A CALCULATION METHOD OF OBTAINING DESORPTION ISOTHERMS OF BEECH (FAGUSMOESL4CA) WOOD

This paper presents the specific methods to obtain sorption isotherms. Sorption isotherms were first obtained experimentally for 20°C and 100°C and then, by using the presented method, isotherms were also obtained for 50°C and 80°C. The same treatment can be applied in finding any isotherm sorption in the temperature range between 20°Cand 100°C.

The experiments were carried out on beech (Fagus moesiaca) and sample dimensions were 3×3×3cm. Based on the results of the experiment, by regression analysis, the most suitable analytic formula was proposed. It relsites temperature and air humidity with the equilibrium moisture content in wood. Experimental results were compared with psychrometric tables and Bramhall's formula for desorption curves with good agreement. This proves that the method presented in this paper is precise and efficient to decrease the lime needed to obtain sorption isotherms experimentally.     

DESORPTION ISOTHERMS FOR JAPANESE NOODLE (UDON)

Desorption isotherms of Japanese noodle (udon) were obtained at 20, 30 and 40°C, and analyzed by several isotherm models. The desorption isotherm data satisfactorily correlated with the GAB equation and the Oswin and Smith equations. The binding energy of moisture was calculated by Clausius-Clapeyron equation and found to be negligibly small above the moisture content of 0.163 kg water/kg solid. The sorption enthalpy calculated from the Arrhenius plot of GAB parameter was similar to the binding energy from Clausius-Clapeyron equation at GAB monolayer moisture content.     

DESORPTION ISOTHERMS FOR JAPANESE NOODLE (UDON)

Desorption isotherms of Japanese noodle (udon) were obtained at 20, 30 and 40°C, and analyzed by several isotherm models. The desorption isotherm data satisfactorily correlated with the GAB equation and the Oswin and Smith equations. The binding energy of moisture was calculated by Clausius–Clapeyron equation and found to be negligibly small above the moisture content of 0.163 kg water/kg solid. The sorption enthalpy calculated from the Arrhenius plot of GAB parameter was similar to the binding energy from Clausius–Clapeyron equation at GAB monolayer moisture content.     

DESORPTION ISOTHERMS AND DRYING CHARACTERISTICS OF SHRIMP IN SUPERHEATED STEAM AND HOT AIR

Desorption isotherms for shrimp were determined at the temperatures of 50, 60, 70 and 80°C. Amongst the moisture equilibrium predictions between the BET and GAB models, the latter has a better predictable capability. The GAB parameters are correlated with the temperatures by the Arrhenius expression. Drying characteristics of shrimp in drying media at the temperature range of 120-180°C for superheated steam and of 70-140°C for hot air have been examined. Drying rate and effective diffusion coefficient are used to quantify quantitatively the difference between the superheated steam and the hot air dryings. The temperature is more important effect on drying rate and effective diffusion coefficient in the superheated steam than in the hot air. Inversion temperature exists between 140 and 150°C. Comparing to the hot air, the shrimp dried by the superheated steam shows a lower degree of shrimp shrinkage. In addition, product colours are slightly different to those from the commercial sources.     

MODELLING OF DESORPTION ISOTHERMS OF CHESTNUT: INFLUENCE OF TEMPERATURE AND EVALUATION OF ISOSTERIC HEATS

The desorption isotherms of chestnuts (Castanea sativa Mill) were determined at 278, 293, 303, 313, and 323K by a gravimetric technique. The range of water activity was from 0.08 at 0.91. The sorption isotherms were of the type II according to Brunauer's classification. The effect of the temperature shows a cross over of the desorption isotherms at water activity 0.6. The experimental data are fitted with several models (Oswin, Smith, Henderson, Halsey, and G.A.B.). Oswin and G.A.B. models gave the best fittings. Particularly, with G.A.B. model parameters some interesting information as monolayer moisture content, heat of sorption of the first and nth layer adsorbed and net isosteric heat were obtained.     

THE DRYING OF SMALL WOOD PARTICLES

Small particles of Douglas fir of characteristic size 0.2 to 1cm have been dried by flowing the wood particles in vitiated air in a long vertical tube. Drying rate, dM/dt, was determined by measuring the increasing humidity of the transporting gas flow, and by measuring the absolute velocity of the particles by a radioactive isotope tagging method. Sawdusts of three sizes and flakes were examined. Moisture content (dry basis) was varied from approximately 2 to 125%. Most of the results were obtained for gas temperatures between 350 and 550 K.

