In this paper, experimental measurements and numerical CFD calculations are carried out for the problem of a vertical thermal water jet into a rectangular water tank. We consider two cases; the first case is to inject a hot-water jet with a uniform inlet temperature (UIT) into a cold-water tank. The second case is to inject a cold-water jet with non-uniform inlet temperature (NUIT) into a hot-water tank. In the UIT case, we examine the effects of the temperature-difference. In the case of NUIT, we studied the effects initial temperatures with constant flow rate; and different flow rates at constant initial temperature. Both turbulence intensity and Reynolds number are formulated to be a function of the inlet temperature for the NUIT case. The numerical simulations are carried out under the same conditions of the experiments. We use the realizable k-ε model to describe the turbulent flow with the energy equation. The symmetrical 3D half of the tank has been considered to reduce the computational cost. The water density is treated as a piecewise-linear of temperature. The turbulence at the inlet is characterized by the hydraulic diameter and the turbulence intensity. Several quantities are obtained and analyzed such as pressure, velocity, temperature, and turbulence. A good agreement between simulation and experimental results at low temperatures, while at high temperatures there is acceptable agreement with some quantitative differences. In spite of there are some differences between the measurements and the simulation in a certain case, nevertheless, the qualitative comparison is quite well. The thermal stratification occurs clearly with high temperature-difference, however, after a certain time, the thermal stratification is mixing. Moreover, when a cold-water jet enters a mixed hot water tank, stratification comes early and after a certain time, it mixes. For the UIT cases, the tank is totally mixing, while, for the NUIT cases the stratification clearly occurs. Keywords: Turbulent flow, Heat stores, Realizable k-ε model, Heat transfer, Turbulent jet, Numerical simulation