How to plot heatlines-

In non-isothermal flows, heatlines are used to depict the energy flow from hot surface to cold surface and help in visualizing the strength of the convective heat transfer as compared to the conductive heat transfer. Traditionally, researchers have plotted heatlines by solving heat-function equation in their solvers during the runtime. However, this requires access to the solver code and is time-consuming to implement. Further, the literature available so far only concerns simple geometric shapes. This work aims to document out-of-the-box methods for the visualization of heatlines which can be done as a post-processing exercise. A comparison of streamlines and heatlines, is at first presented to enhance the understanding of the application of heatlines in heat transfer problems and use the same technique in post-processing computer programs for visualizing heatlines. The procedures to plot heatlines using commercial (tecplot and cfd-post) and open-source (paraview) tools are presented. Illustrative examples of different computational geometries from past literature are validated to establish the efficacy of the method. Further, the method can be also applied to plot heatlines for complex geometries which is not feasible with the traditional approaches.