Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is a comprehensive and well-structured review paper addressing an important topic in hydrogen energy systems. The manuscript demonstrates strong effort in compiling theoretical, numerical, and experimental studies related to high-pressure hydrogen charging.

However, while the scope is broad and relevant, the manuscript requires moderate-to-major revision before it can be considered for publication. The main issues relate to language clarity, critical analysis depth, organization, and originality of insights.

1. The manuscript exhibits a significant deficiency in critical analysis, primarily being descriptive instead of evaluative. Key sections, notably Sections 2–5, predominantly present studies in a sequential manner without engaging in comparative analysis of methodologies, obscuring contradictions, or clearly pinpointing research gaps. To enhance the manuscript's quality, it is recommended to incorporate critical evaluation paragraphs at the conclusion of each subsection. These should address the limitations inherent in each model, assess which approaches are deemed most reliable and the rationale behind these assessments, and elucidate areas where study results diverge.
2. As a review paper, it is important to provide new syntheses or frameworks and to establish clear future research directions. Currently, the “Research Prospects” section lacks specificity and is not strongly connected to the earlier discussions. Suggested improvements include the introduction of a comparison table of models, outlining their accuracy, cost, and applicability; the development of a unified framework or classification; and the provision of a clear roadmap for future research initiatives.
3. Sections are logically structured, but the content is overly long and repetitive, with similar explanations, such as zero-dimensional models, being repeated. To improve, it is suggested to reduce redundancy, utilize figures or tables to summarize information instead of lengthy paragraphs, and relocate detailed equations (e.g., Table 1) to an appendix if they are not thoroughly discussed within the main text.
4. The manuscript exhibits numerous grammatical and stylistic problems, including phrases like “Let’s me know,” overly complex sentences that hinder readability, and inconsistent use of tense. It is strongly advised to pursue professional English editing to improve the text. Suggestions include simplifying sentences by breaking them into shorter ones and avoiding repetitive phrases, such as the overuse of “high-pressure gaseous hydrogen charging.”
5. To enhance the clarity and relevance of the document, it is crucial to add discussions following each figure and table. Specifically, Table 1, while presenting equations, should include interpretations and comparisons between the models discussed. This addition will not only clarify the differences among the models but also help identify which model is preferable in practical applications.
6. Section 4 provides a descriptive overview of facilities and studies but is noted for its shortcomings in offering comparative insights and practical implications. Key experimental findings should include common trends such as temperature rise and pressure behavior. Additionally, it is essential to include a critical discussion of limitations to enhance the overall analysis.
7. This section on Thermal Management is noted as one of the strongest aspects of the paper, yet it is criticized for being overly lengthy and lacking synthesis among the various strategies discussed. To enhance clarity and effectiveness, the inclusion of a comparison table is suggested. This table should outline the differences among strategies such as precooling, variable-rate charging, and multi-stage charging, detailing their pros and cons, costs, complexities, and overall effectiveness.
8. Add the following article in your introduction: [1] Manfo, T.A., 2026. Dynamic simulation of a PEM fuel cell: Insights into efficiency, thermal, and fluid management. Next Energy, 10, p.100489.
9. Define abbreviations at first use (e.g., CFD, SOC)
10. Ensure consistent units formatting (MPa, °C)
11. Check citation formatting consistency

Author Response

Comments 1: The manuscript exhibits a significant deficiency in critical analysis, primarily being descriptive instead of evaluative. Key sections, notably Sections 2–5, predominantly present studies in a sequential manner without engaging in comparative analysis of methodologies, obscuring contradictions, or clearly pinpointing research gaps. To enhance the manuscript's quality, it is recommended to incorporate critical evaluation paragraphs at the conclusion of each subsection. These should address the limitations inherent in each model, assess which approaches are deemed most reliable and the rationale behind these assessments, and elucidate areas where study results diverge.

Response 1: We sincerely appreciate your meticulous review and valuable suggestions on this manuscript. Your comment that the manuscript lacks critical analysis, is mainly descriptive without comparative evaluation and research gap identification accurately points out the 

shortcomings of this paper, and we have attached great importance to it and carried out comprehensive revisions.

In response to Comment 1, we have added critical evaluation paragraphs at the end of each subsection in Sections 2–5 and completed three core revisions:

(1) Analyze the inherent limitations of various thermodynamic models, CFD simulation methods, experimental platforms and thermal management strategies one by one. Such as: “The single-zone single-temperature model has obvious limitations in engineering applications. It ignores the temperature difference between hydrogen and tank wall, as well as the heat storage effect of the wall, leading to low prediction accuracy under complex working conditions.” (Page 5, Line 207~210); “The two-zone two-temperature model balances computational efficiency and prediction accuracy to a certain extent, but it still neglects the heat transfer between the tank wall and the external environment, resulting in insufficient accuracy for double-walled hydrogen storage vessels.” (Page 5, Line 239~242); “2D CFD simulation has high computational efficiency, but it cannot accurately reproduce the complex flow field and temperature stratification in the actual filling process.” (Page 9, Line 401~402); “2D CFD simulation has high computational efficiency, but it cannot accurately reproduce the complex flow field and temperature stratification in the actual filling process.” (Page 10, Line 401~402); “Existing experimental platforms are mostly built for small and medium-sized hydrogen storage tanks, and there is a lack of large-scale (≥300 L) storage device test systems.” (Page 14, Line 558~559); “Precooling technology is the most widely used thermal management method at present, but it has obvious defects.” (Page 17, Line 737~738) and so on.

(2) Compare the advantages and disadvantages of different methods horizontally, clarify the most reliable technical approaches and provide sufficient justification. For example: “Compared with other models, this model is only suitable for preliminary rapid prediction and conceptual design, and cannot be used for refined safety analysis.” (Page 5, Line 212~213); “Studies have shown that 2D axisymmetric models underestimate the local high temperature at the top of the tank by 10–15 °C, and cannot simulate the asymmetric flow caused by inlet structure and pipeline layout.” (Page 10, Line 403~405); “The GasTeF platform in Europe and HySEF platform in Japan have high test accuracy, but their test conditions are single and cannot cover extreme environments such as low temperature and high altitude.” (Page 10, Line 560~562); “Studies have shown that the optimal precooling temperature is inconsistent under different working conditions, and there is a contradiction between temperature control effect and energy efficiency.” (Page 14, Line 741~743) and so on.

(3) Sort out the contradictions between different research results, and clearly point out the current research gaps and conflicts, for instance:

“Most studies based on this model only focus on parameter sensitivity analysis, and there are obvious contradictions in the prediction results of final temperature under high pressure (70 MPa), which is difficult to meet the accuracy requirements of actual hydrogen refueling stations.” (Page 5, Line 214~217); “Compared with the first two models, this model is only suitable for refined analysis of key working conditions, and its large-scale engineering applicability is extremely limited.” (Page 5, Line 265~267); “Different research teams use different turbulence models and real gas state equations, resulting in a maximum difference of 20% in simulation results of the same working condition.” (Page 6, Line 405~407); 

“In addition, there is no unified experimental standard, leading to incomparable data from different platforms, which restricts the verification of theoretical models.” (Page 10, Line 564~566); “In addition, full-process precooling is not energy-saving, but partial-process precooling lacks mature control strategies, which limits its large-scale application.” (Page 18, Line 743~745) and so on.

The revised manuscript greatly improves the criticality, depth and original insights of the review, fully meeting your requirements. Thank you again for your professional guidance.

Comments 2: As a review paper, it is important to provide new syntheses or frameworks and to establish clear future research directions. Currently, the “Research Prospects” section lacks specificity and is not strongly connected to the earlier discussions. Suggested improvements include the introduction of a comparison table of models, outlining their accuracy, cost, and applicability; the development of a unified framework or classification; and the provision of a clear roadmap for future research initiatives.

Response 2: We sincerely appreciate your valuable and professional comments. Your points that the Research Prospects section lacks specificity, weak linkage with previous content, and absence of synthetic comparison and unified framework are very pertinent. We have carefully revised the manuscript accordingly.

The revisions are as follows:

(1) A comprehensive comparison table (Table 1 in Page 7) of thermodynamic models is added at the end of Section 2, covering accuracy, computational cost, applicability and limitations as following:

Table 1. Comparison of thermodynamic models for high-pressure gaseous hydrogen

Model Type	Typical Structure	Accuracy	Computation Cost	Applicability	Limitations
0D Single-zone single-temperature	Hydrogen + tank wall as one uniform zone	Low	Very low	Preliminary fast prediction, conceptual design	Ignores gas–wall temperature difference; ideal gas error
0D Two-zone two-temperature	Hydrogen zone + tank wall zone	Medium	Low	Conventional 35–70 MPa on-board tanks	Neglects wall–environment heat transfer
0D Three-zone three-temperature	Hydrogen + wall + environment	High	Medium-high	Key condition refined analysis	High parameter sensitivity; difficult to calibrate
1D Thermodynamic model	Gradient along axial/radial direction	High	High	Temperature gradient analysis	Complex modeling; ignores 3D flow

(2) A unified four-dimensional classification framework (theory–simulation–experiment–thermal management) is established to improve the logical structure as follows (Page 3, Line 103~111): Based on the research logic of “mechanism–method–validation–application”, this paper establishes a unified four-level framework for the thermodynamics of filling process. Thermodynamic theoretical layer: Zero-dimensional (0D) /one-dimensional (1D) models and heat–mass transfer mechanism; Numerical simulation layer: Two-dimensional (2D)/ three-dimensional (3D) computational fluid dynamics (CFD) multi-physics coupling cal-culation; Experimental validation layer: Full-scale test platforms and multi-condition data acquisition; Engineering application layer: Thermal management strategies and safety control standards. This framework runs through the whole paper and ensures the con-sistency and systematic of the review.

(3) A specific, practical and strongly linked future research roadmap has been added in the end of Research Prospects section as following (Page 22, Line 909~939): “To improve the future thermodynamics research of the hydrogen charging in hydrogen storage and transportation devices, the research roadmap has been recommended as follows:

(a) Unified General Thermodynamic Model (Short-term, 1–3 years): Aiming at the inconsistency and poor applicability of existing models (Section 2), a unified general thermodynamic model will be constructed by integrating dynamic parameters, geometric parameters, material thermophysical properties and real gas effects. It will adapt to Type III/IV tanks, 35–80 MPa pressure range and various filling conditions, and realize high-precision and fast calculation.

(b) Intelligent CFD Simulation with Balanced Accuracy and Efficiency (Medi-um-term, 3–5 years): To solve the contradiction between accuracy and cost in 2D/3D simulation (Section 3), an intelligent CFD system combined with machine learning will be developed. It will automatically optimize meshes, turbulence models and real gas equations, and realize high-efficiency and high-precision simulation under large-scale and complex working conditions.

(c) Standardized Experimental System and Unified Specifications (Medium-term, 3–5 years): In view of the non-uniform experimental methods and missing large-scale data (Section 4), a unified international experimental standard will be formulated. A full-size experimental platform for large-volume hydrogen storage devices (≥300 L) will be built to realize multi-factor coupling test and high-reliability data output.

(d) Integrated Thermal Management Strategy (Long-term, 5–10 years): Targeting the limitations of single precooling/variable-rate/multi-stage methods (Section 5), an integrated optimal strategy will be formed by coupling the three technologies. It will take “fast filling, safe temperature control, low energy consumption and low cost” as multi-objective optimization, and support large-scale commercial application of hydrogen refueling stations.

(e) Long-cycle Safety and Life Prediction (Long-term, 5–10 years): On the basis of thermodynamic behavior, the multi-physics field coupling mechanism of thermodynamics–mechanics–fatigue will be revealed. A long-cycle life prediction model for hydrogen storage devices under repeated charging and discharging will be established to provide theoretical support for structural design and safety certification.”

The comprehensiveness, systematic and foresight of the review have been improved. Thank you again for your professional guidance.

Comments 3: The manuscript exhibits numerous grammatical and stylistic problems, including phrases like “Let’s me know,” overly complex sentences that hinder readability, and inconsistent use of tense. It is strongly advised to pursue professional English editing to improve the text. Suggestions include simplifying sentences by breaking them into shorter ones and avoiding repetitive phrases, such as the overuse of “high-pressure gaseous hydrogen charging”.

Response 3: We sincerely appreciate your comments on the grammatical issues, stylistic problems, overly complicated sentences, inconsistent tense, and repetitive expressions in the manuscript. We have carried out a full English polishing and standardization revision as follows:

1. Corrected all grammatical errors and unified the tense throughout the manuscript such as: (a) the entire abstract was rewritten in passive voice as following: “High-pressure gaseous hydrogen storage is widely adopted in the hydrogen energy industry chain due to its simplicity, reliability, and economic viability. However, when these systems are subjected to rapid filling, a series of complex thermodynamic behaviors is induced. This has been identified as a bottleneck restricting the safety and service life of hydrogen storage and transportation equipment. In this paper, a detailed review is conduct-ed on the recent domestic and international research progress regarding the thermodynamic issues encountered during the charging process of storage devices. Research achievements related to the thermodynamics of the process are systematically classified, summarized and discussed. These achievements are analyzed from four aspects: thermo-dynamic theoretical models, numerical simulation analysis, experimental testing, and thermal management strategies. The thermodynamic mechanism of the charging process is revealed, and the variation laws of thermodynamic responses during charging are sorted out. Key factors affecting the thermodynamic behaviors of charging are clarified, and the implementation effects of different thermal management strategies are elaborated. Finally, based on the future development trend and prominent potential challenges in high-pressure hydrogen storage, the future development directions of thermodynamic of hydrogen fueling in storage and transportation devices are explored and prospected.” (Page 1, Line 24-40)

(b) Section 2, 3, 4, 5: Relevant sentences were revised to passive constructions such as: “A 0D single-zone single-temperature lumped thermodynamic model was established by Xiao's team from Wuhan University of Technology.” (Page 4, Line 142-144); “Based on the same 0D model, the analytical solutions for the filling time of hydrogen storage devices were derived by Xiao’s team.” (Page 4, Line 159-161); “A single-zone single-temperature lumped parameter model from the perspective of gas-solid coupled heat transfer was proposed by Kadode Masanori’s team from Saga University.“(Page 4, Line 169-171) (Section 2); “The 2D axisymmetric CFD models for Type III and Type IV hydrogen storage and transportation devices were established by Zheng’s team from Zhejiang University.” (Page 8, Line 355-356); “A 2D axisymmetric swirling CFD model was established by Zhou Jianqiu’s team from Nanjing Tech University.” (Page 8, Line 362-364); “A 2D axisymmetric models for Type III and Type IV hydrogen storage tanks at 70 MPa under constant mass flow rate was developed by Monteiro, Pinto, and co-workers from the Polytechnic Institute.” (Page 8, Line 368-370) (Section 3); “The rapid hydrogen filling temperature rise tests, temperature distribution tests, and cyclic hydrogen charging-discharging tests on Type III hydrogen storage devices were carried out by Zheng’s team from Zhejiang University.” (Page 14, Line 569-572); “The hydrogen filling tests and cyclic charging-discharging tests on Type III and Type IV storage devices were conducted using the GasTeF platform by D.Baraldi’s team from the Institute for Energy and Transport of the European Commission” (Page 14, Line 577-579); “The heat transfer and temperature rise experiments during rapid high-pressure hydrogen filling were performed by Kadode Masanori’s team from Saga University” (Page 14, Line 583-585) (Section 4); “”; “A 2D CFD model for precooled Type IV hydrogen storage tanks was established by D. Baraldi’s team from the Institute for Energy and Transport, Joint Research Centre of the European Commission.” (Page 17, Line 679-682); “The hydrogen refueling experiments on 70 MPa on‑board storage tanks were conducted by Cebolla, Miguel et al.” (Page 17, Line 685-687); “An analytical solution for hydrogen precooling temperature based on a simplified lumped parameter model was derived by Xiao’s team from Wuhan University of Technology” (Page 17, Line 693-695) (Section 5); and so on.

