Solar Chimney CFD Simulation
Today, the world is using renewable energies such as solar, waves, hydro-static, wind and ground energy.
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Today, due to the challenges of fossil fuel consumption such as increasing air pollution, greenhouse gas emissions, and limited resources, the world is using renewable energies such as solar, waves, hydro-static, wind, and ground energy. One way to utilize solar energy is solar chimney. The basis for a solar chimney is the difference in density and pressure difference due to the increase in temperature inside the solar collectors, which acts as a force. Solar energy is one of the cleanest and most accessible sources of electricity on earth, especially in areas with high annual solar radiation.
In a solar chimney system, there is a transparent roof that is capable of absorbing solar radiation energy. On the other hand, the air entering the system from the sides of this roof collects in the space between the roof and the ground; in fact, the transparent roof and the ground appear as a collector. The heat received by the ceilings of the solar chimney heats the air in this space and moves upwards due to its lightness. In the middle of this roof, there is a vertical chimney or tower, which due to the difference in pressure between the hot airflow and the cold air, causes the hot air to rise up into the upper part of the chimney.
Solar Chimney Types
Generally, we can divide these solar chimneys into two categories:
1. The first category is the chimneys for power generation which are of the industrial scale.
2. The second category is the ventilation chimneys for cooling and heating used with a residential scale.
In this simulation, we model a solar chimney. The lower part of the chimney is a plate to absorb the heat of the solar radiation, which we assume it as a constant temperature in the present simulation. The ground floor below this chimney also has a constant temperature. The chimney wall is assumed to be insulated to prevent heat loss. The inlet section below the absorber surface has a pressure equal to the atmospheric pressure, while the pressure in the outlet of the chimney is lower than the atmospheric pressure. This causes the air to suck upward to the top of the chimney, thereby discharging warm air through the chimney.
For the present simulation, several assumptions are taken into account:
1. The problem is steady-state.
2. Incompressible flow is assumed.
3. The effect of gravity is taken into account.
Geometry & Mesh
Three-dimensional solar chimney modeling was done using Design Modeler software. The meshing of the present model is carried out by ANSYS Meshing software. The mesh is of a structured type and element number is equal to 106323.
Here is a summary of the steps to define and solve the problem in the table:
|near-wall treatment||Standard wall function|
|(boundary conditions) (Solar Chimney)|
|inlet B.C||Pressure inlet|
|inlet air||relative pressure||0 Pa|
|inlet temperature||293 K|
|outlet B.C||Pressure outlet|
|outlet air||relative pressure||-100 Pa|
|absorber roof||temp.||312 K|
|(Methods) (Solar Chimney)|
|discretization||momentum||Second order upwind|
|pollutant||Second order upwind|
|(initialization) (Solar Chimney)|
Suction (Solar Chimney)
As the air temperature is increased by the solar absorber panels, it becomes lighter and its density decreases; this causes a pressure drop and suction for upward flow. Therefore, in boundary conditions, vacuum pressure is used.
Mesh file is available in this product. By the way, the Training File presents how to solve the problem and extract all desired results.