This work analysis the associated uncertainties to the liquid fraction measurements of a phase-ch... more This work analysis the associated uncertainties to the liquid fraction measurements of a phase-change experiment. The images produced by the experiment show the melting of a vertical ice layer into a differentially heated rectangular cavity in presence of natural convection and density maximum. The analysis of the melting problem in the presence of convection is very important for energy storage systems and other engineering applications. The non-linear density variation in the buoyancy term affects the movement of the interface, the flow structure and the heat transfer by natural convection. The test section where the melting experiments were performed allows to visualize the flow, measure temperatures, and take photographs of the flow structure and the interface evolution. Some image-processing techniques are used to analyze the phase-change problem with natural convection. The analysis and interpretation of images are very important for the correct understanding of the phenomenon...
When a liquid solution is cooled as it flows laminarly through a tube, a radial concentration gra... more When a liquid solution is cooled as it flows laminarly through a tube, a radial concentration gradient is established, which causes mass transfer of the solute to occur toward the tube wall. The solute precipitates off the solution in the neighborhood of the wall, and adheres perfectly to it. The deposited mass gradually obstructs the conduit, affecting the pressure and flow fields. A simple model is presented that gives the thickness of the deposited layer as a function of axial position and time. The liquid solution is assumed to behave according to the Herschel-Bulkley rheological model. Results are presented in the form of time evolution of axial distributions of pressure, temperature, layer thickness, global heat transfer coefficient and Reynolds number.
Energy independence and reduction in pollutant emissions are a center of interest for several res... more Energy independence and reduction in pollutant emissions are a center of interest for several researchers and car manufacturers Renewable fuels have gained in popularity because of their sustainability and, in some cases, lower amounts of greenhouse Moreover, energy diversification is also required by all countries One possible solution is the use of biofuels such as ethanol, methanol, etc. These biofuels have been shown as good candidates as alternative fuels for vehicles because they are liquid several physical and combustion properties similar to gasoline. Alcohols have also a higher octane number and oxygen content gasoline. This allows the alcohol engines to have much higher compression ratios (CRs), and thus, better BTE (br efficiency). Brazilian car manufacturing industry has developed flexible-fuel vehicles, introduced in 2003, which became a commercial success. Flex fuel internal combustion engines (ICEs) can run on any proportion of Brazilian gasoline (E27 blend) and hydrous ethanol (E100), allowing the use of the cheaper fuel available. However, conventional flex fuel engines have a fixed CR, generally between the ideals CRs for gasoline and ethanol, which leads to lower BTE and higher fuel consumption. In order to reduce or eliminate these issues, this paper presents the Kopelrot engine, a flexible fuel rotary engine with dynamically variable compression ratio.
Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015
To develop high energy-density power generation engine with variable geometrical compression rati... more To develop high energy-density power generation engine with variable geometrical compression ratio, the performance of an irreversible air standard Miller cycle in a piston rotary engine denominated Kopelrot Rotary Engine (KRE), was analyzed using thermodynamic numerical simulations. With consideration of the characteristics of the working processes in the KRE, corresponding differential equations were established and then simplified by period features. Application of Miller cycle in conventional engines can be realized by either early or late intake valve closing (EIVC or LIVC); in KRE engine this can be achieved varying the position of inlet port. Thermodynamic modeling shows that the Miller cycle has the potential to increase fuel efficiency compared to a conventional Otto-cycle engine, however with the cost of a reduced engine power density.
Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015
Atkinson cycle is already recognized for having a better thermal efficiency then Otto cycle. That... more Atkinson cycle is already recognized for having a better thermal efficiency then Otto cycle. That cycle is used so far mostly on reciprocating internal combustion engines (ICE) by changing the configuration of crank mechanisms. Miller cycle simulates Atkinson cycle by late closing of intake valves on ICE with classical (symmetrical) crank mechanisms. Rotary engines presents several advantages over conventional reciprocating ICE while having, in general, no valves or crankshafts. In this paper, the use of Atkinson / Miller cycle on a valveless rotary engine is proposed. The results highlight the rise on thermal efficiency while keeping inherent advantages of rotary engines.
In the present experimental study, a photovoltaic (PV)-powered system in continuous current (4 kW... more In the present experimental study, a photovoltaic (PV)-powered system in continuous current (4 kW) for the pumping of water in an isolated, rural agricultural zone in Arequipa—Peru was analyzed. A meteorological station was installed in the studied zone, measuring solar radiation, temperature, relative humidity, and wind speed. The electrical and hydraulic parameters of the solar-pumping system (i.e., electric current, voltage, mass flow, and hydraulic pressure) were measured in order to evaluate the efficiency of the energy transformation processes. The results indicate that, during the year of 2017, the PV pumping system in direct current (DC) functions from 07 h 30 min to 15 h 30 min, during an average of 8 h a day. The PV array, hydraulic, and global efficiencies were evaluated. This allows for the interpretation of efficiency independent of solar irradiance. The efficiency of the PV array and global efficiency remained constant (11.5% f and 8.5%, respectively). The functioning ...
