Investigation of Microstructure and Density of Atmospheric Ice Formed by High-Wind-Speed In-Cloud Icing
Round 1
Reviewer 1 Report
Manuscript ID: crystals-2467121
Type of manuscript: Article
Title: Investigation of microstructure and density of atmospheric ice formed by high-wind-speed in-cloud icing
Authors: Ruidi Liu *, Yu Liu, Qiang Wang, Xian Yi *
Comments:
The manuscript reports on the macrostructure and mean density of ice sample collected in an ice wind tunnel located at China Aerodynamics Research and Development Center. The authors did not specify the specific objectives of their study. They only noted that the results are presented considering the influence of high wind speed and that “The improved understanding and characterization of microstructure and density of atmospheric ice would contribute to aircraft icing prediction/detection system and anti-/de-icing system design.”
In fact, several samples are analyzed, the choice of conditions for obtaining which is not explained in any way. Microscopic photographs of the macroscopic structure of these ice samples are given. For some reason, the authors call it the microscopic structure of samples. The mean density of these samples was estimated, which the authors, for unknown reasons, call porosity. There is no clear generalization of the obtained results.
The topic of the article is interesting and relevant, the equipment used to obtain the samples is unique.
However, the research methodology was not well thought out. The article needs a complete revision.
The introduction should deal mainly with atmospheric ice.
Atmospheric temperature and humidity do not depend linearly on altitude. Therefore, the choice of specific characteristics of the experimental conditions should be explained in the Materials and Methods section.
The method of obtaining samples for optical measurements, section 2.3, is completely incomprehensible: “Firstly, the ice sample was sliced to 1 mm and put on a heated objective slide, of which the temperature was slightly higher than ice freezing point. Afterwards, the ice was appreciably melted and solidified at the interface of the heated glass and the ice slice, and then the ice sample was fixed on the objective slice.”
“It could be pointed out immediately that the grains were much larger in the apparent ice rather than the rime ice, which were coordinated well with the different freezing rates.” What are the apparent and rime ice in this case?
What can be learned from the dependencies and groupings shown in Figure 9?
Author Response
Dear reviewer #1,
We would like to thank you for your careful work and useful comments. We have discussed your comments and revised the manuscript in accordance with your suggestions (in blue words). We hope that the revised manuscript could satisfy you, and concurrently meet the requirement of Crystals as well.
Reviewer #1:
The manuscript reports on the macrostructure and mean density of ice sample collected in an ice wind tunnel located at China Aerodynamics Research and Development Center. The authors did not specify the specific objectives of their study. They only noted that the results are presented considering the influence of high wind speed and that “The improved understanding and characterization of microstructure and density of atmospheric ice would contribute to aircraft icing prediction/detection system and anti-/de-icing system design.”
In fact, several samples are analyzed, the choice of conditions for obtaining which is not explained in any way. Microscopic photographs of the macroscopic structure of these ice samples are given. For some reason, the authors call it the microscopic structure of samples. The mean density of these samples was estimated, which the authors, for unknown reasons, call porosity. There is no clear generalization of the obtained results.
The topic of the article is interesting and relevant, the equipment used to obtain the samples is unique.
However, the research methodology was not well thought out. The article needs a complete revision.
Response: Thank you for your carful work. As you mentioned, we only presented and discussed the influence of high wind speed to atmospheric ice. It was ascribed to the fact that the atmospheric ice formed at high wind speed is more difficult to acquire and systematically study, compared with low-wind-speed atmospheric ice, which could be obtained by many artificial climate chambers. For a better understanding, we have added the following sentences in the introduction to highlight the characteristics of our research. (line 68 - 75)
“However, these practical expressions were established only considering low-wind-speed (usually < 40m/s) icing environment with the limit of using simple rotating cylinder as impacted object, which barely supported for aircraft icing predic-tion/detection at high wind speed. Herein, based on 3m × 2m ice wind tunnel located at China Aerodynamics Research and Development Center (CARDC), this article presented and discussed the results of preliminary measurements of atmospheric ice obtained during high-wind-speed icing tests.”
