Airflow Energy Research Articles

COOLING CONDENSERS WITH COLD AIR FLOW OR AIR ELIMINATION IN POWER PLANT TOWERS

Abstract. Evaporative cooling mechanism and specific heat exchange are principles of cooling happening in towers. Air/water mixture releases enthalpy of vaporization. Vapor rises from consumed hot water to cold air flow and water evaporation energy is 1000 Btu per kilogram. This endothermic process from water decreases water temperature. Water loss is the drawback of this process which enters the air from tower in the form of vapor. The vapor is approximately 1.2 percent for each 5.5 Centigrade degrees of tower range in normal condition .Sensible heat which changes temperature also plays an important role in this process. When water is warmer than air, air consequently cools water, leading to increased air temperature .Since water sensible heat transfers to air, released enthalpy of vaporization enjoys cooling effect and this effect forms almost 75 percent of total cooling process of tower and the remaining 25 percent is related to specific heat exchange .Cooling towers are not away from general rules of protection.

A Miniature Radial-Flow Wind Turbine Using Piezoelectric Transducers and Magnetic Excitation

This paper presents a miniature radial-flow piezoelectric wind turbine for harvesting airflow energy. The turbine's transduction is achieved by magnetic “plucking”of a piezoelectric beam by the passing rotor. The magnetic coupling is formed by two magnets on the beam's free end and on the rotor plate. Frequency up-conversion is realized by the magnetic excitation, allowing the rotor to rotate at any low frequency while the beam can vibrate at its resonant frequency after each plucking. The operating range of the device is, therefore, expanded by this mechanism. Two arrangements of magnetic orientation have been investigated, showing that the repulsive arrangement has higher output power. The influence of the vertical gap between magnets was also examined, providing guidance for the final design. A prototype was built and tested in a wind tunnel. A peak power output of 159 μW was obtained with a 270 kΩ load at 2.7 m/s airflow speed. The device started working at 3.5 m/s and kept operating when the airflow speed fell to 1.84 m/s.

Nonlinear piezoelectric devices for broadband air-flow energy harvesting

This paper presents preliminary work on an investigation of a nonlinear air-flow energy harvester integrating magnets and a piezoelectric cantilever array. Two individual piezoelectric cantilevers with the structure of free-standing multi-layer thick-films have been fabricated and assembled with a free-spinning fan. The cantilevers were attached with different tip masses thereby achieving separated resonant frequencies. Also, permanent magnets were fixed onto the blades of the fan as well as the tips of the cantilevers, in order to create nonlinear coupling and transfer fluidic movement into mechanical oscillation. The device has been tested in a wind tunnel. Bifurcations in the spectra of the blade rotation speed of the fan as a function of output voltage have been observed, and a bandwidth (blade rotation speed range) widening effect has been achieved.

Elasto-Aerodynamics-Driven Triboelectric Nanogenerator for Scavenging Air-Flow Energy.

Efficient scavenging the kinetic energy from air-flow represents a promising approach for obtaining clean, sustainable electricity. Here, we report an elasto-aerodynamics-driven triboelectric nanogenerator (TENG) based on contact electrification. The reported TENG consists of a Kapton film with two Cu electrodes at each side, fixed on two ends in an acrylic fluid channel. The relationship between the TENG output power density and its fluid channel dimensions is systematically studied. TENG with a fluid channel size of 125 × 10 × 1.6 mm(3) delivers the maximum output power density of about 9 kW/m(3) under a loading resistance of 2.3 MΩ. Aero-elastic flutter effect explains the air-flow induced vibration of Kapton film well. The output power scales nearly linearly with parallel wiring of multiple TENGs. Connecting 10 TENGs in parallel gives an output power of 25 mW, which allows direct powering of a globe light. The TENG is also utilized to scavenge human breath induced air-flow energy to sustainably power a human body temperature sensor.

An investigation of channel flow with a smooth air–water interface

Experiments and numerical simulation are used to investigate fully developed laminar and turbulent channel flow with an air–water interface as the lower boundary condition. Laser Doppler velocimetry measurements of streamwise and wall-normal velocity components are made over a range of Reynolds number based upon channel height and bulk velocity from 1100 to 4300, which encompasses the laminar, transitional and low Reynolds numbers turbulent regimes. The results show that the airflow statistics near the stationary wall are not significantly altered by the air–water moving interface and reflect those found in channel flows. The mean statistics on the water interface side largely exhibit results similar to simulated Poiseuille–Couette flow (PCF) with a solid moving wall. For second-order statistics, however, the simulation and experimental results show some discrepancies near the moving water surface, suggesting that a full two-phase simulation is required. A momentum and energy transport tubes analysis is investigated for laminar and turbulent PCFs. This analysis builds upon the classical notion of a streamtube and indicates that part of the energy from the pressure gradient is transported towards the stationary wall and is dissipated as heat inside the energy tubes, while the remainder is transmitted to the moving wall. For the experiments, the airflow energy is transmitted towards the water to overcome the drag force and drive the water forward; therefore, the amount of energy transferred to the water is higher than the energy transferred to a solid moving wall.

A11 Towards an integrated evaluation of the effects on health from smoke or toxic gas dispersion in the evacuation of subway tunnels

Background Understanding how subway tunnels perform during accidents or malicious attacks resulting in the release of smoke or hazardous toxins is key in establishing evacuation strategies that reduce the loss of life or effects on public health. During such emergency situation, the natural background air current caused by the air exchange between the station and outside, has an important influence on the dispersion of smoke and/or toxic agents. Over 60% of deaths in fires are caused either wholly or partially by inhalation of smoke or toxic gases. Thus evacuation strategies that provide routes which reduce the exposure time of individuals to a toxic environment could potentially reduce the loss of life or effects on an evacuee's health. The strategy go up and take the nearest exit to the surface might not be the best response. To support this assessment an understanding of; the air flow driving the motion of smoke, its links with internal climatology and external weather conditions and the evacuation capabilities of subway tunnels, is needed. Methods To support this exploration, 3D Computational Fluid Dynamic models have been developed, to validate field measurements and to gain an understanding of the internal airflow momentum and energy transfer capacity of subway stations in relation to external climatic factors and its effect on the dispersion of smoke and/or toxic agents. By integrating results with evacuation simulations, visual diagnostic and predictive tools which display; the background air flow within the subway, the dispersion of smoke and/or toxic substances, the resulting reduction of visibility and the evacuation of pedestrians, are in development to further our understanding in both subway climatology and integrated evacuation strategies. Results Initial results show promising links between external climatic factors, the subway climatology and the ability to predict the dispersal of smoke/toxins. It has also been established that by navigating pedestrians on routes away from smoke and/or toxic dispersion can significantly reduce the number of fatalities and effect on evacuee's health. The possibilities of integrating these findings is allowing for a more integrated assessment to be carried out. Conclusions The study discussed demonstrates that by integrating the datasets mentioned, a greater understanding of the effect subway climatology has on evacuations strategies of subway stations can be understood. It is shown that accessible technology and software, along with methodologies developed, supports the assessment and development of integrated evacuation strategies that reduce the loss of life or effects on public health. Language: en

Hybridized Electromagnetic–Triboelectric Nanogenerator for Scavenging Air-Flow Energy to Sustainably Power Temperature Sensors

We report a hybridized nanogenerator with dimensions of 6.7 cm × 4.5 cm × 2 cm and a weight of 42.3 g that consists of two triboelectric nanogenerators (TENGs) and two electromagnetic generators (EMGs) for scavenging air-flow energy. Under an air-flow speed of about 18 m/s, the hybridized nanogenerator can deliver largest output powers of 3.5 mW for one TENG (in correspondence of power per unit mass/volume: 8.8 mW/g and 14.6 kW/m(3)) at a loading resistance of 3 MΩ and 1.8 mW for one EMG (in correspondence of power per unit mass/volume: 0.3 mW/g and 0.4 kW/m(3)) at a loading resistance of 2 kΩ, respectively. The hybridized nanogenerator can be utilized to charge a capacitor of 3300 μF to sustainably power four temperature sensors for realizing self-powered temperature sensor networks. Moreover, a wireless temperature sensor driven by a hybridized nanogenerator charged Li-ion battery can work well to send the temperature data to a receiver/computer at a distance of 1.5 m. This work takes a significant step toward air-flow energy harvesting and its potential applications in self-powered wireless sensor networks.

An electret-based aeroelastic flutter energy harvester

This paper presents a new airflow energy harvester exploiting fluttering effects coupled to an electret-based conversion to turn the flow-induced movements of a membrane into electricity. The proposed device is made of a polymer membrane placed between two parallel flat electrodes coated with 25 μm thick Teflon PTFE electret layers; a bluff body is placed at the inlet of the device to induce vortex shedding. When the wind or airstream of any kind flows through the harvester, the membrane enters in oscillation due to fluttering and successively comes into contact with the two Teflon-coated fixed electrodes. This periodic motion is directly converted into electricity thanks to the electret-based conversion process. Various geometries have been tested and have highlighted a 2.7 cm3 device, with an output power of 481 μW (178 μW cm−3) at 15 m s−1 and 2.1 mW (782 μW cm−3) at 30 m s−1 with an electret charged at −650 V. The power coefficient Cp of the device reaches 0.54% at 15 m s−1 which is low, but compares favorably with the other small-scale airflow energy harvesters.

Piezoelectric energy harvesting from vibrations induced by jet-resonator system

Inspired by musical instruments that create high amplitude tones corresponding to resonator acoustic modes when subjected to airflow, a new piezoelectric energy harvester for powering the electronic system of aircrafts is developed. It converts the incoming airflow energy into electricity via a piezoelectric transducer during the flight. With the airflow simulated by an air cylinder, prototypes of the developed energy harvester are fabricated and tested. Experimental results show that the curve of sound pressure, corresponding to the first resonator acoustic mode, is a regular sinusoidal pattern. Within the study range of airflow velocity, a linear relationship can be found not only between sound pressure and airflow velocity but also between open circuit voltage and airflow velocity. A power of above 85mW is released on a passive electric load of 3kΩ by using a single piezoelectric element of 10mm diameter at relative airflow velocity of 159m/s. And the maximum total energy conversion efficiency of the piezoelectric energy harvester is about 1.2‰. It has laid a solid foundation for powering sensors or other devices, thus eliminating a need for batteries.

Effects of Solidity Ratio on Performance of OWC Impulse Turbine

Oscillating water column (OWC) wave energy converters, which are capable of extracting power from ocean waves, have been constructed and adopted worldwide. An essential component of an OWC system is the impulse turbine, which plays a significant role in converting the energy of bidirectional airflow into mechanical shaft power. To optimize the starting characteristics and conversion efficiencies of impulse turbines, a considerable number of studies have been conducted to improve their geometric construction. This paper verifies a numerical model established in FLUENT 14.5 with preexisting experimental data and subsequently explores the effects of the solidity ratio on turbine performance. The results show that the coherence between computed and measured data is satisfactory. In addition, they reveal that a solidity ratio of 0.63 is suitable and is recommended for future research.

Airflow energy harvesters of metal-based PZT thin films by self-excited vibration

We developed self-excited vibration energy harvesters of Pb(Zr,Ti)O3 (PZT) thin films using airflow. To enhance the self-excited vibration, we used 30-μm-thick stainless steel (SS304) foils as base cantilevers on which PZT thin films were deposited by rf-magnetron sputtering. To compensate for the initial bending of PZT/SS304 unimorph cantilever due to the thermal stress, we deposited counter PZT thin films on the back of the SS304 cantilever. We evaluated power-generation performance and vibration mode of the energy harvester in the airflow. When the angle of attack (AOA) was 20° to 30°, large vibration was generated at wind speeds over 8 m/s. By FFT analysis, we confirmed that stable self-excited vibration was generated. At the AOA of 30°, the output power reached 19 μW at wind speeds of 12 m/s.

Development of an Indoor Airflow Energy Harvesting System for Building Environment Monitoring

Wireless sensor networks (WSNs) have been widely used for intelligent building management applications. Typically, indoor environment parameters such as illumination, temperature, humidity and air quality are monitored and adjusted by an intelligent building management system. However, owing to the short life-span of the batteries used at the sensor nodes, the maintenance of such systems has been labor-intensive and time-consuming. This paper discusses a battery-less self-powering system that converts the mechanical energy from the airflow in ventilation ducts into electrical energy. The system uses a flutter energy conversion device (FECD) capable of working at low airflow speeds while installed on the ventilation ducts inside of buildings. A power management strategy implemented with a circuit system ensures sufficient power for driving commercial electronic devices. For instance, the power management circuit is capable of charging a 1 F super capacitor to 2 V under ventilation duct airflow speeds of less than 3 m/s.

A nanogenerator for harvesting airflow energy and light energy

Harvesting airflow energy and light energy from the ambient environment to build a self-powered system is attractive and challenging work. In this article, an airflow-induced triboelectric nanogenerator (ATNG) has been fabricated that converts wind energy to alternating electricity. The mechanism of ATNG has also been illustrated. The performance of ATNGs with different sizes was studied, from which we discovered that the ATNG (size: 1 cm × 3 cm, electrode gap: 1.5 mm) could easily collect energy from a gentle wind (5.3 m s−1). Due to the relatively high alternating electricity frequency (179.5–1220.9 Hz), an approximately stable output power (of up to 1.5 mW) was obtained from the ATNG (size: 1 cm × 3 cm, electrode gap: 0.5 mm) with 8.35 μC of charge transferred per second. Meanwhile, the fabricated wind energy harvesting device was used to drive 46 commercial green light-emitting diodes (LEDs) connected in series and charge a 220 μF capacitor to 2.5 V over 50 s. When combined with a dye-sensitized solar cell (DSC), the device can individually and simultaneously harvest wind and light energy. This shows the potential applications of this ATNG in self-powered systems.

Novel Miniature Airflow Energy Harvester for Wireless Sensing Applications in Buildings

This paper presents a novel miniature airflow energy harvester for wireless sensing applications. The energy harvester consists of a wing that is attached to a cantilever spring. The wing oscillates in response to a steady airflow. An electromagnetic transducer is used to extract electrical energy from the airflow-induced oscillations. Both vertical and horizontal orientations are studied. Experiments show that such a generator can operate at airflow speeds as low as 1.5 m·s-1, which compares well to turbines. When the airflow speed is over 2 m·s-1, the average output power exceeds 90 μW, which is sufficient for powering wireless sensor nodes in heat, ventilation, and air conditioning systems in buildings.

Numerical Simulation of Air Flow Arrangement and Energy Conservation of Air-Condition

In this paper, we study the building air-conditioned room in the small space and establishment the mathematical numerical simulation model which is for the designing and energy saving of the air distribution, We analysis the energy effect on five types of the airflow organization based on simulation software developed by our research team to study the designing and energy saving of the air distribution, and the results show that considering both the two ways of the air distribution is more reasonable and energy-efficient.

Electroaeroelastic analysis of airfoil-based wind energy harvesting using piezoelectric transduction and electromagnetic induction

The concept of transforming aeroelastic vibrations into electricity for low-power generation has received growing attention in the last few years. The goal is to convert airflow energy into electricity for powering small electronic components employed in wireless applications. The potential applications for aeroelastic energy harvesting range from aircraft structures to several engineering problems involving wireless electronic components located in high wind areas. The use of a typical airfoil section is a convenient approach to create instabilities and persistent oscillations in aeroelastic energy harvesting. This article analyzes two airfoil-based aeroelastic energy harvesters using (a) piezoelectric transduction and (b) electromagnetic induction. An airfoil with two degrees of freedom is investigated by adding piezoelectric and electromagnetic couplings to the plunge degree of freedom in two separate cases. The governing dimensionless electroaeroelastic equations are given in each case with a resistive load in the electrical domain for predicting the power output at the flutter boundary. The effects of several dimensionless system parameters on the dimensionless electrical power output as well as the dimensionless linear flutter speed are investigated for piezoelectric and electromagnetic energy harvesting from airflow-induced vibrations. The simulations presented in this study can be employed for designing and optimizing airfoil-based wind energy harvesters.

MLVSS에 따른 Jet Loop Reactor (JLR)에서 동력량과 공기량이 산소전달률에 미치는 영향

Abstract : Oxygen transfer rate generally determines the performance of an aerobic wastewater treatment process that treats high strength wastewater such as food wastewater, animal wastewater and landfill leachate. In this paper, OUR and K L ･a were evaluated by using Jet Loop Reactor (JLR) according to the concentration of a mixed liquor volatile suspended solid (MLVSS), oxygen (air) flow rate and energy input as the variable of the operating conditions. Also, a nonlinear regression model was proposed by the statistical methods with the calculated K L ･a. As a results, in case of applying the high strength wastewater which has to maintain high MLVSS, the energy input and the air flow rate are major parameters oxygen transfer rate in JLR. Finally, the final nonlinear regression model had been developed as a function of E/V, Q g , and µ c . Key Words : Jet Loop Reactor (JLR), Oxygen Transfer Rate, Volumetric Mass Transfer Coefficient (K L ･ a) 요약: 산소전달률은 음폐수, 축산폐수 그리고 매립지 침출수와 같은 고농도 폐수처리를 호기성 공정으로 처리할 시 그 성과를 결정하는 아주 중요한 요소이다. 본 논문에서는, Jet Loop Reactor (JLR)를 이용하여 공기유량과 동력량을 운전조건의 변수로 두고 미생물의 농도에 따른 산소소비율(Oxygen uptake rate, OUR)과 물질전달계수(Volumetric mass transfer coefficient, K

‘Nasal’ speech–hyper or hypo?

Vergult et al1 present interesting and useful descriptions of three patients with deletions at 12q15. It would be helpful if they could clarify one point, however. The authors refer throughout the paper to ‘nasal' speech. It is not clear from the description whether their patients have hypernasal speech or hyponasal speech. Hypernasal speech occurs when there is escape of airflow and acoustic energy into the nasal cavity during speech, commonly due to dysfunction (mechanical or neuromuscular) of the velopharyngeal valving mechanism, as in velocardiofacial syndrome.2 Hyponasal speech, by contrast, is caused by reduced nasal cavity resonance during speech, usually due to anatomical obstruction of the nasal cavity. It is easy to demonstrate, by simply pinching the nose closed while speaking. Distinguishing between these two abnormalities is important, both in diagnosis and in management of conditions in which they occur.

Harvesting energy from airflow with a michromachined piezoelectric harvester inside a Helmholtz resonator

In this paper we report an airflow energy harvester that combines a piezoelectric energy harvester with a Helmholtz resonator. The resonator converts airflow energy to air oscillations which in turn are converted into electrical energy by a piezoelectric harvester. Two Helmholtz resonators with adjustable resonance frequencies have been designed—one with a solid bottom and one with membrane on the bottom. The resonance frequencies of the resonators were matched to the complementing piezoelectric harvesters during harvesting. The aim of the presented work is a feasibility study on using packaged piezoelectric energy harvesters with Helmholtz resonators for airflow energy harvesting. The maximum energy we were able to obtain was 42.2 µW at 20 m s−1.

Self-Powered Device Using Aligned Carbon Nanotube Arrays in Multi-Physics Fields

A novel self-powered device based on the aligned carbon nanotube arrays (CNTA) in multi-physics fields has been put forward in this paper. Synthetically utilizing the photic, fluidic and thermic properties of carbon nanotubes, the multi-physical nanogenerators (MPNG) can generate electric currents when the solar irradiation and air flow synchronously effect on the material surface. Various MPNGs are connected in series to construct a unique truncated conus and cylinder shell structure in order to enhance the output voltage for self-powered electronic devices. The multi-physical power mechanism is formed by converting the solar and air flow energy to the thermoelectric effect. By the finite element analysis, the MPNG model including a pair of p-type and n-type CNTA elements is established, and its temperature and potential distribution are simulated. This self-powered device in multi-physics fields can be applied to a more complicated environment and has a fine prospect.