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Nencho Deliiski and Natalia Tumbarkova

Abstract

This paper describes a methodology for experimental research of the change in the temperature and humidity of the air processing medium and also in the temperature at 4 points of the longitudinal section of logs during freezing. The suggested methodology is used to research the change in the mentioned parameters of poplar logs with diameters of 240 mm, lengths of 480 mm and moisture content above the hygroscopic range during 50 h of freezing in a freezer at a temperature of about -30 °C. The automatic measurement and recording of the parameters is carried out with the help of Data Logger type HygrologNT3 produced by the Swiss firm ROTRONIC. The precise instrumentation allowed, for the first time ever, the measuring of the impact the latent heat released by the free water on the log had on the warming up of the wood during water crystallization in the logs.

Open access

Mincho Hadjiski and Nencho Deliiski

Abstract

An advanced control system is considered for wood Thermal Treatment Processing (TTP) in order to cope with the scarcity of on-line measurements as well as cope with a variety of unpredictable operational conditions arising due to disturbances and large uncertainties. The architecture of the proposed control system includes a number of Building Blocks (BB), functionally based on well-established algorithms, so that that the design and operation of the system use mainly parameterisation via simulation, optimization and coordination. In the created BB a set of advances are incorporated: first principle modelling of WEP, inference control, Run-to-Run optimization, Case-Based Reasoning (CBR). Some results of real applications in SMEs are presented.

Open access

Nencho Deliiski, Veselin Brezin and Natalia Tumbarkova

Abstract

A 1D mathematical model for the computation of the temperature on the surface of cylindrical logs, tsr, and the non-stationary temperature distribution along the radiuses of logs subjected to freezing and subsequent defrosting at convective exponentially changing boundary conditions has been suggested. The model includes mathematical descriptions of the thermal conductivity in radial direction, λr, the effective specific heat capacity, ce, and the density, ρ, of the non-frozen and frozen wood, and also of the heat transfer coefficient between the surrounding air environment and the radial direction of horizontally situated logs, αr. With the help of the model, computations have been carried out for the determination of αr, tsr, λsr, and 1D temperature distribution along the radiuses of beech logs with diameters of 0.24 m, initial temperature 20 °C, and moisture content 0.4 kg·kg-1, 0.8 kg·kg-1, and 1.2 kg·kg-1, during their freezing at -20 °C, and during subsequent thawing at 20 °C.