Автор: Natalia Tumbarkova

Статии

CALCULATION OF THE ENERGY CONSUMPTION FOR DEFROSTING OF THE WOOD CHIPS

Автори: Nencho Deliiski, Veselin Brezin, Izabela Radkova, Anton Geffert, Jarmila Geffertova, Natalia Tumbarkova

Резюме

Аn approach for the calculation of the specific mass energy consumption  (in kWh.t-1) needed for defrosting of the wood chips, which contain both frozen bound an free water, has been suggested. For the calculation of the  a software program has been prepared in MS Excel 2010. With the help of the program calculations have been carried out for the determination of  for oak, acacia, beech, and poplar frozen chips with moisture content in the range from u = 0.4 kg·kg-1 to u = 1.0 kg·kg-1 and with an initial temperature at the range from t0 = –40 oC to t0 = –1 oC. At temperature equal to –1 oC the defrosting process of the wood chips has been fully completed.

Ключови думи: wood chips, defrosting, frozen bound water, frozen free water, specific mass energy consumption

EN Version

MATHEMATICAL DESCRIPTION OF THE SPECIFIC HEAT CAPACITY OF THE WOOD ABOVE THE HYGROSCOPIC RANGE DURING WOOD FREEZING

Автори: Nencho Deliiski, Natalia Tumbarkova, Rayko Stanev

Резюме

A mathematical description of the specific heat capacity c of wood above the hygroscopic range during wood freezing has been suggested. The description takes into account the physics of the freezing process of both the free and the hygroscopically bound water in the wood. It reflects also the influence of the fiber saturation point of wood species on the value of their c during wood freezing and the influence of the temperature on the fiber saturation point of the wood during its freezing. A software program has been prepared for the computation of c according to the suggested mathematical description. With the help of the program, computations have been done for the determination of c of often used in veneer and plywood production beech and poplar wood with moisture content 0.4 kg∙kg-1u≤1.2 kg∙kg-1 at the temperature range between 0 oC and –60 oC during freezing of the wood.

Ключови думи: wood, freezing, specific heat capacity, mathematical description, bound water, free water, computatio

EN Version

APPLYING THE SOFTWARE PACKAGE TABLE CURVE 2D FOR COMPUTATION OF PROCESSING AIR MEDIUM TEMPERATURE DURING FREEZING IN A FREEZER AND DEFROSRING OF LOGS

Автори: Natalia Tumbarkova, Nencho Deliiski

Резюме

A mathematical description of the change in the processing air medium temperature Tm during freezing in a freezer and subsequent defrosting of logs using a software package Table Curve 2D v.5.01 has been suggested. This package allows for the selection of equations, which provides the best similarity between the calculated with them values of Tm during the log’s freezing and defrosting processes and the respective experimentally established data for Tm. The values of the coefficients in the selected equations have been determined in the work for the cases of decreasing in Tm in the range from about 20 оС to about –30 оС during separately 30 h freezing and of the following increasing in Tm up to about 20 oC during the subsequent 30 h or 50 h defrosting of 6 pine logs with diameter of 240 mm and length of 480 mm.

Ключови думи: temperature, processing air medium, freezing, defrosting, pine logs, Table Curve

EN Version

COMPUTATION OF THE ENERGY CONSUMPTION FOR WARMING UP OF FLAT OAK DETAILS BEFORE THEIR BENDING

Автори: Nencho Deliiski, Neno Trichkov, Dimitar Angelski, Ladislav Dzurenda, Zhivko Gochev, Natalia Tumbarkova

Резюме

A software program has been prepared in the calculation environment of Visual Fortran for solving of own 1D non-linear model of the one sided heating process of flat wood details. With the help of the program, the 1D non-stationary temperature field in flat oak details with initial temperature of 20 oC, moisture content of 0.15 kg.kg-1, thickness of 12 mm, 16 mm, and 20 mm during their 30 min one sided heating at temperature of 80 oC of the heating metal body has been calculated. After integration of the temperature field, the energy consumption for warming up of the details before their bending in the production of curved back parts of chairs has been calculated. The obtained results are graphically presented and analyzed.

