Properties of solid wood and laminated wood lumber manufactured by cold pressing and heat treatment

Physical, mechanical, and morphological properties of solid wood lumbers which were cold pressed in a press and then heat treated in a kiln. Two different kinds of domestic thinning small-diameter softwood (Ginko biloba L.) and hardwood (Tilia amurensis Rupr.) were used in this study. First 50 mm thick lumbers were cold pressed until 35 mm (30% of control lumber) using a stopper for 5 min. Then the cold pressed lumbers were heat treated in an electric kiln at 180 °C for 6, 12, 24, or 48 h. To increase the utilizability of woods, the LVLs were produced from 4 mm thick veneers prepared from the heat treated lumbers using a veneer saw. Each LVL sample consisted of 5 layers which were subsequently 48 h-, 24 h-, 12 h-, and 6 h-treated veneers and untreated veneer (from top layer to bottom layer). The shrinkage rates of softwood and hardwood were considerably decreased with increasing temperature. The mechanical properties of heat treated samples were better than those of unpressed control samples. The bending strength and modulus of elasticity of the LVLs manufactured from cold pressed and then heat treated lumbers were slightly lower than those of untreated woods. The colour values obtained from the heat treated wood samples showed a clear effect of the temperature on the colour changes.     

Characterization of heat treated wood species

The objective of this work is to investigate the effect of heat treatment on swelling, hardness and surface quality of samples from four species, namely mindi (Melia azedarch L.), mahogany (Swietenia macrophyla), red oak (Quercus falcate Michx.) and Southern pine (Pinus taeda L.). Specimens were exposed to temperature levels of 130 °C and 200 °C for 2 and 8 h. Swelling values of the control and heat treated samples were evaluated by soaking them in water for 2 h. Surface quality and hardness of the species were also determined using a stylus technique and Janka hardness, respectively. Based on the findings in this study dimensional stability of all four types of samples improved with heat treatment. Surface quality of the specimens was also significantly enhanced by exposing them to heat. Micrographs taken from scanning electron microscope revealed that there was some distortion and modification of the cells due to heat treatment. Overall hardness of the samples was adversely influenced by heat treatment. It seems that properties of the species evaluated in this investigation were more pronounced with increasing temperature and time span.     

Analysis of molecular dynamics of moist wood components by applying the stretched-exponential function

On the basis of the molecular dynamics of wood components, the effects of adsorption water molecules on the change of relaxation behavior were examined for wood specimens with various moisture contents using the low of mixture and stretched-exponential function (so-called the Kohlrausch–Williams–Watts (KWW) function). The KWW function has two parameters: the characteristic relaxation time and a parameter related to the dispersion of the relaxation time. Both parameters and the relaxation modulus at time 10 s, E(10), could be separated into three regions corresponding to moisture contents of 0–0.05, 0.05–0.10, and greater than 0.10. Experimental results provided a consistent explanation for the relationships between the isotherm curve analysis of wood, the dielectric relaxation behavior of adsorption water molecules, and the mechanical relaxation behavior of wood.     

Determination of the heat capacity of posistors

A method is proposed for determining the heat capacity of posistors. The temperature dependence of the heat capacity is considered.     

A simple method for calculating Debye heat capacity values using the Einstein heat capacity formula

A procedure for calculating Debye heat capacity values, usually obtained by means of series solutions or by numerical integration, has been developed. The procedure is based on the simpler analytical form of the Einstein heat capacity model. By replacing Θ_E with a simple function of T/Θ_D, the Einstein model can predict heat capacity values which agree with Debye model predictions with an average percentage error of 0.39% over a temperature range of 0.075 ? T/Θ_O ? 12. As the lower temperature limit rises, the agreement is even better. This procedure is particularly useful in analysing experimental data which require many heat capacity calculations over wide ranges of temperature.     

On the heat capacity of nanocrystalline substances

The heat capacity of a nanocrystalline solid possessing a fractal structure is considered within the framework of the Debye model. An expression for the heat capacity is obtained from which the Debye and Dulong-Petit laws follow in particular cases. The heat capacity of nanocrystalline solids may decrease at high temperatures and increase at low temperatures, depending on the fractal dimension of the sample structure.     

Dipolar heat capacity of CMN

The magnetic contribution to the low-temperature specific heat of cerous magnesium nitrate (CMN) was determined by the Casimir-Du Pré ac susceptibility method in the region of 1 K. The value found for the coefficient of the major (T ^?2) term is in good agreement with that determined in this laboratory in magnetic cooling experiments. It is some 10% less than that calculated for the magnetic dipole interaction between the Ce ³⁺ ions.     

