DEVELOPMENT OF WOOD GRINDING. 3. FURTHER TESTING OF GRINDING MODELS

"The study is the continuation of a sequence of works devoted to describing the mechanisms occurring during stone grinding of wood. This part was aimed at further testing of pressurised grinding of spruce wood, which was conducted under controlled laboratory conditions. Testing of the developed theoretical model for power ratio (Pc/Pt) versus energy specific production (Ġw/Pt) produced linears for data representing constant wood moisture content. However, the linears showed almost identical results for fresh woods, and also for drier wood, e.g. wood containing saturated fibres and air-dried wood, although one would expect some differences due to the widely varying constant moisture, from 65% to 15% moisture content. Simplification of the model resulted in (cw + X cm) ΔTp-w ≈ Pt / Ġw, and it led to specific linears, when the members as such were correlated between themselves at several constant wood moisture contents. The results were briefly as follows. Increasing wood feed rate – 0.7, 1.0 and 1.3 mm/s – decreased the specific energy requirement, while increased stone surface speed – 20 and 30 m/s – increased it. The left-hand member or the “X-factor” as named in this context, correlated with the right-hand member or the specific energy requirement and resulted in declining linears. The lower the wood moisture content – 65, 58, 44, 28 and 15% – the smaller was the linear declination, and also the difference due to stone surface speed. The application of an energy balance could be useful in searching for a working wood grinding model. Such a model would enable critical examination of wood grinding conditions. Also, it would help understanding the mechanism of various factors, such as grinding parameters, wood properties and stone burr and sharpness. It seems that there are factors that are not known well enough for further development of grinding. Shower water flow and temperature affect the stone surface temperature as known, but their significance for the energy balance or grinding mechanism are not known. Also, the thin film of pulp slurry between the stone surface and the heat activated wood layer is evidently a significant factor that is connected to the local energy transfer. "

Fabrication and Evaluation of a Cabbage Harvester Prototype

A cabbage harvester prototype was fabricated and tested to save time, cost, and labor for harvesting. This harvester was designed for harvesting operations to drive the prototype and control the harvester. The single-row prototype harvesting meets the functional requirements of the physical properties of the Egyptian cabbage. The performance of the harvester prototype was evaluated on two shapes of cutter disc, four cutter disc speeds, and four cutter disc angles; these parameters were assessed at 88% moisture content of the cabbage head and average forward speed of 1.5 km/h. The results demonstrated that the serrated edge cutter discs and 900 rpm disc speed produced actual productivity of 12.56 ton/h, 2.28 kW power requirements, 0.18 kW h/ton specific energy requirement, and of 3.66 $/h operating cost. It turns out that the harvester did not do major harm to the cabbage and less than 4% damage. Operating the harvester at the optimum parameters saves cost and time compared with manual harvesting.

Development of a Hammer Mill with Double Sieving Screens

A hammer mill with double sieving device was designed and fabricated from locally available materials for grinding grains and other agricultural products. The conceptual design was based on the principle of design by analysis. The test carried out on the machine showed that the crushing capacity of the machine is 51.5 Kh/hr. The moisture content, machine speed and the interaction between them had significant effect on the milling power and specific energy requirement at 5 % level of significance. Milling power and specific energy requirement of the machine increased with increase in moisture content. The maximum crushing efficiency of 79.3 %, minimum milling power and specific energy requirement of 0.09 Kw and 3.04 Kwh/mg respectively were obtained at moisture content of 8 % (wb) and machine speed of 2000 rpm. Regression models that could be used to express the relationship existing between the hammer mill performance indices, product moisture content and machine speed were established. The machine has dual purpose for either electric motor or petrol engine.

Optimization of single locking cotton feeder for maximizing ginning output and minimizing specific energy of double roller gin

The aim of the study was to improve the efficiency of the double roller cotton gin in terms of ginning output and energy consumption. Therefore a spike cylinder–type gin feeder with the concept of single locking of cotton bolls was developed and optimized. The speed of the spike cylinder of the single locking feeder and cotton moisture were optimized using response surface methodology for long and medium staple cotton. Ginning output of the double roller gin was maximized and the specific energy requirement for ginning was minimized during optimization. Quadratic models were fitted for prediction of ginning output and specific energy. Optimum cotton moisture of 7.38 and 7.15% and optimum spike cylinder speed of 307 and 297 rpm with desirability of 0.9185 and 0.8923 were arrived at using multiple regression analysis for long and medium staple cotton, respectively. Use of the single locking cotton feeder for long and medium staple cotton resulted in a 22 and 25% increase in ginning output, respectively, and a 12 and 13.5% reduction in specific energy requirement, respectively, compared to the conventional system, the auto-feeder. The single locking feeder showed significant improvement in the color grade of cotton. Other high volume instrument and advanced fiber information system fiber quality parameters remained unaffected.

Numerical study of H2S-H2O-air mixture conversion to hydrogen via activation of air by an electric discharge

The numerical analysis of H2 production during partial oxidation of H2S–H2O–air in a plug-flow reactor at a rather low temperature (T 0=500 K) was conducted. For the reforming process promotion, the oxidizer (air) was activated by an electrical discharge with different values of reduced electric field E/N and input energy E s. It was shown that a significant hydrogen yield in a flow reactor can be obtained only after mixture ignition. The ignition delay length turned out to be minimal at E/N~4–10 and 120–150 Td, when O2(a1Δg) mole fraction in the discharge products is maximal. If the H2S–H2O–air mixture ignites inside the flow reactor, the H2 mole fraction and its relative yield do not depend on E/N. The relative hydrogen yield increases monotonically with an increase of H2O amount. The specific energy requirement for H2 production in considered process was evaluated.

Convective and microwave drying characteristics, energy requirement and color retention of dehydrated nettle leaves (Urtica diocia L.)

In this research, convective and microwave drying characteristics, energy requirement and color changes of nettle leaves (Urtica diocia L.) were reported. Samples of freshly harvested nettle leaves were dehydrated under three air temperatures of 50 °C, 60 °C and 70 °C and at three microwave power levels of PL-1, PL-2 and PL-3. Selected drying air velocity was 0.30 m/s for all temperatures. This is coming from the fact that it was understood from the preliminary studies that the temperature less than 50 °C and the air speed more than 0.30 ms-1 increase the drying time and energy requirement, extremely for these products. Nettle leaves were dehydrated from the initial moisture content of 320 (percentage dry basis) to a final moisture content of 7 % to 9 %. During convective drying experiments, product were weighted automatically by the balance per (5 to10) min. Data were transferred to the computer and processed by a software. During microwave drying, the product were weighted and data recorded manually per (15 to 60) min. The influence of drying method, drying air temperature and microwave power level have also been studied. Hunter L, a, b values system was also used to evaluate changes in total color difference (DE) on dried products. The results showed that convective drying air temperature and microwave oven power levels influenced the total drying time, total energy requirement, specific energy requirement and color difference for nettle leaves. The minimum specific energy requirement were determined as 6.95 kWhkg-1 and 23.63 kWhkg-1 for 70 °C and PL-2 respectively. 70 °C drying air temperature and PL-3 was found to yield better quality product in terms of color retention of Hunter L, a, b and DE. As a result, to reduce drying energy consumption and to keep better color retention, convective drying can be recommended for this application.