EXPERIMENTAL AND THEORETICAL ANALYSIS OF HEAT TRANSFER MECHANISM IN CIRCULATING FLUIDIZED BED

Standart dışı düşük kaliteli yakıtları tam yanma koşullarına uygun ve içsel SO2,NOx emisyonu tutma özellikleri nedeniyle doğrudan yakabilecek en uygun teknoloji, genelde akışkan yatak, özelde ise dolaşımlı akışkan yatak (DAY)yakma teknolojisidir. Burada yatak sıcaklığının 850-950 °Cde tutulmasına bağlı olarak uygun adsorbent ilavesi ile SO2'nin tutulması ve NOx oluşumunun azalması sonucu genelde ilgili baca gazı arıtma tesislerinin kurulmasına gerek kalmamaktadır. DAY'lı kazanlarda yatağın çok yoğun türbülanslı olması ve yanma odasını doldurması nedeni ile ısıtma yüzeylerine olan ısı transferi, diğer yakma sistemlerine kıyasla çok daha büyüktür. Bu durum yanma odasının ve ısıtma yüzeyi boyutlarını, dolayısıyla ilgili yatırım maliyetlerini düşürmektedir.Dolaşımlı akışkan yataklı sistemlerde, ısıtma yüzeyine olan ısı transferi, yatak çekirdek akım bölgesi ile yüzey arasında, ısıtma yüzeyinin yakın çevresinde bulunan partikül kümelerinin ve dağılmış fazın dinamik davranışının bileşkesel etkisi altında oluşur. Bu çalışmada akışkan yatak ile duvarda konumlanan ısıtma yüzeyi arasında ve yatak ekseninde konumlanan daldırma yüzeyi ile yatak arasındaki ısı transfer özellikleri, bu amaca yönelik tasarımlanmış ve geliştirilmiş bir test sisteminde deneysel olarak incelenmiştir. Çeşitli yatak malzemeleri ve test koşullarında ısı transfer özellikleri deneysel olarak belirlenmiştir. Deneysel sonuçlar sadece test koşullarındaki ısı transfer davranışını ifade ettiğinden, ölçüm sonuçlarının genel olarak tüm sistemlere uygulanabilirliğini sağlayacak matematiksel korelasyonların türetilmesi yoluna gidilmiştir. Bu çalışmada, deney tasarım ve işletme verileri modelin tanımlanmasında kullanılan boyutsuz parametreler biçimine dönüştürülmüş,modeli tanımlayan ve tanımında baskın olan üssel fonksiyonlar, ölçüm değerlerinin kullanıldığı regrasyon analizleri ile belirlenerek, yenilenen küme modeli ölçüm sonuçlarını minumum sapma ile ifade edebilecek biçime getirilmiştir. Bu yaklaşım ile elde edilen yeni korelasyonlar endüstriyel boyuttaki ısı transferi hesaplarında ve ısıtma yüzeylerinin boyutlandırılmasında kullanılabilir. Buna göre sistemdeki ölçme hataları da (±%10) dikkate alınırsa yenilenen küme modelinin literatürde verilen korelasyonları, gerçek ısı transferi davranışını düşük yoğunlukta (silis kumu,kum, alüminyum tozu) % 30, yüksek yoğunlukta (bakır, çelik tozu) % 43 ortalama sapma ile ifade ederken, bu çalışmada geliştirilen yeni korelasyonlar, gerçek ısı transferini düşük yoğunlukta % 19, yüksek yoğunlukta ise % 27 ortalama sapma ile tanımlamaktadır. Yeni model, gerçek ısı transferini literatürde verilene kıyasla düşük yoğunluklu yatakta % 11, yüksek yoğunluklu yatakta ise % 16 daha az sapma oranı ile tanımlayabilmektedir.Fluidized bed and particularly circulating fluidized bed combustion technology is the appropriate technology to directly burn low quality lignite because of the mentioned combustion technologies ability to hold internally SO2 and NOx emissions. With this combustion technology and keeping the bed temperature between 850-950 ºC and also with the addition of absorbents emissions of SO2 and NOx are reduced. As a result, construction of expensive emission filtering systems can be avoided. In circulating fluidized beds highly turbulent bed fills the combustion chamber and this mechanism tremendously increases heat transfer. As a consequence of increased heat transfer from the sizing point of view overall dimensions of the combustion chamber heat transfer area and investment coast as well can be reduced. In circulating fluidized beds, heat transfer to the heating surfaces can be determined from the combination of several different dynamics interaction mechanisms including between bed core flow region and surface, particularly cluster near flow region of heating surface and dispersed phase. In this study, heat transfer characteristics between fluidized bed and heating surface on the wall and between bed and immerse surface perpendicular to bed axis have been experimentally investigated, on a setup designed for this purpose. Heat transfer characteristics have been determined for different bed materials and test conditions. To generalize the experimental results and to be able to use them for out of range values ii correlations have been obtained. In this study, experimental design and working parameters have been obtained in dimensionless form. Power law functions which govern the model have been obtained through regression analysis to correlate test results according to a cluster renewal model with minimum deviation. Correlations can be used for heat transfer calculations (rating) and sizing problems for industrial scale applications. In the developed model uncertainties including measuring errors were around 10 %. In the literature, previous models were able to predict heat transfer with 30 % standard deviation for the low density case (silica sand, sand, aluminum) and 43 % percent standard deviation for high density case (copper, steal). With the cluster renewal model developed from this study low density case heat transfer can be correlated with 19 % standard deviation and for high density case devotion is within 27 %. With this new model, in low density bed 11 % and in high density bed 16 % improvement in the prediction have been obtained compared to previous available model

