The tundish process is complicated due to the periodic nature of its operation during the changing of ladles, which makes it both a transient and nonisothermal process. A nonisothermal water model, with temperature variations in the inlet stream, is described in this article. A three-dimensional (3-D) transient mathematical model to simulate the fluid flow and heat transfer in this water model is also introduced. From the experimental and numerical results, it is shown that there is a significant thermal buoyancy force contributing to the flow in this nonisothermal water model.