Compressed Air Flow Research Articles

On the transient response of the turbulent boundary layer inception in compressible flows

The behavioural characteristics of thermal boundary layer inception dictate the efficiency of heat exchangers and the operational limits of fluid machinery. The specific time required by the thermal boundary layer to be established is vital to optimize flow control strategies, as well as the thermal management of systems exposed to ephemeral phenomena, typically on the millisecond scale. This paper presents the time characterization of the momentum and thermal boundary layer development in transient turbulent compressible air flows. We present a new framework to perform such estimations based on detailed unsteady Reynolds averaged Navier–Stokes simulations that may be extended to higher fidelity simulations. First of all, the aerodynamic boundary layer initiation is described using adiabatic simulations. Additional numerical calculations were then performed by setting the isothermal wall condition to evaluate the additional time required by the thermal boundary layer to establish after the aerodynamic boundary layer reaches its steady state. Finally, full conjugate simulations were executed to compute the warm up effect of the solid during the blowdown of a hot fluid over a colder metallic test model. The transient performance of the turbulent thermal and momentum boundary layers is quantified through numerical simulations of air blowdown over a flat plate for different mainstream flow conditions. The effects of Reynolds number, free stream velocity, transient duration, test article length and free stream temperature were independently assessed, to then define a mathematical expression of the momentum boundary layer settlement. This paper presents a novel numerical correlation of the additional time required by the thermal boundary layer to be stablished after the settlement of the momentum boundary layer. The time scales of the aerodynamic and thermal boundary layers are presented as a function of relevant non-dimensional numbers, as well as the description of the response of the near wall flow to sudden free stream changes. The characterization of the boundary layer mechanisms discussed in this paper contribute to the establishment of an evidence-based foundation for advances in the field of flow control.

Definition of Wingtip Devices Shape and Dimensions for a Subsonic Airliner

The results of flow field numerical simulation on the typical wing-body prototype of the modern DLR-F4 airliner under sub- and transonic compressible air flow are presented. Using the DLR-F4 CAD model, the effect of the wingtip end plate area and of the cant angle of a typical Whitcomb winglet is studied. The dependencies of the model lift-to-drag ratio increment on the flat wingtip end plate relative area and on the cant angle of an airfoil Whitcomb winglet are obtained. The concept of an elliptic winglet with a variable cant angle that similar to the winglet used on Airbus A350 is studied. A technique is developed for solving the multi-parameter design optimization task for the Whitcomb winglet, taking the maximum lift-to-drag ratio of the wing as a criterion for optimization.

Nonlinear multivariable sliding mode control of a reversible PEM fuel cell integrated system

This work proposes a reduced-order sliding mode observer (SMO) based nonlinear control to regulate a multivariable proton exchange membrane fuel cell (PEMFC) integrated system. To make this system reversible, it is integrated with an air compressor, air cooler, primary manifold, supply manifold, humidifier and return manifold. To recirculate the unreacted hydrogen fuel, an ejector and to suppress the fuel cell heat of reaction, a simple water cooled heat exchange system is modeled. Among the three measured outputs, namely output voltage (main product), compressor air flow and fuel cell body temperature, the last two are proposed to control at their desired values to avoid oxygen starvation at cathode side and adverse effect of system temperature, respectively. To increase the lifetime of proton exchange membrane fuel cell and its smooth operation, a model based sliding mode controller (SMC) is synthesized, coupling with a nonlinear sliding mode observer required to estimate the unmeasured state information. This observer is formulated based on the reduced-order process model that leads to a process/model mismatch. Further, a saturation function is included in the sliding mode control theory in order to avoid the chattering effect. The performance of the proposed nonlinear observer based sliding mode controller is finally investigated by comparing with the conventional proportional integral (PI) controller in terms of servo (output voltage and fuel cell body temperature) and regulatory (load current) responses.

Where has all the power gone? Energy production and loss in vocalization

Human voice production for speech is an inefficient process in terms of energy expended to produce acoustic output. A traditional measure of vocal efficiency relates acoustic power radiated from the mouth to aerodynamic power produced in the trachea. This efficiency ranges between 0.001% and 1.0% in speech-like vocalization. Simplified Navier–Stokes equations for non-steady compressible airflow from trachea to lips were used to calculate steady aerodynamic power, acoustic power, and combined total power at seven strategic locations along the airway. A portion of the airway was allowed to collapse to produce self-sustained oscillation for sound production. A conversion efficiency, defined as acoustic power generated in the glottis to aerodynamic power dissipated, was found to be on the order of 10%, but wall vibration, air viscosity, and kinetic pressure losses consumed almost all of that converted power. Thus, the acoustic power, reflected back and forth in the airway was dissipated at a level on the order of 99.9%, with a small fraction being radiated to the listener.

Pattern characterization concerning spatial and temporal evolution of dust pollution associated with two typical ventilation methods at fully mechanized excavation faces in rock tunnels

In order to understand the temporal and spatial evolution pattern of dust pollution under blower and long-compression short-suction (LCSS) ventilation conditions at fully mechanized excavation faces in rock tunnels so as to effectively enhance dust removal efficiency, the present study conducts numerical simulation on the airflow field and dust dispersion associated with these two ventilation methods. The results indicate that the airflow pattern under the blower ventilation method is primarily dictated by the compressive jet field. The LCSS ventilation method leads to a continuous vortical airflow field, which makes the corresponding average dust concentration at fully mechanized excavation face lower than its counterpart associated with the blower ventilation method. The dust concentration roughly stabilizes after 193 s and 244 s for the LCSS and blower ventilation methods, respectively; due to the suction effect at the suction inlet at the front, the average dust dispersion velocity of LCSS ventilation method is lower than that of blower ventilation method, and it takes 141 s and 121 s to disperse dust to the tunnel outlet for the LCSS and blower ventilation methods, respectively. Despite the fact that the LCSS ventilation method is superior to the blower ventilation method, it still fails to deliver an effective dust control. The accuracy of the numerical simulation results is corroborated by field experiments. Furthermore, numerical simulation study is conducted to examine the impact of Lp (i.e., distance between compressed airflow outlet and heading end) for a range between 5 m and 50 m. It is found that for Lp < 30 m, the airflow field is fairly turbulent without forming an air curtain for dust control, which makes the dust dispersion reach the entire tunnel; for Lp > 30 m, a dust-control air curtain is established at the heading machine driver's location, and the dust-control effect of air curtain is improved as Lp increases from 30 m to beyond 35 m. When Lp increases above 35 m, the dust is effectively confined within a space upstream of the driver's location (<5.5 m away from the heading end).

Evaluation of grinding wheel wear in wet profile grinding for the groove of the ball bearing’s inner ring by pneumatic probes

Wear is one of the most influential factors in profile grinding. The measuring of grinding wheel wear is costly and time consuming. We introduce a new online wear measuring method in a wet profile grinding for the inner ring groove of ball bearing. The advantage of this method is the reduction of electromagnetic influence of workpiece as well as the impact of grinding debris and cutting lubricant. Two pneumatic gauging probes are positioned at two different locations with the biggest gap in the wear value on the curved edge surface of the grind stone. When the compressed air flow is blown onto the working surface of the grinding wheel, the back pressure in the measuring chamber corresponding to the gap between the probe and the working surface of the grinding wheel can be measured. Therefore, the radial wear value of grinding wheel can be determined. Based on theoretical calculations and the establishment of its dynamic characteristic curve, it is demonstrated that the first probe measuring wear at the top of the curved edge surface of the grinding wheel with the parameters of the probe d1 = 0.85; d2 = 1.5; P = 4 Bar has a measurement range of 200 μm, a maximum speed ratio of 0.01 Bar/μm. The second probe used to capture wear at the margin of the curved edge surface of the grinding stone with the parameters of the probe d1 = 0.65; d2 = 1.6; P = 4 Bar has a measurement range of 140 μm, a maximum speed ratio of 0.03 Bar/μm. The experimental results show that the grinding wheel wear value varies at different points of the curved edge surface of the grinding wheel. In profile grinding for the inner ring groove of the 6208 ball bearing, the wear value at the edge of the curved edge surface of the grinding wheel is usually bigger than that at the top of the curved edge surface of the grinding wheel.

Study Improving Performance of Centrifugal Compressor In Paiton Coal Fired Power Plant Unit 1 And 2

The compressed air system becomes part of a very important utility system in a Plant, including the Steam Power Plant. In PLN’S coal fired power plant, Paiton units 1 and 2, there are four Centrifugal air compressor types, which produce compressed air as much as 5.652 cfm and with electric power capacity of 1200 kW. Electricity consumption to operate centrifugal compressor is 7.104.117 kWh per year. This study aims to measure the performance of Centrifugal Compressors operating in Paiton’s coal fired power plant units 1 and 2. Performance Compressor is expressed by Specific Power Consumption (SPC) in kW/100 cfm. For this purpose, we measure the compressed air flow rate generated by each compressor and the power consumed by each compressor. The result is as follows Air Compressor SAC 2B : 15.1 kW/100 cfm, Air Compressor SAC 1B : 15.31 kW/100 cfm,Air Compressor SAC 1A : 16.3 kW/100 cfm and air Compressor SAC 2C : 18.19 kW/100 cfm. From the measurement result, air compressor SAC 2B has the best performance that is 15.1 kW / 100 cfm. In this study we analyze efforts to improve the performance of other compressors to at least match the performance of the SAC 2B air compressor. By increasing the Specific Power Consumption from others Compressor, it will get energy saving up to 284,165 kWh per year.

Design and Analysis of Cold Pipe Line Structure with Compressed Air Flow

The experimental pipelines used for research purposes must be structurally analyzed to meet the design requirements. The work carried out here focuses on the structural analysis of a thermal mixer pipeline. There is a cold compressed air flow in this pipeline at 8 bar pressure. Flow rate is to be varied based on mixing ratios; the supports in the pipe are designed to withstand maximum flow through the pipe. The pipeline is analyzed theoretically and by simulation using ANSYS APDL 16.0, finally the number of supports required to meet the design needs is concluded. Similarly in future, the whole experimental pipeline is to be studied individually and as a whole and the support structures are to be designed for the thermal mixer setup based on the analyzed data.

Electrical Discharge Drilling of D3 Die Steel using Air Assisted Rotary Tubular Electrode

This articles focus on developing a hybrid EDM process using liquid cum gaseous dielectrics to study its influence on tool wear rate (TWR), material removal rate (MRR) and over cut (OC) of workpiece. The compressed air flow through a rotary tubular electrode removed and flushed out the debris from the working gap and hence it improves the flushing efficiency and stability of the process. This study describe the experimental investigation of formation of holes in D3 die steel workpiece with conventional EDM and air assisted electrical discharge drilling (AAEDD). An attachment was designed and developed to carry out AAEDD process on the existing EDM machines. The entire arrangement is in the form of an independent unit which could be attached to the existing EDM machine. The influence of various machining parameters such as discharge current, pulse on time, duty cycle and tool speed on output response viz., MRR, TWR and OC have been studied. Under the same machining condition, high MRR and low TWR as well as OC obtained when AAEDD machining was performed as compared to conventional EDM machining. Experimental findings suggested that supply of compressed air through rotary tubular electrode in die sinking electrical discharge drilling have a positive influence on MRR, OC and TWR. However, rotation of tool has a negative effect on OC. The SEM images of selected specimens were also in line with the experimental findings.

Fig extract drying: The relationship between the main operating parameters of a pilot-scale spray dryer and product specifications.

This study aims to optimize extraction and drying conditions of fig syrup. Drying was done in a pilot scale two‐fluid nozzle spray dryer. A total of 27 experiments were conducted with varying inlet air temperatures, air flow rates, and also a maltodextrin (MD)‐ low methoxyl pectin (LMP) ratios. While feed rate, feed temperature, and compressed air flow rate of the atomizer were kept constant. The results of differential scanning calorimetry revealed that high levels of glucose and fructose in the extract resulted in a low glass transition temperature of fig syrup. By an increase in the inlet air temperature, the powder bulk density decreased. However, the MD:LMP ratio and the air flow rate were not significantly effective (p < 0/05) in changing the bulk density. SEM micrographs of spray‐dried particles and particle size distribution analysis showed that particles were largely in a range of 5 to 50 μm. The best powders were obtained at an inlet air temperature of 170°C.

Performance Evaluation of the Minimum Quantity of Lubricant Technique With Auxiliary Cleaning of the Grinding Wheel in Cylindrical Grinding of N2711 Steel

Grinding is an abrasive process mostly used in finishing operations to provide low roughness and narrow limits of form and dimensioning to the workpiece. Due to the large amount of heat generated by friction between the abrasive and the workpiece in this process, the use of large volumes of coolant is encouraged to avoid thermal damage, such as burning and hardness variation caused by subsurface damage. On the other hand, environmental impacts and human health problems caused by coolants have been a key issue toward sustainable manufacturing, mainly because of the chemistry behind them. Thus, is important to seek for strategies to reduce the volume of fluids and their risks as well as guarantee grinding efficiency. One machining strategy is the minimum quantity of lubricant (MQL) technique, which is well consolidated over the past 25 years and one that uses low volumes of fluid mixed with compressed air flow, as well as provides less waste. However, it has generally been reported that sludge formed during grinding is forced into the wheel pores, consequently clogging its pores, thereby reducing the wheel cutting potential and its performance. A possible solution for this problem is to use an auxiliary compressed air system to clean the grinding wheel surface during machining, since the MQL conventional system is not able to clean it. In this context, this work evaluated the performance of the MQL technique with an auxiliary cleaning of the grinding wheel cutting surface in relation to the conventional cooling techniques (flood cooling) during a cylindrical plunge grinding of N2711 steel. N2711 steel is widely employed in manufacturing of molds for plastic injection processes and is one of steels more susceptible to grinding burn. The following output parameters were used to assess the performance: surface roughness, roundness, microhardness, grinding power, and grinding wheel wear. The results showed that the MQL technique, in addition to the environmental and economic advantages achieved, provided superior workpiece quality, and lower power consumed compared to the flood technique. The MQL technique proved to be an alternative method compared to the conventional technique under the conditions investigated. Also, the Malkin’s model was used to predict the grinding ratio (G-ratio) based on the experimental data obtained in this work. After regression analysis, the model predicted the G-ratio from the specific material removal rate and the cutting speed with a satisfactory accuracy of approximately 92%.

Microstructures and Properties of Copper to Stainless Steel Joints by Hybrid FSW

The present research article is focused to investigate the heating- and cooling-assisted friction stir welding (FSW) on dissimilar copper to stainless steel joints along with normal FSW. Gas tungsten arc welding torch was applied for heating-assisted source in front of the FSW tool, wherein preheating current was varied as 20, 40, and 60 A with rest of constant FSW parameters. Similarly, cooling-assisted FSW was performed by compressed air and water behind the FSW tool for constant FSW parameters, wherein the compressed air flow rate was varied as 15 and 30 PSI and water cooling was applied with 75 ml/min one after another. Weld properties of assisted approaches were compared with normal FSW on the scale of macrostructure and microstructure analysis, tensile testing, and microhardness properties. The obtained results reveal that the normal FSW of dissimilar copper to stainless steel joint was observed as superior relative to assisted approaches. Surface oxides were observed for the welds of heating-assisted FSW and cooling-assisted FSW of compressed air. Elimination of surface oxides was noted for FSW assisted by water cooling. Highest tensile strength was reported for normal FSW relative to heating-assisted FSW and cooling-assisted FSW. Tensile strength was deteriorated as cooling conditions increase. The microstructures of the stir zone were observed as metal matrix type with Cu matrix and SS particles, wherein SS particles were reported as in random distribution with its varying size. Major defects were reported around the largely dispersed SS particles inside Cu matrix.

Study of gas dynamics of the intersecting jets in a semi-open channel

The subject of the study is axisymmetric channel with a hemispherical bottom. The compressed air flows into the channel through the holes located on the surface of the hemispherical bottom. The ratio of all holes area to the outlet area of the channel is equal to 0.25. The experimental and numerical study of jets intersecting at a single point is performed. The countermoving jets and the focused jets are investigated. The distribution of pressure over the surface of the channel and the total pressure at the output of the channel are obtained. The main experimental result is as follows: the total pressure recovery coefficient for the focused jets is twice more than that for the countermoving jets.

The extension of the operational range of combined-cycle power plant with a triple-pressure heat recovery steam generator

In the article, the issues of operational flexibility improvement for CCGT with a triple-pressure heat recovery steam generator are described. The factors limiting the operational range of CCGT were identified and analyzed. Analytical dependences for the minimum and maximum load of the CCGT on the ambient air temperature were obtained. The ways of expanding an operational range due to water spray into air-intake path, supplementary firing before the heat recovery steam generator, intensifying regulation of compressor airflow using the IGV and its pre-heating are described.

Multi-objective optimization of IGV position in a heavy-duty gas turbine on part-load performance

More than 60% of the power generated in Iran depends on the technical characteristics of heavy-duty gas turbine power plants. The ability to make changes in the amount of compressor air flow via positioning Inlet Guide Vanes (IGV) has been considered to improve the techno-economic quality of the mentioned gas turbine power in different operational conditions. In this study, system modeling was conducted based on operational data, using the outputs of the industrial code developed in various conditions. This model was derived via thermodynamic equations and linear regression functions. Subsequently, multi-objective genetic algorithm optimization of IGV position was employed to optimize the objective functions in the power generation range of 40%–100% (nominal) load. Thermal efficiency and electricity generation cost, which cover the main decision factors in energy management systems in Iran, were selected as the objective functions.

On the efficiency of vocalization in humans and other vertebrates

Human vocalization is an inefficient process in terms of energy expended to produce acoustic output. A traditional measure of vocal efficiency, the ratio of acoustic power radiated from the mouth to aerodynamic power produced by the lungs, ranges between 0.001 % and 0.1 % in speech-like vocalization. Non-human vertebrates like birds cannot afford to operate with such low efficiency when calling or singing over long distances. A hypothesis is given here that humans have traded away efficiency to maximize phonetic contrast in speech. A Navier-Stokes solution of non-steady compressible airflow from trachea to lips was used to calculate steady aerodynamic power, acoustic power, and combined total power at seven strategic locations along the airway. At low (speech-like) frequencies, it is shown that little power is radiated from the mouth because acoustic wave reflection at the mouth is very high. Wall vibration and kinetic pressure losses consume on the order of 99.99 % of the power produced. With higher freq...

Investigation on the new design of foaming device used for dust suppression in underground coal mines

To solve the drawbacks of the conventional foaming method used for dust suppression, a new foaming device is designed through integrating the foaming agent adding device and foam generator. Its performance is investigated experimentally under different working conditions. Testing results show that foaming agent is automatically added into the device at the working water flow of 0.84–1.12m3/h and water pressure of 0.3–0.52MPa. The reasonable compressed air flow is 45–48m3/h, in which range the foam flow and expansion ratio both reach the maximum. The foaming device requires a minimum air pressure of 0.46MPa to meet the outlet pressure demand. Field application proved that foam technology using the new foaming device made a marked dust suppression effect. The foam dust suppression efficiency was 87.1%–88.3%, much higher than that achieved by the roadheader water spraying. In addition, foam used less water that relieves the water supply burden in coal mines and improves the working environment. Based on the above contributions, it is believed that the proposed foaming device will greatly promote the large-scale application of foam technology used for suppressing dust in underground coal mines.

Recycling Influence in Phosphorus Biossolubilization from Rock Phosphate Concentrate in Air-Lift Bioreactor

The nutrients availability for the plants is a determining factor for their development and growth. Phosphorus is an essential compound to plants, it is necessary to perform photosynthesis, respiration, gene transfer and reproduction. An alternative mechanism to the use of chemical fertilizers for increasing the cultures productivity on the soil phosphorus deficiency is the use of biotechnology by mainly biological processes occurring in the system soil/plant realized by phosphorus solubilizing microorganisms (PSM). Therefore, the objective of this study was to evaluate the phosphorus biossolubilization process from phosphate rock concentrate by Trichoderma harzianum in air-lift bioreactor employing reactive medium recycle. During 6 days was evaluated the phosphorus biossolubilization process by Trichoderma harzianum in air-lift reactor employing ascending air 0.5 vvm (volumetric flow per minute) and reaction medium recycle containing phosphate rock concentrated (5 g/L). Phosphorus biossolubilization by Trichoderma harzianum in air-lift reactor only with upward aeration (0.5 vvm) showed maximum solubilization equal to 212.19 ppm (27.23%), followed by 98,18% of glucose consumption and total acid concentration equal to 1.25 µmol/ml (0.5 µmol/ml of lactic acid, and 0.73 µmol/ml of acetic acid) in the fifth process day at 28 ± 0,5°C. By employing reaction medium recycle flow of 200 mL/min in air-lift reactor with aeration of 0.5 vvm at 28 ± 0.5°C, initial cell inoculum concentration equal to 3.5 ± 0.5 g/L and 5 g/L of phosphate rock concentrate and glucose was obtained on the third day of process 244.9 ppm (31.42% solubilization) of soluble phosphorus. By increasing the volumetric flow rate of recycle to 400 ml/min maintaining the same conditions, in the fourth day was reached 216.1 ppm (27.73% solubilization) of soluble phosphorus and 8.2 µmol/ml of organic acids (lactic and acetic). Comparing the results achieved between the three phosphorus biossolubilization process from phosphate rock concentrate in air-lift reactor by Trichoderma harzianum was observed that by employing recycle of reactive medium at 200 mL/min associated with compressed air flow at 0.5 vvm was obtained for a shorter period (3 days) a higher concentration of phosphorus soluble in a liquid medium (244.9 ppm). Indicative of the positive influence of the reactive medium recycle in the phosphorus availability process by Trichoderma harizianum from the production of organic acids using glucose as substrate.

An approach to turn olive mill wastewater into a valuable food by-product based on spray drying in dehumidified air using drying aids

Several methods have been investigated for olive mill wastewater (OMW) management. However, there has been little success in finding an environmentally friendly and economically viable solution to be generally adopted. The main objective of this work was to develop a new method for OMW management, which simultaneously will lead to the recovery of high-added value substances, based on screening and spray drying. The polyphenol enriched solid fraction derived from screening (OMWS) is spray dried to make an olive powder product rich in antioxidants for dietary uses. A new technique for spray drying OMWS using dehumidified air as drying medium and maltodextrin as drying agent was developed. Different drying experiments were conducted varying the inlet air temperature, the drying air flow rate, the compressed air flow rate, the type of drying agent, and the ratio (OMWS solids)/(drying aid solids). Data for the product collected in the receiving vessel were gathered and the OMWS powders were analyzed for moisture content, bulk density, and solubility. The achieved values of product recovery (87–94%) were much higher than those obtained in a typical spray drying system (<3%). Thus, the combination of maltodextrin addition and use of dehumidified air as drying medium seems to be an effective way of producing a free-flowing olive mill wastewater powder to be included in food formulations.

Investigation of energy saving potentials in T-junction and elbow in compressed air systems

In recent times, the applications of numerical methods are gaining momentum to carry out critical analysis to identify electrical energy and related emission saving potential on real-time application. The chosen specific area of the current work is the simulation of compressed airflow through pipes. The pressure gradient across compressed air pipe junction was simulated, and the result showed that the minimum pressure drop occurs when a branch line is taken at an angle of 46° with horizontal from the main pipe against the conventional T branch. In case of elbow, 150-mm fillet radius gave minimum pressure drop against 90° elbow. The CFD analysis carried out on T and elbow of compressed air pipe network with various inlet air pressures of 4 × 105, 6 × 105, and 8 × 105 Pa showed that a no. of redesigned junction geometry, which is 5000, can reduce compressor electricity consumption by 127.14 MWh per annum and CO2 emission by 37.31 t per annum.