Relationship Between Sick Building Syndrome and Indoor Air Quality in Hospital Staff

Background: Sick building syndrome (SBS) is defined as a condition occurring in those who live or work in a modern building and who suffer from symptoms such as headache, fatigue, lack of concentration and irritation of the skin and mucous membranes. Objectives: The aim of this study was to evaluate the relationship between personal characteristics, environmental factors and the prevalence of SBS among the secretaries working in a hospital. Method: In this cross-sectional study, questionnaires were administered to all secretaries who were working in Kutahya hospital in January and March 2018. The questionnaire used in the study included the sociodemographic characteristics of the participants and the question form "MM 040 NA Hospital" to evaluate SBS symptoms. These symptoms were the clinical symptoms reported by the secretaries as a result of exposure to factors within the hospital. Temperature, humidity, carbon dioxide concentration, light intensity and noise level were measured in the indoor environment of the hospital. Chi square test, Spearman's correlation coefficient and logistic regression models were used in the analysis of data. Results: The study was completed with 177 people, 61.6% women, and the mean age was 30.14 +/- 5.7. The prevalence of SBS was found to be 20.9%. The risk of SBS was found to be 2.9 times higher for females, 2.8 times higher for individuals who described the working environment as dusty, 2.6 times higher for subjects complaining of stuffy "bad" air, dry air and an unpleasant odour. All measurements were found to be within acceptable limits. The risk of SBS was found to be 1.2 times higher with increases in the measured noise level, and 2.1 times higher with increased carbon dioxide (CO2) concentrations. Conclusion: The factors impacting the risk of experiencing SBS were determined. Bearing these factors in mind, we think that hospital administrations should be informed about arrangements and measures that will improve the quality of the internal environment of the hospital

Relationship between sick building syndrome and indoor air quality among hospital staff

Background: Sick building syndrome (SBS) is defined as a condition occurring in those who live or work in a modern building and who suffer from symptoms such as headache, fatigue, lack of concentration and irritation of the skin and mucous membranes. Objectives: The aim of this study was to evaluate the relationship between personal characteristics, environmental factors and the prevalence of SBS among the secretaries working in a hospital. Method: In this cross-sectional study, questionnaires were administered to all secretaries who were working in Kutahya hospital in January and March 2018. The questionnaire used in the study included the sociodemographic characteristics of the participants and the question form "MM 040 NA Hospital" to evaluate SBS symptoms. These symptoms were the clinical symptoms reported by the secretaries as a result of exposure to factors within the hospital. Temperature, humidity, carbon dioxide concentration, light intensity and noise level were measured in the indoor environment of the hospital. Chi square test, Spearman's correlation coefficient and logistic regression models were used in the analysis of data. Results: The study was completed with 177 people, 61.6% women, and the mean age was 30.14 +/- 5.7. The prevalence of SBS was found to be 20.9%. The risk of SBS was found to be 2.9 times higher for females, 2.8 times higher for individuals who described the working environment as dusty, 2.6 times higher for subjects complaining of stuffy "bad" air, dry air and an unpleasant odour. All measurements were found to be within acceptable limits. The risk of SBS was found to be 1.2 times higher with increases in the measured noise level, and 2.1 times higher with increased carbon dioxide (CO2) concentrations. Conclusion: The factors impacting the risk of experiencing SBS were determined. Bearing these factors in mind, we think that hospital administrations should be informed about arrangements and measures that will improve the quality of the internal environment of the hospital

Early Diagnosis of Distal Peripheral Polyneuropathy Due to Glucose Metabolism Disorders via Intraepidermal Nerve Fiber Analysis

OBJECTIVE: Polyneuropathy is the most frequent complication of diabetes mellitus (DM), which is a common disorder worldwide. Early diagnosis of this complication is critical for treatment planning. Recently, intra-epidermal nerve fiber (IENF) analysis has been used for the early diagnosis of diabetic neuropathy and was reported to be superior to both conventional fascicular nerve biopsy and other diagnostic tests. The present study aimed to determine the effect of early glucose metabolism disorders on the peripheral nerves using IENF analysis. METHODS: : This prospective study compared IENF nerve fiber density in 10 patients with early-stage DM and 12 patients with impaired glucose tolerance (IGT) to that of healthy controls in order to investigate fiber loss in the asymptomatic stage. RESULTS: Mean age of the DM and IGT groups was 53.4 ± 10.9 years and 50.8 ± 10.6 years, respectively. Neither the IGT nor DM patients had paresthesia. Neurological examination results of the patients were all in the normal range. Mean fiber density was 6.4 ± 2.7 mm-1 in the DM group, 7.5 ± 3.2 mm-1 in the IGT group, and 13.7 ± 2.7 mm-1 in the control group (p< 0.0001). Paired analysis of the groups showed a significant difference between the 2 patient groups and the control group. There was a statistically significant difference in mean nerve fiber density between the DM and control groups (p< 0.0001, Mann-Whitney U test), and between the IGT and control groups (p< 0.0001, Mann-Whitney U test); however, there wasn’t a significant difference between the DM and IGT groups (p= 0.5, Mann-Whitney U test). CONCLUSION: The results show that IENF density in the IGT and DM groups decreased in the asymptomatic stage of DM. This means that polyneuropathy can begin in the prediabetic period in patients with glucose metabolism disorders. This critical information highlighs the importance of the early diagnosis and treatment of glucose metabolism disorders in preventing neurological complication