This paper discusses a general procedure leading to the process optimization of Multiple Flashing... more This paper discusses a general procedure leading to the process optimization of Multiple Flashing Desalination processes (MSF). The optimal configuration is attained via a novel inverse-design approach that uses the global exergy efficiency as objective function. A fundamental methodological novelty of the proposed procedure is that it does not require the generation of a complete simulated set of results at each iteration step of the optimisation, because the objective function is computed by a functional extrapolation based on the Proper Orthogonal Decomposition (POD) method. With this method, the (often excessively taxing) computational cost for repeated numerical process simulations of incrementally different configurations is substantially reduced by replaci ng much of it by easy-to-perform matrix operations: a certain (small) number of initial process simulations is used only to calculate the basis of the POD interpolation and to validate (i.e., extend) the results. As the accuracy of a POD expansion critically depends on the allowable number of initial simulations (the "snapshots"), the computational intensity of our methodology is certainly not negligible: but, as successfully demonstrated in the paper for a strongly simplified but realistic MSF process de sign problem, the idea that, given a certain number of necessary initial process simulations, additional full simulations are performed only in the "right direction" indicated by the gradient of the objective function in the solution space , leads to a successful strategy at a substantially reduced number of simulations. This "economy" with respect to other classical "optimization" methods is basically due to the capability of the POD procedure to identify the most important "modes" in the functional expansion of the vector basis consisting of a subset of the design parameters used in the evaluation of the objective function.
A GTHV (gas turbine hybrid vehicle) is an electric vehicle (traction entirely electric on 1 or 2 ... more A GTHV (gas turbine hybrid vehicle) is an electric vehicle (traction entirely electric on 1 or 2 axles) equipped with a small turbogas whose only function is that of recharging the battery pack (and possibly other energy storage devices present on board). After a brief review of the history of the GTHV technology, a complete feasibility assessment of a prototype configuration of a GTHV designed by the University of Roma 1 is presented. All issues related to the system and component design, packaging, identification of the “optimal” hybridization ratio, performance of the (gas turbine + batteries + electrical motor) conversion system, braking energy recovery systems (KERS), mechanical and electric storage devices (flywheels, capacitors, advanced batteries), monitoring and control logic, compliance with the European vehicular ECE emission regulations, have been already discussed in several papers of the Authors. The paper analyzes the feasibility to insert “onboard” an innovative and ...
The flow field in the rotor of a low-specific speed radial compressor is computed in a fully 3-D ... more The flow field in the rotor of a low-specific speed radial compressor is computed in a fully 3-D simulation and the irreversible entropy generation rates directly calculated from the local velocity- and temperature values. The code used for the simulation is a commercial CFD-finite volumes package, FLUENT™, augmented by an novel entropy generation routine adapted from the original formulation due to Bejan [1]. The model provides the designer with exact and detailed knowledge of the local values of the irreversibility production, allowing for a separate accounting of viscous- and thermal effects and thus resulting in a valuable tool for the search of design improvements. These local entropy generation rates can of course be integrated over the entire flow field to obtain the global irreversibility production, directly linked with the rotor efficiency: but more important is the possibility of obtaining an exact “mapping” of these local values in some particularly “critical” design are...
An optimization model based on the use of Neural Network surrogate models for the multi-objective... more An optimization model based on the use of Neural Network surrogate models for the multi-objective optimization of small scale Organic Rankine Cycles is presented, which couples the optimal selection of the thermodynamic parameters of the cycle with the main design parameters of InFlow Radial turbines. The proposed approach proved well suited in the resolution of the highly non-linear constrained optimization problems, typical of the design of energy systems. Indeed the use of a surrogate model allows to adopt gradient based methods that are computationally more efficient and accurate than conventional derivative-free optimization algorithms. The intensive numerical experiments demonstrate that assuming a constant efficiency for the InFlow Radial turbine leads to an error in the evaluation of the performance of the system of up to 50 % and that the optimization approach proposed improves the accuracy of the solution and it reduces the computational time required to reach it by two orders of magnitude. An holistic approach in which the turbine and the thermodynamic cycle are designed simultaneously and the use of multi-objective optimization proved to be essential for the design of Organic Rankine cycles that satisfy both size and performance criteria.
