Augmentation of Heat Transfer in a Circular Channel with Inline and Staggered Baffles

This numerical investigation presents the effects of the position of baffles in the shape of a circle’s segment placed inside a circular channel to improve the thermal and flow performance of a solar air heater. Three different baffles’ positions with Reynolds number varying between 10,000 to 50,000 were investigated computationally. The k-omega SST model was used for solving the governing equations. Air was taken as the working fluid. Three pitch ratios (Y = 3, 4, and 5) were considered, while the height of the baffles remained fixed. The result showed an enhancement in Nusselt number, friction factor, j-factor, and thermal performance factor. Staggered exit-length baffles showed maximum enhancement in heat transfer and pressure drop, while inline inlet-length baffles showed the least enhancement. For a pitch ratio of Y = 3.0, the enhancement in all parameters was the highest, while for Y = 5.0, the enhancement in all parameters was the least. The highest thermal performance factor of 1.6 was found for SEL at Y = 3.0.

Profiling of sudden contraction of circular pipe by sharp-edged pipe insert

Measures to reduce energy losses in pipeline transport systems must be implemented already at the design stage. In particular, this also applies to local resistances of pipelines. For symmetrical sudden pipe contraction, one of such measure is profiling using insert. The paper considers a sharp-edged pipe insert, which in comparison with others has larger areas of flow separation. The diameter of the insert was calculated as the arithmetic mean between the diameters forming the sudden pipe contraction. Using the methodology described in the literature, the contraction length ratio as the areas of influence between two symmetrical sudden contractions of a circular pipe during the flow of a single-phase turbulent flow of Newtonian fluid was investigated. The coefficient of mutual influence of these local resistances was determined by formulae for direct-flowing and non-direct-flowing locking devices, which simulated symmetrical and asymmetrical fluid flow after the constriction plane, respectively. The contraction rate from 0.064 to 0.696 inclusive are considered. According to the results of calculations, no mutual influence of two sudden contractions of circular pipe was found. This indicates the unsuitability of using formulae for locking devices in this methodology for determining the contraction length ratio. Therefore, to study this problem on the sudden pipe contraction with different contraction rates, it is proposed to conduct a physical experiment. In a mathematical experiment, you can use formulae to determine the following values: upstream recirculation length and downstream recirculation length; inlet length of cylindrical pipes with turbulized the flow devices; length of the velocity profile stabilization after local resistances.

Parametric design analysis of elliptical shroud profile

<abstract> <p>Parametric design analysis for Eccentric Rotated Ellipsoid (ERE) shroud profile is conducted whereas the design model is validated experimentally. A relation between shroud inlet, length and exit diameter is established, different ratios related to the wind turbine diameter are introduced, and solution for different ERE family curves that passes on the inlet, throat, and exit points is studied. The performance of the ERE shroud is studied under different wind velocities ranging from 5–10 m/s.</p> <p>The method used in creating the shroud profile is by solving the ERE curve equations to generate large family of solutions. The system is modeled as axisymmetric system utilizing commercial software package. The effect of the parameters; shroud length, exit diameter, inlet diameter, turbine position with respect to the shroud throat, and wind velocity are studied. An optimum case for each shroud length, exit diameter and location of the shroud with respect to the wind turbine throat axis are achieved.</p> <p>The simulation results show an increase in the average wind velocity by 1.63 times of the inlet velocity. This leads to a great improvement in the wind turbine output power by 4.3 times of bare turbine. One of the achieved optimum solutions for the shroud curves has been prototyped for experimental validation. The prototype has been manufactured using 3D printing technology which provides high accuracy in building the exact shape of shroud design curve. The results show very good agreement with the experimental results.</p></abstract>

Echocardiographic Follow-Up of Right Ventricular Function After Tetralogy of Fallot Operation

