Numerical study on the properties of an active sun tracker for solar streetlight

In this work, a new active sun tracker for solar streetlight combined with photoelectric tracking mode mainly and time-based tracking mode auxiliary was proposed. The sun tracker was designed through three aspects: mechanical structure, electrical system and control procedure. Then, a proper model named Available Energy Absorption Model was built to study the energy efficiency. The numerical average value of energy efficiency in a year is 36% which shows the superiority of the tracking mode on the available energy absorption. Lastly, the mechanical properties analysis of the tracker was implemented on two aspects which include motion simulation and wind resistance. The numerical results prove the feasibility of the double-slider mechanism and the reliability of the tracker’s strength.     

Mathematical modeling of convective drying: Lumped temperature and spatially distributed moisture in slab

The present study describes the modeling and simulation of the drying process. The model considers fundamentals of the drying process and takes internal resistance to moisture into account. The main connotation of this study regards the possibility of employing a new analytical method for simultaneous heat and mass transfer. The proposed model considers the evaporative heat transfer at the surface of product. The validation of the model is made with a set of numerical and experimental results reported in the literature for carrot sliced in slab form. The results reveal that there is nearly perfect match between the temperature and moisture obtained by the analytical model and the numerical solution.     

Modeling of early age behavior of blast furnace slag concrete based on micro-physical properties

A multi-scale system called DuCOM was enhanced to model behaviors of blast furnace slag (BFS) concrete. Tests on the strength and micro–hygro–physical properties of BFS concrete and Portland cement concrete were conducted. The current model was found to underestimate the strength of BFS concrete at later ages owing to underestimation of the water content inside C–S–H gel pores. To remedy this, enhanced modeling of porosity allowing proper simulation of the porosity of the BFS paste matrix and higher strength development at later ages is proposed. Furthermore, based on the enhanced porosity model, the moisture loss and pore size distribution of the BFS paste matrix were investigated. The pore size distribution was found to be coarser than the test at later ages in the model, resulting in overestimation of moisture loss. Hence, the pore size distribution was enhanced as well, allowing simulation of a finer pore structure of the BFS matrix. Finally, verifications showed that the enhanced model better predicts water desorption, moisture loss and drying shrinkage behaviors.     

Drying characteristics of peppercorns in a rectangular fluidized-bed with triangular wavy walls

An experimental study on drying kinetics of peppercorns has been conducted in two different drying fluidized-bed configurations: rectangular fluidized-bed (RFB) and rectangular fluidized-bed with wavy walls (RFBW). In the RFBW, two opposite triangular wavy walls with three blockage ratios (e/H) are formed to produce vortex/swirl flows leading to stronger turbulence and longer residence time of the flow in the bed. For each bed, three inlet hot airs (T_in) at 60 °C, 80 °C and 100 °C and two superficial air velocity, U* of 1.2 and 2.0 (U* = U/U_mf) are introduced. The experimental results reveal that the air temperature and air velocity show significant effects on the drying rate of both beds, especially at T_in = 100 °C and U* = 2.0. The RFBW performs much better than the RFB due to shorter drying time. The average drying time of the RFBW with e/H = 0.3125, 0.3750 and 0.4375 is, respectively, around 29%, 36% and 43% less than that of the RFB. In addition, three mathematical drying models are offered for both the beds and the effect of the air temperature and velocity on the drying model constants was determined by fitting the experimental data using regression analysis techniques. The three models satisfactorily described the drying characteristics of peppercorns especially for the Henderson and Pabis model. The RFBW with e/H = 0.4375 is preferable in the study.     

Analysis of Freeze-Drying of Tropical Fruits

Abstract

Freeze-drying is a process recommended for drying of heat-sensitive products. Some advantages of this technique are that it allows the shrinkage and the degrading reactions in the material, which are common in conventional drying operations, to be minimized. The knowledge of drying kinetics is essential for modeling and optimization of a freeze-drying process. In this work, drying kinetics for pineapple, guava, and mango pulps were investigated using five empirical equations commonly applied for convective drying of foodstuffs. Increasing constant- and falling-rate periods were observed during the drying of such pulps. The best fittings for the drying kinetics of all the materials were obtained using the Page and Chen and Douglas equations.     

On some aspects of latex drying – ESEM observations

Environmental scanning electron microscopy has been employed to study the drying behaviour of a non-film forming polymethyl methacrylate (PMMA) based latex system. The approach adopted for this study differs slightly when compared to those used previously. Here, by allowing the latex to initially film form, it has been possible to make observations and conclusions regarding the structural development of the specimens under investigation not only in 2D, but also in 3D. The results clearly demonstrate that upon drying, particle packing can yield hexagonal close packed (HCP), square close packed (SCP) and random arrangements, including voids and surface defects that result in the formation of a crystal-like structure. Based on the experimental observations some modifications to the latter stages of the film formation mechanism taking place at temperatures (T) lower than the system glass transition temperature (T_g) have been proposed.     

LAROX压滤机工作机理及故障分析

阐述用于硫酸系统砷、铜、铅滤饼处理的 L AROX压滤机的结构、工作原理和特点 ,同时对这种压滤机在使用过程中出现的故障进行分析与探讨 ,并提出一些可行的办法。     

Solid-liquid separation of faecal sludge using drying beds in Ghana: implications for nutrient recycling in urban agriculture

This study investigated the possibility of recycling nutrients in human excreta and municipal solid waste for use in agriculture. It reports on the use of drying beds in separating solid and liquid fractions of faecal sludge (FS) so that the solids can be co-composted and the organic matter and part of the nutrients captured for urban agriculture. Sludge influent onto drying beds, percolate effluent, and dewatered sludge (biosolids) were monitored over eight loading cycles in 2002. The unplanted drying beds were made of 15 cm of sand (0.2-0.6mm diameter) and 25 cm gravel (10 and 19 mm diameter). The loading rate of sludge ranged from 196 to 321 kg total solids (TS) /m(2)y. Biosolids with TS 20% were obtained after an average drying time of 2 weeks. The drying beds retained 80% of solids and 100% of helminth eggs. The biosolids had average organic matter content of 61%; hence, allowing for co-composting with biodegradable organic solid waste for hygienisation. The process is being investigated further to attain higher efficiency and reliability.     

Effects of Pretreatment and Drying on Composition and Bitterness of High-Dietary-Fiber Powder from Lime Residues

Lime residues after juice extraction were used as a starting raw material to produce high-dietary-fiber powder. The effects of pretreatment—i.e., blanching and ethanol soaking (55–95% v/v)—and hot air drying at 60–100°C on the proximate composition and limonin, a substance responsible for bitterness in citrus fruits, were evaluated. Hydration properties—i.e., water retention capacity and swelling capacity—and visual color were also determined. It was found that using selected pretreatments in combination with the drying process caused significant effects on dietary fiber contents and visual color. The higher reduction in limonin contents was observed for the samples having subjected to higher ethanol concentration and higher drying temperature. Blanching and ethanolic pretreatment also improved the water retention and swelling properties of the final product.