[en] A thermodynamic model of Organic Rankine Cycle (ORC) system and an aerodynamic design model of a centrifugal turbine were conducted in this paper. Thermodynamic performance comparison of ORC using different working fluids (R123, R245fa, R600, R601a, R245ca, R141b) was achieved for a given amount of heat absorbed by the system. For a known heat source term whose thermophysical properties were specified, the aerodynamic and mechanical design of three centrifugal turbines having different stages have been undertaken, in which organic fluid like R123 was used as the working fluid. Three-dimensional modeling and optimization were subsequently applied to improve the design of the centrifugal turbine whose preliminary thermodynamic design was conducted based on one-dimensional theoretical model. The power and efficiency characteristics of the designed centrifugal turbines were then assessed by means of numerical simulations. Numerical results suggested that isentropic efficiency and output work of all the proposed centrifugal turbines operating at design conditions can exceed 82.7% and 330 kW, which satisfy the requirements of ORC system applications. - Highlights: • 1D design and performance assessment of the centrifugal turbine were conducted. • Performance of six different working fluids for use in ORC was analyzed. • One-dimensional design method for the centrifugal turbine was proposed. • The isentropic efficiencies of centrifugal turbines were all higher than 82.7%.

[en] Our previous studies suggest that instead of propulsion, a body undergoing lateral traveling-wave-like motions can also work like a kinetic energy harvester which extracts energy from moving fluids including wind and water currents. Parameters including wavelength, dimensionless wave velocity and amplitude have critical effects on the energy extraction efficiencies of this type of undulating foil energy harvester. In this paper, a two-dimensional, numerical simulation of a flexible plate undergoing a traveling wave motion was then conducted. At a given dimensionless wave speed, it is found that there exits an optimum wavelength at which this type of energy harvester can extract the maximum amount of kinematic energy from the flow. Moreover, the optimum value of the wavelength increases as amplitude increases. A high efficiency area appears under the optimal combination of wavelength and amplitude. At a given amplitude, the optimal dimensionless wave speed for maximum power extraction decreases with increasing wavelength. The high efficiency area of the undulating plate resulting from the optimal combination of wavelength and wave speed is identified. At a given wave length, there is an optimal value of amplitude at which the maximum energy extraction can be achieved. In this case, a high efficiency area representing the optimal combination of amplitude and wave speed has also been discovered.

[en] Our previous studies suggest that instead of propulsion, a body undergoing lateral traveling-wave-like motions can also work like a kinetic energy harvester which extracts energy from moving fluids including wind and water currents. Parameters including wavelength, dimensionless wave velocity and amplitude have critical effects on the energy extraction efficiencies of this type of undulating foil energy harvester. In this paper, a two-dimensional, numerical simulation of a flexible plate undergoing a traveling wave motion was then conducted. At a given dimensionless wave speed, it is found that there exits an optimum wavelength at which this type of energy harvester can extract the maximum amount of kinematic energy from the flow. Moreover, the optimum value of the wavelength increases as amplitude increases. A high efficiency area appears under the optimal combination of wavelength and amplitude. At a given amplitude, the optimal dimensionless wave speed for maximum power extraction decreases with increasing wavelength. The high efficiency area of the undulating plate resulting from the optimal combination of wavelength and wave speed is identified. At a given wave length, there is an optimal value of amplitude at which the maximum energy extraction can be achieved. In this case, a high efficiency area representing the optimal combination of amplitude and wave speed has also been discovered.

[en] In this paper, a comparative study has been done on the long-term stability and deactivation characteristics of IrO₂-type DSA in acidic solutions with the absence and the presence of methanol compound, respectively. The long-term stability is evaluated by accelerated lifetime tests. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements are carried out on the electrodes before and after deactivation, by which the failure characteristics of Ti-supported oxide electrodes are deduced. The service life is found to increase and then decrease with increasing the calcination temperature of the as-prepared electrodes; on the other hand, the lifetime is obviously shortened by the addition of methanol into the testing solution. The latter phenomenon can be interpreted by more severe dissolution of titanium base and active oxide layers in methanol-involved solution than in blank one. But the former one (temperature-dependent lifetime) cannot be simply explained by the progressive enhancement of stability of active IrO₂ layer with the heating temperature, as concluded from the continuous decrease in change rates of crystalline orientation, unit cell volume and microstrains of oxide layers with the temperature, after the deactivation. SEM observation shows a coating peeling off within the oxide layer and the total delamination of oxide coating at the metal/oxide interface of samples prepared at high temperature after the failure, due to the low coating adhesion. The ease of mechanical loss of oxide layer is considered as one of the main reasons for rapid deactivation of Ti/IrO₂ electrodes prepared at high temperature, although the oxide layer itself in these electrodes is chemically stable enough

