Nanofluids are a novel class of heat transfer suspensions of metallic or nonmetallic nanopowders with a size of less than 100 nm in base fluids and they can increase heat transfer potential of the ...base fluids in various applications. In the last decade, nanofluids have become an intensive research topic because of their improved thermal properties and possible heat transfer applications. For comparison, an experiment using water as the working fluid in the heat exchanger without wire coils was also performed. Turbulent forced convection heat transfer and pressure drop characteristics of Al2O3-water nanofluids in a concentric tube heat exchanger with and without wire coil turbulators were experimentally investigated in this research. Experiments effected particle volume concentrations of 0.4–0.8 to 1.2–1.6 vol% in the Reynolds number range from 4000 to 20,000. Two turbulators with the pitches of 25 mm and 39 mm were used. The average Nusselt number increased with increasing the Reynolds number and particle concentrations. Moreover, the pressure drop of the Al2O3-water nanofluid showed nearly equal to that of pure water at the same Reynolds number range. As a result, nanofluids with lower particle concentrations did not show an important influence on pressure drop change. Nonetheless, when the wire coils used in the heat exchanger, it increased pressure drop as well as the heat transfer coefficient.
In this study, the parameters affecting the second law efficiency of panel radiators commonly used in heating systems were investigated. In the experimental system, a total of 6 pc-11 type panel ...radiators in 2 different heights and 3 different heights were used. In this context, the experiments were carried out by changing the feedwater temperature from 30 °C to 60 °C, with 10 °C increments and the flow rate from 2.5 l/min to 10 l/min, with 2.5 l/min increments. The experimental results obtained were analyzed factorially, and a mathematical model was developed between input parameters (feedwater temperature, flow rate, and radiator dimensions) and output parameters (total heat transfer coefficient and entropy generation). Using the novel model, the heat transfer and irreversibilities that can be obtained from the panel radiator in an operating system with known parameters can be calculated directly. This will provide a design methodology for researchers and engineers to be used for applications in the field. The total heat transfer coefficient and entropy generation from the panel radiator; radiator size increases with increasing flow rate and supply temperature; It has been observed that the total heat transfer coefficient decreases with the radiator size and temperature increase and increases with the increase in flow rate. The results showed an inverse relationship between the feedwater temperature and radiator size and the total heat transfer coefficient. It was also observed that the feedwater temperature was the most significant parameter on the total heat transfer coefficient. The main conclusion is that the most efficient energy utilization is provided by operating the heating systems at low temperatures with high flow rates. Consequently, this will lead to more efficient use of energy and reduced costs and environmental impact.
•A factorial experimental study was carried out.•The influence of parameters on model results were analyzed statistically.•A mathematical model was developed.•The parameters exerting the most influence on the total heat transfer coefficient were determined.•The parameters exerting the most influence on entropy generation were determined.
Radiation treatments, which are frequent and hidden hazards in imaging centers in hospitals, seriously affect employee health. In general, people think that there will be nothing to them because they ...do not know the damage of the radiation. It is not possible to stay away from radiation in some professions. For example, the radiology officials, their job is to identify the disease in people with radiographic method has no chance of dealing with radiation. That's why we need to do our job by getting enough information about radiation and its hazards, and by protecting ourselves and our environment from the dangers of radiation. Therefore, our study aimed to determine the level of information about employee safety of the health personnel working in public and private hospitals in Agri city centrum. Data was collected through a questionnaire by answering the questions of the personnel under observation in the imaging centers of hospitals. All official permits required for our work have been obtained from the necessary authorities. Results showed the inadequacy of knowledge related to ionizing radiation of the personnel, and the necessity of the implementation of radiological examinations by planning training for the safe use.
Bu çalışmada PEM yakıt hücresinin katot gaz akış kanalında oluşan sıvı su damlacıklarını gözlemlemek için bir tarafı şeffaf olan bipolar plaka tasarımı yapılmıştır. Katot gaz akış kanalının şeffaf ...olarak imal edilmesi yakıt hücresi içinde oluşan su damlacığının gözlemlenebilmesini mümkün kılacaktır. İmalatı yapılan bipolar plaka malzemesinin gözlem imkanı sağlamasının yanı sıra elektron iletimini de sağlaması gerekmektedir. Bu yüzden; şeffaf yakıt pili oluşturmak için 1 mm kalınlığında saç levha üzerine kanal tasarımı imal edilmiş ve saç levha üzerine 10 mm kalınlığında polikarbonat levha monte edilmiştir. Şeffaf olarak imal edilen yakıt pili deneysel performans sonuçları alüminyum levha üzerine imal edilen kanal tasarımının deneysel performans sonuçlarıyla kıyaslanmıştır. Sonuç olarak, kanal içeresindeki sıvı su oluşumunu gözlemlemek isteyen araştırmacılara şeffaf bipolar plaka imalatı ve imal edilen bipolar plakaların deneysel performansı hakkında çıkarımlarda bulunulmuştur.
