AIR THERMAL POWER EFFICIENCY RISE

TROUGH ROTATIONAL AIR FLOW

George Mamulashvili (G_Mamulashvili@mail.ru)

Candidate of Technical Science

On the right references to the list of the organizations which cooperated with the author of these inventions in development of the given direction of scientific researches and to which the author expresses the sincere gratitude are given

SYNOPSIS

A way of Air-Thermal Power (ATP) technology improvement to make it competitive with the most popular high temperature indirect solar energy source technology is proposed.. The fundamental target of the work is to investigate and develop an Artificial Cyclone Power (ACP) technology for the ATP plant of a “Solar Chimney” type on the basis of the results of an experimental installation of such plant at La Mancha, near Manzanares, Spain, in 1982. The work programme was offered to investigate the version of ATP plant construction with rotational air flow in accordance with the author’s Invention Certificates of the former Soviet Union No 13119654 and 1526335 on so-called “Trailing Solar Chimney” plant. For the rotational air flow systems was offered to study the technology, which uses the special whirlwind turbogenerator assembly. Carrying out theoretical and experimental researches in this direction will allow us to choose after the comparison of received results the optimum technology of transformation of falling solar radiation. Analytic estimations performed in this work show that use of rotational air flow in the plant can several times increase its efficiency.

INTRODUCTION

The Air-Thermal Power (ATP) technology is one of the very perspective power sources technologies of the indirectly producing electric power from solar radiation energy.

As is known that the ATP plant is an energetic system which transforms the solar thermal radiation in the stable air flow harboured in the trunk tower. There are also the aircraft turbine producing the electrical power. To attain the highest power from these air flow the constructions of tower, collector and central foundation is proposed.

There are two trends may be use in the projecting of ATP plants:

• the single flow Upwind system (UWS) so-called "Solar Chimney"

• the rotational flow Whirlwind system (WWS) so-called "Trailing Solar Chimney".

The first testing industrial installation of UWS of small power ATP plant was erected by the German scientific and researching organisations together with European constructing companies. It was made for the Spain Energy Union in 1982. It has the inherent virtues of such kind of power sources - it does not causes any damage of the environment and does not needs fossil fuel. Moreover, ATP technology has a valuable advantage in comparison with the most popular indirect solar power sources such as Central Receiver System (CRS) so called “Solar Tower” and Distributed Collector System (DCS) so called “Solar Farm” which need direct sun light - ATP plant works under diffuse solar radiation as well.

ATP plant's efficiency increases with its size and so with its output and consequently this technology might be useful as an industrial scale power technology.

1. AIR-THERMAL POWER PLANT TECHNOLOGYS AND IT’S PECULIARITYS

1.1. Prototype’s technology.

The reason why ATP technology has not been yet introducing in industrial use is that the acting prototype “Solar Chimney”, described by Shlaich et al in their work [1], provide low efficiency even at the largest plant's sizes which could be ever feasible. The prototype’s tower is 200 m high and has a diameter of 10 m. The solar collector roof’s diametr is 250 m and approximately 2 m it is above the ground (see Co "Schlaich Bergermann und Partner).

The aircraft turbine is support independently of the chimney on a steel frame platform 9 m above the ground. It contains four blades of type FXW-151-A whose angles can adjust during operation in order to maintain a constant rpm or to attain the optimum one. The turbine requires a vertical start-up wind velocity of 3 m/s and can handle velocities up to a maximum of 20 m/s.

The main purpose of constructing the UWS was to analyse the initial statistics obtaining from its long-time period of operation for the following projection of ATP plants by capacity 5, 30, 100 MW.

Side by side with many attractive energy aspects, especcialy in field of the development alternative energy sourses, the UWS under the high tower and gross glass collector has some problems. The main of them is an unprecedented scale of building. For example the 100 MW power plant requires the tower’s height is 950 m and diametr - 115 m. The collector roof’s diametr is 3600 m [2].

This scale frightens a potential buyer. He thinks about the seicmic safety of the thousand meter towers and value of exploitation of the glass collector roof which overlaps is approximately 20 milion square meters.

