A wide range of engineering industrial applications requires both the thermal and optical efficiencies of the system to be maximized with a reasonable low penalty for the friction factor and subsequently low losses in pressure. Amongst the family of concentrated solar power systems, parabolic trough collectors (PTC) which have recently received significant attention, face similar challenges. To effectively enhance the thermal performance of the PTC system four enhancement techniques were numerically investigated and addressed in this thesis; changing heat transfer fluids, replacing the working fluids with nanofluids that have better thermal-physical properties than those of base fluids, inserting different turbulators with various design configurations and finally combining the advantages of nanofluids and swirl generators in the same application. All simulations were assumed to be in steady-state and three dimensions with a range of Reynoldâs number (Re=104-105). For the simulation the Monte Carlo Ray Tracing (MCRT) model was used to represent the non-uniform heat flux around the absorber tube of the PTC. Two low-Reynoldâs turbulence models were used; Launder and Sharma (LS) k-epsilon and Shear Stress Transport (SST) k-omega models. In order to assess the performance of each enhancement technique, a number of parameters were analyzed including average Nusselt (Nu) number, specific pressure drop distributions, thermal losses, overall collector efficiency and exergy efficiency of the PTC system. Three categorized-types of pure fluids were used firstly. Secondly, numerical simulations were performed for a solar collector to test the effectiveness of six non-metallic nanoparticles dispersed individually in three different base working fluids with three different volume fractions. The third step was to study the effect of the variation of geometrical properties of a single canonical insert to find the optimized shape then increase the number of strips to two, three and four around the central rod. The final step was to assess the effect of various straight strip shapes with and without nanofluids. Four different strip arrangements were considered; large conical-shape strips, small conical-shape strips, rectangular-shape strips and elliptical-shape strips. Results showed that, the largest enhancements in the overall collector efficiency and thermal exergy efficiency were achieved by the hybrid system of combining both large conical-shape strips and 6% of SiO2 dispersed in therminol VP-1 which are 15.41% and 15.32% respectively compared to a typical system.
|Date of Award||31 Dec 2021|
- The University of Manchester
|Supervisor||Hector Iacovides (Supervisor), Imran Afgan (Supervisor) & Andrea Cioncolini (Supervisor)|