The obstacle types, have supplied higher thermal stratification, have been determined numerically by using computer simulation. In this situation, the aim is supply hot water as long times as possible with high thermal stratification between the temperatures T4 (cold water enter to the tank from main lines) and T2 (hot water supplied by solar collector). Different kinds of obstacle as in figure 3 with different assembly as in figure 2 have been placed in the tank in order to obtain this higher thermal stratification. These obstacles are placed in the tank with suitable angles and coordinates to decrease contact area between cold and hot water in the tank. T4 flow fibers don’t have to destroy hot water gradient. However, the hot water entering the tank (T2) would destroy the stratification. Therefore, hot water velocity is taken as 0.2 m/s for forced circulation. The flow rate of the hot water from tank to usage must be equal to the cold water flow rate entering to the tank. Therefore, the cold water velocity is assumed as 1 m/s.

Vortexes have occurred in the tank because of the mixing of two different fluids. These two fluids would hit each other towards to the wall and obstacle surfaces. Therefore, calculations are carried out by using wall functions method and standard k — s turbulent models with FLUENT [10] code.

The cold water enters and exit pipes in radial direction are in the same axis as symmetrical condition. So, higher percentage of the cold water entering to the tank would be directed towards to cold water exit channel (T1) from the tank. At the end, the cold water can not produce a lot of vortex inside the tank and destroying effects into thermal stratification inside the tank would be decreased. The hot water exit channel (T3) is generally located at the top of the tank. So, the hot water can be supplied as long as possible because of the positions of the hot water exit channel.