The most popular method to benefit from the solar energy is to use solar water heating systems since it is one of the cheapest way to benefit from the solar energy. The investment cost of a solar water heating system is very low, and the maintenance costs are nearly zero. Using the solar energy for solar water heating (SWH) technology has been greatly improved during the past century. A storage tank is used in many solar water heating systems for the conservation of heat energy or hot water for use when some need it. In addition, domestic hot water consumption is strongly variable in many buildings. It depends on the geographical situation, also on the country customs, and of course on the type of building usage. Above all, it depends on the inhabitants’ specific lifestyle. For that reason, to provide the hot water for consumption at the desirable temperature whenever inhabitants require it, there must be a good relevance between the collectors and storage tank. In this paper, the optimum sizes of the collectors and the storage tank are determined to design more economic and efficient solar water heating systems. A program has been developed and validated with the experimental study and environmental data. The environmental data were obtained through a whole year of operation for Erzurum, Turkey.
In this study, the past investigations of the design criteria of vortex tubes were overviewed and the detailed information was presented on the design of them. Vortex tubes were classified and the type of them was described. All criteria on the design of vortex tubes were given in detail using experimental and theoretical results from the past until now. Finally, the criteria on the design of them are summarized.
The objective of this study was to develop suitable cooling systems for high-power multichip LEDs. To this end, three different active cooling systems were investigated to control the heat generated by the powering of high-power multichip LEDs in two different configurations (30 and 2 × 15 W). The following cooling systems were used in the study: an integrated multi-fin heat sink design with a fan, a cooling system with a thermoelectric cooler (TEC), and a heat pipe cooling device. According to the results, all three systems were observed to be sufficient for cooling high-power LEDs. Furthermore, it was observed that the integrated multifin heat sink design with a fan was the most efficient cooling system for a 30 W high-power multichip LED. The cooling system with a TEC and 46 W input power was the most efficient cooling system for 2 × 15 W high-power multichip LEDs.
In the present study, it was aimed to produce a fundamental i nformation and to investigate the effects of various design parameters on tube performance characteristics by setting up vortex tube experimental system in order to study the parameters predetermined for the design of vortex tubes and by conducting thermodynamic analysis. According to the findings of experiments, as the mass flow rate of cold flow increases (yc) temperature of cold flow also increases, while the temperature of warm flow increases approximately to yc = 0.6 and then decreases. Increases in inlet pressure, inlet nozzle surface and diameter of the cold outlet orifice increased temperature differences between cold and warm flows. Tube with L/D = 10 showed better performance than with L/D = 20. The finding that irreversibility parameter is very close to critical threshold of irreversibility proved that process in vortex tube is considerably irreversible. Coefficient of performance (COP) values in vortex tube were much lower than other heating and cooling systems. This situation may show that vortex tubes are convenient in the processes where productivity is at the second rate compared to other factors.
Energy is an essential factor in overall efforts to achieve sustainable development. Countries striving to this end are seeking to reassess their energy systems with a view toward planning energy programs and strategies in line with sustainable development goals and objectives. Turkey's demand for energy and electricity is increasing rapidly. Since 1990, energy consumption has increased at an annual average rate of 4.3%. Turkey is heavily dependent on expensive imported energy resources that place a big burden on the economy and air pollution is becoming a great environmental concern in the country. As would be expected, the rapid expansion of energy production and consumption has brought with it a wide range of environmental issues at the local, regional and global levels. With respect to global environmental issues, Turkey's carbon dioxide (CO 2 ) emissions have grown along with its energy consumption. States have played a leading role in protecting the environment by reducing emissions of greenhouse gases (GHGs). In this regard, renewable energy resources appear to be the one of the most efficient and effective solutions for clean and sustainable energy development in Turkey. Turkey's geographical location has several advantages for extensive use of most of these renewable energy sources. This article presents a review of the potential and utilization of the renewable energy sources in Turkey.
