Hong Xu

Crack mouth widening energy-release rate and its application

Unlike the classical crack extension energy release rate, the crack mouth widening energy release rate is related to the Mode I stress intensity factor by application of the principle of virtual work. Solutions are derived for cracked beams and pipes while the method applies in a straightforward manner to other crack configurations. The results are shown to agree well with those available in the open literature.

On KI estimates of cracked pipes using an elliptical hole model and elementary beam strength theory of cracked beams

Abstract Based on energy release rates of elementary beams, an approximate expression was proposed by Herrmann et al. [1–4, 6 7] for calculating the stress intensity factors (SIFs). In their method, the cracks in beam were simulated by a rectangular defect. In present paper, an elliptical hole is proposed to describe the discontinuities in stiffness of cracked pipes for estimating SIFs, and the results produced by this proposal are remarkably in agreement with the exact solutions obtained from complete shell analysis.

Microfluidic synthesis of high-performance monodispersed chitosan microparticles for methyl orange adsorption

High-performance monodispersed chitosan microparticles for methyl orange (MO) adsorption were synthesized on a microfluidic platform coupled with a cross-linking approach. Batch adsorption experiments were carried out to evaluate the capacity and kinetics of the as-prepared microparticles on the adsorption of MO. Due to the advantage of microfluidics that all the manipulations and operations are related to independent droplets, the prepared microparticles are controlled to within a narrow size distribution (CV = 1.86%) while exhibiting uniform high performance (adsorption capacity = 182 mg g−1). Adsorption experiments were carried out under various design and operation conditions. It is found that the adsorption isotherm was well described by the Langmuir model and the adsorption kinetics followed a pseudo-second-order kinetic model. The high performance together with biodegradable feature and low-cost raw material give the microfluidic-synthesized chitosan microparticles a promising potential for future dye effluent treatment.

Inhibitory effect of MnCr2O4 spinel coating on coke formation during light naphtha thermal cracking

In this paper, MnCr2O4 spinel coating was fabricated on a HP40 alloy by pack cementation and subsequent thermal oxidation. The spinel coating was dense and uniform, and was applied to inhibit coke formation during light naphtha thermal cracking. Coking behaviors on the HP40 alloy and spinel coated alloy were compared under the same conditions. The anti-coking rate of the MnCr2O4 spinel coating exceeded 60% during light naphtha thermal cracking. Lots of filamentous coke formed on the uncoated HP40 alloy, but catalytic coke was completely inhibited on the MnCr2O4 spinel coated alloy resulting in a granular appearance of coke. Raman spectra analyses indicated that coke deposited on the surface of the spinel coating had a larger proportion of disordered carbon and amorphous carbon compared with that on the uncoated HP40 alloy.

Insight into a high temperature selective oxidation of HP40 alloy under a H2–H2O environment

In the present work, a selective oxidation process of HP40 alloy at 1050 °C under a H2–H2O environment were studied in detail by means of SEM, EDS, GD-OES, XRD, Raman spectra and XPS. The results revealed that selective oxidation of Mn and Cr elements was realized, and the oxide scale preferentially grew via grain boundary rather than via grain lattice. The oxide scales were composed of a majority of MnCr2O4 spinel and a spot of Cr2O3 throughout the oxidation process. Mn existed in the form of Mn2+ ions on the surface, while Cr existed in various species. Metal hydroxides appeared on the surface approved by spectra of the O 1s region, and the relative amount of them decreased with oxidation time.

Numerical Study of the Effect of Staged Gun and Quarl on the Performance of Low-NOx Burners

AbstractThree-dimensional numerical simulations were carried out to study fuel-staged low-NOx burners (LNB). The effect of the number of staged guns (four and six) and quarl style (Venturi and boss) on the performance of the LNBs was investigated. The flow field, flame temperature, OH radical field, and NO emission were analyzed. The turbulence, radiation, and chemical reactions were simulated with the standard k-e model, discrete ordinate (DO) model, and probability density function mixture fraction model, respectively, using a commercial computational fluid dynamics code. The numerical model was validated with experimental measurements at different excess air conditions. The agreement of the calculated and measured NO emission is remarkable; therefore, the present model is considered reliable. The results indicate that the number of staged guns has little effect on the NO emission; the boss quarl increases mean air velocity, changes staged gas flow direction, and reduces peak flame temperature and peak ...

J integral estimation fracture analysis for circumferentially cracked carbon steel piping

Abstract The three-segment fitting method is presented to describe the material stress-strain curves with yield plateaus. A J integral estimation approach for carbon steel piping with circumferential through-wall cracks was developed. Failure assessment curves obtained using three options in the CEGB R6 approach were proposed for GB20 carbon steel piping under bending. The initiation and maximum moments predicted by the J estimation approach presented in this paper are quite close to the experimental values.

Tubes with coated and sintered porous surface for highly efficient heat exchangers

Surface modification is a direct and effective way to enhance the efficiency of heat exchangers. Surface modification by forming a microporous coated layer can greatly enhance the boiling heat transfer and thus achieve a high performance. In this paper, we systematically investigate the boiling behavior on a plain surface with/without sintered microporous coatings of copper powder. The results demonstrated that the sintered surface has a better performance in nucleate boiling due to the increased nucleation sites. The superheat degree is lower and the bubble departure diameter is larger for the sintered surface than for the plain surface, so the heat can be carried away more efficiently on the sintered surface. In addition, the heat transfer capacity on the sintered surface depends on both the powder size and the coating thickness for a high flux tube. The optimum heat transfer capacity can be obtained when the thickness of the microporous coating layer is 3–5 times of the sintered powder diameter. As a result, the heat transfer coefficient tube can be up to 3 times higher for the tube with a sintered surface than that with a plain surface, showing a pronounced enhancement in heat transfer and a high potential in chemical engineering industry application.

3D-printed air-blast microfluidic nozzles for preparing calcium alginate microparticles

Microfluidic technologies have emerged as a promising route for precision fabrication of uniform particles. Equipment required for a traditional microfluidic device manufacturing process is expensive and production efficiency is low. Its also difficult to separate a surfactant and continuous phase impurities from particles prepared by a liquid–liquid two-phase shear method. A novel air-blast microfluidic nozzle fabricated using low-cost and efficient 3D printing technology was proposed to prepare calcium alginate particles. Effects of control parameters and solution composition on particle diameters and homogeneity were systematically investigated. Results showed that inlet air pressure has the most significant impact. A nozzle with an outlet diameter of 300 μm can produce particles with diameters ranging from 360 μm to 2100 μm. Coefficients of variation (CV) range from 5.3% to 2.2%. For the same diameter particle prepared, a smaller nozzle outlet had a narrower particle diameter distribution and needed lower inlet air pressure. This method can be used to handle high viscosity solutions and high concentrations of solutions with insoluble solid particles. The prepared particles can be used in biological and pharmaceutical fields.

Performance and Routes of Nitrogen Oxide Formation of MILD Forward-Flow Furnace with Reflector

AbstractHigh-momentum jets, which are the key parameter to achieve moderate or intense low-oxygen dilution (MILD) combustion may lead to insufficient residence time and high CO emissions, especiall...