Internal flow studies for the characterisation and optimisation of an effervescent atomiser

This thesis is concerned with the study of effervescent atomisation, a two-phase gas-liquid spray generation technique that offers many advantages over conventional atomisers. Following a thorough literature review, it was found that the effects of various parameters were disputed between studies or untested with many reports presenting findings without internal flow regime study – in fact, the quantification of gas injection at the aerator was completely unrepresented throughout the literature. Hence, two purpose-built transparent experiment systems were designed and commissioned at Cardiff School of Engineering to characterise the complete effervescent atomisation, from gas injection to spray generation, and to investigate the effect of various design and operating parameters on the internal two-phase flow. All investigations were performed from unbled start-up conditions, to best simulate industrial applications. The results of this work identified that the droplet size decreases with an increase in the mass ratio of input air to liquid (ALR) and a homogenous flow of bubbles within the mixing chamber (bubbly flow) generates a stable spray compared to alternative heterogeneous flow regimes, due to a regular and consistent atomisation process. Hence, an optimal effervescent atomiser configuration would enable a homogenous bubbly flow at the highest ALRs. Further work was performed to quantify the bubbly flow operating range for various independent parameters. It was determined that bubbling at the aerator was encouraged by the injection of an unstable gas-phase into a strong liquid cross-flow, suiting low ALRs, high liquid flow rates (e.g. large exit orifice diameters, high operating pressures), small aerator orifice diameters, high aeration areas and small mixing chamber diameters. However, a conventional flat-end aerator body design was found to be unsuitable for inside-out effervescent atomisation in a vertically downwards orientation, due to the formation of a gas void in the aerator wake – this was found to be a result of aerator bluff body recirculation and gas-phase buoyancy effects. Hence, bubbly flow was only enabled in a vertically upwards orientation or with a streamlined aerator body profile

Experimental investigation of effervescent atomization: Part I. Comparison of flat-end and streamlined aerator body designs

The present experimental work is concerned with the study of effervescent atomisation, a two-phase gas-liquid spray generation technique that offers many advantages over conventional atomisers. In this study we show the advantage of streamlined aerator design over flat-end aerator type with respect to formation of gas void in the aerator wake in the interior of an inside-out type of effervescent atomizer. The experiments are performed employing high-speed shadowgraphy visualizations. It is observed that in the conventional flat-end type of aerator design the formation of gas void is undesirable and leads to spray characterized by the instabilities, causing fluctuating spray properties. The existence of gas void also prevents the formation of bubbly flow inside the effervescent atomizer which is actually preferred in these type of atomizers to enable stable spray generation and fine atomization. The formation and existence of gas-void is found to be a result of aerator bluff body recirculation and gas phase buoyancy effects. Four different streamlined aerator designs with tips in the shape of circular arc, circular arc/conical hybrid, conical and DARPA SUBOFF afterbody design (which is common in the conventional ship designs) are evaluated to determine the best among them with respect to mitigating the unwanted gas-void in the interior of an effervescent atomizer. These are evaluated with respect to ability to produce bubbly flow over comparatively large operating range and the ability to impart minimum wake (of aerator body) effect. It is concluded upon careful experimental observations that DARPA SUBOFF afterbody design is the best among the streamlined aerator designs

Transformed non‐Hodgkin lymphoma in the rituximab era: analysis of the NCCN outcomes database

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/100290/1/bjh12570.pd

Experimental investigation of effervescent atomization: Part II. Internal flow and spray characterization with novel DARPA SUBOFF afterbody streamline aerator

In this experimental work we report, for the first time, observations of internal flow field involving an DARPA SUBOFF afterbody design aerator body in an inside-out type of effervescent atomizer. The effect of operating parameters like air-to-liquid ratio (ALR), operating pressure, aerator orifice diameter, aeration area and mixing chamber diameter on internal flow within the effervescent atomizer is studied. The effect of increasing ALR on the internal flow is quantified by identifying different gas injection mechanisms at the aerator orifice (into the mixing chamber) and two-phase mixing chamber flow regimes. In particular, it is observed that as ALR is systematically increased the gas injection mechanism transits in the following sequence: single bubbling, pulsed bubbling, elongated jetting, atomized jetting and evacuated chamber. The range of ALRs within which these mechanisms are observed are employed to draw up a flow regime map. Similar analysis on two-phase mixing chamber flow regimes yielded corresponding regime map for internal two-phase stabilized flow in the mixing chamber. The flow regime transited from bubbly flow to slug flow to churn flow and finally to annular flow as the ALR was increased. Dependence of internal flow on other parameters such as orifice aerator diameter (with constant total aerator orifice area), mixing chamber diameter and operating pressure are also studied

Comparison of Surgical and Cadaveric Intestine as a Source of Crypt Culture in Humans

Human small intestinal crypts are the source of intestinal stem cells (ISCs) that are capable of undergoing self-renewal and differentiation to an epithelial layer. The development of methods to expand the ISCs has provided opportunities to model human intestinal epithelial disorders. Human crypt samples are usually obtained from either endoscopic or discarded surgical samples, and are thereby exposed to warm ischemia, which may impair their in vitro growth as three-dimensional culture as spheroids or enteroids. In this study we compared duodenal samples obtained from discarded surgical samples to those isolated from whole-body preserved cadaveric donors to generate in vitro cultures. We also examined the effect of storage solution (phosphate-buffered saline or University of Wisconsin [UW] solution) as well as multiple storage times on crypt isolation and growth in culture. We found that intestinal crypts were successfully isolated from cadaveric tissue stored for up to 144 h post-procurement and also were able to generate enteroids and spheroids in certain media conditions. Surgical samples stored in UW after procurement were sufficiently viable up to 24 h and also allowed the generation of enteroids and spheroids. We conclude that surgical samples stored for up to 24 h post-procurement in UW solution allowed for delayed crypt isolation and viable in vitro cultures. Furthermore, in situ, hypothermic preservation in cadaveric duodenal samples permitted crypt/ISC isolation, and successful culture of spheroids and enteroids from tissues held for up to 6 days post-procurement