美国黑胡桃木干燥性质研究及干燥基准拟定

利用百度试验法对热水处理和未处理美国进口黑胡桃木板材的干燥性质进行分析,拟定了初步的干燥基准并进行了相关的工艺试验及干燥质量检验。结果表明:热水处理试件与未处理试件的干燥性质差异较大,热水处理试件初期开裂、内裂、截面变形和扭曲变形对应的缺陷等级分别为2级、2级、3级和2级;而未处理试件对应的缺陷等级分别为4级、2级、4级和2级,热水预处理可以降低干燥缺陷等级。未处理黑胡桃木采用拟定基准干燥后的质量可达到国家2级锯材干燥标准,未处理黑胡桃木从71%含水率干燥到8%含水率约需26 d。

Experimental research on drying characteristics of PVC powder in a normal fluidized-bed dryer

For obtaining the drying curve of powder under fluidized drying, a normal fluidized-bed dryer is designed to study the drying kinetics of PVC （polyvinyl chloride） powder in the experiment. A new measure system is derived for drying dynamics testing. In the small fluidized-bed dryer, fluidization parameter of PVC powder is tested, and the operating air velocity can be chosen in the range of 0. 41 to 0. 55 m/s. Accordingly, the fluidized number Ua/Umf is from 1.24 to 1.67. A promising drying model is used to describe the drying process, and then the characteristic drying curve of PVC powder derived from a suspension method can be expressed as f = [-0. 622 6 ＋ 1. 254 6exp（2. 561 5Φ -0. 707 2） /[1 ＋ exp（2. 561 5Φ -0. 707 2）] Based on the experiments, the critical moisture content xc and the mass transfer coefficient K are determined to be 0. 02 kg/kg and 6. 0 × 10^-4 kg/（ m2 · s）, respectively. The experimental results in the small fluidized-bed dryer are similar to those of the real fluidized drying process, so the descried method can also be used in determining drying kinetics of powder materials such as PVC powder.

有限元方法在木质材料研究中的应用

本文概述了有限元方法在木质材料分析中的应用。主要有以下几个方面:木质工程材料的机械性能及材料性能;木质连结材;木质材料断裂力学;木材干燥及材料热性质。并展望了有限元法在木质材料研究中的应用前景。

Effects of Calcium Oxide on Physicochemical Properties of Spray-dried Bayberry Powder

[Objective] Effects of different contents of calcium oxide on physicochemi- cal properties of spray-dried bayberry powder were studied. [Method] Bayberry pow- der produced from bayberry juice adding 0, 2 and 4 g/L calcium oxide using the spray drying technique has been selected. The physicochemical properties of the spray-dried bayberry powder were investigated by determining moisture content, colour, apparent density, wettability, angle of repose and moisture absorption rate of bayberry powder. [Result] The results showed that the content of calcium oxide had a significant effect on the moisture content and colour of bayberry powder. Effects of different contents of calcium oxide on the apparent density of spray-dried bayber- ry powder were not obvious. Adding calcium oxide had a significant effect on the wettability, angle of repose and moisture absorption rate of spray-dried bayberry powder, nevertheless, there was not obvious difference on these properties between adding 2 and 4 g/L calcium oxide. [Conclusion] The results confirmed that the con- tent of calcium oxide had a significant effect on the properties of spray-dried bay- berry powder.

Physical Properties in Drying of Food Products with Combined Sublimation and Evaporation

Drying is an important unit operation in processing of biological resources. The drying process may influence the product properties and quality, which may shrink, break or undergo rheological, physical and biochemical changes. The important parameters responsible for such changes are drying conditions, type of drying technology and residence drying time. Thermal conductivity, thermal-mass diffusivity, enthalpy, porosity and density are the main material property and heat-mass transfer parameters, which are essential for understanding the changes in product quality and for designing and dimensioning the drying processes. In this paper physical properties of food products undergoing a combined sublimation and evaporation were studied. Pieces of vegetables and potatoes were dried in a heat pump fluidized bed dryer at combined modes with temperatures below the freezing point in the beginning and a final drying step at temperatures above the freezing point. Samples of products were tested at different moisture contents with respect to physical properties. Physical properties of leek and potato samples were measured and mass diffusivities were determined from drying kinetic data. Based on bulk density and rehydration measurements it was clearly observed that drying temperature and modes influenced the final product physical properties. The potato cube run dried with initial atmospheric freeze-drying step had rehydration ability 430%above a run dried only above the freezing point. The average effective mass diffusivity for 5 mm slabs of leek was 0.5 x 10-11m2·s-1 for the sublimation stage and 2.2 x 10-11m2·s-1 for the evaporation stage.

