Experimental model for an electric, hydro pneumatic wave-powered plant.

Marin, Dorian ; Samoilescu, Gheorghe ; Nicolaie, Sergiu 等

1. INTRODUCTION

The realization of an electric, hydro pneumatic plant adapted to the characteristics of the Black Sea area is preceded by the realization and experimentation of several experimental models in view of choosing the optimal form to build it. The first question was to design and make a wave channel to experiment under conditions as close to the natural ones as possible. Afterwards, a methodology of calculation was devised for the electric, hydro pneumatic wave-powered equipment in order to compare the similarities among several experimental models and choose the optimal method to put it into practice. (Volsanic & Matusevschi, 1985).

The easiest way to produce waves under lab conditions is to use a wing whose axis of oscillation is placed on the bottom of the channel and is powered by a crank mechanism allowing the wing to oscillate against a plane square with the surface of the channel. The disadvantage of such a system is the fact that in order to get the waves at the desired length the oscillation frequency needs increasing which triggers the reduction of both the period of time and the wave-length--a contradiction of the way waves are produced in the nature: there, the increase in the height of the waves leads to an increase in the period of time and wave-length. (Tanasescu, 1986)

Another contradiction within the wing system is that the wing stirs the entire water volume starting from the bottom of the channel, whereas in the nature it is the other way around: water agitation is diffused from the surface to the interior of the water mass.

These contradictions lead to erroneous interpretations regarding the propagation course of pressure propagation and wave energy. (Wave Energy Summit, 2008)

At one end of the channel the experimental model has a 315 mm diameter cylinder which is suspended by its two arms above water level. The arms are attached to an axis close to the bottom of the channel. In its upper part the cylinder is equipped with a chock on which there is a rod activated by crank powered by a worm gear motor. During operation the cylinder moves from the water surface to the bottom and back again.

A deeper penetration of the cylinder into water in order to vary the wave height is achieved through the adjusting control of the distance between the chock on the cylinder and the crack of the gear motor that is by varying the length of the rod.

The system allows a tangential movement of the waves upon water surface and, in the same time, an adjustable penetration in the water depth in order to obtain the desired wave heights.

2. THE DESIGN OF AN AERODYNAMIC DYNAMOMETER AND EXPERIMENTAL MODELS

A dynamometer has been used and it has consisted of a glass tube equipped with a graded scale on its exterior in order to measure both directions of the air flux; the graded scale has been vertically placed in a holder above the orifice in the ceiling of the installation. Inside the glass tube, at the middle of the scale there is a thin aluminum disk of a diameter almost similar to the tube diameter and equipped with several openings whose surfaces are approximately equal to half of the disk surface. These openings allow the circulation of a part of the air flux, assuming the role of the spaces in the turbine blades used in hydro pneumatic equipment. The disk has a small axis in its center and two spiral springs attached to it and leading to the ends of the glass tube. During its operation the disk moves along the graded scale upwards and downwards and measures the aerodynamic force of the air flux during absorption and delivering under pressure. In order to choose among the best model of a piece of hydrodynamic equipment, several models have been designed and tested (Olaru & Lazar, 2005):

1. a model whose interior is formed by straight walls. When building this model, the shape that has been taken into consideration is similar to the one presented by other hydro pneumatic plants that have been built in several other countries.

2. a model whose interior is formed by vertical wall upfront and curved wall behind which allows the increase in the descending speed of the oscillating column. This model is equipped with an opening of 70% out of the height of the front wall.

3. a model whose interior has the front wall made up of an external and inside curved wall while the hind wall is curved.

4. a model whose interior has a curved and oscillating front wall and a curved hind wall. The oscillating front wall allows more easily the waves to penetrate horizontally the inside. The incurvation of the wall allows the waves to come against it from several directions because of the wave pressure. This model is currently studied. In order to check up the function of the one-way axial micro turbine an experimental model has been equipped with such a turbine.

One feature of this micro turbine is the rotor gear which is made up of a central hub where 8 axes are radial thrust and on which oscillate 8 blades built from 0.2 mm iron plates. The hub is provided with a slot that has been centrally placed and its walls are lopsided in order to limit the blade oscillation to a +/- 30[degrees] angle. The rotor axis is attached to the center of the hub and it is supported by several bearings of the gear motor.

Features:

Type- one-way, in-tube; Diameter of micro turbine -19 mm; Length of axis -20 mm; Inclination angle of blades -+/- 30[degrees]; Rated speed -3000 rot/min.

The micro generator is similar to the generator of the hydro pneumatic plant to be built and it includes a micro resized laminated outer casing.

The stator core has a one-layer winding coil fitting all 24 slots in the stator.

The rotator is made up of a small constant two-pole magnet of rare earths that has been micro sized and attached to the rotator axis. Two bronze bearings--also the installation bearings --are attached to the outer casing of the micro generator.

Features:

Type-synchronous, three--phase generator; Engine output -24 mW; Rated speed -3000 rot/min; Voltage rating-0,6 V; Ampere rating-23 mA; Number of slots on stator -24; Slots on pole and phase--4; Winding -one layer; Field magnet-constant magnet of rare earths.

The model has been equipped with a turbine in order to separately check up the turbine way of functioning. This module includes two bearings attached to a metal frame in order to evacuate the air flux. The one-way turbine is placed between these two bearings. In order to better place the turbine, the upper bearing has been provided with a small adjuster. A generator module has been designed in order to check up the electric current generation. This module includes a metal frame which has a piece of equipment in its upper part to which the micro generator has been glued.

The axis of the micro generator is attached to the turbine axis by the help of a rigid gearing. The turbine axis is backed up by a bearing within the upper piece of equipment. The threshold on which the micro generator has been glued is concentrically to the bearing intended for the turbine axis.

3. DESIGNING AN EXPERIMENTAL ELECTRIC WAVE-POWERED PLANT

The experimental stand for wave generation including a wave channel and experimental models was exhibited at the International Fair in Bucharest--TIB 2008.

Features:

Length -3 m; Breadth -0,3 m; Water depth -0,4 m; Diameter of wave generating cylinder -31,5 cm; Height of produced waves-1-12 cm. A schedule has been devised and it has included:

1. Checking up the functioning of the wave channel; the experiment has been performed by taking into account the 3 dimensions of the rod operating on the wave-generator cylinder in accordance with the height of the necessary waves. Several heights, wave periods and wave lengths have been obtained. The waves have come under a sinusoidal shape. The functioning of the channel is stable.

2. Checking up the functioning of the aero dynamic and its stamping; it has produced a rhythmical movement both for the air uptake and intake; in order to balance the dynamometer a 10, 92 g weight has been used and it has brought about a 5, 5 cm movement on the graded scale resulting in a constant value of the dynamometer: K = 1,998 g/cm

3. Envisioning the functioning of the interiors of the experimental models; the way the wave penetrate the interiors, the oscillation column within the interior and the oscillations of the aero dynamic dynamometer have been under observation;

4. Determining the air uptake and intake aero dynamic forces; It has been performed with the help of the aero dynamic dynamometer;

5. Determining the average speed of the obtained air flux; With the help of a hot yarn transducer both the uptake speed and intake speed resulting from some 4-5 cm waves have been recorded on a computer. It has been performed with the help of LabView software;

6. Determining the air feed for each model; Knowing the section of the air passing column and taking into account the obtained average speed and the section of the transducer used to gauge speed, the air feed within the 4 experimental models has been determined

7. Experimenting the functioning of the one-way micro turbine; Regardless the direction of the air flux, the turbine has a one-way spinning direction;

8. Experimenting the recommended model to build the 5 kW --electric plant.

The experiments performed in the wave channel have led us to the selection of the recommended experimental model in order to design and build the 5 kW hydro pneumatic electric plant.

4. CONCLUSIONS

1. The wave pressure exercised horizontally is greater than vertically;

2. The model equipped with a curved double wall and an orifice at 70% out of the height of the wall allows better results;

3. Electric experiments have been limited to the experiment of the gear motor, taking into account the relatively great starting moment of the generator due to the chock frictions, the variable reluctance in the air-gap and a potential anisotropy of the stator disk;

4. The oscillations of the column inside the equipment are strongly influenced by the aerodynamic resistance of the air column;

5. During the experiments on the models the aerodynamic pressure, the variations of the oscillation column, the average speed and the uptake and intake of the air flux have been gauged, also the air flux expelled by the models has been calculated.

5. REFERENCES

Olaru Gh., Lazar P.D. (2005). Rotor for one way turbines, File OSIM A/00752-01.09.2005

Tanasescu F. T. (1986). Energy conversion--Unconventional Techniques Ed. Tehnica, pp. 30-50

Volsanic V. V., Matusevschi G.B. (1985). Wave and sea wind, their transformation principle, in: Hydrotechnical construction, 4, pp 52-74

*** Wave Energy Summit 2008, Available from: http://www.waveenergytoday.com/wave08, Accessed on: 2008-10-07

Tab. 1. Features of the recommended model mounted by the
aerodynamic dynamometer

n, rot/min--rotation speed of the engine of the reducing gear

n, rot/min 150 300 370
hv, cm 1.5 3.5 5
hc, cm 1.5 3.7 6.5
T, s 6 3.16 2.52
D, gf 1.0 7 26
Pmax, mm [H.sub.2] O 0 8 65

Tab. 2. Features of the recommended model with a corked
column orifice

n, rot/min 150 300 370
hv, cm 2.5 3.5 7
hc, cm 1.0 1.2 1.0
T, s 6.03 3.15 2.54
Pmax, mm [H.sub.2] O 4 10 70

Tab. 3. Features of the recommended model with an uncorked
column orifice

n, rot/min 150 300 370
hv, cm 1.5 3.8 4.7
hc, cm 1.5 4.3 8
T, s 6.03 3.15 2.54
Pmax, mm [H.sub.2] O 0 3 20

Tab. 4. The feature related to void operation

n, rot/min 500 1000 1500 2000
U, mV 100 210 320 420

Tab. 5. The charge

I, mA 0 4.7 5.9 6.9
U, mV 210 87 71 67