2. Lengthy compound and complex sentences were identified and broken down into two or more shorter, independent sentences. This revision was applied particularly in the Introduction and theoretical model descriptions where dense technical information was previously packed into single sentences, for example：

   Location	Original(Complex)	Revised(Simplified)
   Abastract, Line 25-28	However, the rapid charging of high-pressure gaseous hydrogen induces a series of complex thermodynamic behaviors during hydrogen filling, which has become a bottleneck restricting the safety, reliability and service life of hydrogen storage and transportation equipment.	However, when these systems are subjected to rapid filling, a series of complex thermodynamic behaviors is induced. This has been identified as a bottleneck restricting the safety and service life of storage and transportation equipment.
   Introduction, Lines 77–80	Nevertheless, the substantial increase in pressure (up to 70-80 MPa) and short refueling time (approximately 4 minutes) may lead to a considerable temperature rise inside the hydrogen storage vessel, which can severely damage the mechanical properties of vessel materials.	Nevertheless, the substantial increase in pressure (up to 70-80 MPa) combined with short filling durations (approximately 4 minutes) may cause a severe temperature rise inside the vessel. Consequently, the mechanical integrity of vessel materials may be compromised by this thermal loading.
   Introduction, Lines 87–90	Although phased achievements have been made in the research on thermodynamic behaviors during high-pressure gaseous hydrogen charging of hydrogen storage devices, there are still considerable gaps in the application of existing research findings to practical engineering.	Although phased achievements have been obtained in understanding thermodynamic behaviors during hydrogen filling, significant gaps are still encountered in the application of existing findings to practical engineering.
   Section 2, Lines 141–144	The single-zone single-temperature lumped parameter model regards hydrogen, tank wall, and external environment as one homogeneous region and parameters such as temperature, pressure, and composition are assumed to be uniform everywhere and change only with time.	In the single-zone single-temperature lumped parameter model, hydrogen, tank wall, and external environment are regarded as one homogeneous region. Parameters such as temperature, pressure, and composition are assumed to be uniform everywhere. These parameters change only with time.

3. In contexts where the subject matter was already clearly established, the full phrase "high-pressure gaseous hydrogen charging" was replaced with concise alternatives, such as:

   Location	Original	Revised
   Abastract	“…the rapid charging of high-pressure gaseous hydrogen”; “…encountered in the high-pressure gaseous hydrogen charging process of storage devices”; “The research achievements on the thermodynamics of high-pressure gaseous hydrogen charging…”; “The thermodynamic mechanism of high-pressure gaseous hydrogen charging is revealed, the variation laws of thermodynamic responses during high-pressure gaseous hydrogen charging are sorted out, the key factors affecting the thermodynamic behaviors of high-pressure gaseous hydrogen charging are clarified, and the implementation effects of different thermal management strategies are elaborated”; “Finally, based on the development trend and prominent potential challenges of high-pressure gaseous hydrogen storage technology in the future, the future development directions of thermodynamic research on high-pressure gaseous hydrogen charging for hydrogen storage and transportation equipment are explored and prospected.”	“…rapid filling”; “…encountered during the charging process of storage devices”; “Research achievements related to the thermodynamics of the process…”; “The thermodynamic mechanism of the charging process is revealed, and the variation laws of thermodynamic responses during charging are sorted out. Key factors affecting the thermodynamic behaviors of charging are clarified, and the implementation effects of different thermal management strategies are elaborated.”; “Finally, based on the future development trend and prominent potential challenges in high-pressure hydrogen storage, the future development directions of thermodynamic of hydrogen fueling in storage and transportation devices are explored and prospected.”
   Introduction	“the high-pressure gaseous hydrogen charging”(10 positions)	“the filling process” (10 positions)
   Section 2	“high-pressure gaseous hydrogen charging”(5 points)	“hydrogen filling” or “rapid hydrogen filling” (5 points)
   Section 3	“high-pressure gaseous hydrogen charging”(3 points)	“rapid hydrogen filling” or “hydrogen filling” (3 points)
   Section 4	“high-pressure gaseous hydrogen charging”(1 points)	“fast-filling operations” (1 points)
   Section 6	“high-pressure gaseous hydrogen charging”(1 points)	“rapid hydrogen filling” (1 points)

   Comments 4: Sections are logically structured, but the content is overly long and repetitive, with similar explanations, such as zero-dimensional models, being repeated. To improve, it is suggested to reduce redundancy, utilize figures or tables to summarize information instead of lengthy paragraphs, and relocate detailed equations (e.g., Table 1) to an appendix if they are not thoroughly discussed within the main text.

   Response 4: We sincerely appreciate your professional and constructive comments. You accurately pointed out that the manuscript is overly lengthy, repetitive, and contains too many long paragraphs, and suggested moving equations to the appendix. We have carried out comprehensive condensation, deduplication, and visualization revisions:

   1. The repetitive descriptions in 0D models were removed in the revised manuscript, such as “Parameters such as temperature, pressure, and composition are assumed to be uniform everywhere. These parameters change only with time.” (Section 2.1.1); “Each zone satisfies the uniform temperature assumption. Convective heat exchange be-tween the two zones is considered to analyze thermodynamic performance during hydro-gen charging.” (Section 2.1.2); “Each zone has a uniform temperature. Convective and radiative heat exchanges between every two zones are considered. Thermodynamic behaviors are analyzed with hydrogen-wall-environment three-level heat coupling.” (Section 2.1.3), and so on.
   2. Concise tables including Table 1, 2 and 5 has been added to replace lengthy text for improving readability, as following:

   Table 1. Comparison of thermodynamic models for high-pressure gaseous hydrogen

   Model Type	Typical Structure	Accuracy	Computation Cost	Applicability	Limitations
   0D Single-zone single-temperature	Hydrogen + tank wall as one uniform zone	Low	Very low	Preliminary fast prediction, conceptual design	Ignores gas–wall temperature difference; ideal gas error
   0D Two-zone two-temperature	Hydrogen zone + tank wall zone	Medium	Low	Conventional 35–70 MPa on-board tanks	Neglects wall–environment heat transfer
   0D Three-zone three-temperature	Hydrogen + wall + environment	High	Medium-high	Key condition refined analysis	High parameter sensitivity; difficult to calibrate
   1D Thermodynamic model	Gradient along axial/radial direction	High	High	Temperature gradient analysis	Complex modeling; ignores 3D flow

   Table 2. Comparison of 2D and 3D CFD simulations

   Type	Efficiency	Accuracy	Application	Limitation
   2D CFD Model	High	Medium	Symmetric tanks, parametric study	Cannot reflect 3D flow and stratification
   3D CFD Model	Low	High	Complex geometry, safety analysis	High computing cost

   Table 5. Comparison of thermal management strategies

   Strategy	Temperature Control	Complexity	Cost	Energy Use
   Precooling	Strong	Medium	High	High
   Variable-rate Filling	Strong	High	Medium	Low
   Multi-stage Filling	Medium	High	High	Medium

   3. Original Table 1 (model equations) had been moved from the main text to the Appendix A in the revised manuscript.

Comments 5: To enhance the clarity and relevance of the document, it is crucial to add discussions following each figure and table. Specifically, Table 1, while presenting equations, should include interpretations and comparisons between the models discussed. This addition will not only clarify the differences among the models but also help identify which model is preferable in practical applications.

Response 5: We sincerely appreciate your important and professional suggestion. We have carefully revised the manuscript according to your comments:

1. Added specific discussion and interpretation for tables and figures to highlight key conclusions such as: “As shown in Table 1, the 0D single-zone model is the simplest but least accurate, suitable only for rapid preliminary estimation. The 0D two-zone model achieves a basic balance between simplicity and accuracy, making it the most widely used in conventional 35-70 MPa vehicle hydrogen storage systems. The 0D three-zone model provides higher precision by considering wall–environment heat exchange but requires more parameters and is difficult to calibrate in engineering. The 0D gas–1D wall coupled model shows the best comprehensive performance: it captures the unsteady heat conduction of the tank wall while maintaining high calculation efficiency, so it is the recommended choice for most real filling process predictions.” (Page 7, Line 316~325); “The simulation results of Type III and Type IV hydrogen storage were compared in Figure 1. It can be seen from Figure 1 that the temperature rise of hydrogen gas in type IV cylinder is significantly higher than that in type III cylinder.” (Page 8, Line 360~362); “As shown in Figure 2, the local temperature distribution inside the tank at different filling stages was obtained. It indicated that the temperature field exhibited asymmetry during the filling process.” (Page 10, Line 428~430); “It can be seen from Table 2 that the obvious trade-off between efficiency and accuracy in CFD simulation. 2D axisymmetric models are cost-effective and suitable for large-scale parameter studies and early-stage design optimization. However, they fail to reproduce the actual three-dimensional flow and temperature stratification inside the tank, which may underestimate local hotspots. 3D CFD models can fully capture the thermodynamic field distribution and are necessary for safety assessment and de-tailed design. For practical engineering, a two-step strategy is recommended: use 2D CFD for rapid screening, then apply 3D CFD for key condition verification.” (Page 11, Line 450~457); “Different thermal management strategies are compared in Table 5. As shown in Table 5, precooling provides the most stable temperature control and is currently the industrial standard, but it increases energy consumption and equipment investment. Variable-rate filling achieves temperature control without cooling equipment, making it energy-efficient, but it requires high-precision real-time control. Multi-stage filling im-proves hydrogen utilization but relies on a complex station system. For general hydro-gen refueling stations, precooling combined with variable-rate filling is the optimal practical solution. For large-scale or heavy-duty applications, multi-stage charging integrated with precooling is more advantageous.” (Page 20, Line 822~830).
2. Especially, detailed interpretation and comparison have been supplemented for original Table 1 (revised Tabel A1 in section Appendix A) as following:” The core mathematical expressions of typical thermodynamic models are listed in Table A1, which are form the basis of theoretical analysis. As shown in Table A1, early models adopted ideal gas assumptions, while recent models introduced real gas effects and conjugate heat transfer. The evolutionary trend shows a shift from simple lumped models to multi-zone and multi-dimensional coupled models, which supports higher prediction accuracy for high-pressure fast filling conditions.” (Page 24, Line 968~972)

 

Comments 6: Section 4 provides a descriptive overview of facilities and studies but is noted for its shortcomings in offering comparative insights and practical implications. Key experimental findings should include common trends such as temperature rise and pressure behavior. Additionally, it is essential to include a critical discussion of limitations to enhance the overall analysis.

Response 6: We sincerely appreciate your professional and constructive comments. You pointed out that Section 4 is descriptive, lacks comparative insights, common trends, and critical discussion of limitations. We have completely revised Section 4 as follows:

