Stellar parameters of Be stars observed with X-shooter

Aims. The X-shooter archive of several thousand telluric star spectra was skimmed for Be and Be-shell stars to derive the stellar fundamental parameters and statistical properties, in particular for the less investigated late type Be stars, and the extension of the Be phenomenon into early A stars. Methods. An adapted version of the BCD method is used, utilizing the Balmer discontinuity parameters to determine effective temperature and surface gravity. This method is optimally suited for late B stars. The projected rotational velocity was obtained by profile fitting to the Mg ii lines of the targets, and the spectra were inspected visually for the presence of peculiar features such as the infrared Ca ii triplet or the presence of a double Balmer discontinuity. The Balmer line equivalent widths were measured, but due to uncertainties in determining the photospheric contribution are useful only in a subsample of Be stars for determining the pure emission contribution. Results. A total of 78 Be stars, mostly late type ones, were identified in the X-shooter telluric standard star archive, out of which 48 had not been reported before. The general trend of late type Be stars having more tenuous disks and being less variable than early type ones is confirmed. The relatively large number (48) of relatively bright (V > 8.5) additional Be stars casts some doubt on the statistics of late type Be stars; they are more common than currently thought: The Be/B star fraction may not strongly depend on spectral subtype.Comment: Accepted for publication in A&

Theoretical and experimental study of a cross-flow induced-draft cooling tower

The main objective of this study is to find a proper solution for the cross-flow water cooling tower problem, also to find an empirical correlation's controlling heat and mass transfer coefficients as functions of inlet parameters to the tower. This is achieved by constructing an experimental rig and a computer program. The computer simulation solves the problem numerically. The apparatus used in this study comprises a cross-flow cooling tower. From the results obtained, the 'characteristic curve' of cross-flow cooling towers was constructed. This curve is very helpful for designers in order to find the actual value of the number of transfer units, if the values of inlet water temperature or inlet air wet bulb temperature are changed. Also an empirical correlation was conducted to obtain the required number of transfer units of the tower in hot water operation. Another correlation was found to obtain the effectiveness in the wet bulb operation

Analiza numeryczna różnic między charakterystykami działania stożkowych wężownic spiralnych i zwykłych wężownic spiralnych stosowanych jako osuszacze w zespołach osuszania i nawilżania w instalacjach odsalania wody

This numerical research is devoted to introducing the concept of helical cone coils and comparing the performance of helical cone coils as heat exchangers to the ordinary helical coils. Helical and spiral coils are known to have better heat and mass transfer than straight tubes, which is attributed to the generation of a vortex at the helical coil. This vortex, known as the Dean Vortex, is a secondary flow superimposed on the primary flow. The Dean number, which is a dimensionless number used in describing the Dean Vortex, is a function of Reynolds Number and the square root of the curvature ratio, so varying the curvature ratio for the same coil would vary the Dean Number. Numerical investigation based on the commercial CFD software fluent is used to study the effect of changing the structural parameters (taper angle of the helical coil, pitch and the base radius of curvature changes while the height is kept constant) on the Nusselt Number, heat transfer coefficient and coil outlet temperature. Six main coils having pipe diameters of 10 and 12.5 mm and base radius of curvature of 70, 80 and 90 mm were used in the investigation. It was found that, as the taper angle increases, both Nusselt Number and the heat transfer coefficient increase, also the pitch at the various taper angles was found to have an influence on Nusselt Number and the heat transfer coefficient. A MATLAB code was built to calculate the Nusselt Number at each coil turn, then to calculate the average Nusselt number for all of the coil turns. The MATLAB code was based on empirical correlation of Manlapaz and Churchill for ordinary helical coils. The CFD simulation results were found acceptable when compared with the MATLAB results.W pracy przedstawiono badania numeryczne mające na celu prezentację koncepcji stożkowych wężownic spiralnych i porównanie charakterystyk ich działania jako wymienników ciepła do charakterystyk zwykłych wężownic spiralnych. Jak wiadomo, wężownice spiralne i stożkowe charakteryzują się lepszym przenoszeniem ciepła i masy niż proste rury, co jest związane z powstawaniem wiru w wężownicy spiralnej. Ten tzw. wir Deana (Dean Vortex) jest przepływem wtórnym, nałożonym na przepływ pierwotny. Bezwymiarowy współczynnik Deana, stosowany do opisu wiru Deana, jest funkcją liczby Reynoldsa i pierwiastka kwadratowego ze współczynnika krzywizny, toteż liczba Deana zmienia się dla danej wężownicy wraz z jej krzywizną. Obliczenia numeryczne wykonano przy użyciu komercyjnego oprogramowania CFD w celu zbadania wpływu zmian parametrów strukturalnych wężownicy spiralnej (kąt zbieżności, skok i promień bazowy krzywizny zmieniały się, podczas gdy wysokość pozostawała stała) na liczbę Nusselta, współczynnik wymiany ciepła i temperaturę na wyjściu wężownicy. W badaniach wykorzystano sześć głównych wężownic, o średnicach rury 10 i 12,5 mm i promieniach bazowych krzywizny 70, 80 i 90 mm. W wyniku badań stwierdzono, że zarówno liczba Nusselta jak współczynnik wymiany ciepła rosną wraz ze wzrostem kąta zbieżności. Stwierdzono również, że przy różnych kątach zbieżności skok spirali ma wpływ na liczbę Nusselta i współczynnik wymiany ciepła. Opracowano program w środowisku MATLAB przy pomocy którego obliczono liczby Nusselta dla każdego zwoju wężownicy; na tej podstawie obliczono następnie wartość średnią liczby Nusselta dla całej wężownicy. Program obliczeniowy był oparty na równaniu empirycznym Manlapaza i Churchilla dla zwykłych wężownic spiralnych. Wyniki symulacji uzyskane przy użyciu oprogramowania CFD okazały się możliwe do przyjęcia w zestawieniu z wynikami obliczeń w programie MATLAB

Synthesis and study the structure, optical, thermal and dielectric properties of promising Glycine Copper Nitrate (GCN) single crystals

Four novel single crystals of α-glycine and γ-glycine doped by copper nitrate: (Glycine)1−X (Cu(NO3)2·3H2O)X abbreviated as (GCN1, GCN2, GCN3, GCN4) were prepared from aqueous solution by the slow evaporation method. Four doping concentrations: x = 0.005, 0.01, 0.02 and 0.04 of hydrated copper nitrate were used. The crystals were studied using powder X-ray diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR), and UV–Vis spectroscopy. The PXRD patterns showed that crystals containing high concentration of Cu(NO3)2·3H2O have triclinic or monoclinic structure. The lattice parameters for all the prepared crystals were found to be in a good agreement with that found in the crystallographic open database (COD). The functional groups of the crystals were determined from FTIR spectra and the optical band gaps were calculated from UV–Vis spectroscopy technique. The properties of the crystals was found to be concentration dependent on copper nitrate salt. The refractive index (n) for all GCN crystals were found around 1.88 in the region of the wavelength: 800–1000 nm, while the least value of n ≈ 1.72 was determined in the visible region of electromagnetic magnetic radiation. The decomposition point of GCN single crystals was identified by a narrow, and sharp peak of differential scanning calorimetry (DSC) curves. The phase transition temperature at 203 °C was observed for GCN2 crystals, is probably due to the transformation from γ-glycine to α-glycine. The dielectric study showed a peak around 30 °C (Curie temperature) that is a characteristic of ferroelectric crystals and the consistency of the dielectric constant at 90 °C indicated glass transition. Photoluminescence spectra of GCN crystals that were recorded at the excitation wavelength of 280 nm showed a maximum emission peaks around 345 nm. This finding indicated that these single crystals can be successfully used for NLO applications. Keywords: Semiorganic crystals, Glycine Copper Nitrate (GCN), XRD, UV–Vis and FTIR spectr

Mixed convection in an eccentric annulus filled by copper nanofluid

A numerical study of mixed convection flow and heat transfer of Copper (Cu)-water nanofluid inside an eccentric horizontal annulus is presented. The inner and outer cylinders are kept at constant temperatures as Th and Tc, respectively. The inner cylinder rotates to generate the forced convection effect. The numerical work was carried out using an in-house CFD code written in FORTRAN. Different scenarios were explored to explain the effects of different parameters on the studied problem. These parameters are Richardson number, eccentricity ratio, and solid volume fraction. The range of the Richardson number Ri, solid volume fraction of the nanoparticles ζ, and the eccentricity ratioe, are 0.01 ≤ Ri ≤ 100 (natural convection), 0 ≤ ζ ≤ 0.05, 0 ≤ e ≤ 0.9 respectively. All results were performed with thermal Grashof number Gr, and radius ratio Rr, equaled to 104 and 2, respectively. The effects of eccentricity, nanoparticles volume fraction, and Richardson number on the average Nusselt number, streamlines and isotherms were investigated. Results were discussed, and were found to be in good agreement with previous works. It was also found that, the eccentricity has a positive remarkable effect on the average Nusselt number, while the effect of nanoparticles concentration was more pronounced at mixed convection region (Ri=1)

Numerical investigation of turbulent flow and heat transfer over partially open cavities: Effect of opening ratio

Partially open cavities are encountered in various engineering systems such as electronic cooling devices and cooling for gas turbine blades, instead of conventional film cooling slots. Flow is to be imparted over the partially open cavity where it induces a shear layer and a shear driven vortex within the cavity, which is subjected to cooling effect at its wall. Depending on the opening ratio, heat and mass transfer occur between the main flow and the trapped vortex through the shear layer. In the present study, RANS simulations of such flow have been conducted for circular and square cavities to investigate the effect of opening ratio on the heat and mass transfer characteristics. The simulations were established on a rigorous numerical approach and proper validation with laser Doppler velocimetry measurements of turbulent flow in circular cavity. Based on the hydraulic diameter of the cavity, opening ratios ranging from 0.2 to 1.0 were investigated for a Reynolds number of 3∙105. Generally, the maximum Nusselt number was achieved at higher opening ratios for both circular and rectangle cavities. On the other hand, the maximum dimensionless temperature gradient, θ, inside the cavity was achieved at L/D = 0.2 for both cavity configurations

Assessment of Active Double Skin Fa\ue7ade Integrated With PV Cell

Integration of semitransparent PV cell inside air cavity of the Double Skin Fa\ue7ade (DSF) buildings can be considered a good ecological solution but the high temperature during the summer period may raise the air temperature in the cavity and reduce the PV cell energy efficiency. Numerical simulation of different DSF configurations is presented to evaluate thermal performance of inner glass , air inside the cavity and the effects on PV cell energy efficiency after cooling the gap by the ventilation air flow rate supplied to the conditioned zone, for the purpose of Indoor Air Quality (IAQ). This work focused the attention on validation of the Computational Fluid Dynamics (CFD) numerical model and analyzed different strategies of DSF air ventilation. A comparison has been carried out to evaluate the best technique in air circulation and the lowest temperature distribution attained on both the PV cell surface and the inner glass at Cairo-Egypt in summer maximum design conditions as well as on the average cooling season time scale. Energy efficiency of PV cell has been calculated for each configuration in order to illustrate the improvement in cell energy conversion performance