Transient Free Convection Mass Transfer of Second-grade Fluid Flow with Wall Transpiration

The study of mass transfer in the non-Newtonian fluid is essential in understanding the engine lubrication, the cooling system of electronic devices, and the manufacturing process of the chemical industry. Optimal performance of the practical applications requires the appropriate conditions. The unsteady transient free convective flow of second-grade fluid with mass transfer and wall transpiration is concerned in the present communication. The behavior of the second-grade fluid under the influence of injection or suction is discussed. Suitable non-dimensional variables are utilized to transform the governing equations into non-dimensional governing equations. A Maple solver “pdsolve” that is using the centered implicit scheme of a finite difference method is utilized to solve the dimensionless governing equations numerically. The effects of wall injection or suction parameter, second-grade fluid viscoelastic parameter, Schmidt number, and modified Grashof number on the velocity and concentration profiles are graphically displayed and analyzed. The results show that with increasing wall suction, viscoelastic parameter, and Schmidt number, the velocity and concentration profiles decrease. Whereas, the velocity profiles show an opposite tendency in situations of wall injection. The wall suction has increased the skin friction and also the rate of mass diffusion in the second-grade fluid.

Performance of a Subsonic Compressor Airfoil With Upstream, End-Wall Injection Flow

The performance of a compressor stator airfoil with end-wall injection was studied experimentally and computationally. The geometry was a high-speed, subsonic, linear cascade. The independent variables studied were airfoil incidence angle and mass flow rate of end-wall injection upstream of the stator. The end-wall injection was intended to simulate upstream “leakage” through hardware gaps in the end-walls of gas-turbine engines. The exit of the cascade was interrogated experimentally by a five-hole-probe and a total pressure Kiel probe to provide total pressure measurements, which were used to calculate total pressure loss coefficients at the exit of the test section. Computational studies were completed to examine the end-wall flow physics and entropy generating mechanisms through the stator section. The experimental results showed a distinct decrease in the downstream total pressure field with end-wall injection flow, and the impact of the upstream injection on the stator loss coefficient was not a function of the incidence angle. The computational investigation found that the majority of the end-wall injection’s effect on the downstream total pressure field was observed as an increase in the size of the secondary flows on the suction-side of the stator near the upper end-wall.

The non-reacting flow characteristics of pylon and wall injections in a dual combustion ramjet engine

The influence of pylon and wall injection in coaxial jets of a Dual Combustion Ramjet engine is numerically investigated in a non-reacting flow field. The supersonic combustor is modeled and analyzed using the commercial CFD software ANSYS 18.0. The three-dimensional compressible Reynolds-averaged Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been used to analyze the coaxial mixing characteristics of the jets. The numerical study is validated with the experimental data of the wall static pressures measured in the combustor’s flow direction. The pylon and wall injectors are located symmetrically at the gas generator’s exit nozzle, and the air is used as the injectant to simulate gaseous fuel. Three injection pressures are used for the study to understand the flow field characteristics in the injector regime. Also, the gas generator downstream direction is investigated. The shock waves generated from the gas generator nozzle enhance the mixing of the coaxial jets with minimum total pressure loss. The shock wave interactions are noticed with reducing intensity within the supersonic combustor for pylon injection, leading to higher total pressure loss than the wall injection. The pylon injection provides the spatial distribution of fuels compared to the wall injection in the coaxial supersonic flow field.

Numerical Analysis on Enhancing Spray Performance of SCR Mixer Device and Heat Transfer Performance Based on Field Synergy Principle

The NH3 uniformity and conversion rate produced by the urea–water solution spray system is an essential factor affecting de-NOx efficiency. In this work, a three-dimensional simulation model was developed with the CFD software and was employed to investigate the effects of two typical injection methods (wall injection and center injection) and three distribution strategies (pre-mixer, post-mixer, pre-mixer, and post-mixer) of two typical mixers on the urea conversion rate and uniformity. The field synergy principle was employed to analyze the heat transfer of different mixer flow fields. The results show that the single mixer has instability in optimizing different injection positions due to different injection methods and injection positions. The dual-mixer is stable in the optimization of the flow field under different conditions. The conclusion of the field synergy theory of the single mixer accords with the simulation result. The Fc of the dual-mixer cases is low, but the NH3 conversion and uniformity index rate are also improved due to the increase in the residence time of UWS.

The Feasibility of an Internal Gas-Assisted Heating Method for Improving the Melt Filling Ability of Polyamide 6 Thermoplastic Composites in a Thin Wall Injection Molding Process

In thin wall injection molding, the filling of plastic material into the cavity will be restricted by the frozen layer due to the quick cooling of the hot melt when it contacts with the lower temperature surface of the cavity. This problem is heightened in composite material, which has a higher viscosity than pure plastic. In this paper, to reduce the frozen layer as well as improve the filling ability of polyamide 6 reinforced with 30 wt.% glass fiber (PA6/GF30%) in the thin wall injection molding process, a preheating step with the internal gas heating method was applied to heat the cavity surface to a high temperature, and then, the filling step was commenced. In this study, the filling ability of PA6/GF30% was studied with a melt flow thickness varying from 0.1 to 0.5 mm. To improve the filling ability, the mold temperature control technique was applied. In this study, an internal gas-assisted mold temperature control (In-GMTC) using different levels of mold insert thickness and gas temperatures to achieve rapid mold surface temperature control was established. The heating process was observed using an infrared camera and estimated by the temperature distribution and the heating rate. Then, the In-GMTC was employed to produce a thin product by an injection molding process with the In-GMTC system. The simulation results show that with agas temperature of 300 °C, the cavity surface could be heated under a heating rate that varied from 23.5 to 24.5 °C/s in the first 2 s. Then, the heating rate decreased. After the heating process was completed, the cavity temperature was varied from 83.8 to about 164.5 °C. In-GMTC was also used for the injection molding process with a part thickness that varied from 0.1 to 0.5 mm. The results show that with In-GMTC, the filling ability of composite material clearly increased from 2.8 to 18.6 mm with a flow thickness of 0.1 mm.

Botulinum toxin abdominal wall injection and post-omphalocele ventral hernia repair: database and proposal of a protocol

Background Post-omphalocele ventral hernias (POVH) are common after giant omphaloceles. Abdominal wall botulinum toxin injections (BTI) are useful to treat complex incisional hernias (CIH) in adults, which may also apply to POVH. We review BTI data in the treatment of CIH and POVH and propose an algorithm applicable to POVH. Results Sixteen papers which described the treatment of CIH on the treatment of POVH in adults (n = 15) and children (n = 1) were reviewed. BTI elongates the lateral abdominal wall and reduces the hernia defect, with a lower incidence of compartment syndrome and respiratory complications. Doses and injection volumes vary. Effects start after 3 days, peak after 10–15 days, stabilize for 2–3 months, and decline after 4–6 months, disappearing after 6–9 months. Patients should be operated on 3–4 weeks after injection. Post-operative complications are uncommon. BTI may be associated with pre-operative pneumoperitoneum (PPP). Children presenting POVH differ from adults presenting CIH. Associated congenital cardiac malformations, genetically determined syndromes, pulmonary hypoplasia, abdominal wall hypoplasia, and thoracic dysmorphism, are common; children need sedation for any procedures; non-absorbable reinforcing meshes are not indicated; and POVH limits are frequently near to the costal margin. Conclusion BTI to induce preoperative muscular relaxation in preparation of CIH repair in adults is effective and safe. Experience with the method in children with POVH is limited, but the proposal is logical and probably safe. POVH differs from CIH in some aspects, especially abdominal wall hypoplasia, proximity to the rib cage, and diaphragmatic biomechanics.