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Abstract In this paper, energy and exergy analyses of the geothermal-based hydrogen production via thermochemical water decomposition using a new, four-step copper–chlorine (Cu–Cl) cycle are conducted, and the respective cycle energy and exergy efficiencies are examined. Also, a parametric study is performed to investigate how each step of the cycle and its overall cycle performance are affected by reference environment temperatures, reaction temperatures, as well as energy efficiency of the geothermal power plant itself. As a result, overall energy and exergy efficiencies of the cycle are found to be 21.67% and 19.35%, respectively, for a reference case.

Balıkesir Üniversitesi, Fen Bilimleri Enstitüsü, Makina Mühendisliği Ana Bilim Dalı ; Ülkemizde ve dünyada değişken soğutucu akışkan debili (VRF) iklimlendirme sistemlerinin kullanımı oldukça yaygınlaşmıştır. Ancak bu sistemlerde sadece ısıtma ve soğutma yükleri karşılanmakta olup taze hava ihtiyacı çoğunlukla ihmal edilmektedir. Bu problemi çözmek için taze hava ihtiyacı yoğun olan ortamlarda Isı Geri Kazanımlı Yerel Havalandırma (HRV) cihazları VRF ile birlikte devreye alınmıştır. Bu HRV cihazlarının ısıl etkinlikleri ila arasında değişebilmekte, bazı modellerde nem geçişine izin veren ısı değiştiriciler kullanılarak nem geri kazanımı da yapılabilmektedir. Son yıllarda HRV cihazlarına havadan havaya ısı pompası eklenmek suretiyle etkinlik değerleri arttırılmış, iç-dış hava değişiminden kaynaklanan konforsuzluklar ortadan kaldırılmıştır. Ayrıca küçük ortamlarda iç ısı yükünün bir kısmı da bu cihazlar ile karşılanabilir hale gelmiştir. Bu çalışmada ülkemizde üretilen bir ısı pompası destekli HRV cihazı Balıkesir yaz-kış koşullarında çalıştırılmış ve farklı sıcaklıklarda performans ölçümleri yapılmıştır. ; The use of variable refrigerant flow (VRF) air conditioning systems in our country and around the world has become very popular. However, in these systems while the heating and cooling loads are met and the fresh air need is often neglected. In order to solve this problem, fresh-air-intensive environments have been commissioned Heat Recovery Domestic Ventilation (HRV) devices together with VRF. The thermal efficiencies of these HRV devices can be range from 35% to 90%, and in some models moisture can be recovered by using heat exchangers that allow moisture transfer. In recent years, air-to-air heat pumps have been added to HRV devices to increase efficiency values and to eliminate the discomforts caused by indoor-outdoor air exchange. In addition, some of the internal heat load in small environments has become affordable with these devices. In this study, a heat pump assisted HRV which is produced in our ...

Assessing the impacts of climate change and land use/land cover changes on water resources within a catchment is essential because it helps us understand how these dynamic factors affect the quantity, quality, and availability of freshwater. This knowledge is crucial for making informed decisions about water management, conservation, and adaptation strategies, especially in regions facing increasing environmental uncertainties and challenges to water resource sustainability. In Pakistan’s Kunhar River Basin (KRB), this investigation explores the potential effects of shifting land use/land cover (LULC), and climate on stream flows. The SWAT (Soil and Water Assessment Tool), a semi-distributed hydrological model, and the most recent Coupled Model Intercomparison Project phase 6 (CMIP6) dataset from multiple global climate models (GCMs) were used to evaluate these effects. The temperature and precipitation data were downscaled using the CMhyd software; for both shared socioeconomic pathways (SSP2 and SSP5), the top-performing GCM out of four was required to produce downscaled precipitation and temperature predictions while taking future land use characteristics into account. The output from the chosen GCM indicated that by the conclusion of the 21st century, relative to the reference period (1985–2014), the study area’s average monthly precipitation, highest temperature, and lowest temperature will be increasing. Precipitation is anticipated to increase between 2015 and 2100 by 20.5% and 29.1% according to the SSP2 and SSP5 scenarios, respectively. This study’s findings, which emphasize the need for project planners and managers taking into account the effects of climate and land cover changes in their management techniques, show that climate change can have a significant impact on the changing seasons of flows in the Kunhar River basin.