Ключови думи: oak details, one sided heating, bending, energy consumption

EN Version

COMPUTATION OF THE CHANGE IN THERMAL CONDUCTIVITIES OF POPLAR LOGS DURING THEIR FREEZING

Автори: Nencho Deliiski, Natalia Tumbarkova

Резюме

A mathematical description of the thermal conductivities λ of frozen and non-frozen wood has been introduced in an own non-linear mathematical model of the logs’ freezing process. For the numerical solution of the model a software program has been prepared in the calculation environment of Visual Fortran Professional. With the help of the program, the 2D non-stationary distribution of the temperature and the change of λ in the longitudinal section of poplar logs with diameter of 240 mm and length of 480 mm during their 50 h freezing in a freezer at about –30 oC have been calculated. The change of λ in the radial and longitudinal directions of the wood on both surfaces and in the center of the subjected to freezing logs during the freezing process has been calculated, visualized and analyzed.

Ключови думи: poplar logs, freezing, radial thermal conductivity, longitudinal thermal conductivity, Visual Fortran

EN Version

MATHEMATICAL DESCRIPTION OF THE CHANGE IN THE ATMOSPHERIC TEMPERATURE DURING DAYS AND NIGHTS

Автори: Nencho Deliiski, Neno Trichkov, Natalia Tumbarkova

Резюме

A mathematical description of the periodically changing during many days and nights temperature of the atmospheric air as a processing medium has been suggested. It is introduced in the boundary conditions of our own mutually connected 2D non-linear mathematical models of the logs’ freezing and defrosting processes. For the numerical solving of the models a software program has been prepared in the calculation environment of Visual Fortran Professional. Results from a simulative investigation of the 2D non-stationary temperature distribution in beech logs with a diameter of 0.24 m, length of 0.48 m, moisture content of 0.6 kg·kg-1, and initial temperature of 0 oC during their 5 days and nights continuous freezing and defrosting at sinusoidal change of the air temperature with initial values of –5 oC and different amplitudes are presented and analyzed.

Ключови думи: mathematical description, atmospheric air, temperature, 2D models, beech logs, freezing, defrosting

EN Version

COMPUTATION OF THE AVERAGE MASS THERMAL CONDUCTIVITY OF OAK FURNITURE ELEMENTS SUBJECTED TO CONVECTIVE HEATING BEFORE LACQUERING

Автори: Nencho Deliiski, Neno Trichkov, Dimitar Angelski, Ladislav Dzurenda, Zhivko Gochev, Natalia Tumbarkova

Резюме

A methodology for the computation and research of the following two mutually connected problems has been suggested: 1D non-stationary temperature distribution in subjected to unilateral convective heating process of flat wooden furniture elements before lacquering and change in their average mass thermal conductivity. For the realization of the methodology, created earlier by the authors 1-dimensional nonlinear mathematical model has been solved for the transient heat conduction in the furniture elements during their unilateral convective heating. The model contains a mathematical description of the average mass thermal conductivity of the elements and their surface layer, which is intended for lacquering. For the numerical solution of the model with the aim of applying the methodology a software program has been prepared and input in the calculation environment of Visual FORTRAN Professional. Using the program, computations have been carried out for determination of the 1-dimensional non-stationary temperature distribution along the elements’ thickness and of the average mass thermal conductivity for flat oak furniture elements with an initial temperature of 20 oC, moisture content of 8 %, thickness of 16 mm, width of 0.6 m, and length of 1.2 m during their 10 min unilateral convective heating at temperature of the processing air medium of 100 oC, which circulates above the elements with a velocity of 2 m·s-1, 5 m·s-1, and 8 m·s-1 aimed at improvement of the conditions for the subsequent lacquering. During the computations a temperature of 20 oC for the surrounding air near the non-heated surface of the carrying rubber band has been used. The change in the average mass thermal conductivity of the studied furniture oak elements and also of their heated surface layers during the heating is graphically presented and analyzed.

Because of the wide range of applications, the need for paulownia is constantly increasing.

Ключови думи: oak furniture elements, one sided convective heating, lacquering, thermal conductivity

EN Version