Katı yüzey ışınımı ile gaz yakıtlı ocaklarda ısı geçişinin arttırılması

The aim of this study is to increase the heat transfer rate in gas-fired furnaces. Since natural gas combustion flame has low emisivity, heat transfer rate from flame to furnace wall decreases and the result is high flame temperature. In gas fired furnaces heat transfer can be increased by increasing the radiation. To accomplish this, solid surface, which was called as filling material, were placed in the furnace. The filling materials were formed in different shapes. Theoretical results showed that the filling material increased the heat transfer in the furnace. In accordance with the increasing heat transfer, the temperature of the furnace decreased. The ratio of the heat transfer also changed with respect to the shape of the filling material. An experimental work was carried out to compare the results with theoretical calculations. It was seen that the results of the experimental work were supporting the theoretical calculations. The experiments showed also that the filling material decreased the furnace temperature and increased the heat transfer rate from flame to the furnace wall. It was determined that the thermal NOx decreased by the decreasing furnace temperature. The filling material can be placed into the present domestic boilers in order to increase the heat transfer and to reduce the emission. Keywords: Filling material, furnace, solid surface, high flame temperature, thermal NOx .    Yapılan bu çalışmanın amacı doğal gaz yakıtlı kazanların ocaklarında ısı geçişini artırmaktır. Gaz yakıtlı ocaklarda ışınımı artırmak için ocak içerisine dolgu olarak adlandırılan farklı geometrilere sahip katı yüzeyler yerleştirilerek ısı geçişindeki etkisi incelenmiştir. Yapılan teorik hesaplamalar neticesinde, gaz yakıtlı ocaklarda ışınım artırıcı katı yüzeylerden oluşan dolgu maddeleri kullanıldığı zaman, ısı geçişinin arttığı, farklı dolgu geometrileri için ısı geçiş oranlarının da farklı olduğu görülmüştür. Isı geçişindeki artışa bağlı olarak ocak sıcaklığının düştüğü tespit edilmiştir. Bu teorik hesaplamaları desteklemek amacıyla bir de deneysel çalışma yapılmış, deneyden elde edilen sonuçların teorik hesaplamalarla uyum içinde olduğu  görülmüştür.  Anahtar Kelimeler: Katı yüzey ışınımı, zayıf ışınımlı alev, ısıl azot oksit, dolgu

High-speed resonant-cavity-enhanced Schottky photodiodes

The top-illuminated Schottky photodiodes were fabricated by a microwave-compatible monolithic microfabrication process. Fabrication started with formation of ohmic contacts to n+ layers. Mesa isolation was followed by a Ti-Au interconnect metallization. Following this, a semitransparent Au Schottky metal and a silicon nitride layer was deposited. Finally, a thick Ti-Au layer was deposited to form an air bridge connection between the interconnect and the Schottky metal. The optical properties of the photodiodes were simulated using a transfer matrix method

Short term effects of a low-carbohydrate diet in overweight and obese subjects with low HDL-C levels

<p>Abstract</p> <p>Background</p> <p>The aim of this study was to evaluate short-term effects of a low-carbohydrate diet in overweight and obese subjects with low HDL-C levels.</p> <p>Methods</p> <p>Overweight (BMI between 25-30 kg/m²) or obese (BMI over 30 kg/m²) subjects with low HDL-C levels (men with HDL-C <1.03, women <1.29 mmol/l) were invited to the study. A 1400 kcal 75-gram carbohydrate (CHO) diet was given to women and an 1800 kcal 100-gram CHO diet was given to men for four weeks. The distribution of daily energy of the prescribed diet was 21-22% from CHO, 26-29% from protein and 49-53% from fat. Subjects completed a three-day dietary intake record before each visit. Anthropometric indices, body fat ratio, blood lipids, glucose and insulin were measured. Baseline and week-four results were compared with a Wilcoxon signed ranks test.</p> <p>Results</p> <p>Twenty-five women and 18 men participated. Basal median LDL-C level of men was 3.11 and basal median LDL-C level of women was 3.00 mmol/l. After four weeks of a low-carbohydrate diet, the median energy intake decreased from 1901 to 1307 kcal/day, daily energy from carbohydrate from 55% to 33%, body weight from 87.7 to 83.0 kg and HDL-C increased from 0.83 to 0.96 mmol/l in men (p < 0.002, for all). After four weeks of a low-carbohydrate diet, the median energy intake tended to decrease (from 1463 to 1243 kcal, p = 0.052), daily energy from carbohydrate decreased from 53% to 30% (p < 0.001) and body weight decreased from 73.2 to 70.8 kg (p < 0.001) in women, but HDL-C did not significantly change (from 1.03 to 1.01 mmol/l, p = 0.165). There were significant decreases in body mass index, waist circumference, body fat ratio, systolic blood pressure, total cholesterol, triglyceride and insulin levels in all subjects.</p> <p>Conclusions</p> <p>HDL-C levels increased significantly with energy restriction, carbohydrate restriction and weight loss in men. HDL-C levels didn't change in women in whom there was no significant energy restriction but a significant carbohydrate restriction and a relatively small but significant weight loss. Our results suggest that both energy and carbohydrate restriction should be considered in overweight and obese subjects with low HDL-C levels, especially when LDL-C levels are not elevated.</p

