Browsing by Author "Mohammed, Hayder Noori"

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Open Access
Exergy efficiency for radiation heat transfer
(IOP Publishing, 2020) Mohammed, Hayder Noori; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Mohammed, Hayder Noori
One of the evaluation criteria for the performance of thermal processes is exergy analysis. Along with energy analysis, exergy calculations provide a clear and highly effective understanding of the performance of a system. Although exergy analysis has been extensively applied to many industrial processes, there are limited works for solar energy conversion systems that include the details of radiation transfer. The use of the Carnot efficiency expressions for calculating the exergy received from the thermal radiation source is questionable because it neglects the directional and spectral aspects of radiation heat transfer. In this study, the exergy efficiency calculations for radiation heat transfer in energy conversion systems are discussed. Comparisons of different expressions for exergy efficiency are presented, and the effects of source and sink temperature variations are explored.
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Radiative energy and exergy analyses of spectrally-selective surfaces for CSP systems
(Inderscience Enterprises Ltd., 2018) Mohammed, Hayder Noori; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Mohammed, Hayder Noori
This work presents a new methodology for calculations of spectral radiative energy and radiative exergy to evaluate the performances of concentrated solar power (CSP) systems. Spectral radiative properties and the operating temperature of selective surfaces, along with the temperature of the environment, are taken into account in analyses. The fundamental expressions needed for the spectral radiative energy and exergy analyses are introduced first. Then, the two approaches are used to assess the spectral performance of five selective coatings. The spectral analysis is performed in the wavelength range of 250 nm to 20,000 nm, while thermal analysis is carried out for the temperature range of 325 K to 800 K. NREL 6A coating was found to result in the highest radiative energy and radiative exergy for both efficiencies and gains, and for the best thermal stability compared to the other coatings.
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Solar radiation exergy and quality performance for Iraq and Turkey
(Inderscience Enterprises Ltd., 2018) Mohammed, Hayder Noori; Mengüç, Mustafa Pınar; Mechanical Engineering; MENGÜÇ, Mustafa Pınar; Mohammed, Hayder Noori
The present study is conducted with two primary objectives: First, a new formulation for the maximum efficiency of the solar radiation conversion is developed by considering the radiative energy transfer between two surfaces at different temperatures for a constant volume system. Second, a new methodology is introduced for estimating the exergy value of the monthly average daily horizontal global radiation, including many parameters, such as monthly average daily value of the horizontal extraterrestrial radiation, the number of sunny hours, the day length, the mean temperature and the mean wind velocity. Seven statistical parameters are used to validate the accuracy of all models. The results of the two new models are found to be more reliable than the results obtained from other models. This study, which was conducted for four locations in Iraq and Turkey. The findings would help in predicting the maximum availability of solar radiation based on weather parameters.
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Thermal and radiative energy/exergy analyses of parabolic trough collector systems
(2018-08) Mohammed, Hayder Noori; Mengüç, Mustafa Pınar; Mengüç, Mustafa Pınar; Başol, Altuğ; Ertunç, Özgür; Şendur, K.; Koşar, A.; Department of Mechanical Engineering; Mohammed, Hayder Noori
The concept of exergy is used to determine the maximum energy that can be extracted from a system. It is based on both the first and the second laws of thermodynamics and allows us to determine the irreversibilities throughout a process and the losses from the system. In this dissertation, the fundamentals of spectral radiative exergy are developed and applied to determine the maximum conversion of solar energy in concentrated solar power (CSP) systems. There are five primary objectives of this study. First, a new formulation is developed for the maximum efficiency of the solar radiation conversion by considering the radiative energy transfer between two surfaces at different temperatures for a constant volume system. Exergy of spectral radiative transfer is determined, and the formulation for the exergy efficiency maximization is presented in a direct and practical manner. For the calculation of maximum efficiency, the mean temperature of the environment and the sink temperature are used. Second, a new methodology is presented for spectral radiative energy and radiative exergy calculations to evaluate the performances of CSP systems. Spectral radiative properties and the operating temperature of selective surfaces, along with the temperature of the environment, are considered in these analyses. The fundamental quantities needed for the spectral radiative energy and radiative exergy formulations are introduced, and then the spectral performances of five selective coatings are assessed. The spectral analysis is performed in the wavelength range of 250 nm to 20,000 nm, while thermal analysis is carried out for the temperature range of 325 K to 800 K. The third objective is to introduce a new approach for estimating the exergy value of the monthly average daily horizontal global radiation, including several parameters, as the monthly average daily value of the horizontal extraterrestrial radiation, the number of sunny hours, the day length, the mean temperature and the mean wind velocity. Seven statistical parameters are used to validate the accuracy of all models. The concept is applied to four locations in Iraq and Turkey, to help predicting the maximum available solar radiation based on different weather parameters. The fourth objective is to outline a comprehensive energy analysis for a parabolic trough collector (PTC) system. The analysis considers all heat transfer modes, optical components, and the details of spectral absorption and reflection of solar radiation on the glass envelope. The energy performance of the PTC system is investigated using five gases in an annular space, five selective coatings of the absorber surface, and four common heat transfer fluids following a two-dimensional approach. A model is built using Engineering Equation Solver (EES). The results obtained are compared against the available results from experimental tests and analytical models. This analysis shows the effects of the properties of the absorbing gas, the selective coating and the working fluid on the energy performance of PTC as the key parameters of energy for various operating conditions. The fifth objective of the study is to establish a methodology to analyze PTC systems using the principles of spectral radiative exergy. The fundamental relations for spectral exergy analyses are derived starting from the first and second law of thermodynamics, and the key performance parameters, including exergy losses, destructions, consumption and efficiency are determined using the same parameters mentioned above in the fourth objective. It is noted that the exergy destruction is directly related to irreversibility throughout processes while the exergy losses are due to the thermal and optical losses. Based on these findings, an improvement of PTC design parameters are discussed.