Search

The briquette porosity is a quality characteristic known to be important for combustion analysis, heat and mass transfer processes during combustion stages, determination of effective thermal conductivity or other related properties. This paper describes a method to quantify the briquette porosity by some surface roughness parameters that can be useful for alternative, inexpensive and at hand evaluations. Porosity of briquettes manufactured with a hydraulic press from waste wood from secondary processing was calculated with three methods suggested in the literature for wood; of these, one was adapted here for a wet porosity model (called “general relation”) proposed for wood briquettes. Briquettes density was obtained by using two stereometric methods and a liquid displacement method. Correlations were examined between porosity, surface roughness parameters and density of briquettes. Very strong correlations with surface roughness were identified for porosity calculated with all three methods, when density was measured by one of the stereometric methods. These correlations can serve as a method to indirect evaluation of the briquettes porosity by assessing the surface quality.

The best-possible valorization of each cut log is a priority. The aim of this research was to evaluate the potential of a solution for increasing the conversion efficiency of tapered logs, by edge-cutting the narrowest sideboards at 45° and joining them by gluing, in order to obtain usable lumber boards. The modality of obtaining the glued elements was described and the values of the density and bending properties (MOE and MOR) of these elements compared to solid wood elements taken from the same logs and the same position within each log was determined. The envisaged outcome was to determine if the bonded products are suited to be used as cores within laminated products for construction.

Flexural properties were evaluated of blockboard with spruce (Picea abies Mill) core and faces made of 2.5-mm fromager (Ceiba pentandra) veneer and 3-mm high-density fiberboard (HDF). For these two types of structures, fiber glass, jute, gauze, and cotton fabrics, were separately bonded under the face layers to improve the strength performance. Flexural properties, modulus of rupture (MOR), and modulus of elasticity (MOE) were determined under laboratory conditions. Improved values were found for MOR and MOE tested in the parallel to core grain direction compared to those perpendicular-to-grain. They were 32% to 49% (MOR) and 39% to 95% (MOE) improvements in case of veneer faces and 142% to 161% (MOR) and 134% to 245% (MOE) improvements in case of HDF faces. The best results of MOR and MOE were obtained for glass fiber used as insertion material, the higher ones being reached for specimens tested in the parallel direction to grain, which were 56.1 N/mm2 (MOR) and 6704 N/mm2 (MOE) for HDF faces. Generally, the improvements were more evident on the blockboard structures with veneer faces oriented perpendicular-to-core grain (30% for MOR and 18% MOE) and for HDF faces with parallel core grain orientation (16% for MOR and 6% MOE).

Three electrical resistive-circuit models were used to determine the effective transverse and longitudinal thermal conductivity of a wood cell as a constituent element of briquettes chips. The models were applied to the briquettes at 0% moisture content and equilibrium moisture content. With the increase in moisture content above equilibrium moisture content, but below fiber saturation point, both fiber swelling and increase in chips interspaces occurred, so that a change in the cell geometry and model was necessary. Since the transverse series resistive model overestimated the thermal conductivity and the transverse parallel resistive model underestimated the thermal conductivity, the wood cells were combined into serial and parallel circuits until the difference between models became insignificant. General equations were developed in the paper, describing effective transverse thermal conductivity of combined cells. Experimental measurements of thermal conductivity significantly validated the resistive models.

The aricle presents the results of a research performed in order to establish whether drying lumber from frozen state (in winter) has repercussions upon its properties, compared to drying under the same conditions lumber parts originating from the same log and position within the log section but that were not frozen prior to drying. To this purpose, spruce (Picea abies L.) lumber specimens, 35 mm and 55 mm thick, cut from the same log, half frozen at − 30°C and half unfrozen, were dried under the same conditions in a climate chamber. Some mechanical properties (hardness, bending strength, and modulus elasticity in static bending), as well as workability (expressed by means of the absorbed power and specific resistance to cutting during milling), were determined The results revealed slight differences between the frozen and the unfrozen samples both during the drying process and afterwards. It was noticed that a significant amount of water was removed from wood during the very beginning of the heating phas...