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[en] Highlights: • Parametric study of H_2 production from phenol-PET steam reforming was studied. • Optimised conditions were 800 °C, 0.10 ml/min feed flow rate, and 7% PET. • High amount of aliphatic branched-chains and cyclic compounds were produced. • PET was efficiently converted to hydrogen and valuable fuels at optimized condition. • Significant influence resulted for all the main independent factors. - Abstract: Production of hydrogen from plastic waste could be a prospective key to the ecological problems resulted from waste. To further explore the process, a 32-runs parametric study on the steam reforming of Polyethylene terephthalate (PET) dissolved in phenol was conducted in a fixed bed reactor using Ni over La_2O_3-Al_2O_3 support. The five factors studied were temperature (A), feed flow rate (B), mass flow (C), phenol concentration (D), and concentration of PET solution (E), whereas the responses were phenol conversion (Y_1) and hydrogen selectivity (Y_2). From the result, it was observed that significant influence resulted for all the main independent variables on the dependent variable of Y_1 and Y_2 with the range of 47.24–97.6% and 49–70.96%, respectively. Moreover, the Y_1 and Y_2 responses have influenced by some interaction variables like AC, CD, CE, ACE, and BCE. As evident from the design, initial variables such as 800 °C, 0.10 ml/min feed flow rate, 10 SCCM mass flow, 10 wt.% of phenol in the feed, and 7% PET concentration were the best preliminary conditions that formed maximum Y_1 (94%) and Y_2 (71%) responses. However, analyses on the product composition revealed that high amount of aliphatic branched-chains along with moderate amount of cyclic compounds were produced from steam reforming of PET-phenol. Due to the short retention time of the compounds on the catalysts bed, the aromatization of PET cracking products was small.
[en] Highlights: • CTPC systems designed under different engine operating conditions are compared. • Partial load is recommended for WHR system design for gasoline engines. • Operating strategies to get optimal performance are given. • The average fuel consumption reduction during the HWY cycle can reach 2.84%. - Abstract: Waste heat recovery by means of a CO_2 transcritical power cycle (CTPC) is suitable for dealing with high-temperature heat sources and achieving miniaturization. Considering the variable operating conditions of engines, the object of current work is to reveal the influence of design condition selection on CTPC systems. Two different engine operating conditions are chosen for system design. System performance has been predicted by a dynamic model and compared by net power output at off-design conditions. Constraints on temperatures, pressures and pump rotational speed have been taken into account. The results show that system designed under a partial load condition possesses a broad range of operation which will be beneficial to operate continuously when engine condition varies. The operating condition determined by driving cycles is recommended for system design of waste heat recovery for gasoline engines. Optimal performance can be obtained by adopting the mass flow rate guided operation strategy. Moreover, the average fuel consumption reduction during the Highway Fuel Economy Test Cycle over the original is 2.84% if system is designed under a partial condition. These preliminary results give reference to system design and optimization for waste heat recovery of engines based on thermodynamic cycles.
[en] Highlights: • Two non-dimensional parameters enabling to design an ideal thermal damper are identified. • Latent energy storage capacity of embedded PCM is estimated and reaches 1.6 J cm"−"2. • Total thermal resistance of thermal damper is estimated via laser flash method. • Dominant thermal resistances are localized at the interfaces between silicon and CNT. - Abstract: The present study focuses on a thermal damper that aims at smoothing the temperature peaks experienced by electronic components during transient solicitations. It consists of a silicon casing containing a densified or undensified carbon nanotube (CNT) array - linking directly both sides of the system - filled with phase change material (PCM). Theoretical consideration enables to define the concept of ideal thermal damper in order to study the foreseeable performance of this kind of system. Its thermal effectiveness can be predicted by means of two non-dimensional numbers, linked to the thermal capacity of the system and to the latent heat of the PCM. A numerical model shows that the behavior of a non-ideal thermal damper can differ from that of an ideal thermal damper: it is mostly affected by the thermal resistance at the interface between the silicon and the CNT and the temperature glide during the PCM phase change. To complete the study, prototypes of thermal dampers are experimentally characterized, in terms of heat storage and heat conduction performance. An estimation method of the total apparent thermal capacity of the tested sample is developed in order to quantify its latent heat storage capacity. The latent energy storage density is 1.6 J cm"−"2 for the best sample and is observed to be preserved after 850 thermal cycles. The total thermal resistance of the thermal damper is estimated by means of a laser flash test and a simple model of the sample. Sensitivity analyses show that the main thermal resistances are located at the interfaces between silicon and CNT.
