Çan Linyiti ile Kayın Ağacı Odununun Sabit Yatakta Birlikte Yakılması

Bu çalışmada, linyit ve belirli oranlarda kayın ağacı odunu tozu karışımlarından hazırlanan 13 mm çaplı peletlerin ön ısıtmalı dikey bir fırın sisteminde doğal konveksiyonla yukarı yükselen hava içindeki yanma davranışları incelenmiştir. Karışımların tutuşma sürelerinin sıcaklık arttıkça kayın ağacının tutuşma süresine yaklaştığı ve uçucu madde yanma süresi boyunca iki yakıtın belirli ölçüde etkileştiği görülmüştür. Yakıtlar arasındaki bu etkileşimden dolayı uçucu madde yanma sürelerinin yanma hızları ile uyumlu olmadığı, ancak iki yakıtın ve karışımlarının karbon yanma sürelerinin genellikle yanma hızları ile uyumlu olduğu gözlendi. Uçucu madde ve karbon yanma hızındaki değişimin fırın başlangıç sıcaklığı ve karışım içerisindeki yakıt oranlarına bağlı olduğu görüldü

Pyrolysis kinetics of pine sawdust in a fixed bed

Currently worldwide studies are being done on the utilisation of lignocellulosic materials or biomasses as substitutes of fossil fuels to afford energy needs of today’s world. Pyrolysis is one of the most promising techniques for apprising biomass into economically viable renewable fuels. In this work, pyrolysis behaviour of pine sawdust was investigated experimentally in a fixed bed system with mass measurements under nitrogen as sweeping gas. The main objective was to interpret mass loss of pine sawdust during pyrolysis at varied heating rates and to estimate kinetic constants using the best mathematical model among the popular solid phase decomposition models. Regression tests are separately applied to conversion data for 473 – 593 K and 593 – 773 K temperature ranges, corresponding respectively decomposition of hemicelluloses and cellulose, and cellulose and lignin. The quality of fit increased with heating rate and none of the proposed models had any superiority to others. The results implied that volatiles evolution during pyrolysis was increasingly controlled chemically with heating rate

Volatiles and char combustion rates of demineralised lignite and wood blends

Today, much interest is given to the utilisation of materials of plant origin as substitutions of fossil fuels in meeting energy needs to reduce the level of atmospheric pollutant emissions and global warming threat, and emphasis has been placed on the co-combustion of coal and biomass. In this study, volatiles and char combustion behaviour of the fuel pellets composed from demineralised lignite and poplar wood sawdust, were investigated in a cylindrical wire mesh basket placed in a preheated tube furnace. The results have shown that ignition times of the pellets decreased with the burning temperature and shortened further due to demineralisation of lignite. Volatiles combustion rates of the samples did not correlate well with combustion times. However, they can be correlated with their respective proximate volatile matter contents. Char burnout times decreased with increasing combustion rates and correlated well with the respective proximate fixed carbon contents of the samples. Deviations were more considerable in the case of rate data.Co-combustion Lignite Poplar wood Volatiles combustion Char combustion

Heat transfers and pressure drops in rotating helical pipes

Helical pipes are employed extensively in chemical reactors, reservoirs, nuclear generators, evaporators and condensation flow systems as well as energy saving applications. In this study, in order to increase the heat-transfer rates in helical pipes of various diameters, the rotation of the pipes was considered experimentally. An experimental set-up for determining the heat-transfer rates and pressure drops occurring, because of the centrifugal effects on the rotating helical pipes, was designed. The heat-transfer rates and pressure drops were measured for various air-flow rates and helical pipe rotational speeds. Although the rotation caused an increase in pressure drop, heat-transfer capacities of the helical pipes were observed to improve notably. The Nusselt numbers rose due to the increases in Reynolds numbers and heat inputs into the system. Beside these, further improvements in heat transfer were observed with the decreasing curvature diameter of the helical pipe.

Is there an association between vitamin B12 level and vitamin D status in children?

Vitamin B12 (vit B12) or cobalamin is a water-soluble vitamin that acts as a coenzyme and is effective in the formation of a healthy nervous system and erythrocytes. In its deficiency, except fatigue and weakness, may cause serious signs and symptoms such as macrocytic anemia, cognitive-developmental delay, irreversible neurological damage. In this study, hemoglobin, leukocyte, thrombocyte, iron, iron-binding, ferritin, and vit B12 levels were evaluated retrospectively during the routine controls of 689 children 5 to 18 years old without any complaints. In addition, the relationship between serum 25-Hydroxyvitamin D (vit D) levels and vit B12 levels, which were evaluated in 487 of the cases, was investigated. Vit B12 deficiency was diagnosed in a total of 160 (23.2%) cases, 99 (24.4%) girls and 61 (21.4%) boys. Vit B12 level was significantly lower in children over 12 years old. Vitamin D deficiency was found to be 49.3% in 487 cases and was significantly higher in the group under 12 years and girls. The frequency of anemia was 7.2% in this group. There was a significant relationship between vit D deficiency and vit B12 deficiency. In conclusion, vit B12 deficiency is common in school-age children, especially in the adolescent age group. It should be known that vit D deficiency may also be present in vit B12 deficiency cases. More comprehensive studies are needed to reveal the relationship between B12 and vit D deficiency