Effect of drying environment on engineering properties of an expansive soil and its microstructure

This paper investigates the effect of drying environment, i.e. temperature and relative humidity, on the engineering properties and microscopic pore size distribution of an expansive soil. The shrinkage tests under different drying temperatures and relative humidity are carried out in a constant climate chamber. Then, the undisturbed samples, prepared in different drying environment, are used for the triaxial tests and mercury intrusion tests. It is found that the drying environment has noticeable influence on the engineering properties of expansive soils and it can be characterized by the drying rate. The linear shrinkage and strength increase with the decrease of the drying rate. The non-uniform deformation tends to happen in the high drying rate, which subsequently furthers the development of cracks. In addition, during the drying process, the variation of pores mainly focuses on the inter-aggregate pores and inter-particle pores. The lower drying rate leads to larger variation of pore size distribution.

Responses of Dodonaea viscosa growth and soil biological properties to nitrogen and phosphorus additions in Yuanmou dry-hot valley

Nitrogen(N) and phosphorus(P) are limited nutrients in terrestrial ecosystems, and their limitation patterns are being changed by the increase in N deposition. However, little information concerns the plant growth and the soil biological responses to N and P additions among different soils simultaneously, and these responses may contribute to understand plant-soil interaction and predict plant performance under global change. Thus, this study aimed to explore how N and P limitation changes in different soil types, and reveal the relationship between plant and soil biological responses to nutrient additions. We planted Dodonaea viscosa, a globally distributed species in three soil types(Lixisols, Regosols and Luvisols) in Yuanmou dry-hot valley in Southwest China and fertilized them factorially with N and P. The growth and biomass characters of D. viscosa, soil organic matter, available N, P contents and soil carbon(C), N, P-related enzyme activities were quantified. N addition promoted the growth and leaf N concentration of D. viscosa in Lixisols; N limitation in Lixisols was demonstrated by lower soil available N with higher urease activity. P addition promoted the growth and leaf P concentration of D. viscosa in Luvisols; severe P limitation in Luvisols was demonstrated by a higher soil available N: P ratio with higher phosphatase activity. Urease activity was negatively correlated with soil available N in Nlimited Lixisols, and phosphatase activity was negatively correlated with soil available P in P-limited Luvisols. Besides, the aboveground biomass and leaf N concentration of D. viscosa were positively correlated with soil available N in Lixisols, but the aboveground biomass was negatively correlated with soil available P. Our results show similar nutrient limitation patterns between plant and soil microorganism in the condition of enough C, and the nutrient limitations differ across soil types. With the continued N deposition, N limitation of the Lixisols in dry hot valleys is expected to be alleviated, while P limitation of the Luvisols in the mountaintop may be worse in the future, which should be considered when restoring vegetation.

Some Physical and Chemical Properties of Clarias gariepinus Dried with Solar Dryers and Solar Tents in Sokoto, Nigeria

A research was conducted to assess the effects of three different drying techniques, namely open sun drying （OSD）, solar dryers （SD） and solar tent dryers （STD）. Data on physical characteristics such as weight, total length and standard length were recorded and proximate composition of the fish sample Clarias gariepinus （Burchell, 1822） was carried out before, during and after drying to assess changes on physical characteristics and nutrient composition at different level. After drying, the samples were subjected to storage for eight weeks. The result obtained shows that there was no significant （P 〉 0.01） difference in the drying weight of the fish samples between the direct SD and the STD. However, for the total and standard length there was significant （P 〈 0.01） difference in the drying techniques, but no significant difference （P 〉 0.05） in the drying period. There was no significant （P 〉 0.05） difference on the physical parameters, storage period, proximate composition of both direct SD and STD and the drying period, respectively. Therefore, direct SD can be substituted with the STD without altering the quality of the product.

Effect of Some Processing Variables on the Quality Attributes of Yam Flour

The effect of varied processing variables （yam slice thickness, drying temperatures and type of drying） were investigated to determine their effects on the proximate and some functional properties of yam flour. The yam flour was produced with different slice thickness of 1, 1.5, 2.0, 2.5 and 5 cm using both conventional sun drying method and oven drying at temperatures; 40 ~C, 50 ~C, 60 ~C and 70 ~C. The moisture content of all the yam flour samples increased with increasing yam slice thickness, with the samples sun dried having the lowest values （6.20%-6.87%） followed by those dried at 70 ~C and then 60 ~C. The protein content of the yam flour samples increased with increase in slice thickness and decreased with increase in drying temperatures while the fat and the crude fibre of all the yam flour samples decreased with increase in slice thickness. The water absorption capacity of the sun dried yam flour samples decreased with increase in slice thickness while the syneresis value, bulk density and the gel strength increased with increase in slice thickness for all drying temperatures and for sun dried yam flour samples but smaller slice thickness had higher swelling capacity.

