Key Words: Logs; frozen bound water; frozen free water; thermal treatment; plasticizing; energy consumption; veneer production.
Abstract. An approach for computing the energy required for warming up and plasticizing of frozen logs subjected to thermal treatment in the production of veneer has been presented. The approach is based on the use of two personal models. With the help of the non-stationary model, the thermal treatment times of beech logs with a diameter of 0.4 m, initial temperatures of –1 °C, –10 °C, –20 °C, –30 °C and moisture content u of 0.4 kg∙kg-1, 0.6 kg∙kg-1, and 0.8 kg∙kg-1 were determined at operating temperatures in the boiling or steaming equipment equal to 80 °C. For different combination of the three values of moisture content and four values of the initial log temperature there are significant differences between the amount of both free and bound frozen water in the logs, which ensures sufficiently large differences between the calculated values of the energy consumption of the logs. Furthermore, the logs with initial temperature of –1 °C contain only frozen free water and no frozen bound water at all. Using the determined logs’ thermal treatment durations, with the help of our second model the change in the energy required for warming up and plasticizing of the investigated logs and that for each of its 4 components was calculated. It was found that the studied energy increases from 55.3 to 67.2 kWh∙m-3 at u = 0.4 kg∙kg-1, from 75.9 to 89.1 kWh∙m-3 at u = 0.6 kg∙kg-1 and from 94.6 to 108.8 kWh∙m-3 at u = 0.8 kg∙kg-1 when the initial temperature of the logs decreases from –10 °C to –30 °C. At initial log temperature of –1 °C the energy required for plastcizing of the wood changes from 46.0 kWh∙m-3 at u = 0.4 kg∙kg-1 to 84.9 kWh∙m-3 at u = 0.8 kg∙kg-1. Four types of individual components of the considered energy have been calculated, namely: for warming um of the frozen and non-frozen wood itself, for melting of the temperature dependent frozen part of bound water, and for melting all
frozen free water in the logs.