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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Energy Systems".

Deadline for manuscript submissions: closed (15 April 2024) | Viewed by 20034

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Special Issue Editors

Dr. Yonggang Lu

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Guest Editor

Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
Interests: hydraulic energy storage; nuclear energy; fluid mechanics; multidisciplinary design optimization; pump-turbine

Dr. Zhong Ma

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Guest Editor

School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China
Interests: biomass conversion; renewable energy technologies; energy conversion; chemical looping; CO₂ capture and utilization

Dr. Xijie Song

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Guest Editor

Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
Interests: complex flow and vortex dynamics in pump turbine
Special Issues, Collections and Topics in MDPI journals

Dr. Yanjie Yuan

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Guest Editor

College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210024, China
Interests: renewable energy technologies; new energy machinery manufacturing; surface processing of biomimetic; micro-nano structure

Special Issue Information

Dear Colleagues,

With the shortage of energy and the change of climate, renewable energy has become the focus of society today. Renewable energy includes solar energy, water energy, wind energy, biomass energy, tidal energy, geothermal energy, etc. This Special Issue on “State-of-the-Art Energy Conversion and Storage” intends to present novel examples of new theories, new concepts and new technologies for all types of renewable energy. Topics include, but are not limited to:

Wind energy, solar energy, hydro energy, pumped storage, nuclear energy;
Biomass Conversion, Renewable Energy Technologies, Energy Conversion and storage.
Wind-solar-water-storage integration, wind-solar-hydropower generation;
Advanced nuclear reactor technology, Nuclear Engineering;
Experimental measurement, numerical simulation, sustainable energy systems and policies.

Dr. Yonggang Lu
Dr. Zhong Ma
Dr. Xijie Song
Dr. Yanjie Yuan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

renewable energy
wind energy
solar energy
hydro energy
biomass conversion
nuclear energy
pumped storage
renewable energy technologies

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Published Papers (11 papers)

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Research

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12 pages, 5261 KiB

Open AccessArticle

Research on the Flow Characteristics in the Gap of a Variable-Speed Pump-Turbine in Pump Mode

by Zhengwei Wang, Lei Wang, Shuang Yu and Sainan Li

Processes 2024, 12(7), 1424; https://doi.org/10.3390/pr12071424 - 8 Jul 2024

Viewed by 685

Abstract

A variable-speed pump-turbine is the core component of a hydraulic storage and energy generation station. When the pump-turbine operates at a constant speed, its response to the power grid frequency is poor. In order to improve the hydraulic efficiency of the pumped storage unit, variable-speed units are used. However, there has been no numerical study on the effect of the rotational flow characteristics within the gap of a variable-speed pump-turbine. This paper calculates the flow characteristics within the gap of a variable-speed pump-turbine under three typical pump modes (maximum head minimum flow condition, minimum head maximum flow condition, and maximum speed condition). The research results indicate that the rotational speed significantly affects the pressure distribution, velocity distribution, and turbulent kinetic energy distribution within the crown and band gaps. The higher the speed, the larger the area of the high-pressure region before the runner inlet compared to other operating conditions, and similarly, the low-pressure area after the runner outlet is also larger than in other operating conditions. The change in speed mainly affects the internal flow field of the crown gap, with the most noticeable changes occurring in the pressure and flow velocity at the inlet and outlet of the crown gap. There is a clear trend of pressure drop and velocity increase within the gap as the speed increases. However, with the increase in speed, the pressure distribution and flow velocity within the band gap remain almost the same. In addition to speed changes, it is observed that the pressure within the gap and the flow velocity within the passages are also related to the head, especially in the condition of maximum head, where this relationship becomes more noticeable. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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18 pages, 2263 KiB

Open AccessArticle

Mitigation of Renewable Energy Source Production Variability in Residential Stock through Small-Scale Gas–Liquid Energy Storage Technology Application

by Andrea Vallati, Miriam Di Matteo, Laura Pompei, Fabio Nardecchia and Costanza Vittoria Fiorini

