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Premixed flame of stoichiometric syngas-air mixture with various hydrogen volume fractions, 10% ≤ X (H2) ≤ 90%, propagating in a duct with both ends open is experimentally investigated in this study. Two representative ignition locations, i.e., Ig-1, locating at the center of the duct, and Ig-2, locating at the right open end, are considered. Results show that the tulip flame is first attained in the duct with both ends open at 10% ≤ X (H2) ≤ 50% as the flame is ignited at Ig-1. However, the flame maintains the convex shape with the cellular structure on the flame surface as the flame is ignited at Ig-2. The cellular structure results from Darrieus-Landau instability, but the Darrieus-Landau instability cannot invert the convex flame front. The flame tip and pressure dynamics have been examined. When the flame is ignited at Ig-1, the flame oscillates violently, and the overpressure profiles oscillate as a Helmholtz-type. When the flame is ignited at Ig-2, the left flame front propagates in an atmospheric pressure with a nearly constant speed. The prominent flame acceleration and oscillation are not observed at Ig-2 because of lacking flame acoustic interaction. What's more, the characteristic time of flame propagation has been compared. The time tw is shorter while the time tp is longer than the calculated value, and the time te has been delayed by both open ends. The flame propagation process is moderated as the flame propagates in the duct with both ends open.

This article focuses on the flow development and the static wall pressure distribution along the circular duct from the convergent-divergent (CD) nozzle. The study aims to examine the quality of the stream in the conduit when the control is employed. The microjets are activated at the base at (PCD) of 13 mm, and the diameter of the microjets is 1 mm. Mach numbers of the investigation are 1.3, 1.9, and 2.4. The length of the duct considered was from L = 10D to 1D. The diameter of the enlarged tube was 16 mm. The experiments were conducted for NPRs from 3 to 11. The results revealed that the lowest duct length mandatory for the flow continued to attach with the circular duct wall are L/D = 1, 2, and 3 for Mach numbers 1.3, 1.9, and 2.4, respectively. The investigation outcome indicates that there are mild oscillations in the flow-field for correctly expanded flows. The oscillatory trend has a pronounced impact on the duct's flow when the jets are operated at higher NPRs. The control does not adversely affect the flow field, and the magnitude of wall pressure is nearly similar.

This paper presents a performance analysis on a novel engine concept, currently under development, in order to achieve hybrid air-breathing rocket technology. A component-level approach has been developed to simulate the performance of the engine at Mach 5, and the thermodynamic interaction of the different working fluids has been analysed. The bypass ramjet duct has also been included in the model. This facilitates the improved evaluation of performance parameters. The impact of ram drag induced by the intake of the engine has also been demonstrated. The whole model is introduced into a multi-platform application for aeroengine simulation to make it accessible to the interested reader. Results show that the bypass duct modelling increases the overall efficiency by approximately 7%. The model calculates the specific impulse at approximately 1800 seconds, which is 4 times higher than any chemical rocket.

An experimental work on heat transfer by forced convection was conducted in order to study the heat transfer from hot rectangular tlat p late (155 x 115 mm) to an air stream. The hot place was situated between unheated p laces array at various locations in the flow direction. The air flow stream enters the tunnel ducc laterally from one side and from two sides. The study was mainly concerned with the effect of the lateral air flow on the average film coefficient of heat transfer . An exp erimental test rig was designed and constructed for chis investigation. The experiments covered the place locations of x = 12.5, 22.5, 32.5, 42.5 and 62.5 mm. and extended over a range of Reynolds number from about 6,800 to 109.000. Two correlations between the average Nusselt numoer and the Reynolds umbes were deduced, one was for the case of air entering the tunnel duct laterally from one side and the other was for the case of air entering the duco from two sides. The exp eriments were performed for the case of uniform heat flux. A comparison with the available work in the literature review was also made.

Since 2015 the processing capacity reconfiguration at the Polar Branch of MMC Norilsk Nickel (hereinafter PB) sets new goals for conventional pyrometallurgical processes of smelting and converting. The design flowsheet of Kolesnikov Nadezhda Metallurgical Abstract: Plant (hereinafter NMP) provided for «cross-converting» when copper matte was first processed in one converter to produce blister copper followed by nickel matte processing to yield copper-nickel converter matte bypassing the discharge of dry coagulated slag. This flowsheet allowed for converter heat balance optimization, decreasing the formation of refractory reverts and significant extension of the converter campaign. PB Nickel Plant shutdown resulted in copper processing elimination at NMP and switching the converters to the conventional nickel converting flowsheet. In turn, it gave rise to the need for solutions to extend converter campaign while maintaining the possibility to process large amounts of nickel slag from the second converting stage at the PB Copper Plant. For this purpose the series of lab experiments were carried out to develop the technology and design documentation for the system to supply oxygen-enriched air (up to 45 %) to horizontal converters using shell-type tuyeres. In addition, literature data were analyzed on this topic along with the experience of smelters in this area. Process design calculations were done. The efforts were taken in cooperation with the PB engineering personnel and Laboratory of Pyrometallurgy of LLC «Gipronickel Institute». The use of reduced diameter shell-type tuyeres to inject the oxygen-air mixture was found to decrease the converter blowing and off-gas volumes. The decline in off-gas quantity leads to reduced heat load on the converter mouth and flue duct system, as well as to lowered converter dust entrainment. The use of oxygen-enriched blowing implies the higher smelt heating rate. Excess heat compensation requires timely charging of cold reverts and flux. In emergencies (if cold reverts are not available) the oxygen content of the blowing has to be reduced until switching over to air blowing. The series of the above efforts will offer a possibility to use the shell-type tuyeres keeping the converter off-gas temperature at the current level. Thus continuous monitoring and efficient control will ensure the off-gas temperature and volume at the inlets of gas cooling and cleaning systems not exceeding the limiting values. The introduction of the reduced diameter shell-type tuyeres for air-oxygen mixture injection does not require any upgrade of the existing gas cooling and cleaning systems. Moreover, switching to these tuyeres will reduce gas load on the flue duct system and heat load on the water-cooled dust cap, lower dust entrainment and non-recoverable dust losses after the gas cleaning system.

