Duct Length Research Articles

Assessment of Inter- and Intra-Rater Reliability of Tablet-Based Software to Measure Cochlear Duct Length.

The objective of this study is to build upon previous work validating a tablet-based software to measure cochlear duct length (CDL). Here, we do so by greatly expanding the number of cochleae (n = 166) analyzed, and examined whether computed tomography (CT) slice thickness influences reliability of CDL measurements. Retrospective chart review study. Tertiary referral center. Eighty-three adult cochlear implant recipients were included in the study. Both cochleae were measured for each patient (n = 166). Three raters analyzed the scans of 166 cochleae at 2 different time points. Each rater individually identified anatomical landmarks that delineated the basal turn diameter and width. These coordinates were applied to the elliptic approximation method (ECA) to estimate CDL. The effect of CT scan slice thickness on the measurements was explored. The primary outcome measure is the strength of the inter- and intra-rater reliability. The mean CDL measured was 32.84 ± 2.03 mm, with a range of 29.03 to 38.07 mm. We observed no significant relationship between slice thickness and CDL measurement (F1,164 = 3.04; p = 0.08). The mean absolute difference in CDL estimations between raters was 1.76 ± 1.24 mm and within raters was 0.263 ± 0.200 mm. The intra-class correlation coefficient (ICC) between raters was 0.54 and ranged from 0.63 to 0.83 within raters. This software produces reliable measurements of CDL between and within raters, regardless of CT scan thickness.

Cochlear duct length and cochlear distance on preoperative CT: imaging markers for estimating insertion depth angle of cochlear implant electrode.

Preoperative estimation of the insertion depth angle of cochlear implant (CI) electrodes is essential for surgical planning. The purpose of this study was to determine the cochlear size using preoperative CT and to investigate the correlation between cochlear size and insertion depth angle in morphologically normal cochlea. Thirty-five children who underwent CI were included in this study. Cochlear duct length (CDL) and the diameter of the cochlear basal turn (distance A/B) on preoperative CT and the insertion depth angle of the CI electrode on postoperative radiographs were independently measured by two readers. Correlation between cochlear size and insertion depth angle was evaluated. Interobserver agreement was calculated using the intraclass correlation coefficient (ICC). The mean CDL, distance A, and distance B of 70 ears were 36.20 ± 1.57 mm, 8.67 ± 0.42 mm, and 5.73 ± 0.32 mm, respectively. The mean insertion depth angle was 431.45 ± 38.42°. Interobserver agreements of CDL, distance A/B, and insertion depth angle were fair to excellent (ICC 0.864, 0.862, 0.529, and 0.958, respectively). Distance A (r = - 0.7643) and distance B (r = - 0.7118) showed a negative correlation with insertion depth angle, respectively (p < 0.0001). However, the correlation between CDL and insertion depth angle was not statistically significant (r = - 0.2333, p > 0.05). The CDL and cochlear distance can be reliably obtained from preoperative CT. Distance A can be used as a predictive marker for estimating insertion depth angle during CI surgery.

Effect of expansion level on the flow development with sudden expansion at high Mach numbers

This paper reports the experimental investigation results to monitor pressure at the base and the duct's flow development. The study aims to assess the influence of favorable and adverse pressure gradient on the flow growth and control efficacy. The experimental tests were conducted at a fixed level of favorable and unfavorable pressure gradient at the nozzles for Mach 1.25 to 3.0 at various duct lengths. Only a few selected cases are considered as representative of all the possibilities. Results show that when the nozzles are under the impact of a favorable pressure gradient, they marginally affect the duct's flow development. However, when nozzles face an adverse pressure gradient, the control acts negatively, resulting in a decline in pressure. Oscillations dominate the flow for the highest pipe length, but the flow becomes smooth for lower duct length. In most cases, flow is not negatively affected by control.

Impact of expansion level on flow field of a circular duct at high Mach numbers

The study discusses the impact of different nozzle pressure ratios and the duct sizes on the duct’s flow field. The duct diameter was 16 mm, and the inertia levels at which the experiments were done are M = 1.87, 2.2, and 2.58. Dynamic regulators as an orifice stationed in the wake region at 6.5 mm from the central jet axis. At M = 1.87, when the jets are operated at NPR = 3, the duct size 1D and 2D, the wall pressure assumes high, and control is not helpful. There is no impact on the flow control management at Mach 2.2 for duct length 1D and 2D at NPR = 3, 5, and 7. But for this Mach, this trend is limited at NPR = 3 and 5. When the Mach value is 2.58, the wall pressure assumes ambient condition, and control has minimal impact on the duct’s flow pattern. When the duct length is 10D, the stream field turns oscillatory for Mach investigated. The control device does not impact the inside flow negatively.

Effect of Nozzle Performance on the Ducted Propeller: A Benchmark-Simulation Study using OpenFOAM

As the modernization of marine transportation, it should be needed the strategy to improve the marine vehicle performances. The propeller is one of the important parts which has a function as an actuator during the operation of marine transportation or vehicle. The propeller design and optimization are packages to gain the best performances, included for the ducted propeller. Since the Nozzle design is one of the crucial aspects that influences the efficiency of the propeller. In the present study, the nozzle design has been proposed by using moving the propeller location based on the percentage of duct length. The propeller and nozzle were modelled in Computer-Aided Design (CAD) program packages and was testing to predict the performance using the OpenFOAM computational fluid dynamics (CFD) with Reynold-Average Navier-Stokes (RANS) method. A Kaplan type propeller is selected with 19A duct. The ducted propeller is analyzed by the Moving Rotating Frame (MRF). The computational results are validated by comparing with the experimental value of J from 0.2 to 0.8. The reasonable results were produced such the thrust, torque and efficiency trends were in good agreement with experimental data. According to the analysis, it can be concluded that by increasing 3% the duct length of the thrust increases about 2.148%

Influence of Inlet Duct Length on the Hydraulic Performance of the Waterjet Propulsion Device

This study uses a combination of computational fluid dynamics (CFD) and experimental research to explore the influence of the length of the inlet duct on the hydraulic performance of the water jet propulsion pump device. By extending the oblique, straight, and long pipe section of the inlet duct, six sets of schemes were designed. The research results show that as the length of the inlet duct increases, the head, thrust, and inlet duct efficiency of the water jet propulsion pump first increase and then decrease, reaching the maximum value in scheme 4, but it has little effect on the efficiency of the entire water jet propulsion system. In addition, after extending the obliquely straight long pipe section of the inlet flow channel, the velocity distribution of the outlet section of the flow channel is gradually uniform, and the absolute value of the vorticity first increases and decreases, but the uniformity of the velocity distribution and the weighted average angle change little. This research enriches the research theory of the inlet duct and also provides a reference for the selection of inlet duct length and its performance optimization.

Intrauterine Low-Protein Diet Exacerbates Abnormal Development of the Urinary System in Gen1-Mutant Mice