Processes 2024, 12(4), 655; https://doi.org/10.3390/pr12040655 - 25 Mar 2024

Cited by 2 | Viewed by 1104

Abstract

Despite renewable energy source integration being a well-established requirement in international policies, energy systems still face some unresolved issues, including the intermittence of production. To tackle this problem, a viable solution could comprise the off-peak storage of electricity production excess, to be consumed later during peak-load hours. The transition from the diffuse pattern of centralized generation to the distributed model, involving energy communities, suggests an additional aspect to manage: the spatial constraints of systems for domestic applications. Compressed-air energy storage represents a promising Power-to-Power technology for small-scale energy integration. This study proposes the application of a gas–liquid energy storage system (GLES) in a residential building, using renewable energy excess from a photovoltaic (PV) array. The performance of the proposed system, whose operation involves the compression of the gaseous mass through a piston operated by mineral oil, was evaluated through energy analysis performed simulating the devices and their coupling with the load profiles of the building. The thermodynamic model of storage was validated using data from an experimental campaign on a prototype. A sensitivity study, acting on the features of the system, such as the compression rate and vessel size, allowed us to compare the absorbed PV energy excess, the coverage of the building energy demand during the expansion phase, and the electrical efficiency of a daily cycle. The results obtained, together with the related economic analysis, were used to quantify the market potential of the proposed solution, to be exploited as a mechanical alternative to conventional electric batteries in dwellings. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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19 pages, 5953 KiB

Open AccessArticle

Flow Characteristics Analysis of a 1 GW Hydraulic Turbine at Rated Condition and Overload Operation Condition

by Chengming Liu, Siyuan Wu, Xingxing Huang, Shuai Zhang, Lingjiu Zhou, Tianli Hu and Zhengwei Wang

Processes 2024, 12(2), 255; https://doi.org/10.3390/pr12020255 - 24 Jan 2024

Cited by 1 | Viewed by 922

Abstract

Flow stability is extremely important for hydraulic turbines, especially for 1 GW hydraulic turbines, and has a strong impact on mesh stability. However, turbines often operate under non-design conditions, and current research on this aspect is still lacking. So a model of the fluid domains of a high-quality installed 1 GW Francis turbine was established to investigate the flow characteristics of the turbine and fluid domains. CFD simulations of a 1 GW Francis turbine under rated load and overload operation conditions were performed. According to simulation results, when the turbine is under the overload operation condition, the internal flow stability of the 1 GW hydraulic turbine can be obviously different from that of the rated load. In the overload condition, the flow field is more turbulent and a large number of vortices are generated in the draft tube, resulting in significant changes in pressure, flow rate, and output. In order to improve calculation accuracy, a pure clearance model containing only clearances and pressure balance pipes was established. The results of the full flow channel and pure clearance were compared. It was found that under the rated operating condition and the overload condition, compared with the pure clearance model, the axial force of the runner calculated by the full flow channel model is approximately 2–7% biased, the radial force is biased by approximately 7–8%, and the leakage flow is smaller. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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21 pages, 5294 KiB

Open AccessArticle

Centrifugal Pump Cavitation Fault Diagnosis Based on Feature-Level Multi-Source Information Fusion

