Thermal Performance Evaluation for Two Designs of Flat-Plate Solar Air Heater : An Experimental and CFD Investigations

The main objective of this research was to create two different configurations of a flat-plate solar air heater, namely, Conventional-Case A and Modified-Case B, and develop a three-dimensional computational fluid dynamics (CFD) model using ANSYS R15.0. The purpose of the CFD model was to simulate the heat transfer behavior of the proposed solar air heaters under unsteady conditions. The RNG k-ε turbulence model was employed for this CFD study. The experiments were conducted on sunny days, under the same conditions as the Egyptian climate. The results of the experiments show that the simulated CFD model and the measured outlet airflow temperatures, relative humidity, and velocities of the two tested solar air heaters were compared. The developed model made very satisfactory predictions. Moreover, the deviations between the average CFD outlet air temperatures and the experimental results were 7% and 7.8% for Case B and Case A, respectively. The CFD-simulated average relative humidity was reduced by 31.6% when using Case B compared with Case A, and it was reduced by 28.8% when comparing the experimental data to Case B. Additionally, the average CFD thermal efficiencies obtained for Case B and Case A were 28.7% and 21.6%, respectively, while the average experimental thermal efficiencies for the cases were 26.4% and 18.2%, respectively. The proposed model can be used to design and simulate other solar air heater designs.Peer reviewe

Manganese pigmented anodized copper as solar selective absorber

The study concerns the optical and structural properties of layers obtained by a new efficient surface treatment totally free of chromium species. The process is made up of an anodic oxidation of copper in an alkaline solution followed by an alkaline potassium permanganate dipping post-treatment. Coatings, obtained at the lab and pilot scales, are stable up to 220 °C in air and vacuum, present low emissivity (0.14 at 70 °C) and high solar absorptivity (0.96), i.e. a suitable thermal efficiency (0.84 at 70 °C)

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Estudio comparativo entre la deshidratación convencional y en microondas del kimbombó.

This study was conducted to evaluate different pre-treatments and dehydration methods on the quality of okra. No significant differences were found among pretreatments and dehydration methods for the chemical composition of dehydrated okra samples. Dipping in 0.1 % sodium metabisulphite solution at room temperature and immersion in 0.1 % sodium metabisulphite solution at 92-95 °C improved the retention of ascorbic acid of okra samples after dehydration by either conventional or microwave oven. Also, the reduced dehydration time required for microwave dehydration produced far less destruction of ascorbic acid. The highest rehydration ratio was found in unwashed okra sample and dehydrated by microwave after immersion in 0.1 % sodium metabisulphite solution at 92-95 °C. Dehydrated okra samples by sun drying and conventional oven had lower retention percentages of total chlorophyll and carotenoids than those of dehydrated okra samples by microwave oven. The general appearance and colour scores of dehydrated okra samples by microwave were significantly different from those of conventionally dehydrated or sun dried okra samples.Este estudio se ha realizado para evaluar los diferentes pretratamientos y métodos de deshidratación en la calidad del kimbombó. No se encontraron diferencias significativas entre ellos respecto a la composición química de las muestras de kimbombó deshidratadas. La inmersión en solución de metabisulfito sódico al 0.1 % a temperatura ambiente y la inmersión en solución de metabisulfito sódico al 0.1 % a 92-95 °C mejoraron la retención de ácido ascórbico de las muestras de kimbombó después de la deshidratación tanto utilizando el homo convencional como el horno microondas. Además el menor tiempo necesario para la deshidratación usando el horno microondas produjo menos destrucción de ácido ascórbico. La mayor relación de rehidratación fue encontrada en muestras de kimbombó no tratadas o deshidratadas usando horno microondas tras inmersión en metabisulfito sódico al 0.1 % y 92-95 °C. Las muestras de kimbombó deshidratadas por secado al sol y homo convencional tuvieron menores porcentajes de retención de clorofilas totales y carotenoides que las de muestras de kimbombó deshidratadas usando homo microondas. La apariencia general y la calidad del color de las muestras de kimbombó deshidratadas mediante horno microondas fueron significativamente diferentes de aquéllas deshidratadas mediante homo convencional o secadas al sol

568 HEAT AND TRANSFER ANALYSIS IN A CONICAL SOLAR STILL: AN EXPERIMENTAL STUDY

ABSTRACT In this paper, an attempt is made to estimate the heat transfer coefficients of a conical solar still. Many researches and development works tried to enhance the productivity of solar stills using different methods. So in this study the productivity enhancement of solar still by decreasing the shadow effect and maximize utilization of solar radiation is discussed. A new conical solar still was designed and manufactured at faculty of engineering Sheben El-Kom -Egypt (latitude 30.56 N and longitude 31.01 E). The still base area was 0.8 m 2 , and the glass (acrylic) cover of still inclined at 31 o which equal to the latitude of Sheben El-Kom. The experimental results of conical solar still were compared with a conventional type solar still which have the same dimensions. The results showed that, the daily productivity for conical and conventional solar stills was 3.38 and 1.93 L/m 2 .day respectively. Heat and mass transfer coefficients were evaluated and the Nusselt and Sherwood numbers were calculated with the aid of both evaporation measurements and Chilton-Colburn analogy. The maximum value of the total heat transfer coefficient were 66 and 32 W/m 2 . o C for conical and conventional solar stills respectively.The analogy between heat and mass transfer coefficients was also investigated

Modelling and practical studying of heat recovery steam generator (HRSG) drum dynamics and approach point effect on control valves

In this paper, we present a simple procedure to build a model of a heat recovery steam generator (HRSG) evaporator and drum within the environment of MATLAB/Simulink. The HRSG is part of combined cycle power plant that is located at Talkha power station (130 km north of Cairo, capital of Egypt). The model captures the response of water and steam inside HRSG evaporator and drum like drum level, pressure, steam quality and others during different conditions. We discuss some practical concepts in HRSG design, and the importance of HRSG approach point value to drum level stability and control. We also discuss how HRSG approach point can have destroying effect on level control valves of the drum and increase the maintenance cost of the combined cycle power plant. Keywords: Heat recovery steam generator, Evaporator, Model, Drum, Combined cycl