摘要:

Unconrolled agglomeration of particles and adhesion of the particulate mass to wall surfaces are common severe problems in many drying operations. This paper reviews the mechanisms of interparticle and particle‐surface attraction as well as the theory and the existing tests for characterising powders in terms of internal strength, wall friction and adhesion. The usefulness of the information obtained from these tests in dryer design and operation is critically reviewed. The importance of powder stickiness in various types of dryers is discussed and established methods of combating the problem are presented Recommendations an made for further research in the area of powder cohesion and adhesion.

ISSN:0737-3937    

DOI:10.1080/07373939208916484

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The author's group is active in research on a wide variety of solid-liquid separation and dewatering methods. Processes examined include coagulation/flocculation, sedimentation, consolidation, drainage, filtration, compression/expression, and desaturation. A number of mechanical and electrical techniques have been used. These have been applied to a few well-defined systems such as clays, and to a wide variety of real suspensions from different industry sectors, from small laboratory to large demonstration scale. The experience of a range of techniques allied widi knowledge of the characteristics and behaviour of suspensions is helping to bridge the gap between scientific understanding and practical application. The present paper, based on both published and unpublished CSIRO work with an emphasis on fine and ultrafine coal and coal tailings, summarises the position. The analysis includes: • conceptual evaluation of the applicability and limitations of established dewatering techniques, • considering better ways of using these techniques, • assessing the potential for combining force fields (how many, what type, what sequence) to provide improved dewatering technologies.

ISSN:0737-3937    

DOI:10.1080/07373939208916485

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A novel technique serves to monitor instantaneous rates of loss of a volatile solute from a suspended drop during drying. A highly sensitive electron capture detector is used to monitor concentrations of SF6 released into a flowing gas stream from a suspended, drying drop. Simultaneously, the appearance and morphological development of the drop are monitored with a video camera. This provides the wherewithal of relating instantaneous rates of loss of the volatile solute to particular events during the development of particle morphology.

ISSN:0737-3937    

DOI:10.1080/07373939208916486

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Drying of films, fibers, and spheres undergoing sol-to-gel transformation is greatly affected by the strong dependence of the diffusion coefficients on composition, molecular weight, and temperature. This dependence is probed by solving the equations of mass and heat transfer by diffusion or conduction and associated convection, along with chemical reaction. A one-dimensional analysis is used that encompasses the planar, cylindrical, and spherical configurations. The solutions are obtained by Galerkin's method with finite element basis functions and entail large-scale computation.

ISSN:0737-3937    

DOI:10.1080/07373939208916487

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The flow and distribution of liquid and vapor in the pore space of drying porous media are represented by a simple network model that incorporates the microscopic mechanisms. A method akin to Monte Carlo and molecular dynamics approaches is described for calculating from any such model the macroscopic, ‘volume- averaged’, or effective transport parameters: relative permeabilities for pressure-driven flow, effective diffusivities for molecular diffusion, and so on.

ISSN:0737-3937    

DOI:10.1080/07373939208916488

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effect of cycling the external conditions on the timber quality and drying time during seasoning has been studied for red beech (Nothofagus fusca), a difficult-to-dry New Zealand hardwood, inalaboratorybatchdryer. Intermittent drying at anair temperature of 45°C and a wet-bulb depression of 10°C takes longer to yield a given moisture content than continuous drying under the same conditions, but produces timber without honeycomb or severe case-hardening as observed in continuous drying. The experiments also indicate that the timber can tolerate a higher air temperature (55°C) in intermittent drying at the same wet-bulb depression with less case-hardening and without showing honeycomb compared with continuous drying at 45°C, having a similar total drying time. Intermittent drying at a slightly higher dry-bulb temperature (60°C) and a much higher wet-bulb depression (18°C) gives a similar degree of case-hardening to that found in samples dried continuously at a dry-bulb temperature of 45°C.

ISSN:0737-3937    

DOI:10.1080/07373939208916489

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The drying of paper under impinging jets of superheated steam and air during the falling rate period was investigated in the range of jet temperatures 150 < Tj < 450oC and basis weights 30 < B < 150 g/m2. The equilibrium moisture content of Kraft and TMP paper was measured. The adsorption energy of water on pulp fibers near the boiling point appears lower than the value extrapolated from Prahl s (1968) measurements made in air at lower temperatures. The critical moisture content was determined for superheated steam and air impingement drying. Complete drying rate - moisture content histories are presented for a series of typical conditions.

ISSN:0737-3937    

DOI:10.1080/07373939208916490

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effectiveness of the rotary drum drying process depends primarily on the contact between the cascading particles and the drying gases within the drum. This paper considers first the factors which contribute to the cascade pattern and which influence the design of the lifting flights which distribute the particles in the top half of the drum. A generalised calculation design procedure for flights is developed and described in detail for the case of Equal Horizontal Distribution (EHD) flights. It is reasoned that the EHD flights, which have an equal distribution of particles across the horizontal diameter of the rotary drum dryer, give the optimum distribution in the context of the heat and mass transfer operations of the rotary drying process. An industrial design which approximates the optimum flight design is suggested.

ISSN:0737-3937    

DOI:10.1080/07373939208916491

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Drying kinetics were examined by introducing one-parameter empirical mass aansfer model, where the characteristic parameter (drying constant), is a function of process variables. The model was tested with data produced in an experimental through dryer, using direct regression analysis. Investigation involved two vegetables (namely, green pepper and onion) and a wide range of characteristic dimensions of samples and air conditions (temperature, humidity, and velocity). The parameters of the model considered were found to be greatly affected by sample characteristic dimension and air temperature.

ISSN:0737-3937    

DOI:10.1080/07373939208916492

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The theoretical analysis was developed to predict the deformation characteristic of formed clay during a drying process in a ceramic production. The three dimensional strain-stress distribution as well as heat and moisture transfer in a slab shape of clay were simultaneously analyzed by a finite element method. Linear viscoelasticity was assumed for the strain-stress analysis to account the effect of creep. The calculated result agreed well with an experimental result performed for a slab clay heated by hot air flow during the preheating and constant drying rate periods. A large tensional stress, which may generate a crack, was observed initially around the surface area. It was also found that the time behavior of the volume change of the formed clay is significantly influenced on the drying conditions and/or the drying rate.

ISSN:0737-3937    

DOI:10.1080/07373939208916493

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor