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We proposed a dual-ejector-based regenerative dual–pressure organic flash cycle (DEj–RDPOFC) with higher performance than the RDPOFC. The effects of high and low pressures and the entrainment ratio of the ejector on the DEj–RDPOFC performance were analyzed from the viewpoints of thermodynamics and thermoeconomics. An exergy-flow distribution diagram revealed why the DEj–RDPOFC outperformed the RDPOFC. Next, the performances of the DEj–RDPOFC and dual–pressure organic Rankine cycle (DORC) were compared under the same boundary conditions. Finally, the performance of the DEj–RDPOFC was optimized using the nondominated sorting genetic algorithm (NSGA-II). According to the results, the power output of the high-pressure (HP) turbine of the DEj–RDPOFC can be increased by replacing the HP throttling valve (TV) with an ejector (which increases the working fluid dryness of the HP vapor separator and the mass flow rate of the HP turbine) and the low-pressure (LP) TV with an ejector (which increases the HP turbine expansion ratio). The DEj–RDPOFC achieves a higher maximum net power output (W net) and a lower corresponding levelized cost of electricity (LCOE) than the DORC. Under the optimum condition, the W net and LCOE of the DEj–RDPOFC are 9.71 % higher and 6.59 % lower, respectively, than those of the RDPOFC. • The effect of the HP and LP ejector on the performance of the regenerative DPOFC (RDPOFC) are analyzed. • The performance of the RDPOFC assisted by ejectors (DEj–RDPOFC) is compared with the dual-pressure ORC. • The DEj–RDPOFC is optimized using a multi-objective optimization algorithms. [ABSTRACT FROM AUTHOR]

An efficient transcritical CO 2 combined cooling, heating and power (CCHP) systems, in which the ejector refrigeration cycle is integrated with power cycle (ER-CCHP), is proposed and analyzed for recovering low-grade energy. The proposed ER-CCHP system is compared to the TR-CCHP system, in which the throttle refrigeration cycle is integrated with power cycle. To evaluate the performance of the two systems, thermodynamic models are built and the effects of turbine parameters and evaporation temperature on the performance of the systems are investigated from the aspects of energy and exergy. The results indicated that the ER- CCHP system can provide more power than the TR- CCHP system due to the introduction the ejector. Furthermore, parametric optimizations are also performed for achieving the maximum net power output. And the maximum power output and the corresponding exergy efficiencies of the ER-CCHP and TR-CCHP systems under different the heat source temperatures are calculated, respectively. It is found that under the heat source of 230 °C the ER-CCHP and TR-CCHP systems could produce the maximum net power output of 7537.5 and 7910.3 kW, respectively. However, it should be noted that the above results are obtained under design conditions, and the off-design performance is not considered. • The performance of TR-CCHP and ER-CCHP systems using CO 2 are investigated. • The effects of turbine parameters and evaporation temperature are studied. • The systems are optimized to produce the maximum net power. [ABSTRACT FROM AUTHOR]

About 2/3 of the combustion energy of internal combustion engine (ICE) is lost through the exhaust and cooling systems during its operation. Besides, automobile accessories like the air conditioning system and the radiator fan will bring additional power consumption. To improve the ICE efficiency, this paper designs some coupled thermal management systems with different structures which include the air conditioning subsystem, the waste heat recovery subsystem, engine and coolant subsystem. CO2 is chosen as the working fluid for both the air conditioning subsystem and the waste heat recovery subsystem. After conducting experimental studies and a performance analysis for the subsystems, the coupled thermal management system is evaluated at different environmental temperatures and engine working conditions to choose the best structure. The optimal pump speed increases with the increase of environmental temperature and the decrease of engine load. The optimal coolant utilization rate decreases with the increase of engine load and environmental temperature, and the value is between 38% and 52%. While considering the effect of environmental temperature and road conditions of real driving and the energy consumption of all accessories of the thermal management system, the optimal thermal management system provides a net power of 4.2 kW, improving the ICE fuel economy by 1.2%. [ABSTRACT FROM AUTHOR]

Abstract: Presents a new system of air source energy independence driven by internal-combustion engine (EIICE), which used natural gas or other fuels as an independent input energy, and could provide the heating, cooling and hot water for the buildings efficiently. It also could provide electricity for electric equipments of the system. The performance of air source EIICE system was investigated theoretically and experimentally. The experimental and simulation results indicated that the heat capacity of plate heat exchanger (P-HE), heat recovered from exhaust gas heat exchanger (EG-HE), input power of compressor, output power of engine and fuel consumption increased with the increase of the rotary speed, water flow rate of the P-HE and evaporation temperature. Heat recovered from the cylinder jacket heat exchanger (CJ-HE) increased with the increase of the rotary speed and evaporation temperature, but decreased with the increase of the water flow rate of P-HE. The coefficient of performance (COP t ) and primary energy ratio (PER t ) of air source EIICE system also increased with the increase of the water flow rate of P-HE and evaporation temperature, but decreased with the increase of the rotary speed. [Copyright &y& Elsevier]

The organic Rankine cycle (ORC) technology is an attractive candidate for waste heat recovery and clean energy utilization. The operating condition of ORC system would change constantly under fluctuant heat source and a dynamic model is able to predict the transient behavior. The ORC dynamic model generally contains some unknown parameters while their identification is often ignored. This paper proposes a detailed calibration mechanism for ORC dynamic model including subcritical and transcritical system. Component models including pump, expansion valve and evaporator are well calibrated and the integrated calibrated system model is validated based on experimental data. Results indicate that calibrated model can capture the system dynamic behavior well. For key system state parameters such as working fluid evaporator pressure and outlet temperature, model prediction can achieve mean absolute relative deviation of less than 2% for both subcritical and transcritical system. Meanwhile, the conventional expansion valve model for transcritical system is found not efficient enough and a modification form is provided. This work can contribute to the calibration mechanism of similar thermodynamic system and enhance the confidence in model application. • An ORC dynamic model applying to subcritical and transcritical system. • A modified expansion valve flow equation for transcritical system. • Two types of correction multipliers in evaporator calibration. • The mean absolute relative deviation of less than 2% for model prediction. [ABSTRACT FROM AUTHOR]

• The reliable model of PR-CMTPC are developed and validated against experimental data. • High operating temperature is more conductive to greater power than pressure. • Optimal control strategy works well in slow step change but fails in transient change. • Constant pressure control is more suitable for transient conditions rather than slow step condition. Carbon dioxide mixture transcritical power cycle (CMTPC) is considered as a new promising technology for waste heat recovery (WHR), while there are still critical challenges arising from the transient fluctuations of heat sources when it comes to the heavy-duty diesel engines (HDDEs) applications. This paper presents a dynamic model of CMTPC systems, which is carefully validated against experimental data. Constant temperature, constant pressure and optimal control strategies are proposed to realize stable and optimal operation. The dynamic performance of the system with different control strategies is predicted under slow step change and transient change conditions. The results demonstrate that under slow step change conditions, the stability of optimal control system and constant pressure control system is better than that of constant temperature control system. In addition, the net power output keeps maximum under the optimal control because of the compromise between operating pressure and temperature. However, under transient conditions the control performance of optimal control is not as obvious as under slow step change conditions. Compared with open loop system, the improvement of system power by optimal control under slow step change is 2.31%, while that is only 0.07% under transient change condition. By contrast, it is found that the constant pressure control achieves the best power improvement of 0.58% under transient conditions because of the satisfactory control effect on operating pressure and relatively small fluctuations of expander inlet temperature. In a word, different control strategies behave obviously different performance under various conditions. [ABSTRACT FROM AUTHOR]