Heat transfer characteristic during crystallization of the phase change material (PCM) dispersed inside an emulsion is investigated theoretically and experimentally by using Differential Scanning ...Calorimeter (DSC) technique. The dispersed PCMs are hexadecane, octadecane and water. Nucleation laws are used to simulate the supercooling phenomenon. The results indicate that the crystallization of the droplets stabilizes the emulsion temperature at a value corresponding to that at which probability of crystallization J(T) increases rapidly. To describe with accuracy the thermal properties of the PCM using DSC technique it is more appropriate to represent these properties versus the sample temperature and not as function of the plate temperature of DSC.
► Supercooling phenomenon during freezing process is modeled employing nucleation laws. ► The crystallization of the droplets stabilizes the emulsion temperature at a value corresponding to that at which probability of crystallization increases rapidly. ► To describe with accuracy the thermal properties of the PCM using DSC technique it is more appropriate to represent them versus the sample temperature and not as function of the plate temperature of DSC.
The interaction of a 3D supersonic turbulent gas flow with a transverse sonic jet injected from the wall has been studied in detail both numerically and experimentally. However, the main drawback of ...such studies is the lack of detailed description of formation and propagation of vortex structures for moderate and large parameters
n
(ratio of pressure in the jet to pressure in the flow). Analysis performed in this study is aimed at revelation and detailed explanation of mechanisms of formation of vortices behind the injected sonic jet in a supersonic oncoming flow depending on
n
for improving the effectiveness of mixing of the jet with the flow. As initial equations, we have used 3D Favre-averaged Navier–Stokes equations closed by the
k
–ω model of turbulence; these equations are solved using the algorithm based on the essentially nonoscillatory scheme of the third approximation order. We have demonstrated the presence of the following vortex structures known from a number of theoretical publications: two oppositely rotating vortices in front of the jet, a horseshoe vortex; and two pairs formed in the mixing zone between the jet and the flow (one in the wake behind the jet and the other on the lateral line of the jet). We have determined the pressure ratios for which extra pairs of vortices appear (one pair emerges at the Mach disk edge as a result of interaction of a retarded flow of the jet behind the Mach disk with a high-velocity ascending flow behind the barrel and the other pair is formed due to the interaction of the ascending jet flow with the incoming main gas flow). As a result of comparative analysis, the pressure ratios for which a clear pattern of additional horn vortices is observed near the wall in the region behind the jet, have been determined. The dependence of the slope of the bow shock on the pressure ratio has been plotted. It is found that the pressure distribution at the wall in front of the jet in the symmetry plane is in satisfactory agreement with experimental data.
Pulsars are rapidly spinning, highly magnetized neutron stars, created in the gravitational collapse of massive stars. We report the detection of pulsed giga–electron volt gamma rays from the young ...pulsar PSR J0540–6919 in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. This is the first gamma-ray pulsar detected in another galaxy. It has the most luminous pulsed gamma-ray emission yet observed, exceeding the Crab pulsar's by a factor of 20. PSR J0540–6919 presents an extreme test case for understanding the structure and evolution of neutron star magnetospheres.
GRB 131108A is a bright long gamma-ray burst (GRB) detected by the Large Area Telescope and the Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope. Dedicated temporal and spectral ...analyses reveal three γ-ray flares dominating above 100 MeV, which are not directly related to the prompt emission in the Gamma-ray Burst Monitor band (10 keV-10 MeV). The high-energy light curve of GRB 131108A (100 MeV-10 GeV) shows an unusual evolution: a steep decay, followed by three flares with an underlying emission, and then a long-lasting decay phase. The detailed analysis of the γ-ray flares finds that the three flares are 6-20 times brighter than the underlying emission and are similar to each other. The fluence of each flare, (1.6 ∼ 2.0) × 10−6 erg cm−2, is comparable to that of emission during the steep decay phase, 1.7 × 10−6 erg cm−2. The total fluence from three γ-ray flares is 5.3 × 10−6 erg cm−2. The three γ-ray flares show properties similar to the usual X-ray flares that are sharp flux increases, occurring in ∼50% of afterglows, in some cases well after the prompt emission. Also, the temporal and spectral indices during the early steep decay phase and the decaying phase of each flare show the consistency with a relation of the curvature effect ( = 2 + ), which is the first observational evidence of the high-latitude emission in the GeV energy band.
The heat transfer characteristics during melting of the (phase change material) PCM dispersed inside an emulsion are investigated theoretically and experimentally by using (differential scanning ...calorimeter) DSC. Genetic algorithm is used to determine the unknown parameters in the physical model. The dispersed PCMs are hexadecane, heptadecane and octadecane. Energy analysis is carried out to understand the thermal behavior of the simple and mixed emulsions. The effect of the heating rate on the thermal behavior of emulsion is also analyzed.
•Thermal behavior of multiple PCM emulsions during melting process is investigated both experimentally and numerically.•Enthalpy and melting point of different paraffins during melting process is determined using DSC thermograms.•Lower heating rates are desirable to describe the melting process of PCM emulsions in DSC cells.
ABSTRACT We perform a comprehensive stacking analysis of data collected by the Fermi Large Area Telescope (LAT) of γ-ray bursts (GRBs) localized by the Swift spacecraft, which were not detected by ...the LAT but which fell within the instrument's field of view at the time of trigger. We examine a total of 79 GRBs by comparing the observed counts over a range of time intervals to that expected from designated background orbits, as well as by using a joint likelihood technique to model the expected distribution of stacked counts. We find strong evidence for subthreshold emission at MeV to GeV energies using both techniques. This observed excess is detected during intervals that include and exceed the durations typically characterizing the prompt emission observed at keV energies and lasts at least 2700 s after the co-aligned burst trigger. By utilizing a novel cumulative likelihood analysis, we find that although a burst's prompt γ-ray and afterglow X-ray flux both correlate with the strength of the subthreshold emission, the X-ray afterglow flux measured by Swift's X-ray Telescope at 11 hr post trigger correlates far more significantly. Overall, the extended nature of the subthreshold emission and its connection to the burst's afterglow brightness lend further support to the external forward shock origin of the late-time emission detected by the LAT. These results suggest that the extended high-energy emission observed by the LAT may be a relatively common feature but remains undetected in a majority of bursts owing to instrumental threshold effects.
A three-dimensional supersonic turbulent flow with symmetric normal injection of circular jets from the channel walls is numerically simulated. The initial Favre-averaged Navier–Stokes equations ...closed by the
k
–
ω
turbulence model are solved by an algorithm based on an ENO scheme. The mechanism of the formation of vortical structures due to the interaction of the jet with the free stream is studied for jet to crossflow total pressure ratios ranging from 3 to 50. It is known from experiments reported in the literature that, for
n
⩾ 10, mixing of the jet with the high-velocity flow leads to the formation of a pair of vortices and of an additional separation zone near the wall behind the jet. It is demonstrated that the present numerical results are consistent with such findings and that the pressure distribution on the wall ahead of the jet in the plane of symmetry is also in reasonable agreement with available experimental data.
PDF