Background: Gen1 mutation can cause various phenotypes of congenital anomaly of the kidney and urinary tract (CAKUT). An intrauterine low-protein isocaloric diet can also cause CAKUT phenotypes in offspring. However, single factors such as gene mutation or abnormal environmental factor during pregnancy can only explain part of the pathogenesis of CAKUT. Objectives: A low-protein isocaloric diet was fed to Gen1-mutant mice throughout pregnancy to establish a Gen1-mutant mouse model exposed to a low-protein isocaloric intrauterine environment. The mice were divided into 4 groups: normal (22%) protein diet (ND) + wild-type mice (CON group), ND + Gen1^PB/+ mice (Gen1^PB/+ group), low (6%)-protein isocaloric diet (LD) + wild-type mice (LD group), and the LD + Gen1^PB/+ groups. Methods: The experimental design included observing proportion and distribution of CAKUT phenotypes of neonatal mice; evaluating the number of ureteric buds (UBs) on embryonic day (E) 11.5, the location of UBs on E11.5, and length of the common nephric duct (CND); isolating embryonic kidneys on E11.5 from the Gen1^PB/+ group and culturing embryonic kidneys in medium containing 10% serum or serum-free medium to observe the branching of UBs; and detecting the p-PLCγ, p-Akt, and p-ERK1/2 in UBs and CND on E11.5, as well as the apoptosis and proliferation of tissues by immunofluorescence staining. Results: We found that the incidence of CAKUT in offspring of Gen1^PB/+ mice under an intrauterine low-protein isocaloric diet environment was significantly increased, and a duplicated collecting system was the dominant phenotype of CAKUT. During the early stage of metanephric development, ectopic protrusion of UBs may appear and lower locations of UBs in Gen1^PB/+ mice under an intrauterine low-protein isocaloric diet environment and the number of UB branches in the serum-free culture condition significantly decreased. Further examination revealed that p-PLCγ signaling and tissue apoptosis were abnormal in UBs and the CND at the early stage of kidney development. Conclusions: The aforementioned findings suggest that an intrauterine low-protein isocaloric diet can aggravate the occurrence of CAKUT in Gen1-mutant mice, which might affect key steps in the metanephric development, such as the protrusion of UBs, which might be related to mediate UBs and CND apoptosis through p-PLCγ signaling.

Evaluation of Buccal Bone Wall Thickness of Anterosuperior Teeth and Nasopalatine Duct Morphology in Cone Beam Computed Tomography of Patients Living at Different Altitudes: A Two-Year Retrospective Study.

ABSTRACTAim:To evaluate the buccal bone wall thickness of anterosuperior teeth and the dimension and morphology of the nasopalatine duct in cone beam computed tomography (CBCT) of patients treated in two cities at different altitudes.Materials and Methods:In this retrospective analytical study, 79 CBCT scans were selected from a total of 347 in Juliaca, Peru (3824 m a.s.l.) and 171 CBCT scans were selected from a total of 622 in Lima, Peru (154 m a.s.l.). The buccal bone wall thickness of anterosuperior teeth was measured at 1 mm, 3 mm, and 5 mm from the alveolar crest. For the nasopalatine duct, its length and diameter were measured, and its anatomical shape was determined in coronal view. Descriptive statistical data such as mean and standard deviation were used, and Mann–Whitney U test was used for bivariate analysis.Results:When comparing the CBCT scans from both cities, significant differences were observed in buccal bone wall thickness at 3 mm and 5 mm from the alveolar crest (P < 0.01 and P < 0.01, respectively); for men, at 1 mm and 3 mm (P = 0.04 and P = 0.04); for the age group from 33 to 47 years, at 3 mm and 5 mm (P < 0.01 and P < 0.01); and for the age group from 48 to 77 years, at 1 mm (P = 0.02). Regarding the nasopalatine duct, significant differences were observed in women in relation to length and nasal opening diameter (P < 0.01 and P < 0.01) and for men, in length (P < 0.01); for the age group from 18 to 32 years, in all three levels (P < 0.01); for the age group from 33 to 47 years, in length and diameter of the oral opening (P < 0.01 and P < 0.01); and for the age group from 48 to 77 years, in length and diameter of the nasal opening (P < 0.01 and P < 0.01). The most frequent nasopalatine duct shape was a single canal with more than 66% of cases, according to sex and age group.Conclusion:Patients living at different altitudes presented significant differences in buccal bone wall thickness according to sex and age; however, there were no differences related to dental inclination. Significant differences were found in the length and diameter of the nasopalatine duct at the nasal opening. In addition, the most frequent shape of the nasopalatine duct was the simple canal.

Research software in cochlear duct length estimation, Greenwood frequency mapping and CI electrode array length simulation.

Background and objectiveThe size of the cochlea varies a lot among the human population bringing the necessity for electrode arrays to be available in various lengths irrespective of the cochlear implant (CI) brand. This research software helps in the estimation of the patient's cochlear duct length (CDL) which is then used for the simulation of the correct length electrode array matching the patient's cochlear size and as well in getting the patient specific cochlear frequency map.MethodsVisual Studio Express 2012 for Windows Desktop is used in the architecture of this research software. The basal turn diameter of the cochlea (“A” value) needs to be measured from the pre-operative computed tomography (CT) image of the patient's temporal bone. This “A” will be taken as the input for the CDL equations proposed by Alexiades et al for estimating the CDL along the basilar membrane for various insertion depths. Greenwood's equation is then used in combination with the CDL for the full length of the cochlea in getting the patient specific frequency map.ResultsThe research software with the help of the “A” value as input, with few button clicks, gives the patient specific CDL for various insertion depths and the Greenwood's frequency map. The users have the choice to select any electrode array of their choice and place it under the frequency map to see how good it fits to that particular patient's cochlea. Also, given the possibility to drag and move the electrode array picture to mimic the post-operative actual electrode insertion depth.ConclusionsThis research software simplifies the overall process of CDL estimation and in getting the patient specific cochlear frequency map. The clinicians get the chance to simulate placing the various electrode array lengths in patient cochlea in identifying the best fit electrode. This could help in pushing the CI field into the concept of individualized CI electrode array solution that ultimately benefits the patients.

Determination of Cochlear Duct Length With 3D Versus Two-dimensional Methods: A Retrospective Clinical Study of Imaging by Computed Tomography and Cone Beam Computed Tomography.

The aim of this study was to compare three different methods for measurement of cochlear duct length (CDL) in the clinical setting for two different imaging modalities, namely computed tomography (CT) and cone-beam computed tomography (CBCT). One hundred temporal bone data sets (CT: n=50; CBCT: n=50) of non-malformed cochleae were retrospectively analyzed using three different CDL estimation techniques: 3D curved multiplanar reconstruction (cMPR), 2D cMPR and the A-value formula. The data sets belonged to 60 patients (34 males, 26 females; mean age=50.28±18.58 years). For both imaging modalities, application of the 3D cMPR estimation technique led to significantly greater mean CDL values than the two-dimensional methods (p<0.0083). The CDL measurements viewed in CT imaging software were significantly shorter than the corresponding CBCT measurements (p<0.05). Using a linear mixed model, differences in CDL by sex (p=0.796), age (p=0.377) and side of ear (p=0.690) were not significant. The 3D cMPR technique was found to provide the most accurate in vivo CDL measurement in non-malformed cochlea in both CT and CBCT imaging compared to 2D methods. The study results also suggest that the higher spatial resolution in CBCT imaging results in more precise CDL determination than in CT.

Influence of cochlear parameters on the current practice in cochlear implantation : Development of aconcept for personalized medicine.

Since the introduction of cochlear implants into clinical routine, the interest in measuring cochlear parameters, particularly the cochlear duct length (CDL) has increased, since these can have an influence on the correct selection of the electrode. On the one hand, coverage of an optimal frequency band is relevant for agood audiological result, and on the other hand, cochlear trauma due to too deep insertion or displacement of the electrode must be avoided. Cochlear implants stimulate the spiral ganglion cells (SGC). The number of SGC and particularly their distribution can also have an influence on the function of acochlear implant. In addition, the frequency assignment of each electrode contact can play adecisive role in the postoperative success, since the frequency distribution of the human cochlea with varying CDL shows substantial interindividual differences. The aim of this work is to provide an overview of the methods used to determine the cochlear parameters as well as of relevant studies on the CDL, the number and distribution of SGZ, and the frequency assignment of electrode contacts. Based on this, aconcept for individualized cochlear implantation will be presented. In summary, this work should help to promote individualized medicine in the field of cochlear implants in the future, in order to overcome current limitations and optimize audiological outcomes.

Influence of microjets on flow development for diameter ratio of 1.6 for correctly expanded nozzles

This paper aims to study the microjet’s efficacy as a management tool for the duct’s flow field. The nozzle was correctly expanded for a diameter ratio of 1.6 (i.e., area ratio = 2.56). The Mach numbers considered were from 1.25 to 2. The investigation shows that the development and recovery of the duct flow are smooth at lower Mach numbers. At Mach 1.48, jet noise was reduced considerably when the control is initiated. For higher Mach numbers of the study, namely Mach 1.6, 1.8, and 2.0, the flow’s oscillatory nature was noticed. This phenomenon reiterates that the nozzles flow is wave-dominated. For most of the flow, the flowing nature remains unaltered due to control. The flow remained connected with the duct for duct length twice the nozzle exit diameter.

Benefit of Mach number and expansion level on the flow development in a cylindrical tube diameter of 18 mm

In this paper, experiments are performed at high Mach numbers to examine the flow control effect located in the separated region at 6.5 mm from the central jet. A circular orifice is placed in the wake region to manipulate the base flow to boost the wake area's pressure and ultimately reduce the base drag. The study also investigates the impact of micro-jets on the stream of the tube. Accordingly, tests are conducted using C-D nozzles fabricated at Mach 1.87, 2.2, and 2.58. Flow generated from these nozzles is exhausted in a duct whose diameter is 18 mm. The results show that for duct length 6D and above, the flow field inside the duct becomes oscillatory, whereas such fluctuations are not noticed when duct size less than 4D. Dynamic control shows mixed trends when jets are operating at design NPR or under the impact of favorable pressure. And within reattachment length, active flow control is not able to impact the flow pattern. When nozzles are running underneath, over-expansion and flow control are initiated; it decreases the duct's pressure. The smallest duct size essential for the stream to continue connected appears to be 1D for Mach 1.87 and Mach 2.2 and 2.58; this requirement is 2D.

Pressure release characteristics of premixed hydrogen-air mixtures in an explosion venting device with a duct

The technology of explosion venting with a duct can effectively reduce the destructive effect generated from gas accidental explosion in the place of intensive industrial production, while it is not applicable to the production site designed for the technology without ducts. Since it is not clear how to quantitatively evaluate the regularity of energy release in explosion venting especially under high cracking pressure, it is still challenging on the safe application of the technology. This paper aimed to explore the basic characteristics of explosion pressure in a 20 L sphere vessel and venting duct during hydrogen explosion venting for safety design. The effects of the cracking pressure and duct length on explosion pressure at different positions were systematically analyzed according to the test of the hydrogen with different concentrations in an explosion venting device with a duct. Comparing the results of explosion pressure characteristics with experiments conducted in a device without a duct, and quantitatively analyzing the pressure release rule, manifested that the presence of the duct reduced the explosion venting efficiency to a certain extent. In the meantime, by comparing the standard NFPA 68 (Pcra ≤ 0.075 MPa, 0.1 m3 ≤ V ≤ 10,000 m3) for safety design of explosion venting devices, the extended implementation scheme with a venting duct was assessed, implying that the calculation results from NFPA 68 were relatively stable in over-scope (Pcra > 0.075 MPa, V < 0.1 m3) measurement. In future industrial productions, the design of high-pressure hydrogen venting is suggested, leaving sufficient safety margin when referring to the result.

