Effect of the velocit profile of incoming flow on the performance of a horizontal axis tidal stream turbine

Compared to solar and wind power generating technologies, tidal stream technology is relatively new and there are many problems that hinder the deployment of tidal stream turbines. One such problem is the effect of the tidal stream velocity profile resulting in varying velocity magnitude and its effect on turbine performance. A study incorporating experimental data and computational fluid dynamics (CFD) simulation is carried out in order to start to understand such effects. A CFD model based on an existing turbine was created and validated by comparing its results against experimental results of a previous study. A velocity profile was measured in a water flume experiment, which was then applied to the CFD model as a new upstream boundary condition. The results show that, due to the variation in flow velocity, the torque generated by each blade will fluctuate as it travels through a complete rotation. Despite this, the trend of torque distribution on individual blade has very little change throughout the rotation. Similar effect also takes place on thrust loading of the blades, meaning that blade deflection will change as the turbine rotates, inevitably affecting the fluid dynamics of the turbine

The performance and hydrodynamics in unsteady flow of a horizontal axis tidal turbine

This paper presents the effect of idealised unsteady tidal velocities on the performance of a newly-designed Horizontal-Axis Tidal Turbine (HATT) through the use of numerical simulations using Computational Fluid Dynamics (CFD). Simulations are conducted using ANSYS FLUENT implementing the Reynolds-Averaged Navier Stokes (RANS) equations to model the fluid flow problem. A steady flow case is modelling in a 2 m/s stream flow and the resulting performance curve was used as the basis of comparison for the unsteady flow simulations. A decrease in performance was seen for the unsteady flow simulation around peak TSR (TSR=6) which has a cyclic-averaged coefficient of performance (CP) of 37.50% compared to the steady CP of 39.46%. Similar decreases in performance with unsteady flow was observed away from the peak performance TSR at TSR=4 and TSR=8. Furthermore, with unsteady flow that it was found that as the TSR increases, the difference between the cyclic-averaged CP and the steady flow CP drops. The effect of variations in the frequency and amplitude of the unsteady flow showed that a decrease in the cyclic-averaged CP was observed and this performance reduced with increasing frequency and increasing amplitude of unsteady incoming flows. For the cases studied here, unsteady flows are detrimental to the performance of the tidal turbine

Minimising microbubble size through oscillation frequency control

Microbubbles are bubbles below 1 mm in size and have been extensively deployed in industrial settings to improve gaseous exchange between gas and liquid phases. The high surface to volume ratio offered by microbubbles enables them to enhance transport phenomena and therefore can be used to reduce energy demands in many applications including, waste water aeration, froth flotation, oil emulsion separations and evaporation dynamics. Microbubbles can be produced by passing a gas stream through a micro-porous diffuser placed at the gas–liquid interface. Previous work has shown that oscillating this gas steam can reduce the bubble size and therefore increase energy savings. In this work we show that it is possible to further reduce microbubble size (and consequently maximise the number of bubbles) by varying the frequency of the oscillating gas supply. Three different microbubble generation systems have been investigated; an acoustic oscillation system and a mesh membrane, a fluidic oscillator coupled to a single orifice membrane and a fluidic oscillator coupled to a commercially available ceramic diffuser. In all three bubble generation methods there is an optimum oscillation frequency at which the bubble size is minimised and the number of microbubbles maximised. In some cases a reduction in bubble size of up to 73% was achieved compared with non-optimal operating frequencies. The frequency at which this optimum occurs is dependent on the bubble generation system; more specifically the geometry of the system, the type micro-porous diffuser and the gas flow rate. This work proves that by tuning industrial microbubble generators to their optimal oscillation frequency will result in a reduction of microbubble size and increase their number density. This will further improve gaseous exchange rates and therefore improve the efficiency of the industrial processes where they are being employed to produce bubbles, leading to a reduction in associated energy costs and an increase in the overall economic and energetic feasibility of these processes

Neoadjuvant chemotherapy and trastuzumab versus neoadjuvant chemotherapy followed by post-operative trastuzumab for patients with HER2-positive breast cancer

Neoadjuvant chemotherapy plus trastuzumab (NCT) increases the rate of pathological complete response (pCR) and event-free survival (EFS) compared to neoadjuvant chemotherapy (NC) alone in women with HER2 positive breast cancer (BC). pCR in this setting is associated with improved EFS. Whether NCT preferentially improves EFS in comparison to NC followed by adjuvant trastuzumab initiated postoperatively (NCAT) has not been addressed. Using clinical data from women with HER2 positive BC treated at 7 European institutions between 2007 and 2010 we sought to investigate the impact on breast cancer outcomes of concomitant (NCT) versus sequential (NCAT) treatment in HER2 positive early BC. The unadjusted hazard ratio (HR) for event free survival with NCT compared with NCAT was 0.63 (95% CI 0.37–1.08; p = 0.091). Multivariable analysis revealed that treatment group, tumour size and ER status were significantly associated with EFS from diagnosis. In the whole group NCT was associated with a reduced risk of an event relative to NCAT, an effect that was confined to ER negative (HR: 0.25; 95% CI, 0.10–0.62; p = 0.003) as opposed to ER positive tumours (HR: 1.07; 95% CI, 0.46–2.52; p = 0.869). HER2 positive/ER negative BC treated with NC gain greatest survival benefit when trastuzumab is administered in both the neoadjuvant and adjuvant period rather than in the adjuvant period alone. These data support the early introduction of targeted combination therapy in HER2 positive/ER negative BC

The Stepwise Reduction of Multiyear Sea Ice Area in the Arctic Ocean Since 1980

The loss of multiyear sea ice (MYI) in the Arctic Ocean is a significant change that affects all facets of the Arctic environment. Using a Lagrangian ice age product, we examine MYI loss and quantify the annual MYI area budget from 1980 to 2021 as the balance of export, melt, and replenishment. Overall, MYI area declined at 72,500 km2 /yr; however, a majority of the loss occurred during two stepwise reductions that interrupt an otherwise balanced budget and resulted in the northward contraction of the MYI pack. First, in 1989, a change in atmospheric forcing led to a +56% anomaly in MYI export through Fram Strait. The second occurred from 2006 to 2008 with anomalously high melt (+25%) and export (+23%) coupled with low replenishment (−8%). In terms of trends, melt has increased since 1989, particularly in the Beaufort Sea, export has decreased since 2008 due to reduced MYI coverage north of Fram Strait, and replenishment has increased over the full time series due to a negative feedback that promotes seasonal ice survival at higher latitudes exposed by MYI loss. However, retention of older MYI has significantly declined, transitioning the MYI pack toward younger MYI that is less resilient than previously anticipated and could soon elicit another stepwise reduction. We speculate that future MYI loss will be driven by increased melt and reduced replenishment, both of which are enhanced with continued warming and will one day render the Arctic Ocean free of MYI, a change that will coincide with a seasonally ice-free Arctic Ocean

An improved cleaning system to reduce microbial contamination of poultry transport crates in the United Kingdom

© 2020 The Society for Applied Microbiology Aim: Following previous research on improving the cleaning of crates used to transport broiler chickens from the farm to the abattoir, a demonstration project was undertaken to investigate improvements in crate washing on a commercial scale. Methods and Results: The soak tank of a conventional crate washing system was replaced with a high-performance washer fitted with high-volume, high-pressure nozzles. The wash water could be heated, and a greatly improved filtration system ensured that the nozzles did not lose performance or become blocked. Visual cleanliness scores and microbial counts were determined for naturally contaminated crates which had been randomly assigned to different cleaning protocols. Conclusions: When a combination of mechanical energy, heat and chemicals (i.e. detergent and disinfectant) was used, the results showed significant improvements to crate cleaning. Reductions of up to 3·6 and 3·8 log10 CFU per crate base were achieved for Campylobacter and Enterobacteriaceae, respectively, along with a marked improvement in visual cleanliness. Significance and Impact of the Study: Broiler transport crates may become heavily contaminated with faeces and this may contribute to the spread of disease between farms. The results of this trial may be of use in reducing the spread of zoonotic pathogens in the poultry meat supply chain