Initial Crossflow Research Articles

Numerical heat transfer investigation of a single impingement jet with combined V-ribs and preliminary optimization of V-rib configuration in initial crossflow

The heat transfer performance of a single jet impingement configuration with V-ribs on the impingement plate and V-ribs on the target plate was numerically investigated for turbomachinery applications. The geometrical parameters of the impingement wall ribs were kept constant. The effects of the height and the rib-to-jet distance of the target wall ribs were analyzed in detail. The studied jet Reynolds number was Re = 35,000, the separation distance was H/D = 3, and the velocity of jet-to-crossflow ratio was R = 1–5. Based on the numerical results, taking the heat flow rate as the objective, the rib geometry was optimized by the Differential Evolution (DE) algorithm. The optimized rib configuration was then numerically simulated to validate whether the DE algorithm can be utilized for similar applications. The results of the optimized configuration were compared to those of the sample cases to verify the effectiveness of the optimization. The pressure differences between the inlet of the main jet and the outlet, and between the inlet of the initial crossflow and the outlet were computed to evaluate the pressure loss introduced by the ribs. Thus, this work provides another perspective on designing high efficient anti-crossflow cooling configurations for turbomachinery applications.

Pilot-scale crossflow ultrafiltration of four different cell-sized marine microalgae to assess the ultrafiltration performance and energy requirements

Four marine microalgae (e.g., Tetraselmis, Picochlorum, Dunaliella, and Synechococcus) with different cell sizes were harvested using pilot-scale ultrafiltration. Average permeate fluxes were 16.75, 19, 25.35, and 33.75 L/m2h at 60 min for Synechococcus, Dunaliella, Picochlorum, and Tetraselmis, respectively. The concentrating factors for Synechococcus, Picochlorum, Dunaliella, and Tetraselmis were 46.6, 42, 39.2, and 39.5, respectively. The highest and lowest microalgal biomass retention was 47.1 and 41.7% for Tetraselmis and Synechococcus, respectively. Due to higher microalgal biomass retention, initial crossflow velocities of 0.16 to 0.18 m/s were reduced to 0.02 to 0.05 m/s for Tetraselmis and Dunaliella sp. The total harvesting energy requirement by membrane and centrifuge was 16.44 – 28.48 GJ/tonne biomass; the smaller the cell size, the lower the energy requirement. The optimum biomass concentrating factor by the membrane filtration process also depended on size; for optimum total energy requirement, tangential flow filtration (TFF) could concentrate a smaller strain more than a larger strain.

Effect of Ultrafiltration Operating Conditions for Separation of Ferulic Acid from Arabinoxylans in Corn Fibre Alkaline Extract

Corn fibre, a co-product of the starch industry, is rich in compounds with high added value, such as ferulic acid and arabinoxylans, which are released during alkaline extraction. This work aims to optimise an efficient separation method for the recovery of these two compounds from a corn fibre alkaline extract, allowing an efficient valorisation of this co-product. Ultrafiltration was selected as separation method, due to its potential to fractionate these compounds. In order to minimise the loss of membrane permeance, due to mass transfer limitations caused by the high arabinoxylan viscosity, the impact of relevant ultrafiltration operating parameters (membrane molecular weight cut-off, fluid dynamics conditions, transmembrane pressure, and operating temperature) were evaluated. A Nadir UP 150 membrane was found to be an adequate choice, allowing for an efficient separation of ferulic acid from arabinoxylans, with null rejection of ferulic acid, a high estimated rejection of arabinoxylans 98.0% ± 1.7%, and the highest permeance of all tested membranes. A response surface methodology (RSM) was used to infer the effect of ultrafiltration conditions (crossflow velocity, transmembrane pressure and operating temperature) on the rejection of ferulic acid, retention of arabinoxylans (assessed through apparent viscosity of the retentate stream), and permeance. Through mathematical modelling it was possible to determine that the best conditions are the highest operating temperature and initial crossflow velocity tested (66 °C and 1.06 m.s−1, respectively), and the lowest transmembrane pressure tested (0.7 bar).

Experimental study of submerged gas jets in liquid cross flow

Gas jets submerged in the liquid cross flow are prevalent in the nature and essential in numerous industrial applications. The interaction between the gas jet and liquid cross flow is not well characterized for the difficulties in experimental research. In the present work, a new experimental method was designed and the evolution of the gas jet in liquid cross flow was captured by the high speed camera. Five experimental cases with different initial liquid cross flow velocities (0.35 m/s, 0.7 m/s, 1.0 m/s, 1.5 m/s, 2.0 m/s) were performed where the momentum ratio of the initial gas jet to liquid cross flow varies to highlight the effects of the liquid cross flow velocity on the flow characteristics. The summation and statistical methods were adopted to analyze the experimental sequences, and the results from the two methods showed good agreement. The gas jet morphology and the gas liquid interface were clearly identified from the experimental results, which showed that the gas jet deflected in a less pronounced manner with less unsteadiness generated at the gas liquid interface as the liquid cross flow velocity decreases. The gas jet penetration length in the momentum region was measured and it was found to be severely influenced by the liquid cross flow, and a power relationship was found between the gas jet penetration length and the cross flow velocity. The expansion angle of the gas jet in the upstream was also shown to grow in a power function with the liquid cross flow velocity. The gas jet diameter indicates the ambient liquid entrainments and the gas liquid interface evolution. In the region where the gas jet momentum is dominant, the evolution of the gas jet diameter followed a similar pattern with the submerged gas jets without liquid cross flow. Finally, empirical correlations were developed to predict the characteristic parameters of the submerged gas jet in liquid cross flow.

Removal of chromium from synthetic wastewater using MFI zeolite membrane supported on inexpensive tubular ceramic substrate

A mordenite framework inverted (MFI) type zeolite membrane was produced on inexpensive tubular ceramic substrate through hydrothermal synthesis and applied for the removal of chromium from synthetic wastewater. The fabricated ceramic substrate and membrane was characterized by diverse standard techniques such as X-ray diffraction, field emission scanning electron microscope, porosity, water permeability and pore size measurements. The porosity of the ceramic substrate (53%) was reduced by the deposition of MFI (51%) zeolite layer. The pore size and water permeability of the membrane was evaluated as 0.272 μm and 4.43 × 10–7 m3/m2s.kPa, respectively, which are lower than that of the substrate pore size (0.309 μm) and water permeability (5.93 × 10–7 m3/m2s.kPa) values. To identify the effectiveness of the prepared membrane, the applied pressure of the filtration process and initial chromium concentration and cross flow rate were varied to study their influence on the permeate flux and percentage of removal. The maximum removal of chromium achieved was 78% under an applied pressure of 345 kPa and an initial feed concentration of 1,000 ppm. Finally, the efficiency of the membrane for chromium removal was assessed with other membranes reported in the literature.

Forward osmosis filtration for removal of organic foulants: Effects of combined tannic and alginic acids

The filtration performance of combined organic foulants by forward osmosis (FO) in active-layer-facing-the-draw-solution (AL-facing-DS) orientation was investigated systematically. Tannic acid and alginate were used as model organic foulants for polysaccharides and humic dissolved organic matters, respectively. The FO could reject combined and single tannic acid and alginate foulants effectively. The more severe fouling flux decline, accompanied with lower combined foulants' retention, was observed with increasing proportions of tannic acid in the combined foulants-containing feed, which was ascribed mainly to the more severe fouling resulting from tannic acid adsorption within the porous support layer of the FO membrane compared to minor alginate deposition on the membrane surface. It was found that the higher the initial flux level and cross flow velocity, the faster the flux decline with lower mixed foulants retention. It was also revealed that the calcium ions in a basic solution enhanced the combined fouling flux reduction and combined foulants retention. As the major constituent of the combined fouling layer, the adsorption of tannic acid might play a more significant role in the mixed fouling of the FO membrane, which was probably influenced by permeation drag caused by water flux and chemical interactions induced by feed solution pH and calcium ion concentration.

Convective heat transfer of a row of air jets impingement excited by triangular tabs in a confined crossflow channel

Abstract Computational and experimental studies were conducted to investigate the conjugated convective heat transfer produced by single row of impinging jets inside a confined channel with non-uniform initial crossflow issued from discrete holes. The effects of the crossflow-to-jet Reynolds number ratio and crossflow holes arrangement (inline or staggered in relative to the impinging jet holes) on the jet impingement behaviors were studied providing the same total cooling air mass flowrate. Particular attention was paid to examine the tab-excited jet impingement behaviors in a confined channel with non-uniform crossflow. The results show that the tabbed excitation on the improvement of convective heat transfer in the vicinity of impingement region is not as well as the situation where no initial crossflow is present. For the inline arrangement of crossflow holes, the location corresponding to the peak laterally-averaged Nusselt number is moved downstream and the peak laterally-averaged Nusselt number is decreased significantly under larger crossflow-to-jet Reynolds number ratios. While for the staggered arrangement of crossflow holes, the location corresponding to the peak laterally-averaged Nusselt number is not affected by the crossflow but the peak laterally-averaged Nusselt number is decreased monotonously with the increase of crossflow-to-jet Reynolds number ratio. Under small crossflow-to-jet Reynolds number ratio, the initial crossflow arrangement has little influence on the laterally-averaged Nusselt number distribution. Among three crossflow-to-jet Reynolds number ratios ranged from 0.5 to 2, the maximum relative difference of peak laterally-averaged Nusselt numbers between two different crossflow arrangements is occurred under crossflow-to-jet Reynolds number ratio of 1.

Electro-catalytic oxidation in treating C.I. Acid Red 73 wastewater coupled with nanofiltration and energy consumption analysis

The research was conducted to study the independent impact of electro-catalytic oxidation on the nanofiltration (NF) performance during the separation of C.I. Acid Red 73 (AR 73) wastewater. Ti/SnO2–Sb2O3 electrode modified with rare element yttrium (Y) was successfully prepared by the sol–gel technology, and then it was used as an anode for the degradation of azo dye AR 73 coupling with NF. The electro-catalytic oxidation could be restrained by painting insulating varnish on the surface of anode. Through comparing the permeation flux with the case of not using insulating varnish, we could identify the independent impact of electro-catalytic oxidation in the coupling process. The influence of operating parameters, e.g., applied voltage, initial feed concentration, operating pressure and cross flow velocity on the electro-catalytic oxidation flux and energy consumption was investigated respectively. The results indicated that the accelerated lifetime of the Ti/SnO2–Sb2O3–Y electrode reached 4.1h, which was 9.1 times longer than that of the Ti/SnO2–Sb2O3 electrode, and the electro-catalytic oxidation flux was enhanced to a great extent by choosing appropriate operating conditions and the coupling process could energy-effectively treat AR 73 wastewater.

A completely theoretical approach for assessing fouling propensity along a full-scale reverse osmosis process

This paper aims to develop a completely theoretical approach for assessing scaling (crystallization/precipitation fouling) propensity through the previously proposed and tested theoretical index of 2nd author (SPI) within a Reverse Osmosis (RO) module. This approach will incorporate the local varying foulants' properties along membrane filtration channel into fundamental transport and conservation equations to achieve a unified and scientific assessment of the scaling potential. Thus, a high accuracy simulation of the local fouling propensity along a full-scale RO module will be obtained. This paper has overcome the challenge of determining and incorporating the locally varying concentration of foulants (and factors affecting it) and effect of concentration polarization to predict the local fouling propensity along the membrane channel. Also it has incorporated the only available theoretical index without any need for empirical parameters and/or constant Therefore, a fundamental more realistic description of fouling propensity and onset of fouling next to membrane along feed channel is developed and explained. Moreover, the effects of initial applied pressure, initial cross flow velocity, initial feed water salinity, clean membrane resistance and feed water temperature on fouling propensity and onset of fouling along the channel are investigated and discussed. Our suggested model is a very powerful tool that could help in the specific design of RO process as well as in simulations of the operating variables for optimization of RO system.

Numerical Study on Flow and Heat Transfer Characteristics of Jet Impingement Cooling

Three-dimensional numerical study is conducted to investigate the heat transfer characteristics for the flow impingement cooling in the narrow passage based on cooling technology of turbine blade.The effects of the jet Reynolds number, impingement distance and initial cross-flow on heat transfer characteristic are investigated.Results show that when other parameters remain unchanged local heat transfer coefficient increases with increase of jet Reynolds number；overall heat transfer effect is reduced by initial cross-flow；there is an optimal distance to the best effect of heat transfer.

An Application for New Reliable Approach to Predict the Onset of Barite, Celestite and Gypsum Scaling during Reverse Osmosis Treatment for Produced Water

Reverse osmosis (RO) desalination is considered a promising solution for Produced Water treatment and reuse in the oil and gas industry. However, scaling problem is one of the main challenges that face Produced Water RO desalination. In this paper, the use of new completely theoretical approach for assessing fouling propensity along a full scale reverse osmosis process is introduced to predict the onset of barite, celestite and gypsum scaling, as major scaling salts facing the RO desalination of Produced Water. Thus, the scaling propensity of barite, celestite and gypsum have been assessed and discussed. Moreover, the effect of applied pressure, initial cross flow velocity, feed salinity and feed temperature on scaling propensity of barite, celestite and gypsum have been examined and discussed. This procedure could be considered as a very important guideline, for any attempt to use RO in Produced Water treatment. It could provide help on the specific design of RO process as well as in simulation of the operating variables for optimization of RO system.

분사홀에 설치된 난류촉진제에 따른 충돌/유출면에서의 열/물질전달 특성

In order to enhance the heat/mass transfer, a turbulator has been installed at the exit of injection hole for the impingement/effusion cooling system. The local heat/mass transfer coefficients have been obtained by a naphthalene sublimation method. Experiments have been carried out at the fixed jet Reynolds number of 10,000. Two turbulators with different diameter have been used in the current study. The result presents that the turbulator leads to the increase in flow mixing and jet velocity, consequently enhancing the heat/mass transfer at a stagnation region. Further, the stagnation region is divided into four small areas with peak value. In the existence of initial crossflow, the stagnation regions move downstream and low heat/mass transfer regions are formed regardless of the installation of turbulator. However, the increased jet velocity by turbulator reduces the crossflow effect against the jet, resulting in decrease of low heat/mass transfer regions. Compared to the case without turbulator, the installation of turbulator yields 5~10% augmentation in averaged Sh value.

경사제트에 따른 충돌제트/유출냉각에서 열/물질전달 특성

An experimental investigation was conducted to investigate the heat/mass transfer for impingement/effusion cooling system with inclined jet. Jets with inclined angle of 60 are applied to impingement/effusion cooling. At the jet Reynolds number of 10,000, the experiments were carried out for blowing ratios ranging from 0.0 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result indicates that the inclined jet causes the non-uniform and low heat/mass transfer compared to the vertical jet. At stagnation region, the peak position is shifted from the geometrical center of injection hole due to Coanda effect and its level is higher than that of vertical jet due to increase in turbulence intensity by steep velocity gradient near the stagnation region. Further, the secondary peak region disappears because the interaction between adjacent wall jets weakens. When the initial crossflow occurs, the distorted heat/mass transfer pattern appears. As the blowing ratio (crossflow rate) increases, the heat/mass transfer distributions become similar to those of the vertical jet. This is because the effect of crossflow is dominant compared to that of inclined jet under high blowing ratio (M≥1.0). At low blowing ratio (M≤0.5), averaged Sh value is 10% lower than that of vertical jet, whereas its value at high blowing ratio (M≥1.0) is similar to that of vertical jet.

원형가이드 설치에 따른 충돌제트/유출냉각에서 열/물질전달 특성

An experimental investigation was conducted to enhance the heat/mass transfer for impingement/effusion cooling system when the initial crossflow was formed. For the improvement of heat transfer, the circular guide is installed on the injection hole. At the fixed jet Reynolds number of 10,000, the measurements were carried out for blowing ratios ranging from 0.5 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result presents that the circular guide protects the injected jet from the initial crossflow, increasing the heat/mass transfer. The heat transfer of stagnation region is hardly changed regardless of the blowing ratio. The secondary peak is obviously formed by flow transition to turbulent flow. At high blowing ratio of 1.5, the circular guide produces augmentation on the averaged heat/mass transfer while the case without circular guide leads to the low and non-uniform heat/mass transfer. With the increased heat/mass transfer, the installation of circular guide is accompanied by the increase of pressure loss in the channel. However, the pressure drop caused by the circular guide is lower than that for other cooling technique with the circular pin fin.

Heat/Mass Transfer with Circular Pin Fins in Impingement/Effusion Cooling System with Crossflow

The purpose of the present study is to investigate the local heat/mass transfer characteristics with circular pin fins in the impingement/effusion cooling with an initial crossflow. The results are compared with those for the cases without pin fins and with rib turbulators. The pin fins are installed between two perforated plates and the crossflow passes between these two plates. A blowing ratio is changed from 0.5 to 1.5 for the fixed jet Reynolds number of 10,000. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. When circular pin fins are installed in the impingement/effusion system, heat/mass transfer is augmented due to the generation of vortex and wake. Especially, locally low heat/mass transfer regions in front of the effusion hole are reduced. Because pin fins divert the crossflow passing in the injection hole region, the wall jet is less swept away than the case without pin fins, which results in the increase of heat/mass transfer. As the blowing ratio increases, the pin fins lead to higher heat/mass transfer than the case without pin fins. Compared with rib turbulators, the pin fins yield lower average Sh value at M = 1.0 but higher average Sh value at other blowing ratios.

가스터빈 연소실 냉각을 위한 충돌제트/유출냉각기법에서 사각핀 설치에 따른 열/물질전달 특성

The present study has been performed to investigate the influences of rectangular fins on heat transfer in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system with initial crossflow, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter. The crossflow passes between the plates, and various rectangular fins are installed on the plates. Reynolds number based on the hole diameter is fixed to 10,000 and the flow rate of crossflow is changed from 0.5 to 1.5 times of that of the impinging jet. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. Also to analyze the flow characteristics, a numerical calculation is performed. When rectangular fins are installed, the flow and heat transfer pattern is changed greatly from the case without fins. In the injection hole region, the jet impinges on effusion plate without deflection and wall jet spreads symmetrically. In the effusion region, the crossflow accelerates due to the decrease of cross-sectional area in the channel. Local heat/mass transfer coefficients are enhanced significantly compared to the case without fins. As the blowing ratio increases, the effect of rectangular fins against the crossflow becomes more significant and then the higher average heat/mass transfer coefficients are obtained than the case without fins. However, the increase of blockage effect gives more pressure loss in the channel.

The Effect of Initial Cross Flow on the Cooling Performance of a Narrow Impingement Channel

Impingement channels are often used in turbine blade cooling configurations. This paper examines the heat transfer performance of a typical integrally cast impingement channel. Detailed heat transfer coefficient distributions on all heat transfer surfaces were obtained in a series of low temperature experiments carried out in a large-scale model of a turbine cooling system using liquid crystal techniques. All experiments were performed on a model of a 19-hole, low aspect ratio impingement channel. The effect of flow introduced at the inlet to the channel on the impingement heat transfer within the channel was investigated. A novel test technique has been applied to determine the effect of the initial cross flow on jet penetration. The experiments were performed at an engine representative Reynolds number of 20,000 and examined the effect of additional initial cross flow up to 10 percent of the total mass flow. It was shown that initial cross flow strongly influenced the heat transfer performance with just 10 percent initial cross flow able to reduce the mean target plate jet effectiveness by 57 percent.

Local Heat/Mass Transfer With Various Rib Arrangements in Impingement/Effusion Cooling System With Crossflow

The present study has been conducted to investigate the effect of rib arrangements on flow and heat/mass transfer characteristics for an impingement/effusion cooling system with initial crossflow. Two perforated plates of square hole array are placed in parallel and staggered arrangements with a gap distance of 2d and the crossflow passes between the injection and effusion plates. Both the injection and effusion hole diameters d are 10 mm and Reynolds number based on the hole diameter and hole-to-hole pitch are fixed at 10,000 and 6d, respectively. Square ribs of various rib arrangements and attack angles are installed on the effusion plate. With the initial crossflow, locally low transfer regions are formed and the level of heat transfer rate become lower as flow rate of the crossflow increases because wall jets are swept and the stagnation regions are affected by crossflow. With rib turbulators, the flow and heat transfer patterns are changed because the ribs protect near-wall flows including wall jets and generate secondary flow in a duct. For M⩾1.0, the overall heat transfer is promoted when ribs are installed on the effusion surface, and higher values are obtained with smaller pitch of ribs. But, the attack angle of the rib has little influence on the average heat/mass transfer. For low blowing ratio of M=0.5, the ribs have adverse effects on heat/mass transfer. Pressure drop between the inlet and exit of the channel increases up to 20% of total loss when ribs are installed while it is only 5% of total pressure loss across the perforated plates without ribs.

초기 횡방향 유동이 존재하는 충돌제트/유출냉각에서 요철이 설치된 유출면에서의 열/물질전달 특성

The present study is conducted to investigate the effect of rib arrangements on an impingement/effusion cooling system with initial cross flow. To simulate the impingement/effusion cooling system, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter. Initial crossflow passes between the injection and effusion plates, and the square ribs (3mm) are installed on the effusion plate. Both the injection and effusion hole diameters are 10 mm and Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and 6 times of the hole diameter, respectively. To investigate the effects of rib arrangements, various rib arrangements, such as 90˚transverse and 45°angled rib arrangements, are used. Also, the effects of flow rate ratio of cross flow to impinging jets are investigated. With the initial crossflow, locally low transfer regions are formed because the wall jets are swept away, and level of heat transfer rate get decreased with increasing flow rate of crossflow. When the ribs are installed on the effusion plate, the local distributions of heat/mass transfer coefficients around the effusion holes are changed. The local heat/mass transfer around the stagnation regions and the effusion holes are affected by the rib positions, angle of attack and rib spacing. For low blowing ratio, the ribs have adverse effects on heat/mass transfer, but for higher blowing ratios, higher and more uniform heat transfer coefficient distributions are obtained than the case without ribs because the ribs prevent the wall jets from being swept away by the crossflow and increase local turbulence of the flow near the surface. Average heat transfer coefficients with rib turbulators are approximately 10% higher than that without ribs, and the higher values are obtained with small pitch of ribs. However, the attack angle of the rib has little influence on the average heat/mass transfer.<br/>

Enhanced Impingement Heat Transfer: The Influence of Impingement X/D for Interrupted Rib Obstacles (Rectangular Pin Fins)

Impingement flat wall cooling, with 15.2 mm pitch square hole arrays, was investigated in the presence of an array of interrupted rib obstacles. These ribs took the form of rectangular pin-fins with a 50% blockage to the cross flow. One side exit of the air was used, and there was no initial cross flow. Three hole diameters were investigated, which allowed the impingement wall pressure loss to be varied at constant coolant mass flow rate. Combustor wall cooling was the main application of the work, where a low wall cooling pressure loss is required if the air is subsequently to be fed to a low NOx combustor. The results showed that the increase in surface average impingement heat transfer, relative to that for a smooth wall, was small and greatest for an X∕D of 3.06 at 15%. The main effect of the interrupted ribs was to change the influence of cross flow, which produced a deterioration in the heat transfer with distance compared to a smooth impingement wall. With the interrupted ribs the heat transfer increased with distance. If the heat transfer was compared at the trailing edge of the test section, where the upstream cross flow was at a maximum, then at high coolant flow rates the increase in heat transfer was 21%, 47%, and 25% for X∕D of 4.66, 3.06, and 1.86, respectively.