ABSTRACT A parametric numerical investigation regarding the ice layer growth outside a vertical t... more ABSTRACT A parametric numerical investigation regarding the ice layer growth outside a vertical tube is investigated. It encompasses heat transfer and removal of energy, applicable to indirect, area-constrained, ice-on-pipe storage tanks. The study is carried out in a vertical annulus, with the inner vertical wall representing one of the tubes packed into a typical storage tank. Further, the outer vertical wall determines the maximum border for the ice layer growth under the conditions established in the present study, corresponding to a full charging process in such devices. Our task is to provide helpful qualitative results for the investigation of ice storage tank heat transfer performance, considering changes in the following parameters: aspect ratio, radius ratio, Grashof and Stefan numbers. For the mathematical model adopted to simulate transient natural convection of water with phase-change (solidification), it was utilized a model based on the finite volume method to solve the set of coupled conservation equations of mass, momentum and energy.
ABSTRACT Not only in simple cycle power plants, but also in combined cycle power plants based on ... more ABSTRACT Not only in simple cycle power plants, but also in combined cycle power plants based on gas turbines, the power output is considerably reduced with the increase of the ambient temperature. Many technologies for power augmentation of gas turbines have ...
This work analysis the associated uncertainties to the liquid fraction measurements of a phase-ch... more This work analysis the associated uncertainties to the liquid fraction measurements of a phase-change experiment. The images produced by the experiment show the melting of a vertical ice layer into a differentially heated rectangular cavity in presence of natural convection and density maximum. The analysis of the melting problem in the presence of convection is very important for energy storage systems and other engineering applications. The non-linear density variation in the buoyancy term affects the movement of the interface, the flow structure and the heat transfer by natural convection. The test section where the melting experiments were performed allows to visualize the flow, measure temperatures, and take photographs of the flow structure and the interface evolution. Some image-processing techniques are used to analyze the phase-change problem with natural convection. The analysis and interpretation of images are very important for the correct understanding of the phenomenon...
When a liquid solution is cooled as it flows laminarly through a tube, a radial concentration gra... more When a liquid solution is cooled as it flows laminarly through a tube, a radial concentration gradient is established, which causes mass transfer of the solute to occur toward the tube wall. The solute precipitates off the solution in the neighborhood of the wall, and adheres perfectly to it. The deposited mass gradually obstructs the conduit, affecting the pressure and flow fields. A simple model is presented that gives the thickness of the deposited layer as a function of axial position and time. The liquid solution is assumed to behave according to the Herschel-Bulkley rheological model. Results are presented in the form of time evolution of axial distributions of pressure, temperature, layer thickness, global heat transfer coefficient and Reynolds number.
Energy independence and reduction in pollutant emissions are a center of interest for several res... more Energy independence and reduction in pollutant emissions are a center of interest for several researchers and car manufacturers Renewable fuels have gained in popularity because of their sustainability and, in some cases, lower amounts of greenhouse Moreover, energy diversification is also required by all countries One possible solution is the use of biofuels such as ethanol, methanol, etc. These biofuels have been shown as good candidates as alternative fuels for vehicles because they are liquid several physical and combustion properties similar to gasoline. Alcohols have also a higher octane number and oxygen content gasoline. This allows the alcohol engines to have much higher compression ratios (CRs), and thus, better BTE (br efficiency). Brazilian car manufacturing industry has developed flexible-fuel vehicles, introduced in 2003, which became a commercial success. Flex fuel internal combustion engines (ICEs) can run on any proportion of Brazilian gasoline (E27 blend) and hydrous ethanol (E100), allowing the use of the cheaper fuel available. However, conventional flex fuel engines have a fixed CR, generally between the ideals CRs for gasoline and ethanol, which leads to lower BTE and higher fuel consumption. In order to reduce or eliminate these issues, this paper presents the Kopelrot engine, a flexible fuel rotary engine with dynamically variable compression ratio.
Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015
To develop high energy-density power generation engine with variable geometrical compression rati... more To develop high energy-density power generation engine with variable geometrical compression ratio, the performance of an irreversible air standard Miller cycle in a piston rotary engine denominated Kopelrot Rotary Engine (KRE), was analyzed using thermodynamic numerical simulations. With consideration of the characteristics of the working processes in the KRE, corresponding differential equations were established and then simplified by period features. Application of Miller cycle in conventional engines can be realized by either early or late intake valve closing (EIVC or LIVC); in KRE engine this can be achieved varying the position of inlet port. Thermodynamic modeling shows that the Miller cycle has the potential to increase fuel efficiency compared to a conventional Otto-cycle engine, however with the cost of a reduced engine power density.
Proceedings of the 23rd ABCM International Congress of Mechanical Engineering, 2015
Atkinson cycle is already recognized for having a better thermal efficiency then Otto cycle. That... more Atkinson cycle is already recognized for having a better thermal efficiency then Otto cycle. That cycle is used so far mostly on reciprocating internal combustion engines (ICE) by changing the configuration of crank mechanisms. Miller cycle simulates Atkinson cycle by late closing of intake valves on ICE with classical (symmetrical) crank mechanisms. Rotary engines presents several advantages over conventional reciprocating ICE while having, in general, no valves or crankshafts. In this paper, the use of Atkinson / Miller cycle on a valveless rotary engine is proposed. The results highlight the rise on thermal efficiency while keeping inherent advantages of rotary engines.
In the present experimental study, a photovoltaic (PV)-powered system in continuous current (4 kW... more In the present experimental study, a photovoltaic (PV)-powered system in continuous current (4 kW) for the pumping of water in an isolated, rural agricultural zone in Arequipa—Peru was analyzed. A meteorological station was installed in the studied zone, measuring solar radiation, temperature, relative humidity, and wind speed. The electrical and hydraulic parameters of the solar-pumping system (i.e., electric current, voltage, mass flow, and hydraulic pressure) were measured in order to evaluate the efficiency of the energy transformation processes. The results indicate that, during the year of 2017, the PV pumping system in direct current (DC) functions from 07 h 30 min to 15 h 30 min, during an average of 8 h a day. The PV array, hydraulic, and global efficiencies were evaluated. This allows for the interpretation of efficiency independent of solar irradiance. The efficiency of the PV array and global efficiency remained constant (11.5% f and 8.5%, respectively). The functioning ...
ABSTRACT A parametric numerical investigation regarding the ice layer growth outside a vertical t... more ABSTRACT A parametric numerical investigation regarding the ice layer growth outside a vertical tube is investigated. It encompasses heat transfer and removal of energy, applicable to indirect, area-constrained, ice-on-pipe storage tanks. The study is carried out in a vertical annulus, with the inner vertical wall representing one of the tubes packed into a typical storage tank. Further, the outer vertical wall determines the maximum border for the ice layer growth under the conditions established in the present study, corresponding to a full charging process in such devices. Our task is to provide helpful qualitative results for the investigation of ice storage tank heat transfer performance, considering changes in the following parameters: aspect ratio, radius ratio, Grashof and Stefan numbers. For the mathematical model adopted to simulate transient natural convection of water with phase-change (solidification), it was utilized a model based on the finite volume method to solve the set of coupled conservation equations of mass, momentum and energy.
ABSTRACT Not only in simple cycle power plants, but also in combined cycle power plants based on ... more ABSTRACT Not only in simple cycle power plants, but also in combined cycle power plants based on gas turbines, the power output is considerably reduced with the increase of the ambient temperature. Many technologies for power augmentation of gas turbines have ...
Energy independence and reduction in pollutant emissions are a center of interest for several res... more Energy independence and reduction in pollutant emissions are a center of interest for several researchers and car manufacturers Renewable fuels have gained in popularity becau sustainability and, in some cases, lower amounts of greenhouses gases. Moreover, energy diversification is also required by all countries. One possible solution is the use of biofuels such as ethanol, methanol, etc. These biofuels have been shown as good candidates as alternative fuels for vehicles because they are liquid several physical and combustion properties similar to gasoline. Alcohols have also a higher octane number and oxygen content gasoline. This allows the alcohol engines to have much higher compression ratios (CRs), and thus, better BTE (br efficiency). Brazilian car manufacturing industry has developed flexible-fuel vehicles, introduced in 2003, which became a commercial success. Flex fuel internal combustion engines (ICEs) can run on any proportion of Brazilian gasoline (E27 blend) and hydrous ethanol (E100), allowing the use of the cheaper fuel available. However, conventional flex fuel engines have a fixed CR, generally between the ideals CRs for gasoline and ethanol, which leads to lower BTE and higher fuel consumption. In order to reduce or eliminate these issues, this paper presents the Kopelrot engine, a flexible fuel rotary engine with dynamically variable compression ratio.
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Papers by Sergio Braga