•In this study, the impact of internal fins in PTC operating with gases is presented.•Air, helium and CO2 are tested in smooth absorber and with fins of 5–10mm and 15mm.•Greater fin length leads to ...higher thermal efficiency and 10mm is the optimum length exergetically.•Helium is the best working fluid exergetically, with CO2 and air to follow.•Up to 290°C, helium performs better energetically, while CO2 in higher temperatures.
In this study, the use of internal fins in parabolic trough collectors operating with gas working fluids is examined. Air, helium and carbon dioxide are the investigated working fluids, while Eurotrough ET-150 is the examined solar collector. The design and the simulation of this solar collector are performed with the commercial software Solidworks Flow Simulation. The internal fins lead to higher thermal efficiency but also to higher pressure losses; something very important for the solar fields of Concentrated Power Plants. Thus, the collector is examined energetically and exergetically in order to take into account the increase in the useful output with the simultaneous greater need of pumping power. Various fin lengths are examined and finally the fin of 10mm was proved to be the most appropriate exergetically. In working fluid comparison, helium is the most efficient working fluid exergetically for all the examined cases. In the thermal efficiency comparison, helium performs better up to 290°C, while carbon dioxide is the best choice in higher temperature levels. Moreover, the optimum mass flow rate for the helium was proved to be 0.03kg/s and for the other working fluids the value of 0.015kg/s seems to lead to the most satisfying results.
This study develops a 3D-CFD model to analyze the thermal performance of perforated fin heat sinks and evaluates four perforated continuous and interrupted fin heat sinks with distinct geometric ...patterns. Using the Finite-Volume Method (FVM) to discretize the governing equations, the SolidWorks 2019 flow simulation software was implemented to solve and validate the latter, demonstrating that the CFD simulation model employed in the current study is reliable. The performance parameters of the heat sink are presented in terms of Reynolds number and heater power. The results indicate that modules B and C achieved higher heat transfer rates, average heat transfer coefficient, and Nusselt number compared to the other modules. Module A had the highest fin efficiency and module D exhibited greater fin effectiveness than the other ones.
Parabolic trough collector is one of the most usual solar collectors for applications up to 400 °C. The thermal enhancement of this collector concentrates a lot of interest and various techniques are ...tested in order for the thermal efficiency to be maximized with a reasonable penalty in the pressure drop. The use of nanofluids as working fluids, as well as the use of flow turbulators, mainly inserts and internal fins or tube dimples are the main techniques which are examined. The objective of this work is to give a complete literature review of the existing studies on this domain and to present a numerical comparative analysis between the most usual thermal enhancement techniques. More specifically, the use of oil-based nanofluids with 6% CuO is compared with the use of internal rectangular fins in the absorber, while the combination of these techniques is also examined. The analysis is conducted with a validated CFD model in SolidWorks Flow Simulation for various fluid temperature levels. According to the final results, the use of nanofluids leads to 0.76% thermal efficiency enhancement, the use of internal fins to 1.10% and the combination of these techniques to 1.54%. Moreover, emphasis is given in the pressure drop of the examined cases and in the evaluation criteria which are used in every case.
Parabolic trough collectors are the most mature technology for utilizing the solar energy in high temperature applications. The objective of this study is the thermal efficiency enhancement of the ...commercial parabolic collector IST-PTC by increasing the convective heat transfer coefficient between the working fluid and the absorber. There are two main factors which influence on this parameter, the working fluid type and the absorber geometry. For this reason three working fluids are investigated, thermal oil, thermal oil with nanoparticles and pressurized water. Moreover, a dimpled absorber tube with sine geometry is tested because this shape increases the heat transfer surface and increases the turbulence in the flow. The final results show that these two techniques improve the heat transfer coefficient and the thermal efficiency of the collector. More specifically, the use of nanofluids increases the collector efficiency by 4.25% while the geometry improvement increases the efficiency by 4.55%. Furthermore, collector parameters such as the heat loss coefficient, the exergetic efficiency, the pressure losses and the absorber temperature are presented for all the examined cases. The model is designed with Solidworks and is simulated by its flow simulation studio.
•The commercial parabolic collector IST-PTC is simulated with Solidworks.•The developed model is validated by data taken from literature.•The use of nanoparticles inside the thermal oil is investigated.•The use of absorber with an internal wavy surface is examined.•The final results show that the two ways increase the efficiency about 4.5%.
•A novel flow insert with star shape in parabolic trough collector is studied.•The insert geometry is optimized by examining 16 different insert shapes.•The analysis is performed using thermal, ...exergy and overall efficiency criteria.•The collector performance is enhanced for all the examined flow inserts.•The maximum thermal efficiency enhancement is found up to 1%.
The use of flow inserts is a common passive technique for enhancing the thermal performance of parabolic trough solar collectors. The objective of this work is to investigate a novel insert with a star shape. The shape of this insert is optimized by examining different combinations of its geometric characteristics. Totally 16 different cases are studied with the fin length to be varied from 15 mm to 30 mm and the fin thickness from 2 mm to 5 mm. The evaluation criteria of the examined cases are the thermal efficiency, the exergy efficiency and the overall efficiency of the solar collector. The exergy efficiency and the overall efficiency are suitable criteria for evaluation the Nusselt number increase with the simultaneous friction factor increase. The collector is examined for inlet temperatures between 400 K and 650 K with a volumetric flow rate equal to 150 L/min. According to the final results, the thermal efficiency, the exergy efficiency and the overall efficiency are increased for all the examined flow inserts. The thermal efficiency enhancement is higher with the inlet temperature increase and it can reach up to 1%. Moreover, it is found that greater dimensions of the insert lead to higher performance enhancements. The pressure drop is found to increases many times with the use of inserts but the pumping work value is extremely low in all the cases. The analysis is conducted with SolidWorks Simulation Studio with a validated model.
A data buoy for measuring coastal wave-action has been designed and constructed. The buoy is essentially a 0.6 m diameter sphere that is made of fiber-glass with aluminum, steel and polymer parts. ...While the overall geometry of the buoy is superficially similar to that of existing commercial spherical buoys (e.g. Wave-Rider by Datawell), the present design is based on a simple robust structure and mass-market electronics. A significant dual-use feature of this design is that the structure is usable as a float in a wave-energy generation device. This is possible due to the essentially isolated central structure and an electronics enclosure that is sealed both from the external environment and from the bulk shell of the buoy. This also allows the electronics to be mounted in an easily- modified, rack configuration that can be removed from the buoy shell. In a wave-energy generation set-up the electronics rack would be removed and the central cylinder will become part of a linear-motion type generator, with at least +/- 25 cm of internal movement available to it that is waterproof (for near surface or shallow immersions). Alternatively, for large wave motions, the buoy can couple to an energy-generating device using flanges that mate with its bolt circle pattern. However, at the moment, the buoy enclosure is dedicated to wave-action measurement, i.e., a data buoy with an onboard inertial measurement unit (IMU) and a radio-link to send real-time data to a receiving unit that can be on a boat or at the seashore. Basic GPS data are also transmitted. This is of interest if the buoy is being deployed in a drifting (un-moored) mode. This paper will only discuss the mechanical design and fabrication of the structure.
•Twelve different internally finned absorbers are examined in the LS-2 PTC.•The thermal enhancement and the pressure drop are the main calculated parameters.•Four evaluation criteria are used for ...determining the optimum fin geometry.•The fin with 10mm length and 2mm thickness is found to be the optimum case.•The optimum fin presents 0.82% thermal efficiency enhancement compared to smooth case.
Among the solar concentrating technologies, parabolic trough collector (PTC) is the most mature and cost-effective technology for medium and high-temperature levels (150–400°C). This paper investigates the utilization of internally finned absorbers in LS-2 PTC module for various operating conditions. Twelve different longitudinal fins are tested and compared with the smooth case. The analysis is performed with SolidWorks Flow Simulation, using a validated model by literature results. Generally, it is proved that both greater length and thickness lead to higher thermal enhancement and to higher pressure losses. Various methods are presented for evaluating together the thermal efficiency or Nusselt number enhancement versus the increase in pressure drop or in the friction factor. Taking into consideration four different criteria, the absorber with 10mm fin length and 2mm fin thickness is found to be the overall optimum case. For this case, the thermal efficiency is enhanced about 0.82%, the Nusselt number increase 65.8%, while the friction factor and the pressure losses are about the double compared to the smooth case.
Summary
This article presents a Model‐Free Adaptive Nonsingular Fast Terminal Sliding Mode Controller with Super Twisting and Multi‐Layer Perceptron (MLP) neural network for motion control of a 10 ...DOFs lower limb exoskeleton used in rehabilitation. The proposed controller employs a second‐order ultra‐local model to replace the complex dynamics of the exoskeleton and uses an MLP neural network to estimate the lumped disturbance of the ultra‐local model. To ensure accurate tracking of the desired trajectory and address the estimation errors of the MLP, an Adaptive Nonsingular Fast Terminal Sliding Mode Controller is introduced. Moreover, a Super Twisting approach is employed to eliminate the chattering phenomenon. The system's stability is analyzed using Lyapunov theory, and the desired trajectories are obtained from surface electromyography (EMG) signal measurements. The effectiveness of the proposed controller is validated through co‐simulation experiments using SolidWorks, Simscape Multibody, and MATLAB/Robotics Toolbox. Results demonstrate significant improvements in stability and precision compared to existing model‐free controllers.
