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Abstract This paper presents the wind tunnel test results from MEXNEXT, an IEA wind task for analyzing the measurements which have been taken in the EU project ‘MEXICO’. A 2/4.5 scaled model of ‘MEXICO’ rotor was tested in the KARI low wind tunnel with 5 × 3.75 m 2 open jet test section. The aerodynamic performance of the blade which was represented by the torque was measured in the wind speed from 0 to 30 m/s by using the torque sensor installed in the rotating axis. The rotational speed of the rotor was controlled by the electric motor to keep the prescribed blade tip speed from 50 m/s to 90 m/s. Two different surface conditions, free and forced transition conditions were used for all blade tip speeds. Transition dots with 0.18 mm height were attached at the 5% chord line on both sides of the blade surface for the forced transition condition. The torque coefficients with respect to the wind speed coefficient for the forced transition condition show same characteristics for all blade tip speed conditions except for the stall region. But, the torque coefficient for the free transition condition gradually increases as the blade tip speed increases until the tip speed reaches 76 m/s and it has the similar value above that speed. The comparison result between the free and the forced transition conditions at the blade tip speed 76 m/s shows that the torque coefficient for the former case is 30% higher than the latter case. The computational results from ‘Rfoil’ and the BEMT method also shows that the aerodynamic performance of the rotor for the forced transition condition is lower than the free transition one at the wind tunnel test condition.

Abstract Serpentine flow-fields are widely used for polymer electrolyte membrane (PEM) fuel cells due to effective water removal. In this study, the effects of serpentine flow-field designs on the performance of a commercial-scale PEM fuel cell stack for micro-CHP (Combined Heat & Power) systems, which use reformed gas as fuel, are investigated by performing both computational fluid dynamics (CFD) simulations and experimental measurements. First, we design four different serpentine flow-fields in which the total channel area (defined as open channel area in this study) of a flow-field plate is altered without changing other design parameters such as the channel cross-sectional area and the channel length. Then, CFD simulations and experimental measurements are performed to assess the performance of each flow-field design. The CFD simulation results show that the current density distributions and average current densities are very insensitive to the open channel area. Thus, the information from the simulations is not sufficient to judge whether the open channel area affects the performance of a PEM fuel cell. On the other hand, the experimental measurements indicate that the performances of four fuel cell stacks, each with one of the four flow-field designs used in the simulations, are considerably different. Increasing the open channel area of a serpentine flow-field improves the performance of the PEM fuel cell up to a certain extent.

Abstract A multi-dimensional transient numerical alkaline water electrolyzer (AWE) model is applied to zero-gap circular shaped cells in which either a porous separator (Zirfon) or a dense polybenzimidazole (PBI) membrane is sandwiched between the negative and positive electrodes of nickel foam. In general, not only do the model predictions compare well with the experimental data collected under various wt% KOH electrolyte conditions, but they also reveal key features that favor the use of the PBI membrane over the porous separator. Moreover, a lower ohmic polarization and resulting higher cell performance are achieved by using the PBI membrane owing to its higher ionic conductivity and thinner thickness compared to those of the separator. Although a thin PBI membrane of around 50 μ m is employed, simulation results demonstrate that the crossover of hydrogen and oxygen gases is effectively suppressed with a 10-fold thicker separator (500 μ m ).

Abstract The urban heat island is increasing the temperature of cities up to 10 °C and has a very important impact on energy, environmental quality and health. Materials used in the building and urban fabric affect the urban thermal balance and contribute highly to urban overheating. The article presents the progress achieved on the design, development and implementation of mitigation materials presenting a low and very low surface temperature. The recent technological progress and developments concerning natural, light colour, IR reflective, PCM doped, thermochromic, fluorescent, photonic and plasmonic materials is presented. Experimental results on the cooling capacity and the thermal performance of conventional and advanced materials are described in a comparative way. It is demonstrated that innovative materials can exhibit sub-ambient surface temperatures and contribute highly to mitigate urban overheating.

Editorial paper of the Renewable Energy's special issue "Integrated biorefinery for the planet's future"

Abstract This paper introduces a novel concept of flap-type wave energy device named the Hull Reservoir Wave Energy Converter (HRWEC). The device is a hybrid of the Pendulum type wave energy converter (PeWEC) and the Pendulor wave energy converter. The device mainly consists of a floating reservoir and a top hinged flap that hangs inside the reservoir. The flap motion is triggered by both the float motion and the fluid motion inside the reservoir and the energy take-off happens through the relative motion between the flap and the float. Because this concept closely resembles the PeWEC, a similar float design is used in the HRWEC to facilitate comparison with available data. The dynamics and power capture are obtained using a frequency domain model, and the power capture is maximized for damping-only control for regular waves. It is shown that this new concept exhibits a broadband response compared to the PeWEC concept, which is linked to an additional mode created by the internal water body motion. As a result, this new concept expected to be suitable candidate for applications in broadband wave climatic conditions.

Abstract This study attempts to improve the efficiency of a given type of cross flow turbine by supplying air from air suction holes. A newly developed air supply method is adopted. CFD analysis of the cross flow turbine is carried out to investigate the performance and internal flow characteristics of the turbine in detail. The air layer prevents shock loss between water flow and axis and suppresses recirculation flow in the runner passage. Hence, it is necessary to measure the amount of air layer in the runner passage and examine its effect on the performance of the cross flow turbine. The result shows that the turbine efficiency has improved more as the newly developed air supply method is applied effectively.