Oscillation drying of beech timber – initial experiments

The paper shows the results obtained by drying 38-mm thick beech timber, namely one control test run under usual, conventional drying schedule and four test runs dried under the same schedule but with oscillations of equilibrium moisture content. During oscillation drying, temperature curve was identical with the temperature curve in the control test run, and the values of equilibrium moisture content oscillated according to previously set amplitudes and frequencies. Oscillation amplitudes were ±10 % in the first two test runs and ±20 % in the second two test runs compared to the value anticipated in the schedule. Duration of each oscillation was 3 h in the first and third test runs and 6 h in the second and fourth test runs. Special addition to the manufacturer’s software was developed for the realization of these oscillations. When comparing the results, drying time (for the same intervals of initial and final timber moisture content), energy consumption and drying quality were taken into consideration. Drying quality was determined at the end of each test run (both before and after conditioning), and based on the value of final timber moisture content, distribution of moisture content across thickness and gap size. Drying time was shorter in all four test runs with oscillations, and energy consumption was lower than in the conventional test run. Slightly shorter drying period was recorded in test runs with oscillation frequency of 3 hours compared to the test runs with 6 hour oscillations. Final timber moisture content was almost even in all test runs. Profiles of moisture content across timber thickness were also similar in the test runs, but the biggest difference between core and surface at the end of drying was achieved in the test run without oscillations. Before conditioning, average gap value of over 2 mm was recorded in all test runs, but the biggest average value was recorded in the test run without oscillations