USE OF THE S-40 DRYER IN TWO-STAGE DRYING OF CORN GRAIN

The paper provides rationale for safe modes and methods for calculating a two-stage drying technology with partial recirculation of grain, in which the grain is under-dried by 2…3% to the standard humidity in a grain dryer, and the hot grain is cooled by active ventilation with outside air, while drying it to the standard humidity. The safe mode of two-stage drying in S-40 provides for partial recirculation of grain with moisture removal close to the standard, and the moisture content of the recirculated mixture not exceeding 18%. The recirculation coeffi cient calculated based on this condition is used to determine the temperature of the recirculating grain mixture, taking into account the reversible component in the shaft dryer. The minimized recirculation ratio provides for the permissible unevenness in drying and minimal fracturing. The recirculation drying process was analyzed according to the standard method, but with the adjusted values of moisture removal and temperature of the grain mixture. Economic tests of the S-40 dryer were carried out using a two-stage technology on corn grain. It has been experimentally established that the S-40 dryer with a recirculation coeffi cient of 2 and a moisture pick-up of 4% per cycle when drying corn grain with a moisture content of 23.5 to 15.6%, at a drying agent temperature of 95°C, provides a throughput of 10 t/h (without refrigeration). Cooling was carried out in the warehouse. No signifi cant changes in the quality of dried and cooled grain have been established: the starch content and fracturing practically did not change; the unevenness of the dried seeds did not exceed the original requirements. The expediency of using the S-40 direct-fl ow dryer in the recirculation mode has been experimentally established.

Reversible and Irreversible Processes in Drying and Wetting of Soil

In this article, we provide a detailed description of a modeling technique for the capillary hysteresis in a soil-like porous material based on a Generalized Preisach Model. The identification of the reversible and irreversible Preisach distributions was performed with the first-order reversal curve (FORC) diagram technique, which is very popular now in magnetism and in other areas of science to give a fingerprint of the studied system. A special attention was given to the evaluation of the reversible component. In this case, we used a set of data published in 1965 by Morrow and Harris which has been used as a reference by many other researchers since. The advantage of this approach is that the experimental FORC distributions can be described with analytical functions and easily implemented in the mentioned Preisach-type model. Our research is also focused on the development of a characterization tool for the soil using the soil-moisture hysteresis. The systematic use of scanning curves provides a (FORC) diagram linked to the physical properties of the studied soil. The agreement between the experimental data and the Preisach model using the set of parameters found through the FORC technique is really noticeable and gives a good practical option to the researchers to use a method with a strong predictive capability.

Experimental Evaluation of a Novel Backflush Controller for Immersed Membrane Systems

Membrane backflush with air or permeate is commonly employed to reduce fouling in immersed micro– and ultrafiltration (MF/UF). Membrane plants traditionally rely on simple timer control automation to initiate periodic backflushes for membrane cleaning. In this study, a closed–loop (feedback) type backflush controller was evaluated experimentally with a bench–scale hollow fibre immersed MF/UF membrane – flocculation hybrid system.The controller showed an unexpected behaviour at low fouling rates, which was manifested in significantly varying filtration periods. The investigation identified the cause in the use of a constant stabilisation lag parameter.The role of this control parameter was to determine the reversible component of fouling in real–time, which is a difficult problem in transient flow conditions that characterise the start of filtration periods. The resulting error became significant at low fouling rates and impaired effective control.Based on this insight, we propose alternative, more robust control parameters, which can provide improved backwash control solutions for MF/UF membrane applications.

Modeling swelling–shrinkage behavior of compacted expansive soils during wetting–drying cycles

This paper presents a straightforward approach for modelling volume change behavior of expansive soils during wetting–drying cycles. The swelling–shrinkage strain of expansive soils induced by cyclic wetting and drying was decomposed with distinctive physical background into a reversible component, which shows a synchronous change with the cyclic change of suction, and an irreversible component, which is generated mainly in the early stage of the wetting–drying process. The mechanisms of the two swelling–shrinkage strain components can be well explained through the double-level structure of expansive soils and its evolution with mechanical and hydraulic loading. The reversible component originates from the reversible deformation behavior of aggregates, and primarily depends on current suction or water content. The irreversible component is associated with the irreversible change of macrostructure, reflecting the difference in soil structures at current state and the equilibrium state. A practical constitutive model was proposed for compacted expansive clays from a global and phenomenological perspective. The model parameters can be calibrated with observed macroscopic deformation behavior without measuring microstructural parameters. The performance of the presented model was validated by simulating cyclic suction-controlled tests as well as an alternately soaked and dried test with irregular amplitudes of suctions.

Diffusion of sulfide into Southern pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.) particles and chips

Sulfide diffusion into wood has a rapid reversible component and a much slower irreversible component. During the initial reversible phase, sulfide is unable to diffuse into parts of the wood structure, probably because of charge exclusion. The diffusion of hydroxide and sulfide into saturated wood was imaged by immersing chips in white liquor, splitting them open and then imaging the hydroxide and sulfide profiles. Sulfide moves into the interior of the chip at a faster rate than hydroxide does because it is prevented from entering some of the pores and must move deeper into the chip to access dilution water.