•Comparative study of water-cooled cooler block arrangements led to optimized PVT-III layout using Response Surface Methodology (RSM).•Introduction of 0.3 wt% TiO2/nanofluid, notably enhancing ...electrical efficiency in PVT systems.•Positive correlation identified between rising nanofluid concentration and improved system performance.•Peak electrical efficiencies were attained under elevated solar irradiance and flow rates.
The current study presents a partitioned rectangular-shaped heat sink for improving the PVT system performance. The experiment was examined under various experimental parameters. Five cooler block types with different dimensions were arranged to share the same total contact area with the panel back surface. These cooler blocks were placed in different arrangements, namely (PVT-I, PVT-II, PVT-III, PVT-IV, PVT-V), and studied comparatively using water. The dimensions and numbers of each cooler block arrangement were altered, while maintaining the same surface area in contact with the photovoltaic panel. Through the response surface methodology (RSM) optimization, the optimal arrangement with the best performance was determined, and then TiO2/nanofluid was applied to that arrangement with different volumetric concentrations. Using water, the highest electrical and thermal efficiencies were obtained by case PVT-III with values of 19.39 % and 63.72 %, respectively. This was followed by PVT-II, PVT-V, PVT-I, and PVT-IV in that order for electrical efficiency; and at the same time by PVT-II, PVT-I, PVT-IV, and PVT-V in that order for thermal efficiency. The RSM method recommended the optimal arrangement case as case PVT-III. By using nanofluid in that case arrangement, the highest electrical efficiency value was recorded upon using 0.3 wt% and operating the system at 1.5 L/m and 900 W/m2. Regarding the thermal efficiency results, in that case, the highest and lowest values were recorded upon using 0.3 wt% and 0.1 wt%, respectively, with values of 72.49 % and 31.19 %. Increasing the volumetric concentrations positively reflected on the system's performance, resulting in high efficiencies being achieved. In addition, the highest electrical efficiencies were obtained at high levels of solar irradiance and flow rates.
•Response surface methodology was applied.•A mathematical model was developed.•The influence of parameters on model results were analyzed statistically.•The thermal and electrical efficiency of the ...PV/T system was calculated.•A partitioned cooler design was used.
Photovoltaic thermal systems (PVT) are systems that can convert solar energy into electricity and thermal energy simultaneously. In this study, the effect of nanofluids on the electrical and thermal efficiency of PVTs was investigated using the Response Surface Methodology (RSM). In the experimental study presently undertaken, SiO2 nanoparticles were suspended in deionized water, which was used as base fluid in 3 different volumetric ratios (0.1–0.2–0.3). A mathematical model has been developed to calculate the thermal and electrical efficiency of the PVT system using the RSM approach. In the RSM method, the flow rate of the nanofluid, the nanofluid volumetric concentration, and the solar radiation were determined as independent variables, and their effects on the thermal and electrical efficiency of PV/Ts were statistically investigated. The model presently developed was validated based on the analysis of variance (ANOVA). The most influential parameters affecting the electrical and thermal efficiencies have been found as radiation, flow rate and volumetric concentration, respectively. The variance between the mathematical models developed and the experimental results was measured in terms of thecoefficient of determination (R2), which was between 0.85% and 1.91% for the electrical efficiency and between −6.34% and 1.06%. for the thermal efficiency. As a result, the mathematical models developed for the electrical and thermal efficiencies of the PV/T system has been successfully verified based on the experimental outcomes.
