Experimental Performance Comparison of High-Glide Hydrocarbon and Synthetic Refrigerant Mixtures in a High-Temperature Heat Pump

Round 1

Reviewer 1 Report

In this work, a high-temperature heat pump using high-glide mixture was modelled, simulated and tested, and the performances of thermodynamics and heat transfer were measured and analyzed. The topic fits the scope of the journal, and the paper title well describes the content of the work. The paper is well structured, with persuasively solid results. Overall, I would like to congratulate the authors for completing such an interesting and valuable work.

However, the quality of the paper can be further improved, while my comments are listed as follows. Therefore, I would like to suggest a ‘Major revision’. I would like to wish the authors every future success with their research and I hope my comments are useful to them.

1. Abstract. The background and significance of this study can be mentioned.

2. Introduction. The authors surveyed several existing studies on heat pump using hydrocarbon-based mixture. However, the literature survey is not thorough enough, so that the related conclusion is not comprehensive. For example, in the following paper (DOI: 10.1016/j.seta.2022.102496), a mixed refrigerant containing butane was simulated in a heat pump under a similar working condition with this study. It is suggested to extend the Introduction section, to better reveal the understanding of the authors in the aspect of high-temperature heat pump.

3. Introduction. Some expressions are not precise enough. For example, the authors mentioned ‘Most of the studies focused on refrigerant mixtures with glides of less than 20 K … there is a need for experimental testing of high-glide HC mixtures …’, while they missed some researches. For example, in the following paper (DOI: 10.1016/j.applthermaleng.2023.121300), the experimental studies on a heat pump using high-glide mixture with hydrocarbon were conducted, with detailed experimental results.

4. Introduction. The significance of this study can be mentioned, to promote reader’s interest.

5. Section 2. The modeling of compressor was not mentioned. How did the authors model the compression process in this study?

6. Table 1. What was the range of relative uncertainty of pressure measurement in experiment? A fixed absolute error may cause a huge relative error when the measured value is little.

7. Section 3.4. The supplier of refrigerant should be mentioned, so as the purity of refrigerant used in experiment.

8. Figure 5. The data of COP was obtained in experiment. What about the other two indicators? For example, it is not mentioned if isentropic efficiency was measured or calculated.

9. Figures in the paper. The error bars can be supplemented.

10. It is obvious that the composition shift of a mixture system has great influence on measurement (e.g., enthalpy). How can the authors evaluate the accuracy of their measured results?

11. Some words in the text are suggested to be defined or explained quantitatively. For example, high-glide, what extent of the glide can be called ‘high’? How high is the temperature called ‘high’ temperature for the heat pump?

12. The limitation and future work can be discussed in a separate paragraph.

13. Generally, this paper is well structured and written. And at the very end, I think the significance of this study should be again emphasized. 

n.a.

Author Response

Please refer to section "Reviewer 1" in the attached PDF.

Author Response File: Author Response.pdf

Reviewer 2 Report

The research delves into the potential of high-glide refrigerant mixtures, particularly hydrocarbon (HC) combinations R-290/600 (propane/butane) and R-290/601 (propane/pentane), in augmenting the Coefficient of Performance (COP) of heat pumps, specifically under conditions characterized by significant temperature differentials between the heat source and sink.

By offering empirical validation to theoretical predictions, this study bridges a critical gap in the field. The dearth of experimental substantiation for theoretical conjectures has impeded progress in understanding the efficacy of high-glide refrigerants. Thus, the empirical data presented here constitutes a significant contribution to the literature.

The comprehensive evaluations conducted in this research, covering COP, compressor performance, pressure drop, and heat transfer characteristics, provide a robust foundation for its conclusions. Notably, the study demonstrates that high-glide HC mixtures hold promise for enhancing COP under specific operational scenarios.

In comparison to existing literature, this research offers a substantial advancement by providing empirical evidence to support theoretical assertions. Such empirical validation is crucial for establishing the practical viability of high-glide refrigerants in real-world applications.

While the methodology employed is commendable, there is room for refinement. Implementing additional controls to account for potential variations in experimental conditions and considering a more exhaustive range of factors influencing heat transfer and pressure drop could bolster the robustness of the findings.

The conclusions drawn from the empirical evidence are coherent and align with the presented data. The study effectively addresses key research questions through meticulously designed experiments, bolstering the credibility of its findings.

The references cited are pertinent, encompassing relevant theoretical studies and previous experimental work in the field, thereby situating the research within the broader scholarly discourse.

The presentation of data through tables and figures is clear and aids in elucidating the key findings. However, enhancing the clarity of figures and providing more detailed captions could further facilitate interpretation.

Overall, this research substantiates the potential of high-glide HC mixtures in enhancing the performance of heat pumps, offering valuable insights for researchers and practitioners in the field.

Author Response

Please refer to section "Reviewer 2" in the attached PDF.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I think the authors have well addressed my comments on the original version, so I would like to suggest an 'accept' for publication. Thanks for the great effort by the authors.