Energy
M. Maghsoudizadeh; M. Ameri; E. Jahanshahi Javaran; A. MotamedSadr; A. A. Feili Monfared
Abstract
In recent years, the use of renewable energy sources and investigation on renewable energy have significantly grown. In this research, parabolic trough and linear Fresnel collectors, which are widely used in the field of solar energy, have been investigated from the point of view of exergy. First, the ...
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In recent years, the use of renewable energy sources and investigation on renewable energy have significantly grown. In this research, parabolic trough and linear Fresnel collectors, which are widely used in the field of solar energy, have been investigated from the point of view of exergy. First, the energy balance equations for different components of the collector were solved using numerical methods and the temperature distribution in each component of the collector was obtained. Then the values of exergy destruction in each component of the system were calculated. The comparison of the results obtained in the present work with the results of the previous research showed a good agreement. The results showed that the exergy efficiency in the parabolic trough collector is approximately 1.5 times that of the linear Fresnel reflector. Also, changes in exergy efficiency, exergy destruction of the whole collector, output exergy cost and CO2 emission with increasing solar radiation intensity and fluid mass flow rate for both collectors have been compared and investigated.
Energy
M. Esmaeili Shayan; M. R. Hayati
Abstract
Having kilometers of asphalt road, yet with this heat going to waste, an attempt has been made in this research to extract the road's renewable energy heat. The purpose of the experiment is to compare the energy and exergy efficiency of various materials of asphalt solar water heaters (ASWH), as well ...
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Having kilometers of asphalt road, yet with this heat going to waste, an attempt has been made in this research to extract the road's renewable energy heat. The purpose of the experiment is to compare the energy and exergy efficiency of various materials of asphalt solar water heaters (ASWH), as well as heat transmission through the water tube and how friction affects exergy destruction. The water flow rate of one ASWH was 0.01 kg/s, while that of the other was 0.02 kg/s. Each ASWH has an area of 0.5 square meters. The copper tube is buried 10 mm deep in the asphalt. 15 degrees is the angle of inclination. The results indicate that the energy and exergy efficiencies are reasonably high for the water flow rate of 0.02 kg/s. Depending on the water flow rate, asphalt temperature, and sunlight intensity, the energy and exergy efficiencies changed from 32% to 65% and 5.8% to 16%, respectively. The water flow rate is an essential parameter for estimating the internal convective heat transfer coefficient and Reynolds number in order to calculate the friction factor in the copper tube based on internal convection heat transfer. In contrast, the friction factor is a consequence of the pressure loss and exergy degradation induced by friction.
S. N. Nnamchi; O. A. Nnamchi; E. O. Sangotayo; S. A. Ismael; O. K. Nkurunziza; V. Gabriel
Abstract
The design of a flat-plate solar collector (FPSC) is accomplished by multiple input multiple output (MIMO) design technique. The design variables (absorber, fluid and glass temperatures; length, width, height of the FPSC) were the unknown variables in the commensurate thermal balance equations based ...
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The design of a flat-plate solar collector (FPSC) is accomplished by multiple input multiple output (MIMO) design technique. The design variables (absorber, fluid and glass temperatures; length, width, height of the FPSC) were the unknown variables in the commensurate thermal balance equations based on; component, overall and yardstick thermal balance on the FPSC. Then, simulator matrices were setup comprising of coefficient and column matrices of design functions. The elements of the coefficient matrix were the partial derivatives of the design functions with respect to the design variables. Besides the convective and radiative heat transfer coefficients were function of the design variables. The initial values of the design variables (307K, 334.5K, 368K, 2 m, 1 m, and 0.045m, respectively) were set, at the seventh iteration, the output variables (306.9K, 339.15K, 368.1K, 2.01m, 1.005m, 0.04m, respectively) merged as the design functions ® 0 with insignificant change in the design variables. The output results were used to simulate FPSC, to track its responses to changes in the physical conditions, the stimulation revealed some constraints in the design of the FPSC, which is vital information for the overall optimization of the FPSC. The design yardsticks; the thermal efficiency (0.76) and the effectiveness (0.4) are quite pragmatic. This shows that MIMO technique to thermal system design is effective as convergence among the design variables was sought. Moreover, MIMO considered all thermal losses instead of basing the yardsticks on top loss overall transfer coefficient alone; thus, neglecting sidewalls and base losses. Moreover, the advent of connecting box prepares the preheating unit for high temperature drying (> 150 oC) on integration with a reheating unit.
