Performance comparison of plate heat exchangers designed using Taguchi method and computational fluid dynamics

In this study, thermal and hydraulic performances of cross flow plate heat exchangers, designed using Taguchi method and Computational Fluid Dynamics, in a small capacity (50-200 m(3)/h) air to air heat recovery device were compared. The plate heat exchangers, which are designed to have high flow effectiveness and sensible effectiveness, number of sub-channel, channel height, average air velocity and sheet material variables were determined. The equations for flow effectiveness and recovered thermal power, including variables and second order interactions of variables, were derived by multiple regression analysis for flow effective and thermally effective plate heat exchangers. The performances of 3-dimensional plate heat exchangers using finite volume based ANSYS/Fluent were compared in different volumetric flow rates. The channel height and average air velocity were determined as the most influential variables in the design of plate heat exchanger. It was found that on average 50% more heat was recovered and thermal effectiveness was on average 35% higher in the thermal effective model, while pressure drop was on average 2.5 times less and flow effectiveness was on average 10% higher in the flow effective model When the recovered thermal power at the fresh side and flow effectiveness are evaluated together, the optimum average flow velocities for both models was determined to be range of 1.5-2 m/s (similar to 90 divided by similar to 110 m(3)/h)

Yüzey modifikasyonu yardımıyla CdS toz bazlı hibrit güneş pillerinde performans artışı

The effects of surface modification of CdS through organic Eosin-Y, indoline D205, and Ru-based complex N719 and N3 dyes on CdS-based hybrid solar cells were studied. Chemical bath deposition (CBD) and doctor blade methods were in turn employed to fabricate the CdS specimens on Indium-Tin Oxide (ITO) covered glass substrates. P3HT material with and without dye coatings was covered through a spin-coater on the surface of CdS specimens. Ag paste was then deposited on the surface of P3HT to obtain hybrid solar cells. Structural analysis indicated that CdS powders showed a cubic growth with the preferred orientation of (111). Morphological analysis demonstrated that CdS powders exhibited hierarchical morphology and the morphology turned to granular structure with some porosity upon deposition of both N3 dye and P3HT layers. Absorption plots indicated that Eosin-Y dye loading led to a rise in the absorbance values of CdS specimens. After dye loading, photoluminescence data of CdS-based heterostructure illustrated a decrement in the luminescence intensity, implying that effective exciton dissociation was obtained. Current density-voltage (J-V) characteristics of the hybrid solar cells depicted that the best overall efficiency was observed for Eosin-Y-modified cell as 0.135%. This proved that surface modification by Eosin-Y dye led to a better interfacial contact between CdS and P3HT bilayer due to the enhancement in the charge separation.CdS-tabanlı hibrit güneş pillerinde, CdS'nin yüzey modifikasyon etkileri organik Eosin-Y, indolin D205 ve Ru bazlı N719 ve N3 boyaları vasıtasıyla incelendi. CdS örneklerini İndiyum-Kalay Oksit (ITO) kaplı cam altlıklar üzerinde büyütmek için, sırasıyla kimyasal banyo çökeltme (CBD) ve doktor bıçak yöntemleri kullanıldı. Boya kaplamaları olan ve olmayan CdS örneklerinin yüzeyine P3HT materyali, spin kaplama (spin-coater) cihazı yardımıyla kaplandı. Devamında Ag pasta, hibrit güneş pillerini tamamlamak için P3HT yüzeyine çökeltildi. Yapısal analiz, CdS tozlarının kübik yapıda ve (111) tercihli yönelime sahip olduğunu gösterdi. Morfolojik analiz, CdS tozlarının hiyerarşik morfolojide olduğunu ve morfolojinin hem N3 boyası hem de P3HT tabakasının çökeltilmesiyle birlikte taneli ve gözenekli yapıya döndüğünü gösterdi. Soğurma (absorbsiyon) grafikleri, Eosin-Y boya kaplamasının CdS örneklerinin soğurma değerinde bir artışa yol açtığını gösterdi. Boya kaplamasının, CdS tabanlı heteroyapının fotolüminesans şiddetinde azalma oluşturması, etkin bir eksiton ayrışması elde edildiğini ortaya koymaktadır. Hibrit güneş pillerinin akım yoğunluğu-voltaj (J-V) karakteristiklerinden, Eosin-Y modifikasyonlu güneş pilinin veriminin % 0,135 olarak en yüksek değerde olduğu tespit edildi. Bu durum, Eosin-Y boyası ile yapılan yüzey modifikasyonunun, yük ayrışmasında oluşturduğu iyileşmeden dolayı, CdS ve P3HT ikili yapısının arasında daha iyi bir ara yüzey teması sağladığını ispatlamaktadır