This work is aimed at evaluating unrestricted duct-vented explosion of hydrogen-air mixture and hydrogen-methane-air mixture. The flame behavior in the venting zone and explosion pressure inside explosion chamber are obtained in the experiments. On the assumption of only fresh mixture venting or only combustion product venting, a mathematical model of unrestricted duct-vented explosion is established by considering chocked venting. The results indicated that the chocked venting could be achieved for unrestricted hydrogen and hydrogen-methane explosion venting due to the fact that the Mach disc structure is appeared in venting zone. Maximum explosion pressure and maximum pressure rise rate could be reduced significantly by unrestricted duct-venting. For the unrestricted hydrogen explosion venting, maximum explosion pressure and maximum pressure rise rate increases until Φ = 1.5, then decreases monotonously with the increase of equivalence ratio. For the unrestricted hydrogen-methane explosion, maximum explosion pressure and maximum pressure rise rate continue to decrease with the increase of methane addition. Maximum explosion pressure in the experiment is between theoretical values of fresh mixture venting and combustion product venting. Maximum explosion pressure and pressure rise rate are increased with increasing burning velocity whether it is fresh mixture venting or combustion product venting. Maximum explosion pressure is increased linearly with increasing nondimensional vent coefficient.

The effects of inert gas (i.e., He, Ar, and N2) and ignition position on flame dynamics in a half-open duct with an aspect-ratio of 10 are analyzed for hydrogen/air mixtures with constant laminar burning velocity SL. The results indicate that hydrodynamic and thermo-diffusive instabilities dominate flame propagations with ignition at the right-half part of the duct, while Rayleigh–Taylor instability dominates with ignition at the left-half part of the duct. The flame-sound interaction results in the periodic pressure oscillations. Due to decreased instability, the He-diluted flame exhibits a weaker sensitivity of explosion parameters to the ignition position. The maximum pressure Pmax is dominated by different mechanisms depending on the ignition position. Although constant SL is used, Pmax for the worst case with N2 dilution is two times that with He dilution, demonstrating the considerable effect of flame instabilities. Finally, a chemical kinetic calculation is performed to clarify the flame stabilities.

The nature of flow field inside the scramjet engine consists of shock-shock interaction and the shock boundary layer interaction. For a sustained combustion, a device called isolator plays a critical role in providing adequate pressure to the combustion chamber by a series of bifurcated shock waves called “shock train”. A small downstream pressure perturbation can cause upstream movement of this shock train and results in engine unstart condition. The propagation speed of downstream disturbance can influence the shock train oscillation. In the present study, computational fluid dynamics analysis is conducted to understand the oscillatory characteristic of shock train in a rectangular duct at M =1.75. The impact of downstream perturbation frequency (f b = 10 – 50 Hz) and the amplitude (A = 0.01 – 0.1) are simulated and discussed. The presence of low-frequency oscillation is observed without back pressure perturbation. The downstream pressure perturbation has a noticeable effect on the shock train excursion length i.e., the maximum upstream to downstream distance moved by shock train. The increase in perturbation frequency leads to decrease in disturbance propagation speed. Similarly, the propagation speed increases with the increase in the perturbation amplitude.

A hybrid numerical-analytical solution to fluid flow in irregularly-shaped microchannels has been developed. The solution is based on the Generalized Integral Transform Technique (GITT) applied to a trapezoid-like duct to account for fabrication imperfections, as commonly found in commercially manufactured microchannels. With this approach, the eigenseries expansion is done using a 2D eigenfunction basis, constructed from a combination of simple 1D eigenfunctions defined within the original irregular domain. In order to improve convergence, a new filtering scheme based on an analytical solution to the problem in a rectangular channel, which is distorted to match the irregular domain, is employed. The solution is tested on a real microchannel geometry, obtained from a SEM image, and compared with micro-PIV measurements for the flow field in the same channel. In addition, the actual velocimetry data is input to an inverse problem implementation for recovering geometric parameters related to the irregular geometry using the GITT results as the forward solution. The numerical results obtained with the GITT presented a very satisfactory convergence, and the inverse solution was able to recover the channel geometric parameters with very reasonable accuracy.

