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•Dynamic model development in Matlab/Simulink proposed.•Analysis of control strategy for the WHR system.•Dynamic performance evaluation under varying heat source ...condition.•Supercritical CO2 power cycle is promising for WHR application.
Large amount of waste heat is available for recovery in industrial processes worldwide. However, significant proportion (up to 50%) of this thermal energy is released directly to the environment. Application of waste heat to power (WHP) technologies can increase the energy efficiency and cut CO2 emissions from these facilities. Steam Rankine cycle (SRC) and organic Rankine cycle (ORC) are commonly deployed for this purpose. The main drawback of SRC and ORC is the high irreversibility in the heat exchangers. In addition, ORC has limited temperature range and low efficiency while SRC has a large footprint. Supercritical CO2 (sCO2) power cycle is considered an attractive option, which provides better matching of waste heat temperature in the main heater (i.e. low irreversibility). It offers compact design, improved performance and it is applicable to a wide range of waste heat source temperature. The conditions of industrial waste heat sources are highly variable due to continuous fluctuations in the operation of the process. This is likely to significantly affect the dynamic performance and operation of the sCO2 power cycle. In this work, dynamic model in Matlab/Simulink was developed to assess the dynamic performance and control of the sCO2 power cycle for waste heat recovery from cement industry. The case of waste heat at 380 °C utilized to deliver 5 MWe of power was considered. Steady state simulation was performed to determine the design point values. Open loop simulation was performed to show the inherent dynamic response to step change in the temperature of the waste heat. The dynamic performance and control of the system under varying exhaust gas flow rate between 100% and 50% of the design value were studied. Similar study was done for varying exhaust gas temperature between 380 °C and 300 °C. The results showed that the thermal efficiency of proposed single recuperator recompression sCO2 is about 33%. Stable operation of the system can achieved by using cooling water control and throttle valve to maintain constant precooler outlet condition. Dynamic simulation result showed that it is best to allow the turbine inlet temperature to vary according to the fluctuation in the waste heat source. These findings indicated that dynamic modelling and simulation of WHP system could contribute to understanding of the behaviour and control system development under fluctuating waste heat source conditions.
Abstract
The exhaust noise is considered to contribute disturbance to large extent in any vehicle. The sound wave cancellation device is used for better noise attenuation without much compromise on ...engine efficiency. This paper aims to design an advanced muffler which gives considerably lower back pressure in exhaust system line, thereby optimizing the power and torque of an engine. Study includes close monitoring of parameters such as power, torque, and transmission loss within the given boundary conditions. The limiting condition laid by Formula Society of Automotive Engineer (FSAE) is satisfied using Ricardo Wave Build software.
•A steady-state thermodynamic model is developed for absorption refrigeration in a ship.•Operation profile of B.Delta37 bulk carrier is used as an initial data.•Suitability of water-LiBr and ...ammonia-water working pairs were validated.•Coefficient of performance (COP) was studied in ISO and tropical conditions.•Estimated energy savings were 47 and 95tons of fuel every year.
This work presents a steady-state thermodynamic model for absorption refrigeration cycles with water-LiBr and ammonia-water working pairs for purpose of application on a ship. The coefficient of performance was studied with different generator and evaporator temperatures in ISO and tropical conditions. Absorption refrigeration systems were examined using exhaust gases, jacket water, and scavenge air as energy sources. Optimal generator temperatures for different refrigerant temperatures were found using different waste heat sources and for the absorption cycle itself. Critical temperature values (where the refrigeration power drops to zero) were defined. All of these values were used in order to evaluate the cooling power and energy production possibilities in a bulk carrier. The process data of exhaust gases and cooling water flows in two different climate conditions (ISO and tropical) and operation profiles of a B. Delta37 bulk carrier were used as initial data in the study. With the case ship data, a theoretical potential of saving of 70% of the electricity used in accommodation (AC use) compressor in ISO conditions and 61% in tropical conditions was recognized. Those estimates enable between 47 and 95tons of annual fuel savings, respectively. Moreover, jacket water heat recovery with a water-LiBr system has the potential to provide 2.2–4.0 times more cooling power than required during sea-time operations in ISO conditions, depending on the main engine load.
