Natural convection cooling of a hot vertical wall wet by a falling liquid film

The system studied is a plane channel delimited by two vertical walls, one of which is imposed an arbitrary temperature profile and may be partially or totally wet by a liquid film, while the other is adiabatic. Air from the environment flows along the channel, driven by buoyancy forces. Its mass flow rate depends on the hydraulic resistances and on the distribution of temperature and humidity (hence, density) along the channel, which, in turn, depends on the heat and mass transfer between hot wall and humid air. Due to evaporative or boiling mass transfer, the liquid film, if present, shrinks as it descends along the hot wall, and may be completely dried out at some height. A simplified computational model of the above system was developed and applied to the prediction of relevant quantities, such as the total energy subtracted to the hot wall, for a range of conditions (hot wall temperature and its distribution; film flow rate; ambient air temperature and humidity; channel height and thickness; localized hydraulic resistance)

Fluid-structure interaction and flow redistribution in membrane-bounded channels

The hydrodynamics of electrodialysis and reverse electrodialysis is commonly studied by neglecting membrane deformation caused by transmembrane pressure (TMP). However, large frictional pressure drops and differences in fluid velocity or physical properties in adjacent channels may lead to significant TMP values. In previous works, we conducted one-way coupled structural-CFD simulations at the scale of one periodic unit of a profiled membrane/channel assembly and computed its deformation and frictional characteristics as functions of TMP. In this work, a novel fluid-structure interaction model is presented, which predicts, at the channel pair scale, the changes in flow distribution associated with membrane deformations. The continuity and Darcy equations are solved in two adjacent channels by treating them as porous media and using the previous CFD results to express their hydraulic permeability as a function of the local TMP. Results are presented for square stacks of 0.6-m sides in cross and counter flow at superficial velocities of 1 to 10 cm/s. At low velocities, the corresponding low TMP does not significantly affect the flow distribution. As the velocity increases, the larger membrane deformation causes significant fluid redistribution. In the cross flow, the departure of the local superficial velocity from a mean value of 10 cm/s ranges between -27% and +39%

Optimization of net power density in Reverse Electrodialysis

Reverse Electrodialysis (RED) extracts electrical energy from the salinity difference between two solutions using selective ion exchange membranes. In RED, conditions yielding a large net power density (NPD) are generally desired, due to the still large cost of the membranes. NPD depends on a large number of physical and geometric parameters. Some of these, for example the inlet concentrations of concentrate and diluate, can be regarded as “scenario” variables, imposed by external constraints (e.g., availability) or chosen by different criteria than NPD maximization. Others, namely the thicknesses HCONC, HDIL and the velocities UCONC, UDIL in the concentrate and diluate channels, can be regarded as free design parameters and can be chosen so as to maximize NPD. In the present study, a simplified model of a RED stack was coupled with an optimization algorithm in order to determine the conditions of maximum NPD in the space of the variables HCONC, HDIL,UCONC, UDIL for different sets of “scenario” variables. The study shows that an optimal choice of the free design parameters for any given scenario, as opposed to the adoption of standard fixed values for the same parameters, may provide significant improvements in NPD

Social geography of rhinoscleroma and qualitatively and quantitatively abnormal cell-mediated immunity

Rhinoscleroma is a progressive chronic granulomatous disease of the upper respiratory tract that may extend to the tracheobronchial tract. It is common belief that the pathology is determined by Klebsiella Rhinoscleromatis. In the authors' opinion, the infection with Klebsiella Rhinoscleromatis may not represent the only etiopathogenic factor of the disease. Rhinoscleroma is reported in many countries, but has a peculiar social and geographic distribution, in that it assumes an endemic character only in some regions of the Middle East, West Russia, North Africa, Indonesia, Central and South America. In Europe, most of the cases are reported in Poland, Hungary and Romania. In Italy, Rhinoscleroma is almost exclusively located in the southern and island regions. Rhinoscleroma is predominantly reported in rural areas, in the presence of poor socio-economic conditions, which according to many authors would be a co-factor triggering the disease. In this article, the authors review some inconsistencies in etiology, histology and epidemiology of Rhinoscleroma. Based on the overall picture, they propose that intrinsic factors, possibly of genetic origin, may give rise to the disease, and suggest possible lines of research to distinguish between extrinsic and intrinsic factors as determinants for Rhinoscleroma