Abstract In this study, the solar radiation variation on horizontal surfaces calculated by the ASHRAE clear-sky model is compared with measurements for Erzurum, Turkey (latitude: 39.55; longitude: 41.15; altitude: 1,869 m). A daily total solar radiation is obtained by integrating the hourly distribution. The results show that the ASHRAE clear-sky model is suitable to estimate hourly solar radiation in Erzurum, Turkey. Also, correlations giving the monthly average clear sky solar radiation on horizontal surfaces are developed. In addition, mean bias error, root mean square error, and t-statistic methods are used to indicate model performance.

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011 ; Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011 ; Bu çalışmada, Tekirdağ Malkara ve Çorum Bayat linyitleri ve biyokütle numuneleri olarak şeftali çekirdeği ile vişne çekirdeğinin; ayrıca, onların değişik oranlarda karışımlarının yanma davranımları incelenmiştir. Termogravimetrik analiz cihazında gerçekleştirilen yanma deneylerinin sonuçları, biyokütle ve kömür-biyokütle karışımlarının yanmasının uçucu madde ve yarıkokun yanmasını temsil eden iki farklı basamakta; kömür numunelerinin yanmasının ise tek basamakta gerçekleştiğini, Çorum Bayat kömürü ile biyokütle numuneleri arasında önemli bir etkileşimin olmadığını ancak, Tekirdağ Malkara kömürü ile biyokütle numuneleri arasında sinerjik etkileşimlerin olduğunu göstermiştir. Bu sonuç aynı biyokütle türlerinin farklı linyitler üzerinde değişik etkilerinin olabileceğini göstermiştir. Deneysel veriler kullanılarak BASIC dilinde yazılmış bir bilgisayar programı ile yapılan kinetik hesaplamalarda, kinetik parametrelerin numuneden numuneye ve kullanılan hesaplama yöntemine göre değiştiği belirlenmiştir. Uçucu maddenin çıkışı ve yanması için f(α) = (1-α)2/3, yarıkokun yanması için ise f(α) = (1-α) denklemlerinin uygun kinetik modeller olduğu bulunmuştur. ; In this study, combustion behaviours of Tekirdağ Malkara and Çorum Bayat lignites, peach stone and sour cherry stone and their blends in different ratios were investigated. The results of combustion experiments which have been carried out in the thermogravimetric analyzer showed that the combustion of the biomass and coal-biomass blends combustion occur in two steps; firstly the volatiles are released and burned, and secondly char combustion takes place. However, coal is characterized by only one combustion stage. No significant interactions were detected between the Çorum Bayat lignite and biomass, but synergistic interactions were detected between Tekirdağ Malkara lignite and biomass. This ...