[en] Highlights: • Dynamic model for transcritical CO_2 ejector refrigeration system is developed. • A model-driven optimal multivariable controller is proposed. • Gas cooler pressure and cooling capacity are tracked independently. • Maximal performance for a given load is achieved by the optimal controller. - Abstract: The fixed ejector has to work under a restricted operating condition to keep its positive effectiveness on the transcritical CO_2 refrigeration cycle, and a controllable ejector will be helpful. In this paper, an optimal multivariable controller based on the dynamic model is proposed to improve transcritical CO_2 refrigeration cycle with an adjustable ejector (TCRAE). A nonlinear dynamic model is first developed to model the dynamic characteristic of TCRAE. The corresponding model linearization is carried out and the simulation results reproduce transient behavior of the nonlinear model very well. Based on the developed model, an optimal multivariable controller with a tracker based linear quadratic state feedback algorithm and a predictor using steepest descent method is designed. The controller is finally applied on the experimental apparatus and the performance is verified. Using the tracker only, the gas cooler pressure and chilled water outlet temperature (cooling capacity) are well tracked rejecting the disturbances from each other. Furthermore, by the predictor, the optimal gas cooler pressure for a constant cooling capacity is actually approached on the experimental apparatus with a settling time about 700 s.
[en] Highlights: • A multi-reservoir system can handle water/energy deficit, flood and sediment damage. • A MWH model is developed for planning a water allocation and energy generation issue. • A mixed fuzzy-stochastic risk analysis method (MFSR) can handle uncertainties in MWH. • A hybrid MWH model can plan human-recourse-energy with a robust and effective manner. • Results can support adjusting water-energy policy to satisfy increasing demands. - Abstract: In this study, a multi-reservoir based water-hydroenergy management (MWH) model is developed for planning water allocation and hydroenergy generation (WAHG) under uncertainties. A mixed fuzzy-stochastic risk analysis method (MFSR) is introduced to handle objective and subjective uncertainties in MWH model, which can couple fuzzy credibility programming and risk management within a general two-stage context, with aim to reflect the infeasibility risks between expected targets and random second-stage recourse costs. The developed MWH model (embedded by MFSR method) can be applied to a practical study of WAHG issue in Jing River Basin (China), which encounters conflicts between human activity and resource/energy crisis. The construction of water-energy nexus (WEN) is built to reflect integrity of economic development and resource/energy conservation, as well as confronting natural and artificial damages such as water deficit, electricity insufficient, floodwater, high sedimentation deposition contemporarily. Meanwhile, the obtained results with various credibility levels and target-violated risk levels can support generating a robust plan associated with risk control for identification of the optimized water-allocation and hydroenergy-generation alternatives, as well as flood controls. Moreover, results can be beneficial for policymakers to discern the optimal water/sediment release routes, reservoirs’ storage variations (impacted by sediment deposition), electricity supply schedules and system benefit plans with an effective/sustainable manner.
[en] Highlights: • A novel cogeneration system driven by a SOFC and Stirling engine is proposed. • Energy and exergy assessments are reported of a novel cogeneration system. • The energy efficiency of the combined system can be achieved 75.88%. • The highest exergy destruction occurs in the air heat exchanger. - Abstract: A cogeneration system based on a methane-fed solid oxide fuel cell (SOFC) integrated with a Stirling engine is analyzed from the viewpoints of energy and exergy. The effects on the system performance are investigated of varying four key system parameters: current density, SOFC inlet temperature, compression ratio and regenerator effectiveness. The energy efficiency of the combined system is found to be 76.32% which is about 24.61% more than that of a stand-alone SOFC plant under the same conditions. Considering exergy efficiency as the only objective function, it is found that, as the SOFC inlet temperature increases, the exergy efficiency of the cogeneration system rises to an optimal value of 56.44% and then decreases. The second law analysis also shows that the air heat exchanger has the greatest exergy destruction rate of all system components. The cooling water of the engine also can supply the heating needs for a small home.
[en] Highlights: • The combined Rankine power and the absorption cooling cycles is investigated. • EES software is utilized to perform the parametric analyses. • The results represent the detailed major effects on the exergy efficiency. • The Genetic algorithm has been used to optimized the combined cycle. - Abstract: This study investigates the combined Rankine power and the absorption cooling cycles. The working fluid used in this cycle is the binary liquid mixture of water and ammonia. It produces both refrigeration and power simultaneously via a single heat source. Parametric analysis has been adopted to evaluate the thermodynamic parameters effects on the operation of the combined cycle where the Engineering Equation Solver (EES) is utilized. The obtained results show that environmental temperatures, heat source, refrigeration, inlet pressure, and temperature, and the density of the ammonia-water dilution have major effects on the exergy efficiency, the refrigeration output, and the net power of the system. In order to obtain the maximum exergy and thermal efficiencies, the optimization of the combined cycle has been performed via the genetic algorithm.
