Scielo RSS <![CDATA[Maderas. Ciencia y tecnología]]> https://scielo.conicyt.cl/rss.php?pid=0718-221X20040002&lang=pt vol. 6 num. 2 lang. pt <![CDATA[SciELO Logo]]> https://scielo.conicyt.cl/img/en/fbpelogp.gif https://scielo.conicyt.cl <![CDATA[OPTIMIZING AIRFLOW REVERSALS FOR KILN DRYING OF SOFTWOOD TIMBER BY APPLYING MATHEMATICAL MODELS]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-221X2004000200001&lng=pt&nrm=iso&tlng=pt After experimental validation of a kiln-wide drying model, a single board drying model and a stress model for kiln drying of softwood timber, these models are integrated and used to investigate benefits of airflow reversals in smoothing moisture content distribution and in reducing drying stresses for commercial kiln drying. In the current study, a high temperature drying schedule (DB/WB of 120/70°C and air velocity of 5 m/s) was simulated and 5 strategies for airflow reversal were evaluated. These strategies are: airflow reversal every hour; airflow reversal every 2 hours; airflow reversal every 3 hours and airflow reversal after 2 and 10 hours of drying. The results are compared to ‘Control’ in which airflow is unidirectional (no reversal). It has been found that, for the moisture content distribution, the first reversal is critical and frequencies of subsequent flow reversals can be varied depending on the drying temperature used. However, more frequent airflow reversal has benefits in reducing drying stresses. These findings are consistent with observations in commercial kiln drying of softwood lumber <![CDATA[The release of Hydrocarbons from softwood drying: Measurement and modeling]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-221X2004000200002&lng=pt&nrm=iso&tlng=pt The release of volatile organic compounds (VOC) during the drying of Norway spruce and Scots pine was experimentally studied. Heartwood and sapwood were separately dried at 60 ºC. The Flame Ion Detector (FID) was used to measure the total amount of hydrocarbons (THC) released during the drying process. A large difference of the emissions course between heartwood and sapwood were found. For heartwood, a release maximum of hydrocarbons followed by a typical negative exponential course was found. When drying sapwood, the released amount of hydrocarbons was evidently more fluctuating before reducing to zero. A model describing the release of hydrocarbons during the drying with only diffusion as transport mechanism was applied. The aim was to obtain a suitable explanation of the characteristic release behavior from sapwood and develop a model describing the process <![CDATA[HEAT PUMPS FOR WOOD DRYING: NEW DEVELOPMENTS AND PRELIMINARY RESULTS]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-221X2004000200003&lng=pt&nrm=iso&tlng=pt This paper succinctly presents new developments, preliminary statements and a number of energy results in the area of high-temperature heat pump technology for wood drying in a Canadian economic environment. A hybrid (electricity/fossil), high-temperature technology has been investigated and then field tested over the last two years. Several technical developments were achieved at the level of fluid selection, refrigerant flow control and system stability, variable dehumidifying capacity and appropriate drying schedules. The present study demonstrates that the thermodynamic efficiency and specific energy performance of the developed high-temperature drying heat pumps have generally reached the initial designed targets. Refinements of the integrated control methods involving variable speed and electronic devices are currently being undertaken in order to avoid undesired operating conditions that could cause mechanical failures or inefficient dehumidifying processes. The current research program aims at diversifying the applicable thermodynamic cycles, testing new environmentally friendly refrigerants and advanced components, and developing more advanced drying control strategies <![CDATA[<B>IDENTIFICATION OF WOOD DESTRUCTION DURING DRYING</B>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-221X2004000200004&lng=pt&nrm=iso&tlng=pt The subject of this paper concerns destruction of timber during drying. The main goal is to propose a method of avoiding destruction through a suitable programming of drying processes, controlled with the help of the acoustic emission (AE) method. Three different programs of convective drying of pinewood (Pinus sp.) samples are presented. The high and slow rate drying programs were applied to show an evident dependence between the intensity of AE signals (their number and energy) and the degree of destruction of pinewood during drying. The third drying program was controlled, i.e. the drying was accelerated, when the acoustic emission was low, or slowed down, when the acoustic emission started to grow rapidly. In this way , the drying process was optimized for the purpose of shortening of the drying time and avoiding a destruction of the material <![CDATA[<B>FLUIDIZATION BEHAVIOR OF WOOD/SAND MIXTURES</B>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-221X2004000200005&lng=pt&nrm=iso&tlng=pt In conversion of biomass to secondary energy carriers, several routes are possible, such as gasification, combustion and pyrolysis. In many of these processes it is necessary or advantageous to dry the biomass before further processing. For wooden biomass, fluidized bed drying in superheated steam is a promising option. Given the difficulty to fluidize wood particles alone, it is very common to fluidize these kinds of particles with sand. This also gives better defined fluidization behavior. Especially when the wood particles come in various size and shape (i.e. from sawdust to chopped wood), this gives a more reliable scale-up. Also heat transfer to the wood particles may benefit from the use of sand. However, not much is known about fluidization behavior in pressurized steam of binary mixtures with large particle size ratio and large particle density ratio. Therefore minimum fluidization velocity and bed porosity of wood/sand mixtures in air have been experimentally determined and compared to correlations known from literature. The experimental values show a clear trend, but correlations from literature appear not to be very accurate. So more experiments have to be done to find a correlation that gives more accurate predictions in case of the specific particles used in this work. From segregation experiments could be found that, to keep the wood/sand bed well-mixed, finer sand (0.1-0.5 mm) with maximum 10 weight-% wood should be used, and the superficial gas velocity should be at least 3-4 times the minimum fluidization velocity <![CDATA[14<SUP>th</SUP> International Drying Symposium (IDS 2004) Conference Report]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0718-221X2004000200006&lng=pt&nrm=iso&tlng=pt In conversion of biomass to secondary energy carriers, several routes are possible, such as gasification, combustion and pyrolysis. In many of these processes it is necessary or advantageous to dry the biomass before further processing. For wooden biomass, fluidized bed drying in superheated steam is a promising option. Given the difficulty to fluidize wood particles alone, it is very common to fluidize these kinds of particles with sand. This also gives better defined fluidization behavior. Especially when the wood particles come in various size and shape (i.e. from sawdust to chopped wood), this gives a more reliable scale-up. Also heat transfer to the wood particles may benefit from the use of sand. However, not much is known about fluidization behavior in pressurized steam of binary mixtures with large particle size ratio and large particle density ratio. Therefore minimum fluidization velocity and bed porosity of wood/sand mixtures in air have been experimentally determined and compared to correlations known from literature. The experimental values show a clear trend, but correlations from literature appear not to be very accurate. So more experiments have to be done to find a correlation that gives more accurate predictions in case of the specific particles used in this work. From segregation experiments could be found that, to keep the wood/sand bed well-mixed, finer sand (0.1-0.5 mm) with maximum 10 weight-% wood should be used, and the superficial gas velocity should be at least 3-4 times the minimum fluidization velocity