An impressive amount of investigation has been devoted to enhancing overall thermal and hydrodynamic performance of microchannel heat sinks. The small size of microchannel heat sinks and their ...ability to dissipate heat generated by modern electronics makes them the first choice for the electronic cooling systems in most devices. In this paper, a comprehensive review of available studies regarding non-circular microchannel heat sinks, with emphasis on rectangular microchannels, was presented and analyzed. This review looked into the methodologies used to analyze and optimize the overall performance of microchannel systems along with channel geometries, flow conditions, the coolants used, structural materials, optimization tools and finally, the form in which the final outcome of each study was presented. The review showed that earlier studies (from 1981 to 1999) were largely conducted using experimental or analytical approaches while more recent studies (from 2000 to the end of 2012) showed a dependency on numerical simulations and evolutionary algorithms. In addition, they also showed that laminar was the prevailing flow condition as out of the 69 articles reviewed, 54 employed laminar flows. Furthermore, the use of liquid coolants was preferable over gaseous coolants. Recent developments in nanofluids are providing alternative coolants that are quickly establishing as coolants to be reckoned with.
In the current investigation, additive friction stir-deposition (AFS-D) of as-cast hypoeutectic A356 Al alloy was conducted. The effect of feeding speeds of 3, 4, and 5 mm/min at a constant ...rotational speed of 1200 rpm on the macrostructure, microstructure, and hardness of the additive manufacturing parts (AMPs) was investigated. Various techniques (OM, SEM, and XRD) were used to evaluate grain microstructure, presence phases, and intermetallics for the as-cast material and the AMPs. The results showed that the friction stir deposition technique successfully produced sound additive manufactured parts at all the applied feeding speeds. The friction stir deposition process significantly improved the microstructure of the as-cast alloy by eliminating porosity and refining the dendritic α-Al grains, eutectic Si phase, and the primary Si plates in addition to intermetallic fragmentation. The mean values of the grain size of the produced AMPs at the feeding speeds of 3, 4, and 5 mm/min were 0.62 ± 0.1, 1.54 ± 0.2, and 2.40 ± 0.15 µm, respectively, compared to the grain size value of 30.85 ± 2 for the as-cast alloy. The AMPs exhibited higher hardness values than the as-cast A356 alloy. The as-cast A356 alloy showed highly scattered hardness values between 55 and 75.8 VHN. The AMP fabricated at a 3 mm/min feeding speed exhibited the maximum hardness values between 88 and 98.1 VHN.
Spheres‐on‐sphere (SOS) silica particles are prepared in a one‐pot scalable synthesis from mercaptopropyltrimethoxysilane with hydrophilic polymer and cationic surfactant under alkaline conditions. ...The SOS particles exhibit solid‐core porous‐shell properties. The fast separation of small molecules and proteins with low back pressure are demonstrated by high‐performance liquid chromatography (HPLC) for the columns packed with SOS‐particles.
The present work focuses on analytical optimization of a rectangular microchannel heat sink using aqueous carbon nanotubes based nanofluid as coolant. The particles weight concentration used in this ...study is 0.01%. The density, the thermal conductivity and the rheological behavior of the nanofluid are experimentally investigated in order to evaluate the thermal resistance and the pumping power in microchannel under laminar flow. An analytical approach of optimization scheme was applied; it is compiled from a systematic thermal resistance model as an analysis method and the elitist non-dominated sorting genetic algorithm (NSGA2). The effects of the temperature, the channel aspect ratio, the channel wall ratio and the use of aqueous carbon nanotubes based nanofluid on the thermal resistance and the pumping power are investigated. The optimized results showed that use of the nanofluid as a working fluid reduce the total thermal resistance and can enhance significantly the thermal performances of the working fluid at high temperatures.
•Optimization of 0.01% weight concentration of aqueous carbon nanotubes based nanofluid as coolant in a rectangular MCHS has been completed using the elitist non-dominated sorting genetic algorithm (NSGA-II) optimization procedure.•The optimized thermal resistance for the nanofluid is better than that of water particularly at high temperature.•The reduction in number of channels is very slight, a large quantity of 1 cm by 1 cm MCHS could mean savings in the production cost using nanofluid.
Increased consideration of medical school prestige by program directors (PDs) has been a well-documented concern with the shift to P/F grading. 2 While those attending highly nationally ranked ...institutions may benefit from this, students from “lower tiered” medical schools who previously depended on a quantitative assessment of their academic caliber may lose a means of strengthening their applications. According to the 2020 residency match results reported by the National Resident Matching Program (NRMP), 4 US allopathic students accounted for only 52% of active applicants; the remainder was made up of osteopathic and international medical students. Conversely, others have argued that a shift to holistic residency screenings may inadvertently increase the importance of non-standardized clinical evaluations, which remain highly subjective and may leave students vulnerable to preceptor microaggressions and implicit biases. 6 Despite the array of opinion on this topic, there is no denying that underrepresented minority students are integral stakeholders in the consideration of the USMLE Step 1 change.
We investigated how COVID-19 infection and vaccination impact elective surgical outcomes.
We retrospectively compared pre-pandemic (P) veterans to those with COVID (C) more than three weeks ...preoperatively or no COVID (NC) history after carotid endarterectomy, CABG, hip replacement, or colectomy. Subgroup analysis considered vaccination. Age and sex propensity matching, and conditional logistic regression analyzed one-year-mortality, 90-day-readmission, and ICU requirements among 519 C, 1038 NC, and 2076 P, culled from 61,641 veterans.
NC, C, and P had similar ICU requirements and mortality, although NC required fewer readmissions. However, NC immunized at least once were readmitted and died less commonly than C who received at least one immunization.
SARS-CoV-2 history increased readmission without affecting ICU requirement or mortality. Further studies should evaluate whether the worse outcomes in postoperative patients with histories of both COVID infection and one vaccination reflect the effects of incomplete vaccination or dataset limitations.
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•Higher readmission after elective surgery after COVID.•One-year mortality and ICU requirements not affected by prior COVID.•However, 2X mortality among patients with both preoperative COVID and vaccination.
Background
Post‐procedural aortic insufficiency (AI) continues to be prevalent following transcatheter aortic valve replacement (TAVR). While several studies have assessed the outcomes of ...moderate‐severe AI following TAVR, the incidence, predictors, and outcomes of mild AI remain unclear.
Methods
A systematic literature review was performed to identify studies reporting on mild AI following TAVR. The primary outcome was pooled incidence of post‐TAVR mild AI. Secondary outcomes included pooled incidence of mild AI at 30 days and long term. The pooled incidence of midterm mortality in patients with post‐TAVR mild AI was also evaluated. The random effect generalized linear mixed‐effects model with logit‐transformed proportions and Hartung–Knapp adjustment was used to calculate pooled incidence rates. Meta‐regression was performed to identify predictors of mild AI.
Results
The pooled analysis included 19,241 patients undergoing TAVR across 50 studies. The mean age of patients ranged from 73 to 85 years, and female patients ranged from 20.0% to 83.3%. The overall pooled incidence of post‐TAVR mild AI was 56.1% (95% confidence interval CI 0.31–0.64). The pooled incidence of mild AI at 30 days was 33.7% (95% CI 0.12–0.37). At mean follow‐up of 1.15 years, the pooled incidence of mild AI was 37.0% (95% CI 0.16–0.45). The overall pooled incidence of Midterm mortality (mean follow‐up 1.22 years) in patients with mild AI was 14.8% (95% CI 0.10–0.25). At meta‐regression, none of the explored variables correlated with a difference in mild AI incidence.
Conclusions
In published studies to date, 50% of patients undergoing TAVR develop mild AI postoperatively. In 37% of patients, this persists in long term. Though the incidence of AI is likely improving with newer generation TAVR valves, the prevalence and outcomes of mild AI should be closely monitored as TAVR volume and indications expand to younger patients with long life expectancy. The long‐term outcomes of mild AI remain unclear. Further dedicated studies on post‐TAVR mild AI are needed.
In the realm of gas turbine engine technology, turbine blades are persistently subjected to extreme thermal conditions due to prolonged exposure to high-temperature gases. Given this operating ...environment, devising effective cooling strategies is paramount for ensuring the turbine’s safety and longevity. Despite the critical nature of this issue, existing literature scarcely addresses cooling channels that incorporate factors like variable cross-sectional attributes and rotational effects. In this study, Computational Fluid Dynamics (CFD) and numerical methodologies were employed to analyze the flow mechanism and performance of three distinct cooling channels characterized by variable cross-sectional features. The results indicate a marginal thermal performance improvement of up to 3% for U-shaped cooling channels, specifically at a Reynolds number of 20,000, in comparison to Net cooling channels. Conversely, jet impingement channels outperform U-shaped channels by an impressive margin of over 11%. Additionally, at a Reynolds number of 60,000, jet impingement cooling channels manifest a significant upsurge of nearly 25% in the ratio between average Nusselt number, and the reference Nusselt number when compared with U-shaped and Net cooling channels.
In this study four new geometries of heat and mass exchanger for dew point evaporative cooling are investigated and their performance is compared to that of the commonly used flat plate and ...corrugated plate exchangers. In the proposed exchangers, each dry channel is completely enclosed by its adjacent wet channels, and each wet channel is completely enclosed by its adjacent dry channels (related detailed information is presented graphically in this paper). In addition, a robust numerical model was developed and is examined under various operational and geometrical conditions. The analysis showed that the proposed dew point evaporative coolers improve the chilled air temperature, water consumption, cooling capacity, and energy efficiency. In particular, the circular concentric tube exchanger, under certain operating conditions (inlet air temperature, humidity ratio, and velocity of 40°C, 6 g/kg, and 3 m/s, respectively), could produce the lowest chilled air temperature of 9.6°C and the highest wet bulb and dew point effectiveness of 148% and 99%, respectively. Additionally, water consumption is reduced to 1.34 L/hr for an inlet air velocity of 1 m/s. A triangular tube exchanger achieved the highest cooling capacity and coefficient of performance, but consumed the largest amount of water. Our geometrical analysis demonstrates that the overall performance of dew point evaporative cooling systems can be improved by employing new geometries for heat and mass exchanger channels.
Practical application: The dew point evaporative cooler is an environmentally friendly air conditioning system used in buildings. It is considered the strongest candidate to replace vapour-compression refrigeration systems because it consumes considerably less electricity while achieving high performance. Our research demonstrates that through revised geometry it is possible to further improve the performance of the system leading to improved energy and water efficiency.
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