5th International Conference on Experiments/Process/System Modeling/Simulation/Optimization 5th IC-EpsMsO

Athens, 3-6 July, 2013 © IC-EpsMsO

TWO INNOVATIVE EXPERIMENTAL ARCHIMEDEAN SCREW ENERGY MODELS IN THE SHADOW OF ARCHIMEDES III

Alkistis V. Stergiopoulou1, Vassilios G. Stergiopoulos2*, Dimitris I. Tsivolas3 and Andreas S. Stylianou3 1Ph.D. Candidate of N.T.U.A., M.Sc. of N.T.U.A., Collaborator of ASPETE, Greece

2 Professor of ASPETE, Higher School of Pedagogical and Technological Education, N.Heraklio, 14121 Athens, Greece, e-mail: bstergiopoulos@aspete.gr

3Student of ASPETE

* ASPETE, Division of Water Resources and Environmental Engineering

Keywords: Experimental Models, Archimedean Screws, Small Hydropower, Renewable Energies.

Abstract. The area of low head hydropower has attracted the attention of many researchers in order to use and develop new and efficient Archimedean cochlear hydropower plants. Such Archimedean screw energy systems are enjoying a renewed interest, since about one decade, and have become increasingly popular throughout Europe. The heightened usage of the new screw hydropower turbines is due to their robustness, simplicity and fish friendliness. This paper intends to prove the useful exploitation of a series of inclined axis and horizontal axis new Archimedean screw techniques, and presents, in the shadow of the research program ARCHIMEDES III, some innovative experimental Archimedean screw hydraulic energy models. These experimental models try to simulate the operation in natural conditions of Archimedean Inclined Axis Cochlear Turbines (AIACT), exploiting the low-head potential of watercourses, and of Archimedean Water Current Turbines (AWCT), without works, harnessing the unexploited flowing hydraulic potential of natural streams, open channels hydraulic works and tidal currents as well, converting hydraulic energy from flowing waters into electricity. The preliminary investigations of the behaviour of these two kinds of AIACT and AWCT experimental models bring to light some very useful Archimedean screw aspects and conclusions.

1 INTRODUCTION

The area of low head hydropower has attracted the attention of many researchers in order to use and develop new and efficient Archimedean cochlear hydropower plants. Such Archimedean screw energy systems are enjoying a renewed interest, since about one decade, and have become increasingly popular throughout Europe. The heightened usage of the screw hydropower turbines is due to their robustness, simplicity and fish friendliness. It seems that hydraulic and Archimedean technology had a very long history in Greece. It began during antiquity, 23 centuries ago, during Hellenistic time, in the technological context of Macedonian Alexandria, in the famous Library and Museum, where the spirit of Aristotle’s was present, with various machines and mechanisms, gears, planetaria, celestial globes, the Antikythera Mechanism, with pumps, various mills driven by water wheels etc [1, 2]. Invention of the water screw is traditionally credited to the scientist and engineer Archimedes of Syracuse, on the basis of numerous Greek and Latin texts. This screw pump was first mentioned by Diodorus of Sicily, Athenaeus of Naucratis, Moschion etc. The Roman engineer Vitruvius gave a detailed and informative description of the construction of an Archimedes screw in his “De Architectura” [3, 4]. The evolution of these spiral hydraulic screw mechanisms continues nowadays thanks to the overtime-continuous Archimedean contribution. This paper intends to prove the useful exploitation of inclined axis and horizontal axis new Archimedean screw techniques, and presents, in the shadow of the research program ARCHIMEDES III, innovative experimental Archimedean screw hydraulic energy models. It gives some preliminary experimental results of a research carried out within the program ARCHIMEDES III, entitled “Rebirth of Archimedes: contribution to hydraulic mechanics study and Archimedean cochlear waterwheels hydrodynamic behaviour, for recovering the hydraulic potential of natural and technical watercourses, maritime and tidal currents”, concerning series of innovative conventional and unconventional inclined and horizontal axis floating Archimedean screw turbines to be installed in a multitude of very promising sites throughout Greece. These experimental models try to simulate the operation in natural conditions of Archimedean Inclined Axis Cochlear Turbines (AIACT), exploiting the low-head potential of watercourses, and of Archimedean Water Current Turbines (AWCT), harnessing the unexploited flowing hydraulic potential of natural streams and open channels hydraulic works and tidal currents as well and converting hydraulic energy from flowing waters into electricity. The preliminary investigations of these two kinds of AIACT and AWCT experimental models bring to light, in the shadow of

Αlkistis V. Stergiopoulou, Vassilios G. Stergiopoulos, Dimitris I. Tsivolas, and Andreas S. Stylianou

642

Archimedes and ARCHIMEDES III, some very useful Archimedean screw aspects and conclusions (figure 1).

