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Monitoring the temperature inside the gasifier of a Shell coal gasification process (SCGP) is very important for safe process operation. However, this temperature cannot be measured online due to the harsh operating condition. Estimating this temperature using the extended Kalman filter (EKF) based on a simplified mechanistic model is proposed in this paper. The gasifier is partitioned into three zones. The quench pipe and the transfer duct are seen as two additional zones. A simplified mechanistic model is developed in each zone and formulated as a state-space representation. The temperature in each zone is estimated by the EKF in real-time. The proposed method is applied to an industrial SCGP and the accuracy of the estimated temperatures is verified by a process variable both qualitatively and quantitatively. The prediction capability of the simplified mechanistic model is validated. The effectiveness of the proposed method is further verified by comparing it to a Kalman filter-based single-zone temperature estimation method.

This research article uncovers a novel mathematical model that interprets the peristaltic flow in elliptic duct with heat and mass transfer for the first time. A unique mathematical technique is introduced in this study that provides exact analytical solutions for partial differential equations. The Cartesian coordinate system is used in the present analysis and the non-circular form of duct is attained by considering equation of ellipse in the boundary conditions. The temperature, concentration and velocity profile are exactly computed and analyzed through graphical results. The axially symmetric flow behaviour is revealed by the graphical outcomes. Concentration, velocity and temperature profiles have parabolic shapes and axially symmetric behaviour.

A NACA0025 coflow jet airfoil model, including the inner and outer airfoils, was designed and manufactured through 3D printing technology. Using the duct connecting the leading- and trailing-edge s...

This novel investigation unfolds the mathematical model of peristaltic flow in an elliptic duct having ciliated walls. The current assessment is carried out by considering a heated Newtonian viscous fluid in this ciliated elliptic duct. A detailed heat transfer study combined with various physical aspects of peristalsis is provided. We have incorporated the appropriate and useful transformations that simplify this mathematical problem into its non-dimensional form with relevant non-dimensional boundary conditions over the surface of ciliated elliptic duct. Finally, the exact mathematical results are computed for this interesting problem. A thorough graphical assessment is also included for a complete understanding of mathematical results. The axially symmetric flow behaviour is noted for both velocity and temperature profiles in this elliptic duct having ciliated walls.

This paper presents a numerical investigation of the laminar flow and pressure drop characteristics of planar Tee joints, a canonical flow of interest for the thermal-hydraulic design of oil-immersed power transformer windings. After formulating the problem in nondimensional form, the steady, constant property flow in planar 90 ∘ Tee joints is computed numerically by integrating the Navier–Stokes equations with fully developed upstream and downstream boundary conditions. The analysis assumes a straight-through configuration in which the straight duct holds flow in the same direction before and after the junction, whereas the flow in the side branch can either divide from the incoming flow or combine with it. The analysis starts with the description of the flow patterns that emerge in the dividing and combining cases for all mass split ratios, 0 ≤ m 1 ≤ 1 , and a wide range of straight duct to side branch width ratios, 1 ≤ α ≤ 3 , and Reynolds numbers of the common branch, 0 < Re3 ≤ 200, values that are representative of the cooling oil flow in oil-immersed transformer winding. Flow maps for planar Tee joints are then presented, showing the existence of different regions in the (Re3, m 1 )-plane that exhibit different number and location of recirculation zones. Pressure distributions and secondary loss coefficients are then computed and analyzed, providing a numerical database that is used to develop new local pressure loss correlations for planar Tee joints in an accompanying paper.

Suppression of shock-induced separation on all the walls of a rectangular duct using arrays of microvortex generators was experimentally investigated. The flowfield was analyzed using normal and in...

A study is undertaken to assess the dynamic control's effectiveness at two supersonic Mach numbers, 2.2 and 2.58 being considerably large Mach number being very significant in the design of High-speed aerospace vehicles. The relief available to the flow while the shear layer exits from the nozzle and enters the enlarged duct. The investigation area ratio is 4.84, and the NPR tested is from 3 to 11, covering the various level of expansion. The investigation was done for eight sizes of circular duct cases. Still, the results are discussed only when a significant change in the wall pressure is noticed during the experimentation. The dynamic control is located at a 6.5 mm radial distance from the primary jet's axis, with a 1 mm diameter generating at sonic Mach from the active flow control management. For lower duct length at NPRs, the wall pressure assumes large values. Later, with a rise in the duct section and NPR, a progressive decline in the pressure values is seen due to the decrease in adverse pressure levels and the intensity of the oblique shock waves. The duct flow mild oscillations are seen for duct section 3D, 5D, 6D, and 10D. The duct length portrays a crucial role while determining the stream development in the enlarged circular tube. When the duct's size is 6D and 10D, the low wall pressure is seen. For NPR = 5, the wall pressure takes moderate values due to the influence of the tube. At NPR = 7, 9, and 11, the pressure rise is limited within the reattachment zone, and ambient conditions are nearly attained within a short duct length. Despite nozzles, they are over-expanded flow control effects in a rise of pressure at Mach 2.58 for duct size 6D and 10D. For the duct size 10D, the attainment of ambient pressure is further advanced towards the upstream.

Part cooling fans are used in FDM 3D printers to control the deposition quality and warping issues. However, the fan ducts used for the purpose are often non-optimized, and therefore, the performance of such ducts can be improved by analyzing the geometry and adopting necessary modifications. This work looks into the geometry of the part cooling fan duct of a common commercial 3D printer, and studies the influence of a convergent-divergent type duct opening on the flow behavior. The inlet and outlet angles and the throat length have been analyzed numerically to identify the most suitable geometry. Results indicate that there are optimum values for all of these three geometrical parameters to obtain the highest air flow velocity at the outlet, and the flow behavior deteriorates beyond such optimum parameters. From the numerical analysis, the optimized convergent-divergent duct having 20° outlet angle, 3 mm throat length, and 40° inlet angle can increase the average air flow velocity by approximately 23% over the air flow velocity of a standard part cooling fan without the convergent- divergent section.

This study investigates the streaming development in the tube and pressure recovery once the flow regulator is activated in the recirculation zone at a different level of expansions. The Mach numbers considered are 1.87, 2.2, 2.58. The duct diameter is 16 mm. Tiny jets of 1 mm diameter are placed at the midplane of the base to regulate the flow. The control jet’s Mach number is unity as they are circular orifice despite the NPR of the control jet being very high. The investigations reveal that the stream remained connected with the duct even for L = 1D for the entire Mach numbers. The pressure’s initial values are very high for an over-expanded nozzle than the under-expanded and ideally expanded nozzles. From the wall duct field, it is seen that the flow becomes oscillatory for lengths L = 10D to 6D owing to the collaborations of the waves, the duct wall, and the influence of the ambient pressure. The recovery of the tube pressure also gets shifted towards the downstream for the more considerable duct lengths. The flow quality with and with no flow control mechanism is identical for duct lengths 10D and 8D. Lower duct lengths show mixed trends regarding flow development, and the flow’s quality is concerned. The flow control mechanism is effective once the nozzle flows with favorable pressure or at the design NPRs. When the nozzle has more pressure than ambient values, the control becomes useful, quickly raising the pressure’s values.

Experimentations were done to analyse the effect of using inclined and transverse ribs separately over the absorber plate as artificial roughness in a double/two pass solar air heater. The material of the absorber plate is Galvanized Iron (GI) with ribs of aluminium attached over it which enhances the rate of heat transfer. The shape of the duct used is rectangular having an aspect ratio of 10. The relative roughness pitch (p/e) ranges between 5 and 20, relative roughness height (e/Dh) ranges between 0.043 and 0.045, angle of attack (α) ranges between 30°- 90° and Reynolds number ranges from 4000 to 18000. The data obtained for heat transfer and friction factor from various roughness placed over the absorber plates are compared with the data obtained for the smooth plate operated in same conditions. It is seen that there is an increase in heat transfer and friction factor characteristics after placing ribs over the absorber plate. At the end the correlations of Nusselt number and friction factor were developed.

A solar air collector (SAC) is a heating device that applies warm air to dry agricultural products and for a variety of engineering purposes. The underside of the absorber plate used discrete double arc reverse shaped artificial roughness, outside testing performance for heat transfer coefficient, h, and thermal efficiency, ηth features of solar air collector were carried out in this article. During the outdoor experimental test, the following parameters were used: relative roughness pitch (p/e) = 8.33, relative roughness height (e/Dh) = 0.027, arc angle (α) = 60°, Reynolds Number (Re) = 3000 to 14000, and aspect ratio (W/H) = 8. Also, the outdoor test was performed at 11:00 A.M. before noon to 2:00P.M. afternoon with solar radiation intensities ranging from 860 W/m2 to 895 W/m2. The impact of various factors on heat transmission and thermal efficiency is compared to that of a smooth absorber duct under identical conditions of flow. Over the smooth duct, the maximum increases in coefficient of heat transfer and thermal efficiency are 2.88 and 1.29 times, respectively.

This article aspires to evaluate the effect of dynamic control on the stream’s nature in an abruptly expanded conduit of a diameter ratio of 2.2. The investigation was done for Mach 1.6, 1.8, 2.0, and 2.5. Results are shown when control renders any change in the flow field. It is found that at Mach 1.6 for NPR = 7 and the tube size of L = 10D, the jets’ noise is considered in the control mechanism’s nonappearance and existence. The results show that there is a significant decrease in the noise level, and jets become quiet. It is also observed that the base pressure is also minimal whenever the jet’s noise is low due to the microjets. At Mach 1.6, 1.8, and 2.5, the control findings decrease the duct’s pressure value for most cases. However, in Mach 2.0, when the control is activated, it increases the duct’s static pressure. The microjets do not interrupt the flow field in the pipe adversely.

The performance investigation of natural and forced convection indirect type solar dryers was performed by drying ivy gourd. The natural convection setup was modified by fitting a trapezoidal duct and central processing unit fans run by photovoltaic panels to promote forced convection. The data from the experiment was used to estimate collector and dryer efficiencies, energies, effective moisture diffusivity, transfer coefficients, specific energy consumption and specific moisture extraction rate. The average actual heat supplied was 776.6 and 997.76 W for natural and forced convections, respectively. The average collector efficiency for the same was 62.56% and 77.2%, respectively. The average drying efficiency for the same was 6.62% and 7.8%, respectively. The average values of activation energy, mass transfer, heat transfer and diffusion coefficients were estimated to be 39.85 and 35.54 kJ/mol, 7.06 × 10−9 and 8.35 × 10−9 m2/s, 0.0033 and 0.0043 m/s, and 3.85 and 4.93 W/m2 K, respectively, for natural and forced convection setups, respectively. The specific energy consumption and specific moisture extraction rate were evaluated where forced convection setup gave the best results. The drying correlations were developed for mass transfer, heat transfer and diffusion coefficients. Uncertainty analysis was performed to check the authenticity of the results.

Aircraft-mounted gas turbine engines may need to employ a variety of inlet ducts to perform various missions. An inertial particle separator (IPS) is a type of inlet duct that can remove harmful du...

This research focuses on reactive hydrogen leakage due to the fracturing of high-pressure hydrogen tanks to develop a coupled computing method that can simultaneously perform reactive fluid-structure interaction analyses. The integrated computational approach to reactive hydrogen leakage with combustion due to wall crack propagation was implemented using a hybrid of the coupled particle and Eulerian methods. This computational method provides valuable safety information for predicting crack propagation and hydrogen leakage with combustion reaction in pressure tanks as an essential part of assessing hydrogen as an energy vector. As a result, the effect of crack formation and wall boundary conditions on hydrogen turbulent diffusion and concentration distribution and the thermodynamic behavior of the chemical reaction were predicted computationally. It was found that a combustion reaction does not occur near the streamwise axis at the duct center because there is an excess of hydrogen fuel, which increases scalar dissipation, and that the combustion reaction separated into upper and lower regions as it proceeded.

The solid fuel ducted Ramjet systems (SFDR) are extremely capable of propelling high- speed missiles. They have a specific application in the configuration of air-to-air missiles with a high degree of interception. It is a modification from the traditional solid fuel ramjet system by using an external duct for thrust variation. This system provides higher effectiveness against maneuvering jets compared to single and dual pulse rocket system as it can vary thrust by varying fuel and air quantity for combustion. Even though with high effectiveness, an enemy fighter jet that is having higher thrust engines can outmaneuver SFDR by gaining significant lift during the end-stage which reduces its killing probability; this emphasized the development of a new missile system that provides more lift during the end-stage. A new SFDR concept is proposed in the present work that can gain more lift. The provision of a deflector is made in the duct to study the lift characteristics. Optimum lift force was obtained from the detailed analysis. Moreover, the study was extended by changing the deflector dimensions. Fluent fluid flow analysis is performed in simulation software named ANSYS to study the lift characteristics. Before that, 3D modelling is done with the help of NX software.

The current numerical study aimed for analayzing heat transfer of a spherical water droplet placed in a rectangular duct. The problem particularly deals with air-cooling of the droplet. The computational fluid dynamic technique is used to treat the problem. In order to study the problem, the effect of evaporation on the droplet's heat transfer is taken into consideration to make the problem more realistic. Moreover, various parameters like the inlet velocity and the temperature of the upstream are numerically checked. It is found out that with involving evaporation, the mean temperature of the droplets increases in comparison with the case that there is no evaporation involved. The outcomes of the current study offer useful and deep insight into the evaporative cooling of a water droplet.

Solar air heater acts as one of the important components in utilization of solar energy. The air heater absorbs the irradiance and converts it into heat energy at the absorbing surface. The thermal energy is further use in heating flowing air through the duct. Solar air heaters are cost effective as well as simple in design. Solar air heater can be used in space heating, timber seasoning and agricultural drying. In spite of all these advantages the solar air heater has certain challenges such as the air has low heat transfer coefficient. The heat transfer rate from the heated absorber surface to the air is low. Hence in order to enhance the heat transfer coefficient the surface area either increases or the flow made to be turbulent. In order to do so the artificial roughened element must be incorporated on the heated surface. The use of artificial roughness is considered as an effective technique to enhance the heat transfer rate of fluid flowing through the duct of solar air heater. The heat transfer and friction characteristics of number of roughness geometries incorporated solar air heater have been investigated. In this paper an attempt has been made to review on element geometries used as artificial roughness in solar air heater in order to improve thermal and thermo hydraulic performance of solar air heater ducts.

Introducing flow turbulators in the duct of a solar air heater has proved to be one of the most effective ways to improve the energy utilization efficiency of the device. In the present investigation, solar air heater accoutered with altered conical vortex generators in a staggered arrangement is analysed for different relative pitch ratio (2.67–15) and relative height ratio (0.17–0.34). The performance is evaluated for an appropriate range of Reynolds number (3500–16000), using the latest computational tool, ANSYS FLUENT 19.2. The numerical results are validated experimentally using a fabricated experimental set up similar to the numerical model. Overall evaluation criteria is employed to achieve an ideal geometrical parameter for the considered range of Reynolds number. Empirical correlations for performance indices, Nusselt number and friction factor as functions of considered geometrical and operational parameters are developed. Employment of modified conical vortex generators in a staggered arrangement resulted in a 257% enhancement in thermal performance. Highest thermohydraulic performance parameter of 2.04 is achieved.

Air balancing is an important technique in heating, ventilation, and air conditioning (HVAC) applications to achieve accurate air supply for satisfactory indoor air quality and better energy saving performance. The existing air balancing methods are usually based on a hybrid duct system model, which includes a data-driven duct system model between terminal flow and static pressure, and an American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) damper model between static pressure and terminal damper angle. Most of the existing methods just focus on how to improve the accuracy of the former part (i.e., the data-driven duct system model), whereas neglecting the latter. However, it is found that the ASHRAE damper model cannot exactly reflect the characteristics of the actual dampers in practice and may lead to unavoidable modeling errors. To fix this issue, this article develops a full data-driven duct system (FD3S) model to directly reveal the relationship between the terminal flow and terminal damper angle in the whole duct system. As a result, the desired terminal damper angle under the design flow conditions can be more accurately predicted. Besides, since the proposed method directly models the relationship between terminal flow and terminal damper angle, it avoids installing extra pressure sensors and reduces the operating cost. Besides, the proposed FD3S model greatly reduces the model complexity compared with the previous hybrid model. The proposed FD3S model-based air balancing method is fully tested on three real duct systems, and the results proved the effectiveness and generality of the proposed FD3S model-based air balancing method.