Bu tezde üç farklı (Bi2O3)1-x(Ln2O3)x (Ln = Dy, Eu, Sm) ikili sistem araştırıldı. Ln2O3 oksijen bileşikleri x değeri 0,01-0,10 mol katkı aralığında olacak şekilde saf monoklinik Bi2O3 içerisine katı hal reaksiyonu yöntemiyle katkılandı. Reaksiyonlar farklı ısıl işlem basamaklarında, açık hava atmosferinde çalışan kül fırınlarında ve alümina krozeler içerisinde gerçekleştirildi.Bütün ikili sistemlerde baskın olarak beta-Bi2O3 tipi katı çözelti bölgeleri sentez edildi. Ln2O3 katkılanmış katı çözeltileri karakterize edebilmek için X-ışınları toz difraksiyon (XRD) analizi yöntemi kullanıldı. Isıl işlem sıcaklarının, süresinin, soğutma hızının ve Ln2O3 katkı miktarının katı çözeltilerin oluşumlarını ve özelliklerini etkilediği belirlendi.Deneysel verilere göre, elde edilen tetragonal tipi katı çözeltilerin kristal örgülerinde O(2-) iyonu boşlukları içermelerinden dolayı stokiyometrik olmayan karaktere sahip oldukları sonucuna varıldı. İletkenlik ölçümleri sonucunda elektrik iletkenliğin, sıcaklık ve Ln2O3 katkı miktarının artışı ile arttığı gözlendi.Çalışmada sentezi gerçekleştirilen katı elektrolit sistemlerinin bir çok endüstriyel uygulamalarda, örneğin katı oksit yakıt hücrelerinin (SOFC) üretiminde kullanılabilecekleri öngörüldü. In this thesis, three different (Bi2O3)1-x(Ln2O3)x binary systems have been investigated. 0,01<=x<=0,1 mole amounts of Ln2O3 compounds were doped in to the pure Bi2O3 by the solid state reactions. Heat treatments were applied to the synthesis reactions at various temperature ranges in air furnaces in alumina crucibles.Tetragonal beta-Bi2O3 solid solutions have been synthesized in all of binary systems as dominant phase. X-ray powder diffraction (XRD) has been used for characterization of the Ln2O3 doped solid solutions. We determined that the factors such as heat treatment temperatures and period, cooling rate and amount of Ln2O3 dopant affected the formation of solution reactions and their properties.Experimental results show that tetragonal type solid solutions are non-stoichiometric because of the O(2-) ion holes in their crystal structure. Conductivity measurements showed that the conductivity increases with increasing temperature and increasing Ln2O3 concentrations.The solid electrolytes we have synthesized in this study can be used in diverse industrial applications such as solid oxide fuel cells (SOFC). 212

Today, hydrogen fuel cells (HFCs) have become very popular in various applications because of their ability to be a clean energy source. One of the difficulties associated with HFCs is their sluggish response to variations in the load. This paper presents a nested control strategy based on a type-2 neuro-fuzzy controller (T2NFC) to improve the HFC's dynamic response in a hybrid stand-alone power network using HFC and battery. A system model is constructed using Matlab-Simulink. An interleaved converter is used to draw the maximal power from the HFC and reduce the ripple in the HFC's current. Two T2NFCs control DC voltage and battery charge/discharge current. The robustness of the T2NFC is evaluated for input disturbance, output disturbance, and both disturbances. The results show that the proposed control strategy is robust against input and output disturbances. Also, it provides improved dynamic response of the HFC, lower ripple in HFC current, and less overshoot or undershoot in DC voltage both in transient and steady-state. For step reference input, the proposed controller improves settling time of 24.06 % and overshoot of 59.55 % compared to the conventional PI controller. The results verify the effectiveness of the proposed controller under different operating conditions of hybrid stand-alone power network with fuel cell and battery.

It is well known that the energy consumption of refrigerating and air-conditioning units is as high as heating systems. It is also clear that cooling loads and availability of solar radiation are approximately in phase. Turkey is located in an ideal position to benefit from solar energy for not only water-heating but also cooling. The use of solar powered absorption refrigerating and air-conditioning systems will save energy, especially in the summer season. The contribution of these systems to the Turkish energy sector and, consequently, to the economy will be considerably high. In this study, a combined water-heating and cooling system based on absorption refrigeration was designed and constructed. The system consists of four flat plate collectors, an evaporator, an absorber, a generator, a condenser, a solution pump and two heat exchangers. Each part was custom designed to provide 4000 kcal/h cooling load. In this system, a mixture of R22 and DMETEG (DiMethyl Ether Tetra Ethylene Glycol) is used as the working fluid. The R22, which has a less damaging effect on the ozone layer compared to other CFCs, was employed as refrigerant. The thermodynamic results of the experimental system were compared with theoretical calculations, and a reasonably good agreement was found. The results show that the present system is efficient and effective.