance requirements, so there are strict requirements for the inner material of the box.
II.Introduction of Special Reefer Container Materials
1)Cold-rolled stainless steel sheet
Special reefer container applies a large number of stainless steel plate materials, mainly SUS304 (austenitic stainless steel referred to as HGSS) and SUS410L and SUS409L (both are ferritic stainless steel, referred to as MGSS for short).
The higher the nickel content, the stronger the corrosion resistance. The lining board of the refrigerated container is in contact with the food, and all use this SUS304 material as the lining plate.
The special reefer container outer frame is the primary stress point, and the frame is made of high-strength weather-resistant steel (CORTEN) and hot-rolled ferritic stainless steel (MGSS). These two plates have good bending and welding properties, and at the same time have good mechanical properties, and can meet the strength requirements of containers. CORTEN is relatively cheap but has poor corrosion resistance, but its outer surface can be compensated by hot spraying zinc; At the same time, MGSS stainless steel is rather expensive, but its corrosion resistance is more robust.
3)Aluminum alloy plate
Interior decoration, roof, box sealing plate, and some green refrigerated box outer plate and outer roof plate all use a grade of AA5052 aluminum-magnesium aluminum alloy, also known as anti-rust aluminum alloy, is an aluminum alloy that can not be strengthened by heat treatment, higher strength than pure aluminum and aluminum-manganese alloy, high corrosion resistance, fatigue strength, and good welding performance.
4)Door sealing adhesive strip (EPDM)
Special reefer container door strips are made of an EPDM (EPDM) synthetic rubber. Door sealing strips made of EPDM glue have good low-temperature performance and aging resistance and are suitable for internal and external door seals.
5)Soft polyvinyl chloride (PVC)
Soft polyvinyl chloride (PVC) is mainly used for outer door sealing of wooden door panels, and it is characterized by beautiful molding and beautiful colors.
6)Polyethylene (PE) extrusion profile and low-pressure polyethylene (PE) tape
Polyethylene (PE) extruded profiles have both specific strength and heat insulation. Moreover, it can be sawed and planed, not moldy, and is an excellent material to replace wood. But the disadvantage is that it has a poor appearance, so it is mainly used for dividers in foam layers, floor mat strips, etc.
III. The internal cooling consumption of a refrigerated container includes
- the cold consumption of the goods in the box to cool down. (Frozen goods are generally transported without this mean consumption because the temperature of the goods when they come out of the cold storage is so low that the goods themselves can become a cold source).
- Cold consumption for cooling down. Special reefer container has the same temperature as the outside world before cooling. After cooling, the box’s inner wall is the same as the internal temperature, the outer wall is the same as the outside temperature at that time, and the average temperature of the box is the average value of the inner and outer walls.
- the cold consumption of goods breathing. Generally speaking, fresh vegetables, fruits, and other goods release breathing heat during transportation.
- Cooling consumption of circulating fan. The evaporator fan brings heat to the box’s contents when it is in operation.
- Other cold consumption. Such as cold consumption of frost melting.
IV.Heat exchange between a refrigerated container and the outside world includes
- Cold consumption of heat transfer.
- Cold consumption of heat leakage. When there is a temperature difference or pressure difference inside and outside a refrigerated container, it will leak heat through holes, holes, and gaps that are not tightly sealed. The size of the heat leakage is related to external climatic conditions, etc.
- additional heat transfer cold consumption for special surfaces. Suppose the temperature of some surfaces of the Special Reefer container is significantly different from other surfaces. In that case, the heat transfer means consumption of that surface should be compensated, for example, the additional cold consumption of a surface directly exposed to solar radiation.
- The cooling consumption of ventilation. Refrigerated containers require ventilation when transporting certain goods, such as uncooked fruits, vegetables, and fresh eggs. When ventilating, if the outside temperature is higher than the inside temperature, the outside air will bring heat into the box. On the one hand, the air needs to be reduced to the temperature inside the box. On the other hand, some water vapor may condense (assumed to fall to the original temperature level in the box), the sum of these two parts of heat is the cold consumption of ventilation.
V. Refrigeration operation method for special reefer container
1.Precautions before refrigeration of refrigerated containers
(1) When we receive the reefer container inspection application form (or refrigeration work order), we first need to see if there are any other special requirements on the application form that require the refrigerated container’s refrigeration temperature.
(2) Inspect the refrigerated container’s internal, external, and bottom structure to check whether it is damaged. If there is damage, it will affect the cooling or heat preservation effect.
(3) Determine the type of refrigerated container. Generally speaking, the refrigerated temperature for fresh-keeping goods is above 0℃, and refrigerated containers for shipping fresh-keeping goods are relatively high. Therefore, in this case, refrigerated sea containers should be used as far as possible.
2.Operational steps for refrigeration of refrigerated containers
(1) Install temperature recording paper dial: When installing the temperature recording paper dial, pay attention to the corresponding date and time on the dial.
(2) Set Temperature: When you set the temperature, pay attention to whether the temperature is set in degrees Celsius or Fahrenheit. If the setting is wrong, the temperature reflected on the temperature recording paper dial after the refrigerated container will be wrong.
(3) Set the defrosting cycle: the automatic defrosting function is determined when the refrigerated container is manufactured. It will automatically defrost when the frost on the evaporator surface must be eliminated.
(4) Turn on the refrigeration switch: Turn the switch on OFF before plugging in to avoid personal accidents and damage to the refrigeration machine.
3.Identification of the working condition of refrigerated containers
Through the above steps, the refrigeration operation of the refrigerated container is completed. However, the functional status of reefer containers needs to be grasped at any time. Therefore, when manufacturing refrigerated containers, a series of indicators are specially set up to remind the working status. The three most commonly used hands have the following meanings:
- Orange or amber light: Indicates that the refrigerated container is at a moderate temperature; the difference between the actual temperature and the set temperature in the container is within the normal range of plus or minus 2, 8 degrees Celsius.
- Greenlight: Indicates that the refrigeration unit is in operation.
- Red light: indicates that it is in frost.
VI.Judgment of common faults of refrigerated containers
Special reefer container often has some faults during the refrigeration process, and there are many reasons for these failures. The most common faults and methods for determining them are as follows:
- Turn on the power switch; if the refrigeration system does not work, you should first check whether the power transfer switch is on the voltage you choose, whether the power outlet is plugged in, and whether the fuse is damaged.
- Turn on the power switch, each system of the chiller is working, but it just does not cool down. In this case, there is generally no refrigerant.
- After starting the machine, the chiller will stop automatically after a few minutes of operation and automatically start again after a few minutes. In this case, the refrigerant is mostly lacking. If bubbles are visible through the refrigerant display mirror 20 minutes after starting the machine, it lacks refrigerant.
- The chiller is working, and the computer cannot store the actual temperature. Generally, the temperature sensor of the chiller or the computer system is broken.
- The refrigerated container systems are working correctly, and the refrigeration condition is normal, but the temperature fluctuation range reflected on the temperature recording paper dial is too large. The reason may be that the air vent is not closed, the refrigerated container door is not tightly closed, or the refrigerated container is partially damaged, causing the air conditioning inside the box to leak.
- Generally speaking, the defrosting cycle of the refrigerator is set before refrigeration, and the defrosting is very regular during the refrigeration process. If the continuous defrosting time occurs for too long while defrosting is performed, the defrost control switch is broken. If the defrost stops while the chiller is working, the heater is broken.
- Special reefer container is running in time if it is found that the set temperature is the same as the temperature measured manually in the box. The reefer temperature record dial shows that the temperature is too different from the former, indicating that the temperature sensor probe is broken.