Periodic forced circulation drying room


 drying chambers ​

Compared with the continuous type, the periodic type has great flexibility, wide adaptability, easy adjustment of temperature and moderate temperature, and can perform humidity control treatment, while the forced circulation is more uniform than the natural circulation, and the loading quantity is large, the drying time is short, and the drying efficiency is high. . Therefore, periodic circulation drying chambers are often used in production. There are many structural forms of this type of drying chamber, and their performance characteristics are not nearly the same.

 Periodic forced circulation drying is divided into four types according to the arrangement of fans in the drying room: indoor top fan type, indoor side fan type, indoor end fan type and jet type.

Top fan type drying room

        The main feature of this drying room is that the interior space is divided into two parts, the upper part and the lower part, with a "false ceiling". The upper part is the extension room, which is used to install fans, heaters, steam spray pipes, intake and exhaust devices, etc. The lower part is the drying room, where the material stack is mainly placed, and generally only the temperature and humidity meter and the moisture content detection device are arranged. The capacity of this kind of drying chamber can be large or small, generally 50-200m3, the air velocity distribution is relatively uniform, and the drying quality is good. It has always been the most commonly used structural form in forced circulation wood drying.

Side fan type forced circulation air drying room

        The fan-type drying room is to install the axial flow fan on the side wall of the drying room, that is, the fan, heater, steam spray pipe, inlet and exhaust ducts and other equipment are all installed on the side of the drying room, each (or Two) fans are equipped with a motor. Since the fans are all on one side of the drying room, they can be driven by indoor and outdoor motors. But the structure of the indoor motor is simpler, and the airtightness of the drying room is better. At present, most of the newly built side fan type drying rooms are indoor electric motors.

The air circulation characteristics of the side fan type drying room are: after the fan sucks air from a part of the material pile, it immediately turns 180o and then enters other parts of the material pile. The air flow does not pass through the fan once, but can pass through the material pile twice, which can reduce the air volume of the fan and increase the drying efficiency. However, due to the sharp turn of the wind direction, the power loss is very large, and strong wind pressure is required. Compared with other room types, the installed power per unit volume not only cannot be reduced, but also slightly increased. Because the fan is close to the material pile, it can only use suction-type one-way air circulation, which cannot realize reversible circulation, and the drying is uneven. Therefore, the width of the pile should not be too wide, and it is best not to use multi-column piles, otherwise the drying effect will be poor, and the capacity of the drying room will be limited.

End fan type forced circulation air drying room

        The advantages of the end-fan type drying room are: good aerodynamic characteristics, can form a "horizontal-horizontal-reversible" air circulation, if the inclined wall design is reasonable, the air circulation is more uniform, and the drying quality is better; the equipment is installed in a convenient maintenance , high capacity utilization; less investment. The disadvantages are: the drying room should not be too long, and the loading capacity is small; if the inclined wall is not designed properly, the air circulation on the section of the pile will be uneven and the drying quality will be reduced.

jet drying chamber

        The aforementioned various types of forced circulation drying chambers place axial flow fans indoors, and all circulating air is driven by the fans. The fan in the jet drying room is placed outside, absorbing 1/5-1/3 of the circulating air from the room, and after being pressurized by the fan, this part of the circulating air is sprayed into the room at a speed of 40-50m/s through a special nozzle , forming a free jet to drive the rest of the circulating air to circulate. Two sets of jet devices in opposite directions work alternately to realize reversible circulation.

        This type of drying chamber has a high volume utilization factor, but its performance is unstable, the structure of the air passage and nozzle is complicated, installation and maintenance are difficult, and the circulation effect is very poor. It is now obsolete and no longer used.

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