Airflow Resistance Research Articles

Experimental investigation of a part air dehumidification cascade-like heat pump drying system

• A part air dehumidification heat pump drying system was proposed and investigated. • The thermal characteristics of the PADHPD were tested. • The improvement of the new HPD system was verified. • The maximum exergy loss occurred in the evaporator for each HPU. • Decreasing the airflow resistance is vital to improve performance of PADHPD system. In the cascade-like heat pump drying system, there are contradictions between the low air flow rate for dehumidification and high air flow rate for anti-overpressure. In order to resolve those contradictions, a new PADHPD (part air dehumidification heat pump drying) system was proposed in this work. A PADHPD system used in the industrial production was designed and manufactured. The thermodynamic performance of this was tested and simulated. The air temperature and humidity in the drying system and the thermal parameters of the HPUs (heat pump units) were analyzed. The hawthorn cake was taken as the drying material. According to the estimation from the experimental results, the average COP (coefficient of performance) of the heat pump system is 3.58 with the average SMER (specific moisture extraction rate) of 2.282 kg kW −1 h −1 when the average temperature and RH (relative humidity) of supplied air is 63.1°C and 20.2 %, respectively. EER (energy efficiency ratio) of the system is 2.68 but SMER is 1.792 kg kW −1 h −1 after the electric energy consumed by circulating fans being considered. Exergy analyses shows that it is necessary to reduce the irreversible loss in the evaporator because it represents the largest exergy loss for each HPU.

On the Dependence of Acoustic Pore Shape Factors on Porous Asphalt Volumetrics

The sound absorption of a road pavement depends not only on geometric and volumetric factors but also on pore shape factors. In turn, pore shape factors mainly refer to thermal and viscous factors (i.e., thermal and viscous effects that usually occur inside porous materials). Despite the presence of a number of studies and researches, there is a lack of information about how to predict or estimate pore shape factors. This greatly affects mixture design, where a physical-based or correlation-based link between volumetrics and acoustics is vital and plays an important role also during quality assurance and quality control (QA/QC) procedures. Based on the above, the objective of this study is to link mixture volumetrics and pore shape factors. In particular, 10 samples of a porous asphalt concrete were tested in order to estimate their thickness, air voids content (vacuum-sealing method, ASTM D6857/D6857M), sound absorption coefficient (Kundt’s tube, ISO 10354-2), airflow resistivity (ISO 9053-2), and permeability (ASTM PS 129). Subsequently, two models (herein called STIN and JCAL) were used to derive both volumetrics and pore shape factors from the estimated parameters listed above, and statistical analysis was carried out to define correlations among the parameters and models performance. Results confirm the complexity of the tasks and point out that estimates of the pore shape factors can be derived based on mixture volumetrics. Results can benefit researchers (in acoustic and pavement mixtures) and practitioners involved in mix design and pavement acceptance processes.

Spontaneous polarization induced electrostatic charge in washable electret composite fabrics for reusable air-filtering application

The performance of disposable face masks in blocking pathogenic microbes mainly relies on the ability of melt-blown fabrics to electrostatically adsorb air droplets. While their easy invalidity in electrostatic effect highly limits their use recyclability, leading to a heavy burden on the surrounding environment due to their decomposing difficulty. Thus, it is urgent to develop reusable air filtration fabrics. In this work, we report a washable electret air-filtering fabrics with negligible cytotoxicity by combining spontaneous polarizing photochromic molecule with electrospinning electret technology. The electrostatic charge and filtration efficiency of the composite fabrics were highly improved compared to the commercial polypropylene melt-blown fabrics. Moreover, due to its electrostatic charge induced by self-polarization, the photochromic Spiropyran(SP)/polystyrene(PS) electret fabrics can maintain high filtration performance (over 95%) towards PM0.3 particles and low air flow resistance (<343.2 Pa) even after 5 times of washing (by 75% ethanol)/drying cycles. The combination of self-polarization photochromic molecule and electret material with negligible toxicity would create high-performance reusable air filtering fabrics, thereby SP/PS composite fabrics have a potential application in eco-friendly recyclable air purification and isolation and protection of pathogenic microbes.