Low-temperature heat capacity of urea

The heat capacity of urea was measured with an adiabatic calorimeter in the temperature range 15–310 K. The data were extrapolated to 0 K by a model function to derive some standard thermodynamic functions including the enthalpy increments ₀ ^T H, the entropy increments ₀ ^T S, and the Giauque function (= ₀ ^TS – ₀ ^T H/T). A simple model for the reproduction of the experimental heat capacities of urea, based on the Debye and Einstein functions, is described. The Debye characteristic temperature determined in this way was compared with those calculated from properties other than the heat capacity. Any positive evidence of a suggested phase transition in urea around 190 K was not observed in the present heat capacity measurements. Possible existence of a phase with a Gibbs energy lower than that realized in the present investigation is discussed briefly.     

Spatial vibrations of eflical heal-exchange pipes excited by internal flow of a heat carrier

Conclusions The principal result of the present work is that on the basis of the variational principle of Hamilton-Ostrogradskii we obtained a complete system of differential equations of the vibrations of helical heat exchange pipes excited by internal flow of the heat carrier, and the analytical formulation of the set of all permissible boundary conditions is provided.It was shown that from the presented system there follow as special cases many results obtained earlier in connection with curved and straight pipes and spatial rods.It was established that depending on the conditions of constraint of the ends of a heat exchange pipe, the system may be conservative or nonconservative. In the former case, loss of stability may be in flexural form when the critical flow rate is exceeded, in the latter case it is the flutter form.We examined actual examples of conservative and nonconservative systems, and we formulated boundary-value problems for them.The suggested equations and dependences may be the basis for further improvement of the theory of vibrations of spatial heat exchange pipes excited by a flow of heat carrier, by taking additionally into account the viscosity of the liquid, the nonsteady state of the flow, the initial stresses in the pipe, the rotary inertia of its sections, damping, and other factors in dependence on the problem under examination and the accuracy required for the actual applications. On the other hand, being very general, the equations and dependences may find applications of their own in practical engineering calculations.Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 11, pp. 83–90, November, 1985.     

利用支撑热容消减ITER低温系统热脉冲方法的分析

国际热核聚变实验堆(ITER)低温系统的一个主要任务就是移除当磁场变化及聚变反应时在磁体系统内产生的大量脉冲热负荷.为了削减回到制冷机的热负荷峰值,在脉冲阶段将部分波动热负荷释放到磁体支撑部分,但这种方法将会导致磁体支撑部分的温度略有升高,从而影响磁体超导线的温度.为此建立了一个纵向场磁体的一维非稳态模型,采用FORTRAN语言编程求解一组非稳态的控制方程进行模拟计算,以此来研究实施这种方法的可行性.计算结果表明依靠磁体支撑部分吸收脉冲热负荷时,超导线的最高温度仍低于5K的最高限制.     

Enthalpy and heat capacity of the actinide oxides

The available enthalpy data on UO₂, ThO₂, PuO₂, (Th, U)O₂, and (Pu, U)O₂ have been analyzed and equations have been derived to fit the data. Phase transitions were found in UO₂, ThO₂, (Th, U)O₂, and (Pu, U)O₂. The high temperature PuO₂ data were too scattered to determine whether a phase transition exists. Above the phase transition temperature, the enthalpy data were fit with a linear equation. Enthalpy data for PuO₂ and ThO₂ below the phase transition temperature were fit with two-term equations whose contributions are due to phonons and thermal expansion. For UO₂ below its phase transition, a term for an electronic contribution was added to this basic equation. Below the phase transitions for (Th, U)O₂, enthalpy data were fit by a mole average of the equations used to fit the ThO₂ and UO₂ data below their phase transitions; however, the mole average equation was not valid for 90 and 92% ThO₂ in the mixed oxide. Since it was found that mole averages of the PuO₂ and UO₂ data do not fit the (Pu, U)O₂ data, these data were fit with an equation of the same form as that that used for UO₂.     

Low-temperature heat capacity of yttrium orthotantalate

The heat capacity of yttrium orthotantalate has been determined as a function of temperature by adiabatic calorimetry in the temperature range 0–340 K. Smoothed heat capacity data have been used to calculate the thermodynamic functions of yttrium orthotantalate.     