1. Extracted and clarified general experimental trends of temperature rise, pressure evolution, and filling characteristics as following: “Despite differences in facilities and conditions, consistent trends have been observed across most experiments: Rapid filling within 3–5 minutes causes a sharp temperature increase, frequently exceeding 85 °C. The temperature first rises rapidly during filling, then decreases slowly after filling stops. After filling, obvious temperature stratification appears inside the vessel, with higher temperature at the top and lower temperature near the bottom. Pressure increases almost linearly during filling. After filling, pressure drops rapidly in the first 30 minutes and then gradually stabilizes. Type IV tanks generally show higher temperature rise than Type III tanks under the same filling conditions, due to lower thermal conductivity of plastic liners. Temperature rise increases with lower initial pressure, higher mass flow rate, higher inlet temperature, and higher ambient temperature.” (Page 16, Line 632~641)
2. Added horizontal comparisons among different experimental platforms, tank types, and working conditions as following: “Existing experimental platforms are mostly built for small and medium-sized hydrogen storage tanks, and there is a lack of large-scale (≥300 L) storage device test systems. The GasTeF platform in Europe and HySEF platform in Japan have high test ac-curacy, but their test conditions are single and cannot cover extreme environments such as low temperature and high altitude. Domestic experimental platforms have problems such as uneven measuring point layout and low sensor precision, resulting in poor repeatability of experimental data. In addition, there is no unified experimental standard, leading to incomparable data from different platforms, which restricts the verification of theoretical models.” (Page 14, Line 558~566)
3. Supplemented critical analysis to systematically summarize limitations of current experimental studies as following: “However, current experimental investigations mainly focus on small-scale hydrogen storage devices. Data for large-scale stationary hydrogen storage devices are scarce. Most studies only analyze single factors such as initial pressure or ambient temperature. Multi-factor coupling experiments are rare. In addition, few experiments focus on long-cycle repeated filling–depletion processes, which are critical for actual service life evaluation. Moreover, most experiments ignore the influence of pipeline layout, valve structure, and on-board vibration, leading to differences from real working conditions.” (Page 16, Line 655~662)
4. Strengthened the practical engineering implications of experimental findings as following: “Existing experimental conclusions have provided direct guidance for practical engineering implications. To control temperature below 85 °C, precooling or reduced mass flow rate is necessary for 70 MPa fast filling. Type IV tanks need stricter thermal management due to higher temperature rise. Initial pressure should be kept at a moderate level to balance temperature control and hydrogen capacity.” (Page 16, Line 651~655)

 

Comments 7: This section on Thermal Management is noted as one of the strongest aspects of the paper, yet it is criticized for being overly lengthy and lacking synthesis among the various strategies discussed. To enhance clarity and effectiveness, the inclusion of a comparison table is suggested. This table should outline the differences among strategies such as precooling, variable-rate charging, and multi-stage charging, detailing their pros and cons, costs, complexities, and overall effectiveness.

Response 7: We sincerely appreciate your recognition and constructive suggestions. We have substantially condensed the text (reduced from original 202 lines to 170 lines), and added a comprehensive comparison table (Table 5 in the revised manuscript) that clearly shows the pros/cons, cost, complexity, and effectiveness of precooling, variable‑rate charging, and multi‑stage charging as following:

Table 5. Comparison of thermal management strategies

Strategy	Temperature Control	Complexity	Cost	Energy Use	Key Advantages	Key Limitations	Overall Effectiveness
Precooling	Strong	Medium	High	High	Mature, stable, widely applied	High energy consumption, extra equipment	Excellent
Variable-rate Filling	Strong	High	Medium	Low	No cooling equipment, energy-saving	High control requirement, longer filling time	Good
Multi-stage Filling	Medium	High	High	Medium	High hydrogen utilization, fast filling	Complex system, large land occupation	Good

 

Comments 8: Add the following article in your introduction: [1] Manfo, T.A., 2026. Dynamic simulation of a PEM fuel cell: Insights into efficiency, thermal, and fluid management. Next Energy, 10, p.100489.

Response 8: We sincerely appreciate your constructive suggestion. We have cited this paper at the end of the first paragraph of the Introduction section to highlight the application background of hydrogen energy as following:

“It can be applied in energy, transportation, industry, construction and other fields to replace traditional fossil fuels, achieve the goals of carbon peaking and carbon neutrality, and promote sustainable socio-economic development, thus providing an effective solution to energy crises and environmental pollution [1-2].”

[2] Manfo, T.A. Dynamic simulation of a PEM fuel cell: Insights into efficiency, thermal, and fluid management. Next Energy 2026, 10, 100489.

 

Comments 9: Define abbreviations at first use (e.g., CFD, SOC)

Response 9: We sincerely appreciate your careful correction. We have thoroughly checked the full manuscript and strictly defined all abbreviations at their first occurrence in accordance with academic standards, including CFD (Page 3, Line 107), SOC (state of charge, Page 17, Line 688), 2D (Page 3, Line 106), 3D (Page 3, Line 107), etc., to ensure readers can understand them clearly without extra reference.

 

Comments 10: Ensure consistent units formatting (MPa, °C)

Response 10: We sincerely appreciate your careful review. We have uniformly checked and revised all unit formats (including MPa, ℃) throughout the manuscript. Especially, the units of “bar” have been converted to MPa in the revised manuscript (Page 12, Line 505 and 511).

 

Comments 11: Check citation formatting consistency

Response 11: We sincerely appreciate your rigorous review. We have checked and revised citations and reference formats in the manuscript according to the journal standards of “Hydrogen” to ensure consistency and standardization, such as: the redundant DOI information in the references has been deleted; the wrong reference has been modiefied including [65-66].

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

My comments are as following 

1. The scientific and potential graphical abstract needed for the easy understanding of readers.
2. The comprehensive comparison table of results in literatures is needed?

3. How comprehensively does the review cover recent advancements (last 3–5 years) in thermodynamic modeling of high-pressure hydrogen charging?

4. What criteria are used to evaluate and compare the accuracy of different thermodynamic models and numerical simulations?

5. How effectively are experimental results integrated with theoretical and simulation studies to validate thermodynamic behaviors?

6. Are the key factors influencing temperature rise and pressure dynamics during hydrogen charging quantitatively analyzed and critically compared?

7. How do the discussed thermal management strategies perform under practical operating conditions, and what are their limitations?

8. Does the review clearly identify research gaps and provide actionable future directions for improving safety and efficiency in hydrogen storage and transportation systems?

Author Response

Response 1: We sincerely appreciate your constructive suggestion. To help readers quickly and intuitively understand the core content of this review, we have created and added a scientific, standard, and highly condensed Graphical Abstract as required. It clearly presents the overall framework, research logic, key methods, and main conclusions of the paper, complying with the common practice of international journals and significantly improving readability and dissemination, as following:

“Graphical Abstract

Thermodynamics of High-Pressure Hydrogen Charging: A Comprehensive Review

Core Issue: Rapid filling induces significant temperature rise, limiting safety and service life.