[en] Highlights: • Effects of cooling on solar PV performance have been experimentally investigated. • As a solar panel is cooled down, the electric output can have significant increase. • A cooled solar PV system has been proposed for resident application. • Life cycle assessment suggests the cost payback time of cooled PV can be reduced. - Abstract: As working temperature plays a critical role in influencing solar PV’s electrical output and efficacy, it is necessary to examine possible way for maintaining the appropriate temperature for solar panels. This research is aiming to investigate practical effects of solar PV surface temperature on output performance, in particular efficiency. Experimental works were carried out under different radiation condition for exploring the variation of the output voltage, current, output power and efficiency. After that, the cooling test was conducted to find how much efficiency improvement can be achieved with the cooling condition. As test results show the efficiency of solar PV can have an increasing rate of 47% with the cooled condition, a cooling system is proposed for possible system setup of residential solar PV application. The system performance and life cycle assessment suggest that the annual PV electric output efficiencies can increase up to 35%, and the annual total system energy efficiency including electric output and hot water energy output can increase up to 107%. The cost payback time can be reduced to 12.1 years, compared to 15 years of the baseline of a similar system without cooling sub-system.
[en] Highlights: • Alternative configuration of HRSG is proposed. • Bottoming of combined cycle power plant with ORC is considered. • Application of efficient gas turbines with low exhaust gas temperature is taken into account. • Energy and exergy efficiencies of heat recovery process are presented. • Computer simulations reveal possibilities for performance improvement. - Abstract: In the paper various configurations of the heat recovery process in combined gas and steam cycle power plants of complex structures are examined. Proposed modifications concern mainly hot side temperature profile. It has been assumed that two gas turbines will be installed in the system with a common single pressure heat recovery steam generator. Exhaust gas from the boiler is introduced into the low-temperature Rankine cycle with an organic working fluid. Two configurations of heat exchangers have been proposed, that can be considered as an alternative solution to the conventional structures currently in use. Energy and exergy efficiency values have been calculated for different parameters of steam. In addition, the temperature of exhaust gas from gas turbines was assumed to be different, which corresponds to the use of turbines of different efficiency classes. It has been shown that, with appropriately high steam parameters and appropriately selected gas turbines, the proposed alternatives lead to an improvement of the system performance.
[en] Highlights: • Effects of injection pressure in CI engine with n-butanol/diesel/PODE3-4 are studied. • PODE3–4 can decrease the maximum pressure rise rate. • Adding PODE3-4 to n-butanol/diesel blend reduces soot, CO and THC. • Adding PODE3-4 to n-butanol/diesel blend reduces the sub-50 nm particles emission. - Abstract: Polyoxymethylene dimethyl ethers (PODEn) are promising alternative biofuels with high cetane number and oxygen content. In this study, effects of PODE3-4 addition to diesel on the macroscopic spray characteristics were studied in a constant volume spray chamber under different injection pressures. The engine performance and emission characteristics of n-butanol/PODE3-4/diesel blends were investigated in a diesel engine under high injection pressures. The results indicate that the spray penetration of BD20 or PD20 was greater than that of D100; the addition of PODE3-4 to BD20 led to a further increase of the spray penetration without significant effects on the spray cone angle. Under an equal fuel injection pressure, the combustion of BD20 showed the greatest Maximum Pressure Rise rate (MPRR), which decreased after the addition of PODE3-4 to the blend. The soot and NOx emissions of BD20 were lower than that of pure diesel. Compared with BD20, the reduction of CO and HC emissions from the combustion of BDP20 were as high as 45.65% and 28.24%, respectively. The soot, NOx, CO and HC emissions of BDP20 were all lower than that of PD20. As the fuel injection pressure increased, a decreasing trend was observed in the number concentration as well as in the mass concentration of total particles. The lowest particle emissions in terms of total particle mass concentration were found for BDP20, followed by PD20, BD20 and D100. The ratio of sub-50 nm particles to total particles was highest for BD20 regardless of the injection pressure, and its value decreased upon adding PODE3-4 to BD20.