Nanoakışkanlı levhalı ısı değiştirici kanallarında ısı geçişinin deneysel ve sayısal incelenmesi

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Bu çalışma, nanoakışkanlı contalı levhalı ısı değiştirici kanallarında taşınımla ısı geçişi ve basınç düşüşünü deneysel ve sayısal olarak incelemek amacıyla yapılmıştır. Deneysel ve sayısal çalışmalarda, balıksırtı şeklinde geometriye sahip dalgalı yüzeyli ısı değiştirici levhaları ve Al2O3/su (40 nm) nanoakışkanı kullanılmıştır. Deneyler süresince ısıyı veren sıcak akışkanın kütlesel debisi 90 kg/h, ısı değiştiricisine giriş sıcaklığı 40 oC'de sabit tutulmuştur. Isıyı alan soğuk akışkanın (nanoakışkan) ise kütlesel debisi 90, 120, 150, 180, 240 ve 300 kg/h debi aralığında değiştirilmiş ve ısı değiştiricisine giriş sıcaklığı 17,5 oC'de sabit tutulmuştur. Levhalı ısı değiştirici kanalları için oluşturulan iki boyutlu (2B) ve üç boyutlu (3B) modellerin, ANSYS-Fluent yazılım (paket) programı ile sayısal çözümlemeleri de yapılmıştır. Sayısal çözümlemelerde tek fazlı (single phase) ve çift fazlı (mixture, Euler) yaklaşımları kullanılmıştır. Sayısal çözüm ile elde edilen ısı taşınım katsayısı ve sürtünme faktörü değerleri, deneysel sonuçlarla karşılaştırılarak sayısal sonuçlar doğrulanmıştır. Deneyler ve sayısal çözümlemeler, hacimsel oranları % 0,25, % 0,5, % 0,75 ve % 1 olan nanoakışkanları için yapılmış ve Reynolds sayısı 500-2000 aralığında seçilmiştir. Nanoakışkanın hacimsel oranı ve kütlesel debisiyle ısı taşınım katsayısının arttığı ancak sürtünme faktörünün azaldığı deneysel olarak belirlenmiştir. Isı geçişinde suya göre iyileşme en küçük hacimsel oran için ortalama % 7,72 en yüksek hacimsel oran için ise ortalama % 42,4 belirlenmiştir. Nanoakışkanlı ısı geçişi için literatürdeki sonuçlar dikkate alındığında, çalışmalarımız sırasında elde edilen deneysel ve sayısal sonuçların uygun olduğu görülmektedir.The aim of this study is to investigate convection heat transfer and pressure drop experimentally and numerically by using nanofluids in the gasket plate heat exchanger channels. In the experimental and numerical studies, chevron type corrugated plates in the plate heat exchanger and Al2O3/water (40 nm) as nanofluids have been used. During the experiments, the mass flow rate of the hot fluid which loss heat was kept constant at 90 kg/h while the heat exchanger inlet temperature was kept constant at 40 °C. In additional to the mass flow rate of the cooling fluid (nanofluids) that the inlet temperature was kept constant at 17.5 °C has been changed as 90, 120, 150, 180, 240 and 300 kg/h. Numerical analysis of the two-dimensional (2D) and three-dimensional (3D) models set up for plate heat exchanger channels has also been carried out using ANSYS-Fluent software (package) programme. Single phase and two phase (mixture, Eulerian) approaches have been used in the numerical analyzes. In order to verifiy the numerical result of convection heat transfer coefficient and friction factor values obtained with the numerical analyzes were compared with the results of the experiments. Experiments and numerical analyzes were carried out in the nanofluids volume fraction of 0.25 %, 0.5 %, 0.75 % and 1 % and in the range of 500-2000 Reynolds number. In the experiments, it has been observed that increases with the volume fraction and mass flow rate of the nanofluids the convection heat transfer coefficient increases while the friction factor decreases. The enhancement heat transfer has been determined to be about 7.72 % for the minimum volume fraction while it is about 42.4 % for the maximum volume fraction compared to water. Upon taking the results of the heat transfer using nanofluids in the literature into consideration, experiments and numerical results obtained have been found out to be coherent