Upon injection into the flowing hot gases, the wood particles initially dried rapidly as they encountered high relative temperature and velocity, and released their surface moisture. Following· this transient regime, the particles dried more gradually accord-     

CONTROL OF THE DRYING PROCESS THROUGH THE RELATIONSHIP OF WOOD AND WET-BULB TEMPERATURES

The ratio of wood temperature to wet-bulb temperature (WT/ WBT) with the wood moisture, aiming at its use in the control of the drying process in drying kilns, were correlated. Slash pine boards measuring 25 mm thick and 750 mm length were dried in an electric forced convection kiln, using four temperatures and two air velocities. The process was controlled through a computerized system comprising a microcomputer and data acquisition unit. The analyses indicated a good correlation (0.97 < r < 0.99) between the coefficient WT/WBT and the moisture content of the wood. The adjustment of polynomial models was satisfactory in the range from green condition to 10% moisture content, at the temperature range and air velocity studied. These results, variables, together with the ease and speed of measurement of the suggest that the coefficient WT/WBT can be used as an alternative for the control of the drying process. However, the practical application of this system still depends on further research and development.     

DESORPTION ISOTHERMS OF WATER IN TRIFOLIATE YAM )Dioscorea dumetorum Pax.(

Abstract

Desorption isotherms of water in trifoliate yam (Dioscorea dumetorum Pax) were determined using a dynamic gravimetric method at temperatures of 20°, 34°, 46° and 62°C, in the relative humidity range from 11 to 86% A nonlinear least squares regression program was used to fit the measured data to the Modified Henderson, the Modified Halsey, the Chung-Pfost, and the GAB sorption models. The GAB model gave the best fit. The net isosteric heat of sorption, estimated using the Clasius-Clapeyron equation, ranged from 1412 kJ/kg at a moisture content of 0.05 kg/kg, dry basis, to 325 kJ/kg at 0.20 kg/kg. Results obtained in this study should be important in controlling the water content of yam during processing, handling, packaging and storage.     

PARAMETERS INFLUENCING DRYING BEHAVIOR OF RUBBER WOOD (HEVEA BRAZILLIENSIS) AS DETERMINED FROM DESORPTION EXPERIMENT

ABSTRACT

In this study, the drying properties of rubber wood, which are the basic parameters for kiln scheduling design, were determined from desorption experiment. Equilibrium moisture content expression was developed. The diffusion coefficients at different drying environments were evaluated. It is more appropriate to determine the diffusion coefficients by the optimum scheme in comparison to other schemes; the logarithmic, square-root and half-fraction of evaporable moisture schemes. Finally, the diffusion coefficient of rubber wood was described by, instead of wood moisture content, the drying temperature and relative humidity, which are the parameters controlling the drying kiln operation.     

PARAMETERS INFLUENCING DRYING BEHAVIOR OF RUBBER WOOD (HEVEA BRAZILLIENSIS) AS DETERMINED FROM DESORPTION EXPERIMENT

In this study, the drying properties of rubber wood, which are the basic parameters for kiln scheduling design, were determined from desorption experiment. Equilibrium moisture content expression was developed. The diffusion coefficients at different drying environments were evaluated. It is more appropriate to determine the diffusion coefficients by the optimum scheme in comparison to other schemes; the logarithmic, square-root and half-fraction of evaporable moisture schemes. Finally, the diffusion coefficient of rubber wood was described by, instead of wood moisture content, the drying temperature and relative humidity, which are the parameters controlling the drying kiln operation.     

Exergetic Analysis of Textile Convective Drying with Stenters by Subsystem Models: Part 2—Parametric Study on Exergy Analysis

In this study, the effects of exhaust air humidity ratio, the residual moisture content of fabric outlet, and the temperature of the drying air on the exergy destruction and efficiency of stenters were investigated. The exergy efficiencies of the direct gas heated stenter (DGHS) and hot oil heated stenter (HOHS) were calculated to be varying from 8.5 to 17.5% and from 6.8 to 14.0%, depending on the exhaust air humidity ratio, respectively. The increase in the drying air temperature led to an increase in the exergy efficiency, especially in the constant rate and second rate period of the drying. On the other hand, the application of the gradual temperature method caused the highest total exergy efficiency due to the highest drying rates in the first chambers where considerably high air temperatures were set. Overdrying resulted in the higher irreversibility due to the increase in the fuel consumption in the falling rate period of drying. Thus, the exergy efficiency decreased drastically.     

由干湿球温度计算相对湿度的简捷法

通过对相对湿度与干湿球温度间数据的分析,推导出了由干湿球温度计算相对湿度的两个数学公式,计算中不需查阅水蒸气数据表和试差,准确度较高,适于工程计算。在相对湿度≥４０％,湿球温度０～８０℃,风速＞５ｍ／ｓ的空气—水蒸气系统,平均相对误差为１．７％和１．１％。     

MATHEMATICAL MODELLING OF MDF FIBRE DRYING: DRYING OPTIMISATION

ABSTRACT

In the production of MDF, wet resinated fibre must be dried to its target moisture content, normally 9 to 11%, before compaction into a board by hot pressing. Fibre drying can be interpreted as an incorporated process involving gas-solid two phase-flow, inter-component transfer, and heat and mass transfer within the fibre. Based on these mechanisms, a mathematical model has been developed to simulate the MDF fibre drying process. From the model, fibre moisture content, air temperature and air humidity along the dryer length can be predicted and factors affecting the drying rate examined. The model can be employed to optimise drying conditions and to evaluate improvements in dryer design. A case study of drying improvement in reduction of dryer emissions and heat consumption is given to demonstrate the potential application of the developed dryer model.     

