Solar chimney power plants represent an innovative approach to renewable energy generation, utilizing the fundamental principles of buoyancy-driven flow and thermal convection. These systems combine three key elements: a central chimney structure, a transparent solar collector canopy, and power-generating turbines. Due to the greenhouse effect produced by the collector canopy, which usually has a diameter of several hundred meters, the trapped air is heated to temperatures between thirty and seventy degrees Celsius above room temperature. Natural convection caused by this temperature differential pushes the hot air upward through the central chimney, where carefully positioned turbines use the kinetic energy to generate electricity. The collector portion, where the important heat transfer and flow development take place under conditions of constant heat flux, is the focus of the current CFD study, which uses ANSYS Fluent to evaluate the thermal-fluid dynamics within a 2D axisymmetric model. The objective of the present simulation is to simulate this widely used industrial device.

Figure 1: Schematic of solar chimney collector portion

Simulation Process

To start with, only half of the geometry is designed using Ansys Design Modeler software because an axisymmetric planar option will be selected in the solver. In ANSYS Fluent, the axisymmetric option allows users to model systems that exhibit rotational symmetry around a central axis. Fluent solves the governing equations in a two-dimensional domain when this option is selected. Besides, a structured grid is the primary option for dividing the computational domain. Thus, a correct split in this step needs to be considered. Later, in ANSYS Meshing software, 40750 elements are produced.

As mentioned in the introduction, the effect of solar irradiation is exerted on the wall, considering a constant heat flux. It should be noted that the dominant mechanism of mass and heat transfer in solar chimney collectors is natural convection caused by density gradient. Thus, it is crucial to bear in mind that the density is completely temperature–dependent.

Post-processing

The collector’s thermal-fluid behavior shows an intriguing interaction between fluid dynamics and heat transfer. The air temperature reaches its maximum values close to the absorber wall, where a steady heat flux is applied, forming a clear thermal boundary layer. This heated air layer causes buoyancy-driven flow to begin because of its decreased density (ρmin at maximum temperature zones). The velocity field shows a unique pattern: when air gets closer to the chimney entrance, near-stagnant conditions at the collector intake (V = 0 m/s) change into accelerating flow streams. The velocity profile most noticeably displays maximum values (Vmax) concentrated in a narrow region close to the chimney inlet, where buoyancy effects and the reduction in cross-sectional area combine to greatly speed up the flow.

Figure 2: Velocity distribution inside  Solar Chimney Collector CFD Simulation

Figure 3: Temperature distribution inside  Solar Chimney Collector CFD Simulation

The temperature distribution and the density stratification patterns have an inverse relationship; as the temperature rises, the density falls correspondingly, forming vertical density gradients which power the natural convection process. Since the temperature differential between the heated air and the surrounding air is most close to the absorber surface, these gradients are most noticeable there. A thermal boundary layer growth zone close to the collector inlet, a center region dominated by buoyancy-driven vertical acceleration, and a convergence zone at the chimney entrance where flow streamlines compress and velocities peak are the three distinct development regions shown in the flow structure. With the temperature-dependent density variation acting as the main force behind flow circulation, this behavior shows how well the collector converts solar thermal energy into kinetic energy through natural convection.

Figure 4: Density changes inside Solar Chimney Collector CFD Simulation