Performance analysis of Germencik Geothermal Power Plant

The objective of this study is to calculate the efficiency of exergy in Germencik Geothermal Power Plant, which has a power output of 47.4 MWe. As being the largest one in Turkey, this plant is operated by double-flash system which is based on the method of analysis of energy and exergy to evaluate its performance. The exergy analysis has been applied to the whole plant considering the first and the second laws of thermodynamics for each equipment. In this study, by using the actual data values the losses of exergy have been determined and the flow diagram of exergy has been illustrated. When making calculations, we have accepted dead state temperature as 15 degrees C, and dead state pressure as 101.325 kPa s. The plant has 7 production and 6 reinjection wells. From these production wells, geothermal fluid reaches the plant at an average temperature ranging from 194 degrees C to 214 degrees C, pressure of 23 bars-30 bars and a total flow rate of 688.87 kg/s. An exergy input of 134,124 kW is obtained from these wells. The largest exergy input of 36,395 kW is obtained from OB-14 and this accounts for 27.1% of total exergy input. Moreover, major exergy losses and their exergy input account for 3.34% (4478 kW) for valves, 22.72% (30,477 kW) for high and low-pressure separation process during the decomposition of geothermal fluid, 5.1% (6837 kW) for turbine-generator during the conversion of steam into mechanic work, 9.41% (12,622 kW) for cooling tower, 5.53% (7414 kW) for internal use, and finally 22.68% (30,415 kW) for reinjection wells. Additionally, the second law efficiency of turbine-generator has been found to be 87.4% and the second law efficiency of overall plant has been found to be 3534%. The obtained results have been given in tables and the largest loss of exergy has been determined to occur in separators. (C) 2013 Elsevier Ltd. All rights reserved

The coexistence of focal segmental glomerulosclerosis with carcinoid syndrome: A case report

Carcinoid tumor is originated from neuroendocrine tumorfamily and a rarely presents in humans. Membranous andmembrano-proliferative glomerulonephritis were rarelyreported with presence of carcinoid tumors. However,the coexistence of focal segmental glomerulosclerosis(FSGS) with carcinoid syndrome have not been definedpreviously. We herein present a firs case report of FSGSduring follow up of carcinoid syndrome.Key words: Carcinoid sydrome, focal segmental glomerulosclerosis,glomerulonephriti

A atudy on hydrothermal grown CdS nanospheres: effects of Cd/S molar ratio

The study reports the influences of altering of Cd/S molar ratio on some physical properties of hydrothermal grown CdS nanospheres. Cd/S molar ratios were chosen as 1:0.5, 1:1, 1:2, 1:3 and 1:4 in the stock solution. X-ray diffraction (XRD) data showed the occurrence of nano-amorphous CdS structure. Scanning electron microscopy (SEM) conclusions illustrated that increasing Cd/S molar ratio up to 1:3 caused a growth in the sphere size whereas further rising of Cd/S molar ratio led to smaller sphere size. The presence of Cd and S atoms in CdS structure was approved by Energy dispersive x-ray spectroscopy (EDS) analysis. Optimum transparency was found by Cd/S molar ratio of 1:3. Band gap scores of CdS nanospheres were determined to be above 2.60 eV that was bigger than bulk CdS (2.42 eV) because of quantum confinement effect. Photoluminescence (PL) results showed that a gradual decrease in each peak was attained upon increasing Cd/S molar ratio, which could be due to the formation non-radiative recombination phenomenon. Electrical data demonstrated that CdS nanosphere having Cd/S molar ratio of 1:1 exhibited the best carrier density (1.48X1015cm-3) and resistivity (1.27X103 ?.cm) values. Thus, it can be deduced that Cd/S molar ratio of 1:3 was obtained to be optimum one since it possesses both bigger sphere size and better transparency, facilitating the effective use of CdS nanospheres in the solar cells

Fabrication of CdS nanospheres-based hybrid solar cells having increased efficiency

