The biological aerated filter (BAF) reactor is regarded as an effective biological wastewater treatment method. It can remove pollutants by carrier filtration and biodegradation. Due to its advantages, which include high biomass retention, tolerance to toxicity, excellent removal efficiency, and slurry separation, BAF has been widely used to remove COD, NH4 + -N, phosphorus, and other harmful organic substances. In this study, the BAF reactor was used to remove organic contaminants of domestic wastewater of Korea at both the benchand pilot-scale. The main objectives of this study are to: (i) investigate the removal efficiency of organic contaminants (ex. COD, nitrate, phosphorus) in BAF reactors at both scales; (ii) characterize the small-scale wastewater treatment plant using the BAF reactor. The concentration of COD in the influent increased from 69 to 246 mg/L. During the operation period, the final effluent concentration of COD remained maximum 4.0 mg/L, and the average removal efficiency was above 88%. The present study investigated the removal efficiencies of COD, TN, TP and NH4 + -N from smelting wastewater by BAF system. When treating wastewater in both bench and pilot-scale reactors, the BAF worked well.
An organic Rankine cycle was analyzed to work at the optimal operating point when the heat source is fluctuated. R245fa was adopted as a working fluid, and an axial-type turbine as expander on the cycle was designed to convert the heat energy to the electricity since the turbo-type expander works at off-design points better than the positive displacement-type expander. A supersonic nozzle was designed to increase the spouting velocity because a higher spouting velocity can produce more output power. They were designed by the method of characteristics for the operating fluid of R245fa. Three different cases, such as various spouting velocities, various inlet total temperatures, and various nozzle numbers, were studied. From these results, an optimal operating cycle can be designed with the organic Rankine cycle when the available heat source as renewable energy is low-grade temperature and fluctuated.
A low-noise regenerative blower is developed for fuel cell application by combining the FANDAS-Regen code and design optimization algorithm under several performance constraints for flow capacity, static pressure, efficiency and power consumption. The optimized blower design model is manufactured with some impeller modification based on low noise design concept and tested by using aerodynamic performance chamber facility and narrow-band noise measurement apparatus. The measured results of the optimized blower satisfy the performance requirements and are also compared favorably with the FANDAS-Regen prediction results within a few percent relative error. Furthermore, the present study shows the remarkable noise reduction by 26 dBA can be achieved through design optimization and low noise design concept.
The development of efficient systems for water quality improvement for water sources such as lakes, dams and reservoirs has become a necessity to provide not only a cleaner and safer water to the urban society, but also to provide a cleaner and safer environment for the aquatic organisms living in lakes, dams and reservoirs. This study concentrates on the outlet design and internal flow analysis of an axial flow pump used in a floating type water treatment system completely powered by renewable energy source. The treatment system is designed to raise water from depths of about 3∼5m up to the water surface where it is naturally mixed with air as it is released back to the reservoir. The outlet of a typical axial flow pump is modified to suit the floating type water mixer. The performance of the axial flow pump is studied by investigating the internal flow of the system. Results show that the change in outlet shape does not alter the performance of the original pump at the maximum efficiency point as long as the cross sectional area of inlet is the same as the outlet. The axial pump for floating type water treatment system has good cavitation performance in the whole flow passage.
Organic Rankine Cycle is widely used to convert the low-grade thermal energy to the electrical energy. However, usually available thermal energy is not supplied constantly. This makes hard to use positive displacement expanders. Hence, turbo-expander has merits to apply as an expander in ORC because it can operate well off-design points even though the mass flowrate is fluctuated. The thermal energy fluctuation causes the turbo-expander to operate in partial admission. In addition, supersonic nozzles are required so that the partially admitted turbine operates efficiently. In this study, R245fa was chosen as a working fluid of ORC. A design method and an analysis technique of supersonic nozzle based on R245fa were developed. The shape of the nozzle was designed by the characteristic method. The thermal properties within the nozzle were estimated and the predicted results were agreed well with the computed results.
Experimental results are given for the vertical motion of water in the water chambers for wave energy converter aligned along the wave propagation direction in order to avoid the impulsive wave forces. This paper mainly focuses on the property of the amplitude of the vertical motion of the water surface in the chambers. The amplification has been investigated by dimensionless parameters of wave period to resonance period ratio of the U-shaped oscillation, T/Tr , chamber size to wave length ratio, ι/L, water depth to wave length ratio, h/L, amplitude of up-down motion of water particles to draft of the front wall ratio,?/D . It has been shown that ι/L should be less than 0.1 and as T/Tr approaches unity the up-down of the water in the chambers is amplified. Also, the structure of the walls which form th water chambers has been examined roughly. It is deduced that the chambers set on both sides of the hull of a single-point moored floating vessel is preferable to those set along a fixed structure such as breakwaters.