Abstract The S-shaped shock wave vectoring nozzle with afterdeck can significantly improve the overall performance of the exhaust system, taking into account Thrust vectoring, infrared stealth and ...afterbody fusion. One of the technical difficulties in its design process lies in the complex flow field characteristics under different operating conditions. Currently, the mainstream method is to obtain nozzle flow field characteristics through CFD numerical simulation, but the CFD method is time-consuming and costly. Therefore, based on the depth learning principle, a depth Convolutional neural network based on U-NET framework is established to quickly predict the flow field of S-shaped shock wave vectoring nozzle with afterdeck. Using CFD data for training, the results show that the depth learning model has high prediction accuracy and can clearly predict the flow field characteristics inside the nozzle, especially the secondary flow and the complex wave structure near the afterdeck. The correction Coefficient of determination of the prediction model is greater than 0.97. And the time consumption is about 0.0689% of that of a conventional solver. It has good application prospects in quickly evaluating the flow field of S-shaped nozzles.
•W7-X achieved several of its project goals during the first operation phases.•Boronisation reduced the impurity content strongly and allowed high-density operation.•Stationary full detachment with ...strongly reduced target heat flux was demonstrated.•The next operation phase will feature water cooling of in-vessel components.•W7-X is a key project to verify the physics models for stellarator reactor.
The Wendelstein 7-X project is aimed at demonstrating that an optimised stellarator is an attractive candidate for a fusion reactor. This requires the achievement of a number of technical and physics goals. Several of these goals have already been achieved in the first three experimental campaigns. We shall exemplify this by a number of results. One important goal is the demonstration of quasi-steady-state operation at high plasma density and temperature for half an hour, which encompasses the physical and technical requirements of stable operation with density and impurity control, cw heating, water-cooled targets, particle exhaust, and an appropriate control and data acquisition system for long-pulse operation. In the previous experimental campaigns, with uncooled targets, stationary discharges for up to 25 s with 5 MW heating power and up to 100 s with 2 MW heating power were achieved. For the next operational phase, to start in 2022, water-cooled targets are being installed, water cooling will be provided for all first-wall components, and a number of further upgrades to plasma heating, vacuum and fuelling systems as well as diagnostics will become available. With this equipment, the further goals of the project will be tackled, including the stepwise extension of discharge intervals to the multi-minute range. The experimental results so far have confirmed the neoclassical theory underlying several of the optimisation goals. At the same time, they showed that an optimisation is also required with respect to anomalous transport. In the future operational phases we aim at building a solid theoretical, experimental and technical foundation for the design of a next-step stellarator device.
•One-dimensional steady state models of desiccant cooling systems were developed.•The models of DEC system and the indirect evaporative cooler were verified.•The optimal regeneration temperature of ...the IEC was obtained.•The cooling performance of DEC, IEC, and HDC systems have been compared.•This study finds out the most efficient cooling systems at actual weather conditions.
Desiccant cooling systems have been regarded as alternative residential air conditioning systems, owing to their potential for considerably reducing electricity power consumption. In particular, when they are combined with distributed power generations, the overall efficiency of the system can be significantly enhanced by utilizing the system exhaust heat for the adsorption of water from the solid desiccant. However, desiccant cooling systems have a limited cooling capacity and consume an extremely high amount of thermal energy. Hybrid desiccant cooling (HDC) systems can extend their cooling capacity to satisfy the cooling load on the hottest day in the summer season by combination with an electric heat pump (EHP). In this study, one-dimensional steady state models of desiccant cooling systems were developed using MATLAB-Simulink®. Three types of desiccant cooling system models, direct evaporative cooling (DEC), indirect evaporative cooling (IEC), and HDC systems, have been simulated, and their cooling performance under various temperatures ranges from 25 °C to 50 °C and various humidity conditions ranges from 4% to 98%, which represent the weather of summer seasons worldwide, have been compared. DEC system has enough cooling performance to satisfy the target cooling load only when the outdoor temperatures becomes lower than 35 °C. When the outdoor temperature becomes exceeds 40 °C, the total COP of the HDC system is significantly increased and becomes higher than that of the IEC system.