The possibility of high-temperature heat capacity measurements by differential scanning calorimetry

We have been conducting series of heat capacity measurements by differential scanning calorimetry (DSC) on various latent thermal storage materials such as NaOH-NaNO₃. Our concern is now shifting to higher temperature applications of latent thermal storage: space solar dynamic power systems (solar thermal electric power generation systems in space) and so on. Such applications require storage materials which can be operated above 1000 K. Needs for heat-capacity measurements at higher temperatures are increasing. In the present paper, some results of our heat capacity measurements by DSC at intermediate temperatures are presented. Several items which should be considered in order to realize the heat capacity measurements above 1000 K by DSC are discussed.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

A study of the heat capacity of coated metal materials by the laser flash method

Results of laser-flash measurements of the specific heat capacity of samples of metallic materials (12Kh18N9T stainless steel, VZhM-4 nickel superalloy) coated with heat-resistant silicate enamel in a temperature range of 20–1300°C are described. In this temperature range, the coating is characterized by a high emissivity factor with a constant magnitude of 0.9. Analysis of the measurement results for the specific heat capacity of the steel samples and comparison of these results with the reference data and the most reliable literature data reveal that a decrease in the apparent specific heat capacity in a temperature range of 850–1100°C is attributed to an exothermic heat effect. The deviation of the measurement results from the reference data is no more than 3%. New data on the heat capacity of the VZhM-4 nickel alloy are derived. The temperature dependences of the apparent (with allowance for the heat effect of dissolution of the γ' phase) and true specific heat capacities are described. The discrepancy between the calculated and measured values does not exceed 2%.     

Bonding strength of heat treated compressed Eastern redcedar wood

The objective of this study was to evaluate effect of heat treatment and compression on some properties of Eastern redcedar (Juniperus virginiana) including bonding strength, hardness and surface quality. Specimens were exposed to three temperature levels of 120 °C, 160 °C and 190 °C for 6 h before they were compressed using 2.5 MPa pressure for 5 min. Polyvinyl acetate (PVAc) bonded specimens showed 23.6% reduction in their shear strength when they were exposed to a temperature of 120 °C. Such strength reduction values were 44.4% and 64.1% for the specimens exposed to temperature levels of 160 °C and 190 °C, respectively. The lowest average Janka hardness value of 214.08 kg was determined for the samples exposed to a temperature of 190 °C while those treated with a temperature of 120 °C had the highest hardness value of 397.73 kg. It appears that combination of heat treatment and compression enchanced overall surface quality of the samples in the form of their roughness determined using stylus type equipment.     

Specific heat capacity of molybdenum chalcogenides. IV. An investigation of the heat capacity of binary and halogen-substituted molybdenum chalcogenides

Results of heat capacity measurements of Mo₆X₈ and Mo₆X₆Y₂ compounds (X = 5, Se, and Te; Y = Br and I) in the temperature range from 2 to 30 K and in a magnetic field of 50 kG are reported and discussed. The analysis of the C results is done on the basis of a lattice term composed of two Debye functions and one T ³ term. The characteristic frequencies for the phonon spectrum show systematic changes dependent on the structural parameters and the composition of the samples. The results obtained could be supplemented by means of Raman spectra. The determined coefficients exhibit an apparent correlation to T _c. The results are discussed with consideration of the superconducting properties of the studied compounds.     

Effects of wood constituents and content,and glass fiber reinforcement on wear behavior of wood/PVC composites

In flooring applications, experimental data and insight from scientific investigations on wear properties of wood/polymer composites (WPCs) are important for engineers to understand how to design and formulate WPC materials with high resistance to wear. In this work, three different types of wood flour – namely Xylia kerrii Craib & Hutch., Hevea brasiliensis Linn., and Mangifera indica Linn. – were utilized and incorporated into poly(vinyl chloride) (PVC) with a fixed content (10 phr) of E-chopped strand glass fiber. The physical, mechanical and wear properties, in terms of specific wear rate, were then assessed as a function of wood content and sliding distance. The experimental results suggested that the addition of wood flour increased the flexural modulus and strength up to 40 phr; beyond this concentration, the flexural properties decreased. Hardness was not affected by the addition of wood flour. The mechanical and wear properties of WPVC composites were found to improve with the addition of the E-glass fiber. Xylia kerrii Craib & Hutch. wood exhibited the lowest specific wear rate for non-reinforced WPVC composites, whereas Hevea brasiliensis Linn. wood showed the lowest specific wear rate for the glass fiber reinforced WPVC composites. The longer the sliding distance, the greater the specific wear rate in all cases.