The EC energy commision note that “... Similarly the proposed project of Solar Chimney Plant based on huge plastic tent and chimney creating a major depression used for driving a large turbine is higly speculative and not demonstrated on a large scale, staing at the research level;...” [3].

It will be noted that the nessasary to receive wind velosity is 16.3 m/sec into the collector and pressure loss on the turbine at nominal load is 703.5 Pa for the 200 MW UWS which has the overall plant effeciency is 1,10% [4]. It causes the low competitive capabilitys of such plant against to other renewable energy sources. Thereof the presented work’s target is to obtain requisite useful load on the turbines within power characteristics of plant and without it's problems of large building scales and to provide high efficiency.

The efficiency of 1% can be achieved at the plant's tower 1 km high for ATP plant of Solar Chimney type as it is showed by Mullet in his work [5].

The aim of our work programme is to propose a way of ATP technology improvement, which substitutes linear air flow in the plant by an air whirl, to make it competitive with the solar energy technologies which are in us now. Analytic calculations for the improved technology shows that the use of rotational air flow in the plant can several times increase its efficiency.

2. AIR THERMAL POWER PLANT’S EFFICIENCY WORK MECHANISM

The principal components of ATP are as follows: the collector - a greenhouse where air is heated, the tower which provides up draft of the heated air and the machinery converting energy of air flow into electric power.

The work mechanism of ATP plant with linear (radial in the collector and up draft in the tower) flow is thoroughly described by Shlaich et al in their works and the use of rotation does not changes its main principles.

In ATP plant with rotational flow air gets rotational velocity at the periphery of the collector e. g. from outer wind through special slits in the collector. For plant's constructional sizes considering in this work the energy needed to provide sufficient rotation at the periphery is much less then plant's output and tangential velocity at the periphery is no more then wind speed at calm weather, which was approved by calculations.

However, in a plant of small size and while the much wind the energy input from the wind can substantially increase plants power. It is approved by operating of another type of power sources - wind power plant described by Berkovski et al in their book [6]. This plant has a tower of special construction with slits to acquire wind energy and to convert it into energy of air whirl which is maintained in tower.

Morover there has yet been developed and discribed in the invention [7] a technical solution of ATP plant's tower where could be maintained an air whirl. The France Patent No 2524530 is the prototipe of this inventions. The France project “Centrales aerothermiwues a cyclones artificiels” making by Ingenieur d’Aeronautique Edgard Nazare is a most near to the autor’s project “Trailing Solar Chimney”. Typical capasity of the france project is an aproximately 4000 MW under temperature rise 50 C beetwin external and internal temperatures. Such power coud to compare with the capasity of the nuclear power plant This project has not the solar collector. It has the wind collector and external base which absorbing air streams in bottom. [8].

The construct solution of the ATP “Trailing Solar Chimney” is based on the use of a self-exhausting spiral tower and collector together with a special carousal turbine mounted at basement level.

Air heated under the transparent collector adjoined the tower, is emitted through the tower. The density and the temperature of the air on the basement level increases several times allowing some high technologies of energy conversion, which combining with the use of ascending streams substantially improves the efficiency of the power plant.

The large prototype of the Traling Solar Chimney is 333 m high and has a diameteter of 30 . The solar collector roof is 600 m in diameter and approximately 3 m above the ground.

The collector roof will composed of rectangular, at first flat, panels of dimension 6 x 6 m respective 4 x 6 m which were clamped along their periphery in metal cables supported on the reinforced concrete perimetr with tube columns in one side and on the lower tower's support hoop in other side.

The Chimney Tower will composed of panels too which were clamped along their periphery in metal cables supported on the lower tower's ring-shaped truss beam in one side and on the upper tower's ring-shaped truss beam in other side. The sheets will overlapped and bolted wertically by intermediate external ring-shaped truss beams. The Tower's bottom will supported 42 m above the ground. The Tower will stayed vertically at four levels and in three different ditections to foundation blocks along the periphery of the collector roof.

The wind turbine will suppoerted independently of the chimney on a steel frame platform. The turbine requires a gorisontal start-up wind velocity of 0.5 m/s.

So, yet not having performed complete investigation in this field, we suggest that the problem of creation and maintenance of stable rotational flow in plant by means of ambient wind is technically soluble.

At last well known that a group of Israel engineers, architects and scientists under liadership of prof. Dan Zaslavsky has been working on a project to harness the heat of the desert to produce energy and water for rise of the ATP plat’s efficiency. Water is pumped to the top of the tower and sprayed into the centre, where it rapidly evaporates in the dry desert heat.

As the air is cooled by the evaporation, it grows denser and falls downward, accelerating under gravity so that, by the time it gets to the bottom, it is moving at the rate of 80 km/hour. This downdraft is used for driving turbines to generate power.

Desert Sluices Ltd, a new company set up by the cillege is to exploit the new SNAP technology (Sneh Aeroelectric Power).

A typical full-size SNAP plant would generate 500 MW. At the same time it would desalinate 100x106 m of water annually. It would incorporate a wind tower about 1 km high and 503 m in diameter.

That technology looks very attractive but its use is restricted only dy regions where the dry air and water are present at the same time and place [9].

All this assumptions were applied in calculations and approved both theoretically and experimentally for ATP of Solar Chimney type by prof. Jorg Shlaich et al in their work. In case of rotational flow the velocity of flow and its path through the plant considerably increases and so the first assumption seems groundless. However, because of high flow speed in the tower and the nearest to it part of collector the friction there becomes

turbulent and so lows and thus this assumption can be applied.

Moreover there is assumed that

* radial flow velocity is much less then rotational velocity.

This condition rises plant's efficiency and also substantially simplifies calculations. It means for the fixed constructional sizes and periphery rotational velocity an upper boundary for air expenditure, which can be provided varying load of turbine.

Though at this work's stage friction and heat transfer have not yet been included in calculations and so only the ''ideal'' system's efficiency was calculated, we made an attempt to consider losses in the plant by an empiric coefficient , which's order could be estimated from data provided by Shlaich et al in their works.

The equations shows that in case of linear flow and constant air pressure over the whole collector - the conditions in which the efficiency was estimated by prof. Jorg Shlaich et al in their works - the value of plant's efficiency approaches to , which agrees with the equation they derived.

As it is seen from the value of tends to as energy input with rotational velocity becomes much less then energy of solar radiation, which is true for numeric example given below.

The most part of the efficiency rise comes from drop of , that increases with speed of air rotation and is much in case of potential flow in the collector then for cyclostrophic flow.

3.3.Numerical calculations.

As a numeric example there have been estimated efficiency of a plant with potential rotation in the collector and cyclostrophic flow in tower.

Considering low friction losses in natural whirl winds we assumed the tornado's values for the whirl in the tower [10].

Allmost the numerical calculations was accompleshed by the computer simulation programme. The structure of the simmulation programme represent below. The mathematical modelling of the WWS physical behaviour accomplish in the 4 stages for the arrange of the simulation programme . The exist energy balancing model is use for the orientation in the connect area of the individual model objects at first. Then (second stage) the finite element and finite difference models will be select by the method of the successive complication depending on the necessary speed of the calculation and the degree of the errors for each objects (collector, chimney, turbine). After this ( third stage) we will be use the general finite element model for the making more precise and comparison with the way out data of the exist energy balancing model.

On the fourth stage the finite element model is use for the Optimisation Program which can be arrange after finish of the primary stages. The Visual C++ computer languages is use by the simulation programme.

Structure of the WWS computer simulation programme

Table 3

1. Weather and time data:

* Day number

* Time of the day

* Delta f for the time steps over the day (5 min to 15 min)

* Global insulation

* Ambient temperature

* Wind speed

* Wind direction

* Station pressure

* Temperature decrease with height in the outer atmosphere coupled in dependence of the solar insulation level (W/m

&

#178;) and the wind velocity in (m/s)

2. Input of plant dimensions:

* Height of the chimney

* Diameter of the chimney

* Wall thickness on top

* Wall thickness at the bottom

* Diameter of foundation

* Collector radius

* Collector height at the outer rim, at the chimney entrance and about

15 heights in between at different radii, equally distributed

3 Collector cover:

* Thickness of each glass layer

* Glass properties as there are reflectivity in the visible range in

dependence of the incident angle, transmission in the visible range

and in the IR. range, emission in the in the IR. range, conductivity,etc.

* It should be possible by a flag to mark each collector element whether it is double glassed or single glassed

* Dirt factor

4. Properties of the soil beneath the collector

* Absorption coefficient (in order so simulate the effect of black plastic

foil on the ground or natural soil)

* Reflectivity of the plastic foil or the ground in the visible range

* Emission coefficient of the plastic foil or the soil

* Thermodynamic properties of the ground in order to calculate the

amount of heat stored in the soil which will be released during night time

* The temperatures in the soil should be calculated to depth level of about 5m

5. Machinery data

* Efficiency curves in the dependence or rated power of the gears (to be first

assumed and later on adjusted to data from suppliers)

* Efficiency curves in dependence of rated power of the blades (to be first

assumed and later on adjusted to data from suppliers)

* Efficiency curves in dependence of rated power of the transmission (to be

first assumed and later on adjusted to data from suppliers)

* Efficiency curves in dependence of rated power of the generators (to be first assumed and later on adjusted to data from suppliers)

* Efficiency curves in dependence of rated power of the transformers (to be

first assumed and later on adjusted to data from suppliers)

6.Calculated data for each time step

* Air temperatures in the collector at all radius intervals (approx. 15) and in

three different heights of the collector

* Air temperature in the chimney at different heights (for example every

50 m)

* Temperatures of each glass cover (inner and outer surface)

* Temperature profile in the ground (approx. 5m depth)

* Rotational air velocity at each radius interval of the collector and in the chimney

* Mass flow at each radius interval and in the chimney

* Pressure at each radius interval and in the chimney

* Friction losses of the collector (at the ground surface, glass surface),at

transition to the chimney, at the chimney walls

* Humidity at each radius interval and in the chimney

* Reflection, convection, conduction, IR-emission losses for each radius

interval

* Total useful available pressure difference

* Pressure drop at the turbine

* Power generated for each time step

* Losses at the chimneys top

* Energy stored in the ground or extracted from the ground during night time

* Efficiency of the collector, turbine (gears, blades, generator, transformer),

chimney, overall plant efficiency.

* Energy production

7. Accumulated calculations for one day and one year

* Accumulated reflection losses of the collector

* Accumulated convection losses or gains

* All averaged efficiencies (collector, chimney, turbine)

* Operation hours

* Full load hours

* Energy production

The graphical illustrations of the numerical calculations shows that the efficiency of the ATP whirlwind system energy producing depend on the definite correlation between the plant’s construct parameters and velocity of the air twisting on the chimney collector periphery under the definite climate conduction in general. Any variations of the climate conditions evinces the necessary of the variations of the thermo- and air- dynamic parameters of the power plant for the guaranteeing of the maximum energy producing that it is require the optimisation of the correlation between power plant’s active constructions.

The chimney height must correspond to each climate conduction and global insulation for the stabilisation of the rotational air flow into the power plant.

For the north latitude where the variation of the temperature difference possible in limits of 20-35C the chimney height may the variations in limits of 275-578 m that the usually for the tower structure and has not specially build problems. For South latitude where the variations of the temperature difference possible in limits of 35-50C the chimney height may the variations in limits of 200-275 m.

Under this correlation of the build parameters the necessary as appropriate to safe the definite rotational velocity on the collector periphery for the whirlwind stabilisation .

The variation of the requires rotational velocity Vt with the ratio of Chimney diameter - D tow to the Collector diameter - Dcol.

Under the rise of the chimney height the ATP capacity will rising too but the dependence carries the not direct proportional character.

It is explain that the whirlwind ATP adiabatic process is characterised by the fall of the mass flow depending on the temperature difference exponents into the unclosed volume of ATP plant.

Take into account that the adiabatic expansion of air essence the fall of the chimney height and radial velocity too ..

The fall of the chimney height evinces the falling of the capacity in dependence of the temperature difference rise but this process non direct proportional too .

The efficiency of ATP plant with rotational air flow will fall as appropriate with the fall of the temperature difference because the necessary to safe the definite correlation between parameters of the ATP active constructions , especially the chimney height for stabilisation of the whirlwind .

Thereof the necessary to find the optimal correlation between main ATP elements with the possible maximum efficiency of ATP plant. The Specific Investment Cost plays the main part in the optimisation .

Development of the WWS research program.

Investigations

In a next time the precise equation for the top efficiency for the plant with the rotational air flow in a part of the Collector and in the Tower depending on the flow parameters will be derived.

Then the heat transfer and viscosity will be involved in the air flow calculations and computer aided calculations will be performed to estimate the real such type plant's efficiency.

The next task will be the rotational flow maintenance stability calculations.

The work programme schedule includes three stages comprising the theoretical and experimental investigation and the stages of the small prototype’s design . The basic ones are following:

First step (1995) - the theoretical investigation, analytic design, selection the mathematical model and making the simulation programme of the ATP physical behaviour with the rotational air flow and spiral turbo generator assembly, preparing the annual research report and according it with the partner;

Second step (1996) - the experimental investigation comprising with and adding to the simulation programmes, the design and testing of the turboo generator assembly, the design of the small prototype ; Third step (1997) -selection of the most effective version of the new technology and testing of the definite elements of the small prototype, preparing the general research report and according it with the partner;

The feasibility of the research on rotational ATPP is ensured by former USSR experiments on energy conversion with whirl giving high efficiency. But this work was cancelled for problems of whirl flow stabilization. In the research this problem must be solved by widening the rotation's radius decreasing Reynolds number and involving automatic regulation.

In addition the feasibility of the whole ATP conception itself and its ability to be improved has been approved by long time experience of the German side on the operating power plant.

In the research are involved both theoretical and experimental methods of investigation. The using techniques include analytic estimates and design, computer simulation and laboratory modelling of the physical processes in the power plant. The turbines and the shape of the part of collector attached to the tower will be investigated in wind tunnel.

Translational nature of the collaboration on the project arises from the mutual influence of different theories of solar energy transformation in Air-Thermal Power and provides the possibility of use the existing scientific and technical solutions of Germany, United Kingdom and FSU for working out optimal technology.

"Schlaich, Bergermann und Partner" Civil Engineering Consultants, Institutes of Air- and Gas-dynamics, Thermodynamics and Active Constructions of Stuttgart University, which participate in the programme from the German side, have designed ATP prototype built in 1982 in Spain, near Madrid and carried out research work on it. Prof. Dr. Jorg Schlaich, author of the operating prototype, is the Programme Coordinator .

Prof. Dr. Paul O'Callaghan participates from School of Mechanical Engineering of Cranfield University, UK. The department's research includes wind turbines and solar collectors development, the basic elements of ATP, the special design of which is a part of the proposing new technology.

The role of partners in the project is determined by the trends of their scientific and technical activities. It is supposed that scientific consulting company "Schleich, Bergermann und Partner" will take part in organizing real scale tests of new technology in similar climate conditions on the working experimental and industrial plant and co-ordinate the results of separate stages with leading Institutes of Stuttgart University by their comparison with data received before in final scientific and technical report, and also will take part in selection and co-ordinating draft constructional solutions of using new technology.

On the preliminary agreement School of Mechanical Engineering of Cranfield University will support organizing and carrying out experimental research work on the special turbo generator devices.

Scientific consulting enterprise TSM performs theoretic and design work on energy conversion technology, develops particular devices and systems, and submits.

Projecting.

Bearing in mind the World Bank opinion that “... the costs of all commercial forms of renewable energy (primarily solar energy, biomass, geothermal energy, hydropower, and wind) have declined remarkably over the past two decades...” the author’s group prepare the project of ATP plant together with hydrogen’s manufacture by volume of 20000 m/h for Georgian market conditions. At present the market prise of the nature gas is 670 US$ per tonne. This prise will rise in next time. The ATP project may be is commercial if it use the modern electrolysers demanding 3.8-4.2 kWh/m of hydrogen and has electric energy cost is 3.5-4 /kWh. As a whole the prise of hydrogen may be 1300-1400 US$ per tonne for compensation period (see table

CONCLUSION

• The proposed whirlwind technology decreases the building dimensions of the ATP of a “Solar Chimney” type several times and allows power producing in an industrial scale. It will be give possible to continue the research works in this direct.

• The principal components of the ATP “Solar Chimney” are well known: the Collector - a kind of a greenhouse where air is heated and thus is expanded, the Tower which provides up draft of the heated air, and the Machinery to transform the energy of the air ascending through the Tower. The construct solution of the ATP “Trailing Solar Chimney” is based on the use of a small modification of the self-exhausting spiral tower and collector together with a special carousal turbine mounted at basement level. Air heated under the transparent collector adjoined the tower, is emitted through the tower too. Only the density and the temperature of the air on the basement level increases several times allowing some high technologies of energy conversion, which combining with the use of ascending streams substantially improves the efficiency of the power plant. It will be give the possible to use the accumulate experience of the usually building of the power plants.

• The preliminary numerical calculation showed that the necessary to use the Analytic model calculation of the adiabatic process under the design of the ATP plants both the UWS and the WWS. The computer simulation programme could to optimise this process.

• The results of the calculations show the advantages of the use of following innovations under the design of the ATP plant:

1. The combination of the upwind process with rotational air flow in the ATP of the Solar Chimney type in accordance with the author’s Invention Certificates of former Soviet Union No 1319654 with the priority of 08.10.85;

2. The air-dynamic design of the ATP spiral panels twisted around the central column for the tower and air collector in accordance with the author’s Invention Certificates of former Soviet Union No 1170100 with the priority of 26.01.84;

3. The air-dynamic design of the tower and collector on the special geometry in accordance with the author’s Invention Certificates of former Soviet Union No 1526335 with the priority of 25.03.88;

4. The air-dynamic design of the carousal turbine and constricting it on the basement level of ATP in accordance with the author’s Invention Certificates of former Soviet Union No No 1526335 with the priority of 25.03.88.

5. The design of the dynamic stability active constructions of the whirlwind ATP in accordance with the author’s Invention Certificates of former Soviet Union No No 1641962 with the priority of 27.01.91.

References

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13. Kato Yoshio, Tanabe Shinichi The House with Solar Chimney and the House with rock tower three passive Solar Houses at north latitude 35 degrees in Japan, Waseda Univ, Tokyo, ASES 9th Natl Passive Solar Conf, Columbus, OH, Sep 24-26, 84, P143 (6).

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15. Lodhi M.A. Solar-Desert Chimney a concept and device for large scale Solar Power Production at low cost, Texas Tech Univ, NSF/ET Al renewable energy sources intl sym.lahore, Pakistan, mar 18-22,83, P199 (18).

16. Haisley Robert J.Solar Chimeny theory basic precepts Presented at ISES-AS/ET Al passove * Hybrid cooling INTL Conf, Miami Beach. Nov 6-16,81,P211(5)

17. De Winter Francis Double Water Chimneys as a solar DHW storage tank and a gas fired backup tank Atlas Corp,Calof,Presenred at ISES-AS/ET Al 1980 annual conf, phoenix, Jun 2-6, 80, V3.1,P182 (4)

18. The World Bank World Development Report 1992 " Development and the Environment" * 1992 The Internationak Bank for Reconstruction and Development, Published by Oxford University Press, Inc. ISSN 0163-5085.

In addition to materials of research the list of the organizations and the scientists which were taking part in the project and other documents