摘要:

A transient three-dimensional analysis was carried out on internal strain-stress as well as heat and the moisture transfer in a ceramic slab during drying. A model was developed to analyze viscoelastic behavior, heat conduction and moisture diffusion. The basic equations were solved by the finite element method. The effects of several dimensionless parameters are discussed to find an optimum drying process and a precise design of molds in ceramic production. The stress and the gradient of moisture content were influenced significantly by the Biot or Lewis number. When the moisture diffusion is enhanced or the drying is controlled well so as to form only gentle gradients of moisture content in the slab, the maximum tensile stress can be reduced. Nonuniform drying results in the develoment of warp and increase in the maximum tensile stress. The drying characteristics were not appreciably influenced by shrinkage.

ISSN:0737-3937    

DOI:10.1080/07373939708917216

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The process and the technology of fine - dispersed rubber powder production on thebasts of spray - drying for latexes were considered. The practical recommendations on usage of physical modification method for elastomers on the basis of interaction mechanism between solid -phase dispersed filler and polymeric panicles were given.

ISSN:0737-3937    

DOI:10.1080/07373939708917217

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A continuous schedule for the drying of Australian ironbark timber has been optimised using non-linear model-predictive control techniques. Initially, an experimental study was carried out using a conventional schedule to dry nine 600 mm long × 250 mm wide × 25 mm thick boards in order to obtain information on the drying behaviour and the extent of timber cracking. A diffusion model accurately fitted the average moisture contents observed when using this conventional drying schedule. The fitted coefficients in the diffusion model were used to optimise the drying schedule with the aim being to keep the strain below 0.02 mm/mm and the surface moisture above 7%. The resulting optimised schedule set gentler conditions at the start of drying and more aggressive ones towards the end than the conventional schedule. The new schedule was tested in an experiment using the same number of boards from the same tree, and was found to reduce the number of small and medium-sized cracks to less than 25% of the number observed from the conventional schedule with a significant improvement in the value of the timber produced. The fitted diffusion model predicted the drying behaviour observed during the optimised schedule adequately. This optimisation technique has considerable scope for improving drying schedules and, thus, productivity rates, for other timber species. It should be noted that a significant requirement for the use of

ISSN:0737-3937    

DOI:10.1080/07373939708917218

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Two experimental devices. Capped Column and Open Column, were used to measure four heat and mass transfer coefficients of four vegetables: potato, yam. butterquash and turnip. Two classical coefficients, thermal conductivity. KT, and moisture diffusivity. DM, and two coupled coefficients. moisture gradient induced heat transfer coefficient, KM, and temperature gradient induced moisture migration coefficient Dr(or δT=DT/DM), were measured. The mean measured values of KTobtained for potato, yam, buttersquash and turnip were 0.50, 0.58, 0.54 and 0.51 W/m-K, respectively. The mean measured values of KMfor potato, yam. buttersquash and turnip were 117.1, 32.8, 41.0 and 190.8 W/m, respectively, of δTwere 0.00059, 0.00065, 0.00024and 0.00047 per degree K, respectively and of DMwere 1.32×10-9, 1.16×10-9, and 1.58×10-4m2/s, respectively. Smaller interocellular spaces seemed to have a positive effect on the thermal conductivity. Moisture content and size of intercellular spaces both seemed to have positive effect on KM. The value of δTwas lower for vegetables with higher moisture content which is consistent with the results reported in literature. The value of DMseemed to be positively affected by both the porosity and the size of the intercellular spaces in the test vegetables.

ISSN:0737-3937    

DOI:10.1080/07373939708917219

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Beds of various model paricles were vibrated vertically at frequencies varying from 0 – 25 Hz and half-amplitudes from 0 – 4 mm. Alumina, glass and molecular sieve particles (27 μm to 1400 μm) were used as model particles. Air flow rates varied from 0 to 3 times the minimum fluidizing velocity through a single slot, a single central orifice or a multiplicity of orifices in the supporting bottom plate. With increasing vibration frequency, the bubble size was found to attain a maximum while the bubble rise velocity and frequency reach minima at the resonance point which is achieved only in vibrated beds of fine panicles (dp< I50 μm). At the resonant point. bubble sizes are up to 215% their value in the absence of vibration. On the other hand, bubble frequencies and bubble rise velocities are up to 75% lower than their values in the absence of vibration.