The efficacy and requirement were investigated for water mist to extinguish fires in circular, horizontally-oriented ducts, in which the air flow was provided by a blower at the duct inlet at velocities ranging from 0.84 m/s to 3.89 m/s under no fire conditions. Water mist was made discharging in the air flow direction. The fire hazard was simulated with propane release into insulated stainless steel ducts of 0.30 and 0.61 m in diameter. The insulation corresponded to the thermal resistance of combustible ducts commonly used for exhaust applications in industrial settings. The investigation was carried out by first estimating the water mist requirement for fire extinguishment, then by a series of evaluation fire tests. For each duct diameter, water mist was discharged inside the duct with a nominal spacing of 3.1 m along the duct length. The 0.30-m duct tests were mainly conducted with a water mist discharge rate of 44 l/min at each duct location, with a volume-median droplet diameter of about 77 μm. Limited testing was also performed with a higher discharge rate of 64 l/min at each location, with a median droplet size of about 88 μm. The tests showed that the fire could be successfully extinguished, and the extinguishment was independent of fire size when the water mist concentration exceeded 300 g/m3 in the air flow. Based on the result, the 0.61-m duct tests were conducted with a water mist discharge rate of 142 l/min at each location. The tests showed that the fire could be extinguished similarly as observed in the 0.30-m duct tests. Based on the duct-wall temperature measurement, the cooling of the tested protection was deemed adequate to maintain the structure integrity of exhaust ducts made of steel, fiber-reinforced-plastic and fiberglass during the process of fire extinguishment.

This investigation focuses on the mixed initial boundary value problem with Caputo fractional derivatives. The studied pour an incompressible fractionalized Oldroyd-B fluid prompted by fluctuating rectangular tube. The explicit expression of the velocity field and shear stresses for the fractional model are obtained by utilizing the integral transforms, i.e., double finite Fourier sine transform and Laplace transform. Furthermore, the confirmation of the analytical solutions is also analyzed by utilizing the Tzou’s and Stehfest’s algorithms in the tabular form. In limited cases, ordinary Oldroyd-B fluid similar solutions and classical Maxwell and fractional Maxwell fluid are derived. The flow field’s graphs with the influences of relevant parameters are also mentioned.

The mean and instantaneous flow separation of two different three-dimensional asymmetric diffusers is analysed using the data of large-eddy simulations. The geometry of both diffusers under investigation is based on the experimental configuration of Cherry et al. (Int J Heat Fluid Flow 29(3):803–811, 2008). The two diffusers feature similar area ratios of $$\mathrm{AR}=4.8$$ AR = 4.8 and $$\mathrm{AR}=4.5$$ AR = 4.5 while exhibiting differing asymmetric expansion ratios of $$\mathrm{AER}=4.5$$ AER = 4.5 or $$\mathrm{AER}=2.0$$ AER = 2.0 , respectively. The Reynolds number based on the averaged inlet velocity and height of the inlet duct is approximately $${\textit{Re}}=10{,}000$$ Re = 10 , 000 . The time-averaged flow in both diffusers in terms of streamwise velocity profiles or the size and location of the mean backflow region are validated using experimental data. In general good agreement of simulated results with the experimental data is found. Further quantification of the flow separation behaviour and unsteadiness using the backflow coefficient reveals the volume portion in which the instantaneous reversal flow evolves. This new approach investigates the cumulative fractional volume occupied by the instantaneous backflow throughout the simulation, a power density spectra analysis of their time series reveals the periodicity of the growth and reduction phases of the flow separation within the diffusers. The dominating turbulent events responsible for the formation of the energy-containing motions including ejection and sweep are examined using the quadrant analysis at various locations. Finally, isourfaces of the Q-criterion visualise the instantaneous flow and the origin and fate of coherent structures in both diffusers.

Heat transfer enhancement (HTE) efforts spent during the last half-century have become one of the most important working areas of researchers from both academia and industry. One of the most popular passive methods, with regard to the price-performance ratio, is to place wire coils in a pipe or duct. In this study, the heat and pressure drop characteristics of diamond, triangular, and circular cross-sectional wire coils (DWC, TWC, and CWC) in a square duct were investigated by using the FLUENT program. In addition to the cross-section examination, the thermo-hydraulic behavior of three different pitches (p = 54, 72, and 90 mm) for the specified geometries were also investigated. The Reynolds number was between 4387 and 18,415. The square duct was 1.25 m in length, and was 18 mm in diameter. The results showed that the Nusselt number of CWC, TWC, and DWC were higher than that of a smooth pipe within 38–88%, 37–93%, and 38–98% range, respectively. The friction of CWC, TWC, and DWC was observed to be higher than that of a plain tube within a range of 87–278%, 82–266%, and 107–366%, respectively. The TWC with 90 mm pitch showed the highest heat transfer performance evaluation criteria (PEC) with a performance coefficient of 1.3 at Reynolds number of 4504, whereas the DWC with 54 mm pitch was observed to show the lowest PEC. Thus, the as-obtained PEC, which is 30% higher than that of a plain tube, indicates the prominence and effectiveness of the numerical study in increasing the heat transfer.

Ventilation ducts can have a negative effect on the sound reduction index between two rooms if they pass through the dividing structure without treatments. The overall sound reduction of a ventilation duct is dependent on several factors including the transmission loss when sound is breaking in and out from the duct. This study aims to model the sound reduction of a combined system with a separating wall and a ventilation duct through it. Three walls, characterized according to ISO 717-1, are combined with three different ventilation ducts, two circular and one rectangular with different dimensions. Laboratory measurement data are used to determine the sound reduction of the different configurations and the type of treatments needed for each configuration. A proposed model with existing theory for describing sound transmission losses of circular and rectangular ventilation ducts predicts the shape of the measurement data for many frequency bands. A new theory part is developed through an iterative process for circular ducts, which is based on measurements with previous methods and studies as a guide because the existing prediction scheme is somewhat perplexing. For rectangular ducts, the existing theory has been updated to better match measurement data. The application of the proposed theory and model in this article shows similar results when compared to measurements. The difference in weighted sound reduction index between developed theories and measurement data is 0–1 dB for every configuration.

Currently propeller boss cap fin (PBCF) and propeller duct are among the well-known energy saving devices (ESD) for their effectiveness in recovery of energy losses during practical operation. These two devises prominently reduce the hub vortex as well tip vortex and hence improve propeller efficiency. Combined study of PBCF and propeller duct has become important and is essential to observe their impact in propeller efficiency. Here, numerically the importance of duct angle of attack and duct position in a ducted propeller in the presence of PBCF has been investigated to improve the overall efficiency. Five different angles of attack (0°, 2.5°, 5°, 7.5°, 10°) with 2.5° interval and five different positions (0.1, 0.15 m before propeller, at the propeller, 0.1, 0.15 m after the propeller) of duct have been considered to investigate the overall efficiency in the presence of both ESDs. Reynolds Average Navier Stokes (RANS) equations are utilized for numerical simulation in moving reference frame (MRF) approach. The simulations reveal that a maximum improvement of 7.05% is obtained in propeller efficiency at 0° angle of attack and it proportionally reduces with the increase in angle of attack. It is also observed that duct placed before propeller produced a maximum enhancement in efficiency of about 9.86% in comparison with other duct positions. Variation of pressure coefficient, vortices, skin friction coefficient and turbulence kinetic energy are also studied in detail in order to have a better understanding about the flow behaviour.

The present research focuses on dynamic flow control management using tiny jets with three combinations; the first one located at 90° intervals of the base, the second one located at 0.5D (duct diameter) of the wall, and the third one located at both base and wall with a 0.05 radius respectively which injects the air. Comparative analysis with these controls and without control is considered. The wind tunnel tests were done in existence and the absence of the tiny jets. For the experiments, the duct diameter ratio considered was 1.8, the duct length L = 10D, Mach numbers 1.87, 2.2, and 2.58, and NPR's range from 3 to 11. Additionally, the experiments were repeated to design experiments (DOE) method based on the factorial design-L9 orthogonal array (OA). Three variables with two parameters were designated for flow and the DOE. An analysis of variance, response surface analysis, regression equations, response optimization and data distribution were executed to optimize the experimental results. The established prototypes are statistically appropriate and achieved in generating realistic forecasts for all instances. From the results, it is apparent that for a conferred constraint, one can find a duct length of the circular pipe, which will result in the highest growth or decline of pressure in the base region.

The flow in a U-turn duct with a 180-degree curved section is a typical model of various applications such as the bend and return channel in multi-stage radial turbo-machines. The flow exhibits complex patterns including the separation on the inner wall, highly sheared flow in the curved and downstream sections, and recovery of deficit flow to uniform flow. Most of current researches focus on the simplified models of two-dimensional plane duct or three-dimensional duct with constant cross-section, while in realistic circumstances the duct can be varying in the shape and area of the cross-section to meet the design requirement. In this work, we performed a numerical investigation on the turbulent flow in a U-turn duct with spanwise diverging at Reynolds number Re = 106. The effect of diverging, as represented by the height of the duct, on the formation of secondary flow, flow separation and recovery is explored, and the three-dimensionality of the separated flow is quantitatively assessed. Numerical results reveal that with stronger spanwise diverging, the flow separates earlier from the inner wall and the size of the separated vortex is larger; the primary characteristics of the secondary flow also change significantly. The three-dimensional separated flow substantially affects the flow in the downstream straight duct that both streamwise and radial velocities exhibit fluctuating patterns as a result of the spatially non-uniform separation. The characteristics of boundary layer flow on all solid walls are also analyzed and discussed regarding the pressure field and local shearing.

The inlet duct length may affect the gas flow field and performance of a cyclone separator with a contracted inlet duct. In this study, a numerical simulation using the Eulerian-Lagrangian approach with a one-way coupling method was conducted to evaluate the gas flow field and separation efficiency of the cyclone separators with contracted inlet ducts of different lengths. The simulation results indicated that increasing the inlet duct length led to higher gas tangential velocity in the cyclone body. The effect of the inlet duct length on gas axial velocity was inferior to that on gas tangential velocity. A longer inlet duct reduced both the pressure drop and the separation efficiency. The reductions of the expansion loss at the inlet of the cylinder and friction loss inside the cyclone body contributed the most reduction of the pressure drop as the inlet duct length increased. Generally, when the inlet duct was 1.5 times longer than the cylinder diameter, the effect of inlet duct length on the gas flow field and performance of a cyclone separator became slight.

The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps. However, increasing the speed beyond the limit always accompanies cavitation, leading to the decrease of the volumetric efficiency. The pressure loss in the suction duct is considered a significant reason for the cavitation. Therefore, this paper proposes a methodology to optimize the shape of the suction duct aiming at reducing the intensity of cavitation and increasing the speed limit. At first, a computational fluid dynamics (CFD) model based on the full cavitation model (FCM) is developed to simulate the fluid field of the axial piston pump and a test rig is set to validate the model. Then the topology optimization is conducted for obtaining the minimum pressure loss in the suction duct. Comparing the original suction duct with the optimized one in the simulation model, the pressure loss in the suction duct gets considerable reduction, which eases the cavitation intensity a lot. The simulation results prove that the speed limit can increase under several different inlet pressures.

In the current analysis, the effect of perforated baffles in V-down pattern as artificial roughness on the thermal and hydraulic response of a solar air heater having equilateral triangular passage has been examined. A thorough numerical investigation has been done using ANSYS FLUENT-19.0. Effect of change in roughness parameters, viz., baffle height (e) and open area ratio (β) on thermo-hydraulic performance has been explored. Flow Reynolds number is systematically varied. Study reveals that upon varying the baffle height from 5 mm to 11 mm and open area ratio from 20% to 29%, maximum heat transfer rate is attained at e = 9 mm and β = 20%, respectively. Axial Velocity and Turbulence Kinetic Energy have been plotted for clear view of change in variables. Also, the correlations have been developed for Nusselt number and Friction factor. The thermo-hydraulic performance factor of proposed perforated baffle geometry has been observed to be 2.54 at e = 9 mm and β = 20%. Performance of the SAH with suggested roughness is found to be advantageous than other type of roughness elements studied in recent times.

In premixed H2/air explosion venting, an under-expansion jet may be caused by the pressure difference between the inside and outside of the explosion vent. Based upon the under-expansion jet, studying the structure of the under-expansion jet flame and the factors influencing its formation is essential to hydrogen safety in explosion venting. This study explored the basic characteristics of the under-expansion jet flame in premixed H2/air explosion venting, and discussed the formation of two under-expansion structures (Mach disk and diamond shock wave) of such jet flames by conducting a premixed H2/air explosion venting experiment. The influences of hydrogen fraction, explosion venting diameter, and duct length on the structure of under-expansion jet flames were evaluated. The results showed that after successful explosion venting, the under-expansion jet flame would be generated when the hydrogen fractions were 30–60 vol.%, and as the hydrogen fractions were 30–50 vol.%, the lengths of the venting duct were 30 and 50 cm. The duration of under-expansion jet flame was the longest when the hydrogen fraction was 40 vol.%. With the explosion venting diameter and hydrogen fraction increased, the spacing between under-expansion jet flame structures (S) increased. However, an increase in duct length led to the attenuation of the S. During the explosion venting, the under-expansion jet caused a pressure imbalance near the explosion vent and high-intensity convection forms on both sides of a jet, which can generate two or more explosions. Therefore, understanding the basic characteristics of under-expansion jet flame can aid the effective development of measures to prevent, mitigate, and protect against premixed H2/air explosions.

Waveguides allow grating lobe free beamforming for air-coupled ultrasonic phased-arrays by reducing the effective inter-element spacing to half wavelength. Since the sound waves propagate through the waveguide ducts, additional time delays are introduced. In this work, we present analytical, numerical, and experimental methods to estimate these time delays. Afterwards, two different waveguides are compared. The first one consists of equal-length ducts, requiring a time-consuming assembly process of the ultrasonic phased-array. In contrast, the second waveguide consists of Bézier-shaped ducts of unequal lengths but a planar input port allowing fast assembly. The analytical model is based on the geometric lengths of the waveguide ducts. The numerical model relies on a transient finite element analysis. All simulations are validated in an anechoic chamber using a calibrated microphone. The analytical (7.6% deviation) and numerical (3.2% deviation) propagation time models are in good agreement with the measurements. By using the analyzed propagation times for the compensation of the unequal waveguide duct lengths, we restored the beamforming capability without significant sound pressure level (SPL) loss. This work shows the possibility of reduced transducer assembly time for waveguided air-coupled phased-arrays without a reduced SPL.

In this article, we proposed a scheme of modeling an air heater system with a long airflow duct, predominantly available in many industrial plants to maintain the desired temperature by simultaneously befitting the transport delay, nonlinearities, model uncertainties, and nonuniform disturbances. At first, the nonlinear delayed air heater system is formulated by combining linear fuzzy system models utilizing fuzzy parallel distributed compensation (PDC) logic. Then, a newly developed L 1 adaptive control strategy is modified by replacing its conventional state feedback controller with fuzzy PDC control logic to maintain the desired temperature by nullifying nonlinearities, transport delays, uncertainties, and disturbances. The novelty of the proposed work lies in the fact that the proposed fuzzy PDC law augmented L 1 adaptive scheme explicitly deals with the delays and nonlinearities by means of fuzzy PDC logic as well as eliminates time-varying uncertainties and disturbances utilizing L 1 adaptive control strategy. The results obtained from real-life laboratory-scale experiments suitably demonstrate the usefulness of the proposed approach.

The sound propagation across a sound leaking section along an infinite rectangular duct-like structure near to the lower order duct eigenfrequencies is investigated numerically in the present study. The sound leakage is achieved by finite length rectangular slots located at a corner of the duct-like structure cross section. The finite-element simulations are performed, in the first place, to gain insights into the modal development inside the structure. A semi-analytical model, which considers the wavy air motions along the slots with oblique sound radiation patterns, is developed. An empirical framework is also proposed to estimate the complex longitudinal wavenumber along the slot using the numerical results and dimensional analysis. The performance of the proposed semi-analytical model, together with the complex wavenumber prediction framework, is tested using two duct-like structures with different cross section aspect ratios. The results show that the present proposed approach gives predictions close to the finite-element simulations. The deviations are well within engineering tolerance.

A simplified geometric model of a circular tube with a sedimentary layer is proposed and named as sedimentary duct. Based on h = 1/4d (h is the thickness of sedimentary layer and d is the pipe diameter), the flow field (Re = 40000) and particle distribution (5, 10, 50 μm and St = 0.6, 2.5, 63) in the sedimentary duct are simulated using Large Eddy Simulation (LES) coupled with Lagrange Particle Tracking (LPT) method. As a result, four streamwise eddies are found in the sedimentary duct as distributed in pairs near the corner. The eddy center near ceiling is found to be farther from the corner than that from the floor. Small particles (5 μm, St = 0.6) tend to move with the secondary flow as their upward movements distribute in both sides. Their centripetal movement is near the floor and preferential distribution near the top. For large particles (50 μm, St = 63), it is the drag force that dominates their motion while for medium particles (10 μm, St = 2.5) lift force may have significant influence on their motion. This study is the first work to investigate the characteristics of particle behavior in turbulent sedimentary duct flows.

At the outset, this work aims to carried out an analytical investigation of forced convection by establishing a laminar flow into circular duct under convective boundary conditions of the third type for non-Newtonian nanofluid, the fluid containing TiO2 uniformly dispersed in aqueous solution with 0.5wt% of CMC solutions (Carboxymethyl Cellulose) is used as working fluid. The viscous dissipation effects are taken into account, the employed methodology is based on a combination of the Ritz variational approach with the Laplace transformation technique, so the power-law fluids flow model is used to describe the non-Newtonian fluid behavior. The effect of dimensionless parameters such as Biot (Bi), Brinkman (Br), Peclet (Pe) numbers, power-law index (n), and nanoparticles concentration (φ) on the temperature distribution contours and on the examined local Nusselt number. Our results have been compared with those found in the literature in particular the cases of base fluids (φ=0) with and without viscous dissipation effects.

The insulation materials are used to reduce heat loss to/from the ducts with additional investment. This study introduces an air gap between insulation and duct surface to reduce the quantity of insulation. It uses lifecycle cost (LCC) analysis to determine the economic benefits of the air gap, considering four insulation materials for insulating the duct and natural gas as an energy source for chiller operation. The preliminary data regarding design and operating parameters were obtained from a renowned pharmaceutical company. The duct’s annual energy loss was estimated for given operation hours in a year using the preliminary data and ambient conditions. The estimated energy loss through the duct was fed in LCC analysis to determine the impact of the air gap on optimum insulation thickness (OIT) corresponding to the minimum LCC and payback period. Results revealed that OIT thickness for a duct with an air gap was lower than insulated duct without an air gap, resulting in maximum cost savings within a shorter payback period. Among different insulation materials, insulated duct with expanded polystyrene was investigated as cost-effective insulation material with maximum cost savings of USD (508.8–766.8)/m/year and a payback period of 1.15–1.17 years. On the contrary, the air gap was the most effective in terms of cost savings for the ducts insulated with rock wool. In conclusion, an air gap is a cost-effective design approach for duct applications.

Parameters affecting drying process has been studied experimentally as it associated with heat and mass transfer between porous bed to be dried and air which flows through the porous bed. To perform this study, a test rig is designed and constructed as it consists of vertical circular duct packed with wet porous bed which is made from clay balls of 20 mm in diameter. Drying process occurs as a result of forcing hot air vertically to pass through the wet porous bed, evaporation of moisture is existed in the bed due to the simultaneous heat and mass transfer. The studied operating parameters are inlet air temperature, inlet air mass flux, porous bed depth and porosity of balls. The average heat and mass transfer coefficients are estimated for flow of hot air through the wet porous bed. The results indicated that, the drying rate is directly proportional to inlet air temperature, mass flux of air, dimensionless bed depth and ball porosity. So, Drying process can be achieved in lower time as increasing both air mass flux and or inlet air temperature and decreasing bed depth. Also, heat transfer coefficient and mass transfer coefficient increase with increasing inlet air temperature, inlet air mass flux, and ball porosity, but they decrease with increasing bed depth. Comparison between the obtained experimental results and the previous work gave the same trend.

In the current paper, the dust transfer system in production line 4 of the Tehran cement factory has been simulated using computational fluid dynamics and a method has been presented to improve the system’s performance by changing the geometry. In this line to separate the particles from the gas, three electrostatic precipitators have been utilized in a parallel format. The shape of this line was modeled using Gambit software, and the distribution plates that are positioned at the beginning of electrostatic precipitators have been under consideration; then, grid generation was carried out for the created model. The model was transferred into Fluent software and solved numerically as a two-phase flow using the discrete phase model. Velocity values were obtained at different points of this system, and the trajectory of particles was drawn. The obtained results demonstrate a remarkable reduction in the velocity value before one of the electrostatic precipitators due to the horizontal duct; the considerable proportion of particles deposited on the walls of this duct. To improve this issue, a method has been proposed. In the modified case, the geometry of the horizontal duct was changed and the model was run again and the velocity and particles deposition values were compared with the current case. The results showed an increase in the velocity and a decrease in the sedimentation rate by 79.3 and 42.9%, respectively.

In this work, the propagation of CH4/air deflagration flames in three semi-confined ducts with different obstacles was numerically investigated using large eddy simulation (LES). The shape of the premixed flame, flow field structure, and overpressure characteristics of the interaction between the flame and the obstacle are simulated accurately in three ducts with obstacles of different heights. The results show that the structure of the flame is changed by the presence of obstacles, and a change in the shape of the hemispherical conical brush appears, and a flame vortex is generated by the entrapment of unburned premixed gas on the left side of the obstacles. In the process of CH4/air deflagration, the existence of obstacles would lead to the change in combustion velocity and overpressure relief velocity and then have a certain influence on the peak of overpressure and the shape of the premixed flame.

INTRODUCCIÓN: Se aborda la problemática de confirmar resultados experimentales a través de un modelo matemático que permita predecir el comportamiento de variables térmicas, en un módulo de aprovechamiento solar para la generación de aire caliente. OBJETIVO: Desarrollar un modelo matemático que describa los procesos internos de intercambio de calor en un colector solar de placas planas. MÉTODO: La investigación se realiza bajo el doble enfoque: teórico y experimental. Se procede a la medición de los principales parámetros de funcionamiento del colector solar de placas planas, la elaboración del modelo matemático y la realización del balance térmico. RESULTADOS: Utilizando el recurso Guide de MATLAB, se programó una aplicación para la ejecución del modelo matemático, estableciéndose las constantes que corresponde a datos geométricos del módulo solar y del ducto, características del aislante y condiciones térmicas de radiación de los materiales utilizados. Finalmente, definidos los datos de entrada, se realizan las iteraciones correspondientes y se obtienen los resultados de cálculo, los ajustes de temperaturas se realizaron con una divergencia inferior al 1%. DISCUSIÓN Y CONCLUSIONES: El error promedio que representaría el desface entre el modelo propuesto respecto a los parámetros reales de funcionamiento, fue de un 2,55%, aceptables desde el punto de vista estadístico. Se confirman resultados de investigaciones precedentes en cuanto a buenos rendimientos para un caudal másico de 0,0204 kg/s. Se logró la evaluación de un módulo del aprovechamiento solar para la generación de aire caliente que posee enormes potencialidades para la calefacción de viviendas de la región sierra ecuatoriana.

This paper examines the results of experiments conducted on a glazed solar air heater duct which is modified with an additional rectangular duct insert having perforation on its top surface. This modified rectangular duct of varying height is designed to split the incoming air into the absorber. This is presumed to create a pressure difference above and below the perforated surface that will enhance the convective heat transfer due to the cross-flow effect. It is observed from the experiments that the drop in pressure along the absorber passage decreases with an increase in the height, increase in hole diameter, and the number of rows of the hole. It is established from the experiments that thermal efficiency is found to be maximum for the height ratio (h/H) of 0.66 when compared to height ratios of 0.50 and 0.83, perforated duct inserts. Further, by varying the hole diameter ratio and the number of rows, it is noted that two rows of holes with hole diameter ratio of 0.096 configuration gives the maximum thermal efficiency of 84.8% and thermo-hydraulic efficiency of 81.06%.

Existing models of extended-tube liners are mainly applicable to the normal-incidence case, and the influence of the grazing-flow effect is often ignored. In the current paper, an impedance model i...

This article proposes a data-physical hybrid-driven air balancing (DPH-AB) method for the ventilation system. First, a data-driven model is proposed to establish the relationship among the airflow, path pressure drop, pressure, and damper angle in the duct system. Specifically, the airflow-path pressure drop relationship is modeled by the denoising autoencoder neural network (DAENN) while the pressure-angle relationship is obtained by the ridge regression method. Then, the physical information of the duct system is considered together with the proposed data-driven model to find the optimal angle for each damper to minimize the total fan power. With the proposed DPH-AB method, the airflow of all terminals can be accurately adjusted to the desired value while the energy consumption of the duct system can reach the lowest value. It is easy to identify which damper needs to be fully open to save the energy. The experiments verify the accuracy of the proposed DPH-AB method and its energy saving potential. The experiments also demonstrate that the DPH-AB method is robust against the noise in the actual duct system.

This study evaluated the effects of the adding of flow momentum using artificial external source on the controlling of oblique shock wave of a supersonic flow in a three dimensional duct with low-aspect-ratio (based on experimental data) through a numerical investigation by employing an OpenFoam extended solver. The oblique shock occurred due to a 20° compression ramp which placed on the top of the low-aspect-ratio duct. The flow characteristics were consistent with the published data, suggesting that the numerical methodology successfully resolved the interaction between the shock-waves and flow boundary-layer. To investigate the effect of momentum adding, based on literature, three different cases with various forces exerted on the upper and lower walls of the duct were considered. The results showed that momentum adding led to a decrement in the separation region and shock strength. Moreover, adding the momentum sources on the lower wall of the duct suppressed the lambda shock that happened by the collision of separated and incident shocks and Mach stem. However, by applying the momentum source on the upper wall (upstream of the compression ramp) had more effects on the interaction between shock wave and boundary layer, as compared to the lower wall. Therefore, based on the obtained results, to achieve the best performance of momentum source, it must apply at the critical point with the greatest effect on discontinuities in the flow structure.

The contribution from the base drag due to the sub-atmospheric pressure is significant. It can be more than two-thirds of the net drag. There is a need to increase the base pressure and hence decrease the base drag. This research examines the effect of Mach Number on base pressure. To accomplish this objective, it controls the efficacy in an enlarged duct computed by the numerical approach using Computational Fluid Dynamics (CFD) Analysis. This experiment was carried out by considering the expansion level and the aspect cavity ratio. The computational fluid dynamics method is used to model supersonic motion with the sudden expansion, and a convergent-divergent nozzle is used. The Mach number is 1.74 for the present study, and the area ratio is 2.56. The L/D ratio varied from 2, 4, 6, 8, and 10, and the simulated nozzle pressure ratio ranged from 3 to 11. The two-dimensional planar design used commercial software from ANSYS. The airflow from a Mach 1.74 convergent-divergent axi-symmetric nozzle expanded suddenly into circular ducts of diameters 17 and 24.5 mm with and without annular rectangular cavities. The diameter of the duct is taken D=17mm and D=24.5mm. The C-D nozzle was developed and modeled in the present study: K-ε standard wall function turbulence model was used with the commercial computational fluid dynamics (CFD) and validated. The result indicates that the base pressure is impacted by the expansion level, the enlarged duct size, and the passage’s area ratio.

The understanding of magnetohydrodynamic phenomena associated with the flow of electrically-conducting fluid in complex ducts is important and necessary in the study of liquid-metal blankets for fusion reactor. This study numerically investigates the lead-lithium (Pb-17Li) magnetohydrodynamic (MHD) splitting flows. The effects of the splitting angle of the duct geometry, the magnetic field orientation and the partly different electrical conductivity of the structural walls on the flow characteristics are analyzed in detail. Furthermore, the combined effects of the splitting angle, the magnetic field orientation and duct electrical conductivity on the mass flow rate and pressure drop are considered with many sub-cases. The results show that the mass imbalance and the pressure drop depend on the splitting angle of the duct geometry, on the discrepancy of the electrical conductivity of the sub-channels and also on the magnetic field orientation. In a word, this study can support several approaches to improve the flow imbalance and to reduce the pressure drop in the sub-channels of the liquid-metal (LM) MHD splitting flow system.