Investigation of airflow characteristics under parallel fan conditions in a block cave mine

ABSTRACT Block caving is an efficient underground mining method for extracting massive and low-grade ore deposits, which are too deep for traditional open-pit mining. However, in the case of orebodies with uranium mineralization, the extraction of broken rock from drawpoints will bring harmful radon gas into working areas. Airborne diesel particulate matter and dust produced from mining activities also contribute to the emissions on the production level. Maintaining relatively negative pressure in the cave by installing exhaust fans is one of the most effective approaches to mitigate gas emission concerns. The selection of proper fan systems is highly related to airflow behavior within the cave. Due to the dynamic caving process and complex cave structure, estimation of cave airflow resistance through field studies is difficult. This study developed a 1:100 scaled experimental and numerical model to investigate the effects of cave parameters (cave porosity, particle size, and undercut structure) on airflow resistance under parallel fan conditions. Results showed that cave airflow resistance increases with decreasing cave porosity and particle size; cave airflow behavior is significantly affected by undercut drift closure and the use of additional fans. This study provides valuable information to optimize ventilation system design in block cave mines.

A STUDY TO ASSESS KNOWLEDGE REGARDING DEEP BREATHING EXERCISE AMONG THE CHRONIC OBSTRUCTIVE PULMONARY DISEASE PATIENTS

Chronic obstructive pulmonary disease (COPD) is an inflammatory disease of airways which is irreversible airway disease characterized by emphysema and chronic bronchitis which results to increase airflow resistance leading to breathlessness, cough and sputum. Deep breathing exercise minimizes dyspnoea, improve oxygenation and maintain normal respiratory rate. A study was undertaken to assess the knowledge regarding Deep breathing exercise among the Chronic Obstructive Pulmonary Disease patients Objectives: To assess the knowledge of deep breathing exercise among COPD patient, to determine the association of level of knowledge scores regarding deep breathing exercise with their selected demographic variable. Method: A total of 100 patients were enrolled using convenient sampling in this cross sectional study. Structured questionnaire was used to collect data from the subjects Result: The study findings shows that majority 66% had inadequate knowledge, followed by 23% had moderate knowledge and 11% had adequate knowledge regarding deep breathing exercise among the COPD patients. In the present study there is a significant association between demographic characteristics namely; History of exposure to smoke, Duration of exposure to pollutants, Duration of Illness (p&lt;0.05) and remaining characteristics are not significant (p&gt;0.05) Conclusion: This study showed the Chronic Obstructive patients have inadequate knowledge regarding deep breathing exercise.

Swim performance with and without snorkel and the underlying energetic differences

Swimming requires frequent lifting and rotating of the head to inhale. A snorkeler saves energy by avoiding this maneuver, but the snorkel adds breathing work due to air flow resistance. The needed power of these head movements has never been examined, although the extra power of breathing through a snorkel was studied recently. This study aimed: 1) to model the work of vertically lifting and rotating in comparison with the breathing work added by a snorkel; 2) to compare heart rate (HR) and velocity (v) while swimming under both conditions; 3) to evaluate the results for surface-swimming divers. Presumably the power when using a snorkel is less, and the difference in power predicts the difference in swimming velocity. Kinematics of head lifting and rotation, and the difference between the hydrodynamics were modeled. A swim test lasting 12 minutes at maximum speed (Cooper swim test) was performed in a pool by nine recreational divers in the front crawl style, with face mask but without fins. All subjects performed the test both with and without snorkel. The average velocity with a snorkel, 0.72±0.09 m∙s-1, was 4.4±3.9% higher than without (p=0.008), but HR (144±16 bpm) showed no difference (0.8±3.4%). The model based on our subjects’ performance showed that 7.5% of the total power is spent in the inhaling maneuver while crawling and 2.7% while snorkeling. Theoretically this would allow the snorkeler to swim 5.2% faster. It is concluded that snorkeling is energetically advantageous as well as for divers swimming on the surface.