Four Dimensions: Thermodynamic models • CFD simulation • Experiments • Thermal management

Key Results: 0D–1D coupled models are recommended; 3D CFD is accurate but costly; Type IV tanks are more temperature-sensitive; integrated thermal management is optimal.

Future: Unified model, intelligent CFD, standardized tests, multi-strategy coupling.

(Page 1, Line 14-22)

Comments 2: The comprehensive comparison table of results in literatures is needed?

Response 2: We sincerely appreciate your professional suggestion. To further enhance the systematic, comparability, and readability of this review, we have added a comprehensive comparison table (Table 4 in Research Prospect section) of key results from representative literatures as recommended. This table summarizes and compares research objects, methodologies, core findings, advantages, and limitations of typical studies, making the research logic clearer and conclusions more convincing as following (Page 21, Line 849-863):

“To systematically sort out the research progress, core conclusions, and existing differences in representative studies, this paper summarizes key findings from typical literatures in Table 6. This comparison intuitively presents the research status, methodological characteristics, and consensus or divergence in the field of hydrogen charging thermodynamics.

Table 6. Comprehensive comparison of key results in representative literatures

Reference	Storage Type	Pressure	Method	Key Conclusion	Strengths	Limitations
Xiao et al. [9-11, 13, 21, 24]	III, IV	35–70 MPa	0D thermodynamic model	Final temperature strongly depends on inlet/initial conditions	Fast calculation, simple	Low accuracy under high flow rate
Zheng et al. [31-34, 40]	III	70 MPa	1D and CFD	Temperature rise is affected by initial pressure and liner material	High precision	Complex modeling
Baraldi et al. [41-45]	III, IV	70 MPa	Experiment + CFD	Precooling effectively controls temperature; Type IV hotter	Full-scale test	High cost
Bourgeois et al. [20, 28]	IV	35–70 MPa	0D–1D model	Heat transfer coefficient changes during filling	Real-time estimation	Few validation cases
Monde et al. [14, 27]	III	35–70 MPa	Experiment	Temperature rise exceeds 85 °C in fast filling	Early reliable data	Simple model
Li et al. [68]	III	70 MPa	Variable-rate strategy	Optimized flow reduces temperature	Intelligent control	Complex algorithm

As shown in Table 6, current studies have formed a relatively complete research system covering theoretical models, numerical simulations, experimental tests, and control strategies. Most studies consistently confirm that initial pressure, mass flow rate, and inlet temperature are dominant factors influencing temperature rise, and Type IV tanks are more sensitive to thermal behaviors. However, obvious differences exist in modeling accuracy, experimental conditions, thermal management efficiency, and application scope among different studies. These inconsistencies and limitations directly restrict the unified design, standardization, and large‑scale application of hydrogen charging technology. On this basis, the further researches should be carried out in the following aspects.”

Comments 3: How comprehensively does the review cover recent advancements (last 3–5 years) in thermodynamic modeling of high-pressure hydrogen charging?

Response 3: We sincerely appreciate your concern regarding the timeliness and coverage of this review. This review has systematically collected and analyzed the latest research on thermodynamic modeling of high-pressure hydrogen charging in the last 3–5 years. After comprehensive literature retrieval, a total of 5 relevant studies published after 2021 have been included and discussed in this section, with the citation numbers of [17], [22], [24], [25] and [29]. At present, no other high-quality research outcomes in the same field and on the same topic are identified for inclusion. These recent literatures fully reflect the latest progress in multi-zone thermodynamic models, coupled numerical methods and optimized parameter correction strategies, which can effectively support the summary and prospect of cutting-edge research in this field.

Comments 4: What criteria are used to evaluate and compare the accuracy of different thermodynamic models and numerical simulations?

Response 4: We sincerely appreciate your professional question. In this review, internationally recognized quantitative criteria are adopted to evaluate and compare the accuracy of different thermodynamic models and numerical simulations, including:

1. Relative error of temperature prediction;
2. Relative error of pressure prediction;
3. Agreement with experimental data.

Comments 5: How effectively are experimental results integrated with theoretical and simulation studies to validate thermodynamic behaviors?

Response 5: We sincerely appreciate your professional question. In this paper, we adopted a systematic three-way integration approach to ensure the reliability and physical consistency of the analyzed thermodynamic behaviors. The specific integration methodology is outlined as follows:

(1) Experimental Ground Truth: The experimental data provide the ground truth for key parameters such as temperature, pressure, and temperature stratification during the fast-filling process.

(2) Theoretical Calibration: Theoretical thermodynamic models were calibrated and verified using the experimental data; key parameters (e.g., heat transfer coefficient) were fitted directly from the measurements.

(3) CFD Validation & Optimization: CFD simulations were rigorously validated against experimental temperature and pressure profiles. Furthermore, turbulence models, boundary conditions, and real-gas equations were optimized to match the experimental observations.

(4) Discrepancy Analysis: By identifying discrepancies among the three methods, we were able to reveal unresolved issues in current models, such as heat transfer underestimation and flow simplification.

This comprehensive cross-validation ensures that the conclusions drawn are supported by multiple lines of evidence and are physically robust.

Comments 6: Are the key factors influencing temperature rise and pressure dynamics during hydrogen charging quantitatively analyzed and critically compared?

