An efficient indium-mediated 2-bromoallylation of aldehydes at low temperature in aqueous DMF

An efficient synthesis of 2-bromohomoallylic alcohols was carried out via an indium-mediated Barbier-type 2-bromoallylation of aldehydes in moderate yields. The reaction was performed at low temperature (−20 °C) in aqueous DMF in order to minimize decomposition of 2-bromoallylindium reagent to allene.     

An assessment of models for predicting refrigerant characteristics in adiabatic and non-adiabatic capillary tubes

Small vapor compression refrigeration systems incorporate a non-adiabatic capillary tube called a capillary tube-suction line heat exchanger (SLHX) in order to improve performance. The thermodynamic properties of the refrigerant in the capillary tube and suction pipe are influenced by associated phenomena. This study compares various relevant models. Based on the comparison recommended correlations were selected and the simulation results show that the friction factor model has the most dominant.     

Autoignition of methanol: Experiments and computations

An experimental and computational investigation into the autoignition of methanol under high‐pressure and low‐to‐intermediate temperature conditions is conducted. The ignition delay results have been obtained using a heated rapid compression machine, over a pressure range of 7–30 bar, a temperature range of 850–1100 K, and an equivalence ratio range of 0.25–2.0. Using kinetic schemes recently reported in the literature for the combustion of methanol, the experimental results are compared to computationally obtained values. The kinetic schemes studied are found to significantly underpredict ignition delays for the conditions investigated. A sensitivity analysis of the computed results to reaction rate constants is also conducted. It is shown that the reaction of methanol with HO₂ radical is critical to the predicted values of ignition delays under the current experimental conditions. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 175–184, 2011     

Direct numerical simulation of a turbulent boundary layer up to Reθ = 2500

Direct numerical simulations (DNSs) of a turbulent boundary layer (TBL) with Re_θ = 570-2560 were performed to investigate the spatial development of its turbulence characteristics. The inflow simulation was conducted in the range Re_θ = 570-1600 by using Lund’s method. To resolve the numerical periodicity induced by the recycling method, we adopted a sufficiently long streamwise domain of x/θ_in,i = 1000 (=125δ_0,i), where θ_in,i is the inlet momentum thickness and δ_0,i is the inlet boundary layer thickness in the inflow simulation. Furthermore, the main simulation with a length greater than 50δ₀ was carried out independently by using the inflow data, where δ₀ is the inlet boundary layer thickness of the main simulation. The integral quantities and the first-, second- and higher-order turbulence statistics were compared with those of previous data, and good agreement was found. The present study provides a useful database for the turbulence statistics of TBLs. In addition, instantaneous field and two-point correlation of the streamwise velocity fluctuations displayed the existence of the very large-scale motions (VLSMs) with the characteristic widths of 0.1-0.2δ and that the flow structure for a length of approximately ∼6δ fully occupies the streamwise domain statistically.     

Self-sustained oscillations of turbulent flows over an open cavity

The mechanism of self-sustained oscillations in laminar cavity flows has been well characterized; however, the occurrence of self-sustained oscillations in turbulent cavity flows has only previously been characterized by direct observation of flows. Here, the quantitative characteristics of vortical structures in turbulent flows over an open cavity were determined, and then statistical properties were examined for evidence of self-sustained oscillations. Specifically, instantaneous velocity fields were measured using PIV and wall pressure fluctuations were determined from microphone data. Cavity geometries of L/D = 1 and 2, where L and D are the length and depth of the cavity, respectively, were used under conditions where the incoming boundary layer was turbulent at Re _θ  = 830. Statistical analyses were applied based on the instantaneous velocity fields of PIV data. The spatial distributions of vertical velocity correlations (v–v) showed alternating patterns that reflect the organized nature of the large-scale vortical structures corresponding to the modes of N = 2 for L/D = 1 and N = 3 for L/D = 2. These values were consistent with the numbers of vortical structures obtained from a modified version of Rossiter’s equation. Furthermore the numbers of vortical structures determined in the statistical analyses were consistently observed in instantaneous distributions of the swirling strength (λ _ci). The incoming turbulent boundary layer can give rise to the formation of large-scale vortical structures responsible for self-sustained oscillations.