An isolation is specific for one element and is placed between the fluid and its sourrounding. For an element with surface area $S$ and temperature difference $\Delta T$ towards the ambient, the heat flux $\dot{Q}$ towards the ambient is given as $$\dot{Q}=S\cdot R\cdot\Delta T.$$ The thermal resistance $R$ is computed as the series of the convective heat transfer coefficient $\alpha$ (see @{../Models}) an the layers thermal resistances $R_i$: $$R=\left(\sum_i \frac{1}{R_i} + \frac{1}{\alpha}\right)^{-1}$$ For elements with circular profiles are computed as $$R_i=\frac{\lambda_i}{r_i\cdot\ln\left(1+\frac{d_i}{r_i}\right)}$$ where $\lambda_i$ is the heat conductivity, $d_t$ the thickness and $r_i$ is the radius of the layers inner side: $$r_i=\left\lbrace\begin{matrix}\frac{D}{2} & \text{if }i=0\\r_{i-1}+d_{i-1} & \text{else}\end{matrix}\right.$$ For all other profile types, the thermal resistances are computed as $$R_i=\frac{\lambda_i}{d_i}$$