Heat Transport Capacity of an Axial-Rotating Single-Loop Oscillating Heat Pipe for Abrasive-Milling Tools
Round 1
Reviewer 1 Report
Summary:
The work presented a technique to improve heat transfer in the abrasive-milling process with oscillating heat pipes. The abrasive-milling process was stimulated with heating wires incorporated in the evaporator of the oscillating heat pipes under various rotational speeds. The authors presented the effect of varying rotation speed, heat flux,, and working fluid on the thermal resistance.
Positive:
The work presented was explained in detail with precise results presentation.
Negative:
- Authors have to improve the sentence structures, as it's confusion in some areas. I would request the authors to read through the sentences and improve it
- Authors should Figure 3, as it isn't clear and challenging to follow what the authors in the main paragraph.
- In Figure 6b, why is thermal resistance is reducing with increasing centrifugal acceleration up to 300 m2/s and then increases at 750 m2/s
- In Figure 8, what do the authors mean by 0g to 75g? Is it the fill mass? It will be better to be presented by the fill volume fraction.
Author Response
Reviewer 1’s comments:
Summary:
The work presented a technique to improve heat transfer in the abrasive-milling process with oscillating heat pipes. The abrasive-milling process was stimulated with heating wires incorporated in the evaporator of the oscillating heat pipes under various rotational speeds. The authors presented the effect of varying rotation speed, heat flux, and working fluid on the thermal resistance.
Answer:
Thank you for your appreciation!
Positive:
The work presented was explained in detail with precise results presentation.
Answer:
Thank you for your comments!
Negative:
- Authors have to improve the sentence structures, as it's confusion in some areas. I would request the authors to read through the sentences and improve it.
Answer:
Thank you for your comments! The language has been again checked and improved.
- Authors should Figure 3, as it isn't clear and challenging to follow what the authors in the main paragraph.
Answer:
Labels have been added in Figure 3. Moreover, the expression in the paragraph has been also improved to make it clearer. The modification is as follows:
“Under the static state and heat flux of 22,750 W/m2, the flow pattern of working fluid, acetone, is a veering circulation with the annular flow and slug flow. When the vapor bubbles and plugs generate, expand, and move up to the condenser, the vapor easily penetrates the liquid slugs to form the annular flow (see Fig. 3(a) i-iii), while the flow in the neighboring tube remains a train of liquid slugs and vapor plugs (see Fig. 3(a) ii and iii). Besides, the direction of circulation changes from time to time, as shown in Fig 3(a) ii and iii.
When the axial-rotation is applied, as mentioned in the theoretical analysis in Section 3.2, the resistance for the vapor to penetrate the liquid slug becomes larger, as a result, it is more difficult for the vapor to penetrate through the liquid slug to form the annular flow. The flows inside the axial-rotating SLOHP at the speed of 60, 150, and 300 rpm, are shown in Fig. 3(b), (c), and (d), respectively. At the rotating speed of 60 rpm, the flow is a transient slug flow, it generates a train of liquid slugs and vapor plugs (see Fig. 3(b) ii). Sometimes, when a train of liquid slugs and vapor plugs moves from evaporator to condenser, it will slow down and stop, and a new train of liquid slugs and vapor plugs generates in the neighboring tube and move upwards, the flow direction changes consequently (see Fig. 3(b) ii and iii). The whole process is illustrated in Fig. 3(b). At the rotating speed of 150 and 300 rpm, the unidirectional circulation forms. Since the SLOHP rotates clockwise, the inertia causes the working fluid to flow in a one-way, clockwise direction inside the SLOHP. In this case, liquid slugs generate and move up to the condenser in the left tube, while in the right tube, liquid slugs and vapor plugs oscillate at the adiabatic section (see Fig. 3(c) i and iii, and Fig. 3 (d) ii and iv). Though flows at rotational speed of 150 rpm and 300 rpm are similar, new trains of liquid slugs and vapor plugs generate at the speed of 150 rpm (Fig. 3(c) i and iii), whereas, just one liquid slug forms and moves up at a time at the speed of 300 rpm (Fig. 3(d) ii and iv).”
Figure 3. Flow inside the axial-rotating SLOHP filled with acetone under 22750 W/m2: (a) at static state, (b) at 60 rpm rotating speed, (c) at 150 rpm rotating speed, and (d) at 300 rpm rotating speed.
- In Figure 6b, why is thermal resistance is reducing with increasing centrifugal acceleration up to 300 m2/s and then increases at 750 m2/s
Answer:
The thermal resistance of the axial-rotating SLOHP filled with DI water reduces and then increases with the centrifugal acceleration as shown in Fig. 6(c). With respect to water, we do not have yet a solid conclusion. We are conducting further research to figure out the reason. The reasons for such different behavior can be found in water’s higher viscosity (Table 2) which increases the flow friction, the higher thermal conductivity which can produce local transient dry-out, and the lower value of (dp/dT)sat which brings to a weaker expansion, i.e. a weaker flow circulation (see also Section 3.1). Another reason could be that the local temperature of the fluid in the evaporator does not reach the boiling point, so there is no phase change under higher centrifugal accelerations and such heat flux. It is clear that it is very difficult to answer to all these points, using an experimental methodology: We believe that only through a numerical simulation, we will be able to understand the effects of the parameters. But a numerical study is beyond the goals of the present work.
- In Figure 8, what do the authors mean by 0g to 75g? Is it the fill mass? It will be better to be presented by the fill volume fraction.
Answer:
The “0g to 75g” are the centrifugal accelerations. Labels are added in the Figure 8, as follows:
Figure 8. Effects of heat flux: (a) methanol; (b) acetone; (c) DI water
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The reviewer thinks that the authors did a great job on the investigation on the thermal performance of the oscillating heat pipe mainly in terms of the centrifugal acceleration for milling process; the concept was interesting; the results and discussion seemed enough to be published in the Energies for the scientific field of the heat transfer. Here are some minor comments for future work if the authors plan to keep working on the related research.
(a) In the real situation, i.e, during the actual milling process with other materials, more severe or unexpected vibration may take place, perhaps resulting in the change in flow patterns or thermal performance. In the future work, if any, the reviewer would like to see the comparison between the present results and new results obtained from the real situation
(b) The values of thermal resistances obtained from the authors are of course OK to understand the thermal mechanism, but the values intuitively seem a little higher than the values proposed in other open literature. In future work. it might be better to find a way to reduce the contact resistance of the OHPs to have better performance.
(c) In Fig. 8 for water case, the trend of 75g seems different, i.e., there has the intersection of the 75g line with others. The quality of the present manuscript could be improved if the appropriate explanation is included.
Thank you for the interesting work.
Author Response
Reviewer 2’ comments
The reviewer thinks that the authors did a great job on the investigation on the thermal performance of the oscillating heat pipe mainly in terms of the centrifugal acceleration for milling process; the concept was interesting; the results and discussion seemed enough to be published in the Energies for the scientific field of the heat transfer. Here are some minor comments for future work if the authors plan to keep working on the related research.
Comment 1:
In the real situation, i.e, during the actual milling process with other materials, more severe or unexpected vibration may take place, perhaps resulting in the change in flow patterns or thermal performance. In the future work, if any, the reviewer would like to see the comparison between the present results and new results obtained from the real situation
Answer:
Thank you for your suggestion! Indeed, the authors are already planning to conduct abrasive-milling experiments by OHP tools. The effect of the mentioned vibrations will be considered. On the positive side, it is known from microgravity experiments, where the g-jitters are important, that vibration effects can be recovered by the OHP very fast. Not only, high frequency vibrations can help bubbles to detach from the surfaces (boiling enhancement through ultrasound, for example), and this can be even a positive effects for the OHP performance.
Comment 2:
The values of thermal resistances obtained from the authors are of course OK to understand the thermal mechanism, but the values intuitively seem a little higher than the values proposed in other open literature. In future work. it might be better to find a way to reduce the contact resistance of the OHPs to have better performance.
Answer:
Thank you for the suggestion. The contact resistance is very important, and the authors will try to reduce the contact resistance of the OHPs. To notice, when we are dealing with heat pipes, since their thermal resistance is very small, the contact resistance becomes even more important. We are very aware of this issue.
Comment 3:
In Fig. 8 for water case, the trend of 75g seems different, i.e., there has the intersection of the 75g line with others. The quality of the present manuscript could be improved if the appropriate explanation is included.
Answer:
Thank you for your comments. For water case, it changes differently from the acetone and methanol cases. The reason for this strange phenomenon is not quite clear. Authors are conducting some works to figure out the reasons. For example, a new apparatus will be built, so the visualization under 75g will be captured to deeply understand the flow motion and heat transfer inside the OHP.
Other revision:
The mistakes are all revised carefully. Some sentences have been amended or added for describing the research results concisely and completely in the revised manuscript.
Please contact me in time if there are still some problems.
Author Response File: Author Response.pdf