Comparison of Experimental and Empirical Approaches for Determination of Sound Absorption Properties of Bagasse and Cornhusk Fibers

ABSTRACT The significant physical, economic and environmental properties of some agricultural wastes have made them viable alternatives for the conventional sound-absorbing materials. Therefore, it is necessary to identify these types of agricultural wastes and investigate the acoustic behavior and applicability of mathematical predictive models for sound absorption of the samples fabricated from such wastes. In this regard, this study was conducted to investigate the sound absorption coefficient (SAC) values of the samples made from sugarcane and corn husk wastes using experimental and empirical methods. The morphological examination of sugarcane and corn husk fibers was performed by Field emission scanning electron microscopy (FESEM). Having prepared the fibers, several cylindrical samples with a constant density (150 kg/m3) and different thicknesses (20, 30 and 40 mm) were fabricated. The SAC values, porosity and airflow resistivity of these samples were then measured using ISO 10534–2 (impedance tube system), SEM and ASTM C522–03, respectively. The Delany-Bazley (DB) analytical model and the reversed Delany-Bazley model with Nelder-Mead Simplex (DB-NMS) were also used to predict the SAC values. Based on the acoustic performance of the fabricated samples, the SAC values for the thickness of 40 mm and frequency of 500 Hz were, respectively, 0.42 and 0.54 for sugarcane and corn. Increasing the thickness of the samples and creating an air gap behind them were found to be the acceptable approaches for improving the sound absorption. It was found that the DB-NMS model would appropriately follow the experimental results. The purposeful application of agricultural waste and analytical acoustic models because of their outstanding benefits and an effective approach will encourage the usability of natural materials (as eco-friendly, cheap and efficient acoustic products) in indoor and outdoor commercial applications.

Estimation of sound absorption coefficient of composite structured aluminum foam by radial basis function neural network

In order to better understand the acoustic performance of composite structured open-cell aluminum foam in the low and medium frequency bands, this paper presents a method for predicting the absorption coefficient of a given structure in the low and medium frequency bands using radial basis function (RBF) neural networks. The method uses a number of easily measurable structural parameters to obtain the sound absorption coefficient of composite structural aluminum foam and then compares the predictions with those of two conventional transfer matrix methods (TMM). Therefore, in the experimental part, 165 composite structured open-cell aluminum foams were, firstly, designed using three different thickness of aluminum open-cell foam with a density of 0.914 kg/m3 and three different thickness of aluminum open-cell foam with a density of 0.711 kg/m3. Next, the two main structural parameters of airflow resistivity and porosity of each layer were measured as inputs to the radial basis function neural network. Seventeen of these data sets were then used as a test set to compare the results of the absorption coefficients with the experimental values of the other two numerical models at 10 low frequency frequencies, respectively. Finally, a maximum root mean square error of 0.023, and a mean root mean square error of 0.012 were derived using radial basis function neural networks, which were numerically much lower than the other two TMM models, and RBF had higher accuracy, indicating that the method was effective.

Comparison of Subjective and Objective Success of Septoplasty in Patients with Nasal Septum Deviation: A Before and After Study

Objective: Aim of the study is to evaluate the subjective outcomes and objective outcomes postoperatively and investigate correlations between these measurements. Material and Methods: This prospective before and after surgical study was conducted with patients admitted with symptomatic nasal septum deviation (NSD) and who underwent Cottle’s septoplasty. Morphometric diameters of the nasal cavity were measured using a multi-detector computed tomography. Preoperative and postoperative one-month Nasal Obstruction Symptom Evaluation Scale (NOSE) score, acoustic rhinometry (AR), and anterior active rhinomanometry (AAR) measurements were used to evaluate the success of surgery. The correlations between these measurements were also evaluated. Results: The study population consisted of 30 patients, including 19 males and 11 females, with a median age of 27.5 years. There was a statistically significant difference between pre and postoperative NOSE scores, with a mean difference of 53.17 points (p&lt;0.001). There were statistically significant differences between pre and postoperative AR parameters of both the deviated side (DS) and non-deviated side (NDS) of the nose both before and after decongestion. There were statistically significant improvements in all postoperative airflow and airway resistance parameters of the DS of the nose before decongestion when compared to preoperative measurements. There were moderate to large positive correlations between morphometric diameters and differences in NOSE score. Further, there were several statistically significant correlations between differences in AR and AAR measurements and differences in NOSE score. Conclusion: Our findings showed that the objective measurements are strongly correlated with the NOSE score.

