# The Influence of Wood Moisture Content on the Processes of Freezing and Heating
## 4 Conclusions  
The aim of this work was to determine the effect of pine wood moisture content on the processes of freezing and heating of frozen wood in a gaseous environment. Temperature profiles on wood cross-sections, decreases in wood moisture content due to the freezing process, and moisture gradients were analyzed. The theoretical calculation of the time required for defrosting and heating the wood was compared to experimentally measured data. The test specimens had a thickness of 30 mm and different initial _MC_. The following conclusions were drawn from the measured data:  
* Wood moisture content has a significant effect on the wood freezing process. Negative temperature values in the middle of the wood were more quickly achieved in samples with lower _MC_ than in samples with higher _MC_. After 4 h of freezing, the temperature in the middle of the samples with a lower _MC_ was \(-11\)\({}^{\circ}\)C; the temperature in the samples with higher _MC_ (81%) was \(-0.8\)\({}^{\circ}\)C.
* Samples with lower _MC_ froze faster, but their temperature was higher (\(-13.2\)\({}^{\circ}\)C); samples with higher _MC_ reached the lowest temperature (\(-20\)\({}^{\circ}\)C).
* The initial moisture content of the wood did not have a remarkable effect on the loss of average moisture content during the freezing process. On average, moisture content was reduced by 4.2% in both groups.
* The humidity of the samples affects the size of the moisture gradient after freezing. Higher values were measured for samples with higher _MC_. The freezing process removes water mainly from the surface layers due to the sublimation of free water.
* The heating time of the frozen samples is significantly affected by the moisture content of the samples. Samples with a higher _MC_ were heated approximately 1 h longer than samples with a lower _MC_. This was due to the lower initial temperature of the samples, but also to the longer stage of change in the state of water in the samples. The difference in the total heating time was due to the longer defrosting time of the samples with a higher _MC_.
* The values of _MC_ loss and moisture gradients after heating indicate a significant influence of the relative humidity of the environment in which the heating is performed.
* Theoretical calculation of heating time of the frozen samples, derived from boundary conditions of the III kind, was longer than the measured times (values). The differences were due to the characteristics of the device in which the heating of samples was conducted.
* The heating time for the frozen wood, which is prescribed according to [18], is unnecessarily long and can be remarkably reduced.  
Freezing and heating of frozen wood are often encountered in wood processing. It is important to more thoroughly understand the influence of the factors that impact these processes. This will enable the optimization of the heating times of the wood under specific conditions and thus reduce the energy intensity of drying the wood.  
Conceptualization, I.K.; methodology, I.K.; software, I.K. and P.V.; validation I.K. and P.V.; formal analysis, P.V.; investigation I.K. and P.V.; resources, T.V.; data curation, I.K.; writing--original draft preparation, I.K.; writing--review & editing, T.V.; visualization, I.K. and P.V.; supervision, I.K.; project administration, P.V.; funding acquisition, I.K. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Slovak Research and Development Agency under contracts no. APVV-17-0583, SK-PL-18-0052, and APVV-18-0378.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** The authors would like to thank the Slovak Research and Development Agency under contracts no. APVV-17-0583 and no. SK-PL-18-0052 and also no. APVV-18-0378.  
**Conflicts of Interest:** The authors declare no conflict of interest.