Aim: Although limited in assessing right ventricular (RV) function, echocardiography is widely used after correction for tetralogy of Fallot (TOF). The change in echocardiographic measurements of RV in asymptomatic patients after TOF repair over a long follow-up time is not explored yet. The variation in simple echocardiographic measurements during follow-up of our TOF patients are presented. The predictive value of those parameters in determining a future pulmonary valve replacement is sought. Method: Asymptomatic patients surviving the first year after correction for simple TOF from February 2007 to December 2019 at Başkent University, Istanbul Hospital are enrolled. Patients are followed annually with echocardiography including: RV area, volume, length, RV outflow tract (RVOT) diameter and gradient, tricuspid annulus diameter, tricuspid lateral annular tissue velocities, tricuspid annular plane systolic excursion, TEI index RV ejection fraction (EF) measurements. The change in the consecutive echocardiographic measurements during follow-up is analysed. Patients are evaluated with a cardiac magnetic resonance (CMR) imaging when deemed necessary and compared with echocardiographic measurements. Results: A total of 66 patients (54.5% males) are operated at age 14.4±9.3 months (78.8% with transannular patch). Twelve patients had pulmonary valve replacement (PVR) operation at an age 10.1±3.1 years. During follow-up of 7.2±4.3 years, tricuspid annulus diameter, RV area, RV inlet length, RV volume, RV volume index significantly increased (p=0.001 for all), whereas RV inlet length index, TEI and TEI z score decreased (p<0.0001 for all). When means are compared, tricuspid annulus (28.8mm vs 25.0mm; p=0.013), RV volume (72.2ml vs 52.2ml; p=0.042), RV inlet length index (77.9mm/m2 vs 60.2mm/m2 ; p=0.013), RVOT diameter (28.7 vs 23.0; p=0.007) are increased. RV EF is decreased (51.3% vs 60.5%; p=0.011) in those requiring PVR. Those with higher RV area index, RV volume index, tricuspid annulus diameter and tricuspid annular z score in their first echocardiography after the TOF repair, are more likely to have a PVR operation later on (p<0.05 for all). RV volume index ≥39ml/m2 predicts a PVR within 7 years with 100% sensitivity and 74% specificity. Tricuspid annular z score less than -0.43 seems to eliminate the possibility of having a PVR within 7 years with a sensitivity of 44% and specificity of 100%. Conclusion: Observing the sequential change in echocardiographic parameters like RV volume index, RV area index, tricuspid annulus z score is reliable in determining right ventricular function and can limit the costly CMR applications. Cut off values of RV volume index >39ml/m2 and tricuspid annulus z score ≥ - 0.43 after the initial TOF repair may determine patients with higher possibility of having early PVR and indicate a closer follow-up.

Identification of efficient geometries for variable pitot inlets for supersonic transport

Purpose This paper aims to reveal the influence of selected geometric parameters on the aerodynamic performance of circular variable aero engine inlets in transonic and supersonic civil aviation. Design/methodology/approach The trade-off in inlet design and aerodynamic evaluation parameters is presented. The approach to investigate the dependencies between the aerodynamic and geometric parameters at different flight conditions by means of a parametric design study is introduced. Findings The dependencies of inlet drag and efficiency from geometric parameters at flight speeds of Mach 0.95 up to Mach 1.6 are identified. Although entailing additional weight, the inlet length represents the parameter with the highest potential for drag reduction by up to 50% in the selected design space. Ideal geometries for variable pitot inlets are determined. After considering weight, their potential range benefit nearly disappears for subsonic applications, but remains above 20% for supersonic flight at Mach 1.6. Originality/value Hence, the technology of circular variable pitot inlets for supersonic transport aircraft could be a way to achieve the ambitious ecological, safety and economic goals for future civil aviation.

Parametric Design Study on Aerodynamic Characteristics of Variable Pitot Inlets for Transonic and Supersonic Civil Aviation

This paper reveals the influence of selected geometric parameters on the aerodynamic performance of circular variable aero engine inlets in transonic and supersonic civil aviation. The trade-off in inlet design and aerodynamic evaluation parameters are presented. The approach to investigate the dependencies between the aerodynamic and geometric parameters at different flight conditions by means of a parametric design study is introduced. The dependencies of inlet drag and efficiency from geometric parameters at flight speeds of Mach 0.95 up to Mach 1.6 are identified. Although entailing additional weight, the inlet length represents the parameter with the highest potential for drag reduction by up to 50% in the selected design space. Ideal geometries for variable pitot inlets are determined. After considering weight, their potential range benefit nearly disappears for subsonic applications, but remains above 20% for supersonic flight at Mach 1.6.

Study of burner geometry effects on non-premixed flame response under acoustic excitation

The study of the flame under the acoustic excitation contributes to the study of flame self-excited thermoacoustic instability. Although non-premixed combustion is widely used in industry, research on its combustion instability characteristics is relatively few. This paper experimentally studies the response of a non-premixed swirl flame under excitation. The geometry modifications are the length of the inlet section which is set to be 0.245 m, 0.345 m and 0.445 m and the installation of separation plates. Through the analysis of flame response behavior at different excitation frequencies, combined with the calculation of acoustic mode, we find that for the 0.245 m and 0.345 m inlet length cases, the maximum flame heat release fluctuation responds near 144 Hz. This mode is due to the resonance of the fuel pipe. For the 0.445 m inlet length cases, the maximum flame heat release responds near 134 Hz. This mode is a mixed mode of fuel pipe and combustion chamber. The maximum flame response occurs at the point where the pressure fluctuation reaches the maximum in the inlet section. The image analysis shows the same mode distinction trend between short and long inlet length. Besides, the removing of separation plates leads to a more stable response of the flame in low inlet airflow rate. However, at high airflow rate, the flame tends to be more unstable. Moreover, the higher acoustic forcing frequency than quarter-wave mode will cause the quarter-wave resonant frequency to appear. The results of our work can benefit the implications of thermoacoustic instability in non-premixed flame.

Limitations of Traditional Capacity Equations for Long Curb Inlets

Recent work with full-scale experiments indicates that there are fundamental problems with standard curb inlet design equations when applied to depressed curb inlets of 10 ft (3 m) or longer. A full-scale laboratory experiment showed that the latter part of a long inlet does not have a simple linear water surface profile at 100% interception, which is assumed for the form of Izzard’s equation that is adopted for many common design approaches [including the Hydraulic Engineering Circular 22 (HEC-22) design equations recommended by FHWA]. For a long inlet, thin flow sheets were observed for a substantial portion of the inlet length, which is consistent with previous observations that have not been incorporated into standard design equations. Experimental results indicate that the HEC-22 design equations significantly overestimate the interception capacity of long, depressed curb inlets for an on-grade gutter. This issue has potential safety implications in that the gutter bypass and spread for a design storm will be larger than expected for such inlets. The present work is preliminary, so an L2 measure previously proposed by Izzard is recommended as a maximum inlet length pending the outcome of further studies.

Optimise inlet condition and design parameters of a new sewer overflow screening device using numerical model

After heavy rainfall, sewer overflow spills to receiving water bodies cause serious concern for the environment, aesthetics and public health. To overcome these problems this study investigated a new self-cleansing sewer overflow screening device. The device has a sewer overflow chamber, a rectangular tank and a slotted ogee weir to capture the gross pollutants. To design an efficient screening device a numerical computational fluid dynamic (CFD) model was used. A plausibility check of the CFD model was done using a one-dimensional analytical model. Results showed that an inlet parallel to the weir ensured better self-cleansing than an inlet perpendicular to the weir. Perforations should be at the bottom of the weir to get increased velocity and shear stress to create a favourable self-cleaning effect of the screening device. Increasing inlet length from 0.3 to 1.5 m reduced wave reflection up to 10%, which increased flow uniformity downstream and improved self-cleansing effect. The orientation of the ogee weir with the rectangular tank was found most uniform with a 1:3 (horizontal:vertical) slope. These results will help to maximise functional efficiency of the new sewer overflow screening device. Otherwise it would be too expensive to alter after installation and at times difficult to customise accordingly to existing urban drainage systems.