A Hybrid Flow Energy Harvester to Power an IoT-Based Wireless Sensor System for the Digitization and Monitoring of Pipeline Networks
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper presents an innovative type of energy harvester that integrates piezoelectric and electromagnetic transduction to capture energy from fluid flow in pipelines, with the goal of powering wireless sensor nodes for the digitization of pipeline networks.
The paper is too long and offer a long literature review also. The introduction is also presenting separately with proper references.
The paper is well written and presented while its theoretical foundation has the required novelty. The present work’ connection with the open literature background is well and adequately justified.
The authors affirm that there has been no development of a pipeline flow-based hybrid energy harvester with a circular piezoelectric plate and two wound coils.
The study investigated how flow pressure, frequency, flow rate, and external resistance affect the performance of hybrid FEH. This innovative solution addresses the limitations of existing systems and ensures continuous power availability for IoT-based, digitized pipeline monitoring systems.
The paper presents clearly the structure and the operational mechanism of a harvester and the modeling and simulations results. The paper presents also the fabrication and experimental results.
The developed HFEH performance is evaluated by comparing it with previously developed FEH from literature.
The paper can be improved by presenting also a comparison between the experimental and the simulation results.
Some specific corrections are needed:
- Figure 5 caption is repeated for two different figures (…the number 5). Pease correct also the citation in the paper text.
- Please correct the Figure notations…sometime you se a dot otherwise not. Please be consistent: Figure 4 or Figure .4 (for example)…
- Please check in all paper text for similar mistakes.
Author Response
Comment 1: The Figure 5 caption is repeated for two different figures (…the number 5). Please also correct the citation in the paper text
Response 1: Yes, it is correct now in the revised manuscript, and all the figure numbers are updated accordingly
Comment 2: Please correct the Figure notations…sometime you se a dot otherwise not. Please be consistent: Figure 4 or Figure .4 (for example)…
Response: Figures notations have been corrected and it is used as Figure 1 throught out the manuscript
Comment 3: Please check all the paper text for similar mistakes.
Response 3: The Whole manuscript was revised for similar mistakes, and all typos and grammatical mistakes were corrected in the revised manuscript
Reviewer 2 Report
Comments and Suggestions for AuthorsReviewer comments, Major Revision required before publication
The manuscript title “A hybrid flow energy harvester to power IoT based wireless sensor system for the digitization and monitoring of pipeline networks”
The manuscript addresses an significant challenge and establishes promising results the design, modeling, fabrication, and experimental validation of a hybrid flow energy harvester which take part piezoelectric and electromagnetic transduction mechanisms. The device, intended for powering wireless sensor nodes in the study or analysis of different pipelines or pipeline monitoring systems. The integration and adoption of an IoT-based wireless pressure monitoring node is presented. A comparative analysis with existing standalone harvesters suggests superior performance. However, this publication is suitable for publication, some important improvements are required in the manuscript experimental validation (realistic conditions), arrangement quality (figures, English language), and contextualization of results need to be further improved.
Comment 1; The modeling section in the manuscript is mathematically dense, it could be better linked to experimental validation. For example, predicted vs. measured and voltage outputs should be compared.
Comment 2; The usage of an air blower as a proxy for gas flow is understandable. However, authors should discuss scaling effects (e.g., turbulence, multiphase flow, pipeline diameter differences).
Comment 3; efficiency metrics (harvested power relative to flow energy) are not provided, incorporation of metrics can strengthen the engineering evaluation.
Comment4; The charging experiment (Figure 16) is convincing, but it is unclear if charging is sustainable under fluctuating flow conditions typical in pipelines.
Comment5; performance under variable flow rates, should be examined in more depth if possible.
Comment 6; The integration of two electromagnetic coils with a piezoelectric unimorph plate is excellent. Though, the manuscript should more explicitly emphasize how this hybridization improves power density beyond additive contributions.
Comment 7; all the Figures require improvement in clarity such as captions, units, higher resolution. Some sections (e.g., equations 2–26) may overwhelm readers summarizing key outcomes would advance readability.
Comment 8; Discussion of limitations and future work is brief and should be expanded if possible.
Minor Comments: Numerous grammatical errors, typing issues, phrasings, and uneven tense usage need to be corrected. An in-depth English-language edit is required. Ensure reliable use of subscript/superscript in equations. table formatting (e.g., Table 2 is difficult to read), figure captions are descriptive but not fully explanatory are need to be revised. Confirm each figure is with proper units and labels.
Comments on the Quality of English Language
Numerous grammatical errors, phrasings, and inconsistent tense usage. A thorough English language edit is required.
Author Response
Comment 1: The modeling section in the manuscript is mathematically dense; it could be better linked to experimental validation. For example, predicted vs. measured values, and voltage outputs, should be compared.