Nasal pathologies in patients with obstructive sleep apnoea

Nasal obstruction is a frequent condition in patients with obstructive sleep apnoea (OSA). Nasal obstruction leads to mouth breathing, which is thought to destabilise the upper airway to aggravate the condition. Three conditions could be considered as the cause of the nasal breathing obstruction: anatomical conditions of the nose (septum deviation, hypertrophy of the inferior turbinates), chronic rhinosinusitis (CRS) and chronic nasal inflammation caused by allergic rhinitis or non-allergic cellular rhinitis. In this prospective study, we present an evaluation of all these possible rhino-sinusal aspects in OSA patients to correlate different nasal pathologies with nasal obstruction. Fifty patients with a diagnosis of OSA were enrolled in the study. In 70% of OSA patients, nasal obstruction was confirmed by clinical evaluation and rhinomanometry testing. Normal rhino-sinus aspects were present in only 20% of OSAS patients, whereas one or more pathological rhino-sinus conditions were present in the remaining 80%. The percentage of OSA patients with a diagnosis of allergic rhinitis and non-allergic rhinitis was 18% and 26% respectively. Non-allergic rhinitis with neutrophils (NARNE) was the most frequent type of cellular rhinitis diagnosed in OSA patients (20% of cases). The results of the present study support and extend the observation that rhinitis is present in OSA patients. Mucosal inflammation caused by these conditions could be the cause of upper airway patency impairment inducing nasal mucosa swellin

Cfd investigation of spacer-filled channels for membrane distillation

The membrane distillation (MD) process for water desalination is affected by temperature polarization, which reduces the driving force and the efficiency of the process. To counteract this phenomenon, spacer-filled channels are used, which enhance mixing and heat transfer but also cause higher pressure drops. Therefore, in the design of MD modules, the choice of the spacer is crucial for process efficiency. In the present work, different overlapped spacers are investigated by computational fluid dynamics (CFD) and results are compared with experiments carried out with thermochromic liquid crystals (TLC). Results are reported for different flow attack angles and for Reynolds numbers (Re) ranging from ~200 to ~800. A good qualitative agreement between simulations and experiments can be observed for the areal distribution of the normalized heat transfer coefficient. Trends of the average heat transfer coefficient are reported as functions of Re for the geometries investigated, thus providing the basis for CFD-based correlations to be used in higher-scale process models

Olfactory evaluation in obstructive sleep apnoea patients

The sense of smell has a high impact on the quality of life. The aim of the present study was to investigate olfactory dysfunction in patients with obstructive sleep apnoea syndrome (OSAS) and correlate the severity of disease with olfactory dysfunction. The relationships between nasal obstruction, nasal mucociliary cleareance and olfactory tests were also evaluated. Sixty patients with a diagnosis of OSAS were enrolled and underwent olfactory function evaluation. In all patients olfactory performance was tested with the Sniffin’ Sticks method. Mucociliary transport times and anterior rhinomanometry were performed to identify eventual nasal obstruction and deficits in nasal mucociliary clearance. Olfactory dysfunction was present in 22 (36.6%) patients of the study group: of these, hyposmia was present in 19 (86.4%) and anosmia in 3 (13.6%). The mean TDI score in the study group was 30. A strong correlation between the olfactory dysfunction and severity of sleep apnoea measured using the AHI was found. Patients with OSA would seem to have a high incidence of olfactory dysfunction. The degree of olfactory dysfunction appears to be related to the severity of disease. However, other co-factors such as nasal obstruction and reduced mucociliary clearance might also play a role in of the aetiology of this condition