Modern heavy duty diesel engines can well extend the goal of 50% brake thermal efficiency by util... more Modern heavy duty diesel engines can well extend the goal of 50% brake thermal efficiency by utilizing waste heat recovery (WHR) technologies. The effect of an ORC WHR system on engine brake specific fuel consumption (bsfc) is a compromise between the fuel penalty due to the higher exhaust backpressure and the additional power from the WHR system that is not attributed to fuel consumption. This work focuses on the fuel efficiency benefits of installing an ORC WHR system on a heavy duty diesel engine. A six cylinder, 7.25 heavy duty diesel engine is employed to experimentally explore the effect of backpressure on fuel consumption. A zero-dimensional, detailed physical ORC model is utilized to predict ORC performance under design and off-design conditions. The ORC model includes a detailed exhaust gas heat exchanger model and a thermodynamic ORC submodel to explore the effect of recovering various amounts of waste heat on ORC thermal efficiency under the same engine load and speed conditions. This study focuses on maximum engine power conditions where the engine exhaust gas and temperature are maximized. The results show that increasing the heat exchanger surface area leads to higher heat recovered at the expense of higher exhaust backpressure and higher WHR system weight, as the T between the fluids approaches zero. At the same time, the weight increase of the heat exchange is illustrated as the main parameter that limits the ORC system design in vehicular applications. Finally, the optimum heat exchanger length is a trade-off between exhaust backpressure, the required net ORC power and weight increase
Huge greenhouse gas (GHG) emission from fossil fuel combustion and unsatisfied energy requirement... more Huge greenhouse gas (GHG) emission from fossil fuel combustion and unsatisfied energy requirement have forced China to inquire into and change to environmental friendly alternatives that are renewable to sustain the increasing energy demand. Therefore, renewable energy in China has experienced a prosperous development in the last decade and will continue to be the focus and key issue of future energy development planning. However, some environmentalists have long argued that whether renewable energy sources such as wind are preferable to fossil fuels (oil, natural gas and coal), and which kind of renewable energy are more clean and sustainable. Quantitative evaluation to answer these questions thereby should be conducted. As extended exergy accounting (EEA) is a systematic exergo-economic method that adopts a single quantifier to account for materials, energy, labor and capital and to compute a presumed environmental impact based on remediation costs, it is a powerful tool for handl...
AbstractPlug-in hybrid electric vehicles are commonly designed to work in Charge Depleting/Charge... more AbstractPlug-in hybrid electric vehicles are commonly designed to work in Charge Depleting/Charge Sustaining (CD/CS) mode, depletingthe battery by driving in only-electrical mode until the SoC reaches its minimum acceptable threshold, and then sustaining the stateof charge till the end of the mission, operating as a traditional hybrid vehicle. Nonetheless, a simple application of an optimalcontrol framework suggests a blended discharge strategy, in which the powertrain is operated as to gradually deplete the SoC andreach the lower threshold only at the end of the trip. Such an algorithm has the drawback that the optimal solution can only bereached offline, depending on the a-priori knowledge of the driving event, making it unsuitable to be implemented online, as it is.The paper presents a methodology to design a heuristic controller, to be used online, based on rules extracted from the analysisof the powertrain behavior under the optimal control solution. The application is a parallel...
It is commonly (but erroneously) assumed that the best way to treat upstream boundaries for hyper... more It is commonly (but erroneously) assumed that the best way to treat upstream boundaries for hyperbolic equations is to let the numerical value be equal to the imposed value. What is erroneous in this assumption is that it ignores the presence of spurious numerical solutions which may have originated inside of the computational domain and which may be present near the boundary. Such spurious solutions are characterized by short wavelength spatial oscillations, with a group velocity, which is opposed to the direction of flow and are therefore moving as "packets" toward the boundary. They are reflected by the "standard" treatment whereas a better numerical treatment of the boundary should attempt to absorb them. This paper describes two methods for the modified numerical treatment of upstream boundaries of hyperbolic equations, which are effective in absorbing those purious solutions with a remainder which decreases as O (r-~J) and 0~~VA"-) respectively, where ...
