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Four Causes Affecting the Heat Diffusion of Wood Chips in Wood Chip Dryer

Time:2019年07月18日      Hits:

Thermal diffusivity is an important parameter of wood chip thermal properties in wood chips dryer, that is, the physical quantity of reaction temperature change speed in the woodchip drying process. The higher the thermal diffusivity is, the faster the wood chips temperature will rise evenly, which is more conducive to the final moisture control of woodchip drying process .
wood chips dryer, wood chip drying machine
The factors affecting the thermal diffusion of wood chips in the work of woodchip dryer are as follows:

(1) Wood chip size and density:
The thermal conductivity of wood chips usually decreases slightly with the increase of density and its size. Because wood chip is a porous material, the density of wood chip is small, the porosity is large, and the pore is filled with air, while the static air temperature conductivity is very large, two orders of magnitude larger than sawdust, so the low density woodchip, its temperature conductivity is correspondingly higher.

(2) Water content of wood chips:
The thermal conductivity of water is two orders of magnitude smaller than that of air. With the increase of water content, some air in wood chip is replaced by water, and the thermal conductivity of sawdust decreases. There are different forms of moisture in wood chips above and below the fiber saturation point, so the degree of reduction of thermal conductivity varies in different water content ranges.

(3) Temperature of hot air:
The relationship between thermal conductivity and temperature can be regarded as a synthesis of the relationship between temperature and thermal conductivity, specific heat capacity and density. Because the temperature change has little effect on the density, and the thermal conductivity and specific heat capacity increase with the increase of temperature, the influence of temperature on thermal conductivity is greater than that of specific heat capacity, and the thermal conductivity increases with the increase of temperature.

(4) direction of hot air flow:
The influence of heat flow direction on thermal conductivity is the same as that on thermal conductivity. The thermal conductivity along the grain is the largest, followed by the radial and chord directions. In the process of wood chip drying system, the length of wood chip is much longer than the width and thickness, and the main direction of heat transfer is transverse, so the transverse thermal conductivity and thermal conductivity of sawdust are usually measured only.

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