CFD simulation of channels for direct and reverse electrodialysis

Flows within very thin channels, typically filled with spacers, can be often encountered in many processes such as electrodialysis (ED) and reverse electrodialysis (RED). Although the ED and the RED processes have been studied for a long time, the optimization of the fluid dynamics within the channels is still an open problem. In the present work, realized within the EU-FP7 funded REAPower project, computational fluid dynamics simulations were carried out in order to predict the fluid flow field inside a single ED/RED channel. Some different configurations were tested which includes: an empty channel, a channel provided with a spacer, and a channel filled with a purposely manufactured fiber porous medium. Two types of spacers were investigated: (1) a commercial type made of woven perpendicular filaments and (2) an overlapped perpendicular filament spacer. A sensitivity analysis concerning computational grid size and topology was performed. For the cases investigated, adopting the hybrid grids mainly composed of hexahedral volumes was found to be more reliable and less computational demanding than tetrahedral grids. As concerns the dependence of the pressure drops on the flow rate, the empty channel was found to guarantee the lowest pressure drops at a given fluid flow rate, as expected. Conversely, the woven spacer filled channel was found to provide larger pumping costs. The pressure drops along the channel filled with a porous medium even at low flow rate were very high thus suggesting that this specific configuration may be unsuitable and that further investigations should be devoted to this topic

Flow and mass transfer in spacer-filled channels for reverse electrodialysis: a CFD parametrical study

In reverse electrodialysis (RED) concentration polarization phenomena and pressure drop affect strongly the power output obtainable; therefore the channel geometry has a crucial impact on the system optimization. Both overlapped and woven spacers are commonly commercialised and adopted for RED experiments; the latter exhibit some potential advantages, such as better mixing and lower shadow effect, but they have been poorly investigated in the literature so far. In this work, computational fluid dynamics was used to predict fluid flow and mass transfer in spacer-filled channels for RED applications. A parametric analysis for different spacer geometries was carried out: woven (w) and overlapped (o) spacers with filaments at 90\ub0 were simulated, and Reynolds number, pitch to height ratio (l/h) and orientation with respect to the main flow (\u3b1=0\ub0 and \u3b1=45\ub0) were made to vary. The filament arrangement was found to be a crucial feature; for any given pumping power, higher Sherwood numbers were provided by the w-arrangement. The influence of flow attack angle and filament spacing depends on Reynolds number and filament arrangement. Only the configuration w-\u3b145 avoids the presence of poorly mixed zones near the wires. Among the cases investigated here, the configuration that provided the best mixing conditions was w, l/h=2, \u3b1=45\ub0

CFD Simulation of Mass Transfer Phenomena in Spacer Filled Channels for Reverse Electrodialysis Applications

Salinity Gradient Power via Reverse Electrodialysis is a topic of primary importance nowadays. It allows to get energy from the \u201ccontrolled\u201d mixing of solutions at different salt concentration. The performance of this technology depends on many factors such as: components properties (i.e. membranes, spacers, electrodes), stack geometry, operating conditions and feeds features. Concentration polarization phenomena may significantly affect the actual membrane potential, thus reducing the gross power produced. On the other hand, C-polarization phenomena may significantly be reduced by suitably choosing the hydrodynamic regime within the stack. Such a choice may in turn significantly require higher pumping power, thus reducing the net power output. In this work, carried out within the EU-FP7 funded REAPower project, CFD simulations were carried out in order to study the fluid flow behaviour and mass transport phenomena within spacer-filled channels for SGP-RE technology. The effect of different parameters (channel geometry, feed flow rate, feed solution concentration and current density) on concentration polarization was assessed. The well known unit cell approach was adopted for the simulations in order to reduce their computational requirements as well as to increase the level of detail. Results show that the electrical potential loss due to polarization phenomena should be regarded as little significant in the case of seawater-brine for the operating conditions and geometrical configurations investigated. Conversely, a great attention should be devoted to such phenomena when very diluted solutions are to be employed (e.g. river water)