In this study, experiments on the vented deflagration of hydrogen–methane–air mixtures were performed in a vertical rectangular duct with a vent at its top end. A nondimensional vent coefficient ( K v ) was employed to characterize the effects of vent area ( A v ) on flame evolution and pressure buildup within and outside the duct. The maximum internal overpressure was attained near the duct bottom for a certain K v . As K v was increased from 2.2 to 11.9, the maximum internal overpressure near the vent and at the center of the duct increased monotonically; however, a nonmonotonic trend was observed at the duct bottom. Helmholtz oscillations of the internal flame and overpressure were observed in the tests for low K v , and acoustic oscillations of the internal overpressure with a frequency of ~1200 Hz appeared in all tests. The maximum external overpressure first increased and then decreased with an increase in K v . The external explosion induced a pressure peak in the duct, and the effect of external explosion on the venting of the internal deflagrations was weakened as K v ≥ 7.8.

In this study, the discrete adjoint approach with the grid deformation technique based on radial basis function was presented to solve the tough problem that the complex shape of the defrosting duct is very difficult to be optimized with multiple parameters in the improvement of the defrosting performance of vehicle. Firstly, the defrosting performance of a light truck was analyzed. Then the discrete adjoint approach was applied by taking the average Nusselt-number as the objective function. The normal surface sensitivity was used in the deformation of the defrosting duct. After 10 optimization cycles, the optimal model was acquired. The results show that, after optimization, the sum of the average Nusselt-number is increased from 3164.16 to 3350.54, which has a positive effect on improving the convection and heat transfer capacity on the windshield effectively. Compared with the initial model, the airflow of the outlet near the windshield is increased from 95.07 g/s to 96.94 g/s, the defrosting time required by the optimal model is reduced by more than 20s. Therefore, the discrete adjoint approach can optimize the complex shape of defrosting duct with multiple parameters effectively, which provides an effective method in the study of automobile defrosting performance.

Energy from the sun can either be stored (as electricity, using solar panels) or used as a heat source to do some work (solar heating and dying applications). Solar Air Heaters (SAH) come in the se...

Experiments are conducted to study the heat transfer and friction in a rectangular duct roughened by arrays of alternate ribs (square-, triangle-. and circle-shaped ribs). The Reynolds number Re based on duct hydraulic diameter rages from 12.000 to 60.000. whereas the rib pitch-to-height ratio (P/h) varies from 6 to 18. To understand the mechanism of heat transfer enhancement the measurements of streamwise mean velocities are also conducted in the square-ribbed duct. The results show that the flow of air through the ribbed duct becomes periodically fully developed after the third rib from the duct inlet. The data indicate also that the triangular type ribs have a substantially higher heat transfer performance than any other ribs in the studied range. The experimental results show that the heat transfer enhancement factors are greater than the friction factor ratios associated with the use of rib-turbulators in the rectangular ducts. Also, the rib conductivity affects significantly on the heat transfer enhancement factor. Correlations for friction and heat transfer in square-ribbed ducts are developed to account for rib spacing to height ratio and flow Reynolds number.

Theoretical and experimental studies were carried out 10 investigate the effects of duct velocity, sin density and tip-to-shroud clearance on the flow bypass and its impact on the pressure drop across a longitudinal aluminum fin array and its thermal performance. The clearance was varied parametrically, stating with the fully shrouded case and variations of the channel height giving partially shrouded configuration of different clearance ratios were also carried out. The slow bypass was found to increase with increasing sin density and insensitive to the air slow rate. That effect of fin density decreased as the clearance increased. The calculated total pressure was greatly affected by fin density. For fully-shrouded sin array, with H/S equals to 8 and 12.72, the pressure drop increased by a factor of 4.3 and 20 of that with Hf/S equals to 3.4, respectively. The total pressure drop and the average convective heat transfer coefficients corresponding to the fully and partially shrouded fin array of Hf /S=3.4 were compared. Going from fully to partially shrouded one of the largest clearance ratio (C/Hf =0.89), the total pressure drop reduced by about 50%. For clearance ratios equal to 0.36, 0.56, and 0.89, the average heal transfer coefficients were reduced by about 12, 17, and 30 percent of those for the fully shrouded configuration at ReD of about 3x103. That percentage reduction in heat transfer coefficients decreased with the increase of air flow rate.

The presence of coal particles, as well as the acidic aerosol in the exhaust gases from the coal-fired power plants, present a major threat to the global atmosphere. Here, the hydrodynamics of the orthogonal injection of the steam into the square duct flow channel through which the air containing coal particulates has been investigated. The steam was injected into the flow channel to wet the coal particles to enable their separation from the air based on the particles becoming heavier. The experimental setup used in the present study consisted of the 2 cm × 2 cm square flow duct made of the transparent Perspex and was 50 cm long. The mixture of air and coal particles was introduced at one end of the duct, and a centrifugal rotator was located at the other end of the duct, which was used to separate the coal particles from the wet coal particles from the air. And swirling steam was injected into the duct by two nozzles located at lower and upper surfaces of the duct. PIV images of the flow field at varying steam and air pressure and making use of the measurements of the turbulent fluctuating velocities, relative velocity and transient analysis, spike in removal efficiency of the coal particles from the air was found as 4–7%, corresponding to the range of particle sizes, 0.30–0.45 μm, inlet steam pressure of 1.5 bars and air pressure varying from 0.4 to 3.0 bars. However, the overall separation efficiency was obtained as 51%.

All commercial aircraft employ a system called Environmental control system (ECS) to ensure an environment that accomplishes the physiological and comfort demands by passengers and aircrew. This task requires functionalities like temperature control, humidity regulation apart from the governing of cabin pressure. The energy source for ECS is a pressurized hot air bleed (180 °C-250 °C, 2.75 bar) from the engine or Auxiliary Power Unit (APU) along with the ram air. During the functional operation, the unit of Heating, Ventilation, and Air Conditioning (HVAC) duct experiences repetitive temperature fluctuations in addition to the cyclic pressurization leading to thermal fatigue and cyclic stress over the duct material, promoting crack propagation at weld zones in the duct. Therefore, a comparative investigation on conjugate heat transfer analysis is done at welded joints annexed to the bypass valve and trim air valve using airflow bench set up and validated by computational fluid dynamics. During this investigation, the circular duct with spherical junction (D/d = 3.84 & L/d = 6) was the most efficient and economical design that could fit in for designing air conditioning duct undergoing high thermo-cyclic stress.

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.

A combined numerical and experimental study is conducted to test the heat transfer enhancement and friction factor characteristics for a rectangular duct fitted with three cases of ribs turbulators: continuous ribs, intermittent-continuous-intermittent ribs, and intermittent ribs. Experiments are conducted within a turbulent flow for Reynolds numbers values varied from 10000 to 35000, pitch ratio equal to 5 and height ratio of 0.33. The numerical study carried out using ANSYS FlUENT17.2. The turbulence is modeled by using k-? model. The results showed that the case of intermittent ribs provide the highest over performance factor while the continuous ribs indicate less overall performance factor among the considered cases. In addition, the results show that the highest values of the friction factor are marked from the case of intermittent ribs and then the case of intermittent-continuous-intermittent ribs followed by continuous rib case. The continuous rib case showed the lowest friction factor.

This paper aims to assess the control mechanism's efficiency and flow pattern in the pipe. The flow was investigated for Mach numbers M = 1.25, 1.3, 1.48, 1.6, 1.8, 2.0, 2.5, and 3.0 for a step height of 3 mm. The NPRs of the tests were from 11 to 3. The flow revealed the minimum duct requirement for a given Mach number and NPR as L = 2D. Only some selected cases where control mechanism impacts considerably are presented. In most of the cases, the flow field was the same. There is a reversal in control in the flow field; only such cases are discussed. At low Mach numbers, the flow regulator raises the pressure, and for the rest of the Mach numbers, the control findings are to reduce the pressure except at NPR = 9 at Mach M = 3.0, a reversed trend.

The laminar forced convection of fluids flow inside a non-circular duct has been investigated both experimentally and numerically by numerous researchers. These studies mainly focused on exploring the characteristics of nanofluid flow and duct shape to increase the heat transfer coefficient and decrease the pressure drop using various nanoparticle concentration. However, there still exists many challenges which need to be resolved to find out perfect nanofluid and suitable duct shape. This paper summarizes most of the laminar forced convective heat transfer literatures concentrated on the flow inside non-circular ducts in order to identify the challenges and propose the targeted solutions of these problems to improve the overall heat transfer efficiency. This research also analyzed the several parameters such as types of nanoparticles, particle size, host fluid, particle volume concentration, various thermal and hydrodynamic effects characteristics of laminar convective heat transfer with nanofluids. In addition, the paper also offers details on the most widely used correlations used to predict the efficient thermophysical properties of nanofluids.

The jet from a round Laval nozzle followed by a cylindrical duct with an inner diameter of 10 mm and a length of 50 mm is investigated experimentally. The Laval nozzle has a design Mach number of 1.5. Quantitative flow visualization of the jet issued from the duct exit is performed over a range of nozzle pressure ratios from 2.0 to 4.5 using the rainbow schlieren deflectometry combined with the computed tomography to investigate the jet three-dimensional structure. The flow features of the near-field shock systems in the jets are displayed with the density contour plot at the cross-section including the jet centerline. Effects of the nozzle pressure ratio on the density profile along the jet centerline are clarified quantitatively. In addition, a comparison between the present experiment and the previous one with a conventional Laval nozzle for jet centerline density profiles is carried out to examine the effect of the cylindrical duct. Furthermore, the three-dimensional structures of overexpanded and underexpanded jets are demonstrated with the isopycnic surfaces to visualize the internal flow features.

This paper concerns the motion of the supersonic potential flow in a two-dimensional expanding duct. In the case that two Riemann invariants are both monotonically increasing along the inlet, which means the gases are spread at the inlet, we obtain the global solution by solving the problem in those inner and border regions divided by two characteristics in \begin{document}$ (x, y) $\end{document} -plane, and the vacuum will appear in some finite place adjacent to the boundary of the duct. In addition, we point out that the vacuum here is not the so-called physical vacuum. On the other hand, for the case that at least one Riemann invariant is strictly monotonic decreasing along some part of the inlet, which means the gases have some local squeezed properties at the inlet, we show that the \begin{document}$ C^1 $\end{document} solution to the problem will blow up at some finite location in the non-convex duct.

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%

Large-eddy simulations are used to demonstrate the effects of Rayleigh-Taylor instabilities (RTIs) on constant-pressure, turbulent premixed flames stabilized in a curved rectangular duct. A splitter plate of constant radius separates a reactant and pilot stream such that the flame stabilizes in the mixing layer between the two streams. Centrifugal acceleration due to the duct curvature induces the RTI, increasing the mixing of the higher-density reactant stream with the lower-density pilot stream. In both non-reacting and reacting flows, the resulting mixing layer thickness grows at rates comparable to those in unconfined RTIs until the flame occupies approximately half of the duct, at which point the duct walls limit the growth rate. The conservative equations are modified with artificial body forces to negate the centrifugal effect (and the RTI) to isolate the impact of the curved geometry. A comparison between the flames with and without the RTI shows that the RTI increases the turbulent flame speed primarily through increased flame surface area. The RTI also increases the range of local flame stretches and curvatures. The increased turbulent flame speed and growth rates due to RTI suggest a viable mechanism to increase turbulent flame speed in gas turbine engines though the application of flow path curvature.

This article presents a solar air heater channel artificially made rough with a transverse roughness in square-wave shape, investigated for the enhancement in heat transfer and fluid flow characteristics. Non-uniform profile of the ribs has been used by providing periodic gaps for reduction in eddies behind the rib. The research incorporates relative roughness width from 10–310, relative roughness pitch = 10, relative roughness height = 0.043, and Reynolds number from 3000–15000, respectively. The procedure followed for the CFD investigation has been confirmed with the experimental results. The maximum increment in Nusselt number was 2.22, and the consequent value for the friction factor increment of 3.44 was obtained. The highest THPP value of 1.49 was obtained while maximum thermal efficiency of 68.6% was achieved. The non-uniform ribs were found better as compared to uniform ribs. The results have been demonstrated using graphical contours and streamlines.

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 is 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.

Acoustic performance of dissipative silencer was evaluated to determine the effectiveness of perforated duct porosity and absorbent material density in reducing occupational noise exposure propagated from centrifugal fan. Design charts were applied to predict noise reduction and length of a dissipative silencer. Dissipative silencers with various punched duct porosity (14%, 30% and 40%) and sound absorbent density (80 Kg/m3 , 120 Kg/m3 , and 140 Kg/m3 ) were designed and fabricated. According to ISO9612 and ISO11820, noise level was measured before and after installing all nine test silencers at fixed workstations around the discharge side of a centrifugal fan in a manufacturing plant. On average, the noise level at the discharge side of a fan without silencer was measured to be 93.6 dBA, whereas it was significantly mitigated by 67.4 dBA to 70.1 dBA after installing all silencers. Dynamic insertion loss for a dissipative silencer with 100 cm length was predicted to be 27.9 dB, which was in agreement with experimental ones. Although, there was no significant differences between insertion loss of silencers, the one with 30% porosity and 120 Kg/m3 rock wool density had the highest insertion loss of 26.2 dBA. Dissipative silencers noticeably reduced centrifugal fan noise exposures. Increasing sound absorbent density and duct porosity up to a certain limit could probably be effective in noise reduction of dissipative silencers.

In this paper, the Pseudo shock structure in a convergent–long divergent duct is investigated using large eddy simulation on the basis of Smagorinsky–Lilly,​ Wall-Adapting Local Eddy-Viscosity and Algebraic Wall-Modeled LES subgrid models. The first objective of the study is to apply different subgrid models to predict the structure of Lambda form shocks system, while the ultimate aim is to obtain further control of the shock behavior. To achieve these goals, the dynamic grid adaption and hybrid initialization techniques are applied under the 3D investigation to reduce numerical errors and computational costs. The results are compared to the existing experimental data and it is found that the WMLES subgrid model results in more accurate predictions when compared to the other subgrid models. Subsequently, the influences of the divergent section length with the constant ratio of the outlet to throat area and, the effects of discontinuity of the wall temperature on the flow physics are investigated. The results indicate that the structure of compressible flow in the duct is affected by varying these parameters. This is then further discussed to provide a deeper physical understanding of the mechanism of Pseudo shock motion.

Under the dual effects of aerodynamic heating and high-power electronic equipment heating, the heat sink and power demand of advanced high-speed aircraft have been exponentially rising, which seriously restricts the aircraft performance. To improve system cooling and power supply performance and reduce engine performance loss, a power and thermal management system (PTMS) with high performance, low energy consumption, and light weight urgently needs to be developed. In this paper, three modes of a potential PTMS with different heat sinks and bleed air sources are further discussed to analyze and compare the optimal matching with the flight mission at Mach 1-4.4. The equivalent mass method is used to uniformly assess the costs of the fixed weight, bleed, resistance, etc. as a function of the fuel weight penalty, which is chosen as the optimization objective. The optimization variables consist of the compressor outlet temperature, cooling air flow rate, and fan duct heat exchanger structure size. The results show that the intermediate-stage bleed air and fan duct heat sink are more suitable when the Mach number is less than 2, but the ram air bleed is highly suitable for flight missions at a high Mach number. Especially at Mach 3.4-4.4, the ram air bleed mode can respond to the cooling and power demands with a simple architecture.

Natural draft chimneys are the traditional chimneys, which are being the most used because of its low cost and simple design compared to solar and other smart chimneys. However, the use of traditional chimneys reported the problem of back drafting particularly in colder regions. Utilization of various suction devices such as exhaust fan, vacuum cleaner and dryers lead to the development of negative pressure inside the house, which in turn causes possibilities of back drafting in chimneys. This allows the outside air to get into the house and affects the entire ventilation system. Stack effect of dwellings and other environmental factors such as seasonal temperature and pressure changes are the influential factors for back drafting along with the furnace on and off conditions. A numerical analysis of the flow of motion in the chimney was performed to visualize its behavior under all conditions including back drafting. CFD simulation results shown that the inside pressure gradient and temperature gradient of chimney determine the direction of hot dry air gases because of the variation in density of gas with respect to temperature change. The numerical study can be used to modify the design of vertical chimney duct such that flow can get only accelerated on moving towards the top of the chimney.

This manuscript reports computational fluid dynamic simulations of turbulent air forced-convection and friction loss in a horizontal-duct air-heat exchanger. Epsilon-shaped baffles are inserted on the bottom wall of the channel to augment its thermal efficiency. The working fluid is flowing under Reynolds numbers (Re) within the range [17,000–32,000]. The presence of the epsilon-shaped vortex generator (VG) in the duct heat exchanger forced a considerable increase of the convective thermal transfer in the domain, but it caused also significant friction losses. For all Re numbers used, the heat transfer rate in epsilon-shaped baffle case was upper than that in no-baffle case, which indicates that the epsilon-baffled exchanger is more efficient than the simple exchanger with no VG.

2-D numerical investigation of rib implementation on smooth plates of the solar air heater (SAH) to enhance the heat-transfer coefficient was carried out. Semi-circular contrived shapes of ribs are considered for numerical investigation. ANSYS Fluent 16 is used to analyse the turbulent airflow for different arrangement of ribs and the outcomes were compared with a smooth duct in order to understand the enhancement in Nusselt number with the Reynolds number investigated in the range of 3800 to 18000. The renormalization k-∊ model was used to simulate the proposed geometry with varying pitch distance P = 10, 15, 20, 25 mm for investigation. Results reveal that semi-circular rib with pitch distance P = 15 mm shows the best Nusselt number and gradual reduction of friction factor.

This study focuses on the investigation of enhancing convective heat transfer between the absorber and the air inside a channel. The investigation approaches modeling different absorber through CFD simulation and validating the result with experimental data. Supplying air to both sides of the top and the bottom surfaces of the absorber increase the air mass flow rate and therefore increases the thermal efficiency of the dryer. The studies in a V-grooved absorber attain high hot air velocity; high thermal efficiency resulted from high turbulence created in the duct. For the sample taken with a flow range, 0.01kg/s to 0.06 kg/s, the high output temperature was observed in a lower temperature range and increases as the flow rate increases. At a flow rate 0.01 kg/s, the velocity of hot air passing over the V-grooved absorber attain 0.28 m/s and increased to 1.4 m/s as the mass flow rate increased to 0.06 kg/s. For the rectangular absorber, the velocity of hot air attains 0.15 m/s at a flow rate of 0.01 kg/s and increased to 1.46 m/s as the mass flow rate increases to 0.06 kg/s. The double-sided V-grooved absorber contributes 8 – 12.40% value more efficiency compared to the rectangular plate with the same flow orientation. Further investigation is recommended taking the quantitative analysis obtained in this study and generating qualitative data.

In present communication, analytical expressions have been developed for electrical efficiency of an opaque (G-T) and a semitransparent (G-G) Photovoltaic panels in different photovoltaic thermal (PVT) configurations. Water and air are used for withdrawing the heat linked with the solar panel. Four configurations of opaque and semitransparent type PV modules have been discussed here. Namely case I: opaque solar panel where water flows above the module; case II: semitransparent solar panel where water flows above the panel; case III: opaque solar panel where air flows at beneath of the panel through duct and water flows above the panel and case IV: semitransparent solar panel where air flows at beneath of the panel through duct and water flows above the panel have been considered for the present study. It has been observed that case IV gives better results with related to the electrical energy generation among all four cases. Average electrical efficiency is increased by 2.29% and 4.17% respectively from case I to III and from case II–IV.

To effectively examine the flame propagation of premixed hydrogen-air explosion in a closed duct with obstacles, this paper conducts a numerical study of the flame propagation during the hydrogen explosion in a closed duct with obstacles. Fractal dimensions are used to represent the flame structure. When the number of obstacles is 1, 2, and 3, the fractal dimensions corresponding to flame propagation are 1.632, 1.655 and 1.661 respectively. The research shows that the propagation of explosion flame under obstacle conditions accords with typical self-similarity. The more the number of obstacles, the stronger Kelvin-Helmholtz (K–H) instability and Rayleigh -Taylor (R-T) instability formed, the more obviously the flame is stretched, and the greater the turbulence of the flame propagation. When the number of obstacles is 1, 2 and 3, the corresponding maximum speeds are 108 m/s, 176 m/s and 196 m/s respectively, and thus the flame propagation speed is proportional to the number of obstacles. Flame acceleration is caused by the flow compression due to reduced flow area at the cross-section of obstacles. The flame propagation speed manifests different characteristics through the spherical flame propagation, transformation from the finger flame to twisted flame propagation, and the twisted flame propagation, corresponding to three stages of slow growth, continuous growth and turbulent growth in explosion overpressure.

In this paper, the sound transmission loss by different materials at aircraft noise is measured experimentally. The main objective of this paper is to measure the acoustical or sound absorption properties of glass material, polypropylene material and glass fiber reinforced composite material. The composite material is manufactured at three different fiber volume fractions. The fiber volume fractions are 10%, 20% and 30%. A three dimensional wooden sound proof duct is manufactured in which a long duct is enclosed. An acoustic source is used to generate an aircraft noisy signal. The generated signal is passing through the samples of the different material to measure their sound absorption properties. It is observed that for each fiber orientation, glass material is absorbing more aircraft sound than neat polypropylene and composite specimens. It is concluded that composite material with 10% volume fraction of fiber is performing better than the rest of specimens. This is due to the fact that with the increase in volume fraction of fiber, porosity decreases due to which sound transmission loss decreases. Also, the sound transmission loss of composite specimen with 10% volume fraction of fiber is comparable with that of the glass material.

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 gradients on 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 the lower duct length. In most cases, flow is not negatively affected by control. � 2021 Elsevier Ltd. All rights reserved.

When undertaking a numerical solution of Helmholtz problems using the Boundary Element Method (BEM) it is common to employ low-order Lagrange polynomials, or more recently Non-Uniform Rational B-Splines (NURBS), as basis functions. A popular alternative for high frequency problems is to use an enriched basis, such as the plane wave basis used in the Partition of Unity Boundary Element Method (PUBEM). To the authors’ knowledge there is yet to be a thorough quantification of the numerical error incurred as a result of employing high-order NURBS and Lagrange polynomials for wave-based problems in a BEM setting. This is the focus of the current work, along with comparison of the results against PUBEM. The results show expected improvements in the convergence rates of a Lagrange or NURBS scheme as the order of the basis functions is increased, with the NURBS basis slightly outperforming the Lagrange basis. High-order Lagrange and NURBS formulations can compare favourably against PUBEM for certain cases. In addition, the recently observed pollution effect in BEM is studied for a travelling wave in a duct and the numerical dispersion presented for all three sets of basis functions.

The solar air heater is widely used to dry agricultural products such as fruits, vegetables & crops. The problem observed in earlier solar air heater is to develop a fully developed flow inside the casing solar air heater. Being the outlet of the blower is restricted to a small cross-section by the manufacturers, hence providing the trapezoidal-shaped duct is essential. The flow is not fully developed flow inside the casing of SAH. To overcome this problem guide vanes, provided inside the trapezoidal-shaped duct, and that did not solve the problem. Then flow-restricting devices are incorporated inside the duct to make a fully developed flow. Flow restriction devices, also known as perforated plates with various percentage openings. The experiment has been carried to test the solar air heater with and without flow-restricting devices and guide vanes. A velocity reading has been taken across the cross-sectional area of the casing of solar air heater. To validate the experimental results, CFD analysis has been done for the solar air heater. The computational results are good in agreement with the experimental values. Then the solar air heater was analyzed at a different angle of inclination such as 20°, 30°, 40°, 50° & 60°. In all these angle of inclination, the absorber plate material is aluminium. By comparing all these results, 20° inclination angle gives more outlet temperature than the others. Then the absorber plate material is changed to copper, and comparing the copper results with aluminum, aluminum gives more outlet temperature as the aluminum has higher heat holding capacity than the copper.

To grasp the effects of forced-air volume and suction region on the migration and dust suppression of air curtain during fully mechanized tunneling process, the 1:1 proportional physical models of the 2-5082 fully mechanized tunnel were constructed, the CFD-DPM based numerical simulations were conducted. The results showed that during the migration process of the air curtain, the decrease of the forced-air volume and the arrangement of the suction region near the side wall opposite to the forced-air duct were conducive to the formation of a uniformly distributed axial airflow region. At the same time, the dust pollution area satisfied the rule of reducing with the decrease of the forced-air volume as well. When the forced-air volume was 350 m3/min and the suction region was near the side wall opposite to the forced-air duct, the diffusion distance of high concentration dust reached to the minimum, the dust concentration at the place that the tunneling driver located had fallen below 50 mg/m3, the best dust suppression performance could be achieved. The model effectiveness was finally validated by comparing the simulation results with the field measured values. This study could provide new insights into the environmental sustainability of tunneling process. The achievements could meet the requirements of process safety and environmental protection in fully mechanized tunnels.

The present paper examines the hypothetical and empirical effects of geometrical parameters via transverse ribs on the back of a jet-impingement solar air heater absorber plate. MATLAB software environment was utilised to develop and solve equations on the steady-state energy balance. Moreover, verification of the performance was done through indoor experiments by employing a solar simulator. The range of parameters included rate of mass flow (ṁ), from 0.007 to 0.039 (kg/s), height of the rib (e) from 0.0017 to 0.0032 (m), relative pitch (P) from 0.01 to 0.04 (m), aspect ratio of the duct was 12, and solar irradiance (I) from 500 to 1000 (W/m2). Finally, the outcomes were compared to smooth ducting hose based on the same condition of flows to examine the improvement of solar air heater thermal efficiency. Therefore, the optimum thermal efficiency was found to be 78% at a (i) mass flowrate of 0.039 (kg/s), (ii) ambient temperature of 297(K), and (iii) a solar irradiance of 1000 (W/m2).

A novel environmentally friendly silencer concept for noise control in HVAC applications is presented and its acoustic properties are studied in this paper. As a sustainable alternative to the mass-produced, nowadays unfavourable fibrous material filled silencers, the silencing effect of the new solution is based on multi-layered microperforated elements. A prototype silencer following standard HVAC dimensions has been composed and optimal design and technological aspects of the fibreless solution are described. The paper also provides overview of experimental methods for the determination of primary acoustic characteristics, including low frequency transmission loss spectra in various mean flow conditions and insertion loss results for the silencer. The acoustic effect is hereby validated by comparison of the results with experimentally obtained characteristics of typical fibrous material filled units commercially available in the region. The conclusions of the acoustic study demonstrate the suitability of the silencer type for a variety of HVAC implementations were reliable and eco-friendly noise cancellation is important.

This article investigates the wall pressure dissemination on a circular duct when the flow is exhausted into a CD nozzle. This study aims at to scrutinize the static pressure on the duct wall and its growth when the control is activated. The microjets are employed at the base at pitch circle radius (PCR) of 6.5 mm, and the radius of the microjets are 0.5 mm. The Mach numbers and the duct area ratio used are 2.56, Mach (M) 2 and 3. The lift to diameter ratio (L/D) and nozzle pressure ratio (NPR) of the study were from L/D = 10 to 1 and NPRs from 3 to 11. The NPRs tested were at different expansion level for M = 2. The oscillations in the duct flow field are seen when they are under expanded, and this trend continues for the total length of pipe. When the nozzles are ideally expanded the oscillations are absent as at this NPR only the Mach waves will be present. Similar trends are also seen at NPR 3 as well as whenever there is an adverse pressure gradient at Mach 2. With the decline in pipe length, the wavy nature of the flow is getting died out, and pressure recovery is smooth. The duct length and the backpressure has a crucial role to play in dictating the magnitude of wall pressure. L/D = 2 seems to be sufficient for M = 2 to continue to remain committed with the pipe, whereas for M = 3 the lowest duct size required is L/D = 4.

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.

This article deals with the analysis of planar trifurcated lined waveguide backed by a line walled cavity involving multiple step discontinuities. The duct configuration is placed symmetrically abo...

In hot climatic regions, some kind of cooling system is necessary to avoid warmth and humidity. Many of the available cooling systems are not economic and sustainable. In this study, sustainable and feasible space/room cooling systems have been experimentally analyzed. A solar operated cooling system with two options have been designed and their performances are compared. Phase Change Material (PCM) is proposed to store thermal energy instead of a costly battery. A 1200-watt compressor and fin-type condenser are used to construct the vapor compression system. When the incoming air is passed through the cooling coil, it gets cool. For this cooling coil, 50 feet copper tube is used. The front side copper tube diameter of the fan is 3/8 inch and the backside tube diameter is 1/2 inch. It took about 35 minutes and 5 minutes to minimize the room temperature at the desired level in the case of the stand fan and duct fan, respectively. Furthermore, the stand fan and duct fan systems reduced 3 ℃ and 6 ℃ of the outside temperature, respectively.

Condensation process, from moist airflow over flat plate, is investigated theoretically and experimentally. This process has many important engineering applications, which are concerning with moist air treatment. In The theoretical analysis of the present work, the flow is assumed to be laminar, steady and of constant physical properties. The process is described by continuity, momentum, energy and concentration partial differential equations expressed in Cartesian coordinates system. Due to the nature of the studied problem and with proper transformation of the problem dependent and independent variables, these governing equations are transformed to set of ordinary differential equations. Accordingly, one can obtain similar solutions of the problem, which are obtained by application of the well-known numerical method Rung-Kutta accompanied with shooting method. According to this solution, the values of Nusselt and Sherwood numbers, for all values of Reynolds number are obtained. The test section, of the experimental work, is a rectangular duct with cooled bottom. The moist air is forced to flow inside the duct, where some of water is condensed over its lower surface. The values of dry bulb temperature and wet bulb temperature are measured through out the flow field for different values of flow velocity. In accordance heat and mass transfer coefficients are estimated for different operating conditions. A correlation formula of the problem parameters is proposed. According to the obtained experimental results, the average heat and mass transfer coefficients increases by increasing velocity up to certain value of it then decreases for more increase of velocity. Comparisons are made between present obtained experimental results and those results obtained in previous work, exhibit good agreement in the studied region.