In most heat transfer textbooks, the fundamentals of internal forced convection in circular tubes are typically presented in two categories: uniform heat flux and uniform wall temperature. The concept of uniform wall temperature is commonly associated with practical scenarios involving phase change processes like boiling or condensation at the outer surface of a tube. Many experiments have been conducted using this approach, but it appears that there are no published measurements of wall temperature demonstrating a truly "uniform wall temperature" on the tube wall. The objective of this paper was to demonstrate that achieving a uniform wall temperature necessitated a high heat flux at the tube inlet, which exponentially decreased towards the tube outlet. To accomplish this, an innovative experimental set-up was designed and constructed, capable of generating such a heat flux and thereby achieving a uniform wall temperature on a circular tube. This setup facilitated the experimental determination of developing and fully developed Nusselt and friction factors, which were then compared with computational fluid dynamics (CFD) results. Additionally, the set-up enabled the generation of simultaneously developing flow, a previously unexplored aspect. The obtained results were also compared to identify a significant fundamental trend difference between cases of developing uniform wall temperature and uniform heat flux results, thus revealing valuable insights.