Transient Thermoelastic Analysis of a Solid Cylinder Containing a Circumferential Crack Using the C–V Heat Conduction Model

This article presents the transient thermoelastic analysis in a long solid cylinder with a circumferential crack using the C–V heat conduction theory. The outer surface of the cylinder is subjected to a sudden temperature change. The Laplace transform technique is adopted to solve the one-dimensional hyperbolic heat conduction equation, and the axial thermal stress is obtained for the un-cracked cylinder in the Laplace domain. Then this axial thermal stress with a minus sign is applied to the crack surface to form a mixed boundary value problem in the cylindrical coordinate system. A singular integral equation is derived by applying the Fourier and Hankel transforms to solve the mode I crack problem. The transient thermal stress intensity factors are obtained by solving the singular integral equation numerically. The influences of thermal relaxation time, crack geometry, and Biot's number upon transient temperature distributions, axial stress fields, and stress intensity factors are analyzed.     

Biodiesel production from olive–pomace oil of steam-treated alperujo

Recently interest has been revived in the use of plant-derived waste oils as renewable replacements for fossil diesel fuel. Olive–pomace oil (OPO) extracted from alperujo (by-product of processed olives for olive oil extraction), and produced it in considerable quantities throughout the Mediterranean countries, can be used for biodiesel production. A steam treatment of alperujo is being implemented in OPO extraction industry. This steam treatment improves the solid–liquid separation by centrifugation and facilitates the drying for further extraction of OPO. It has been verified that the steam treatment of this by-product also increases the concentration of OPO in the resulting treated solid, a key factor from an economic point of view. In the present work, crude OPO from steam-treated alperujo was found to be good source for producing biodiesel. Oil enrichment, acidity, biodiesel yield and fatty acid methyl ester composition were evaluated and compared with the results of the untreated samples. Yields and some general physicochemical properties of the quality of biodiesel were also compared to those obtained with other oils commonly used in biodiesel production. As for biodiesel yield no differences were observed. A transesterification process which included two steps was used (acid esterification followed by alkali transesterification). The maximum biodiesel yield was obtained using molar ratio methanol/triglycerides 6:1 in presence of sodium hydroxide at a concentration of 1% (w/w), reaction temperature 60 °C and reaction time 80 min. Under these conditions the process gave yields of about 95%, of the same order as other feedstock using similar production conditions.     

Progress in the development of solid–gas sorption refrigeration thermodynamic cycle driven by low-grade thermal energy

Heat-powered solid–gas sorption refrigeration technology has been regarded as one of the effective methods for reutilization of low-grade thermal energy such as industrial waste heat, renewable energy, and exhaust gases from engines. A number of advanced solid sorption refrigeration systems have been developed to improve energy efficiency by reducing the primary energy consumption as the recognition of energy saving. These advanced solid sorption refrigeration cycles mainly include heat recovery sorption cycle, mass recovery sorption cycle, mass and heat recovery sorption cycle, double/multi-effect sorption cycle, combined double-way sorption cycle, double-effect and double-way sorption cycle, two/multi-stage sorption cycle, etc. In this paper, the progress in the development of solid–gas sorption refrigeration thermodynamic cycle is reviewed. The operating principles of these advanced solid–gas sorption refrigeration cycles are introduced in detail, and the representative working performances of different sorption refrigeration cycles are presented and compared. Moreover, the key problems of advanced sorption refrigeration cycles are described and discussed. Finally, the future development of solid–gas sorption refrigeration cycle is also proposed.     

Fault diagnosis of wind turbine planetary gearbox under nonstationary conditions via adaptive optimal kernel time–frequency analysis

Planetary gearboxes play an important role in wind turbine (WT) drivetrains. WTs usually work under time-varying running conditions due to the volatile wind conditions. The planetary gearbox vibration signals in such an environment are hence highly nonstationary. Conventional spectral analysis and demodulation analysis methods are unable to identify the characteristic frequency of gear fault from such nonstationary signals. As such, this paper presents a time–frequency analysis methods to reveal the constituent frequency components of nonstationary signals and their time-varying features for WT planetary gearbox monitoring. More specifically, we exploit the adaptive optimal kernel (AOK) method for this challenging application because of its fine time–frequency resolution and cross-term free nature, as demonstrated by our simulation analysis. In this study, the AOK method has been applied to identify the time-varying characteristic frequencies of gear fault or to extract different levels of impulses induced by gear faults from lab WT experimental signals and in-situ WT signals under time-varying running conditions. We have demonstrated that the AOK is effective diagnosis of: (a) both the local damage (a single chipped tooth) and distributed faults (wear of all teeth), (b) both sun gear and planet gear faults, and (c) faults with very weak signature (e.g., the sun gear fault at the low speed stage of a WT planetary gearbox).     

Low-temperature water–gas shift reaction over supported Cu catalysts

The low-temperature water–gas shift (WGS) reaction has been carried out at a very high gas hourly space velocity (GHSV) of 36,201 h⁻¹ over supported Cu catalysts prepared by an incipient wetness impregnation method. The preparation method was optimized to get a highly active CeO₂ supported Cu catalyst for low-temperature WGS. Co-precipitated Cu–CeO₂ exhibited excellent catalytic performance as well as 100% CO₂ selectivity. The high activity and stability of co-precipitated Cu–CeO₂ catalyst is correlated to its easier reducibility, high surface area and the nano-sized CeO₂ with CuO species interacting with the support.