The impact of surface modification through diverse dyes (Eosin-Y, D205, N719 and N3) on structural, morphological, optical, and electrical properties of CdS/P3HT hybrid solar cells is studied. X-ray diffraction (XRD) pattern shows that CdS nanospheres have a hexagonal structure with a preferential orientation of (002) with respect to indium tin oxide (ITO) coated glass slide. Scanning electron microscopy (SEM) results indicate that compact and dense spherical morphologies of CdS occurred, and the P3HT layer also consisted of small spherical grains. The bandgap of CdS is found to be 2.52 eV according to Tauc's plot analysis. Absorption spectra demonstrate that interfacial modification via each dye leads to an increase in the absorption in the wavelength range of 300-1000 nm. Photoluminescence (PL) data prove that surface modification of CdS nanospheres with diverse dyes causes a decrease in the spectral intensity of PL curve, implying that efficient exciton separation is taking place upon dye loadings. Fabricated devices with and without modification show photovoltaic effects that can be seen from current density-voltage (J-V) curves obviously, and the highest power conversion efficiency (PCE) is obtained as 0.881% for N719-modified (ITO/CdS/N719/P3HT/Ag) device (almost 70-fold of pristine one) with a short-circuit current density (J(sc)) of 2.878mA/cm(2) and open-circuit voltage (V-oc) of 0.92V, respectively. This enhancement can be attributed to a better surface area between CdS and P3HT after dye modification

IOP Conference Series-Earth and Environmental Science

In this study, the availability of waste heat in a power generating capacity of 47.4 MW in Germencik Geothermal Power Plant has been investigated via binary geothermal power plant. Refrigerant fluids of 7 different single components such as R-134a, R-152a, R-227ea, R-236fa, R-600, R-143m and R-161 have been selected. The binary cycle has been modeled using the waste heat equaling to mass flow rate of 100 kg/s geothermal fluid. While the inlet temperature of the geothermal fluid into the counter flow heat exchanger has been accepted as 110 degrees C, the outlet temperature has been accepted as 70 degrees C. The inlet conditions have been determined for the refrigerants to be used in the binary cycle. Finally, the mass flow rate of refrigerant fluid and of cooling water and pump power consumption and power generated in the turbine have been calculated for each inlet condition of the refrigerant. Additionally, in the binary cycle, energy and exergy efficiencies have been calculated for 7 refrigerants in the availability of waste heat. In the binary geothermal cycle, it has been found out that the highest exergy destruction for all refrigerants occurs in the heat exchanger. And the highest and lowest first and second law efficiencies has been obtained for R-600 and R-161 refrigerants, respectively

The Seroprevalence of Hantavirus in Patients with Chronic Renal Failure in Two Provinces of Central Anatolia

Amaç: Çeşitli çalışmalarda hantavirus seropozitifliğiyle kronik böbrek yetmezliği arasında ilişki olduğu bildirilmiştir. Bu çalış- manın amacı Ankara ve Kırıkkale illerinde yaşayan son dönem böbrek yetmezliği nedeniyle hemodiyaliz ve sürekli ayaktan periton diyalizi uygulanan hastalarda hantavirus antikor sıklığının araştırılmasıdır. Yöntemler: Çalışmaya hemodiyaliz ya da sürekli ayaktan periton diyalizi tedavisi uygulanan 68 kadın (yaş ortalaması 48) ile 57 erkek (yaş ortalaması 45.8) olmak üzere kronik böbrek yetmezliği olan toplam 125 hasta ile 24 kadın (yaş ortalaması 55.9) ve 23 erkek (yaş ortalaması 49.5) olmak üzere 47 sağlıklı birey dahil edildi. Hantavirus IgM ve IgG antikorları ELISA yöntemiyle araştırıldı. Bulgular: Hastaların ve kontrol grubundakilerin hiçbirinde hantavirus IgM ve IgG pozitifliği saptanmadı. Sonuçlar: Hantavirus infeksiyonunun kronik böbrek yetmezliğindeki rolünün belirlenebilmesi için, endemik bölgelerdeki hasta grubunda daha fazla sayıda olguyla yapılacak kontrollü çalışmalara gereksinim vardırObjective: The association between hantavirus seropositivity and chronic renal failure has been reported in several studies. The objective of this study is to investigate the prevalence of hantavirus antibodies among patients with end-stage renal failure undergoing hemodialysis and continuous ambulatory peritoneal dialysis in Ankara and Kırıkkale cities. Methods: A total of 125 patients including 68 females (mean age, 48 years) and 57 males (mean age, 45.8 years) with chronic renal failure undergoing hemodialysis or continuous ambulatory peritoneal dialysis, and 47 healthy subjects including 24 females (mean age, 55.9 years) and 23 males (mean age, 49.5 years) were included in the study. Hantavirus IgM and IgG antibodies were investigated by ELISA. Results: Hantavirus IgM and IgG positivity were not detected in any of the patients and control group. Conclusions: Controlled studies performed on endemic patient groups including more cases are required to establish the role of hantavirus infection in patients with chronic renal failure