by Mengbin Song, Yifan Zhi, Mengdong An, Wei Xu, Guohui Li and Xiuli Wang

Processes 2024, 12(1), 196; https://doi.org/10.3390/pr12010196 - 16 Jan 2024

Cited by 2 | Viewed by 1354

Abstract

In nuclear power systems, centrifugal pumps often need to operate under extreme conditions. However, accurately determining the cavitation status of centrifugal pumps under such extreme conditions is challenging. To improve the recognition accuracy of the three statuses of non-cavitation, incipient cavitation, and severe cavitation while improving the anti-interference capability of the monitoring system, this study extracted cavitation features from centrifugal pumps’ motor current and vibration signals under three different operational conditions. It fused the features using feature-level multi-source information fusion (MSIF) based on the backpropagation neural network (BPNN) or support vector machine (SVM) to construct a cavitation status recognition model and analyzed the results to compare with those of recognition without information fusion. The results show that, compared with one signal source, MSIF can significantly improve the recognition accuracy of cavitation statuses. Combined current and pump casing axial monitoring based on the BPNN is the optimal scheme, with an overall recognition accuracy of 97.3% for all operational conditions, compared to 73.9% for the single current signal and 89.3% for the single casing axial vibration signal. These research results can guide the monitoring of cavitation statuses in practical engineering, as well as timely intervention at incipient cavitations to reduce structural damage to centrifugal pumps and prolong service life. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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17 pages, 9580 KiB

Open AccessArticle

Analysis of Cavitation-Induced Unsteady Flow Conditions in Francis Turbines under High-Load Conditions

by Haobo Wang, Daqing Zhou, An Yu and Junxun Guo

Processes 2024, 12(1), 72; https://doi.org/10.3390/pr12010072 - 28 Dec 2023

Viewed by 1169

Abstract

Hydraulic vibrations in Francis turbines caused by cavitation profoundly impact the overall hydraulic performance and operational stability. Therefore, to investigate the influence of cavitation phenomena under high-load conditions, a three-dimensional unsteady numerical simulation is carried out for a Francis turbine with different head operating conditions, which is combined with the SST k-w turbulence model and two-phase flow cavitation model to capture the evolution of cavitation under high-load conditions. Additionally, utilizing entropy production theory, the hydraulic losses of the Francis turbine during cavitation development are assessed. Contrary to the pressure-drop method, the entropy production theory can quantitatively reflect the characteristics of the local hydraulic loss distribution, with a calculated error coefficient τ not exceeding 2%. The specific findings include: the primary sources of energy loss inside the turbine are the airfoil cavitation and cavitation vortex rope, constituting 26% and 71% of the total hydraulic losses, respectively. According to the comparison with model tests, the vapor volume fraction (VVF) inside the draft tube fluctuates periodically under high-load conditions, causing low-frequency pressure pulsation in the turbine’s power, flow rate, and other external characteristic parameters at 0.37 Hz, and the runner radial force fluctuates at a frequency of 1.85 Hz. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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13 pages, 6270 KiB

Open AccessArticle

Research on the Hydraulic Excitation Characteristics of the Top Cover Caused by the Radial Installation Deviation of the Seal of a 1GW Francis Turbine

by Kun Jin, Yonggang Lu, Peng Lin, Zequan Zhang, Juan Li, Yun Zhao, Xingxing Huang and Zhengwei Wang

Processes 2023, 11(11), 3172; https://doi.org/10.3390/pr11113172 - 7 Nov 2023

Cited by 1 | Viewed by 1029

Abstract

The radial installation deviation of the turbine runner will change the gap flow between the upper crown and the lower ring seal, which will affect the radial force of the runner and the hydraulic excitation characteristics of the top cover. This research focuses on the 1GW Francis turbine on the right bank of the Baihetan hydropower station. The pressure distribution along the circumference of the top cover was analyzed, and the effects of deviations on the specific generation of hydraulic excitation forces were studied. This research shows that the increase in radial deviation will slightly reduce the output and efficiency, and the radial force on the runner increases parabolically. When the radial deviation is 1.5 mm, the radial force is 5.9 times higher compared to the case without any deviation, and the radius of the fitting circle of the radial force behavior trajectory increases with the increase in radial deviation. In addition, the radial deviation has little effect on the internal flow of the runner and the pressure distribution in the upper crown chamber. The dominant frequency components at the upstream monitoring points include fn, 15 fn, 24 fn, and 30 fn. The dominant frequency components at the downstream monitoring points include the blade passing frequencies of 15 fn and 30 fn. However, with the increase in radial deviation, the fluctuation amplitudes exhibit an asymmetric distribution, the uniformity of the pressure distribution in the circumferential direction of the labyrinth seal area becomes significantly worse, and the waveform of the downstream monitoring points changes significantly and presents a non-uniform distribution in one rotation cycle. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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16 pages, 7187 KiB

