Discussion on ventilation of transport containers

Due to the increasingly fierce competition in the refrigerated cargo transportation market and the unidirectional nature of refrigerated cargo transportation, in order to increase the flexibility of container shipping, there have been many full container ships loaded with air-cooled reefer containers in cargo holds. The 1850TEU ship designed by the Yangzijiang Shipyard, designed by me, is such a full-type container ship. The following is a description of the issues related to the ventilation design of the cargo hold.

In the case of cargo tank ventilation in the past with water-cooled reefer containers, it is necessary to consider ventilation cooling in the case of a small amount of chilled container water cooling failure, so ventilation is also required. However, because only a small number of reefer containers are considered to discharge heat to the cargo hold, the amount of ventilation is small. For example, the 171TEU reefer container ship designed by our company in 1995, the cargo compartment ventilation is considered to be ventilated 4 times per hour (the volume is calculated according to the empty space). For cargo holds loaded with air-cooled reefer containers, the amount of ventilation required is large and cannot be determined simply by the number of air changes. The purpose of ventilation is to discharge the heat discharged from the refrigerated container refrigeration unit into the cargo compartment, reduce the temperature of the cargo compartment, and make the refrigeration equipment of the reefer work normally, and maintain the temperature of the goods in the tank. It is obvious that the amount of ventilation in the cabin is related to the number of reefer containers shipped, however the number of reefer containers loaded in different container cargo holds is determined according to the requirements of the shipowner. The ventilation of the cargo hold can be obtained by calculating the heat removal capacity of the refrigerated container refrigeration unit and the heat transfer and ventilation heat transfer of the cargo hold.

However, different manufacturers' container refrigeration devices have different heat rejections; the cargo tank temperature used in the calculation is a hypothetical uniform temperature, and the temperature distribution in the cargo compartment is not uniform. Therefore, the calculation process is complicated and the result is not completely satisfactory. It is only a design estimation method. The volume of the cargo compartment can also be determined by the air volume of the refrigerated container refrigeration unit fan. Table 1 lists the representative 40 ft container (60 Hz) refrigeration unit condensing fan air volume values ​​as found in the reference.

By blowing the air outside the cabin to the suction portion of the refrigerating device of the refrigerating container at a high speed by the blower, the temperature near the suction port of the condenser of the refrigerating device can be effectively reduced, and the normal operation of the refrigerating device can be ensured. Then, the hot air in the cabin is naturally discharged through the air outlet on the enclosure between the adjacent two cabins and the air outlet on the hatch cover to achieve the purpose of ventilation and heat exchange.

The design and arrangement of the air inlet and outlet are a major problem. In order to maintain the quality of the transported goods, it is necessary to ensure that the temperature of the cabin is not too high and the normal operation of the refrigeration unit is affected during navigation. In a word, it is to ensure the smooth flow of the wind. However, there are too many limiting factors in ship design. The height of the venting opening shall not exceed the height of the hatch cover, and sometimes it shall not be higher than the height of the hatch coaming; the height of the hatch coaming shall be low, and the requirements of the load line shall be met. The distance from the lower edge of the vent opening to the freeboard deck shall be at least 900 mm. Also consider the switch position of the weathertight cover. In addition, the hull structure, the boudoir, the container column on the deck, the lashing bridge, etc. also bring great difficulties to the rational design of the air inlet. Therefore, the design and arrangement of the air inlet and outlet are often only compromised.

Refrigerant Oil

This item includes two types of Refrigerant Oil, one is PAG 100 oil and the other is POE oil.

The purpose of oil in a refrigeration system is to lubricate the compressor that produces cold air. Oil reduces friction on metal parts, reducing wear on the compressor and prolongs the life of the system.

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