11.5.2.2 Fourier method

Problem: The diffusing substance with concentration \( C_{0}= \) const is in an infinite layer \( -h \leq x \leq h,-\infty< \) \( y, z<+\infty \) and are kept there by impenetrable partitions, located at \( \pm h \) until the \( t=0 \) moment of time, when the partitions are removed and the diffusion process in a wider layer begins \( -H \leq x \leq \) \( H(H>h) \). Find the distribution of the concentration of the diffusing substance when \( t>0 \), if on the surfaces \( x= \pm H \) there is a mass exchange with the environment, having a constant concentration of the diffusing substance \( C_{1} \).