Drying Characteristic of Anchovy Fish

This paper focuses on the drying characteristic of anchovy fish （Anchovia engraulidae）. It is necessary to understand the drying behavior, quality of the products and time required to optimize the energy consumption of the process. The optimum velocity and temperature of drying air for good quality dried anchovy fish was determined. In average, the fish are 7 cm in length and 3.0-3.5 g in mass. Although some research on fish drying has been done, the study of drying of anchovy fish and its characteristic has not been well reported. The fish to be dried were arranged on 15 × 15 cm2 tray in the drying chamber of 17 × 30 cm2. The hot air of 40 -70 ℃ was delivered parallel to the tray with the velocity of 0.6 and 0.9 m s-1. It is found that thermal conductivity （k） and specific heat （cp） of anchovy fish are function of the moisture content （MC）. The higher moisture content results in higher thermal conductivity and specific heat. Critical water content is also found in this experiment as well as the optimum drying condition. Drying rate period of anchovy fish will change from the constant drying rate period to the falling drying rate period when critical moisture content is about 48.8%-50.3% （wet basis）. At these experiments, there is no case-hardening, even at temperature of 70 ℃. To achieve the optimum result, the drying process should be implemented in three steps, drying process at 70 ℃ for 150 min followed by drying at 50℃ for 100 min, and finally drying at 40℃ till achieving equilibrium moisture content. This research will contribute to improvement of drying method to achieve good quality of dried fish.

The Structure of a Typical Mei-Yu Front Identified by the Equivalent Temperature

In China's Mainland, the summer monsoon rainy band is referred to as the mei-yu precipitation front, which extends northward from South China to the Yangtze River, Huaihe River, and Yellow River, depending on the season. This paper describes the structure of the mei-yu front associated with a persistent heavy rainfall event that occurred in the summer of 2007. The mei-yu front occurs when the subtropical oceanic warm, moist air mass and the extra tropical continental dry, cold air mass converge on the lee side of the Tibetan Plateau. The authors defined the equivalent temperature using two terms of dry-air temperature and the specific humidity and calculated its horizontal gradient to indicate the mei-yu front. The vertical structure of the mei-yu front and the moist thermal winds surrounding it were examined based on the equivalent temperature.

Physical Properties and Heat Transfer of Tectona grandis L.f. Wood

Tectona grandis L.f. （teak） is native to the Indian subcontinent and southeast Asia, and today is grown in almost every tropical region, for the physical and mechanical properties of its wood. Also, important qualitative aspects render it one of the most expensive wood species in the world. This work presents a study about the physical properties and heat transfer of T. grandis wood from plantations in C.ceres, Mato Grosso, Brazil. Six trees planted at three different intervals were used--two from each planting density--selected at random and with good phytosanitary characteristics, as well as having representative diameters and heights. The following properties were determined： basic and apparent densities, volume contraction, heat transfer and fiber saturation point. The basic and apparent mean general density of the samples was 0.48 g/cm3 and 0.55 g/cm3, respectively. The mean volume contraction of the teak wood was 8.57%. With decreased levels of wood humidity, loss of volume and planting effects were not significant at 5% probability. Mean heat transfer was 7.3 h/cm and the wood fiber saturation point was 17.25%, below the range found in literature, and there was no influence of the planting density on this property. According to the results, it was concluded that planting density significantly influenced the base density of the wood; the same effect does not occur for the other physical properties, and with respect to heat transfer, the wood was considered difficult to dry.

Performance and Economic Analysis of Mulberry Paper Handmade Dryer by Using Downdraft Gasifier

The mulberry paper handmade dryer uses downdraft gasifier, which is a continuous hot air dryer. The downdraft gasifier uses charcoal or wood chip as fuel to produce the producer gas for a dryer heat source. Two steps operation of a dryer as follows： The frst was to reduce mulberry paper pulp moisture by an air vacuum pump; the second was a continuous hot air drying process. The optimum condition drying, the capacity of dryer, the fuel consumption, the drying constant （k） and economics analysis were investigated. It was found that the first step could be to reduce mulberry paper pulp moisture content about 25% and the suitable condition drying was 80 ~C drying temperature, 0.04 kg/s air mass flow rate and 0.29 m/min chain conveyor speed, respectively. The capacity of this dryer was 20 sheets per hour. The quality of mulberry paper product was very good （based on the standard of mulberry paper community 41/2546） and the fuel consumption rate was 5 kg/h （charcoal）. The drying constant was about 0.532933-0.541367 min~ and the drying constant was a function of drying temperature （T）, air mass flow rate （F） and conveyor speed （10 as equation of k（T, F, V） = 0.567494 ＋ 0.000422T- 1.40588F- 0.000205 V （R2 = 0.9254） and the breakeven point of dryer was 0.79 years.