“…If additional information is available for a particular tube on burial depth variations or other factors that might introduce a significant axial variation in the temperature or heat flux boundary condition, there are a few analytic solutions available that factor in axial variations in wall heat flux or temperature [Shah and London, 1978]. For example, for a linear variation in wall temperature for the circular tube, see Sellars et al [1956], or for wall heat flux variations, see Bhattacharyya and Roy [1970]. Predictably, wall temperatures are higher where heat flux rates are higher.…”