Review on the aerodynamics of intermediate compressor duct

In a turbofan engine, the air is brought from the low to the high-pressure compressor through an intermediate compressor duct. Weight and design space limitations impel to its design as an S-shaped. Despite it, the intermediate duct has to guide the flow carefully to the high-pressure compressor without disturbances and flow separations hence, flow analysis within the duct has been attractive to the researchers ever since its inception. Consequently, a number of researchers and experimentalists from the aerospace industry could not keep themselves away from this research. Further demand for increasing by-pass ratio will change the shape and weight of the duct that uplift encourages them to continue research in this field. Innumerable studies related to S-shaped duct have proven that its performance depends on many factors like curvature, upstream compressor’s vortices, swirl, insertion of struts, geometrical aspects, Mach number and many more. The application of flow control devices, wall shape optimization techniques, and integrated concepts lead a better system performance and shorten the duct length. This review paper is an endeavor to encapsulate all the above aspects and finally, it can be concluded that the intermediate duct is a key component to keep the overall weight and specific fuel consumption low. The shape and curvature of the duct significantly affect the pressure distortion. The wall static pressure distribution along the inner wall significantly higher than that of the outer wall. Duct pressure loss enhances with the aggressive design of duct, incursion of struts, thick inlet boundary layer and higher swirl at the inlet. Thus, one should focus on research areas for better aerodynamic effects of the above parameters which give duct design with optimum pressure loss and non-uniformity within the duct.

Precise Evaluation of the Cochlear Duct Length by Flat-panel Volume Computed Tomography (fpVCT)-Implication of Secondary Reconstructions.

Flat-panel volume computed tomography (fpVCT) and secondary reconstruction allow for more accurate measurements of two-turn length (2TL), cochlear duct length (CDL), and angular length (AL). Cochlear geometry is a controversially debated topic. In the meantime, there are many different studies partly reporting highly divergent values. Our aim is to discuss the differences and to propose a radiological possibility to improve cochlear measurements using 3D-curved multiplanar reconstruction and fpVCT. Performing different image modalities and settings, we tried to find a clinically usable option that allows for a high degree of accuracy. Therefore, we tested them against reference values of high-definition micro-computed tomography. Comparison of 99 μm slice thickness secondary reconstruction of fpVCT and reference showed no significant differences for 2TL and CDL (p ≥ 0.05). Accordingly, ICC (intraclass correlation) values were excellent (ICC ≥ 0.75; lower limit of confidence interval [CI] ≥ 0.75; Cronbach's alpha [α] ≥ 0.9). Evaluating AL, there was a significant difference (difference: -17.27°; p = 0.002). The lower limit of the CI of the ICC was unacceptable (ICC = 0.944; lower limit of CI = 0.248; α = 0.990). Regarding the Bland-Altman plots, there were no clinically unacceptable errors, but a systematic underestimation of AL. Secondary reconstruction is a suitable tool for producing reliable data that allow the accurate measurement of 2TL and CDL. The option of generating these reconstructions from raw data limits the need for higher radiation doses. Nevertheless, there is an underestimation of AL using secondary reconstructions.

3D morphological classification of the nasolacrimal duct: Anatomical study for planning treatment of tear drainage obstruction.

The purpose of this study is to analyze and classify morphological features of the nasolacrimal duct (NLD) through 3D reconstruction to help understand the causes and treatment of NLD obstruction. In this study, we included 63 males and 55 females who underwent autopsy without NLD obstruction with ages ranging from 20 to 78 years. The NLD was defined from the lacrimal fossa to the opening of the BNLD to the inferior meatus, and all continuous CT images showing the NLD were selected. Segmentation was performed semi-automatically, and the reconstruction and measurement of NLD was performed using the Mimics program. Overall NLD length, bony nasolacrimal duct (BNLD) length, anteroposterior and transverse diameters at the entrance to the BNLD, anteroposterior and transverse smallest diameters of the BNLD, BNLD volume, and lacrimal sac BNLD angle were significantly higher in males than females (p < .05). BNLD direction in the coronal plane was slightly more likely to be inward. The most common type in both sexes was cylinder type (42.0%), males were more likely to have lower-thicker types (34.1%), and females more likely to have upper-thicker types (22.7%). There were sex differences in NLD measurements, and females had significantly smaller NLDs. These results may partially explain the increased prevalence of primary acquired NLD obstruction in females. The BNLD tends toward the midline, and inclines posteriorly.

Mapping Cochlear Duct Length to Electrically Evoked Compound Action Potentials in Cochlear Implantation.