[en] US cities are beginning to experiment with a regulatory approach to address information failures in the real estate market by mandating the energy benchmarking of commercial buildings. Understanding how a commercial building uses energy has many benefits; for example, it helps building owners and tenants identify poor-performing buildings and subsystems and it enables high-performing buildings to achieve greater occupancy rates, rents, and property values. This paper estimates the possible impacts of a national energy benchmarking mandate through analysis chiefly utilizing the Georgia Tech version of the National Energy Modeling System (GT-NEMS). Correcting input discount rates results in a 4.0% reduction in projected energy consumption for seven major classes of equipment relative to the reference case forecast in 2020, rising to 8.7% in 2035. Thus, the official US energy forecasts appear to overestimate future energy consumption by underestimating investments in energy-efficient equipment. Further discount rate reductions spurred by benchmarking policies yield another 1.3–1.4% in energy savings in 2020, increasing to 2.2–2.4% in 2035. Benchmarking would increase the purchase of energy-efficient equipment, reducing energy bills, CO₂ emissions, and conventional air pollution. Achieving comparable CO₂ savings would require more than tripling existing US solar capacity. Our analysis suggests that nearly 90% of the energy saved by a national benchmarking policy would benefit metropolitan areas, and the policy’s benefits would outweigh its costs, both to the private sector and society broadly. (letter)

[en] Highlights: • A novel vertical axis wind turbine with deformed blades is designed. • The universal tendency of power characteristics for simulated turbine is found. • The whole flow field of different turbines from the aspect of vortex is analyzed. • The tracking analysis of vortex at different positions for a blade is conducted. • The aerodynamic performance of turbine with three deformed blades is analyzed. - Abstract: In this paper, a novel Darrieus vertical axis wind turbine was designed whose blade can be deformed automatically into a desired geometry and thus achieve a better aerodynamic performance. A series of numerical simulations were conducted by utilizing the United Computational Fluid Dynamics code. Firstly, analysis and comparison of the performance of undeformed and deformed blades for the rotors having different blades were conducted. Then, the power characteristics of each simulated turbine were summarized and a universal tendency was found. Secondly, investigation on the effect of blade number and solidity on the power performance of Darrieus vertical axis wind turbine with deformable and undeformable blades was carried out. The results indicated that compared to conventional turbines with same solidity, the maximum percentage increase in power coefficient that the low solidity turbine with three deformable blades can achieve is about 14.56%. When solidity is high and also turbine operates at low tip speed ratio of less than the optimum value, the maximum power coefficient increase for the turbines with two and four deformable blades are 7.51% and 8.07%, respectively. However, beyond the optimal tip speed ratio, the power improvement of the turbine using the deformable blades seems not significant and even slightly worse than the conventional turbines. The last section studied the transient behavior of vortex and turbulent flow structures around the deformable rotor blade to explore the physical mechanism of improving aerodynamic performance. The adaptive blades could obviously suppress the separation of flow from the blade surfaces.

[en] Any technique or method that can improve the efficiency in exploiting renewable wind or marine current energy has got a great significance today. It has been reported that adding a winglet at the tip of the rotor blades on a horizontal axis wind turbine can increase its power performance. The purpose of this paper is to adopt a numerical method to investigate the effects of different winglet configurations on turbine performance, especially focusing on the direction for the winglet tip to point towards (the suction side, pressure side or both sides of the main blade). The results show that the new design of an integrated fusion winglet proposed in this paper can generally improve the main blade's power producing ability, which is further enhanced with the increase of turbine's tip speed ratio with a maximum power augmentation of about 3.96%. No matter which direction the winglet tip faces, the installation angle of the winglet should match well with the real angle of incoming flow. As a whole, the turbine with winglet of two tips facing to both sides of the main blade can produce much more power than the one of winglet configuration whose tip faces only one side for different blade hub pitch angles and vast majority of tip speed ratios. The working principle behind the winglet in improving turbine performance may be that it can block the downwash fluid easily flowing around the tip section of the main blade from the pressure side to suction side, and hence diffuse and spread out the tip vortex. As a result, it finally decreases the energy loss. Besides, the relative projected rotor area in incoming flow direction will also be reduced due to the addition of the winglet, which is also helpful to turbine's power coefficient. - Highlights: • Added winglet generally increase the turbine energy extraction performance. • Winglet facing blade both sides is usually superior to that of facing one side. • Winglet can isolate downwash fluid easily flowing around blade tip end. • Winglet can weaken and diffuse tip vortex, thus decrease the energy loss.

[en] The ER321 stainless steel was fabricated by laser and wire additive manufacturing (LWAM) assisted with ultrasonic vibration (UV) under synchronous motion conditions. It was found that the grain structure of ER321 stainless steel varied from coarse columnar dendrites (without UV) to equiaxed dendrites (with UV). And, the UV effectively weakened the texture strength and homogenized the grain structure of the deposition layers. The improvement of grain structure enhanced the microhardness (~10.7%) and yield strength (~11.9%) of ER321 stainless steel. These results show that this innovative manufacturing approach can effectively improve the problem of coarse columnar dendrites in the additive manufactured complex large-scale components.

[en] This paper identifies six myths about clean electricity in the southern U.S. These myths are either propagated by the public at-large, shared within the environmental advocacy culture, or spread imperceptibly between policymakers. Using a widely accepted energy-economic modeling tool, we expose these myths as half-truths and the kind of conventional wisdom that constrains productive debate. In so doing, we identify new starting points for energy policy development. Climate change activists may be surprised to learn that it will take more than a national Renewable Electricity Standard or supportive energy efficiency policies to retire coal plants. Low-cost fossil generation enthusiasts may be surprised to learn that clean generation can save consumers money, even while meeting most demand growth over the next 20 years. This work surfaces the myths concealed in public perceptions and illustrates the positions of various stakeholders in this large U.S. region. - Highlights: ► Clean energy myths help lock Southern energy policy in the status quo. ► Efficiency and renewable measures could meet most projected electricity growth without escalating rates. ► Cost-effective efficiency and renewable energy policies alone will not retire coal plants. ► Energy modeling can move energy policy debate beyond misconceptions and illustrate common ground for moving forward.

[en] Highlights: • An enhanced conceptual design for CACRS-ORC integrated system is developed. • An optimization-based method is proposed to achieve the optimal design. • The configuration and operating parameters are optimized simultaneously. • Multi-objective optimization and sensitive analysis have been carried out. Waste heat recovery techniques can greatly improve the energy efficiency and relieve the energy crisis. The integration of compression-absorption cascade refrigeration system (CACRS) and Organic Rankine Cycle (ORC) can achieve cooling and power cogeneration utilizing waste heat. However, the simultaneous optimization of integrating configuration and operating parameters has not been considered in recent studies, neglecting the complex interactive relationship within the integrated system consequently. To overcome these limitations, an enhanced CACRS-ORC integrated system, containing more coupling possibilities and more routes in driving the integrated system with waste heat, is proposed and investigated in this paper. To examine the trade-off in the economic and thermodynamic performances, a multi-objective optimization-based method, aiming at the simultaneous minimization of the total annualized cost (TAC) and the total exergy destroy (${\mathit{Ex}}_{\mathit{destroy}}^{\mathit{total}}$), is developed to determine the optimal configuration and operating parameters of the integrated system. The derived Pareto solutions reveal the contradictory relationship between the two objectives, and the thermo-economic analysis is executed to show the impact of system configuration and operating parameters on economy and thermodynamics. Sensitive analysis is also performed to reveal the effects of key parameters on the structural configuration and thermo-economic performances.