Differences in residual volume above different tracheostomy tube cuffs depending on tube structure, tube tilt angle, and liquid viscosity

INTRODUCTION

Proper management of aspirated material above the tracheostomy tube cuff is crucial to prevent complications, such as aspiration pneumonia. This study aimed to thoroughly examine the effects of aspirated liquid viscosity, suction port positioning, and tube tilt angle on residual volume above the cuff (RVAC).

METHODS

Five types of tracheostomy tubes (approximately 9 mm outer diameter) were placed through a transparent cylinder with an inner diameter of 18 mm. The cuff was inflated to completely seal the interior of the cylinder. Four liquids with different viscosities were poured onto the cuff, and the liquid above the cuff was suctioned from the side port. The cylinder was angled at 90° and 20°, and each test was performed thrice to determine the average RVAC.

RESULTS

After side-port suctioning, some liquid residue was observed on the cuff of all tracheostomy tubes. The RVAC increased with higher liquid viscosity. The tubes with a longer distance from the suction port opening to the cuff top exhibited more RVAC. Moreover, the RVAC was almost the same regardless of the cylinder angle for tubes with a suction port on the lateral side. However, tubes with backside ports showed a decreased RVAC with cylinder tilt.

CONCLUSIONS

This study underscores the persistence of residual material on cuffed tracheostomy tubes even with regular subglottic secretion drainage. This emphasizes the need for specialized tracheostomy tube development aimed at reducing post-suction RVAC. Improved designs can potentially minimize complications associated with residue accumulation.

Numerical simulation of slug flow in pipelines using drift flux constitutive equations for gas-viscous oil two-phase flow

Transient simulation of multiphase flow in pipes has been performed using Two-Fluid Model and Drift-Flux Model. The main advantage of the Drift-Flux Model is the reduced number of differential equations, which results in a lower computational time. However, the accuracy of the model depends on a suitable constitutive equation for the velocity of the dispersed phase, commonly, the gas phase. The gas velocity constitutive equation includes two important parameters, namely, the distribution coefficient and the void-fraction-weighted drift velocity. A drift-flux-model code was developed, by using the Finite Volume Method (FVM) with staggered grid system, to evaluate the effect of highly viscous liquid and pipe geometry (pipe diameter and pipe inclination) in the prediction of liquid hold-up and pressure drop gradient. The gas phase compressibility was also included in the model. The results show that the energy consumption to pump the fluids through the lift system has been overestimated when highly viscous liquids are produced. For the case of a vertical upward flow, the overestimation can be up to 10 % of energy consumption. We strongly recommend incorporating the effects of pipe inclination and liquid viscosity into the estimation of the Distribution Coefficient of the dispersed phase, encompassing both C 0 and gas drift velocity.

Experimental study on the mesoscale causes of the influence of viscosity on material erosion in a cavitation field

Cavitation is a very important hydrodynamic phenomenon in many scientific and engineering fields, such as acoustics, medicine, and hydraulics. The relationship between the physical characteristics of liquid media and the erosion status of materials in a cavitation field is a crucial concern for many researchers. In this study, we adopted underwater low-voltage discharge technology to generate cavitation bubbles. We studied the effect of the viscosity of liquid media on cavitation bubble dynamics at the mesoscale level by using high-speed photography and a transient stress test system to illustrate the mechanism and the characteristics of material erosion under viscosity changes at the macroscopic level. It was found that high liquid viscosity delays shrinkage of the cavitation bubble and increases the minimum volume to which the cavitation bubble shrinks. The shrinkage characteristics of a cavitation bubble in a solution with high viscosity can reduce the speed of micro-jet formation during the collapse of the cavitation bubble near a wall. In addition, they can delay the impact of the micro-jet on the wall surface and reduce the impact strength when the cavitation bubble collapses. The effect of viscosity on cavitation bubble dynamics at the mesoscale level can explain the erosion law of solid-wall surfaces in a cavitation field from a mechanical point of view. These conclusions present significant potential for cavitation application and prevention in the fields of ultrasonic cleaning, medicine, and hydraulic machinery.

Towards improved accuracy in modeling aeration efficiency through understanding bubble size distribution dynamics

Aeration is the largest energy consumer in most water and resource recovery facilities, which is why oxygen transfer optimization is fundamental to improve energy efficiency. Although oxygen transfer is strongly influenced by the bubble size distribution dynamics, most aeration efficiency models currently do not include this influence explicitly. In few cases, they assume a single average bubble size. The motivation of this work is to investigate this knowledge gap, i.e. a more accurate calculation of the impact of bubble size distribution dynamics on oxygen transfer. Experiments were performed to study bubble size distribution dynamics along the height of a bubble column at different air flow rates for both tap water and solutions that mimic the viscosity of activated sludge at different sludge concentrations. Results show that bubble size is highly dynamic in space and time since it is affected by hydrodrynamics and the viscosity of the liquid. Consequently, oxygen transfer also has a dynamic character. The concept of a constant overall volumetric oxygen transfer coefficient, K_La, can thus be improved. A new modeling approach to determine the K_La locally based on bubble size distribution dynamics is introduced as an alternative. This way, the K_La for the entire column is calculated and compared to the one measured by a traditional method. Results are in good agreement for tap water. The modeled K_La based on the new approach slightly overestimates the experimental K_La for solutions that mimic the viscosity of activated sludge. The difference appears to be lower when the air flow rate increases. This work can be considered as a first step towards more accurate and rigorous mechanistic aeration efficiency models which are based on in-depth mechanism knowledge. This is key for oxygen transfer optimization and consequently energy savings.