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•Study of forced convection heat transfer through packed beds.•Discrete pellet effects in narrow tubes with spheres, cylinders and Raschig rings.•Significant local deviations from ...pseudo-homogenous model predictions.•Exposition of length-dependence of effective heat transfer parameters.
We investigate forced convective heat transfer in packings of spheres, cylinders and Raschig rings, made of glass, steel and alumina, in relatively narrow tubes. A detailed comparison is made between resolved pellet-scale, azimuthally-averaged temperature profiles, and 2D-axially-dispersed pseudo-homogenous plug flow (2D-ADPF) predictions. The local temperature deviates significantly from azimuthally-averaged profiles, which in turn deviate from 2D-ADPF predictions. We show that the length dependency of effective heat transfer parameters is caused by thermal (non-)equilibrium between fluid and solid phases along the bed and not related to inadequate insulation of the calming section or the thermocouple’s cross or an under-developed velocity and thermal field at the bed inlet. The influence of pellet shape and thermal conductivity and tube-to-pellet diameter ratio on ker and hw are assessed. We conclude that the models of Specchia/Baldi/Gianetto/Sicardi for all flow regimes and of Martin/Nilles for the turbulent regime are recommended for practical use for spherical particles.
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•Electromagnetic, heat transfer and fluid dynamics coupled for MW heating simulation.•Dielectric properties of NaY zeolite measured as a function of temperature 298–623 K.•Temperature ...evolution and distribution results validated with experimental data.•Model predicts thermal runaway of zeolite under MW heating.
Three-dimensional mathematical model was developed for a rectangular TE10n microwave heating cavity system, working at 2.45 GHz. Energy/heat, momentum equations were solved together with Maxwell’s electromagnetic field equations using Comsol Multiphysics® simulation environment. The dielectric properties, ε' and ε'', of NaY zeolite (Si/Al = 2.5) were evaluated as a function of temperature. Considering these values, the microwave heating of a porous fixed-bed made of dry NaY zeolite was simulated. Electric field distribution, axial and radial temperature profiles and temperature evolution with time were obtained. The zeolite fixed bed was heated up to 180 °C in 5 min, with 30 W power. The fixed-bed temperature evolution under non-steady state conditions showed the same trend as the one observed experimentally with only an average deviation of 10.3%. The model was used to predict microwave heating of other materials improving energy efficiency of the microwave cavity. Furthermore, the developed model was able to predict thermal runaway for zeolites.
Purpose
Parathyroid hormone (PTH) concentrations are routinely measured in the diagnosis and management of bone and kidney diseases, but reference ranges can be overestimated if determined in ...otherwise healthy individuals for whom vitamin D deficiency was not evaluated. We establish PTH reference ranges in apparently healthy, normocalcemic, normophosphatemic individuals categorized by 25-hydroxyvitamin D (25(OH)D) status using the Elecsys
®
PTH (
cobas e
601) and Elecsys
®
Vitamin D total II electrochemiluminescence immunoassays (
cobas e
411).
Methods
This prospective, non-interventional study measured PTH in serum from 653 apparently healthy adults 56.7% female; 68.2% white/Caucasian; 28.6% African American; median age 44 years (range 21–83) from three diverse geographic sites across the USA during summer and winter months. Subjects were classified by concomitant vitamin D sufficiency (≥ 30 ng/mL), insufficiency (> 20 to < 30 ng/mL) or deficiency (≤ 20 ng/mL).
Results
In vitamin D sufficiency, median PTH was 31.9 pg/mL range (2.5th–97.5th percentile) 17.9–58.6 compared with 35.5 pg/mL (17.0–60.4) for insufficiency, and 39.8 pg/mL (19.5–86.4) for deficiency. A significant inverse relationship was found between PTH and 25(OH)D (
P
< 0.001). After accounting for vitamin D, potential effects of race or season as covariates were relatively small or absent.
Conclusions
Upper reference limits (URL) for PTH in vitamin D sufficiency/insufficiency were similar and lower than current values. Clinically important PTH elevations were observed in vitamin D deficiency, where revised reference ranges with a higher URL may be appropriate. These data may help to distinguish vitamin D-related PTH elevations from other causes e.g., primary (normocalcemic) or secondary hyperparathyroidism.
The purpose of this paper is to investigate the influence of nanoconfinement on the molecular mobility, as well as on the physical stability, of amorphous ezetimibe drug. Two guest/host systems, ...ezetimibe–Aeroperl 300 and ezetimibe–Neusilin US2, were prepared and studied using various experimental techniques, such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS). Our investigation has shown that the molecular mobility of the examined anticholesterol agent incorporated into nanopore matrices strongly depends on the pore size of the host system. Moreover, it was found that the amorphous ezetimibe confined in 30 nm pores of Aeroperl 300 has a tendency to recrystallize, while the drug incorporated into the smaller5 nmpores of Neusilin US2 is not able to crystallize. It has been shown that this significant stabilization of ezetimibe drug can be achieved by an interplay of three factors: changes in molecular dynamics of the confined amorphous drug, the immobilization effect of pore walls on a part of ezetimibe molecules, and the use of host materials with pores that are smaller than the critical size of the drug crystal nuclei.
This paper brings a review of the alternative sources and forms of energy that can be utilized in order to achieve drastic improvements in the efficiency of chemical and biochemical processes ...(process intensification). Literature data on achievable intensification effects are provided. Also, some alternative ways of introducing energy in the chemical process equipment are presented. Although the process intensification potential of many of those alternative sources and forms of energy has already been proven in the laboratories, their application on the industrial scale still presents a formidable challenge for the chemical engineering community. In the paper the most important design and scale-up problems in those novel technologies are discussed and recommendations are given regarding the future research activities. To achieve radical progress in this area more research effort on the interface between the chemical engineering, chemistry, material science and applied physics is needed.
With read-head structures becoming very small (<;30 nm typical size), thermal fluctuations of the free and reference layers, occurring in the gigahertz range of frequencies, may become relatively ...large (>20°) and cause the appearance of considerable magnetic noise in the read-back function. For instance, the experimental test of a read-head sensor shows that a considerable low-frequency noise appears in the measured signal in coincidence with the superposition of high-frequency eigenmodes of the stack. To shed light on these experimental data, we perform extensive micromagnetic simulations to analyze the spin-wave spectrum of the read-head sensor and its evolution under the application of an external magnetic field. We show that the nonuniformity of both the bias field and the demagnetizing field induces pronounced spatially dependent dynamics within each layer. Moreover, the derived read-back function is characterized by different peaks that reflect the underlying eigenmodes spectrum, as suggested also by simple macrospin approach. However, for large precession amplitude, nonlinear and mixing effects appear, leading to the presence of extra peaks and of a low-frequency tail in the readback signal, in qualitative agreement with experiments.
This review paper focuses on the effects of microwave irradiation on heterogeneous gas phase catalytic reaction systems. Both experimental and modeling approaches are discussed. The currently ...available methods for temperature measurements in the microwave heating of solid particles are critically examined. The existence of microwave‐created temperature gradients in beds of solid particles is discussed. The not fully established mechanism of catalyst (nano)particle heating and imperfect temperature measurement techniques implicate that different effects are often observed and contradictory conclusions are drawn. For further progress here, the development of accurate and possibly non‐invasive techniques for local temperature measurements under microwave irradiation is needed.
Microwave technology will probably become the most common organic synthesis technique in the chemical laboratory. The experimental and modeling approaches are discussed and the currently available methods for temperature measurements in microwave heating of solid particles are examined. The existence of microwave‐created temperature gradients in beds of solid particles is discussed.
Variations in the relative proportions of individual macerals in shales can significantly influence the geochemical characteristics of bulk organic matter. Density fractions of kerogen from the ...thermally immature New Albany Shale (Devonian and Mississippian) with contrasting maceral compositions exhibit strong geochemical differences. The parental shale is characterized by a vitrinite reflectance (Ro) of 0.45%, a total organic carbon content of 13wt.%, and a sulfur content of 6.2wt.%. Organic matter is dominated by amorphinite and alginite, with vitrinite and inertinite accounting only for 1% by volume. Alginite-dominated density fractions (density ca. 1.0–1.15g/cm3) contain significantly more aliphatic hydrogen, a stronger carboxyl/carbonyl contribution, and reduced Fourier transform infrared spectroscopy absorbance in the 1000 to 1100cm−1 region assigned to ether bonds (COC), as compared to the amorphinite-dominated density fraction (density ca. 1.2–1.6g/cm3). Aromaticity generally increases from alginite-dominated to amorphinite-dominated fractions. Density fractions dominated by amorphinite are more deuterium-depleted (δDn values of nonexchangeable hydrogen up to −105‰) than alginite-rich density fraction (δDn values reach −90‰). In contrast, changes in relative proportions of alginite and amorphinite in the New Albany Shale do not significantly affect the amount of isotopically exchangeable hydrogen in total hydrogen (i.e., hydrogen exchangeability). Alginite is relatively 13C-enriched, whereas density fractions having a high content of amorphinite are relatively 13C-depleted. Our results suggest that even small bulk geochemical and isotopic differences can gain relevance after deconvolution from maceral-related variability. The masking influence of maceral abundance patterns must be considered when interpreting bulk geochemical data as paleoenvironmental proxies. The findings of this study on shale and Type II kerogen are relevant for all types of kerogens in sediments and rocks.
► Density of kerogen in shales depends on maceral composition. ► Maceral composition influences chemistry and isotopic compositions of kerogen. ► Isolation procedure of bulk kerogen must avoid bias against any organic density fractions.
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