Capítulos
Permanent URI for this collectionhttps://pepa.une.es/handle/123456789/68679
Browse
4 results
Now showing 1 - 4 of 4
- Results Per Page
- Sort Options
Thermodynamic analysis of a novel pumped thermal energy storage system with waste heat integrationZhang, Meiyan; Shi, Lingfeng; Hu, Peng; Pei, Gang; Shu, GequnPumped thermal energy storage (PTES) system is a large-scale electricity storage technique, and the thermally integrated PTES system has been brought forward to raise the energy storage efficiency and extend feasible ways to utilize the low-grade waste heat (<100 °C). The solutions to raise the power-topower efficiency of the thermally integrated PTES system have aroused much attention worldwide. This paper presents an innovative thermally integrated PTES system, in which the two-stage heat pump with an economizer is incorporated into the PTES system. Despite utilizing the waste heat at charge time, the low-grade waste heat is also poured into the discharging process innovatively. The simulation model of the thermally integrated PTES system is established in the software MATLAB, and the physical properties of the substances are acquired from the software Refprop 10. The parameters of the PTES system are displayed and the power-to-power efficiency of the PTES system is investigated under various thermal storage temperatures. The results indicate that the power-to-power efficiency increases first and then declines as the low heat storage temperature rises when the high heat storage temperature is deemed. However, the energy storage density of the system dwindles with the increment of low heat storage temperature. The rise of the component efficiency contributes to the improvement of the powerto- power efficiency obviously, which can reach 87.3% as the isentropic efficiencies are 90%. The exergy destruction in the heat exchangers and mechanical components occupy a large proportion of the overall exergy destruction, which infers that the modification of the heat transferring and expansion/ compression processes are viable for performance enhancement.- Advanced control of compressor inlet temperature in supercritical CO2 Brayton cycleWang, Rui; Wang, Xuan; Tian, Hua; Shu, GequnThe supercritical CO2 (sCO2) Brayton cycle has gained much interest because of its flexibility, compactness and high efficiency. The sCO2 at the inlet of compressor should work near the critical point to obtain high system efficiency, while the physical properties of sCO2 near the critical point change dramatically, which brings great challenges to the control of the compressor inlet temperature. At present, cooling far from the critical point and adjusting the cooling water flow rate with Proportion- Integration-Differentiation (PID) controller is the commonly used method, but it loses system efficiency and may be out of control sometimes. Therefore, in this study Linear Model Predictive Control (LMPC) and Deep reinforcement learning (DRL) are used to control the compressor inlet temperature and compared with PID. A dynamic model of a recompression sCO2 Brayton cycle is established, and the cooler model is carefully validated against experiment data. The results indicate that both the LMPC and DRL can control the sCO2 temperature near the critical temperature much better than the PID. LMPC works the best because the cold end parameters fluctuate slightly and the cooler model can be regarded as approximately linear, thus LMPC can find almost the global optimal solution. Nevertheless, DRL control exhibits the fastest real-time computation ability and proves good extrapolation ability.
- Thermodynamic modification of CO2-based combined cooling and power cycle with ejectorZhang, Yonghao; Shi, Lingfeng; Shu, GequnCO2-based combined cooling and power cycle (CCP) has received increasing attentions especially in scenarios with diversified energy desires for its excellent natural properties. In this paper, an ejector is introduced into a conventional CCP system to reduce exergy loss in refrigeration throttling. A refrigerated truck is selected as the typical application scenario. And the simulated results indicate that approximately 28% of the expansion work during throttling can be recovered by the ejector, concurrently saving 0.3kW and 0.7kW compression work with respect to 10.8kW and 6.5kW cooling load under the freezing and refrigeration conditions. To extend the application of CCP system in more general scenarios, the ejector based CCP system is further modified to suit single heat source conditions. Two modified ejector based CCP systems namely ME-CCP-I and ME-CCP-II are proposed to recover waste energy from the compressor discharge. The adaptations to various heat source and refrigerating temperature are comprehensively studied. And the results demonstrate the ME-CCP-II system will be more suitable for air-conditioning scenarios while the ME-CCP-I system is advanced in freezing scenarios. In addition, recovering waste energy from the compressor discharge contributes great to the total energy efficiency of the CCP system as well as the heat transfer in regeneration process. With the mass split ratio increased from 0.1 to 0.9, the total energy efficiency of the ME-CCP-I system can raise from 0.27 to 0.64 and the relative enhancement is ranging from 1.26% to 11.86% versus the baseline system. Meanwhile, the ME-CCP-I system can reduce 48.6% irreversible loss in the heat regeneration process versus the baseline one when the same amount of exhausted energy after expansion is recovered
- A novel combined cooling and power cycle integrated ejector refrigeration and composition adjustment for stationary engine waste heat recoverySun, Xiaocun; Shi, Lingfeng; Tian, Hua; Shu, GequnThe combined cooling and power cycle has wide applications ascribed to the feasibility of simultaneously providing cooling and electricity. The layout comprised of vapor compression refrigeration cycle and Organic Rankine Cycle by sharing condenser is one of the most common structures. However, for this kind of structure, the high temperatures of working fluid in compressor outlet and expander outlet aggravate the condensation load and lead to the decline of system performance. This study proposes a novel combined cooling and power cycle integrated of ejector refrigeration and composition adjustment running with CO2 mixture. Liquid separation condenser is introduced to realize composition adjustment. Working fluid with higher CO2 mass fraction flows to power sub-cycle and evaporation process of refrigeration sub-cycle. On the other hand, working fluid with smaller CO2 mass fraction is pumped to the inlet of ejector and heated by expansion exhaust. A stationary engine is chosen as the research objective. The co-generation system recovers waste heat of engine exhaust and coolant to provide cooling to refrigerating chamber. The results show the priority of the novel proposed co-generation system. Under the requirement of 0 ℃ chilled fluid, the basic combined cooling and power cycle could export 8 kW cooling capacity and 6.63 kW electricity, while the novel proposed system can export 4.5% more net power output with 8 kW cooling capacity output or export 18.6% higher cooling capacity with 6.63 kW electricity.