This paper discusses a general procedure leading to the process optimization of Multiple Flashing... more This paper discusses a general procedure leading to the process optimization of Multiple Flashing Desalination processes (MSF). The optimal configuration is attained via a novel inverse-design approach that uses the global exergy efficiency as objective function. A fundamental methodological novelty of the proposed procedure is that it does not require the generation of a complete simulated set of results at each iteration step of the optimisation, because the objective function is computed by a functional extrapolation based on the Proper Orthogonal Decomposition (POD) method. With this method, the (often excessively taxing) computational cost for repeated numerical process simulations of incrementally different configurations is substantially reduced by replaci ng much of it by easy-to-perform matrix operations: a certain (small) number of initial process simulations is used only to calculate the basis of the POD interpolation and to validate (i.e., extend) the results. As the accuracy of a POD expansion critically depends on the allowable number of initial simulations (the "snapshots"), the computational intensity of our methodology is certainly not negligible: but, as successfully demonstrated in the paper for a strongly simplified but realistic MSF process de sign problem, the idea that, given a certain number of necessary initial process simulations, additional full simulations are performed only in the "right direction" indicated by the gradient of the objective function in the solution space , leads to a successful strategy at a substantially reduced number of simulations. This "economy" with respect to other classical "optimization" methods is basically due to the capability of the POD procedure to identify the most important "modes" in the functional expansion of the vector basis consisting of a subset of the design parameters used in the evaluation of the objective function.
A GTHV (gas turbine hybrid vehicle) is an electric vehicle (traction entirely electric on 1 or 2 ... more A GTHV (gas turbine hybrid vehicle) is an electric vehicle (traction entirely electric on 1 or 2 axles) equipped with a small turbogas whose only function is that of recharging the battery pack (and possibly other energy storage devices present on board). After a brief review of the history of the GTHV technology, a complete feasibility assessment of a prototype configuration of a GTHV designed by the University of Roma 1 is presented. All issues related to the system and component design, packaging, identification of the “optimal” hybridization ratio, performance of the (gas turbine + batteries + electrical motor) conversion system, braking energy recovery systems (KERS), mechanical and electric storage devices (flywheels, capacitors, advanced batteries), monitoring and control logic, compliance with the European vehicular ECE emission regulations, have been already discussed in several papers of the Authors. The paper analyzes the feasibility to insert “onboard” an innovative and ...
The flow field in the rotor of a low-specific speed radial compressor is computed in a fully 3-D ... more The flow field in the rotor of a low-specific speed radial compressor is computed in a fully 3-D simulation and the irreversible entropy generation rates directly calculated from the local velocity- and temperature values. The code used for the simulation is a commercial CFD-finite volumes package, FLUENT™, augmented by an novel entropy generation routine adapted from the original formulation due to Bejan [1]. The model provides the designer with exact and detailed knowledge of the local values of the irreversibility production, allowing for a separate accounting of viscous- and thermal effects and thus resulting in a valuable tool for the search of design improvements. These local entropy generation rates can of course be integrated over the entire flow field to obtain the global irreversibility production, directly linked with the rotor efficiency: but more important is the possibility of obtaining an exact “mapping” of these local values in some particularly “critical” design are...
An optimization model based on the use of Neural Network surrogate models for the multi-objective... more An optimization model based on the use of Neural Network surrogate models for the multi-objective optimization of small scale Organic Rankine Cycles is presented, which couples the optimal selection of the thermodynamic parameters of the cycle with the main design parameters of InFlow Radial turbines. The proposed approach proved well suited in the resolution of the highly non-linear constrained optimization problems, typical of the design of energy systems. Indeed the use of a surrogate model allows to adopt gradient based methods that are computationally more efficient and accurate than conventional derivative-free optimization algorithms. The intensive numerical experiments demonstrate that assuming a constant efficiency for the InFlow Radial turbine leads to an error in the evaluation of the performance of the system of up to 50 % and that the optimization approach proposed improves the accuracy of the solution and it reduces the computational time required to reach it by two orders of magnitude. An holistic approach in which the turbine and the thermodynamic cycle are designed simultaneously and the use of multi-objective optimization proved to be essential for the design of Organic Rankine cycles that satisfy both size and performance criteria.