Experimental Study on the Ventilation Resistance Characteristics of Paddy Grain Layer Modelled with Response Surface Methodology

The ventilation resistance of air flow through rice grain layers is one of the key parameters affecting drying uniformity as well as the energy consumption of the drying process. In order to reveal the variation of characteristics of the ventilation resistance with paddy grain moisture content, the air velocity and the bed layer depth are needed. A second order model was fitted to pressure drop using the response surface methodology and the results are compared with those of the Ergun model. The results showed that the pressure drop increases with the increase of paddy grain moisture content, air velocity and the bed layer depth, and the interactions between the air velocity and the bed layer depth have the most significant influence on the pressure drop. Moreover, a second-order polynomial pressure drop model based on RSM was established and compared with the Ergun model. The results showed that the pressure drop model established by RSM is similar to that of the Ergun model.

Warmth Property of Clothing Assembly - Part III: Theoretical Approach for Calculating the Warmth Parameters of Clothing Assembly. (Dept. T)

The present work deals with the theoretical prediction of warmth parameters of clothing assembly. Theoretical expressions are derived for calculating both air flow resistance and thermal resistance of clothing assembly. Three different cases which represent the most common wearing cases in winter season were selected for applying the theoretical expressions. The derived relations were found to be fairly close to those observed experimentally. Also an empirical relationship is fitted to the measured thermal resistance data of clothing assembly using stepwise multiple regression analysis. The regression analysis relates the thermal resistance of the clothing assembly to the parameters of weight per unit area, thickness and air resistance. This empirical relationship is shown to predict the thermal resistance of clothing assembly accurately.

Indirect determination of airflow resistance of textiles with reference samples

Airflow resistance is a non-acoustic parameter of great relevance in the acoustic characterization of porous materials. It is used in several sound absorbing material prediction models and it is also a control parameter for acoustic conditioning and insulation in different building solutions. The ISO 9053 standard defines several methods to obtain it, using both direct measurements and indirect techniques. However, both procedures may involve problems related to the placement of the textile samples in the tube or to the stability of the samples during testing. In this work, the use of reference materials to stabilize the measurement of thin materials is proposed. Airflow resistance results obtained for different materials in an impedance tube are presented. The tests have been carried out by following the Ingard &amp; Dear method, as an indirect technique accepted by the standard. Several material compositions with a wide range of airflow resistance values have been analyzed with different reference materials.

Effect of fiber cross-section on the transport and acoustic properties of fibrous materials

Fibrous materials can efficiently dissipate acoustic energy, and their intrinsic properties are determined by fiber geometries (microscale). In this study, the effect of cross-sections of fibers on the transport and acoustic properties of fibrous materials was investigated. First, fibers of various cross-sections were modeled by adjusting their open porosity. The representative elementary volumes of fiber structures were generated to describe the periodic unit-cell structures. Next, the transport properties (such as static airflow resistivity, high-frequency limit of the dynamic tortuosity, viscous characteristic length, thermal characteristic length, and static thermal permeability) of fibrous materials were calculated by solving numerical problems using the finite element method. These properties of fibrous materials with complex cross-sections were compared with those with circular cross-sections. Finally, the sound absorption coefficients were predicted using the Johnson-Champoux-Allard-Lafarge (JCAL) model and rigid frame approximation, and the differences in sound-absorbing behavior were analyzed. This study can provide insights into the design of lightweight fibrous materials while maintaining optimal sound absorption performance.

How small-scale variation in mineral wool products effect random incidence sound absorption

Mineral wool products are produced by creating a spray of fibres, that is collected and made into slabs. This randomized spray can lead to small variations across a slab. Nevertheless, mineral wool slabs are often treated in acoustics as locally reacting perfectly homogeneous, isotropic materials. This means that small-scale characterisations are extrapolated to large-scale without considering the impact from possible variations in a large-scale setup. The question is how the small-scale characterisations should be used for large-scale setups with this in mind. Three products with the same thickness and density, but with significantly different specific airflow resistances were selected for random incidence sound absorption tests. The products were all specially made ceiling tiles and measurements were conducted in E200 setup according to ISO 354:2003. The tiles were gradually exchanged in a random fashion, so measurement results were obtained using a combination of tiles with different specific airflow resistances. Results showed a surprisingly linear relation between the sound absorption and the average specific airflow resistance of tiles used in the measurements. The results point to that variations in products must be observed, but also that small variations in specific airflow resistance in standardized products are insignificant.

