In wastewater treatment plants, aeration plays a significant role as it encourages aerobic respiration of microbes, which are necessary to break down carbonaceous matter in the waste stream. This process can account for the majority of energy use in wastewater treatment plants. The aeration process is also necessary in odor control in lagoons and in the aquaculture industry. Generally, the aeration process is accomplished with compressors or blowers which can be of low efficiency due to ideal gas laws. This study introduces the idea of increasing aeration efficiency by looping water from a reservoir through a piping network which includes a venturi aspirator at its inlet. For this purpose, an experimental study has been conducted in a laboratory setup with a pump which pulls water from a tank, passes it through a Venturi aspirator and a helical piping network intended to increase bubble residence time, before depositing it back into the bulk fluid tank. This same process is modeled computationally, using a discrete bubble method (DBM), with good agreement with experiments. The overall purpose here is to determine the optimal configurations for standard aeration efficiency (SAE) and the standard oxygen transfer rate (SOTR). A parametric study has been implemented using the DBM based on different hydraulic and flow parameters. The model is also used to predict the SAE of a hypothetical aeration system. Results indicate that it is possible to achieve SAE values in the range of surface aerators or submersed jet aerators using the proposed aeration system with less complex components, thereby decreasing overall costs.

Vertical-axis wind turbines (VAWTs) have drawn increased attention for off-grid and off-shore power generation due to inherent advantages over the more popular horizontal-axis wind turbines (HAWTs). Among these advantages are generator locale, omni-directionality and simplistic design. However, one major disadvantage is lower efficiency, which can be alleviated through blade pitching. Since each blade must transit both up- and down-stream each revolution, VAWT blade pitching techniques are not yet commonplace due to increased complexity and cost. Utilizing passively-morphing flexible blades can offer similar results as active pitching, requiring no sensors or actuators, and has shown promise in increasing VAWT performance in select cases. In this study, wind tunnel tests have been conducted with flexible and rigid-bladed NACA 0012 airfoils, in order to provide necessary input data for a Double-Multiple Stream-Tube (DMST) model. The results from this study indicate that a passively-morphing VAWT can achieve a maximum power coefficient (Cp) far exceeding that for a rigid-bladed VAWT CP (18.9% vs. 10%) with reduced normal force fluctuations as much as 6.9%. Operational range of tip-speed ratio also is observed to increase by a maximum of 40.3%.

Electricity production from concentrated solar power (CSP) plants has been more commonplace in the last decade since the sun is one of the most abundant, renewable energy sources. The heat transfer fluid temperature in a CSP plant may go up to 1000 C; however, most of the current power plants operate on temperature ranges between 220 C and 565 C due to decomposition of molten salts in high temperatures. Since the sun is not available at nights and cloudy days, an important consideration is how to store the energy received by the sun to use at other times. In this study, a three-dimensional borehole heat exchanger model is developed to store solar energy underground using concrete and molten salt as a storage medium and heat transfer fluid, respectively.While molten salt is circulating through a pipe, which is placed into the concrete, heat is transferred from the molten salt to the concrete or vice versa during the charging and discharging processes. Numerous simulations are conducted using ANSYS Fluent, with varying borehole diameters, mass flow rates, and thermal resistances of the borehole wall. Average concrete temperature, outlet heat transfer fluid temperature, and energy and exergy efficiencies are investigated for each case. It was found here that while concrete temperature increases with increasing mass flow rate, the increasing trend is minimal after the mass flow rate increases beyond 6 kg/s. There exists a negative relation between the borehole diameter and average concrete temperature during the charging process, and vice versa in discharging. Energy and exergy efficiencies varied from 0.2% to 98.1% and 0.1% to 77.9%, respectively. While the most efficient system was found at a borehole diameter of 550 mm for adiabatic cases, it was found to be 750 mm when heat leakage is taken into consideration. Borehole diameters of 2000 mm performed the worst among all cases due to low heat transfer rates. Heat leakage was found to have a significant impact on energy and exergy efficiencies, especially in energy efficiencies for higher borehole diameters and low mass flow rates in the discharging process.

Concentrated Solar Power (CSP) is one of the most promising ways to generate electricity from solar thermal sources. In this situation, large tracking mirrors focus sunlight on a receiver and provide energy input to a heat engine. Inside the receiver the temperature can be well above 1000°C, and molten salts or oils are typically used as heat transfer fluid (HTF). However, since the sun does not shine at night, a remaining concern is how to store thermal energy to avoid the use of fossil fuels to provide baseline electricity demand, especially in the late evenings when electricity demand peaks. In this study, a new method will be investigated to store thermal energy underground using a borehole energy storage system. Numerical simulations are undertaken to assess the suitability and design constraints of such systems using both molten salt as HTF.

Every compressor has a stall line. In the vicinity of the stall line, the flow field is inherently unsteady due to the interactions between adjacent rows of blades, formation of small stall cells, flow separation and the viscous effects including shock-boundary layer interactions. These factors may aggravate to a state of local breakdown of flow or a total breakdown of flow or with a disastrous flow reversal. This paper starts with an overview on the previous researches about compressor stall and surge. Subsequently, it describes the effects of these instabilities in overall engine performance and design with/ without any control. The main objectives of this paper are to review the phenomenon of instability and methodology to suppress the rotating stall and surge by enlarging the stable operating range of compressor with the application of various control systems. This paper surveys research developments in this field and also tries to find an improved solution to increase the engine performance by applying various surge control strategies. Finally, the paper focuses on some recommendations towards a better design of compressor especially for aircraft power plant.