Inception criteria for droplet entrainment in two-phase concurrent film flow

Transient CFD Modelling of Air–Water Two-Phase Annular Flow Characteristics in a Small Horizontal Circular Pipe

The liquid film formed around the inner walls of a small horizontal circular pipe often exhibits non-uniform distributions circumferentially, where the film is thinner at the top surface than the bottom one. Even with this known phenomenon, the problem remains a challenging task for Computational Fluid Dynamics (CFD) to predict the liquid film formation on the pipe walls, mainly due to inaccurate two-phase flow models that can induce an undesirable ‘dry-out’ phenomenon. Therefore, in this study, a user-defined function subroutine (ANNULAR-UDF) is developed and applied for CFD modelling of an 8.8 mm diameter horizontal pipe, in order to capture transient flow behaviour, flow pattern formation and evolving process and other characteristics in validation against experiments. It is found that CFD modelling is able to capture the liquid phase friction pressure drop about maximum of 30% in deviation, consistent to the correlated experimental data by applying an empirical correlation of Chisholm. Due to the gravity effect, the liquid film is generally thicker at the bottom wall than at the top wall and this trend can be further enhanced by increasing the superficial air–water velocity ratios. These findings could be valuable for HVAC industry applications, where some desirable annular flow features are necessary to retain to achieve high efficiency of heat transfer performance.

The dominant frequency analysis of interfacial wave in wet-gas pipeline transportation based on NIR absorption

During the long-distance transportation of wet-gas, the dominant frequency is of great significance for the study of pipeline fatigue and damage, and the safety production. Therefore, the theoretical and experimental researches for dominant frequency are carried out increasingly. However, most of the current prediction correlation of dominant frequency are mainly applicable to atmospheric pressure conditions (0.1 MPa), and the prediction accuracy is not accurate enough. The paper obtains the time series signal of liquid film thickness by near-infrared (NIR) sensor, and then calculates the wave frequency by the power spectrum density (PSD). The performance of typical predictive correlation is evaluated and analyzed by utilizing the experimental data at different flow and pressure conditions (0.1–0.8) MPa. The structure of Strouhal number and Lockhart-Martinelli (L-M) parameter are optimized reasonably, the mean velocity of the liquid film surface, the density increment of gas core, the gas core mass flow and average liquid film velocity are considered in the L-M parameter, a modified interfacial wave frequency correlation is proposed. The results indicate that the mean absolute error of the predictive correlation is 9.06% (current data) and 25.64% (literature data). The new correlation has a better predictive accuracy.

Impact of spacer on inter sub-channel mixing of coolant in nuclear fuel bundle: a survey and future patterns of research and advances

Broad efforts have been ended in the last decade for the development of spacer and its effect on droplets that present in the vapour core. The spacers operate as droplet collectors and accumulate considerable amount of the droplet flux in an emblematic spacer section. This development paved the way for engineers and researchers to come up with spacer that exhibit better inter subchannel mixing in the reactor. The review is based on the correlation developed by different researchers for the spacer modelling, grey areas and challenges for further improvement in the prediction and some of the good models have been recommended. The effect of spacer on liquid films and droplet depositions before spacer and near spacer have been studied and finally based on this investigation a proposed LDV measurement techniques have been applied on 1/12th segment of Advanced Heavy Water Reactor for further analysis of spacer effect on annular flow. Efforts are made to uncover the investigated gaps from the precedent literatures, as an effect of which it is concluded that there is extremely inadequate work published in the field of thermal-hydraulics incorporating spacer effect such as turbulent mixing, droplet deposition and liquid film thickness in the case of AHWR.

Data of numerical simulation and experimental research on the design of a cyclone separator with a high flux density

This article contains data related to the research article entitled "Cyclone separator for gas-liquid mixture with high flux density" (Mikheev et al., 2018 [1]doi: 10.1016/j.powtec.2018.08.040). This work was aimed at the development of an effective gas-liquid cyclone separator at a high flux density. Within the implementation of the project, the goal was to choose the schematic construction of the separator provides the reduced dynamic head of flow in the zones with increased liquid phase concentration to prevent the entrainment of separated liquid and layer losses. The paper presents the numerical simulation data and experimental data allowed estimation of separation efficiency of the separator.

Viscous Wave Breaking and Ligament Formation in Microfluidic Systems

Rapid layering of viscous materials in microsystems encompasses a range of hydrodynamic instabilities that facilitate mixing and emulsification processes of fluids having large differences in viscosity. We experimentally study the stability of high-viscosity stratifications made of miscible and immiscible fluid pairs in square microchannels and characterize the propagation dynamics of interfacial waves, including breaking and viscous ligament entrainment from wave crests at moderate Reynolds numbers. For large viscosity contrasts, parallel fluid streams adopt widely different velocities and provide a simple model system to probe the role of inflectional instabilities of stratified microflows in relation with classic inviscid-stability theory. We reveal novel viscous wave regimes and unravel dispersion relationships in the presence and absence of interfacial tension. Detailed examination of wave celerity shows the existence of optimal operation conditions for passively disturbing miscible fluid flows and continuously dispersing low-and high-viscosity fluids at the small scale.