Response 1: We appreciate the reviewer’s valuable comment. The validation between numerical and experimental results is indeed an important step in further strengthening the work. However, for the scope of this manuscript, the focus is limited to the experimental characterization and verification of the hybrid energy harvester under different flow conditions. The experimental data presented have been thoroughly analyzed and verified to demonstrate the feasibility and practical performance of the proposed system.
It is worth noting that the numerical modeling of the device’s natural frequency was carried out and validated using COMSOL Multiphysics simulations, which confirmed the resonance behavior of the harvester components. A comprehensive comparison between simulated and experimental voltage outputs is planned for future work, where the modeling framework will be expanded to predict system performance under various operating conditions.
Comment 2: The usage of an air blower as a proxy for gas flow is understandable. However, authors should discuss scaling effects (e.g., turbulence, multiphase flow, pipeline diameter differences).
Response 2: We appreciate the reviewer’s insightful observation. In this work, an air blower was used as a controllable and safe substitute for gas flow to experimentally evaluate the performance of the hybrid energy harvester under laboratory conditions. This method is commonly adopted in experimental studies of flow energy harvesters, as it allows stable and repeatable flow control for accurate performance assessment. We fully agree that real gas pipelines may exhibit additional effects such as turbulence variation, multiphase flow behavior, and differences in pipeline diameter, which can influence overall performance. To address this, a detailed discussion has been added in the revised manuscript highlighting the potential impact of these scaling effects. The present setup was designed to maintain dynamic similarity under controlled flow conditions, and large-scale testing under real gas pipeline environments is planned as part of future work. Despite these limitations, the current experimental results clearly demonstrate the harvester’s scalability, adaptability, and suitability for diverse low-power industrial pipeline monitoring applications.
Change to the manuscript:
Comparison and discussion section, page 26, paragraphs 1 and 2 are added
Comment 3: efficiency metrics (harvested power relative to flow energy) are not provided, incorporation of metrics can strengthen the engineering evaluation.
Response 3: We thank the reviewer for this valuable suggestion. The efficiency metrics relating harvested electrical power to the total flow energy are indeed important for a complete engineering evaluation. However, in the present experimental setup, it was not feasible to accurately quantify the total mechanical flow energy available to the harvester, as the setup was designed primarily for electrical characterization rather than fluid power measurement. Parameters such as localized pressure distribution, flow turbulence, and fluid–structure interaction within the enclosed T-joint introduce significant uncertainty in estimating the true available flow energy, which could lead to misleading efficiency values.
Therefore, this work focuses on experimentally measured electrical outputs (voltage, current, and power) as direct and reliable indicators of device performance. These results effectively demonstrate the harvester’s capability and scalability under realistic flow conditions. In future studies, a more advanced setup incorporating flow power sensors and CFD-based analysis will be developed to evaluate overall conversion efficiency with higher accuracy
Comment 4: The charging experiment (Figure 16) is convincing, but it is unclear if charging is sustainable under fluctuating flow conditions typical in pipelines.
Response 4: We thank the reviewer for this valuable observation. The charging experiment shown in Figure 16 was conducted under specific flow conditions (flow pressure = 2.90 kPa, flow rate = 11.08 L/s, and flow frequency = 428 Hz) to ensure repeatable testing and performance validation. In real pipeline environments, flow conditions naturally fluctuate; however, charging will still occur under such variations. This is because the hybrid harvester combines piezoelectric and electromagnetic mechanisms that respond dynamically to changes in flow velocity and pressure. In fact, moderate fluctuations can enhance vibration amplitude and momentarily increase power generation. Although the instantaneous charging rate may vary with flow instability, the integrated energy storage element (battery or supercapacitor) smooths these effects by accumulating energy during high-flow periods and delivering it steadily to the load. Therefore, the overall charging process remains continuous and sustainable, demonstrating the robustness of the proposed hybrid design under realistic pipeline conditions
Comment 5; performance under variable flow rates, should be examined in more depth if possible.
Response 5 : We thank the reviewer for this valuable suggestion. The performance of the proposed hybrid energy harvester has indeed been examined under variable flow conditions in terms of both flow pressure and flow rate. All experiments were conducted by varying these parameters to evaluate the device response comprehensively. Specifically, the results presented in Figures 11–13 and 14-16 demonstrate the effect of different flow conditions on the harvester’s output. In particular, the load resistance versus voltage and power characteristics and the frequency versus voltage and power plots were obtained at three distinct flow pressures and corresponding flow rates. These measurements clearly reflect the device’s performance variations with changing flow conditions, confirming that the harvester remains functional and effective across a wide range of operational parameters.
Comment 6: The integration of two electromagnetic coils with a piezoelectric unimorph plate is excellent. Though, the manuscript should more explicitly emphasize how this hybridization improves power density beyond additive contributions.
