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In the present world there are conventional and many other renewable energy generating methods are used for electricity generation. The world is leading towards renewable energy generation because the conventional methods are more harmful to environment, limited resources and create more costs. Researchers are looking for more various methods that can convert renewable energy sources to electricity.Generating electricity using Vortex induced vibrations (VIV) is a latest technology which is used in power generation. Kinetic energy of a moving fluid is converted in to electricity is the basic.
Traditional method of generating using turbines doesn't work for slow fluid flows. A fluid flow past a bluff body, such as a circular cylinder, will result in the periodic shedding of vortices into the body's wake for all but the lowest flow speeds. This process gives rise to oscillatory lift and drag forces which, if the body is compliant or elastically supported, can result in Vortex-Induced Vibrations. Using this oscillatory kinetic energy electricity can be generated.Concept of Smart Buildings is coming to the topic nowadays.
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Its areas of application currently focus on using of small autonomous wireless sensors (thus eliminating the need of wires), in structural health monitoring, HVAC (Heat Ventilation and Air Conditioning) and building automation applications.
This project is to design and develop a power supplying unit for wireless sensing and data transmitting (Humidity and temperature) device of HVAC (Heat Ventilation and Air Conditioning) application. The process of extracting energy from the environment or from a surrounding system and converting it to usable electrical energy to power up these sensing and transmitting devices is taken into action.
According to the application the power requirement may vary. Applications like wireless sensing and data transmitting devices required a small scale power range (Between 0.5mW - 2W, it vary with the device). This project will help to eliminate the need of wires and satisfy the power demand of small scale autonomous wireless sensors for HVAC duct system in the concept of smart buildings.Aim and ObjectivesAimDesign and Fabrication of small-scale (0.5mW - 2W) energy harvesting device by using Vortex-Induced VibrationsObjectivesTo design of a mechanism to convert energy of the moving fluids to vibrating motionTo design of conversion method to produce electrical energy using vibrationTo develop prototype energy harvesting deviceTo evaluate the performance of the designed energy conversion device.R.A.P. Dhanuka150120N
Subsection 1
HVAC SYSTEM RELATED VORTICESHVAC Systems What is HVAC?Heating, Ventilating, and Air Conditioning (HVAC) equipment perform heating and/or cooling for residential, commercial or industrial buildings. A vital requirement for all-air ventilation systems are their functionality to operate both in cooling and heating mode. [1]The HVAC system may also perform as a fresh outdoor air supplier and remover of interior airborne contaminants such as odors from occupants, volatile organic compounds (VOC's) emitted from interior furnishings, chemicals used for cleaning, etc. A properly designed and maintained system will provide a comfortable interior environment throughout the year.1010346191717Figure 2.1 Air handling unit [2]Why HVAC?When we are talking about HVAC system, there are lot of critical measurements that we have to observe and measure. As energy efficiency and indoor air quality become more important, and your customers opt for Internet of Things (IOT) capability, sensors are becoming a bigger part of HVAC. Some, like pressure sensors, are most useful to HVAC techs. Pressure sensors play a key role in making HVAC systems more efficient by measuring air flow and pressure throughout the system for effective air distribution. By measuring pressure of individual rooms and monitoring the air flow to each room, the HVAC system can optimize a building's cooling, heating and air flow and reduce energy consumption.Some sensors which are using in HVAC systems,Pressure sensorsDuct smoke detectorsOccupancy sensorsVOC sensorsThermostat sensorsIn this project we are going to use Piezoelectric Energy Harvesting (PEH) by using Vortex Induced Vibrations (VIV) phenomena to power up these sensors. Piezoelectric energy harvesting (PEH) is one of the most promising technologies. It consists in the conversion of mechanical energy into electrical, either by converting mechanical vibrations into an electrical charge. These harvesters generate electricity based on the amount of force used in compressing or deforming a material, as well as the amount and type of deformation on the material's crystal structure and the speed or frequency of compressions or vibrations to the material. [2] Use of this technology will lead this project to create predictable and simple air flow nature. HVAC duct systems would be the ideal scenario for these requirements. Then we moved to air flow in the HVAC ducts. HVAC systems were chosen since they offer an attractive environment for energy harvesting from fluid flow due to the predictable nature of their flow and their prevalence in buildings. Air flow in HVAC systems is typically unidirectional with a slug- shaped velocity profile and operating speeds from 2 to 5 m s-1. While other environments such as liquid or gaseous water pipes and natural gas lines also exhibit similar characteristics, they offer more challenging environment in which to work. [3]
Vortex Shedding VorticesIn fluid dynamics, vortex shedding is an oscillating flow that takes place when a fluid such asair or water flows past a bluff body at certain velocities, depending on the size and shape of the body. In this flow, vortices are created at the back of the body and detach periodically from either side of the body. The fluid flow past the object creates alternating low- pressure vortices on the downstream side of the object. The object will tend to move toward the low-pressure zone. Due to periodic vortices, this kind of movement occurs in the object to upside and down periodically. For this vibration we can call as Vortex Induced Vibration (VIV). In subsection 2, we will describe VIV phenomena in detail.1941195240833
Figure 2.2 Vortex street created by a cylindrical objectReynolds NumberLike many fluid flow phenomena, vortex shedding has been observed to be directly dependent on the Reynolds number of the flow, which is defined in following equation,(1)? =?U is the free stream velocity, D is the cylinder diameter, and ? is the kinematic viscosity of the fluid. As a note, most studies in literature were in fact performed using a submerged cylinder. So the correlation length of cylinder diameter used in Re is appropriate and widely applicable, as many submerged structures are typically cylindrical in shape.We can see the changing pattern of vortex shedding patterns according to the Reynolds number in Figure 2.1.3. Below the 40 of Re (1st two regimes) cannot see vortex shedding around the bluff body and no resulting lift forces act on the body. After 40 of Re, periodic vortices start tobegin around the body and act varying lift forces since the vortices shed non symmetrically from the top and bottom of the cylinder. 150<Re<300 would be the transition region from laminar to turbulent. 300 < Re < 3¤" 105 region is vortex street is fully turbulent and strong periodic shedding results. The second transition region occurs when the flow around the cylinder changes from laminar to turbulent, and again vortex shedding is disrupted and irregular. The agreed upon ranges for this transition region were found to be varying, with the results of Lienhard giving 3x105<Re< 3.5x106 (Blevins), but experimental measurements by Bernitsas give the range as 3x105<Re< 5x105. Above this final transition region, from Re>5x105 to 3.5x106, both the vortex street and cylinder boundary layer are turbulent, and regular vortex shedding resumes. The ranges of no periodic vortex shedding, or dead zones (Bernitsas), must obviously be avoided for any device extracting energy from VIV. [4]1001027122073Figure 2.3 Vortex shedding Regimes [4]Strouhal NumberAn additional non-dimensional parameter has been established to relate the frequency of vortex shedding fs to the flow conditions. Strouhal number directly proportional to fs and diameter of the cylinder D and inversely proportional to free stream velocity U. For a wide range of Reynolds number, the Strouhal number varies very little, and can essentially be taken asconstant of 0.2. [2],[4]1036722215578Figure 2.4 Strouhal Number vs. Reynolds number [4]
Many researches were done in the past for different ranges of flow velocities. But most of the time typical airflow that for residential applications are in the range of 2 to 5 ms-1, while in industrial applications the upper value can be higher [2] and done some researches on this range.The harvester is tested at various flow speeds (up to 11 m/s), with the peak energy obtained at a speed close to 1.2 m/s and rapidly decreasing beyond this value, while smaller amounts of energy are harvested in speeds above 6-7 m/s due to the involvement of additional vibrationsmodes. [2]
There is another experiment was done on different range and which range of wind speeds is0.82 ‰¤ ?€— ‰¤ 7.03, where ?€— = ?/?, with ? being the free stream velocity in m/s and ? being the natural frequency in Hz. According to the experiment, voltage output reaches the maximum value when ?€— = 5; this indicates that the system is in the largest amplitude is obtained. [5]Another research was done on investigate analytically the harvesting capacity of a piezoelectric coupled cantilever harvester with an attached proof mass from cross wind-induced vibration due to the Vortex Shedding phenomenon. In their case, they consider a constant wind flow ofm/s, and they account also for small variations in the order of 0.5 m/s. [6]Flow velocity range also depend on the HVAC application and according to these experiments applicable flow velocity range would be 0 " 15 ms-1. [9]
Bluff BodiesBluff Body vs. Streamlined BodyWhen a body is submerged in a moving fluid, body can experience a drag force, which is usually divided into two parts such as Frictional drag and Pressure drag. Frictional drag occurs from friction between the fluid and the surfaces over it is flowing. Pressure drag occurs from the eddying motions around the body. This drag is related to the formation of a wake. Both drags are due to viscosity. (If the body was moving through an inviscid fluid there would be no drag at all)2008505154940Figure 2.5 Wakes around a streamlined body (a), Wakes around different types of bluff bodies (b)When the drag is dominated by Frictional drag, we say the body is streamlined and when it is dominated by Pressure drag, we say the body is Bluff. Domination of the drag depends entirely on the shape of the body, whether the flow is Frictional-drag dominated or Pressure-drag dominated. A streamlined body looks like a fish or an airfoil at small angles of attack, whereas a bluff body looks like a brick, a cylinder or an airfoil at large angles of attack. For a given frontal area and velocity, a streamlined body will always have a lower resistance than a bluff body. [7]
Bluff Body TypesThere are lot of bluff body types using in different engineering applications. But most of the researches are done for cylindrical type bluff bodies and near cylindrical ones. Here are some researches for different types of bluff bodies.A research was done on optimizing the energy consumption inside buildings. Different relevant aspects are explored in wind tunnel testing, after a thoughtful investigation using analytical methods. Two different configurations for the fin (circular and T-section) are compared. [2] And they strongly suggested to have T-section fin as the attachment. Because the harvested power reaches values of 200јW and 400јW at an airflow velocity of 3m/s for the cylindrical and the T-section prototype respectively.Another research was done for observe amplification by the interactions between (a) an aerodynamic fin attached at the end of the piezoelectric cantilever and (b) the vortex shedding downstream from a bluff body placed in the air flow ahead of the fin/cantilever assembly. The positioning of small weights along the fin enables tuning of the energy harvester to operate at resonance for flow velocities from 2 to 5 m s-1, which are characteristic of HVAC ducts. In a 15 cm diameter air duct, power generation of 200 јW for a flow speed of 2:5 m s-1 and power generation of 3 mW for a flow speed of 5 m s-1 was achieved. [3] This device, which required a minimum duct height of 12 cm and the obstacle was chosen to be a 2.5 cm diameter cylinder. The fin was created from balsa wood due to its high stiffness to density ratio and the optimum distance between the bluff body (obstacle) and the fin was chosen as 7.5cm.Figure 2.6 Diagram illustrating the idea behind the operation of the harvester. [3]
Abdelkefi et al. provide numerical analysis for the validation of a galloping harvester. Their device consists in a bar with an equilateral triangle cross-section attached to two multi-layered cantilever beams. [8]Abdelkefi et al. investigate galloping energy harvesting using bluff bodies of different geometries (square, D-shape, and triangular cross-sections) and different electrical load resistance, for flow speeds up to 15m/s. In their numerical results, the optimal bluff body section changes with the flow speed. [9] There were 2 triangle cross section bluff bodies and they were isosceles triangle with ґ=30, isosceles triangle with ґ=53. The results showed that, for small wind speeds, the isosceles triangle with ґ=30 cross-section is the best cross-section for enhancing the level of harvested power. On the other hand, at relatively high wind speeds, the D-section is the best cross-section for power harvesting.24048721384974Another different shape was tested in this research and converter consisting of an elastically mounted circular cylinder and a free-to-rotate pentagram impeller is proposed to harness hydrokinetic energy from water currents. The vibration energy of the cylinder and the rotation energy of the impeller are harvested simultaneously. The simulated Reynolds number range was 14,000 < Re < 80,000. [10]
Figure 2.7 A circular cylinder with an attached free-to-rotate pentagram impeller [10]A research was done to investigate that the influence of the second Piezoelectric Energy Harvester (PEH) (No.2) on combined PEH device and its distance from No.1 PHE (W). Both the output voltage and the Effective Output Range of Flow Speed (EORFS) of the Dual PEH system were observed and compared to the SPEH system. And also investigated that how affect the cylinder (bluff body) diameter (D) and the specific gravity (S.G) of the cylinder to the system. They used 3 configurations to compare the effect of D and S.G. [11]Figure 2.8 Names and different characteristics of PEHs. [11]
Experiments were conducted in the case of seven different spacing distances (W= 2D, 2.5D, 3D, 3.5D, 4D, 5D, 6D) in this part.As the result of experiments, they could be able to observe that RMS value of the output voltage of the 2nd harvester is greater than 1st one. Here is the observations and conclusion of this research.When increasing the specific gravity of the cylinder, the output voltage was decreased.When increasing the radius, the output voltage was increased.The output voltage of the DPEH system were significantly improved, compared to the SPEH system. And the improved percentage was almost 99% compared to SPEH and 94% compared to No. 1 cylinder.W = 2D was the optimum distance for a DPEH system [11]
Renewable energy sources. (2019, Aug 20). Retrieved from https://studymoose.com/renewable-energy-sources-essay
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