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 ...
Read More
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.
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 ...
Read More
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.
H. Farzan; M. Ameri; S. M. Jaafarian
Abstract
Asphalt solar collectors (ASCs) offer a low-cost and reliable alternative to harvest energy from available infrastructures such as roads and pathways by employing the simple techniques. This paper represents an experimental study to evaluate the effectiveness of continuous and discontinuous-flow strategies ...
Read More
Asphalt solar collectors (ASCs) offer a low-cost and reliable alternative to harvest energy from available infrastructures such as roads and pathways by employing the simple techniques. This paper represents an experimental study to evaluate the effectiveness of continuous and discontinuous-flow strategies in the dynamics and performance of a self-constructed ASC under field conditions. To this aim, an ON/OFF switching controller commands to run and stop the system at different time intervals. During the experimental simulations, all the crucial environmental and operational parameters were measured and monitored. This approach assesses the effects of numerous scenarios with different intervals of time on the dynamics of the constructed collector. Continuous and discontinuous-flow strategies were evaluated by comparing three different scenarios, including continuous-flow mode, 5 min OFF-mode and, 10 min OFF-mode. The results show that by extending the OFF-mode, the water is kept stagnant in the hot embedded pipes for more extended periods. Therefore, the temperature difference at the inlet and outlet of collector reduces, and the water leaves the collector at higher temperatures; however, the efficiency of the ASC decreases. Also, even though extending the OFF-mode results in heated water exits the collector at higher temperatures, but the mass of heated water decreases due to continuous interruption of current flow. The test results prove that in continuous-flow strategy, cumulative heat gain improves. Therefore, the continuous-flow strategy shows higher performance than introduced discontinuous-flow strategy. The exergy analysis illustrates that the available useful exergy has significantly affected by considering the pump consumed energy.
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 ...
Read More
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.