Efficient use of energy is crucial to reduce the energy costs and also to reduce the greenhouse gases and the environmental pollution. The vast majority of energy consumption originates from heating ...needs. Therefore, efficient use of heating systems means less energy consumption, and also less emission to the environment. One fundamental way of reducing the energy used for heating purposes is to develop more efficient heating equipment. The main purpose of this study is to investigate the effects of panel radiator type, operating temperature and flow rate of heating systems on heat transfer coefficient and entropy generation. In the present study, a mathematical model was developed using the Response Surface Method to determine the total heat transfer coefficient and entropy generation for three different types of panel radiators (pc-11, pccp-22 and pccpcp-33). The accuracy of the model was tested through validation experiments and thus the model was validated. The radiators were then evaluated using the validated model by determining the total heat transfer coefficient and entropy generation for feed water temperatures of 40 °C, 50 °C and 60 °C and flow rates of 7.5, 5 and 2.5 l/min. As a result, the most important parameter on the total heat transfer coefficient (U) was found to be the volumetric flow rate while the most effective parameter on entropy generation (Sgen) was the number of panels.
•A correlation has been developed between the experimental inputs and outputs.•The most effective parameters for total heat transfer coefficient were determined.•The most effective parameters for entropy generation were determined.•The lower the temperature of system, the higher the total heat transfer coefficient.•The lower the temperature of system, the lower the entropy generation.
In this study, the effect of different nanofluids on the electrical and thermal efficiencies of photovoltaic thermal (PVT) systems was investigated experimentally and the variables affecting the ...efficiency were optimized by the Taguchi method. Experiments were carried out under laboratory conditions on the PVT system presently developed. In this study, a novel partitioned cooler block in the form of a rectangular prism was designed and used. Thus, the contact between the cooler block and the back surface of the PV panel and the associated PVT efficiency were increased. The following physical characteristics have been identified as the independent variables for the experiments carried out: SiO2/Water, Al2O3/Water and CuO/Water as different types of nanofluid, 0.1, 0.2 and 0.3 as volumetric concentration, 0.55, 1.1 and 1.65 lpm as volumetric flow rate and 300, 600 and 900 W/m2 as irradiance level. The reliability of the measurements made during the experiments was ascertained through the uncertainty analysis performed. The maximum electrical efficiencies of the PVT system for SiO2/Water, Al2O3/Water, and CuO/Water nanofluids were found to be 20.69 %, 21.18 %, and 20.77 %, and the maximum thermal efficiencies to be 57.06 %, 63.01 %, and 66.49 %, respectively. As the optimization method for determining the most optimum combination of variables, Taguchi analysis has been employed. As a result of this analysis, it has been shown that the most effective variables on the electrical efficiency of the PVT system are the irradiance, flow rate, volumetric concentration, and nanofluid type, respectively. On the other hand, regarding the thermal efficiency of the PVT system, the most effective variables are the irradiance, flow rate, nanofluid type, and volumetric concentration, respectively.
Photovoltaic (PV) cells have the capacity to absorb up to 80% of incoming solar radiation, converting a part of this radiation into electricity. The power output of PV panels are rated at 25 °C and ...an increase over this nominal operating cell temperature causes a decrease in the energy conversion efficiency of PV panels when compared to the rated power. With photovoltaic thermal (PVT) systems, it is possible to reduce the panel temperature and thus increase the electrical efficiency, and simultaneously obtain electrical and thermal energy. Various thermal collector designs used in PVTs have been studied experimentally and numerically in the literature. In the present study, a detailed literature review for such thermal collector designs was carried out and then a novel cooler design that is different from the designs existing in the literature was developed, manufactured and tested. The effect of the present design on the efficiency of the PVT system was analyzed experimentally and statistically. Experiments were designed by factorial design approach and carried out in laboratory conditions. Furthermore, a mathematical model was developed for the electrical and thermal efficiencies of the PVT system presently studied. Experiments were carried out at volumetric flow rates of 0.55 L/min, 1.1 L/min and 1.65 L/min and radiation values of 300 W/m2, 600 W/m2, and 900 W/m2. The highest electrical efficiency of the PVT system was 17.69% at 900 W/m2 and 1.65 L/min and the thermal efficiency 58.5% at 900 W/m2 and 0.55 L/min. When compared with the electrical efficiency of the conventional PV panel at 900 W/m2 radiation, it was observed that the electrical efficiency of the novel design increased by 4.67%. In addition, it was observed that the electrical efficiency decreased and the thermal efficiency increased with the increase of the panel temperature.
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•Full factorial method was applied.•The influence of parameters on results were analyzed statistically.•The thermal and electrical efficiency of the photovoltaic thermal system was calculated.•A novel partitioned cooler design was used.
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