B. G. Emyat
Abstract
The main aim of this study is to use waste heat for cooling effect production from cement rotary kiln shell by applying vapor absorption refrigeration system. The plant has performance to manufacture 2000 tons of clinker per day. Energy and exergy analysis has been performed to assess first and second ...
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The main aim of this study is to use waste heat for cooling effect production from cement rotary kiln shell by applying vapor absorption refrigeration system. The plant has performance to manufacture 2000 tons of clinker per day. Energy and exergy analysis has been performed to assess first and second law efficiencies and rotary kiln is used as a control volume on dry type cement plant. Result shows that about 4.3MW energy is lost from kiln shell. From the analysis, 31.13% total exergy is wasted to the surrounding in case of pre-calcining and pre-heating of raw material. The overall result for exergy analysis of kiln indicates 59.46% of irreversibility and also the first and the second law efficiency of the rotary kiln is 53.39% and 40.54%, respectively. By using convective mode of heat transfer about 11% of energy is extracted by the generator for production of cooling effect which is wasted from kiln shell. About 300kW cooling effect is produced in the evaporator by applying absorption cycle with system performance 0.67 and exergetic efficiency 87%. From heat recovery there is direct savings by reducing fuel consumption and indirect savings by decreasing environmental impact. Hence, use of waste heat results in reduction of thermal pollution and energy consumption in auxiliary equipment.
S. A. Azeez; U. Garba; B. G. Danshehu
Abstract
Hydrogen production from glycerol via autothermal reforming (ATR) has been widely investigated. However, little is known about the influence of impurities in glycerol on thermodynamic performance of the process. This study focused on the effects of impurities in glycerol on hydrogen productivity, energetic ...
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Hydrogen production from glycerol via autothermal reforming (ATR) has been widely investigated. However, little is known about the influence of impurities in glycerol on thermodynamic performance of the process. This study focused on the effects of impurities in glycerol on hydrogen productivity, energetic and exergetic efficiencies. The model of the entire process was simulated under thermoneutral condition in Aspen HYSYS using pure glycerol (PG) and crude glycerol (CG) as feeds. The two cases were optimized for maximum hydrogen production. From the optimized results, the hydrogen production per mole of the feed was 4.937 and 6.160 for the case of PG and CG, respectively. The thermal and exergetic efficiency of PG as feed were computed as 79.51% and 57.04% while that of CG were obtained to be 77.7 and 54.08%, respectively. The exergy destroyed to produce 1 mole of H2 was found to be 133.5kJ and 157.3kJ for the case of PG and CG, respectively. It could be concluded that the presence of other constituents in CG contributed to increase in hydrogen productivity by increasing the energy demand of the plant but due to increase in both energy and exergy input, they decrease both the thermal and exergetic efficiencies.
F. Chabane; E. Sekseff
Abstract
Our work an experimental study of a double-glazed solar air collector in the BISKRA site. The main objective of our work minimized thermal losses forward. The experimental model used is based on the addition of second glass and the increase in distance between the two panes. The study was carried out ...
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Our work an experimental study of a double-glazed solar air collector in the BISKRA site. The main objective of our work minimized thermal losses forward. The experimental model used is based on the addition of second glass and the increase in distance between the two panes. The study was carried out for the comparison between the average absorber temperature, glass and the outlet temperature and the efficiency for the single-pane and double-pane solar air collector with variable distance (1cm, 2cm and 3cm). Correspond to the three flow rates used. Experimental results show that the addition of second pane is effective in minimizing forward thermal losses for a solar air collector. The results obtained from the experimental readings show that the minimization of thermal losses forward is a very important factor for improving the performance of a solar collector. Experimental results show that the addition of second glazes is effective in minimizing forward thermal losses for a solar air collector.