Open AccessArticle

Hydraulic Characterization of Variable-Speed Pump Turbine under Typical Pumping Modes

by Linmin Shang, Jingwei Cao, Zhengwei Wang and Xiaobing Liu

Processes 2023, 11(10), 2903; https://doi.org/10.3390/pr11102903 - 2 Oct 2023

Cited by 3 | Viewed by 1378

Abstract

The pump turbine is a crucial component of pumped storage hydropower plants. When operated at a constant speed, it does not respond well to variations in the grid frequency. To improve the hydraulic efficiency of pumped storage units, variable-speed units have been introduced. However, the mechanism of variable-speed pump turbines has not been extensively studied numerically. In this study, the flow characteristics of a variable-speed pump turbine were computed under two typical pumping modes, the maximum head and minimum flow rate condition, as well as the minimum head and maximum flow rate condition. The computed results aligned with experimental results, and the changing trends of hydraulic thrust under these two pumping modes were discussed. The error for the Hmax, Qmin condition was 1.3%, and the error for the Hmin, Qmax condition was −1.9%. These error values fell within a reasonable range. The research findings indicate that in the H_max, Q_min condition, the flow within the flow passage exhibited higher velocity, which was 84.87 m/s, increased flow turbulence, larger pressure fluctuations, and poorer unit stability. On the other hand, in the H_min, Q_max condition, both the axial hydraulic thrust and radial forces were greater, and there were sudden changes in the extreme values of pressure fluctuations over a certain period of time. It is recommended to avoid operating the variable-speed pump turbine under these two conditions during pumping operations. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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12 pages, 7990 KiB

Open AccessArticle

Numerical Prediction of Erosion of Francis Turbine in Sediment-Laden Flow under Different Heads

by Jinliang Wang, Xijie Song, Hu Wang, Ran Tao and Zhengwei Wang

Processes 2023, 11(9), 2523; https://doi.org/10.3390/pr11092523 - 23 Aug 2023

Cited by 5 | Viewed by 1182

Abstract

Hydropower stations are an important source of clean energy, usually operating in sandy water flow, and the turbine wheels may suffer severe wear and tear. In addition, during the operation of the unit, it is necessary to operate at different water heads according to the actual situation, which will result in varying degrees of wear and tear. In this paper, the Lagrange method is used to study the wear characteristics of a Francis turbine under different water heads. The research object is the water turbine in Wanjiazhai Hydropower Station. Research has shown that wear on the walls of the turbine volute, guide vanes, and runner is inevitable, and the clearance walls are also vulnerable to wear. The difference in the water head mainly affects the movement trajectory and impact speed of particles. The higher the water head, the more severe the wear on the wall surface of the flow passage components. Both the crown and lower ring of the runner are worn. The impact of particles causes wear at this location, and the greater the relative velocity relative to the runner, the more severe the wall wear. This indicates that reasonable head operating conditions can effectively reduce wall wear, which provides guidance for the operation of hydraulic turbines. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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15 pages, 10251 KiB

Open AccessArticle

Study on the Internal Flow Characteristics of Long and Short Blade Runners of a 1000 MW Francis Turbine under Different Opening Conditions

by Hao Chen, Yonggang Lu, Kui Liu, Zequan Zhang, Honghui Li, Xingxing Huang, Weiqiang Zhao and Zhengwei Wang

