What is the significance of thermal penetration depth considering study of pulse tube cryocooler? How to calculate it? At which temperature and pressure one need to calculate thermo-physical properties which are required for calculating thermal penetration depth ?
The thermal penetration depth is an equivalent of thermal boundary layer thickness in oscillatory heat transfer (or fluid flow). The thermal and viscous penetration depths are the most significant parameters to study oscillatory flows. For instance, viscous penetration depth is one of the parameters to judge whether flow is turbulent or not. The ratio of characteristic length (e.g. tube radius) to the thermal penetration depth is a key parameter to formulate oscillatory heat transfer. One can easily calculate it via the following relation:
thermal penetration depth=(2*a/w)^0.5
Where, a is thermal diffusivity and w is the frequency (2*pi*f) in rad/sec.
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