The 3m × 2m icing wind tunnel is one of the National Large Infrastructures, thus icing test only serves for icing safety verification of national aircraft models and is not available for designable fundamental research. Therefore, the ice formed on models in icing test can be exactly used to explore the high-wind speed atmospheric ice, but the choice of conditions cannot be designed. At present, it is still in the stage of methodology exploration and development, but the topic is worth doing deeply.
(1) The introduction should deal mainly with atmospheric ice.
Response: As you suggested, the introduction of ice formed by water colling has been simplified as follows: (line 50-59)
“Currently, the research objects mainly focused on the ices which were formed by water cooling or originally from precipitation of snow, for instance, seasonal lake (in-cluding reservoirs) ice [1] and sea ice [14], polar ice cores. Many progresses have been made in exploring the microstructures, physical properties and related engineering applications of the ice [15-18]. However, compared to ices which have abundant re-serves and can be regularly sampling, atmospheric ice, usually assembled on aircraft wings, cables and blades, are much more difficult to acquire and characterize. More-over, there are still many difficulties of handling such a material which is easily broken and modified by a slight change of temperature [10]. Despite centuries of exploration has been focused on atmospheric ice, detailed and in-depth understanding of ice microstructures is still lacked [19].”
(2) Atmospheric temperature and humidity do not depend linearly on altitude. Therefore, the choice of specific characteristics of the experimental conditions should be explained in the Materials and Methods section.
Response: As you suggested, the choice of specific characteristics of the experiment conditions were added as follows:
“The aircraft atmospheric ice sample library was established since the 3m × 2m icing wind tunnel went into operation in 2013, and the icing conditions were chosen according to FAA.FAR (Federal Aviation Administration Regulations) Appendix C, which summarized and provided atmospheric icing conditions in real aeronautical meteorology.” (line 97 - 99)
(3) The method of obtaining samples for optical measurements, section 2.3, is completely incomprehensible: “Firstly, the ice sample was sliced to 1 mm and put on a heated objective slide, of which the temperature was slightly higher than ice freezing point. Afterwards, the ice was appreciably melted and solidified at the interface of the heated glass and the ice slice, and then the ice sample was fixed on the objective slice.”
Response: Thank you for your suggestion, the introduction of ice formed by water colling was simplified as follows: (line 110 - 114)
“Firstly, the top and bottom surface of the ice sample was flatly sliced, and then the suitable-thickness ice sample was placed on a heated glass slide, of which the temperature was slightly higher than ice freezing point. Thus, the bottom of the ice was slightly melted, and immediately refrozen and fixed at the surface of glass slide in the cold environment for further observation.”
(4) “It could be pointed out immediately that the grains were much larger in the apparent ice rather than the rime ice, which were coordinated well with the different freezing rates.” What are the apparent and rime ice in this case?
Response: The apparent and rime ice corresponded to ices formed at different temperature (-5.8 ℃ and -20 ℃), which were different in exterior appearances. (line 137 - 141)
“Differentially, their exterior appearances and internal structures were completely in an extreme variation. The two produced samples respectively had a transparent and a milky white appearance, which were called apparent ice and rime ice. The corre-sponding microstructures were discussed afterwards in detail, including grain size, bubble size, bubble distribution.”
(5) What can be learned from the dependencies and groupings shown in Figure 9?
Response: Different groups related to different characteristics (i.e. spanwise or chordwise) of the airfoil. It can be learned from Figure 9 that R was strongly affected by the wind speed, thus the samples in our atmospheric ice library were all in the high value of R. The density functions of R which developed by data points from previous work were in the range of low wind speed(less than 40 m/s), obviously lack of rigour in taking into account the influence of flow field and the characteristics of the impacted surface. Thus, it is necessary for us to establish a better practical density predicting model which can considered all icing conditions and the shape of the airfoil for aircraft icing. The corresponding discussion was added in the revised-manuscript. (line 255 – line 293)
“Herein, referring to the transformation theory of ice wind tunnel test[27], has been proposed and defined as Equation 5, which considered as a reasonable combination of parameters to define the effect of the characteristics of the impacted surface, the conserved momentum and energy in the flow field and icing environment. In the equation, presented the freezing factor of impacting water on the surface, which was deduced from the energy conservation equation of Messinger model[28]. was the droplet collection coefficient, which could be influenced by the droplet trajectories related to the flow field. LWC and were the liquid water content in and the flow velocity in , respectively.
Among them, was latent heat of freezing, and was specific heat capacity of water on model surface. In addition, three parameters were introduced to describe the process of heat balance: relative heat coefficient , droplet energy transfer potential and air energy transfer potential .
where was surface temperature, was static temperature and was water film temperature, was vapor pressure of water in the atmosphere and was vapor pressure of water over liquid water, was convective heat transfer coefficient and was gas-phase mass transfer coefficient, and was latent heat of evaporation.
was droplet inertia coefficient and defined as follows[29]:
where was average resistance ratio in connection with MVD, and Altitude, while was uncorrected droplet inertia coefficient[30].
Figure 10. Measured apparent densities and the estimated curve relating densities and ice accretion rates obtained by high-wind-speed impacting ices.
A curve relating to rateice for impacting ices was estimated to better describe the relationship between apparent density and icing conditions as shown in Equation 12 and Fig.10.
The predictable densities obtained from this equation could well explain the effect of icing conditions on microstructures and densities of ices formed at high wind speed, which were matched with the speed of aircraft takeoff/landing, although the relationship needs to be further optimization due to the small amount of the acquisition data.”
Thank you very much for your careful work and a sense of responsibility.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review of the manuscript:
Investigation of microstructure and density of atmospheric ice formed by high-wind-speed in-cloud icing
This manuscript interested in the observation and analysis of the microstructures of atmospheric ice formed by high-wind-speed in-cloud icing using microscopic observation method. The results of preliminary measurements of atmospheric ice obtained during high-wind-speed icing tests in the 3m × 2m ice wind tunnel located at China Aerodynamics Research and Development Center were presented.
1. The findings are sufficiently novel to warrant publication.
2. The conclusions are not adequately supported by the data presented.
3. The article is not clearly and logically written so that it can be understood by one who is not an expert in the specific field.
4. The work provides an important contribution to its field, consistent with the scope of the journal. Discussion with different authors is needed. Errors of the model are not described. The computer image analysis is needed more effectively described. Conclusions have to be expressed more quantitatively and discussion with other authors is needed.
Comments:
Row 92: Please introduce provider and country of provider of wind tunnel.
Row 107: Please exactly describe the aircraft model icing test and examples in the Fig.3.
Row 118: Please introduce provider and country of provider of the microscope. Fig. 4 is not mentioned in the text of the article.
Row 124: Please introduce provider and country of provider of the density instrument.
Row 157: Please describe image processing of the images on Fig. 6, mainly detection of the grains by the red color.
Row 182: Please define Circularity, please apply some quantitative evaluation of a fractions of the micro bubbles and not only qualitative evaluation.
Row 201: Please introduce the version of software and describe the method of image processing.
Row 229: Please explain the very different level of the density on the vertical axes on the Fig. 9a, b. (on 9a is range of density 0.1 and on 9b is range 1). Please use only ROI.
Thank You very much
Sincerely Your,
Lubomir
Author Response
Dear reviewer #2,
We would like to thank you for your careful work and useful comments. We have discussed your comments and revised the manuscript in accordance with your suggestions (in blue words). We hope that the revised manuscript could satisfy you, and concurrently meet the requirement of Crystals as well.
Reviewer #2:
This manuscript interested in the observation and analysis of the microstructures of atmospheric ice formed by high-wind-speed in-cloud icing using microscopic observation method. The results of preliminary measurements of atmospheric ice obtained during high-wind-speed icing tests in the 3m × 2m ice wind tunnel located at China Aerodynamics Research and Development Center were presented.
- The findings are sufficiently novel to warrant publication.
- The conclusions are not adequately supported by the data presented.
- The article is not clearly and logically written so that it can be understood by one who is not an expert in the specific field.
- The work provides an important contribution to its field, consistent with the scope of the journal. Discussion with different authors is needed. Errors of the model are not described. The computer image analysis is needed more effectively described. Conclusions have to be expressed more quantitatively and discussion with other authors is needed.
Comments:
Row 92: Please introduce provider and country of provider of wind tunnel.
Response: The 3m × 2m ice wind tunnel is one of the National Large Infrastructures of China, which was designed, researched, and developed by China Aerodynamics Research and Development Center.
Row 107: Please exactly describe the aircraft model icing test and examples in the Fig.3.
Response: As you suggested, the aircraft model icing test were descrives in the revised manuscript as follows:
“The aircraft atmospheric ice sample library was established since the 3m × 2m icing wind tunnel went into operation in 2013, and the icing conditions were chosen according to FAA.FAR (Federal Aviation Administration Regulations) Appendix C, which summarized and provided atmospheric icing conditions in real aeronautical meteorology.” (line 96 - 99)
Row 118: Please introduce provider and country of provider of the microscope. Fig. 4 is not mentioned in the text of the article.
Response: As you suggested, the provider and country of provider of the microscope were introduced in the revised manuscript (line 115). In addition, the description of Fig. 4 was added as follows: (line 108 - 110)
“The test specimens for microstructure measurement and density measurement were prepared form the same ice sample and the whole testing process was carried out in a cryogenic incubator, as shown in Fig.4. ”
Row 124: Please introduce provider and country of provider of the density instrument.
Response: As you suggested, the provider and country of provider of the microscope were introduced in the revised manuscript (line 121 - 122).
“The density of the ice was carried out by an electronic liquid density instrument (MH-100E, Qunlong Tech, China). ”
Row 157: Please describe image processing of the images on Fig. 6, mainly detection of the grains by the red color.
Response: Thank you for your suggestion, the original pictures were shown below, the contours of the grain boundaries can be obviously observed in the original pictures and highlighted by the red color. To have a better readability, the corresponding description was insteaded by the following sentence: (line 147- 149)
“The red dashed line highlighted the contours of the grain boundaries within the ice samples at the same LWC, speed, MVD and altitude, but at different temperature of -5.8 ℃ and -25 ℃, as shown in Fig.6. ”
Row 182: Please define Circularity, please apply some quantitative evaluation of a fractions of the micro bubbles and not only qualitative evaluation.
Response: Thank you for your valuable suggestion. The circularity of the bubble was defined as in the following sentece: (line 179 - 181)
“As displayed in Fig.7 (e-f), the circularity of the bubble, which was defined as the ratio of long axis to short axis, changed along with the decreased temperature. ”
Based on the two-dimensional pictures of the microstructure of the ice, the analysis of the bubbles could not be well quantitatively studied. Three-dimensional computed tomography will be carried out to quantitatively analyse the micro bubbles in the future reasearch.
Row 201: Please introduce the version of software and describe the method of image processing.
Response: As you suggested, the version of the Imageview and the method of image processing have been introduced in the revised manuscript. (line 199 - 202)
“Due to the gradient gray level, the observed air inclusion edges could be extracted with the aid of image analysis software (Imageview version 2018), in which the original picture was binarized. Afterwards, the statistical of bubble size distribution was carried out under the assumption that the bubbles were perfect sphere.”
Row 229: Please explain the very different level of the density on the vertical axes on the Fig. 9a, b. (on 9a is range of density 0.1 and on 9b is range 1). Please use only ROI.
Response: Thank you for your suggestion. As you suggested, the Fig.9 was modified in the revised manuscript. (line 251)
Figure 9. (a) Measured density values of the atmospheric ice formed by high-wind-speed in-cloud icing; (b) Measured densities in this work fitted with previous density functions of R (Macklin Curve[21], Bain and Gayet Curve[23], Makkonen Curve[24] and Jones Curve[25]).
Thank you very much for your careful work and a sense of responsibility.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper is devoted for investigation of microstructure and density of atmospheric ice formed by high-wind-speed in-cloud icing. The topic is generally interesting, however the paper contain unexplained places (below) and need major revisions.
The aim of the paper should be more clearly formulated.
Line 236 ‘’As listed in Table. 1’’ . Unfortunately, I not found Table 1 in the paper.
Fig. 8 should be more commented.
Lines 248-249 ‘’establish a better practical density predicting model’’, please explain in which way such model can be established.
List or references should be expanded and more comparison with similar results presented in literature should be added in the paper text.
Conclusions should be rewritten
Author Response
Dear reviewer #3,
We would like to thank you for your careful work and useful comments. We have discussed your comments and revised the manuscript in accordance with your suggestions (in blue words). We hope that the revised manuscript could satisfy you, and concurrently meet the requirement of Crystals as well.
Reviewer #3:
The paper is devoted for investigation of microstructure and density of atmospheric ice formed by high-wind-speed in-cloud icing. The topic is generally interesting, however the paper contain unexplained places (below) and need major revisions.
(1) The aim of the paper should be more clearly formulated.
Response: As you suggested, the establishment of the practical density predicting model has been established thus the aim of the paper has been concentrated. (line 255 - 293)
“Herein, referring to the transformation theory of ice wind tunnel test[27], has been proposed and defined as Equation 5, which considered as a reasonable combination of parameters to define the effect of the characteristics of the impacted surface, the conserved momentum and energy in the flow field and icing environment. In the equation, presented the freezing factor of impacting water on the surface, which was deduced from the energy conservation equation of Messinger model[28]. was the droplet collection coefficient, which could be influenced by the droplet trajectories related to the flow field. LWC and were the liquid water content in and the flow velocity in , respectively.
Among them, was latent heat of freezing, and was specific heat capacity of water on model surface. In addition, three parameters were introduced to describe the process of heat balance: relative heat coefficient , droplet energy transfer potential and air energy transfer potential .
where was surface temperature, was static temperature and was water film temperature, was vapor pressure of water in the atmosphere and was vapor pressure of water over liquid water, was convective heat transfer coefficient and was gas-phase mass transfer coefficient, and was latent heat of evaporation.
was droplet inertia coefficient and defined as follows[29]:
where was average resistance ratio in connection with MVD, and Altitude, while was uncorrected droplet inertia coefficient[30].
Figure 10. Measured apparent densities and the estimated curve relating densities and ice accretion rates obtained by high-wind-speed impacting ices.
A curve relating to rateice for impacting ices was estimated to better describe the relationship between apparent density and icing conditions as shown in Equation 12 and Fig.10.
The predictable densities obtained from this equation could well explain the effect of icing conditions on microstructures and densities of ices formed at high wind speed, which were matched with the speed of aircraft takeoff/landing, although the relationship needs to be further optimization due to the small amount of the acquisition data.”
(2) Line 236 “As listed in Table. 1”. Unfortunately, I not found Table 1 in the paper.
Response: Thank you for your careful work, we had missed the table before and already added in the revised manuscript. (line 255)
(3) Fig. 8 should be more commented.
Response: Thank you for your careful work, as you suggested, we have added more comment to Fig.8 in the revised manuscript. (line 195 – 223)
(4) Lines 248-249 “establish a better practical density predicting model”, please explain in which way such model can be established.
Response: As you suggested, the establishment of the practical density predicting model for aircraft icing was added in the revised manuscript. (line 255 - 293)
(5) List or references should be expanded and more comparison with similar results presented in literature should be added in the paper text.
Response: Thank you for your advisement, we have expanded our reference and the similar results were described and commented in the revised manuscript. (line 226 - 234).
“Since Macklin first calculated the atmospheric ice density by measured the weight and volume of the ice accreted on the rotating cylinder, many researchers have developed and modified practical expressions to construct the curves relating to (, as shown in Fig 9[21, 23-25], where was the impacting speed, was the effective median volume droplet diameter for each cylinder, and represented the surface temperature. However, unlike ice accreted on simple rotating cylinder, the volume of atmospheric ice obtained at airfoil in our work could not be easily estimated due to the irregular shape neither on spanwise or chordwise.”
(6) Conclusions should be rewritten.
Response: Thank you for your advisement, we have rewritten the conclusion. (line 295 - 309).
“Herein, the low-temperature microscopy method that we developed allowed the observation of many features as the boundaries of ice grains, the size and shape of air bubbles, and promoted a better understanding of the formation and evolution of the microstructures for atmospheric ice formed by high-wind-speed in-cloud icing. Furthermore, the accurate density measurement we developed could be used to measure the ice density formed on irregular bodies such as airfoils. It has been demonstrated that the porosity calculated by microstructure characterization coordinated well with the result estimated by density measuring method. Based on the aircraft atmospheric ice sample library, which was collected from 3m × 2m icing wind tunnel icing test since 2013, the density prediction formula considering characteristics of impacted object, the effect of flow field for atmospheric ice formed at high wind speed was conducted, which could be matched well with the speed of aircraft takeoff/landing. The improved description and characterization of microstructures and densities will facilitate a better understanding for atmospheric ice of physical properties and pave the road to in-cloud icing prediction/detection system and anti-/de-icing system design.”
Thank you very much for your carful work and a sense of responsibility.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I have no more comments that would necessitate another review cycle.
Author Response
Thank you for your careful work.
Reviewer 2 Report
Row 147-149 - please describe software or method of the realization of the red line in the Fig. 6
Row 229: Please explain the very different level of the density on the vertical axes on the Fig. 9a, b. (on 9a is range of density 0.1 and on 9b is range 1). You did not corection of the images on the same level. from 0.8 to 1.0 od the each picture.
Conclusions have to be expressed more quantitatively and discussion with other authors is needed.
Author Response
Dear reviewer #2,
We would like to thank you for your careful work and useful comments. We have discussed your comments and revised the manuscript in accordance with your suggestions (in blue words). We hope that the revised manuscript could satisfy you, and concurrently meet the requirement of Crystals as well.
Reviewer #2:
- Row 147-149 - please describe software or method of the realization of the red line in the Fig. 6.
Response: As replied, the contours of the grain boundaries can be obviously observed in the original pictures (listed below), and we use red dashed highlighted the contours of the grain boundaries to make the reader more intuitive to observe.
- Row 229: Please explain the very different level of the density on the vertical axes on the Fig. 9a, b. (on 9a is range of density 0.1 and on 9b is range 1). You did not corection of the images on the same level. from 0.8 to 1.0 of the each picture.
Response: As you suggested, the density on the vertical axes in Fig.9a and Fig.9b was adjusted to the same range. It could be observed in Fig.9 that the empirical formula of ice density established in other literatures used the data of ices formed at low wind speed. While the ice density we obtained originated from large-scale icing wind tunnel tests at high wind speed, which meant that the value of R was high enough so the existing formulas were not applicable, thus it was necessary to establish a new density formula suitable for ices formed at high wind speed.
Figure 9. (a) Measured density values of the atmospheric ice formed by high-wind-speed in-cloud icing; (b) Measured densities in this work fitted with previous density functions of R (Macklin Curve[21], Bain and Gayet Curve[23], Makkonen Curve[24] and Jones Curve[25]).
- Conclusions have to be expressed more quantitatively and discussion with other authors is needed.
Response: As you suggested, the conclusion has been expressed more quantitatively and discussion with other authors was added. (lines 300-309)
“It has been demonstrated that the porosity calculated by microstructure characterization coordinated well with the result estimated by density measuring method, which verified the reliability of the measurement. Based on the selected ice samples from the aircraft atmospheric ice sample library, the densities were systematically investigated and demonstrated in the range of [0.85, 0.89], which could not be accurately predicted by existing empirical formulas, such as Macklin Curve[21], Bain and Gayet Curve[23], Makkonen Curve[24], and Jones Curve[25]. Thus, the density prediction formula for atmospheric ice formed at high wind speed was conducted using icing rate , which combined characteristics of the impacted object and the effect of flow field.”
Author Response File: Author Response.pdf
Reviewer 3 Report
Authors make proper corrections according to reviewer remarks and I suggest to publish the paper as it is.
Author Response
Thank you for your careful work.