Birçok mühendislik uygulamalarında kullanılan sistemler, işlevleri gereği ısı üretmektedirler. Isı üreten sistemlerin verimli bir şekilde çalışması ve tahrip olmaması için üretilen ısının sistemlerden etkili ısı transfer mekanizmaları ile uzaklaştırılması gerekmektedir. Bu çalışmada, üzerine yarıklar açılmış boru tipi elemanların ısı transferi ile akım karakteristiklerini belirlemeye yönelik deneysel bir çalışma yapılmıştır. Tasarım parametresi olarak kanatçık yüksekliği (H) için 30, 45 ve 58 mm, akış yönünde kanatlar arası mesafe (S y ) için 18, 27 ve 36 mm, yarık sayısı (N) için 1, 2 ve 3 ve Reynolds sayısı (Re) için 8000, 16000 ve 25000 değerleri seçilerek Yanıt Yüzey Yöntemi yardımıyla Nusselt sayısı (Nu) ve sürtünme faktörü (f) için matematiksel modeller kurulmuştur. Deneysel sonuçlar, bu çalışmada kullanılan modelin Nusselt sayısını ve sürtünme faktörünü belirlemek için kullanılabileceğini göstermektedir. Boru tipi kanatçıklara açılan yarıkların ısı transferini iyileştirmede kayda değer bir etki sağlandığı gözlemlenmiştir. Elde edilen sonuçlardan Reynolds sayısının Nusselt sayısı üzerine, kanat yüksekliğinin ise sürtünme faktörü üzerine en etkili parametre olduğu belirlenmiştir.
Renewable energy is a key for sustainable development all over the world and renewables used in many areas including water heating. For water heating, among many options, electrical and solar energy can be used to assist heat pumps. This study explores usage of photovoltaic and thermal collectors to assist heat pump for supplying DHW in an efficient way. Firstly, experimental tests have been performed in a climatic room and using the experimental results, the simulation model developed in TRNSYS software has been validated. Four different scenarios were created based on collector type and number supporting the DHW heat pump system and were compared with each other in terms of energy efficiency. For systems supported by heat pump and maximum of three collectors, the best options saved 564.71 kWh-e for one thermal collector and 1051.77 kWh-e for two collectors, one thermal and one photovoltaic. When the heat pump is supported by three collectors, the configuration with one thermal and two photovoltaic collectors, which is the best option, produces 107.39 kWh-e more energy than the energy consumed. Consequently, this study clearly illustrated that the right combination of thermal and photovoltaic collectors significantly reduces the energy consumption of DHW solar heat pump systems.
In the applications of solar energy, the solar radiation data and their components in a region must be known for the design of a system. In the locations where no solar radiation data is available, this parameter can be determined by performing a reasonable correlation. In the study, the models of global solar radiation on the horizontal surface in the literature are investigated, and new empirical models based on the sunshine hour data for Erzincan, Turkey are developed. In order to indicate the performance of the models, the statistical test methods of mean bias error (MBE), root mean square error (RMSE) and mean relative error (MRE) are used. The results obtained indicate that the correlations developed in the study predict the global solar radiation reasonably well for the future projections. Key words: Solar energy, global solar radiation, sunshine hours, correlation, empirical models.
In this research, an exemplary study has been conducted in order to draw attention to the importance of evaluating the existing potential on the roofs of buildings. This research offers an evaluation of the existing solar energy and rainwater potential on the total roof area of the buildings in the Izmit district, which is a central district of Kocaeli province, one of the busiest centers of industry in Turkey. The calculations in this study were carried out by using the data obtained from various institutions. As a result of these calculations, the ratio of electrical energy that can be provided with photovoltaic systems on roofs to meet the annual electricity consumption of the district was found to be 203.581%, and the annual solar energy utilization rate for a family of 4 to bring 240 liters of daily use water temperature to 60°C with an 8 m2 collector area was calculated as 66%. In addition, the ratio of rainwater that can be collected from the total roof area of the existing buildings in the district to meet the domestic water consumed by the district was found to be 33.27%.
No abstract is provided for this article.
Cavitation is a major problem in pump operation because this phenomenon may lead to hydraulic performance loss, increased noise levels, and various types of instabilities. Therefore, fast and robust calculation methods that the industry can confidently use to predict cavitation are being actively studied. In the present work, the cavitation performance of pumps designed at two specific speeds is studied numerically and experimentally. Net positive suction head (NPSH) measurements for the pumps are performed over their operating ranges. Moreover, Q-NPSH3 and head drop curves are obtained for the pumps at metric specific speeds of 22.4 (rotating at 2950 rpm) and 12.5 (rotating at 1475 rpm), respectively. Cavitation is visualized by a stroboscopic light source and recorded at various NPSH levels for three different flow rates. The relationship between cavity length and head drop is revealed. The Singhal [18] model, a homogeneous mixture cavitation model, is typically used in numerical calculations. A turbulent viscosity correction for the multiphase calculations of cavitating flow around hydrofoils is proposed in the literature. In the present work, this correction is applied to modify the Singhal [18] cavitation model, and the head drop curve of the pump with ns = 22.4 is computed using this modified model. Consequently, the compatibility between the numerical and experimental results is found to improve. Accordingly, the cavitation calculations for the pump with ns = 12.5 are performed using the modified model. The computed cavitation structures at various points on the head drop curves are compared with experimental images. Geometrically similar forms are achieved.
