Solar energy is a viable source to fulfill the energy demands of a solar rich country such as Pakistan. Various types of solar thermal technologies are being used around the world, including flat plate, evacuated tube, and compound parabolic trough collectors. However, the performance of these collectors is strongly influenced by the nature of work fluid. Utilization of nanofluids with high thermal conductivity is a very attractive way to further enhance the performance of solar collectors. Therefore, this study deals with the characterization and thermal performance enhancement of compound parabolic collectors (CPC) by using non-metallic nanofluids such as water-based multi-wall carbon nano tubes (H2O-MWCNT) with a thermal conductivity of 3000 W/m·K. In the current work, multiple tests are performed to analyze the thermal conductivity and stability of nanofluids through thermal analyzer and UV-Vis Spectroscopy, respectively. Test results show that the thermal conductivity of water-based MWCNT nanofluid is 37% higher than water at a concentration of 0.075%. Prepared nanofluids are then employed in CPC, and detailed experimentation is performed by varying the concentration of nanoparticles (0.025, 0.05, 0.075%) and their flow rate (0.015, 0.02 kg/s). Maximum temperature difference of 10.5oC with volumetric concentration of 0.075% is achieved in experimental analysis at flow rate 0.015 kg/s. Thermal efficiency enhancement of 19.37% with volumetric concentration 0.075% is recorded as compared to water at flow rate 0.015 kg/s.
Solar thermal collectors such as flat plate and evacuated tube collectors are used for maximum of 60-80 ℃ temperature and parabolic trough collectors are used for 700-900 ℃ temperature ranges. It is needed to develop and analyse solar collector, such as compound parabolic collectors (CPC) which can operate for intermediate temperature range from 50-300 ℃ for industrial and domestic applications. However, optical and thermal performance of CPC is strongly influenced by concentration ratio. The current study presents a comparative optical and thermal analysis of CPC with fixed (4.58) and variable (4.58 to 5.87) concentration ratio by using model-based transient simulation approach. Two profiles of compound parabolic collector are analysed with fixed and variable concentration ratio for the subtropical climate of Taxila, Pakistan. 2D profiles of both collectors are modelled and designed in MATLAB and are then analysed optically by using Monte Carlo ray tracing technique through TracePro. In addition, thermal analysis of both profiles is also performed through ANSYS. The resulted optical efficiency with fixed and variable concentration is 91 % and 96 %, respectively at a given tilt angle. Whereas maximum temperature achieved with both profiles is 5°C and 7°C, respectively. Thus, it is concluded that performance of CPC with variable concentration ratio is much better compared to fixed value.
Solar thermal collectors, such as flat plate and evacuated tube collectors, are used for maximum of 60–80 °C temperature and parabolic trough collectors are used for 700–900 °C temperature ranges. It is needed to develop and analyze solar collectors, such as compound parabolic collectors (CPC) which can operate in an intermediate temperature range from 50–300 °C for industrial and domestic applications. However, optical and thermal performance of CPC is strongly influenced by concentration ratio. The current study presents a comparative optical and thermal analysis of CPC with fixed (4) and variable (4.5 to 5.7) concentration ratio by using model-based transient simulation approach. Two profiles of compound parabolic collector are analyzed with fixed and variable concentration ratio for the subtropical climate of Taxila, Pakistan. 2D profiles of both collectors are modeled and designed in MATLAB and are then analyzed optically by using Monte Carlo ray tracing technique through TracePro. In addition, thermal analysis of both profiles is also performed through ANSYS. The resulting optical efficiencies with fixed and variable concentration are 72% and 79%, respectively. Whereas maximum temperature achieved with both profiles is 352 K and 367 K, respectively. Thus, it is concluded that performance of CPC with variable concentration ratio is much better compared to fixed value.
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