Validating insertion loss predictions for HVAC silencers

Ventilation systems normally contain large dissipative splitter silencers that are used to attenuate fan noise. Recently, numerical models have been developed that seek to predict the insertion loss of these silencers; however, there is very little experimental data available in the literature that is suitable for validating these insertion loss predictions and so questions marks still remain regarding the accuracy of the models. This issue is investigated here by comparing theory with experiment for a range of splitter silencers. Here, the insertion loss predictions are compared against experimental measurements obtained on a test rig that conforms to ISO 7235. Measurements are presented for silencers of differing geometry, although each silencer is restricted to one central splitter with two baffles lining the opposite walls of the duct. Furthermore, validation of the numerical models is based on measurements taken both with and without flow. Comparison between prediction and experiment is reported in one-third octave frequency bands up to a frequency of 8 kHz. Results indicate that the theoretical model is capable of providing accurate predictions for silencers of high percentage open area, but when the percentage open area is low significant discrepancies appear between prediction and experiment at higher frequencies

On the collapse behaviour of oil reservoir chalk

Oil exploitation in North Sea Ekofisk oilfield started in 1971, the reservoir is located in a 150 m thick layer of porous chalk (n = 40-50%) at a 3000 m depth. Enhanced oil recovery procedure by sea water injection (waterflooding) was initiated in 1987. Starting from this date, seabed subsidence due to chalk compaction evolves at a fairly constant rate (i.e. 40 cm/year). Nowadays, the decrease of the seafloor level is of about 10 m. Reservoir management and production strategies are at the origin of the growing interest of petroleum industry in disposing of a comprehensive description of the chalk mechanical behaviour. In this note the subsidence due to waterflooding is interpreted within a framework taken from the mechanics of unsaturated soils. By considering oil as the non-wetting fluid and water as the wetting fluid, chalk compaction is depicted as a collapse phenomenon due to oil-water suction decrease. A series of suction controlled tests in the osmotic oedometer cell are presented. Water weakening effects and chalk compaction (collapse) seem likely to occur through the lost of strength of the inter-granular links existing in the oil saturated sample. The nature of these links includes both capillary and physico-chemical fluids-chalk interactions, and is well characterised by the oil-water suction

Relationship between age, comorbidities and complications in head and neck cancer patients undergoing curative surgery

BACKGROUND: Both age and comorbidity are accepted as significant prognostic factors for adverse perioperative outcomes in major surgery. Elderly patients may be overlooked for radical treatment for fear of poor perioperative outcome. We aim to assess the relationship between age, comorbidities and post-operative outcomes in a tertiary head and neck unit. METHODS: A retrospective analysis was undertaken on 651 patients who underwent surgery for head and neck cancer at a tertiary hospital between 2007 and 2014. RESULTS: A total of 253 (38.9%) patients were aged ≥70 years and 398 (61.1%) patients were ≤69 years. Age alone did not predict prolonged post-operative stay, perioperative complications nor perioperative mortality. Congestive cardiac failure and/or complicated diabetes were significantly associated with poor outcomes, as was male sex. CONCLUSION: Patients of any age with cardiac failure or complicated diabetes have a higher rate of post-operative complications in head and neck surgery

Three-dimensional printing as a tool in otolaryngology training: a systematic review

AbstractObjectiveThree-dimensional printing is a revolutionary technology that is disrupting the status quo in surgery. It has been rapidly adopted by otolaryngology as a tool in surgical simulation for high-risk, low-frequency procedures. This systematic review comprehensively evaluates the contemporary usage of three-dimensional printed otolaryngology simulators.MethodA systematic review of the literature was performed with narrative synthesis.ResultsTwenty-two articles were identified for inclusion, describing models that span a range of surgical tasks (temporal bone dissection, airway procedures, functional endoscopic sinus surgery and endoscopic ear surgery). Thirty-six per cent of articles assessed construct validity (objective measures); the other 64 per cent only assessed face and content validity (subjective measures). Most studies demonstrated positive feedback and high confidence in the models’ value as additions to the curriculum.ConclusionWhilst further studies supported with objective metrics are merited, the role of three-dimensional printed otolaryngology simulators is poised to expand in surgical training given the enthusiastic reception from trainees and experts alike.</jats:sec

Pore Scale Observations of Trapped CO2 in Mixed-Wet Carbonate Rock: Applications to Storage in Oil Fields

Geologic CO2 storage has been identified as a key to avoiding dangerous climate change. Storage in oil reservoirs dominates the portfolio of existing projects due to favorable economics. However, in an earlier related work (Al-Menhali and Krevor Environ. Sci. Technol. 2016, 50, 2727−2734), it was identified that an important trapping mechanism, residual trapping, is weakened in rocks with a mixed wetting state typical of oil reservoirs. We investigated the physical basis of this weakened trapping using pore scale observations of supercritical CO2 in mixed-wet carbonates. The wetting alteration induced by oil provided CO2-wet surfaces that served as conduits to flow. In situ measurements of contact angles showed that CO2 varied from nonwetting to wetting throughout the pore space, with contact angles ranging 25° < θ < 127°; in contrast, an inert gas, N2, was nonwetting with a smaller range of contact angle 24° < θ < 68°. Observations of trapped ganglia morphology showed that this wettability allowed CO2 to create large, connected, ganglia by inhabiting small pores in mixed-wet rocks. The connected ganglia persisted after three pore volumes of brine injection, facilitating the desaturation that leads to decreased trapping relative to water-wet systems