The optical performance of solar central tower (CT) systems on hillsides of mountain areas is investigated based on the biomimetic spiral heliostat field distribution algorithm. The optical efficiencies and the field characteristics of different hillside solar field configurations are examined. The effect of various geometric parameters such as hillside tilt angle and the location of the receiver on the optical efficiency of the field are investigated and documented. The study is based on generating a 25 MWth power plant at the location of Sierra Sun Tower in California, USA, using Planta Solar 10 (PS10) heliostats' parameters. This study is performed numerically using a specially developed code using matlab software. The biomimetic spiral distribution pattern and the particle swarm optimization (PSO) method were used to obtain optimum solar fields. The spiral distribution shape factors were optimized for pursuing maximum annual weighted field efficiency. It is found that the annual optical weighted field efficiency for hillside solar fields is always lower than that for a flat field for same receiver height. On the other hand, the field land area for small hillside-slopes is smaller than that of a flat field area. It is found that there is an optimum field tilt angle where the land area is minimum. The minimum field area for the system studied in this paper was associated with (15 deg) field tilt angle. Furthermore, it was found that as the tower height increases the annual optical field weighted efficiency increases until it reaches a peak value. It was also found that, the closer the tower to the beginning of the heliostat field, the higher the field efficiency with less number of heliostats and less land area.
In this work, the effect of the inner opening ratio on the J-shaped airfoils aerodynamic performance was studied and documented for symmetrical airfoils. Three different airfoil thicknesses were investigated: small, medium, and large. For each airfoil thickness, effects of three inner opening ratios were analyzed: one-third, one-half, and two-thirds. The performance of each opening ratio was compared with the performance of the solid airfoil “zero opening ratio”. All designs were simulated using the Computational Fluid Dynamics (CFD) technology against experimental results for solid NACA4412 airfoil in the UWM Wind Tunnel facility and other published experimental data. It was found that Large Eddy Simulation yields accurate solutions with a smaller number of mesh cells compared to k-ω turbulence model but with much more computational time. The lift to drag ratio for all studied airfoils has a maximum value for solid airfoils compared to their corresponding ones equipped with openings. For airfoils equipped with a 00.00% opening ratio ‘solid,’ airfoil with a thickness of 15% has the maximum lift to drag ratio. Furthermore, it was found that NACA0008 equipped with a 33.33% opening ratio has the best performance of all studied J-shaped airfoils.
This study investigates the optimum operating conditions and design configurations that can optimize the power reclaimed by small hydro turbines derived by the rising water-bubble current. The rising current is generated by the compressed air introduced by the diffusers at the bottom of aeration basins of Wastewater Treatment Plants (WWTPs). While optimizing the power production, the standard oxygen transfer efficiency (SOTE) is monitored since it is a significant parameter that cannot be sacrificed in the operation of WWTPs. Using one set of turbine blades, it was found out that the highest velocity is obtained in the upper half of the water column (70% - 80%). In contrast, the lowest velocities were obtained just above the air diffuser and at the water surface. Testing started with using a single turbine (ST) to determine the location of the optimum power reclaimed at each tested airflow (1.18, 1.42, 1.65, and 1.89 L/s). Then using double turbine (DT) and triple turbine (TT) to compare their performance to the ST’s maximum power increased power reclamation. The maximum percentage of increase in power reclamation for DT is 19.59%, while it is 20.24% in the case of TT. At a commonly used airflow in WWTPs (1.42 L/s), the optimum configurations of DTs and TTs were selected to investigate the effect of having the proposed setup on the SOTE. For membrane diffusers, DTs and TTs limited the dispersion of the air bubbles in the tank, therefore, reducing the SOTE (8.3% for DT and 3.7% for the TT). The ceramic and sharp-nub diffusers were also tested versus rubber membrane ones to determine the effect of using the ceramic and sharp-nub diffusers on the power reclamation and SOTE. Ceramic diffusers neither achieve higher power reclamation than the membrane nor increases the SOTE. In contrast, sharp-nub diffusers increase the SOTE for all configurations compared to membranes, but this came into account of power reclamation, where sharp-nub diffusers cause a DT and a TT to produce less power than ST does.
This study targets one of the major energy consumers in the U.S. It suggests a new mechanical system that can recover a portion of the energy in Wastewater Treatment Plants (WWTPs). The proposed system entails a hydro-turbine installed above the air diffuser in the aeration tank to extract the water-bubble current's kinetic energy and converts it to electricity. Observing the optimum location of the turbine required multiple experiments where turbine height varies between 35% and 95% (water height percentages above the diffuser), while varying the airflow between 1.42 L/s (3 CFM) and 2.12 L/s (4.5 CFM) with a 0.24 L/s (0.5 CFM) increment. Additionally, three water heights of 38.1 cm (15”), 53.4 cm (21”), and 68.6 cm (27”) were considered to study the influence of the water height. It was noticed that the presence of the system has an adverse effect on the Standard Oxygen Transfer Efficiency (SOTE). Therefore, a small dual-blade propeller was installed right above the diffuser to directly mix the water in the bottom of the tank with the incoming air to enhance the SOTE. The results showed that the maximum reclaimed power was obtained where the hydro-turbine is installed at 65% - 80% above the diffuser. A reduction of up to 7.32% in SOTE was observed when the setup was placed inside the tank compared to the tank alone. The addition of the dual-blade propeller showed an increase in SOTE of 7.27% with a power loss of 6.21%, ensuring the aeration process was at its standards.
Non-uniformity of the exit flow temperature represents one of the significant damages to gas-turbine components, particularly turbine blades. This may occur in the course of gas turbine operation. This paper aims to provide passive techniques by modifying the combustor design rather than changing the flow parameters to improve the thermal uniformity and turbine blades to reduce thermal stresses and increase turbine blades' life span. An acceptable agreement between the numerical and experimental results has been achieved, and the agreement includes the velocity and temperature profile. Four different angles have been tested numerically and experimentally with a maximum error of 5% at two different Reynolds numbers. Designing the outer combustor surface with a 45 angle bend can give a more uniform temperature distribution of 37% higher than the basic design with only a 0.5% higher pressure drop.
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