摘要:

Lumber must be conditioned to relieve transverse drying stresses. The standard prong test has been used for many decades to determine the conditioning time needed for complete stress relief. However, no work has been directed at the proper procedures or interpretation of this test. The purpose of this study was to obtain initial information on the factors influencing the prong test and stress development. The major factors studied were prong thickness and surface moisture content Data on stress distribution, moisture gradient, and prong response were obtained periodically throughout conditioning of red oak. Slicing, a residual strain release method, was used to obtain the stress distributions. The results demonstrated that the prong response is a function of prong thickness and stress distribution. Additionally, an explanation of how the stresses are altered was proposed. Further studies concerning conditioning schedules need to be performed before standard test procedures can be suggested.

ISSN:0737-3937    

DOI:10.1080/07373930008917710

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The textural properties of apple, banana, carrot and potato were experimentally determined by uniaxial compressive tests of cylindrical specimens at a constant deformation rate of 5mm/min. Compression tests were performed, following air drying, at various moisture contents ranging from 0.2 to 6 kg/kg db. The tests were performed using a universal texture testing machine and simple mathematical equations were used to correlate the maximum experimental stress and the corresponding strain to the moisture content. It was shown that the maximum stress decreases as the moisture content decreases, until a critical moisture content of 1.8 kg water/kg dry solids. Further removal of water tends to increase the maximum stress. The maximum experimental strain was found to increase as water was removed. The stress-strain data of compression test were modelled using a simple mathematical model, containing parameters such as the maximum stress (ow), the maximum strain (dim), the elastic parameter (E) and the viscoelastic exponent (p). The effect of the moisture content on the compressive behavior of dried materials was introduced through its effect on the model parameters. The shift in compression behavior at 1.8 kg water/kg solids leads to the conclusion that there is an important change of structure at this moisture content.

ISSN:0737-3937    

DOI:10.1080/07373930008917711

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Effects of size (whole and sliced), pre-treatment (blanching in water and 0.5% NaCl solution at 95° C) and temperature of drying air (40, 55 and 70° C) on the drying characteristics and quality of okra were studied. Estimation of the drying rate established that the drying of okra takes place under the falling rate period. Page's model was found to adequately describe the drying behavior of okra over a wide range of drying conditions used in the study. The coefficients of Page's model were correlated with air temperature and it was found that the dependence of the rate constant on the drying air temperature can be described using the Arrhenius law. The quality of the dried product was found to be best when okra was sliced and blanched at 95° C in 0.5% NaCl solution for 5 min and then dried at 55° C.

ISSN:0737-3937    

DOI:10.1080/07373930008917712

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Fufu was dried using rotary drier, cabinet drier and sun drying methods. The effects on the physical, chemical and sensory properties of fufu by the different drying methods were evaluated. The drying methods did not appreciably affect the yield, proximate composition or acidity of fufu, but affected pasting properties. Panellists (P < 0.05) rated the rotary dried fufu best.

ISSN:0737-3937    

DOI:10.1080/07373930008917713

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

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×l0-11m2/s and the activation energies varied in the range of 23·5−30·3 kJ/gmol depending on the temperature and sample thickness.

ISSN:0737-3937    

DOI:10.1080/07373930008917714

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Mathematical models and numerical techniques for simulation of parallel flow grain drying has been proposed and tested. Concurrent flow drying has been simulated using a steady state model. In order to overcome numerical difficulties that appears in simulation of countercurrent flow drying under operational conditions that leads to thermodynamics equilibrium in any section of the dryer stage, a robust approach has been developed based on simulation of the operation starting from initial transient conditions. A lab unit for grain drying has been developed, composed of a countercurrent flow stage coupled on a concurrent flow stage. The mathematical models and numerical techniques has been tested through the comparison between calculated results and experimental data measured for com drying.

ISSN:0737-3937    

DOI:10.1080/07373930008917715

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Pressure drops through oat (Oat Sp.) beds were evaluated in the range of airflow rate from 0·0097 to 0·459 m3/s-m2using two airflow directions to determine the effect of grain moisture and foreign material on the resistance to airflow. Horizontal airflow resistance was lesser than vertical airflow resistance (e.g., for oat with 9·0% moisture content the pressure drop in horizontal direction was 4–17% of corresponding in vertical direction). The resistance decreased with the increase of moisture content and increased when the fraction of foreign material. An increase in the moisture content from 9·0 to 24·9% produced a decrease on the bulk density from 583 to 513 kg/m3. Mattel's model (1969) fitted adequately the experimental data. The Haque et al.'s equation (1982) have an adequate representation of the data for both airflow directions. The Paterson et al. (1971) and Bern-Charity (1975)equations resulted applicable only for vertical airflow direction. A simplification planed of this model in function of the bulk density conduced to a good relation DP-Q.

ISSN:0737-3937    

DOI:10.1080/07373930008917716

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The water sorption isotherms of the cefotaxime sodium salt were determined at 30 and 40° C. Cefotaxime sodium salt was maintained at equilibrium relative humidities ranging from 40 to 80 %. Equilibrium moisture content was determined by the Karl Fischer method. The moisture sorption isotherms showed that the equilibrium moisture decrease while the temperature increase. The experimental curves of equilibrium humidity were fitted by different models (Bradley, Halsey, Henderson, Kuhn, Smith and Iglesias and Chirife and GAB). Parameters of each equations were determined by non-linear regression analysis. The best fit was obtained by Iglesias and Chirife model. The isosteric heat of moisture sorption calculated by Claussius Clapeyron equation varied from 64·45 to 48·03 kJ/mol when moisture content changed from 7 to 9·5 %.

ISSN:0737-3937    

DOI:10.1080/07373930008917717

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A mathematical model of a heat pump fruit dryer was developed to study the performance of heat pump dryers. Using the moisture content of papaya glace' drying, the refrigerant temperature at the evaporator and condenser and the performance, was verified. It was found that the simulated results using closed loop heat pump dryer were close to the experimental results. The criteria for evaluating the performance were specific moisture extraction rate and drying rate. The results showed that ambient conditions affected significantly on the performance of the open loop dryer and the partially closed loop dryer. Also, the fraction of evaporator bypass air affected markedly on the performance of all heat pump dryers. In addition, it was found that specific air flow rate and drying air temperature affected significantly the performance of all heat pump dryers.

ISSN:0737-3937    

DOI:10.1080/07373930008917718

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In the manufacture of granular NPK fertilizer the product is cooled before packaging and storage in moisture-proof bags. It has been shown that the temperature of the fertilizer prior to packing is significant in that at high temperatures, drying of the granules takes place in the bag which causes an increase in the humidity of the air surrounding the granules and thus an increase in moisture content at the granule - granule interface. This surface moisture was shown to increase the likelihood of agglomeration in the fertilizer by a capillary adhesion / unconfined yield stress model. An iterative model was set up to establish conditions that would prevent drying occurring, which takes into account fertilizer drying rate, fertilizer cooling rate cooling rate and the effect of coaling oils on the drying mechanism.

ISSN:0737-3937    

DOI:10.1080/07373930008917719

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor