The efficient conversion of solar radiation into heat at high temperature levels requires the use of concentrating solar collectors. The goal of this paper is to present the optical and the thermal analysis of a parabolic dish concentrator with a spiral coil receiver. The parabolic dish reflector consists of 11 curvilinear trapezoidal reflective petals constructed by PMMA with silvered mirror layer and has a diameter of 3.8 m, while its focal distance is 2.26m. This collector is designed with commercial software SolidWorks and simulated, optically and thermally in its Flow Simulation Studio. The optical analysis proved that the ideal position of the absorber is at 2.1m from the reflector in order to maximize the optical efficiency and to create a relative uniform heat flux over the absorber. In thermal part of the analysis, the energetic efficiency was calculated approximately 65%, while the exergetic efficiency is varied from 4% to 15% according to the water inlet temperature. Moreover, other important parameters as the heat flux and temperature distribution over the absorber are presented. The pressure drop of the absorber coil is calculated at 0.07bar, an acceptable value.
In this study, the optical design of a solar parabolic dish concentrator is presented. The parabolic dish concentrator consists from 11 curvilinear trapezoidal reflective petals made of polymethyl methacrylate with special reflective coating. The dish diameter is equal to 3.8 m and the theoretical focal point distance is 2.26 m. Numerical simulations are made with the commercial software TracePro from Lambda Research, USA, and the final optimum position between absorber and reflector was calculated to 2.075 m; lower than focus distance. This paper presents results for the optimum position and the optimum diameter of the receiver. The decision for selecting these parameters is based on the calculation of the total flux over the flat and corrugated pipe receiver surface; in its central region and in the peripheral region. The simulation results could be useful reference for designing and optimizing of solar parabolic dish concentrators as for as for CFD analysis, heat transfer and fluid flow analysis in corrugated spiral heat absorbers. [Projekat Ministarstva nauke Republike Srbije, br. III42006: Research and development of energy and environmentally highly effective polygeneration systems based on renewable energy resources i br. III45016: Fabrication and characterization of nanophotonic functional structures in biomedicine and informatics]
Maximum Oxygen Consumption (VO 2 max) is considered to be one of the most relevant indicators of the level of functional ability of the cardiorespiratory system in individuals and athletes. It is an indicator of the functional state, and knowledge of the value of VO 2 max is of great importance in order to improve the functional form for athletes and recreational exercisers, as well as to properly plan, program and dose activities. The aim of this study was to review the literature in order to determine whether physical exercise can improve VO 2 max in people with spinal cord injuries. The following electronic databases were used to collect the papers: KoBSON, Google Scholar, MEDLINE, PEDro, DOAJ and Open J Gate. The key words that were used to find the papers are: physical exercise, VO 2 max, spinal cord injury, adaptation, training, effects, patients, intensity, aerobic, anaerobic, heart rate. Based on inclusive and exclusive criteria, eight papers were selected that met the set criteria. Analyzing the papers, only four papers examined the differences in terms of the intensity of the exercise with the goal of finding out which intensity is suitable for improving the VO 2 max value. They have found that the VO 2 max value can be enhanced by physical exercise of increased intensity (HIIT) relative to physical exercise of moderate intensity (LI). Considering the high level of heterogeneity of the scientific papers, the sample of participants, measuring instruments, and experimental research, the conclusions should be taken with caution.
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