Augmentation of convection heat transfer from a horizontal cylinder in a vented square enclosure with variation of lower opening size

Natural and mixed convection heat transfer from a horizontal cylinder placed in a vented square enclosure has been investigated using numerical method with ANSYS Fluent 16.1 software for laminar and turbulent flow. Navier- Stokes equations and energy equation with standard k-? transport equation turbulence model have been used to simulate both flow and thermal behaviors. The operating conditions covered a range of the Rayleigh number from 103 to 106 and the Richardson number range between 0.1 and 100 at variable sizes of the lower open vent with constant upper opening size. The Nusselt numbers, velocity lines and isotherms are presented to display the flow and thermal behaviors. The results displayed that the average Nusselt number is affected by Rayleigh number, Richardson number, enclosure width and lower opening size. The Nusselt number is enhanced by controlling the lower opening size. The maximum enhancement range for Nusselt number is between 20-85% depending on the Rayleigh number, Richardson number, enclosure width to cylinder diameter, and lower opening size. The velocity lines and isotherms are directly affected by the Rayleigh number, Richardson number, enclosure width to cylinder diameter, and lower opening size.

Risk factors for developing subdural hematoma: a registry-based study in 1457 patients with shunted idiopathic normal pressure hydrocephalus

OBJECTIVESubdural hematomas and hygromas (SDHs) are common complications in idiopathic normal pressure hydrocephalus (iNPH) patients with shunts. In this registry-based study, patients with shunted iNPH were screened nationwide to identify perioperative variables that may increase the risk of SDH.METHODSThe Swedish Hydrocephalus Quality Registry was reviewed for iNPH patients who had undergone shunt surgery in Sweden in 2004–2014. Potential risk factors for SDH were recorded preoperatively and 3 months after surgery. Drug prescriptions were identified from a national pharmacy database. Patients who developed SDHs were compared with those without SDHs.RESULTSThe study population consisted of 1457 patients, 152 (10.4%) of whom developed an SDH. Men developed an SDH more often than women (OR 2.084, 95% CI 1.421–3.058, p < 0.001). Patients on platelet aggregation inhibitors developed an SDH more often than those who were not (OR 1.733, 95% CI 1.236–2.431, p = 0.001). At surgery, shunt opening pressures had been set 5.9 mm H2O lower in the SDH group than in the no-SDH group (109.6 ± 24.1 vs 115.5 ± 25.4 mm H2O, respectively, p = 0.009). Antisiphoning devices (ASDs) were used in 892 patients but did not prevent SDH. Mean opening pressures at surgery and the follow-up were lower with shunts with an ASD, without causing more SDHs. No other differences were seen between the groups.CONCLUSIONSiNPH patients in this study were diagnosed and operated on in routine practice; thus, the results represent everyday care. Male sex, antiplatelet medication, and a lower opening pressure at surgery were risk factors for SDH. Physical status and comorbidity were not. ASD did not prevent SDH, but a shunt with an ASD allowed a lower opening pressure without causing more SDHs.

Fatigue Degradation of the Structure of Parachute Systems

Parachute systems are in widespread use in aviation. Up to now, parachutes are the most uncertain air vehicles because of their complex and unsteady opening characteristics, changes in geometry up to 30% and vulnerability from unsteady atmospheric turbulence. Fatigue is a problem that the designers of long living parachute systems need to cope with. Authors demonstrate complexity of parachute exploitation and means to lower opening forces and extend service life without influencing safety.

The effects of CO2 on organic groups in bituminous coal and high-rank coal via Fourier transform infrared spectroscopy

