A Parabolic trough solar collectors CFD simulation is a computer model of a powerful renewable energy system. These collectors use large, curved mirrors to focus sunlight onto a pipe. This pipe, called a receiver tube, contains a fluid that gets very hot. This is a key technology for Concentrated Solar Power CFD. To analyze it, engineers use a powerful two-step method. First, Soltrace software is used for optical analysis. It is a Ray Tracing CFD Analysis tool that calculates exactly how sunlight hits the receiver tube. This gives us the heat pattern. Second, this heat pattern is used in an ANSYS Fluent simulation. The Solar collector Fluent model then calculates how the fluid inside the tube heats up and flows. Combining parabolic trough Soltrace and Fluent helps engineers design better collectors for maximum efficiency.

• Reference [1]: Abubakr, Mohamed, et al. “An intuitive framework for optimizing energetic and exergetic performances of parabolic trough solar collectors operating with nanofluids.” Renewable Energy157 (2020): 130-149.

Figure 1: Schematic showing the main parts of the Parabolic Trough CFD model: the large collector (right) and the heat collection element (left).

Simulation process: Fluent-Soltrace Setup,Optical Modeling and UDF for Heat Flux

This Coupled Optical-Thermal Simulation started with building an optical model in Soltrace software. Soltrace uses a Monte Carlo ray tracing method, which is very accurate for solar applications. We modeled the Euro trough collector, which has a mirror aperture width of 5.76 m and reflectivity of 94%. The receiver tube, or heat collection element (HCE), was modeled with a steel absorber pipe inside a glass tube, using the exact dimensions and material properties from the reference paper. The simulation in Soltrace calculated how the sun’s rays reflect off the mirrors and focus onto the HCE. This gave us a very detailed map of the heat flux around the pipe’s surface.

The next step was to use this heat map in ANSYS Fluent. To do this, we wrote a special program called a User-Defined Function (UDF) in the C language. This Fluent UDF Heat Flux code is the critical link between the two software. The UDF reads the heat flux data from Soltrace and applies it as a spatially varying boundary condition onto the absorber tube’s wall in the Fluent model. This makes the CFD simulation very realistic.

Figure 2 : A comparison plot from the Soltrace software showing the calculated Local Concentration Ratio (LCR) on the solar receiver surfaces.

Post-processing: CFD Analysis, Correlating Non-Uniform Heating with Thermal Performance

The results from the Soltrace optical analysis are the foundation of this study. The contours and plots show a highly non-uniform heating pattern, which is a key characteristic of parabolic troughs. The heat is not spread evenly around the receiver tube. Instead, the Local Concentration Ratio (LCR) plot in Figure 3 shows two distinct peaks. These peaks reach a maximum LCR of about 58 at angles of 60° and 120°. This is direct proof that the mirrors are focusing the sunlight onto the sides of the bottom half of the tube. The heat flux contour in Figure 4 visually confirms this, showing peak heat flux values of approximately 50,000 W/m² (the red areas) exactly where the LCR is highest. The back side of the tube is blue, showing it receives almost no direct heat. From an engineering perspective, understanding this uneven heating is the most important challenge in designing these systems.

Figure 3:  A plot showing the detailed distribution of the Local Concentration Ratio (LCR) around the circumference of the heat collection element.

The Fluent thermal analysis shows the direct consequence of this heating on the Heat Transfer Fluid (HTF). The simulation shows that water entering the tube at 200°C is heated to 205.4°C by the time it exits. This temperature rise of 5.4°C is the proof that the solar energy, concentrated by the mirrors and applied by our UDF, is being successfully transferred to the water. The CFD simulation’s ability to calculate this temperature gain while accounting for the complex, non-uniform heat load is a major success. It connects the optical performance directly to the thermal output. The most important achievement of this simulation is its successful coupling of Soltrace optical data with a Fluent thermal model through a custom UDF, creating a high-fidelity tool that accurately predicts the thermal performance (a 5.4°C temperature rise) based on a realistic, non-uniform solar heat flux.

Figure 4: A heat flux contour from the Solar Thermal Simulation Fluent analysis, showing the non-uniform heat pattern applied to the absorber tube using a custom UDF.