Waste heat recovery (WHR) from exhaust gases in natural gas engines improves the overall conversion efficiency. The organic Rankine cycle (ORC) has emerged as a promising technology to convert medium ...and low-grade waste heat into mechanical power and electricity. This paper presents the energy and exergy analyses of three ORC–WHR configurations that use a coupling thermal oil circuit. A simple ORC (SORC), an ORC with a recuperator (RORC), and an ORC with double-pressure (DORC) configuration are considered; cyclohexane, toluene, and acetone are simulated as ORC working fluids. Energy and exergy thermodynamic balances are employed to evaluate each configuration performance, while the available exhaust thermal energy variation under different engine loads is determined through an experimentally validated mathematical model. In addition, the effect of evaporating pressure on the net power output, thermal efficiency increase, specific fuel consumption, overall energy conversion efficiency, and exergy destruction is also investigated. The comparative analysis of natural gas engine performance indicators integrated with ORC configurations present evidence that RORC with toluene improves the operational performance by achieving a net power output of 146.25 kW, an overall conversion efficiency of 11.58%, an ORC thermal efficiency of 28.4%, and a specific fuel consumption reduction of 7.67% at a 1482 rpm engine speed, a 120.2 L/min natural gas flow, 1.784 lambda, and 1758.77 kW of mechanical engine power.
Ammonia is a promising energy carrier and carbon-free fuel for power generation using combined-cycle gas turbines. However, its use results in the generation of relatively large amounts of NOx in the ...combustor. To address this issue, we propose a combined-cycle configuration including exhaust gas recirculation (EGR), in which the gas turbine is operated under fuel-rich conditions and the uncombusted hydrogen is burned in the heat-recovery steam generator (HRSG). Thus, hydrogen in the flue gas of the gas turbine increases the output power and improves the thermal efficiency of the system. Furthermore, in the combined system with EGR, the exhaust gas does not contain O2 and the combustion temperature can be reduced without altering the equivalence ratio. The proposed system is evaluated by thermodynamic modeling, and we find that low NOx emissions can be achieved while maintaining high thermal efficiency. Cold EGR is likely to be required to maintain the turbine inlet temperature below a technically feasible level, and a tradeoff between thermal efficiency and the NOx concentration at the combustor outlet is observed. The ideal operating conditions for this process thus depend on the technically feasible turbine inlet temperature, EGR ratio, and the permissible NOx concentration in the exhaust gas.
•A new concept for low-NOx ammonia combustion in a combined-cycle power plant with EGR is suggested.•Ammonia fuel-rich combustion in a gas turbine incorporating H2 burner in the heat-recovery steam generator is proposed.•Hydrogen in the flue gas from the gas turbine increases the output power and improves the thermal efficiency of the system.•In the proposed system with EGR, the combustion temperature can be reduced without changing the equivalence ratio.•Thermodynamic analysis shows that high efficiency and low NOx emissions are possible with the proposed system.
•The whole experiment is running in a stoichiometric dual fuel engine.•The effects of inert gases (Ar, N2, CO2) in EGR on engine performance were carried out.•Adding Ar can obtain the highest engine ...power and lowest exhaust temperature at same dilution ratio.•CO2 dilution can simultaneously achieve lower THC and NOx emission.
Using three-way catalytic converter can greatly reduce emissions in stoichiometric condition as soot is very low in diesel pilot natural gas dual fuel engine. Previous studies have shown that EGR can improve engine performance at partial load in gasoline engine. To better understand the effect of EGR on engine performance of stoichiometric dual fuel engine, a detailed study on inert gases (Ar, N2, CO2) in EGR were conducted on a 6-cylinder turbocharged intercooler diesel/natural gas dual fuel heavy-duty engine at stoichiometric condition. In this experiment, the total fuel quantity, gas injection strategy and diesel injection strategy were kept unchanged. The results show that different inert gas has different effect on engine power and combustion characteristics. The engine power increased for Ar and N2 dilution, while it decreased for CO2 dilution with increasing the dilution ratio. The engine power with Ar dilution is highest, followed by N2 and CO2 dilution at same dilution ratio. Adding CO2 into the intake charge made the combustion process of the engine deteriorated most, including start of combustion, CA 50, heat release peak, the cylinder pressure peak, followed by N2 dilution. While, these parameters show opposite changes except heat release rate for adding Ar. What’s more, when considering different performance targets of dual fuel engine, different dilution gases are corresponding.
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