Polyvinyl alcohol/silver electrospun nanofibers: Biocidal filter media capturing virus-size particles.

In response to the nowadays battle against SARS‐CoV‐2, we designed a new class of high performant filter media suitable to advance the facemask technology and provide new efficient widespread solutions against virus propagation. By means of the electrospinning technology we developed filter media based on polyvinyl alcohol (PVA) nanofibers doped with AgNPs combining three main performance requirements: high air filtration efficiency to capture nanometer‐size particles, low airflow resistance essential to ensure breathability and antimicrobial activity to inactivate aerosolized microorganisms. PVA/AgNPs electrospun nanofibers were produced by electrospinning the dispersion of colloidal silver into the PVA water solution. A widespread physicochemical characterization was addressed to the Ag colloidal suspension. The key functional performances of the electrospun nanofibers were proven by water stability, antibacterial activity, and filtration efficiency and pressure drop measurements performed under conditions representative of facemasks. We assessed a total bacterial depletion associated to a filtering efficiency towards nano‐aerosolized particles of 97.7% higher than required by the EN149 standard and a pressure drop in line with FFP1 and FFP2 masks, even at the highest filtration velocity. Such results pave the way to the application of PVA/AgNPs electrospun nanofibers in facemasks as advanced filtering media for protecting against airborne microorganisms.

High-Temperature and Low-Frequency Acoustic Energy Absorption by a Novel Porous Metamaterial Structure

In this paper, we propose a novel porous metamaterial structure with an improved acoustic energy absorption performance at high-temperature and in the low-frequency range. In the proposed novel porous metamaterial structure, a porous material matrix containing periodically perforated cylindrical holes arranged in a triangular lattice pattern is applied, and additional interlayers of another porous material are introduced around these perforations. The theoretical model is established by adopting the double porosity theory for the interlayer and the cylindrical hole which form an equivalent inclusion and then applying the homogenization method to the porous metamaterial structure formed by the equivalent inclusion and the porous matrix. The temperature-dependent air and material parameters are considered in the extended theoretical model, which is validated by the finite element results obtained by COMSOL Multiphysics. The acoustic or sound energy absorption performance can be improved remarkably at very low frequencies and high temperature. Furthermore, the underlying acoustic energy absorption mechanism inside the unit-cell is investigated by analyzing the distribution of the time-averaged acoustic power dissipation density and the energy dissipation ratio of each constituent porous material. The results reveal that regardless of the temperature, the acoustic energy is mostly dissipated in the porous material with a lower airflow resistivity, while the acoustic energy dissipated in the porous material with a higher airflow resistivity also becomes considerable in the high-frequency range. The novel porous metamaterial structure proposed in this paper can be efficiently utilized to improve the acoustic energy absorption performance at high temperature.

Determination of the permeability coefficient and airflow resistivity of nonwoven materials

Air penetration behavior plays a vital role in the performance of fibrous material in various industrial applications. Two parameters, the permeability coefficient and airflow resistivity, can describe the air penetration behavior of fibrous material. FX 3300 Textech Tester III and AFD300 AcoustiFlow devices were used to respectively characterize the permeability coefficient and airflow resistivity of nonwoven materials. Nonwoven samples were compressed due to the load from the test head of the FX 3300. Finite element analysis along with the mathematical method were implemented to recover the airflow permeability of samples at the uncompressed state. The effects of pressure drop on the airflow velocity and permeability coefficient were analyzed by the Ergun-type model. The determination of airflow resistivity based on the permeability coefficient is carried out via two approaches, that is, the direct method and the extrapolation method. The results show that the airflow velocity is not linearly related to the pressure drop, which differs from Darcy's law. This non-linear relation is mainly attributed to the influence of frictional loss. By comparing the relative error between assessed and measured airflow resistivity, most of the assessed values of the compressed samples are overestimated. The results also suggest that the direct and extrapolation methods are applicable to assess airflow resistivity on an airflow velocity (or air permeability) test device. Moreover, the Ergun-type model is also applicable to determine the permeability coefficient and airflow resistivity of nonwoven materials.