Objective measurements may assist in indicating cochlear implants and in predicting outcomes of cochlear implantation surgery. Using electrically evoked compound action potentials (ECAP), information about the function of the auditory nerve can be obtained by analyzing responses to electrical stimulation transmitted and derived by the recording electrode. The aim of this study was to determine whether ECAP characteristics differ depending on the stimulated intracochlear region and the size of the cochlea. Retrospective cohort study. University Medical center, tertiary academic referral center. Patients undergoing cochlear implant surgery between 2015 and 2018. Cochlear implantation with FLEXsoft electrode arrays (length 31.5 mm, 12 stimulating channels). The cochlear duct length (CDL) and the cochlear coverage (CC) were measured using a new computed tomography-based software and correlated to the postoperative speech performance. Additionally, ECAP were measured and associated to the CDL. A total of 59 ears of 53 cochlear implant users with a mean age of 63.6 (SD 14.9) years were included. The mean estimated CDL was 35.0 (SD 2.2) mm. The mean CC was 90.3% (SD 5.5%). A total of 4,873 ECAP were measured. A statistically significant, moderate, negative correlation between the ECAP slope and the site of stimulation was found (r = -0.29, 95% confidence interval: -0.32 to -0.27, p < 0.0001). No correlation between the CC and the speech performance was found (r = -0.08, 95% confidence interval: -0.33 to 0.18 p = 0.52). ECAP slopes seem to be a reliable tool to identify the electrode's position inside the cochlea and also showed correlations to the anatomy of the patient. A combination of objective measurements such as anatomical parameters and ECAPs are helpful to assist the postoperative fitting and are promising tools to improve patient care.

Study of the Greitzer Model for Centrifugal Compressors: Variable Lc Parameter and Two Types of Surge

In this paper, the Greitzer surge model was systematically analysed with the model compressor duct length Lc as the tuning parameter. The surge phenomenon is known to induce a serious risk to centrifugal compressor operation. The two-dimensional Greitzer model is a well-established way of modelling this dangerous instability, but the determination and changes of the model parameters are still being discussed. In this paper an automated procedure determines the Lc value providing the best fit with the experimental data has been presented. The algorithm was tested on five valve positions and revealed that the best fit was obtained for different Lc values following a linear trend against the mass flow rate. The study has also shown that the Greitzer model has two solutions for a given pressure oscillation amplitude: one similar to the deep surge (low Lc) and one similar to the mild surge (low Lc). This suggests that this model can be used to simulate both types of the phenomenon known from the experimental analyses. The study proposes the dimensionless average pressure as the parameter allowing to distinguish which surge cycle was observed at a given instance. Past papers were analysed to observe the surge type that appeared in different experiments. It was found that most researchers obtained low Lc surge. The results show that both deep and mild surge could be simulated with the Greitzer model. It also revealed that the Lc should not be treated as a constant value for a given machine and that it changes with the mass flow rate.

Investigation of pressure drop in flexible ventilation ducts under different compression ratios and bending angles

Due to the large degree of freedom in terms of design and installation, flexible ventilation ducts are commonly used in ventilation systems. However, excessive use of flexible ducts may lead to greater pressure drop and higher energy consumption. This study conducted experimental measurements to characterize the pressure drop in flexible ventilation ducts with different compression ratios and bending angles. This investigation first measured the pressure drop in straight flexible ducts with four compression ratios under various airflow rates. The calculated friction factor for the straight flexible ducts was negatively associated with the compression ratio. Next, the pressure drops in single-bend flexible ducts with various bending angles from 30° to 150° were measured under various airflow rates. The calculated loss coefficient of the bend increased with the bending angle for single-bend flexible ducts. Finally, the influence of the intermediate duct length on the pressure drop across two bends was experimentally investigated. When the length of the intermediate duct was greater than eight times the inner diameter, the pressure drop across a double-bend flexible duct could be calculated from the friction factors and loss coefficients with a relative error less than 1%. The data obtained in this study can be used to calculate the total pressure loss in flexible ventilation ducting systems in buildings.