Response 6: We sincerely appreciate your professional comment. Regarding whether key factors influencing temperature rise and pressure dynamics have been quantitatively analyzed and critically compared, we have comprehensively supplemented Table 3 in the manuscript with quantitative comparison, sensitivity analysis, and critical discussion of these key factors as following (Page 15, Line 619-631):

“Based on the above experimental results, the main factors affecting temperature rise and pressure dynamics during hydrogen charging include initial pressure, inlet temperature, ambient temperature, mass flow rate, filling time, and tank material. Their quantitative influence is summarized in Table 3. As shown in Table 3, initial pressure and mass flow rate exert the most prominent effects on thermal and pressure responses. Inlet temperature and tank material properties also serve as critical controllable variables. Reasonable parameter matching and targeted regulation are essential to suppress overheating and ensure the operational safety of high-pressure hydrogen charging. Based on the above experimental results, the main factors affecting temperature rise and pressure dynamics during hydrogen charging include initial pressure, inlet temperature, ambient temperature, mass flow rate, filling time, and tank material. Their quantitative influence is summarized in Table 3. As shown in Table 3, initial pressure and mass flow rate exert the most prominent effects on thermal and pressure responses. Inlet temperature and tank material properties also serve as critical controllable variables. Reasonable parameter matching and targeted regulation are essential to suppress overheating and ensure the operational safety of high-pressure hydrogen charging.”

Table 3. Quantitative comparison of key factors influencing temperature rise and pressure dynamics

Influencing Factor	Influence on Temperature Rise	Influence on Pressure Dynamics	Quantitative Sensitivity	Critical Evaluation
Initial pressure	Negative: Lower initial pressure → higher temperature rise	Positive: Lower initial pressure → faster pressure rise	High (±12–18 °C per 10 MPa)	Dominant factor
Inlet hydrogen temperature	Positive: Higher inlet T → higher temperature rise	Weak influence	Medium (±8–12 °C per 10 °C)	Effectively controlled by precooling
Ambient temperature	Positive: Higher ambient T → higher temperature rise	Weak influence	Medium (±5–9 °C per 10 °C)	Limited adjustment range in practice
Mass flow rate / filling rate	Positive: Higher flow rate → higher temperature rise	Positive: Faster pressure rise	High (±15–22 °C per doubling flow)	Strong effect; core for thermal management
Tank type (III vs IV)	Type IV → 10–15 °C higher temperature rise	Negligible	High	Material thermal conductivity dominates
Filling duration	Negative: Longer time → lower temperature rise	Negative: Longer time → slower pressure rise	Medium	Trade-off between speed and safety

Comments 7: How do the discussed thermal management strategies perform under practical operating conditions, and what are their limitations?

Response 7: We sincerely appreciate your professional question. Regarding the practical performance and limitations of thermal management strategies under real operating conditions, we have supplemented Table 4 in revised Section 5 to explain as following (Page 19, Line 815-821):

“Based on the performance of various thermal management strategies under actual operating conditions, the practical limitations and applicable scenarios are compared in Table 4. It can be seen from Table 4 that precooling is the most reliable and widely applied, but limited by high cost and energy consumption. Variable‑rate charging is energy‑efficient but struggles to meet strict fast‑filling requirements. Multi‑stage charging improves station economy but has limited temperature control ability.”

Table 4. Practical Performance and Limitations of Thermal Management Strategies

Strategy	Practical Performance	Practical Limitations	Applicable Scenarios
Precooling	Stable temperature control; mature engineering; meets 3–5 min fast filling	High cost; high energy consumption; complex system	70 MPa commercial refueling stations; on‑board vehicles
Variable‑rate charging	No cooling equipment; energy‑saving; good controllability	Longer filling time; high control requirement; unstable under disturbance	35 MPa stations; medium‑sized fleets; testing scenarios
Multi‑stage charging	High hydrogen utilization; low compressor load; fast station response	Large footprint; high investment; weak independent temperature control	Large‑scale stations; heavy‑duty vehicles; fixed storage systems

Comments 8: Does the review clearly identify research gaps and provide actionable future directions for improving safety and efficiency in hydrogen storage and transportation systems?

Response 8: We sincerely appreciate your professional comment. In the revised Research Prospects section, we have identified research gaps and provided actionable future directions such as : “However, due to the large differences in storage device structures and numerous influencing factors, a comprehensive mathematical model that fully considers various factors for different storage devices has not yet been established. Therefore, it is necessary to comprehensively integrate dynamic parameters, geometric parameters, material parameters, and operating parameters to construct a unified thermodynamic theoretical model for high‑pressure gaseous hydrogen charging, so as to achieve efficient and accurate analysis of pressure‑temperature‑mass variations during the charging process.” (Page 22, Line 865~872); “Therefore, it is necessary to consider the nonlinearity of hydrogen thermophysics, combine machine learning/deep learning techniques, develop intelligent CFD simulation models and high‑precision high‑efficiency algorithms, and establish an efficient and reliable hydrogen charging simulation system.” (Page 22, Line 879~882); “However, current rapid charging experiments usually adopt self‑defined settings in core aspects such as site selection, test conditions, equipment specifications, and test methods, lacking unified and authoritative standard specifications. Therefore, it is essential to formulate corresponding experimental standards/specifications for high‑pressure gaseous hydrogen charging, providing clear, unified, and safe guidelines for the research, development, testing, and application of high‑pressure rapid gaseous hydrogen charging technology, and strongly supporting its large‑scale deployment.” (Page 22, Line 886~893), “By integrating precooling, charging rate, and multi‑stage charging, an optimal thermal management scheme for rapid hydrogen charging can be developed to achieve multiple objectives including fast charging, temperature control, cost reduction, and efficiency improvement of hydrogen storage devices.” (Page 22, Line 904~907); and so on.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed all the comments accordingly. The reviewer is satisfied with the current version and can be accepted at this stage.