Influence of the using of methanol instead of water in the preparation of Co–B–TiO2 catalyst for hydrogen production by NaBH4 hydrolysis and plasma treatment effect on the Co–B–TiO2 catalyst

In this work, methanol was used as an alternative to water. Our objective is to study the influence of the using of methanol instead of water in the preparation of Co–B–TiO2 catalyst. It is also expected to improve the activity of Co–B–TiO2 catalyst by plasma treatment for the hydrogen generation from hydrolysis of NaBH4. The prepared catalysts were characterized using BET (N2 adsorption), SEM (scanning electron microscopy), XRD (X-ray diffraction) and FTIR (Fourier transform infrared) methods. The Co–B–TiO2 catalyst prepared in methanol shows maximum hydrogen generation rate, which is about 3.0 times higher than that obtained for Co–B–TiO2 catalyst prepared in water. The maximum hydrogen generation rates for the Co–B–TiO2 catalysts prepared in water and methanol were 1017 and 3031 mL/min/g, respectively. In addition, the maximum hydrogen generation rates for the plasma treated Co–B–TiO2 catalysts prepared in water and methanol were 1320 and 2656 mL/min/g, respectively. The activation energies of nth-order reaction model for the hydrogen production from hydrolysis of NaBH4 with the plasma treated Co–B/TiO2 catalyst prepared in methanol and Co–B/TiO2 catalyst prepared in methanol can be obtained from the slope and intercept of the regression line, being 41.29 and 36.24 kJ/mol, respectively

Hydrogen production through the cooperation of a catalyst synthesized in ethanol medium and the effect of the plasma

In the present study, nanostructured Ni-B catalysts were successfully prepared in ethanol medium using the chemical reduction method for hydrogen production from the catalytic hydrolysis of sodium borohydride (NaBH4). Ni-B nanostructures were characterized by several analysis methods including XRD, SEM/EDS, FT-IR and BET. The effects of factors such as solution temperature, NaBH4 loadings, catalyst amount and NaOH concentration on the performance of these catalysts in the production of hydrogen from alkaline NaBH4 solutions were investigated in detail. In addition, the Ni-B catalyst prepared in ethanol medium and subjected to plasma for the hydrogen production from the catalytic hydrolysis of NaBH4 was investigated. The Ni-B catalyst prepared in ethanol medium showed maximum hydrogen production rate (1000 mL min-1gcatalyst-1) which was approximately 2 times higher than the rate obtained from the Ni-B catalyst prepared in water (400 mL min-1gcatalyst-1) and acethone (550 mL min-1gcatalyst-1). The Ni-B nanoparticles showed the best catalytic activity at 333 K with a maximum hydrogen production rate of 7134 mL min-1gcatalyst-1 and activation energy of 46.83 kJmol-1 for the NaBH4 hydrolysis reaction in the Ni-B catalysts prepared in ethanol and subjected to plasma. As the Ni-B catalyst is inexpensive and easy to prepare, it is feasible to use this catalyst in the construction of practical fuel cells for portable and in situ applications.BEBA

Hydrogen production by using Ru nanoparticle decorated with Fe3O4@SiO2–NH2 core-shell microspheres

Noble metals are commonly used in order to accelerate the NH3BH3 hydrolysis for H2 production as heterogeneous catalysts. The nanoparticles (NPs) of these metals can be applied as active catalysts in fluid reactions. Metal NPs included in the core-shell nanostructures emerged as well-defined heterogeneous catalysts. Additionally, unsupported NPs catalysts can be gathered easily among neighboring NPs and the separation/recovery of these catalysts are not efficient with traditional methods. For this reason, here, silica-shell configuration was designed which was functionalized with a magnetic core and amine groups and Ru NPs were accumulated on Fe3O4@SiO2–NH2 surface for H2 production from NH3BH3. Fe3O4@SiO2–NH2–Ru catalysts demonstrated high catalytic activity as long as it has a hydrogen production rate of 156381.25 mLgcat−1 min−1 and a turnover frequency (TOF) of 617 molH2molcat−1min−1 towards the hydrolysis dehydrogenation of AB at 30 °C. This result is significantly higher than most of the known catalysts

Initial diagnosis of lumbar disc herniation is associated with a delay in diagnosis of ankylosing spondylitis.

Objective. There is often a considerable delay in diagnosis of ankylosing spondylitis (AS). In this multicenter study, we analyzed the delay and possible associated factors, including an initial diagnosis of lumbar disc herniation (LDH), which we frequently encounter in daily clinical practice