Development of adiabatic shear band in cold-rolled titanium

The evolution of adiabatic shear localization in commercial titanium subjected to heavy cold rolling was investigated. The evolution of the morphology, microhardness, local shear strain, and local temperature increments were systematically studied and estimated. A shear band with about 25m in width was formed and fine nanograins with a range of dimensions varying from 20 to 160nm and had a mean size of about 70nm were observed inside the centre of shear band after 83% cold-rolling. Microhardness test shows that hardness within the shear band is markedly higher than that of the surrounding matrix. The calculated shear strain and maximum temperature increase within the shear band are much higher than that of the overall deformed sample. The initiation of shear localization may depend on geometric perturbation instead of thermal ones.

Convection suppression in an attic shaped enclosure

In recent times there has been growing interest in the integration of solar collectors, for water heating, into the façade of buildings. However, the design methodology of these devices remains largely the same as typical “stand-alone” collectors. As such it is still common for materials with a high thermal resistance to be used for insulating the rear surface of these collectors.

Unlike a “stand-alone” solar collector that is exposed to the atmosphere at all faces; a building integrated system allows the opportunity for air to act as an insulator at the rear surface of the solar collector. The use of convection suppression devices has been widely discussed in the literature as a means of reducing natural convection heat loss from the front surface of glazed solar collectors. However in this study the use of baffles in an attic was examined as a means of suppressing heat loss by natural convection from the rear surface of a roof-integrated solar collector. The aim of the study was to examine whether the use of baffles would allow the cost of building integrated collectors to be reduced by removing the cost of insulating material.

To determine the effect of baffles in the attic space at the rear surface of the collector, a 3-dimensional triangular cross sectioned enclosure with a vertical aspect ratio of 0.5 and a horizontal aspect ratio of 3.3 was modelled. The flow patterns and heat transfer in the enclosure were determined for Grashof Numbers in the range of 106 to 107 using a commercially available finite volume CFD solver.
It was found that the use of a single adiabatic baffle mounted vertically downwards from the apex, and extending the length of the enclosure, would alter the flow such that the heat transfer due to natural convection was reduced with respect to the length of the baffle.

Furthermore, it was observed that a series of convection cells, not previously reported in the literature, appeared to exist along the length of the enclosure. As such, it may be possible to derive additional benefit in reducing the heat transfer by adding lateral baffles in addition to the single longitudinal baffle modelled in this study.

Reactive ball milling to produce nanocrystalline ZnO

Ball milling of zinc powders in oxygen atmosphere leads to nanocrystalline ZnO. The average grain size has a value of 9 nm. The zinc oxidation proceeds gradually. It is compared with the combustion oxidation reactions of metals (Zr, Ti, Fe and Sn) reported previously. We propose a new parameter ΔH/C_p(metal) instead of simplified adiabatic temperature to judge if the mechanochemical oxidation of a particular metal happens via gradual or combustion reaction.

A non-darcian numerical modeling in domed enclosures filled with heat-generating porous media

Numerical study of the natural-convection flow and heat transfer in a dome-shaped, heat-generating, porous enclosure is considered. The general conic equation for the top dome is used to consider various conical top sections such as circular, elliptical, parabolic, and hyperbolic. The individual effect of fluid Rayleigh, Darcy, and heat-generating parameters on flow patterns and heat transfer rates are analyzed and presented. The predicted results show that the heat-generating parameter has the most significant contribution toward the growth of bicellular core flow. Moreover, there is significant change in temperature distribution in comparison to rectangular enclosures, due to the existence of the domed-shape top adiabatic cover. The results also show that, regardless of Darcy and Rayleigh values, a flat adiabatic top cover tends to yield the highest value of Nusselt number, followed by circular, elliptical, parabolic, and hyperbolic top covers, respectively.

Ultra-wideline 14N solid-state NMR as a method for differentiating polymorphs: glycine as a case study

Nitrogen-14 solid-state NMR (SSNMR) is utilized to differentiate three polymorphic forms and a hydrochloride (HCl) salt of the amino acid glycine. Frequency-swept Wideband, Uniform Rate, Smooth Truncated (WURST) pulses were used in conjunction with Carr-Purcell Meiboom-Gill refocusing, in the form of the WURST-CPMG pulse sequence, for all spectral acquisitions. The ¹⁴N quadrupolar interaction is shown to be very sensitive to variations in the local electric field gradients (EFGs) about the ¹⁴N nucleus; hence, differentiation of the samples is accomplished through determination of the quadrupolar parameters CQ and ηQ, which are obtained from analytical simulations of the ¹⁴N SSNMR powder patterns of stationary samples (i.e., static NMR spectra). Additionally, differentiation of the polymorphs is also possible via the measurement of ¹⁴N effective transverse relaxation time constants, T^eff2(¹⁴N). Plane-wave density functional theory (DFT) calculations, which exploit the periodicity of crystal lattices, are utilized to confirm the experimentally determined quadrupolar parameters as well as to determine the orientation of the ¹⁴N EFG tensors in the molecular frames. Several signal-enhancement techniques are also discussed to help improve the sensitivity of the ¹⁴N SSNMR acquisition method, including the use of selective deuteration, the application of the BRoadband Adiabatic INversion Cross-Polarization (BRAIN-CP) technique, and the use of variable-temperature (VT) experiments. Finally, we examine several cases where ¹⁴N VT experiments employing Carr-Purcell-Meiboom-Gill (CPMG) refocusing are used to approximate the rotational energy barriers for RNH3⁺ groups.