The modelling process was carried out for 3D analysis using CFD-Fluent 6.2 software. Gambit 2.2 was used to mesh the model. The simple and regular geometry of the model suggested the use of a quad structured mesh of size 1mm. Two different boundary condition types were applied on the absorber plate for tests, depending on the purpose of the simulation. Optimisation simulations used constant heat flux of 300W/m2 as the boundary condition on the absorber plate. Constant absorber plate temperature boundary condition was taken when comparing the heat absorbed by the two ICS-SWH designs. According to those conditions the program calculated the temperature field in the geometry and as a result values at the nodes were displayed.

3. Modelling results

Stratification is essential for the good performance of a solar collector and is significant when trying to optimise the collector for draw off. However better mixing in the tank results in higher rates of heat transmission when trying to get solar energy into the water. Then the addition of fins might give a differential of temperature lower from the top to the bottom of the ICS-SHW but will optimise the transfer of energy into water. A CFD stratification analysis was developed for the four fin ICS-SWH design and then undertaken for a second design using five fins to compare both water stratification and velocity magnitude for a given time and heat transfer through time.

3.1. Extended heat transfer fins

A good understanding of the influence of extended surfaces is important when seeking performance enhancement of the ICS-SWH. Figure 2 represents the temperature of the fins with height after a lapse time of 60 minutes and a simulated heat flux on the absorber plate of 300 W/m2. Heat is transferred through the fins from the top of the collector to the bottom where the water temperature is cooler. This results from gravity and buoyancy effects. Water with different temperatures will settle at a corresponding height in the ICS-SWH according to the density of the fluid. Hot water of low density will naturally settle in upper layers while cold water of high density will fall to the bottom layers. During the first three hours of the charging process, high temperature stratification occurs in the ICS-SWH. With time, temperature in the upper layers get fully established and reach an equilibrium influencing the lower layer to increase in temperature and therefore decrease the density gradient of water inside the ICS-SWH.

In order to ease the comprehension of the analysis process a discussion of the original four fin collector design is discussed below.