The Effect of Pine Wood Thickness on the Freezing and Heating Process in Warm-Air Drying

Wood is subject to various environmental conditions during its processing, with temperatures being one of the most relevant to the material’s behaviour. The heating process during drying is crucial for both the final quality of the dried wood and heat consumption. As the first stage of the drying process, it is essential to achieve adequate overheating in the middle of the thickness without causing damage. The present article focuses on the influence of pine wood thickness on the freezing process and heating during the warm-air drying process. Similarity theory was applied to the theoretical calculation of the time to heat the frozen wood, where Fourier and Biot’s criteria were used. The calculated times were confirmed by experimental measurements. Theoretical calculations of heating time for frozen wood align with measured values for larger thicknesses. For smaller thicknesses (<50 mm), the heating time was shown as unnecessarily long. The results showed that wood thickness significantly affected both freezing and heating processes. Specifically, the thickness of the samples had a notable impact on the heating of frozen samples, only after changing the water gradient in the wood from solid to liquid state. The optimal solution would be if the time and course of heating were regulated according to the actual measured temperature in the centre of the wood.