Modern heavy duty diesel engines can well extend the goal of 50% brake thermal efficiency by util... more Modern heavy duty diesel engines can well extend the goal of 50% brake thermal efficiency by utilizing waste heat recovery (WHR) technologies. The effect of an ORC WHR system on engine brake specific fuel consumption (bsfc) is a compromise between the fuel penalty due to the higher exhaust backpressure and the additional power from the WHR system that is not attributed to fuel consumption. This work focuses on the fuel efficiency benefits of installing an ORC WHR system on a heavy duty diesel engine. A six cylinder, 7.25 heavy duty diesel engine is employed to experimentally explore the effect of backpressure on fuel consumption. A zero-dimensional, detailed physical ORC model is utilized to predict ORC performance under design and off-design conditions. The ORC model includes a detailed exhaust gas heat exchanger model and a thermodynamic ORC submodel to explore the effect of recovering various amounts of waste heat on ORC thermal efficiency under the same engine load and speed conditions. This study focuses on maximum engine power conditions where the engine exhaust gas and temperature are maximized. The results show that increasing the heat exchanger surface area leads to higher heat recovered at the expense of higher exhaust backpressure and higher WHR system weight, as the T between the fluids approaches zero. At the same time, the weight increase of the heat exchange is illustrated as the main parameter that limits the ORC system design in vehicular applications. Finally, the optimum heat exchanger length is a trade-off between exhaust backpressure, the required net ORC power and weight increase
Huge greenhouse gas (GHG) emission from fossil fuel combustion and unsatisfied energy requirement... more Huge greenhouse gas (GHG) emission from fossil fuel combustion and unsatisfied energy requirement have forced China to inquire into and change to environmental friendly alternatives that are renewable to sustain the increasing energy demand. Therefore, renewable energy in China has experienced a prosperous development in the last decade and will continue to be the focus and key issue of future energy development planning. However, some environmentalists have long argued that whether renewable energy sources such as wind are preferable to fossil fuels (oil, natural gas and coal), and which kind of renewable energy are more clean and sustainable. Quantitative evaluation to answer these questions thereby should be conducted. As extended exergy accounting (EEA) is a systematic exergo-economic method that adopts a single quantifier to account for materials, energy, labor and capital and to compute a presumed environmental impact based on remediation costs, it is a powerful tool for handl...
AbstractPlug-in hybrid electric vehicles are commonly designed to work in Charge Depleting/Charge... more AbstractPlug-in hybrid electric vehicles are commonly designed to work in Charge Depleting/Charge Sustaining (CD/CS) mode, depletingthe battery by driving in only-electrical mode until the SoC reaches its minimum acceptable threshold, and then sustaining the stateof charge till the end of the mission, operating as a traditional hybrid vehicle. Nonetheless, a simple application of an optimalcontrol framework suggests a blended discharge strategy, in which the powertrain is operated as to gradually deplete the SoC andreach the lower threshold only at the end of the trip. Such an algorithm has the drawback that the optimal solution can only bereached offline, depending on the a-priori knowledge of the driving event, making it unsuitable to be implemented online, as it is.The paper presents a methodology to design a heuristic controller, to be used online, based on rules extracted from the analysisof the powertrain behavior under the optimal control solution. The application is a parallel...
It is commonly (but erroneously) assumed that the best way to treat upstream boundaries for hyper... more It is commonly (but erroneously) assumed that the best way to treat upstream boundaries for hyperbolic equations is to let the numerical value be equal to the imposed value. What is erroneous in this assumption is that it ignores the presence of spurious numerical solutions which may have originated inside of the computational domain and which may be present near the boundary. Such spurious solutions are characterized by short wavelength spatial oscillations, with a group velocity, which is opposed to the direction of flow and are therefore moving as "packets" toward the boundary. They are reflected by the "standard" treatment whereas a better numerical treatment of the boundary should attempt to absorb them. This paper describes two methods for the modified numerical treatment of upstream boundaries of hyperbolic equations, which are effective in absorbing those purious solutions with a remainder which decreases as O (r-~J) and 0~~VA"-) respectively, where ...
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