Slug flow is one of the main flow regimes encountered in multiphase flow systems especially in oil and gas production systems. In the present study, the rise of single Taylor bubble through vertical stagnant Newtonian liquid is investigated by performing complete dimensionless treatment followed by an order of magnitude analysis of the terms of equations of motion. Based on this analysis, it is concluded that Froude, Eötvös and Reynolds numbers are the sole physical parameters influencing the dimensionless slug flow equations. Using the guidelines of the order of magnitude analysis, computational fluid dynamics simulation is carried out to investigate the dynamics of Taylor bubbles in vertical pipe using the volume-of-fluid (VOF) method. Good agreement with previous experimental data and models available in the literature is established confirming that the density ratio, viscosity ratio and the initial ratio of bubble size to pipe diameter (/) have minimal effect on the main hydrodynamic features of slug flow. Based on the developed results, correlations for the terminal velocity of the Taylor bubble and the dimensionless wall shear stress are proposed showing the significance of these main dimensionless parameters and support other important theoretical and experimental work available in the literature.
Cooling and heating are extremely important in many industrial applications, while the thermal performance of these processes generally depends on many factors, such as fluid flow rate, inlet temperature, and many more. Hence, tremendous efforts are dedicated to the investigation of several parameters to reach an efficient cooling or heating process. The interest in adding nanoparticles in regular heat transfer fluids delivered new fluids to the market, the nanofluids. In this paper, a new nanoparticle-enhanced fluid based on polyethylene glycol with ZnO nanoparticles is considered and its hydrothermal performance is investigated for HVAC applications. The thermophysical properties of PEG 400—ZnO and their variation with temperature at different nanoparticle loading are previously determined on experimental bases and here implemented in a numerical application. The numerical results are completed at Reynolds number from 200 to 2000, while the nanoparticle concentration varies from 0.5 to 5%. Results are discussed in terms of Nusselt number, friction factor, and dimensionless pressure drop ratio at different temperatures and ZnO loading in the PEG 400 base fluid. Additionally, the evaluation performance criteria (EC) are calculated and discussed. Concluding, the newly developed fluid enhances the heat transfer up to 16% with a 13% pressure drop penalty, while the performance evaluation criteria are enhanced. Plus, several correlations are developed for both Nusselt number and friction factor as a function of relevant operating conditions.
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