The interactions between supercritical CO2 and coal and their effects on changes in the coal pore structure and organic groups play a critical role in the CO2 geological storage-enhanced coalbed methane recovery. To investigate the effects of supercritical CO2 on organic groups in coals of different ranks and its mechanisms under different temperature and pressure conditions, CO2 sequestration processes in bituminous coals and high-rank coals were replicated using a high-pressure reactor. Four coal samples of different ranks were exposed to supercritical CO2 and water under three temperatures and pressures for 240 h. Fourier transform infrared spectroscopy was used to provide semiquantitative ratios and Fourier transform infrared spectra of coal samples before and after the supercritical CO2–H2O treatment. The results show that interactions between supercritical CO2 and coal were controlled by the coal macromolecular structure, and semianthracite is the inflection point of interaction characteristics for coal samples of different ranks. Bituminous coal, including high- and low-volatility bituminous coal, has a low degree of condensation of its aromatic structure, and its aromatic nuclei can facilitate addition reactions. Swellings primarily break cross-links between aromatic nuclei in the same aromatic layer. These characteristics favor the polymerization addition of aliphatic side chains of aromatic nuclei, causing an increase in the degree of condensation of the aromatic structures in bituminous coal. High-rank coals including semianthracite and anthracite have a high degree of condensation of their aromatic structures, and the aromatic nuclei favor substitution reactions. Swellings primarily break cross-links connecting different aromatic layers, and bond dissociation reactions and sulfuration reactions are more significant for high-rank coal. These characteristics cause a decrease in the degree of condensation of the aromatic structure in high-rank coal. Temperature and pressure have a great impact on interactions between supercritical CO2 and coal and are controlled by the reaction types of the organic groups. With the increase in experimental temperature and pressure, the changes in the organic group content can be classified as the descending type, the rising type, the lower opening parabola type, and the upper opening parabola type. 45.0°C and 10 MPa is the inflection point of the changes in the organic group content. Descending- and rising-type changes favor addition, bond dissociation, and sulfuration reactions, which are endothermic. The reaction rate of supercritical CO2 and the organic groups increases, and the effects caused by temperature and pressure decrease as the temperature and pressure increase. Lower opening parabola- and upper opening parabola-type changes favor substitution, oxidation, and addition polymerization reactions, which are exothermic. These changes were significantly affected by a variety of reactions and were suppressed by high temperature and pressure. When the temperature is ≤45.0°C and the pressure is ≤10 MPa, supercritical CO2 has remarkable effects on alkyl and hydroxy groups and has a stronger effect on bituminous coal. When the temperature is >45.0°C and the pressure is >10 MPa, supercritical CO2 has remarkable effects on oxygen- and sulfur-containing groups and has a greater effect on high-rank coals.

The discharge plume parameter and its implications for an emptying–filling box

The natural ventilation flow driven by an internal buoyant plume in a box involving an upper opening (vent) located at the ceiling (for the outflow) and a large lower opening at the floor (for the inflow) is examined theoretically in a general non-Boussinesq case. Analytical solutions of this emptying–filling box problem allow the characteristics of the flow at the vent to be determined. From these characteristics, a non-dimensional parameter $\unicode[STIX]{x1D6E4}_{d}$ (called the discharge plume parameter) is expressed. This parameter characterizes the initial balance of volume, buoyancy and momentum fluxes in the plume-like flow that forms above the vent. We then note that the value of $\unicode[STIX]{x1D6E4}_{d}$ allows the buoyant fluid layer depth in the box to be estimated, which is a new and interesting result for natural ventilation problems. Following previous experimental results, the decrease of the vent discharge coefficient $C_{d}$ when $\unicode[STIX]{x1D6E4}_{d}$ increases is discussed and a theoretical model based on plume necking is proposed. The emptying–filling box model is then extended for a variable $C_{d}$ (depending on $\unicode[STIX]{x1D6E4}_{d}$). Even though the discharge coefficient may be markedly reduced at high values of $\unicode[STIX]{x1D6E4}_{d}$, our results show that this only affects transients and the steady state of an emptying–filling box for relatively thin buoyant fluid layers.

Congenital First Branchial Fistula: Study of 10 Cases

Congenital auriculocervical fistula is a rare occurance and reporting of the challeges in diagnosis andmanagement is not common. Ten cases of congenital first branchial fistula were reviewed. Of these, 8underwent fistulectomy with facial nerve dissection and partial parotidectomy and 2 underwent simplefistulectomy. The inner openings (upper opening) of fistulae lay in the following sites: inferioposterior wallat the junction of cartilaginous and bony segments of the auricular canal and inferior wall of cartilaginousauricular canal. The outer openings (lower opening) lay along the anterior border of uppersternocleidomastoid muscle, at the mastoid tip and posterior to the mandibular angle. Complete fistulaeresection was achieved in all but not one case. Eight cases were followed for 5 year with no recurrence.Recurrence occurred in 1 case 6 months after the primary surgery and revision surgery was performedConclusions Pre-operative radiography for the location and course of the fistula is crucial for successfulfistula resection, especially in cases with past infections. Facial nerve dissection should be done routinelyfor deeply located fistulae.

Numerical Simulation of Smoke Movement in Vertical Shafts during a High-Rise Building Fire

A numerical study on the smoke flow in a shaft, representing the stairwells, the elevator shafts and warehouses, is conducted during a high-rise building fire. It is of vital importance to predict the movement of smoke throughout the tall structure, because smoke is the major and leading cause of fatalities. The stack effect takes place due to the temperature differences between the smoke in shafts and the environment. The cold air enters in at a lower opening and exhausts at a higher ones, and this leads to the concept of the horizontal elevation called the neutral pressure plane, where the air flow equals zero. The location of neutral plane plays a key role on the management of smoke. The numeral results obtained with the FDS (Fire Dynamic Simulator) illustrate how the smoke movement can be managed in order to mitigate dangerous conditions within the structure.