摘要:

Industrial and pilot plant spray-dried materials were obtained from various manufacturers and qualitatively examined in order to identify structural and morphological features. Three distinct categories of particle morphology were identified. Namely, crystalline, skin forming and agglomerate. A number of unusual morphological phenomena were also noted Selected properties such as powder flowability. particle size and particle friability, were found to be directly related to morphological structure. Single particles were also produced in a convective drying process analogous to spray drying, in which, different solids or mixtures of solids were dried from solutions, slurries or pastes as single suspended droplets. The localised chemical and physical structures were analysed, and the results related to experimental conditions viz. drying air temperature and initial solids concentration. There was a strong similarity between the industrial spray-dried material and those dried experimentally. The morphologies of multicomponent mixtures were found to be complex, with the respective migration rates of the solids being dependent on drying temperature. The results are of relevance to dryer optimisation and to the optimisation of product characteristics, They also go some way to validating the single droplet drying technique as a useful analytical tool in spray drying research, and possibly other particulate processing industries.

ISSN:0737-3937    

DOI:10.1080/07373930008917822

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A rotary drum dryer prototype was designed, fabricated and tested to combine convection drying with conduction heating of paddy to increase moisture reduction rates. Ambient air forced inside the drum counter-flow to the direction of the cascading grains brought about “dryeration” of the hot grains, resulting in cooler grain output and increased moisture reduction rates. Its partial drying capacity doubled that of the benchmark pre-dryer at 5 rpm drum speed and quadrupled at 7 rpm, requiring only a single-pass operation. Tests using freshly harvested and re-wetted paddy showed that partial drying capacity, final moisture content and moisture reduction rate were all significantly affected by counter-flow air velocity, Its overall thermal efficiency was also 50% higher.

ISSN:0737-3937    

DOI:10.1080/07373930008917823

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An investigation of the thermal drying of lignite has been carried out, by using an indirect heat pilot rotary drum. The process aims at the production of dry lignite and clean steam as part of a gasification procedure. Both flighted and bare drum modes have been employed. Temperature profiles along the dryer length, the amount of evaporation (moisture conversion) and the solids residence time distribution (RTD) were measured. A non-isothermal model was tested under three different regimes of solids flow. Model integration, by taking account of experimental amount of evaporation at dryer exit and temperature profiles along the dryer length, has been utilized in the validation of drying kinetics and heat transfer correlations. Model predictions compare satisfactorily with the operating data of an indirect heat industrial lignite dryer. Overall heat transfer coefficients of the pilot rotary dryer were found to agree well with those reported for direct heat dryers.

ISSN:0737-3937    

DOI:10.1080/07373930008917824

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, the ventilation of a “crêpe” paper-processing workshop containing dryers, which generate a high thermal load, is considered. Displacement ventilation has been used for many years in industries with high thermal load. The main ventilation design problem is to find the appropriate ventilation flow that guarantees that the interface between the fresh air zone and the hot air zone is located above the occupied region of the room. The paper presents a mathematical model, implemented in a general computer code that can provide detailed information on the velocity, temperature and moisture fields in three-dimensional buildings of any geometrical complexity. The simulation results could be used as a base for further analysis for ventilation design for other industrial processes producing high levels of thermal loads and moisture, intending to a proper ventilation system selection for a more healthy and comfort environment in a building.

ISSN:0737-3937    

DOI:10.1080/07373930008917825

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper a physically based mathematical model for the description of particle wetting, temperature and humidity characteristics during a non-stationary fluidized bed spray-drying of granules or during a non-stationary fluidized bed coating in a Hüttlin®-Kugelcoater HKC 05-TJ is introduced. Using this model it is possible to calculate the humidity and temperature of the air, the degree of particle wetting, the temperatures of both the liquid layer and the particles under consideration and the influence of the wall of the apparatus and its surroundings. The effects of start-up and shut-down processes on the results as well as the time dependence of the discontinuous process with varying process parameters such as the amount of liquid sprayed in and its temperature, the amount of fluidising air and its temperature are simulated and the results were compared with those obtained experimentally using a Hüttlin -Kugelcoater HKC 05-TJ. Furthermore, the growth of the bed and the increase of particle masses during a discontinuous coating and granulation processes were taken into account in a simplified manner.

ISSN:0737-3937    

DOI:10.1080/07373930008917826

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Moisture sorption isotherms of okara soy milk were determined using the gravimetric method in the range 20 - 50 °C. The sorption isotherms exhibited hysteresis along all the water activity range (0·1 - 0·9). The amount of sorbed water increased as the temperature was decreased. The GAB and Halsey models gave a good fit for okara isotherms over the range of water activity 0·1 - 0·9. As temperature increased, GAB k-values increased towards unity where the GAB equation reduces to the BET equation. The influence of temperature on the constants of GAB and Halsey models was evaluated through Arrhenius-type equations. The Clausius Clapeyron equation was used to estimate the isosteric heats of sorption.

ISSN:0737-3937    

DOI:10.1080/07373930008917827

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The water adsorption and desorption kinetics of okara were determined at different relative humidities (51·4- 83·6 %) at 30 °C. Initial rates of water sorption and the specific rate constants showed different responses to increased RH. Both the adsorption and desorption rate constants dropped significantly at RH 51-55 %; this behaviour is related to occurrence of glass transition phenomenon.

ISSN:0737-3937    

DOI:10.1080/07373930008917828

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Results of the experimental measurement of sorption isotherms at different temperatures obtained by the standard gravimetric method showed the typical sigmoid shape of products rich in carbohydrates. The temperature had the expected effect predicted by the theory of physical adsorption i,e the quantity of sorbed water at a given water activity increased as the temperature decreased. The amount of adsorbed or desorbed water per unit weight of solid depends on the equilibrium temperature. The increase of the temperature results in increase of water activity for the same moisture content which in increases the rates of reactions leading to quality deterioration. As the water activity is raised beyond the intermediate region, water is sorbed by low molecular weight constituents resulting in shifting the isotherm upward. The values of the net isosteric heat of desorption were found to be higher than those or adsorption, which indicates that the binding energy for the latter is higher. At low moisture content the heats of desorption is much higher than that of adsorption.

ISSN:0737-3937    

DOI:10.1080/07373930008917829

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The drying kinetics of Muscatel grapes at 60°C and a relative air humidity of 22% were determined after various pretreatments had been applied to the grapes. The pretreatment parameters varied were the chemical agent (potassium carbonate solution with or without olive oil, or sodium hydroxide solution); the duration of pretreatment; and the temperature and concentration of the solution. A 3 minute pretreatment with an aqueous solution of K2CO3and olive oil at 60°C reduced drying time from about 80 h to 20 h. Optimal drying load corresponded to a single layer of almost close-packed grapes on each tray. The experimental drying kinetics were satisfactorily reproduced by a model in which both grape size and the effective coefficient of diffusion are functions of moisture content.

ISSN:0737-3937    

DOI:10.1080/07373930008917830

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This work reports the application of powder pycnometry in density measurement of granular material instead of the traditional liquid pycnometry. Fine dense silica powder was employed as fluid in an experimental set up to measure the density of wood chips taken as porous media. In order to verify the validity and efficiency of the proposed method, the density of soybean (Glycine max L. Merryl) was also measured. The results of soybean density using ethanol as fluid were compared with the proposed method, obtaining a relative deviation of 7·74%. Relative deviations between the samples of wood chips varied from 1·99% to 7·04%, which indicates that the silica method is efficient in determining the density of porous bodies. Liquid pycnometry technique using paraffin covering did not present satisfactory results.

ISSN:0737-3937    

DOI:10.1080/07373930008917831

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor