@article{pang_ngaile_2023, title={A Robust Bubble Growth Solution Scheme for Implementation in CFD Analysis of Multiphase Flows}, volume={11}, ISSN={["2079-3197"]}, DOI={10.3390/computation11040072}, abstractNote={Although the full form of the Rayleigh–Plesset (RP) equation more accurately depicts the bubble behavior in a cavitating flow than its reduced form, it finds much less application than the latter in the computational fluid dynamic (CFD) simulation due to its high stiffness. The traditional variable time-step scheme for the full form RP equation is difficult to be integrated with the CFD program since it requires a tiny time step at the singularity point for convergence and this step size may be incompatible with time marching of conservation equations. This paper presents two stable and efficient numerical solution schemes based on the finite difference method and Euler method so that the full-form RP equation can be better accepted by the CFD program. By employing a truncation bubble radius to approximate the minimum bubble size in the collapse stage, the proposed schemes solve for the bubble radius and wall velocity in an explicit way. The proposed solution schemes are more robust for a wide range of ambient pressure profiles than the traditional schemes and avoid excessive refinement on the time step at the singularity point. Since the proposed solution scheme can calculate the effects of the second-order term, liquid viscosity, and surface tension on the bubble evolution, it provides a more accurate estimation of the wall velocity for the vaporization or condensation rate, which is widely used in the cavitation model in the CFD simulation. The legitimacy of the solution schemes is manifested by the agreement between the results from these schemes and established ones from the literature. The proposed solution schemes are more robust in face of a wide range of ambient pressure profiles.}, number={4}, journal={COMPUTATION}, author={Pang, Hao and Ngaile, Gracious}, year={2023}, month={Apr} }
 @article{pang_ngaile_2022, title={Utilization of Secondary Jet in Cavitation Peening and Cavitation Abrasive Jet Polishing}, volume={13}, ISSN={["2072-666X"]}, DOI={10.3390/mi13010086}, abstractNote={The cavitation peening (CP) and cavitation abrasive jet polishing (CAJP) processes employ a cavitating jet to harden the surface or remove surface irregularities. However, a zero incidence angle between the jet and the surface limits the efficiency of these two processes. This limitation can be improved by introducing a secondary jet. The secondary jet interacts with the main jet, carrying bubbles to the proximity of the workpiece surface and aligning the disordered bubble collapse events. Through characterizing the treated surface of AL6061 in terms of the hardness distribution and surface roughness, it was found out that the secondary jet can increase the hardening intensity by 10%, whereas the material removal rate within a localized region increased by 66%. In addition, employing multiple secondary jets can create a patched pattern of hardness distribution. Another finding is that the hardening effect of the cavitation increases with the processing time at first and is then saturated.}, number={1}, journal={MICROMACHINES}, author={Pang, Hao and Ngaile, Gracious}, year={2022}, month={Jan} }
 @article{pang_ngaile_2021, title={Modeling of a valve-type low-pressure homogenizer for oil-in-water emulsions}, volume={160}, ISSN={["1873-3204"]}, DOI={10.1016/j.cep.2020.108249}, abstractNote={The geometric configuration of a valve-type homogenizer can have a significant influence on the performance of the emulsification process. Three new variants of low-pressure valve-type homogenizers which differ from one another by how the valve nose profiles and the upstream fluid chamber geometries are constructed were used to study fluid flow characteristics. All the three variants were conceived such that hydrodynamic cavitation can be induced as the oil-in-water emulsion passes through the valve. The computational fluid dynamic (CFD) simulations showed that by changing the valve nose shape from smooth profile to serrated nose profile, a substantially higher strain rate in the gap can be achieved, leading to higher stress on the droplet thus increasing the emulsification efficiency. The CFD simulations have also demonstrated that, incorporating a stagnation bluff in the upstream chamber results in a violence collapse of cavitating bubbles. This in turn promotes turbulence inertial and viscous effects which are essential parameters for enhancing emulsification efficiency. Droplet size analysis of oil-in-water emulsions from the physical experiments found that the serrated nose valve profile and the bluff in the chamber resulted in a mean droplet size of about 95 nm.}, journal={CHEMICAL ENGINEERING AND PROCESSING-PROCESS INTENSIFICATION}, author={Pang, Hao and Ngaile, Gracious}, year={2021}, month={Mar} }
 @article{pang_ngaile_2020, title={Formulation of SiO2/oil nanolubricant for metal forming using hydrodynamic cavitation}, volume={234}, ISSN={["2041-1975"]}, DOI={10.1177/0954405420933120}, abstractNote={ A novel hydrodynamic cavitation–based dispensing process was developed to disperse SiO2 nanoparticles into the base oil, and the effects of process parameters on dispersity and tribological properties of SiO2/oil nanolubricants were studied using the dynamic laser scattering and ring compression tests. With this process, nanolubricants with fine nanoparticles (139–1240 nm) were formulated. A mean particle size reduction of 78% was achieved in 60 min. This process can be scaled up for mass production with relative ease. The formulated SiO2/oil nanolubricants exhibited better tribological performance over that of base oil. Lubrication mechanisms of the SiO2/oil nanolubricant in metal forming were ascertained through analysis of the dispersity of nanolubricants and characterization of dents appearing on the surface of the deforming material. The study revealed the importance of formulating nanolubricants with specific particle size distribution that relate to the surface morphology of the deforming material. In this study, a nanolubricant with particle size of 3.6 μm exhibited better lubrication on ring samples with dent depth of 4.7 μm, implying that most nanoparticles were encapsulated in the dents facilitating hydrostatic lubrication. }, number={12}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART B-JOURNAL OF ENGINEERING MANUFACTURE}, author={Pang, Hao and Ngaile, Gracious}, year={2020}, month={Oct}, pages={1549–1558} }
 @article{pang_ngaile_2019, title={Development of a non-isothermal forging process for hollow power transmission shafts}, volume={47}, ISSN={["2212-4616"]}, DOI={10.1016/j.jmapro.2019.08.034}, abstractNote={This paper presents a new forging process for hollow power transmission shafts. The key aspect of the process is altering the flow characteristics of the material via differential heating of the tubular stock. The process is conceived in three main stages namely, partially heat the tubular stock with induction heating; upset the heated section of the tube to form a solid section; and finally shape the solid section into a flange or a conical head by further upsetting the workpiece. Parametric study was also carried out for various internal diameter to external diameter (ID/ OD) tube ratios. With the aid of finite element analysis (FEA), the feasibility of the process was evaluated based on formability, forming loads and dimensional accuracy. FEA results showed that it is feasible to produce hollow axle shafts, stepped gear shafts, and pinion gear shafts. Scaled down models of hollow axle shaft and hollow pinion gear shaft were successfully fabricated using the proposed methodology.}, journal={JOURNAL OF MANUFACTURING PROCESSES}, author={Pang, Hao and Ngaile, Gracious}, year={2019}, month={Nov}, pages={22–31} }
 @article{lowrie_pang_ngaile_2017, title={Weight reduction of heavy-duty truck components through hollow geometry and intensive quenching}, volume={28}, ISSN={["1526-6125"]}, DOI={10.1016/j.jmapro.2017.04.021}, abstractNote={Increasing environmental awareness has put pressure on heavy duty truck manufacturers to improve the fuel economy and reduce the emissions of their vehicles. Light weighting efforts are a useful tool in meeting these goals. As a demonstration of how light weighting practices can be applied to the power trains of heavy duty vehicles, this paper focuses on reducing the weight of the rear axle shaft. Two methods are focused on, i) hollow shaft geometry and ii) intensive quenching, as possible avenues to shed mass from the shaft. Load mapping is used to establish a finite element model which can be used to evaluate the light weight designs and techniques proposed in the paper. It is discovered that weight savings of around 26% can be achieved by changing the traditionally solid axle shaft into a hollow shaft. The intensive quenching process is shown to be superior to the oil quenching process in regards to both residual stresses and strength, allowing for material removal accounting for 3% of the shaft weight. Additionally, the compressive residual stresses created on the surface of the part during the intensive quenching process may also serve to slow crack initiation and increase fatigue life. Further optimization of the intensive quenching process may provide additional weight reduction opportunities.}, journal={JOURNAL OF MANUFACTURING PROCESSES}, author={Lowrie, James and Pang, Hao and Ngaile, Gracious}, year={2017}, month={Aug}, pages={523–530} }