Zijian Zhao

Reducing wood drying time by application of ultrasound pretreatment

ABSTRACT Industrial wood is typically dried artificially after felling. The drying process is often very lengthy and consumes a large amount of energy, however, and inappropriate drying schedule can cause defects in the wood. Pretreatments such as ultrasound show the potential to reduce wood drying time without impacting quality. This study investigated the influence of ultrasound pretreatment on vacuum drying behavior, hydroxyl content, and microstructural properties of fast-growing wood samples. Pretreatments were performed at ultrasound intensity of 10 W cm−2 and frequencies of 28 and 40 kHz, respectively, for 30, 60, and 90 min, respectively, then pretreated samples were dried at 40°C temperature under absolute pressure of 0.08 MPa. Results showed that ultrasound pretreatment did shorten the wood vacuum drying time, increase effective water diffusivity, open water channels, decompose wood extractives, and decrease hydroxyl content. In effect, ultrasound pretreatment can be applied to successful reduce wood drying time.

Effect of ultrasound pretreatment on wood prior to vacuum drying

The influence of ultrasonic pretreatment prior to vacuum drying of Chinese fir specimens was examined in this work. In the pretreatments, wood samples were immerged in a distilled water bath and were treated using two wave frequencies for four different elapsed times to investigate effects of ultrasonic frequency and treatment duration. Then the wood samples were vacuum-dried at 80°C and absolute pressure of 0,05 MPa. After the pretreatment, microscopic analysis was carried out on the wood samples to check micro-cracks, the loss of extractives from the cell walls and other micro-structural changes on the wood. Results show that the ultrasonic treatment prior to vacuum drying significantly shortened the wood drying time. The drying time decreased with increase in the wave frequency and the treatment time. Furthermore, ultrasound pretreatment tended to reduce the content of extractives in the wood cell walls and cause cell-wall micro-cracking.

Influence of ultrasound-assisted extraction on the pyrolysis characteristics and kinetic parameters of eucalyptus

In this study, the influence of ultrasound-assisted extraction on eucalyptus samples with special focus on pyrolysis characteristics and kinetic parameters was explored. Ultrasound and Soxhlet extraction were used to pretreat samples respectively, then samples were assayed by component analysis, TG-FTIR, and kinetic analysis. Ultrasound-assisted extraction did change the physiochemical characteristics of eucalyptus samples, particularly in regards to the quantity of extractives obtained. In TG and DTG curves, ultrasound-extracted samples reflected lower residual weight ratio (17.77%) and higher maximum weight loss rate (-22.92%/min), and were accompanied by a slight shift in the weight loss rate peak to lower temperature (366°C). The volatiles produced during pyrolysis and the discrepancies of product distribution between experimental and controlled groups were explored based on TG-FTIR spectra. According to kinetic analysis results, ultrasound-treated samples showed higher activation energy at the primary portion of thermal degradation with an average of 206.09kJ/mol.

Heat Transfer Characteristics during Superheated Steam Vacuum Drying of Poplar

Abstract Superheated steam vacuum drying shows major advantages in terms of reducing the boiling point of water and speeding up the drying process, but to our knowledge, no researcher has addressed the effects of drying conditions on heat transfer characteristics during superheated steam vacuum drying of wood. In this study, we did so using fast-growing poplar. Temperatures inside the wood were measured and the convective heat transfer coefficients calculated under temperature conditions of 35°C, 55°C, and 70°C and absolute pressures of 0.03, 0.06, and 0.1 MPa. The results of our subsequent analysis showed that the ultimate temperatures inside wood increase alongside increasing absolute pressure at the set temperature conditions and are lower than that of the drying medium. In addition, we found that convective heat transfer coefficients increase as absolute pressure increases at the set temperatures and also increase as temperature increases at set absolute pressure conditions. We then established a conv...