Temperature distributions inside different the tank models

The best obstacle type and angle for supplying higher thermal stratification has been found numerically between all investigated cases. The aim is supply hot water as long 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). In order to obtain this higher stratification, different kind of obstacles as cylindrical, semi-cylindrical and conic are inserted to the tank. 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 0.02 m/s for natural circulation. The flow rate of the hot water from tank to usage would be equal to the cold water entering to the tank from the main lines. The cold water velocity from the main lines is assumed as 1 m/s.

There would be vortexes in the tank. Because two different fluids are mixed in the tank and they are hitting 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].

Higher percentage of the cold water entering to the tank would be directed towards to cold water exit channel (T1) from the tank. Because the cold water enters and exit pipes in radial direction are in the same axis as symmetrical condition. So, 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 water is wanted to be hot as possible as for usage. In order to achieve this, the hot water exit channel (T3) is generally located at the top of the tank.