In this study, the effect of heat sink geometries on the performance of a thermoelectric generator was researched. In this context, fins with different geometries (flat fin, square pin fin, hexagonal pin fin, and circle pin fin) placed on an aluminum heat sink, and their effects on heat transfer and electricity generation were investigated numerically. Calculations were carried out according to three different hot surface temperatures and five different air velocities. As a result of this study, it was determined that the electrical output increased with the increase in air velocity and hot surface temperature in all geometries. The highest electrical outputs were obtained at 150 °C hot surface temperatures and 15,000 Reynolds numbers, while the lowest electrical outputs were obtained at 50 °C hot surface temperatures and 5000 Reynolds numbers in all geometries. The best thermal and electrical performance was obtained with a flat fin heat sink, and the worst performance was seen in the thermoelectric generator (TEG) system without a heat sink. The highest power outputs of the flat fin heat sink and without heat sink TEG systems were 6.42 W and 1.12 W, respectively. In addition, the highest conversion efficiencies of the flat fin heat sink and without heat sink TEG systems were 14.94% and 5.54%, respectively.

Energy demand is increasing with the rising world population. Energy consumption for heating purposes are very high in our country so energy saving is very important especially in buildings. The outer walls of the buildings which are designed to have a minimal heat loss will reduce fuel consumption and so it will provide economic benefits. In this study, two dimensional numerical analysing of the buildings having a various aspect ratio (AR) were performed for different wind velocities by using different turbulence models. The standard k-ε model, RNG k-ε model and realizable k-ε model were used for modelling the turbulent flow. For these different geometrical situations, velocity vectors on buildings, heat transfer rate from buildings and turbulence models effects on the solution were investigated in detail. It was observed that with the decreasing wind speeds and aspect ratio, the average heat flux of all surfaces of the building increased depending on the convection coefficient. For the all three models used in the study it was seen that the average heat flux on all of the building surfaces increased depending on the heat transfer coefficient. With the decreasing wind velocities and the building aspect ratio. On the condition of AR=1:1, the three models gave very similar results. The results obtained showed differences with the decreasing in the building aspect ratio. The difference between the results was very little in low velocities, but this difference became clear with the increase in the average wind velocity. Depending on AR and the surface of the building, the heat flux-velocity curves gave similar results in all three models. Hızla artan dünya nüfusu ile birlikte enerji kaynaklarına duyulan ihtiyaç giderek artmaktadır. Ülkemizde ısınma amaçlı enerji tüketimi oldukça fazladır. Bu manada özellikle binalarda ısı tasarrufu oldukça önemlidir. Bina dış duvarları üzerindeki akış ve ısı transferinin modellenerek en az ısı kaybı olacak şekilde tasarlanması yakıt tüketimini düşürerek ekonomik kazanç sağlama konusunda son derece etkilidir. Bu çalışmada farkı en-boy oranlarına (EBO) sahip üç bina ele alınarak, bu binaların etrafındaki akış farklı rüzgâr hızları için üç boyutlu olarak modellenmiştir. Türbülans modeli olarak standart k-ε model, RNG k-ε model ve realizable k-ε model ayrı ayrı kullanılmıştır. Bu farklı durumlar için elde edilen binalar üzerindeki hız vektörleri, binalardan meydana gelen ısı transfer miktarları ve kullanılan türbülans modellerinin çözüm üzerindeki etkileri incelenerek değerlendirmeler yapılmıştır. Çalışmada kullanılan üç modelde de rüzgâr hızları arttıkça ve bina en-boy oranları azaldıkça, taşınım katsayısının artışına bağlı olarak binanın tüm yüzeylerindeki ortalama ısı akısının arttığı görülmüştür. Genel olarak, EBO’nun 1:1 olması durumunda üç model de yakın sonuçlar elde edilmiştir. Bina en-boy oranının azalmasıyla elde edilen sonuçlar farklılıklar göstermiştir. Sonuçlar arasındaki fark düşük hızlarda yok denilecek kadar az iken ortalama rüzgâr hızının artması ile bu fark belirginleşmiştir. EBO’ya ve binanın yüzeyine bağlı olarak ısı akısı-hız değişim eğrileri üç modelde de benzerlik göstermiştir.

Domestic and industrial energy requirements since the beginning of industrial revolution have been largely met by fossil fuels. This leads to a continuous increase in the Earth's atmosphere of carbon dioxide and other harmful components. Also fossil energy resources decreasing day by day and scientists have turned to new research. In this context alternative energy sources have an important role to reduce dependence on fossil fuels. One of the alternative energy sources is biomass and pellet fuel is one of them. In this study, combustion characteristics of pellet fuel in a model smoke tube boiler at different loading conditions were investigated numerically. As a Computational Fluid Dynamic (CFD) program FLUENT package program was used. Calculations were performed at two dimensional conditions. According to various loading conditions, temperature and stream function contours, velocity vectors, exhaust gas temperatures and efficiencies were investigated and results were discussed.