Evaluation of Nasal Function and Upper Airway Morphology After Bi-Maxillary Surgery Using Rhinomanometry and Computed Tomography.

This study was performed to evaluate changes in nasal airflow, nasal airway resistance, nasal cross-sectional area, pharyngeal horizontal area, nasopharyngeal and oropharyngeal volume following Le Fort I osteotomy (L1) impaction with sagittal split ramus osteotomy (SSRO) in classes II and III. The subjects consisted of 35 patients (6 males and 29 females, 70 sides) 17 of which were diagnosed as class II and 18 as class III who underwent L1 and SSRO. Nasal airflow and resistance were measured using the rhinomanometry system (GM NR-6 EXECUTIVE) before and at 1 and 6 months after surgery. Nasal, cross-sectional area, and volume were measured using a 3-dimensional computed tomography respectively, before and 1-year after surgery. Although a significant decrease was found in nasal volume after surgery (P = 0.0042), there was no difference between before and after surgery in the nasal airway resistance in class II.A significant decrease in nasal volume was found after surgery (P = 0.0005) and there were no postoperative changes in both nasal airflow and resistance in class III. The study suggested that L1 impaction with SSRO did not worsen nasal function such as nasal airflow and nasal airway resistance, although nasal volume significantly decreased in both groups.

What is the impact of distraction osteogenesis on the upper airway of hemifacial microsomia patient with obstructive sleep apnea: a case report

BackgroundCurrent research about hemifacial microsomia (HFM) patients after distraction osteogenesis (DO) most emphasize the morphologic changes. This case report shows the outcome of DO on the upper airway of a HFM patient with obstructive sleep apnea (OSA) based on the use of computational fluid dynamics (CFD).Case presentationAn 11-year-old boy was diagnosed as HFM with OSA, and underwent unilateral DO. Polysomnography and CT scans were performed before and 6 months after treatment. After DO, lowest blood oxygen saturation increased from 81% to 95% and apnea and hypopnea index decreased from 6.4 events/hour to 1.2 events/hour. The oropharynx and nasopharynx were obviously expanded. We observed apparently increased average pressure, decreased average velocity and pressure drop in all cross-sections, and largely decreased airflow resistance and maximum velocity entirely in the airway.ConclusionsThe results suggest that DO might be effective for the treatment of OSA by expanding the upper airway and reducing the resistance of inspiration.

A hybrid approach for modelling the acoustic properties of recycled fibre mixtures for automotive applications

The acoustic modelling of fibrous materials is fundamental for the design of a sound-absorbing acoustic treatment. Several analytical formulas have been proposed to calculate the acoustic performance of materials made of fibres with a homogeneous diameter and a mono, bi, or three-dimensional distribution, while only a few studies have been carried out on materials made up of a mixture of fibres with non–homogeneous diameter. Fibrous materials for automotive applications, developed both for acoustic and thermal applications, are commonly obtained by moulding mixtures of recycled fibres of different nature, bonded together and compacted with a wide range of variability in density and thickness. The acoustic modelling of the mixtures is thus relevant for the simulation of the performance of the final component.The main goal of the study was to determine the physical properties of a given mixture of fibres to compute its acoustic performance, based on the knowledge of the characteristic of each kind of fibre in the blend composition. A homogenisation process is proposed to determine the effective density and radius of a given mixture according to its composition and the characteristics of each kind of fibre. The normal incidence sound absorption coefficient of the investigated mixtures was computed according to the Johnson-Champoux-Allard-Lafarge (JCAL) model, by using the physical parameters, analytically computed from the effective properties of the mixture, as input data. The reliability of the approach was validated by comparing the computed results with the experimental airflow resistivity and the normal incidence sound absorption coefficient measured for five different fibre mixtures, at different compression rates.