Processes 2023, 11(6), 1796; https://doi.org/10.3390/pr11061796 - 13 Jun 2023

Cited by 5 | Viewed by 1263

Abstract

The 1000 MW Francis turbine unit at the Baihetan hydropower station is the maximum capacity unit in the world at present, and it has adopted the runner type with long and short blades. For this ultra-high output Francis turbine, especially with the breakthrough runner structure, the hydraulic excitation phenomenon caused by internal dynamic and static interference is the key factor for the stability of the unit. In this study, the 1000 MW Francis turbine unit is taken as the research object, and the rated output conditions with different guide vane openings are selected for comparative analysis. The flow field structure and the pressure pulsation characteristics inside the guide vane and runner under different openings are obtained. The distribution characteristics and evolution law of the vortex in the runner under different guide vane openings are analyzed. The results show that the dynamic and static interference between the runner and the guide vane induces the local high-speed flow to appear in the vaneless area, and the larger the guide vane opening, the smaller the dynamic and static interference between the runner and the guide vane; the vortex in the runner mainly develops and evolves from the inlet to the outlet and is mainly distributed near the blade wall surface. The pressure pulsation inside the runner is mainly due to the action of dynamic and static interference. The pressure pulsation induced by the dynamic and static interferences shows a decreasing law from the runner inlet to the runner outlet. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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14 pages, 7693 KiB

Open AccessArticle

Research on Two-Way Contra-Rotating Axial-Flow Pump–Turbine with Various Blade Angles in Pump Mode

by Yiming Chen, Ce An, Rongyong Zhang, Qiang Fu and Rongsheng Zhu

Processes 2023, 11(5), 1552; https://doi.org/10.3390/pr11051552 - 18 May 2023

Cited by 3 | Viewed by 1429

Abstract

In tidal two-way contra-rotating units, significant differences in performance often occur when arranging the front and rear impellers, which requires an optimized design of the impellers. To solve this problem, by reducing the blade inlet and outlet angles, the impact of different blade angles on the performance of two-way pump–turbines and the internal flow was explored, and the effects of the blade inlet angle of the impellers on the performance of the counter-rotating pump were obtained. Afterward, the streamline and vorticity of the two-stage impeller at different angles were analyzed. The results show that different blade angles will have a certain impact on the internal flow of the two-way pump–turbine. Different blade outlet angles have a significant impact. The variation in different inlet blade angles is not significant for the vorticity changes in the front impeller and rear impeller. In addition, changes in the outlet blade angle will have an impact on the location of LE impact water of the rear impeller, which in turn affects the contours of vorticity of the rear impeller near LE, which also means that the vorticity in this area is mainly dominated by the vortex stretching term. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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Review

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16 pages, 859 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Current, Projected Performance and Costs of Thermal Energy Storage

by Laura Pompei, Fabio Nardecchia and Adio Miliozzi

Processes 2023, 11(3), 729; https://doi.org/10.3390/pr11030729 - 28 Feb 2023

Cited by 14 | Viewed by 7599

Abstract

The technology for storing thermal energy as sensible heat, latent heat, or thermochemical energy has greatly evolved in recent years, and it is expected to grow up to about 10.1 billion US dollars by 2027. A thermal energy storage (TES) system can significantly improve industrial energy efficiency and eliminate the need for additional energy supply in commercial and residential applications. This study is a first-of-its-kind specific review of the current projected performance and costs of thermal energy storage. This paper presents an overview of the main typologies of sensible heat (SH-TES), latent heat (LH-TES), and thermochemical energy (TCS) as well as their application in European countries. With regard to future challenges, the installation of TES systems in buildings is being implemented at a rate of 5%; cogeneration application with TES is attested to 10.2%; TES installation in the industry sector accounts for 5% of the final energy consumption. From the market perspective, the share of TES is expected to be dominated by SH-TES technologies due to their residential and industrial applications. With regard to the cost, the SH-TES system is typically more affordable than the LH-TES system or the TCS system because it consists of a simple tank containing the medium and the charging/discharging equipment. Full article

(This article belongs to the Special Issue State-of-the-Art Energy Conversion and Storage)

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