Figure 1. Experiences in the shadow of Archimedes

2 EXPERIMENTAL ARCHIMEDEAN HYDROPOWER SCREWS IN ASPETE

In the shadow of ARCHIMEDES III and the research program “Rebirth of Archimedes: contribution to hydraulic mechanics study and Archimedean cochlear waterwheels hydrodynamic behaviour, for recovering the hydraulic potential of natural and technical watercourses, maritime and tidal currents”, by following the similarity methodology of the Buckingham’s π-theorem, some experimental and theoretical researches towards the inversion of the energy flow in Archimedian screw operation, and a series of innovative small-scale models of new Archimedean turbines were designed, developed and tested in the water channels of ASPETE [4, 5]. Buckingham's π theorem states that, if a quantity dependent on n physical variables and k is the number of primary independent dimensions, then the dimensionless dependent variable corresponding to this quantity can be expressed in terms of only n-k dimensionless variables. Then the equation relating all the variables will have (n-k) dimensionless and independent of each other π groups. The final equation obtained is in the form of πl = f(π2, π3 ,….. πn-m ). It is well known that in Fluid Mechanics, there are only three independent dimensions, mass (M), length (L) and time (T). Thus, k = 3. In most fluid problems, the physical variables are the density (ρ), the velocity (V), the body length (l or c), the viscosity (μ) and the speed of sound (a). Thus, n = 5. The two dimensionless variables are the Reynolds number (Re) and the Mach number (M). By selecting ρ, D, and N as variables containing the fundamental dimensions to be combined with the remaining variables and giving π1= μaρbDcNd or π1 = ρ D2N/μ = Re, and deriving other π-terms π2 = M 2 and π3 = P/[ρ D5N 3 π4 = Q/[D3N], π5 = H/[ D2N 2]. A large number of prototype/model equations can be used for scaling both for turbines. During our experimental and theoretical efforts for scaling Archimedean turbines we had used the following efficiency prototype/model correlation developed by Moody (1− η1) / (1−η2) = (D2/D1)0.25 (H2/ H1)0.1, where η is the efficiency, D the diameter, H the hydraulic head, and the indices 1 and 2 correspond to the prototype and model condition. Experiments have shown that, for geometrically similar Archimedean cochlear turbomachines and for incompressible flows, the Reynolds number effect Re is small and may be ignored and we could assume the relationships f{P, D, N, Q, H, η}=0, or H/[D2N2] = f’{ Q/[D3N], η}, , where P is the installed capacity, N the rotation speed and Q the flow discharge. Taking into account that the first two groups are both functions of the third and weak functions of Re are usually ignored it is easy to obtain the following relations Q1/Q2=(N2

1D21)/(N2

2D22), Q1/Q2 = (N1D3

1)/(N2D32), P1/P2 = (N3

1D51)/(N3

2D52).

By following the similarity methodology a first spiral wheel having the dimensionless ratios, s/d = 2, dm/d = 0,24 and g/d = 0,04, with s the spiral lead, d the circular duct dimension, dm the circular mandrel dimension, and g the thickness of the spiral profile. Figure 2 gives definitions of the dimensionless ratios of a spiral wheel and some views of small-scale Archimedean rotors models developed.

Our first measurements and calculations of the Archimedean spiral turbine rotors showed the important effect of inflow water level to diameter, and seem to give efficiencies between 60 and 80%, making these an interesting alternative for turbines in low head hydropower applications.

Αlkistis V. Stergiopoulou, Vassilios G. Stergiopoulos, Dimitris I. Tsivolas, and Andreas S. Stylianou

643

Figure 2. Definition of the dimensionless ratios of a spiral wheel and some views of small-scale

Archimedean rotors models developed.

3 EXPERIENCES OF ARCHIMEDEAN INCLINED AXIS COCHLEAR TURBINE (AIACT)

During the last years various Archimedean experiences had been made in the open flume hydraulic channel experimental channel of the Hydraulic Laboratory of ASPETE concerning various Archimedean wheel configurations, by using our small-scale models. Figure 3 gives representative view of the first Archimedean Turbine Model in the open Armfield flume channel of ASPETE.

Figure 3. View of the first Archimedean Turbine Model

Figure 4 shows characteristic views of the second Archimedean Turbine Model in the same open flume channel.

Figure 4. Views of the second Archimedean Turbine Model

Αlkistis V. Stergiopoulou, Vassilios G. Stergiopoulos, Dimitris I. Tsivolas, and Andreas S. Stylianou

644

Dimensions of the experimental spiral small-scale models are connected with circular duct dimensions using specific parameters given by relation of a spiral lead s, a thickness of a spiral profile g, and cylindrical mandrel diameter dm to a constant circular duct diameter d, and are presented as s/d, g/d and dm/d ratios, respectively. Some flow measurements and visualizations have been made in the S3/TILTING FLUME ARMFIELD channel, for two spiral rotor models designed and developed. These wheels have the dimensionless ratios, s /d = 0.7 (1.4), dm/d = 0.2 (0.15), g/d = 0.035, with s =5 cm the spiral lead, d = 7.2 cm the circular duct dimension, dm the circular mandrel dimension (1.4 cm for the first cochlear wheel and 1.1 cm for the second one). Figure 5 illustrates the small-scale Archimedean screw models used and their spiral geometrical definition. Τhe maximum water depth in the open channel was 31 cm [5]. The orientation angle of the rotors was variable between 22-33ο.

Figure 5. Photos and geometrical definition of the spiral models used.

Figure 6 gives a schematic view of the experiences made in the Armfield flume channel and illustrates two

representative Archimedean experiences in this open channel. The first calculations and measurements of the Archimedean spiral turbine rotors showed the important effect of inflow water level to diameter, and seem to give good efficiencies, making these an interesting alternative for turbines in low head small hydropower applications.

Figure 6. Representative Archimedean experiences in the S3 Armfield open flume channel of ASPETE.

Αlkistis V. Stergiopoulou, Vassilios G. Stergiopoulos, Dimitris I. Tsivolas, and Andreas S. Stylianou

645

An optical tachometer was used to measure the rotation speed of the turbine. An arc was used to measure the slope α of the turbine shaft, and a steel ruler to estimate the water level and the depth of the water h = L.sin α , where L = the length of the water screw rotor = 35 cm. The inner diameter of the screw axis is dm= L/20 – L/25, and d = 7.2 cm is the outer diameter of the screw turbine. The flow discharge Q (m3/s) was measured by using a water mill [4, 5] . The rotation speed n (rev/s) is measured by using an optical tachometer. The efficiency η is a function of the geometry of the screw, of the diameter d, of the flow passing through Q, and of the rotation speed n. The efficiency η = Pout/Pin is calculated by determining Pin and Pout, with Pin (W) = Pth = ρ.g.Q.H and Pout (W) = T. ω = Τ . 2.π. n, where ω is the angular speed, and T (N.m) is the torque on the shaft. Figure 7 presents the experimental results of Pth , rotation speed n (rev/s), and torque (N.m) in function of Q (l/s). The efficiency η, a function of the geometry of the screw, the diameter d, the flow passing through Q, the rotation speed n, tend to obey the following correlation: η = [1-0.01125.d2/Q].(2.n+1) / (2.n+2) . The rotation speed seems to follow the correlation n (rev/s) = 0.85/ d2/3.

Figure 7. Measured screw turbine power, rotation speed and torque, in function of Q.

4 TOWARDS ARCHIMEDEAN WATER CURRENT TURBINES

Recent ASPETE and NTUA common efforts proved the useful exploitation of a new Archimedean screw technique and the efficient rediscovering of the old Archimedean screws under the form of innovative Archimedean horizontal floating cochlear rotors, the Archimedean Water Current Turbine (AWCT), harnessing the unexploited flowing hydraulic potential of natural streams and open channels hydraulic works and tidal currents as well, converting hydraulic energy from flowing waters into electricity. AWCT’s are defined as floating spiral systems that convert hydro kinetic energy from flowing waters into electricity, taking advantage of water’s density, which is 850 times greater than air. AWCT systems rely mainly on the existing kinetic energy in the water stream. These floating Archimedean systems, utilizing the kinetic energy available, do not require the diversion of water through manmade channels, riverbeds, or pipes, although they may have applications in such conduits [3, 4, 5]. They may operate in unidirectional and/or bi-directional tidal flowing waters and they do not require waves for operation. A series of similar or different floating Archimedean energy screws could be installed for recovering the hydraulic kinetic energy potential of the Euripos tidal channel (figure 8).

Figure 8. Floating AWCT’s in the strait of Euripos

A floating Archimedean spiral hydro-generator developed in the Hydraulic Laboratory of ASPETE has been

Αlkistis V. Stergiopoulou, Vassilios G. Stergiopoulos, Dimitris I. Tsivolas, and Andreas S. Stylianou

646

already virtually tested in an irrigation channel, simulating the sea and current flow, with good results. The same floating Archimedean spiral rotor without civil word should be tested in rivers and in the entrance or the exit of the natural canal of the mysterious sea river current of Cephalonia (figure 9).

Figure 9. Photorealistic views of floating horizontal-axis Archimedean hydro plants in a river and in the

sea-river current of Cephalonia.

The preliminary theoretical, experimental and simulation results prove that technically feasible Archimedean hydraulic energy conversion could become the future lead green technology and be the alternative solution for hydro electricity generation in a large number of sites throughout the whole country. Some new AWCT systems were developed recently and are under experimental investigation in the Hydraulic Department of ASPETE. Figure 10 gives an idea of such a new experimental AWCT system under recent investigation.

Figure 10. New experimental AWCT system under investigation

5 TOWARDS FUTURES EXPERIENCES OF ARCHIMEDEAN INCLINED AXIS TURBINES

Recently, various Archimedean experiences are under elaboration concerning two different cochlear Archimedean wheels configurations and new small-scale models. The first one concerns a rotor of 21 length, with a step of 3cm, an angle of inclination 26o, and a diameter ratio 1/7, for an independent stand-alone

Αlkistis V. Stergiopoulou, Vassilios G. Stergiopoulos, Dimitris I. Tsivolas, and Andreas S. Stylianou

647

Archimedean small hydropower plant, build in the shadow of ARCHIMEDES III, and illustrated in figure 11.

Figure 11. New stand - alone Archimedean small hydropower plants developed in the shadow of ARCHIMEDES III

Some other new preliminary experiences are under elaboration for a new fiberglass cochlear rotor installed in the ARMFIELD open flume hydraulic channel experimental channel of the Hydraulic Laboratory of ASPETE, concerning new Archimedean small-scale model. Dimensions of this new spiral small-scale model are characterized by a 3/6=0.5 diameter ratio, a step of 3.5cm and a length 28cm. Figure 12 illustrates the new small-scale Archimedean screw model used and their spiral geometrical definition.

Αlkistis V. Stergiopoulou, Vassilios G. Stergiopoulos, Dimitris I. Tsivolas, and Andreas S. Stylianou

648

Figure 12. New small-scale Archimedean screw model used and its spiral geometrical definition.

The present paper tried to prove the useful exploitation of inclined axis and horizontal axis new Archimedean screw techniques, and to present, in the shadow of the research program ARCHIMEDES III, two kinds of innovative experimental Archimedean screw hydraulic energy models, the Archimedean Inclined Axis Cochlear Turbine (AIACT), exploiting the low-head potential of watercourses and of the Archimedean Water Current Turbine (AWCT). The preliminary experimental results obtained and the new investigations under elaboration underline the very promising behaviour of the AIACT and AWCT experimental models. ACKNOWLEDGEMENTS This research has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program ARCHIMEDES III (Investing in knowledge society through the European Social Fund).

REFERENCES [1] Stergiopoulou, A. and Stergiopoulos, V. (2009). From the old Archimedean Screw Pumps to the new

Archimedean Screw Turbines for Hydropower Production in Greece, Proceedings of SECOTOX and CEMEPE Conference, Mykonos, 21-26 June 2009.

[2] Stergiopoulou, A. and Stergiopoulos, V. (2009). Return of Archimedes: Harnessing with new Archimedean spirals the hydraulic potential of the Greek watercourses, Proceedings of the Conference for Climate Change-Sustainable development and Renewable Energy Sources, Thessaloniki, October 2009.

[3] Stergiopoulou, A. and Kalkani, E. (2012). Investigation of the hydrodynamic behaviour of innovative cochlear turbines, Proceedings of the 12th EYE and 8th EEDYP Conference, Patras, 11-13 October 2012.

[4] Stergiopoulos, V., Stergiopoulou, A. and Kalkani, E. (2010). Quo Vadis Archimedes Nowadays in Greece? Towards Modern Archimedean Turbines for Recovering Greek Small Hydropower Potential, 3rd International Scientific "Energy and Climate Change" Conference, Athens, October 2010.

[5] Stergiopoulou, A., Stergiopoulos, V., Kalkani, E. (2013). Back to the Future: Rediscovering the Archimedean Screws as Modern Turbines for Harnessing Greek Small Hydropower Potential, PSP Volume 22, No 6a. 2013, Fresenius Environmental Bulletin.