MATHEMATICAL MODELLING OF MDF FIBRE DRYING: DRYING OPTIMISATION

In the production of MDF, wet resinated fibre must be dried to its target moisture content, normally 9 to 11%, before compaction into a board by hot pressing. Fibre drying can be interpreted as an incorporated process involving gas-solid two phase-flow, inter-component transfer, and heat and mass transfer within the fibre. Based on these mechanisms, a mathematical model has been developed to simulate the MDF fibre drying process. From the model, fibre moisture content, air temperature and air humidity along the dryer length can be predicted and factors affecting the drying rate examined. The model can be employed to optimise drying conditions and to evaluate improvements in dryer design. A case study of drying improvement in reduction of dryer emissions and heat consumption is given to demonstrate the potential application of the developed dryer model.     

STUDIES ON STIFLING AND DRYING OF COCOONS FOR LONGER STORAGE

ABSTRACT

Long term storage of stifled cocoons is an important problem during unfavourable seasonal conditions. Cocoons could be stifled within 20 minutes by using steam al 90°C. The shade drying of steam stifled cocoons in thin layers reduced the moisture content from 228 per cent (db) to 3 1.7 per cent (db) within 10 days. By hot air conditioning method the cocoons could be stifled and dried simultaneously. Using hot air at 90°C the cocoons could be stifled within 10 minutes, and dried to the equilibrium moisture content within 2 hours. The cocoons stifled by the hot air conditioning method could be reeled even just after stifling.     

浅析影响原丝烘干的因素

概述湿纱含水对增强型玻璃纤维的重要性,影响原丝烘干的因素。主要介绍干燥过程的几个阶段,相对湿度,固含量及几个工艺参数对原丝烘干的影响,尤其减少原丝含水率可提高产品质量降低能耗,其中,提高固含量,减少原丝含水的影响最为有效。     

EFFECT OF A TEMPERING PERIOD ON DRYING OF CARROT IN A VffiRO-FLUlDIZED BED

ABSTRACT

Drying of diced carrot in a vibrofluidized bed was studied experimentally for various air temperatures, bed heights and size of the cubes. Effect of a tempering period that mav be implemented into ¦ drying cycle was examined with respect to drying kinetics and energy consumption. Although two stage drying with a tempering period increases the overall drying time, it shortens the drying time in a VFB dryer thus reduces energy consumption     

MODELING VACUUM-CONTACT DRYING OF WOOD: THE WATER POTENTIAL APPROACH

ABSTRACT

A two-dimensional mathematical model for vacuum-contact drying of wood is presented. The moisture and heat equations are based on the water potential concept whereas the pressure equation is formulated considering unsteady state conservation equation of dry air. Most of the model parameters were determined during independent experiments. The set of equations is then solved in a coupled form using the finite element method. The validation of the model is performed using experimental results obtained during vacuum-contact drying of sugar maple sapwood. The experimental and calculated data are in good agreement. Nevertheless, some discrepancies are observed which can be attributed to the boundary conditions used and to the fact that heat transfer by convection was neglected.     

MEASUREMENTS OF THERMAL CONTACT CONDUCTANCE FOR A PAPER/METAL INTERFACE AND EFFECTIVE CONDUCTIVITY OF MACHINE SAMPLES

ABSTRACT

The thermal contact conductance for a paper/metal interface and the effective thermal conductivity of paper samples were determined using an experimental contact conductance apparatus. The effects of pressure and moisture content on the thermal contact conductance and the effective thermal conductivity were investigated. The samples considered in the experiments consisted of paper machine samples from different sections of the drying section. The results are compared to those of the handsheets prepared in our laboratory.     

LOW TEMPERATURE MUSHROOM (A. bisporus) DRYING WITH DESICCANT DEHUMIDIFIERS

ABSTRACT

Cultivated mushrooms (Agaricus bisporus) slices of 2·5 and 5 mm thick were dried with dehumidified air at 20°, 30° and 40°C. Rehydration ability of dried mushrooms was used as criteria for the evaluation and determination of optimum conditions. Drying mechanism of the mushroom slices was expressed by unsteady state diffusion and the results were interpreted by Fickian model. Drying temperatures lower than 40°C promoted the production of light coloured mushrooms with high rehydration ratios. Diffusivity constants were in the range of 2·6?12×l0^-11 m²/s and the activation energies varied in the range of 23·5?30·3 kJ/gmol depending on the temperature and sample thickness.