A parametric study on anti-vortex holes for turbine blade cooling was investigated numerically. Three-dimensional Reynolds-averaged Navier-Stokes equations and shear stress transport turbulence model were used for analysis of anti-vortex film cooling. Validation of numerical results was carried out comparing with experimental data. The cooling performance of anti-vortex holes was assessed by two geometric variables, the ratio of diameters of holes and the lateral distances between the primary hole and anti-vortex hole at blowing ratios of 0.5 and 1.0. The results showed that the spatially-averaged film-cooling effectiveness increases as the ratio of the diameters increases and the distance between the primary hole and anti-vortex hole decreases.
Propellent should be pressurized inside the turbopump to gain high thrust in a projectile. Turbopump is composed of an inducer, which prevents impeller performance deterioration, and an impeller. Several types of cavitation occur inside the inducer, numerous experiments and CFD simulations are conducted. Though, an inducer takes only small portion of total head of the pump and the following impeller determines whole turbopump performance. In addition, low inlet pressure makes the flow to be cavitated not only at the inducer, but also at the impeller in real cases. Therefore, flow through an inducer and an impeller should considered simultaneously. In this study, LOX pump composed of an inducer and an impeller is analyzed by using commercial CFD code ANSYS CFX 13.0. Non-cavitating flow with high inlet pressure and cavitating flow with low inlet pressure are both simulated and head, suction performances are shown. Evolution of the flow and the cavitation by reducing cavitation number and effect of cavitation on ump performance are studied.
A long term passive cooling system is considered as the most important safety feature for the nuclear design after the Fukushima Daiichi nuclear power plant accident in 2011. The conventional active pump driven safety systems are not available during a station Black Out (SBO) accident. The current design requirement on cooling time of the Passive Auxiliarly Feedwater System (PAFS) is about 8 hours only. To meet the 72 hours cooling time, the pool capacity of cooling water tank should be increased as much as 3~4 times larger than that of current water cooling tank. In order to extend the cooling time for 72 hours, a new passive air-water combined cooling system is proposed. This paper provides the feasibility of the combined passive air-water cooling system. The current pool capacity of water cooling system is preserved, and the cooling capability is extended by an additional air cooler.
This paper presents a design optimization for meridional profile and blade angle θ of a centrifugal compressor with DOE (design of experiments) and RSM (response surface method). Control points of the 3rd order Bezier curve are used for design parameters and specific overall efficiency is used as object function. The response surface function shows good agreement with the 3D computational results. Three different optimized designs are proposed and compared with reference design at design point and off-design point. Contours of relative Mach number, static entropy, and total pressure are analyzed for improvement of performance by optimization. Off-design performance analysis is conducted by total pressure and efficiency.
In this study, a new model for calculating the liquid film thickness and condensation heat transfer coefficient in a vertical condenser tube is proposed by considering the effects of gravity, liquid viscosity, and vapor flow in the core region of the flow. In order to introduce the radial velocity profile in the liquid film, the liquid film flow was regarded to be in Couette flow dragged by the interfacial velocity at the liquid?vapor interface. For the calculation of the interfacial velocity, an empirical power ?law velocity profile had been introduced. The resulting liquid film thickness and heat transfer coefficient obtained from the proposed model were compared with the experimental data from other experimental study and the results obtained from the other condensation models. In conclusion, the proposed model physically explained the liquid film thinning effect by the vapor shear flow and predicted the condensation heat transfer coefficient from experiments reasonably well.
Small hydro power, among other renewable energy resources, has been evaluated to have enough development value because it is a clean, renewable and abundant energy resource. In addition, small hydro power has the advantage of low cost development by using existing facilities like sewage treatment plants, water works and similar resources. But in the case of small hydro power systems, there are problems with degraded operation efficiency of turbine due to changes in flow rates. In order to overcome this, variable speed control can be achieved by using the power rectifier and permanent magnetic synchronous generator(PMSG) as a possible method to respond to the changes in flow rates. In this study, a commercial ANSYS CFD code was used to analyze the performance of 10kW class propeller hydro turbine and to also investigate flow characteristics at variable flow rates and runner vane.
In Ocean, the temperature of the deep sea water is always lower than that of the surface sea water. The temperature difference between the surface water and deep sea water is about 20℃. Based on thermodynamics, this temperature difference can be converted into mechanical power. The mechanical power can be converted to electricity through a generator. However, the temperature difference is relatively small compared with that of traditional steam turbines. It is difficult to apply the steam turbine technology for this small temperature difference directly. Therefore, the turbine for OTEC system using low temperature difference should be designed to meet the system requirement. The present study focuses on the development of the turbine for 20 kW OTEC system using R32. The paper includes the determination of working fluids, meridional design, turbine layout and 3D CFD results. With off-design points analysis, the full performance of 20kW OTEC turbine is investigated. Through the research, one stage radial type turbine with R32 as working fluid is successfully developed and can be applied to other high temperature heat source.
The effectiveness of a perforated plate installed additionally at butterfly valve to reduce cavitation which can cause vibration, noise, erosion, and flow path blockage has been investigated using CFD. Rayleigh-Plesset equation was applied to simulate cavitation phenomena. 3D flow simulations have been performed for 6 cases to consider the occurrence of cavitation at the downstream of the valve. From the present results, the perforated plate was thought to be very effective to suppress the cavitation inside of the pipe.
A multi-objective optimization of a regenerative fan for enhancing the aerodynamic and aeroacoustic performance was carried out using an integrated fan design system, namely, Total FAN-Regenⓡ. The Total FAN-Regenⓡ was developed for non-specialists to carry out a series of design process, viz., computational preliminary design, three-dimensional aerodynamic and aeroacoustic analyses, and design optimization, for a regenerative fan. An aerodynamic analysis of the regenerative fan was conducted by solving three-dimensional Reynolds-averaged Navier-Stokes equations using the shear stress transport turbulence model. And, an aeroacoustic analysis of the regenerative fan was implemented in a finite/infinite element method by solving the variational formulation of Lighthill’s analogy based on the results of the unsteady flow analysis. An optimum shape obtained by Total FAN-Regenⓡ shows the enhanced efficiency and decreased sound pressure level as much as 1.5 % and 20.0 dB, respectively, compared to those of the reference design. The performance test was carried out for an optimized regenerative fan to validate the performance of the numerically predicted optimal design.
This paper aims to present the design and performance evaluation of a counter-rotating tidal turbine using CFD and to compare its performance with single rotor. The device scale is 10kW and the rotating part consists of two rotors which rotate in opposite direction. Compared with conventional single rotor, the counter-rotating system shows higher power efficiency at high stream velocity but lower efficiency at low stream velocity. The added counter-rotated rotor together helps improve the energy absorption capacity but has influence on the upstream rotor that reduces its performance. In terms of power capture, the designed counter-rotating tidal turbine is more advantageous in high speed tidal condition.
During the international effort to develop the next generation nuclear reactor technologies, many new power cycle concepts were derived to improve efficiency and reduce the capital cost. Among many innovative power cycles, it was identified that the supercritical CO₂ (S-CO₂) Brayton cycle technology has a big potential to outperform the existing steam cycle and eventually replace it. The S-CO₂ cycle achieves high efficiency with very compact size, which is the ultimate advantage for a power cycle to have. The S-CO₂ cycle has a great potential not only for the future nuclear applications but also for general heat sources such as coal, natural gas, and concentrated solar. In this paper, a brief introduction to the S-CO₂ power cycle technologies will be first provided, and a short summary of current research and development status of the power cycle technology around the world will be followed. Especially the research works performed by KAIST, KAERI and several related research institutions in Korea will be reviewed in more detail, since they have recently developing a strong infrastructure to test these ideas by constructing a demonstration facility while producing many innovative ideas to improve and realize the concept.
In the present work, design optimization of film-cooling hole array on the pressure side of high pressure turbine nozzle was conducted. There are four rows of fan-shaped film cooling holes on the nozzle pressure side surface and each row has a straight array of holes in the spanwise direction for baseline model. For design optimization, hole distributions in streamwise and spanwise directions for three rows of holes except first row are parameterized as a 2nd-order shape function. Three-dimensional compressible RANS equations are used for flow and thermal analysis around the nozzle surface and optimization technique using Design of Experiment, Kriging surrogate model and Genetic Algorithm is used . The results shows that averaged adiabatic wall temperature at the whole nozzle surface decreases about 2.7% and averaged film cooling effectiveness at the pressure side of nozzle increased about 8.2%.
The vessel of integral reactor contains its major primary components such as the fuel and core, pumps, steam generators, and a pressurizer, so its size is proportional to the required space for the installation of each component. The steam generators take up the largest volume of internal space of reactor vessel and their volumes is substantial for the overall size of reactor vessel. Reduction of installation space for steam generators can lead to much smaller reactor vessel with resultant decrease of overall cost for the components and related facilities. A printed circuit heat exchanger is one of the compact types of heat exchangers available as an alternative to conventional shell and tube heat exchangers. Its name is derived from the procedure used to manufacture the flat metal plates that form the core of the heat exchanger, which is done by chemical milling. These plates are then stacked and diffusion bonded, converting the plates into a solid metal block containing precisely engineered fluid flow passages. The overall heat transfer area and pressure drops are evaluated for the steam generator based on the concept of the printed circuit heat exchanger in this study. As the printed circuit heat exchanger is known to have much larger heat transfer area density per unit volume, we can expect significantly reduced steam generator compared to former shell and tube type of steam generator. For the introduction of new steam generator, two design requirements are considered: flow area ratio between primary and secondary flow paths, and secondary side parallel channel flow oscillation. The results show that the overall volume of the steam generator can be significantly reduced with printed circuit type of steam generator.