Response 6:
We sincerely appreciate the reviewer’s positive feedback and valuable suggestion. The integration of two electromagnetic coils with a piezoelectric unimorph plate was intentionally designed to achieve a synergistic hybridization effect that enhances the overall power density beyond the simple additive output of the individual transducers. As presented in Table 4, the proposed hybrid energy harvester achieved a power density of 14.47 µW/cm³, which is higher than most reported standalone piezoelectric and electromagnetic harvesters operating under similar flow conditions. Although a few studies, such as [32] and [44], report higher values, it is essential to note that these results are based on simulation models rather than fabricated and experimentally tested prototypes. In contrast, our device has been fully fabricated and experimentally validated, confirming its practical feasibility and superior real-world performance. The enhanced power density clearly demonstrates the positive effect of hybridization, where the complementary interaction between the piezoelectric and electromagnetic mechanisms results in greater energy conversion efficiency and stability.
Comment 7; all the Figures require improvement in clarity such as captions, units, higher resolution. Some sections (e.g., equations 2–26) may overwhelm readers summarizing key outcomes would advance readability.
Response 7:
We thank the reviewer for this constructive observation. In response, the captions of Figures 2, 4, 15,16, and 17 have been revised to provide clearer descriptions, including relevant parameters, units, and experimental conditions. Additionally, Figures 1, 2,3, 10, 12, 13, 14, 16 and 17 have been updated with higher-resolution images and improved labeling to enhance overall clarity and readability. Furthermore, a new Figure 5 has been added as a visual summary of the analytical modeling section to help readers better understand the derivation flow and key relationships among the equations. These revisions collectively improve figure clarity and make the modeling section more accessible without compromising technical depth.
Comment 8: Discussion of limitations and future work is brief and should be expanded if possible.
Response 8 : We sincerely thank the reviewer for highlighting the need to expand the discussion on limitations and future work. The revised manuscript now includes an extended discussion section addressing these important aspects.
the following paragraph are added to the manuscript in the comparision and discusion section after table 4 "
The developed hybrid energy harvester is highly scalable and adaptable for various pipeline configurations. Although it was initially designed for installation within a standard 32 mm T-joint, it can be seamlessly integrated into pipelines of different diameters using standard reducer or enlarger fittings. The upscaling of the harvester for larger pipelines enhances its performance by providing space for larger piezoelectric and electromagnetic components, which allows stronger fluid interaction and higher vibration amplitudes, resulting in increased output voltage and power. This scalability makes the proposed design versatile for diverse industrial applications where pipeline dimensions and flow characteristics vary significantly.
In practical implementation, several engineering challenges must be addressed to ensure long-term durability and stability. In water pipelines, for example, direct contact between the piezoelectric plate and the working fluid can cause corrosion and erosion over time. Therefore, using waterproof coatings and effective sealing methods is crucial to maintaining the structural integrity of the piezoelectric elements. Similarly, since the design includes permanent magnets, additional magnetic shielding or non-magnetic housings are necessary to prevent interference when the harvester is installed in steel pipelines. Tackling these challenges will enhance the system's reliability and lifespan in real operational environments.
In this study, an air blower was used as a safe and controllable alternative to gas flow during experimental testing. This method is commonly accepted for laboratory-scale evaluation of flow energy harvesters because it allows precise control of flow rate and pressure, ensuring consistent data collection. Although real gas pipelines may experience more complex behaviors like turbulence, multiphase flow, and varying diameters, the current setup was designed to maintain dynamic similarity under controlled conditions. Future research will focus on large-scale field trials to verify performance in real pipeline environments, along with detailed comparisons between analytical and experimental results to improve the theoretical model. Additionally, professional winding of electromagnetic coils will be developed to increase winding accuracy, reduce resistive losses, and improve overall energy conversion efficiency. These improvements will help enhance the durability, scalability, and performance of the harvester for sustainable, self-powered industrial monitoring systems."
Reviewer 3 Report
Comments and Suggestions for AuthorsPlease see file attached below.
Comments for author File: 
Comments.pdf
Author Response
Response to reviewer 3:
We thank the reviewer for this important comment and for recognizing the relevance of the performance comparison presented in Table 4. The section discussing Table 4 has been revised to clarify the comparative evaluation of the developed hybrid flow energy harvester (HFEH) with previously reported electromagnetic (EM) and piezoelectric (PE) harvesters. The revised text now explicitly highlights that the developed HFEH achieves superior performance metrics in terms of output voltage, power, and power density due to the synergistic hybridization of the two transduction mechanisms.
As detailed in Table 4, the proposed HFEH attained a maximum power density of 14.47 µW/cm³, which exceeds the values reported for most standalone EM and PE harvesters under similar flow conditions. While a few devices such as those reported in [29], [32], and [44] show higher values, it is important to emphasize that these results are simulation-based and do not involve fabricated or experimentally validated prototypes. In contrast, the performance values in this work are obtained through actual experimental measurements, confirming the device’s practical efficiency and reliability.
Round 2
Reviewer 2 Report
Comments and Suggestions for Authorsauthor has revised the manuscript carefully and incorported the major changes.
