Some considerations of the flow of air in timber seasoning kilns.
Creators: name: Greenhill, WL
Publisher: name: University Of Tasmania
Year: 2023

description: The present investigations have been initiated with the object of studying the air circulation and relation between ‚Äö the air movement and the drying of the timber in timber seasoning kilns. The work has been divided into five separate experiments, each of which is summarised separately as follows :- Experiment 1 - The Measurement of the Flow of Air Through 'Timber Stacks. - A method of measuring the air velocity through timber stacks by means of vane anemometer p has been established. Correction factors, which, for ar49ne size and type of anemometer depend on the thickness of the timber and of the separating strips, on the velocity, and on the position in which the anemometer is held, have been determined for a number of cases. These have been plotted against record- ed anemometer readings on a number of graphs. Experiment 2 - The Effect of the Rate of Air Circulation on the rate of Drying. - A number of kiln runs has been made with narrow stacks of matched material using the same temperature and humidity in each run but different rates of air circulation. The object has been to determine the effect of the rate of air circulation on the rate of drying timber apart from the question of change of drying rate from one side of a wide stack to the other due to fall in temperature and increase in humidity of the air. The results indicate that with the same air conditions the rate of drying is independent of the rate of air flow provided that this rate is greater than some minimum value which is probably in most cases less -than 140 feet per minute. Experiment 3 - The Relation Between the Quantity of Air Circulate* and the La in Dr in From the Enterin to the Leaving Air Side of a Kiln Charge of Timber. - A number of tests has been carried out in an experimental kiln to determine the change in air conditions and the lag in the drying rate from the entering to the leaving air side of a stack of timber 5 feet wide. Different sized separating strips and different quantities of circulating air have been used. The theoretical relation between the quantity of air circulated, the amount of moisture evapdrated, and the change in air conditions has also been established; the results so calculated have been compared with those determined experimentally. Experiment 4 - The Relation Between Air Flow and Fall in Pressure Across a Timber Stack. - The flow of air through a rectangular duct consisting of boards and separating strips and similar to the openings through a timber stack has been investigated. Curves showing the relation between static pressure change and rate of flow have been prepared for different sized strips and for board surfaces of different degrees of roughness. Equations for the pressure loss during flow through the duct and for the entrance pressure loss have been determined. Experiment 5 - The Effect of Various Features of Kiln Design on the distribution of the Air over the Side of a Stack of Timber in a Commercial Kiln. - A series of tests has been carried out in commercial kilns of the cross shaft internal fan type to determine the effect of various distances between the kiln walls and the sides of the stack on the distribution of the circulating air over the side of the stack The results of the tests are shown diagrammatically. The conclusion:: is reached that the 16 inch wide space commonly adopted for the particular design of kiln tested is reasonably satisfactory although more comprehensive tests on an experimental kiln of commercial proportions appear desirable.