Energy Science and Technology
Hamed Khoshkam; Kazem Atashkari; Mehdi Borji
Abstract
Carbon deposition has a serious effect on the failure mechanism of solid oxide fuel cells. A comprehensive investigation based on a two-dimensional model of a solid oxide fuel cell with the detailed electrochemical model is presented to study the mechanism and effects of carbon deposition and unsteady ...
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Carbon deposition has a serious effect on the failure mechanism of solid oxide fuel cells. A comprehensive investigation based on a two-dimensional model of a solid oxide fuel cell with the detailed electrochemical model is presented to study the mechanism and effects of carbon deposition and unsteady state porosity variation. Studies of this kind can be an aid to identify the SOFC optimal working conditions and provide an approximate fuel cell lifetime. It has been revealed that, due to carbon deposition, the porosity coefficient of the fuel cell decreases. Consequently, a reduction in the amount of fuel consumption along the fuel cell and the chemical and electrochemical reaction rates are resulted which can be clearly seen in the off-gases molar ratio. The percentage of output fuel changes in the timeframe is useful information for optimizing CHP systems including fuel cells. The percentage of the output water vapor, which usually increases compared to the input, decreases by 17% at the end of the working period. Also, unreacted methane in the output of the fuel cell increased by 12%; in other words, it is wasted. The other consequence of carbon deposition reduced electrochemical and chemical reaction rates and the reduction of temperature difference along the cell. The study shows that after 145 working days, the temperature difference along the cell varies from 117 °C for the starting time to 7 °C. Also, by reducing the current density, the cell output power density decreases by 72% after 145 working days.
Energy Science and Technology
Ahmed F Hasan; Salah N Farhan
Abstract
Phase change materials have attracted a considerable attention in thermal energy storage research recently due to their thermal characteristic. Composite materials have great potential as one of the best alternative approach that would be utilized to increase the thermal performance of this sort of materials. ...
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Phase change materials have attracted a considerable attention in thermal energy storage research recently due to their thermal characteristic. Composite materials have great potential as one of the best alternative approach that would be utilized to increase the thermal performance of this sort of materials. This work aims to improve the Latent Heat energy Storage Unit (LHSU) in terms of thermal performance during the melting process by utilizing honeycomb metal structures configuration. An experimental study has been carried out to examine the thermal behavior of this particular material in honeycomb LHSU. The thermal performance evaluation in terms of melting time of the proposed honeycomb LHSU was conducted in comparison with the normal LHSU. The influences of using different heat transfer fluid temperature on the charging power are considered for the enhanced geometrical configuration. The results showed significant enhancement in the melting time which reached 87%. Also, the melting range in the lower part of the storage unit was improved compared with the normal one from 190 to 24 min in case of using honeycomb. For the propose of configuration, by increasing the fluid temperature, charging power was accelerated, which in turn reduces the charging time from 14% to 16.
Energy Science and Technology
Jamasb Pirkandi; Amirali Amiralaei; Mohammad Omian
Abstract
In this research, a combined cooling, heating and power system (CCHP) has been analyzed from the perspective of entropy and exergy. The primary driver and the cooling system for this combined system consist of a micro gas turbine and a hot water lithium bromide single-effect absorption chiller, respectively. ...
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In this research, a combined cooling, heating and power system (CCHP) has been analyzed from the perspective of entropy and exergy. The primary driver and the cooling system for this combined system consist of a micro gas turbine and a hot water lithium bromide single-effect absorption chiller, respectively. The effects of compressor pressure ratio, micro turbine inlet gas temperature and chiller cooling capacity on important system efficiencies and other operational parameters (e.g., electrical efficiency, thermal efficiency, combined heating and power cogeneration efficiency, and combined cooling, heating and power cogeneration efficiency) have been investigated. The findings indicate that the system has its highest electrical efficiency at a compressor pressure ratio of 5. Also at this pressure ratio, the cogeneration efficiency (combined heating, cooling and power) and the exergy efficiency are about 48% and 24%, respectively. Moreover, the increase of the turbine inlet gas temperature has had a positive effect on the investigated parameters. The results show that the increase of cooling capacity reduces the cogeneration efficiencies, but has no effect on the exergy efficiency. Also, by considering specific values for the studied parameters, the amounts of generated entropy and destroyed exergy in various parts of the system have been calculated. The results indicate that the highest amounts of entropy and exergy have been generated and destroyed in the combustion chamber. Parts of the results indicate a system state in which the overall efficiency (combined heating, cooling and power cogeneration efficiency) of the system has increased 13% relative to the system’s initial state.
Energy Science and Technology
VINOTH KANNA I; Subramani K; DEVARAJ A
Abstract
The petroleum product has seen a drastic demand in the recent past. Biofuels are the only solution to overcome this power crisis. In the view of sustainable energy development, biodiesel and its additives have become the best options for fossil fuel-based engines. In this work, a biodiesel mix was used ...
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The petroleum product has seen a drastic demand in the recent past. Biofuels are the only solution to overcome this power crisis. In the view of sustainable energy development, biodiesel and its additives have become the best options for fossil fuel-based engines. In this work, a biodiesel mix was used to show the possible utilization of different biofuels. An experimental investigation was carried out on a direct-injection constant-speed (Rated speed- 1500 rpm) diesel engine at different injection pressures of 180, 220 and 260 bar with natural aspiration and supercharging modes. The blends of Biodiesel (used cooking oil, with a mix of algae) and diesel fuels are the selected fuel to investigate. At lower injection pressures, brake specific fuel consumption of the engine was low and further lowered with supercharging operation. With the reduction of injection pressures, brake thermal efficiency values are improved, and the same was observed with supercharging. With the rise in injection pressures, NOx emissions increased due to rise in temperature, and unburnt hydrocarbon emissions were slightly increased. The algae biodiesel was used as an additive to increase the stability of biodiesel. The overall observation indicates that a moderate injection pressure of 220 bar is advisable.
Energy Science and Technology
Saeed Ahmadipour; Mohammad Hossein Aghkhani; Javad Zareei
Abstract
Start of fuel injection and fuel type are two important factors affecting engine performance and exhaust emissions in internal combustion engines. In the present study, a one-dimensional computational fluid dynamics solution with GT-Power software is used to simulate a six-cylinder diesel engine to study ...
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Start of fuel injection and fuel type are two important factors affecting engine performance and exhaust emissions in internal combustion engines. In the present study, a one-dimensional computational fluid dynamics solution with GT-Power software is used to simulate a six-cylinder diesel engine to study the performance and exhaust emissions with different injection timing and alternative fuels. Starting the fuel injection was from 10 °CA BTDC to the TDC with an interval between two units and from alternative fuel bases (diesel), including methanol, ethanol, diesel, and ethanol compounds, biodiesel and decane was used. To validate the model, a comparison is made between simulation data and experimental data (including torque and power) showing the validation error is less than 6.12% and indicating the software model validation. Also, the modeling results show that decane fuel has higher brake power and brake torque of more than 6.10 % while fuel is injected at 10 °CA BTDC compared to the base fuel, and illustrates a reduction of 5.75 % in specific fuel consumption due to producing higher power. In addition, with the advance of injection timing compared to baseline, the amount of CO and HC in biodiesel fuel reduces to 83.88% and 64.87%, respectively, and the lowest NOX emission with the retardation of starting injection, to decane fuel is awarded. In general, the results show that decane fuel could be a good alternative to diesel fuel in diesel engines when it starts fuel injection at 10 °CA BTDC.
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