ISSN:0737-3937    

DOI:10.1080/07373939708917220

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The response surface methodology (RSM) was used to derive an optimum drying condition for garlic drying. The responses analyzed were L* value and Optical Index (OI) as a measure of color and rehydration ratio (RR) as well as final moisture content (Mf) which are important quality attributes of dehydrated products. L*, OI, RR and Mf varied from 70.6 to 85.0, 72.0 to 191.1, 2.2 to 3.2 and 5.4 to 10.2 % MC, respectively. An analysis of variance (ANOVA) revealed that drying temperature and slice thickness significantly (90% confidence level) affected L*, OI and RR while no effect was observed for airflow rate and relative humidity (RH). An optimum drying temperature of 70°C for drying 2 mm garlic slices is recommended.

ISSN:0737-3937    

DOI:10.1080/07373939708917221

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Several thermodynamic properties for maize, rough rice and wheat has been calculated using desorption isotherms available in the literature. It was obtained an analytical expression to predict the differential heat (isosteric) as function of moisture content using a three parameters equilibrium model, based on enthalpy-entropy compensation effect, which takes into account the effet of temperature. Two integral heats of sorption were calculated, the first from the slopes of the iso-spreading pressure lines and the second from integration of the differential heat. This last one was used to estimate the energy requirement to remove water from initial moisture content to different final moisture levels, which is useful in drying area. Finally it was calculated the differential and integral entropies of sorption as function of moisture content.

ISSN:0737-3937    

DOI:10.1080/07373939708917222

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The purpose of this research was to investigate strategies for papaya glacé drying in tunnel. To evaluate the optimum conditions of drying, corresponding mathematical models were also considered. The criteria set for this study included low drying time, low specific energy consumption and acceptable qualities of papaya glace. The results obtained from the model of batch tunnel drying were in good agreement with the experimental ones. From the mathematical models, it was found that the optimum conditions of the first stage of drying of papaya glace (3.1×7.8×1.4 cm) were drying temperature of 70°C, specific air flow rate of 12 kg/h-kg dry papaya glace (velocity of 1.25 m/s) and air recycle ratio of 70%. In the second stage of drying papaya glace (0.98×0.98×0.98 cm), it was found that the optimum drying conditions were: drying air temperature of 55°C, specific air flow rate of 10 kg/h-kg dry papaya glace (velocity of 0.6 m/s) and air recycle ratio of 80%. Ambient air temperature and relative humidity were 30°C and 70% respectively.

ISSN:0737-3937    

DOI:10.1080/07373939708917223

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In order to evaluate the effect of path diffusion on the average moisture diffusivity in carrot. drying curves for different shaves (slices and cylinders) and temperatures of 50, 60 and 70°C were ohtained takine into consideration the use of an average leneth of carrot sample (slice thickness or the cylinder radio). The. results showed significant differences betuecn radial and axial average diffusivities. Significant differences were also observed between core and annular diffusivity. The experimenta1 drying curves did not show enough evidence on the effect of drying temperature on the average moisture diffusivity.

ISSN:0737-3937    

DOI:10.1080/07373939708917224

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The mechanism of drying and the diffusion of water in green (fresh), red and whole lentils (4.20–4.32 mm diameter and 2.20–2.30 mm thickness) were successfully interpreted and modelled by using Fick's law. The moisture content of fresh green lentil was 55 % and moisture content of the red and whole lentils was increased to 39–40 % and drying temperature (45-60°C) was varied, but the velocity and the humidity of the drying air was kept constant.

ISSN:0737-3937    

DOI:10.1080/07373939708917225

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor