Application of the Response Surface Methodology for Designing Oscillation Drying of Beech Timber

Round 1

Reviewer 1 Report

Dear authors

Your paper is very good. Some small improvements have recommended you. 

For authors

• Line 9: “Oscillation drying is a potential method...” Please reformulate this phrase, because the method is not a newly one to have a great potential for promote or emphases. The originality of your paper is not here and is in the modelling of drying process.
• Line 34-35: The basic principle for drying hardwood sawn timber is to reduce drying intensity at early stages of the process, i.e., for moisture content higher than the Fiber Saturation Point (FSP) [1–4]. Why do you think by reducing the drying intensity over FSP will improve the drying quality? It is known that during this period the wood does not shrink, so it has no internal stresses and does not deform or have other serious defects. In fact, it is recommended to make a natural drying until this moisture content in order to reduce the costs of artificial drying. If we look at figure 2, we clearly notice that up to 30%, the drying speed is very fast, which is normal. Please explain your personal idea logically or change it accordingly.
• Line 37: …the shell (surface)... I think the expression "exterior surface" is enough. The word "shell" is not often used in the field of wood engineering.
• Line 46-47: “The accelerated drying schedule at higher air velocity reduced both drying time and wood defects.” Really? I think that an accelerated drying regime with a high circulation speed produces more drying defects. Please meditate on this expression once again.
• Line 49-50: “...at a dry-bulb temperature of 45°C and wet-bulb depression of 10 K...”. Please use the same unit, respectively degrees Celsius for both thermometers. Do this throughout the paper for a good understanding of all readers.
• Line 59-60: “the impact of oscillation drying of 105-mm-square Pacific coast hemlock was more distinct during the early stages of drying for moisture content values above FSP”. In what sense was the impact, good or bad? Please explain that.
• Line 84: “initial moisture content was above the FSP”. Say what the initial moisture content was? Approximately, not exactly. It is not the same if MC was 90% or 33%.
• Line 266: “The theoretical findings reported by Salin [16] were confirmed by the present analysis...” . Please reformulate this sentence. A research paper does not have the role of confirming the results of other authors, but of bringing something new. That is why it is not good for this sentence to appear in the conclusion section.

Author Response

Comment #1.1. Line 9: “Oscillation drying is a potential method...” Please reformulate this phrase, because the method is not a newly one to have a great potential for promote or emphases. The originality of your paper is not here and is in the modelling of drying process.

Answer. The sentence was modified in the revised version of the manuscript according to the suggestion of the Reviewer.

Comment #1.2. Line 34-35: The basic principle for drying hardwood sawn timber is to reduce drying intensity at early stages of the process, i.e., for moisture content higher than the Fiber Saturation Point (FSP) [1–4]. Why do you think by reducing the drying intensity over FSP will improve the drying quality? It is known that during this period the wood does not shrink, so it has no internal stresses and does not deform or have other serious defects. In fact, it is recommended to make a natural drying until this moisture content in order to reduce the costs of artificial drying. If we look at figure 2, we clearly notice that up to 30%, the drying speed is very fast, which is normal. Please explain your personal idea logically or change it accordingly.

Answer. The sentence was modified in the revised version of the manuscript. It is primary due to the fact that the definition of the Fiber Saturation Point is at least misleading as it has to be applied to an individual cell or group of cells. When analyzing drying processes “mean moisture content of ca. 30%” is much more appropriate as the term “mean moisture content” is a result of integration of moisture content values over board thickness. It reflects typical moisture content gradient even at early stages of drying, i.e. core with moisture content much higher than the FSP together with near surface layer characterized by moisture content values below the FSP. Therefore, the drying processes of hardwood sawn timber are usually characterized by reduced intensity even for mean moisture content values higher than 30%.

Comment #1.3. Line 37: …the shell (surface)... I think the expression “exterior surface” is enough. The word “shell” is not often used in the field of wood engineering.

Answer. The term was changed in the revised version of the manuscript into more clear one, i.e. “the outer layer”. The new term is more often used in wood science, especially in the context of timber drying.

Comment #1.4. Line 46-47: “The accelerated drying schedule at higher air velocity reduced both drying time and wood defects.” Really? I think that an accelerated drying regime with a high circulation speed produces more drying defects. Please meditate on this expression once again.

Answer. The explanation of the observation might be related to the fact that the study was made for easy-to-dry softwood. Definitely the statement by Aquino-González et al. (2010) has to be treated with reserve. Therefore, we put a short comment on that problem in the revised version of the manuscript.

Cited reference

Aquino-González LA, Rodríguez-Ramírez J, Méndez-Lagunas LL, Sandoval-Torres S (2010) Evaluation of drying schedules for chalamite wood (Pinus pseudostrobus). Madera Bosques 16(2): 35–46.

Comment #1.5. Line 49-50: “...at a dry-bulb temperature of 45°C and wet-bulb depression of 10 K...”. Please use the same unit, respectively degrees Celsius for both thermometers. Do this throughout the paper for a good understanding of all readers.

Answer. We would like to keep the original unit as it is a correct one. It is absolutely legal to express temperature in degrees Celsius (°C), while any temperature difference should be given in Kelvin (K). The approach is commonly used in engineering thermodynamics. Moreover, it has special importance for preserving unit coherency when constructing a heat balance.

Comment #1.6. Line 59-60: “the impact of oscillation drying of 105-mm-square Pacific coast hemlock was more distinct during the early stages of drying for moisture content values above FSP”. In what sense was the impact, good or bad? Please explain that.

Answer. The sentence was modified in the revised version of the manuscript. We tried to be more specific with this modification of the text.

Comment #1.7. Line 84: “initial moisture content was above the FSP”. Say what the initial moisture content was? Approximately, not exactly. It is not the same if MC was 90% or 33%.

Answer. At this stage of the material preparation we used freshly harvested beech wood. Therefore, the initial moisture content was ca. 90%. The text was improved. Please refer to the revised version of the manuscript..

Comment #1.8. Line 266: “The theoretical findings reported by Salin [16] were confirmed by the present analysis...” . Please reformulate this sentence. A research paper does not have the role of confirming the results of other authors, but of bringing something new. That is why it is not good for this sentence to appear in the conclusion section.

Answer. The study presented by Salin was purely theoretical. It delivered valuable observations resulting from the performed analyses. However, the results obtained by Salin were never validated by confronting with empirical observations. We found that the results of our experiments are in accordance with conclusions derived by Salin from his theoretical analyses. Therefore, it is “something new” in our study.

Reviewer 2 Report

The manuscript "Application of the Response Surface Methodology for Designing Oscillation Drying of Beech Timber" describes the known effect of drying parameters changes on the intensity of moisture evaporation from wood in the area above the FSP.

Below I discuss my main comments and suggestions, which hopefully could help the authors to improve this work.

• The chapter Materials and Methods lacks sample density data for each drying schedules.
• 24 samples were used for one drying? - specify.
• In the Table 2, it is unnecessarily shows the drying schedule 5, which is essentially the same as the drying schedule 1.
• In the discussion, add the aspect of a possible impact on the quality of wood, not just on the drying time. The drying schedules with the shortest drying time had the highest moisture content gradient values. This factor is not discussed in the results in terms of drying quality.

Author Response

Comment #2.1. The chapter Materials and Methods lacks sample density data for each drying schedules.

Answer. The applied sampling procedure ensured minimum variation in wood density. Therefore, we supplemented the revised version of the manuscript in the subsection “2.1. Sample preparation”.

Comment #2.2. 24 samples were used for one drying? - specify.

Answer. We supplemented it in the revised version of the manuscript.

Comment #2.3. In the Table 2, it is unnecessarily shows the drying schedule 5, which is essentially the same as the drying schedule 1.

Answer. We would like to keep drying schedules #1 and #5 in Table 2 as it is a result of the applied method for designing the schedules. This duplication in Table 2 was intentional.

Comment #2.4. In the discussion, add the aspect of a possible impact on the quality of wood, not just on the drying time. The drying schedules with the shortest drying time had the highest moisture content gradient values. This factor is not discussed in the results in terms of drying quality.

Answer. The problem of drying quality was briefly discussed in the revised version of the manuscript.