Flowing Air Stream Research Articles

Radiant recuperator modelling and design

Recuperators are frequently used in glass production and metallurgical processes to preheat combustion air by heat exchange with high temperature flue gases. Mass and energy balances of a 15 m high, concurrent radiant recuperator used in a glass fiber production process are given. The balances are used: for validation of a cell modeling method that predicts the performance of different recuperator designs, and for finding a simple solution to improve the existing recuperator. Three possible solutions are analyzed: to use the existing recuperator as a countercurrent one, to add an extra cylinder over the existing construction, and to make a system that consists of a central pipe and two concentric annular ducts. In the latter, two air streams flow in opposite directions, whereas air in the inner annular passage flows concurrently or countercurrently to flue gases. Compared with the concurrent recuperator, the countercurrent has only one drawback: the interface temperature is higher at the bottom. The advantages are: lower interface temperature at the top where the material is under maximal load, higher efficiency, and smaller pressure drop. Both concurrent and countercurrent double pipe-in-pipe systems are only slightly more efficient than pure concurrent and countercurrent recuperators, respectively. Their advantages are smaller interface temperatures whereas the disadvantages are their costs and pressure drops. To implement these solutions, the average velocities should be: for flue gas around 5 m/s, for air in the first passage less than 2 m/s, and for air in the second passage more than 25 m/s.

Numerical study of mixed convection heat transfer of various fin arrangements in a horizontal channel

The mixed convection of a three-dimensional square duct with various arrangements of fins in both laminar and turbulent flow is numerically characterized and studied. This study focuses on the ability of fin arrangements to enhance a heat transfer while flow is incompressible and the fluid is air. In our models, the lower duct wall is defined with a constant heat flux condition while the two side walls and upper wall are insulated. The finite volume method with the SIMPLE (Semi Implicit Method for Pressure Linked Equations) algorithm is used for handling the pressure–velocity coupling. The numerical results are validated with experimental data and show good agreement. The computations confirm that fin arrangement significantly changes the temperature distribution and cooling performance of the fins. This study focuses on the new arrangements of the fins that are not presented in previous studies. These arrangements have 3 Models with two angles (30 and 45°). According to the results, heat transfer highly improves (approximately 40–50% in the laminar flow stream and 15–20% in turbulent flow in comparison to base plate heat transfer) as the simple fin arrangement is replaced by inclined fins. Moreover, the influence of limited heat flux on temperature distribution is extensively investigated. It is notable that the temperature of fins significantly reduces as the best arrangement of the fins is presented in the air flow stream. Therefore, an enhanced cooling zone occurs when the fin arrangement is adjusted according to the location of the source of the heat flux on the base plate.

Determination of the Zone Endangered by Methane Explosion in Goaf with Caving of Longwalls Ventilated on „Y“ System

Abstract One of the most dangerous and most commonly present risks in hard coal mines is methane hazard. During exploitation by longwall system with caving, methane is emitted to mine heading from the mined coal and coal left in a pile. A large amount of methane also flows from neighboring seams through cracks and fissures formed in rock mass. In a case of accumulation of explosive methane concentration in goaf zone and with appropriate oxygen concentration and occurrence of initials (e.g. spark or endogenous fire), it may come to the explosion of this gas. In the paper there are presented results of numerical analysis of mixture of air and methane streams flow through the real heading system of a mine, characterized by high methane hazard. The aim of the studies was to analyze the ventilation system of considered heading system and determination of braking zones in goaf zone, in which dangerous and explosive concertation of methane can occur with sufficient oxygen concentration equal to at least 12%. Determination of position of these zones is necessary for the selection of appropriate parameters of the ventilation system to ensure safety of the crew. Analysis of the scale of methane hazard allows to select such a ventilation system of exploitation and neighboring headings that ensures chemical composition of mining atmosphere required by regulation, and required efficiency of methane drainage. The obtained results clearly show that numerical methods, combined with the results of tests in real conditions can be successfully used for the analysis of variants of processes related to ventilation of underground mining, and also in the analysis of emergency states.

An efficient photo-catalytic VOC removal process by one-pot synthesized N-F/TiO2 nanoparticles in fluidized-spouted bed reactor

ABSTRACTPhotocatalytic degradation under visible light irradiation is an important task of using solar energy for the removal of environmental pollutants. N-F/TiO2 nanoparticles were synthesized in one-pot sol–gel condition using tetra-isopropyl-orthotitanate as the TiO2 precursor and NH4F as the N-F doping source. Diffuse reflectance spectroscopy (DRS) analysis of the material has shown a reduction of band gap energy and shifting absorption edge to the visible wavelengths. A fluidized-spouted bed reactor equipped with the light source was designed and constructed for the oxidation process of VOC from the high airflow rate under Hg lamp irradiation using synthesized N-F/TiO2 nanoparticles. Acetaldehyde was used as the air pollutant model molecule of VOC in this process. The effluent acetaldehyde concentration was analyzed continuously along the time by an online Gas Chromatography (GC) from the start up to reaching steady conditions. The results have revealed significant enhancement of acetaldehyde removal by the N-F/TiO2 sample fabricated with an equal weight ratio of NH4F/Ti. After steady conditions, almost 100% removal of acetaldehyde was observed in the spouted bed reactor from a high airflow stream of 5 L/min polluted with 1000 ppm acetaldehyde at room-temperature conditions, under 80 W Hg with 500 Lux intensity.

Heat transfer behavior of flat plate having spherical dimpled surfaces

In the present study, heat transfer analysis of dimpled surfaces of external flow was investigated. A total of 14 types of dimpled surfaces are studied. The effect of dimple pitch was examined. The experiments were carried out with air stream flows over the heated surface with dimples. The temperature and velocity of air stream and temperature of dimpled surfaces were measured. The heat transfer of dimpled surfaces was investigated and compared with the result of smooth surface. For the staggered arrangement, the computed results show that the maximum Nusselt number for dimpled surfaces are about 26% better than smooth surface. And for the inline arrangement, the results show that the maximum Nusselt number for dimples surfaces are about 25% better than smooth surface.

Effect of cooling pad installation on indoor airflow distribution in a tunnel-ventilated laying-hen house

Extra cooling pads on the sidewalls are needed for larger poultry houses using tunnel ventilation system. Preliminary study showed that the airflow velocity going through different aisles varies greatly when the extra pads are installed at the end of sidewalls, making a “[”-shape air inlet. Combined with field tests, the CFD (computational fluid dynamics) technology was used to study the uniformity of airflow distribution in a tunnel-ventilated laying-hen house. The air distribution was first monitored in a layer house to find the main reason resulting in the variations of airflows in different aisles. Then CFD simulations were carried out with different distances (D=2 m, 3 m or 4 m) between the pads on end-wall and the extra pads on side walls. The field test showed that airflow streams from the different groups of cooling pads collided vertically at the house corners, mixed with each other, then flew towards the center of the house. This was the main reason that the wind speed in the middle aisle was much higher than in other aisles, leaving large zones of lower ventilation in the aisles adjacent to the sidewalls. The results of CFD simulations indicated that air distributions could be significantly improved when the extra pieces of pads were moved away for an appropriate distance from the end coolingpads. As far as conventional poultry house with a span of 12 m, the air speeds in different aisles were more uniform when this distance was about 3 m. Keywords: Pad cooling system, air distribution, air speed, laying-hen house; CFD DOI: 10.3965/j.ijabe.20160904.2447 Citation: Hui X, Zhu Q, Ni J Q, Li B M, Shi Z X, Zhao S M, et al. Effect of cooling pad installation on indoor airflow distribution in a tunnel-ventilated laying-hen house. Int J Agric & Biol Eng, 2016; 9(4): 169－177.

Laminar flow and heat transfer between a regularly distributed elliptical hollow fiber membrane tube bank

Effects of the various semiaxis ratios (ble/ale, bri/ari), longitudinal and transverse pitch-to-diameter ratios (SL/d, ST/d) on the longitudinal fluid flow and heat transfer between a regularly distributed elliptical hollow fiber membrane tube bank (EHFMTB) employed for air humidity control are investigated. In the tube bank, the liquid stream flows inside the fibers, while the air stream flows axially between the fibers in a counter flow arrangement. Two regularly populated arrangements of the tube bank, in-line and staggered, are considered. Two representative elements containing two fibers and the air stream flowing axially between the fibers are selected as the calculating domains. The governing equations for the fluid flow and the heat transfer between the EHFMTB are established and numerically solved via a boundary-fitted coordinate transformation method. The fully developed Poiseuille numbers (fRe) and local Nusselt numbers under a uniform temperature condition (NuT) under various semiaxis ratios, longitudinal and transverse pitch-to-diameter ratios are then obtained. It can be found that the fRe and NuT have their largest values when the ble/ale and bri/ari both are equal to 1.0 and 1.5 for the in-line and the staggered arrangements, respectively. The SL/d and ST/d have larger influences than the ble/ale and bri/ari on the fRe and NuT.

Drying and recovery of aerobic granules

To dehydrate aerobic granules to bone-dry form was proposed as a promising option for long-term storage of aerobic granules. This study cultivated aerobic granules with high proteins/polysaccharide ratio and then dried these granules using seven protocols: drying at 37°C, 60°C, 4°C, under sunlight, in dark, in a flowing air stream or in concentrated acetone solutions. All dried granules experienced volume shrinkage of over 80% without major structural breakdown. After three recovery batches, although with loss of part of the volatile suspended solids, all dried granules were restored most of their original size and organic matter degradation capabilities. The strains that can survive over the drying and storage periods were also identified. Once the granules were dried, they can be stored over long period of time, with minimal impact yielded by the applied drying protocols.

Performance prediction of solid desiccant – Vapor compression hybrid air-conditioning system using artificial neural network

In the present study, ANN (artificial neural network) model for a solid desiccant – vapor compression hybrid air-conditioning system is developed to predict the cooling capacity, power input and COP (coefficient of performance) of the system. This paper also describes the experimental test set up for collecting the required experimental test data. The experimental measurements are taken at steady state conditions while varying the input parameters like air stream flow rates and regeneration temperature. Most of the experimental test data (80%) are used for training the ANN model while remaining (20%) are used for the testing of ANN model. The outputs predicted from the ANN model have a high coefficient of correlation (R > 0.988) in predicting the system performance. The results show that the ANN model can be applied successfully and can provide high accuracy and reliability for predicting the performance of the hybrid desiccant cooling systems.

A Shape Memory Alloy-based Morphing Axial Fan Blade: Functional Characterization and Perspectives

In a traditional automotive cooling system, energy optimization could be achieved by controlling the engine temperature by means of several sensors placed inside the cooling circuit. Nevertheless, in some cases the increasing use of a great number of sensor devices makes the control system too bulky, expensive and not sufficiently robust for the intended application. This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by Shape Memory Alloy (SMA) strips that work as actuator elements in the polymeric blade structure. The blade was designed to achieve the activation of the strips (thermo-mechanically treated on purpose) by means of an air stream flow. With the aimof studying the morphing capability of the adaptive structure together with the recovery behavior of the NiTi strips, four different polymeric compounds have been compared in a specifically-designed wind tunnel. As the airstream flow increases its temperature, the strips recover the memorized bent shape, leading to a camber variation. To study the possibility of employing SMA strips as actuator elements, a comparison with common viscous clutchbehavior is proposed. The time range actuator response indicates that the SMA strips provide a lower frequency control that fits well with the engine coolant thermal requirement. The experimental results demonstrate the capability of SMA materials to accommodate the lower power actuators in the automotive field. This innovative passive control system results from the selection of (i) the memorized shape of the SMA strips and (ii) the polymeric compound used for the blade structure.

A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part II: Blade Shape and Computational Fluid Dynamics Analyses

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper, experimental and computational fluid dynamics (CFD) numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed. Starting from the experimental results proposed in the first part of this work, a morphing blade, made of shape memory alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques. After the analyses in the wind tunnel, CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with nonactivated blades and with activated blades. The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in the fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan. This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life, thanks to a strong relationship between the engine thermal request and the cooling fan performance.

Numerical investigation of injection within an axisymmetric rotating detonation engine

This investigation characterizes the mixing processes and injection flow field within a rotating detonation engine. The axisymmetric baseline geometry produces poor fuel/air mixing in the immediate injection region due to reduced fuel penetration into the wide, perpendicularly flowing air stream. Injection parameters including reactant flow rate, injection area, and placement of the fuel injection are varied from the baseline geometry to assess the impact on mixing. Decreasing reactant injection areas improves fuel penetration into the cross-flowing air stream, and turbulent diffusion of the fuel is enhanced within the annulus increasing local equivalence ratio. When fuel is injected into the air slot, local equivalence ratio is enhanced due to the increasing mixing length between the recirculation region and fuel injection. Emulating nozzle integration by increasing annulus back-pressure increases local equivalence ratio in the injection region due to increased convection residence time.

Bump-Type Foil Bearings and Flexure Pivot Tilting Pad Bearings for Oil-Free Automotive Turbochargers: Highlights in Rotordynamic Performance

Oil-free turbochargers (TCs) require gas bearings in compact units of enhanced rotordynamic stability, mechanical efficiency, and improved reliability with reduced maintenance costs compared with oil-lubricated bearings. Implementation of gas bearings into automotive TCs requires careful thermal management with accurate measurements verifying model predictions. Gas foil bearings (GFBs) are customarily used in oil-free microturbomachinery because of their distinct advantages including tolerance to shaft misalignment and centrifugal/thermal growth, and large damping and load capacity compared with rigid surface gas bearings. Flexure pivot tilting pad bearings (FPTPBs) are widely used in high-performance turbomachinery since they offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability. The paper details the rotordynamic performance and temperature characteristics of two prototype oil-free TCs; one supported on foil journal and thrust bearings and the other one is supported on FPTP journal bearings and foil thrust bearings of identical sizes (outer diameter (OD) and inner diameter (ID)) with the same aerodynamic components. The tests of the oil-free TCs, each consisting of a hollow rotor (∼0.4 kg and ∼23 mm in OD at the bearing locations), are performed for various imbalances in noise, vibration, and harshness (NVH; i.e., cold air driven rotordynamics rig) and gas stand test facilities up to 130 krpm. No forced cooling air flow streams are supplied to the test bearings and rotor. The measurements demonstrate the stable performance of the rotor–gas bearing systems in an ambient NVH test cell with cold forced air into the turbine inlet. Post-test inspection of the test FPTPGBs after the hot gas stand tests evidences seizure of the hottest bearing, thereby revealing a notable reduction in bearing clearance as the rotor temperature increases. The compliant FPTPGBs offer a sound solution for stable rotor support only at an ambient temperature condition while demonstrating less tolerance for shaft growth, centrifugal, and thermal, beyond its clearance. The current measurements give confidence in the present GFB technology for ready application into automotive TCs for passenger car and commercial vehicle applications with increased reliability.

Experimental and Numerical Calculation of Turbulent Timescales at the Exit of an Engine Representative Combustor Simulator

To deepen the knowledge of the interaction between modern lean burn combustors and high pressure (HP) turbines, a nonreactive real scale annular trisector combustor simulator (CS) has been assembled at University of Florence (UNIFI), with the goal of investigating and characterizing the combustor aerothermal field as well as the hot streak transport toward the HP vanes. To generate hot streaks and simulate lean burn combustor behaviors, the rig is equipped with axial swirlers fed by a main air flow stream that is heated up to 531 K, while liners with effusion cooling holes are fed by air at ambient temperature. Detailed experimental investigations are then performed with the aim of characterizing the turbulence quantities at the exit of the combustion module, and specifically evaluating an integral scale of turbulence. To do so, an automatic traverse system is mounted at the exit of the CS and equipped to perform hot wire anemometry (HWA) measurements. In this paper, two-point correlations are computed from the time signal of the axial velocity giving access to an evaluation of the turbulence timescales at each measurement point. For assessment of the advanced numerical method that is large Eddy simulation (LES), the same methodology is applied to a LES prediction of the CS. Although comparisons seem relevant and easily accessible, both approaches and contexts have fundamental differences: mostly in terms of duration of the signals acquired experimentally and numerically but also with potentially different acquisition frequencies. In the exercise that aims at comparing high-order statistics and diagnostics, the specificity of comparing experimental and numerical results is comprehensively discussed. Attention is given to the importance of the acquisition frequency, intrinsic bias of having a short duration signal and influence of the investigating windows. For an adequate evaluation of the turbulent time scales, it is found that comparing experiments and numerics for high Reynolds number flows inferring small-scale phenomena requires to obey a set of rules, otherwise important errors can be made. If adequately processed, LES and HWA are found to agree well indicating the potential of LES for such problems.

A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part I: Blade Structure Design and Functional Characterization

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of shape memory alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called shape memory effect (SME) takes place. This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the nonstationary operating conditions. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures (TTRs) were experimentally evaluated by imposing the actual operating thermal gradient. The SMA strips were then thermomechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating, they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with the SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered. According to these results, the best coupling of SMA strips and polymeric structure is assessed and its timewise behavior is compared to the traditional timewise behavior of a viscous fan clutch.

Using shape memory alloys for improving automotive fan blade performance: experimental and computational fluid dynamics analysis

In recent years, a considerable effort has been devoted towards the application of advanced techniques for turbomachinery efficient fluid dynamic control during operations. A novel strategy to dynamically modify and optimize the performance during operations takes advantage of shape memory alloys properties. Experimental and numerical analyses on a morphing polymeric blade for an automotive axial fan are presented. The blade shape change was achieved by shape memory alloys strips, thermomechanically treated, embedded in the blade and thermally activated by hot air stream flow. Measurement of fluid temperature, blade surface temperature pattern and three-dimensional shape change of the blade during activation was performed by means of an innovative image analysis technique in a purpose-built wind tunnel. Computational fluid dynamics numerical simulations were performed to study performance variations and three-dimensional fluid dynamic behavior of the fan originated from the shape memory effect.

Non-Thermal Plasma Combined with Cordierite-Supported Mn and Fe Based Catalysts for the Decomposition of Diethylether

The removal of dilute diethylether (DEE, concentration: 150 ppm) from an air stream (flow rate: 1.0 L min−1) using non-thermal plasma combined with different cordierite-supported catalysts, including Mn, Fe, and mixed Mn-Fe oxides, was investigated. The experimental results showed that the decomposition of DEE occurred in a one-stage reactor without the positive synergy of plasma and supported catalysts, by which ca. 96% of DEE was removed at a specific input energy (SIE) of ca. 600 J L−1, except when the mixed Mn-Fe/cordierite was used. Among the catalysts that were examined, Mn-Fe/cordierite, the catalyst that was the most efficient at decomposing ozone was found to negatively affect the decomposition of DEE in the one-stage reactor. However, when it was utilized as a catalyst in the post-plasma stage of a two-part hybrid reactor, in which Mn/cordierite was directly exposed to the plasma, the reactor performance in terms of DEE decomposition efficiency was improved by more than 10% at low values of SIE compared to the efficiency that was achieved without Mn-Fe/cordierite. The ozone that was formed during the plasma stage and its subsequent catalytic dissociation during the post-plasma stage to produce atomic oxygen therefore played important roles in the removal of DEE.

The Use of Filtration Theory for Performance Optimization of Volume

Experimental data reveal that dry filters utilizing filter papers tend to change their operational characteristics whilst in service. When the airflow stream in the filter is constant, the pressure losses, and hence energy losses, will increase. On the other hand, when a constant pressure head is maintained to induce the flow, the flow rate of the flowing medium will decrease. A possible solution is a filter made from several filtering layers, their density varying along the dusted air flow path. Basing on the theory of filtration, the density of filter layers shall be chosen such that the amount of particulate matter settling on individual filter layers should be identical. The paper summaries the results of experimental testing of five-layered filters. Of particular interest is the distribution of collected dust mass along the airflow path in the filter in relation to the layer density.

Design Optimization of an Oil-Air Catch Can Separation System

The Positive Crankcase Ventilation (PCV) system in a car engine is designed to lower the pressure in the crankcase, which otherwise could lead to oil leaks and seal damage. The rotation of crankshaft in the crankcase causes the churn up of oil which conducts to occurrence of oil droplets which in turn may end in the PCV exhaust air intended to be re-injected in the engine admission. The oil catch can (OCC) is a device designed to trap these oil droplets, allowing the air to escape from the crankcase with the lowest content of oil as possible and thus, reducing the generation and emission of extra pollutants during the combustion of the air-fuel mixture. The main purpose of this paper is to optimize the design of a typical OCC used in many commercial cars by varying the length of its inner tube and the relative position of the outlet from radial to tangential fitting to the can body. For this purpose, CFD parametric analysis is performed to compute a one-way coupled Lagrangian-Eulerian two-phase flow simulation of the engine oil droplets driven by the air flow stream running through the device. The study was performed using the finite volume method with second-order spatial discretization scheme on governing equations in the Solid Works-EFD CFD platform. The turbulence was modelled using the k-? model with wall functions. Numerical results have proved that maximum efficiency is obtained for the longest inner tube and the tangential position of the outlet; however, it is recommended further investigation to assess the potential erosion on the bottom of the can under such a design configuration.

NOISE EMISSION LEVEL VERSUS THE STRUCTURE OF THE AIRCRAFT TURBINE ENGINE

This article presents the problem of noise generated by turbine jet engines. It points out possible directions of noise decrease with particular emphasis upon structural changes within the engines, the task of which is to reduce the noise mission. The example of the modernization is based upon the “bypass” type of one-flow turbine jet engine. The essay contains theoretical basis of calculation of the noise emission level and the results, which graphically indicate a relative level of noise of this type of engine depending upon the amount of discharged air and the diameter of the discharge nozzle and the radius, upon the basis of which the noise level is determined. This work also includes a comparison of the relative noise level of this type of engine with regard to one-flow turbine engine equipped with the function of air discharge to the environment and with regard to two-flow turbine jet engine equipped with air stream flow mixing device. The essay ends with short conclusions. In order to struggle with the air noise special “Environmental Protection Programmes” are prepared. Civil airports and military airports prepare new procedures for taking off and approaching planes as well as optimize the approach and take off airport flight zone corridors. Unfortunately, in the case of so big surfaces, acoustic screens would not bring desired effects, also due to costs.