Кey Words: Concrete pits; non-frozen logs; boiling; energy consumption; energy efficiency; veneer production.
Abstract. An approach for computing the energy consumption and energy efficiency of pits during boiling of non-frozen logs intended for veneer production has been presented. The approach is based on the use of two personal mathematical models: 1D non-linear model of the unsteady distribution of the temperature along the radius in the central cross section of non-frozen logs subjected to boiling at conductive boundary conditions, and model of the thermal balance of concrete pits during boiling of wood materials in them. For numerical solving of the models and practical application of the suggested approach, a software packages were prepared in the calculation environment of Visual FORTRAN Professional and in Excel respectively. With the help of the first model, the boiling times of beech logs with a diameter of 0.4 m, initial temperature of 0, 10, and 20 °C and moisture content of 0.6 kg∙kg-1 were determined at water temperatures in the pit equal to 70, 80, and 90 °C. Using the determined logs’ boiling durations, with the help of the second model the change in energy required for the entire boiling process and that for each of the components of the thermal balance was calculated. Computer simulations were performed for a well-insulated concrete pit with working volume of 20 m3 and degree of filling it with logs 45%, 60%, and 75%. It was found that the energy consumption of the pit decreases from 159.7 to 145.3 kWh·m-3 when the initial temperature of the logs increases from 0 °C to 20 °C at temperature of the boiling water of 80 °C and maximum possible degree of feeling of 75%. In this case, the thermal efficiency of the pit decreases from 32.2% to 26.1%. It was found also that at the same degree of feeling of the pit the increase in the boiling water temperature from 70 °C to 90 °C causes an increase in the energy consumption of the pit from 135.3 to 170.9 kWh·m-3 when the initial temperature of the logs is equal to 10 °C. Under these conditions the thermal efficiency of the pit decreases from 29.9% to 28.8%. The approach can be applied to compute the energy consumption and thermal balances of concrete pits during boiling of non-frozen logs to any desired final average mass temperature required for the mechanical processing of the plasticized wood. It could be easily modified and used to calculate the energy consumption and efficiency of concrete pits of any design and construction parameters.