|SCIENCE TRIBUNE||Thursday, June 19, 2003, Chandigarh, India|
little discharge can yield electricity
Realising the importance of production and conservation of electricity, the world today is showing a renewed interest in small hydro stations to exploit power potential of every little discharge and every small head available in running canals or distributaries. This has led to the emergence of finer technology with special emphasis on making the turbines most efficient. Turbine technology is now aiming at full automation and maximum cost effectiveness with "versatility" as the key word in the manufacturing process.
Of many types of turbines developed these days, a careful choice with respect to existing parameters may lead to innumerable benefits during the running of hydro stations. The factors that we generally look for while selecting a turbine are :
Choice of the turbine to be used for a given discharge, given head and possible variation in discharge is to be made to achieve the above factors to maximum possible extent. Among discharge and head, it is the head that governs the selection of turbine while the discharge determines the capacity of turbine. Momentary rise in speed of turbine on sudden reduction of load from full to zero and momentary drop in speed on increasing load from zero to full at rated speed are further factors to study before making final selection.
Water turbines are basically machines that convert hydraulic energy into mechanical energy. The hydraulic action divides the turbines into two classes: impulse turbines and reaction turbines. Impulse turbines convert the available energy first into kinetic energy through one or more nozzles throwing free jets of water on runners and making them rotate. In reaction turbines, the entire flow from head race to tail race takes place in a closed conduit system and only part energy is available while most of it remains in form of pressure head. Impulse turbines are used when the head available is very high i.e. 60 metres or above. Reaction turbines are used for lower heads though one of their kinds ( Francis Turbine ) can also be used for high heads.
Keeping in view the head and discharge available and the variation in discharge and load, specific speed and efficiency of the turbines is determined and the turbine is chosen. More is the head available, lesser is the specific speed of turbine. It is always tried that turbine with highest possible specific speed is chosen. High specific speed leads to reduction in cost of turbine and lends high rotational speed thus helping in keeping the size of turbine, of generator and thus of power house smaller. However, specific speed cannot be increased indefinitely as very high speed may result in chances of cavitation.
While the Pelton, Turgo and Crossflow are Impulse type turbines, Francis Turbines, Propeller turbines, Bulb Turbines, Vertical Kaplan Turbines, and Tubular turbines fall under Reaction Turbines category. Till today, Francis, Vertical Kaplan and Bulb turbines have ruled the scene. These days, Tubular Turbines are also making their presence felt because of their simplicity, easier erection and operation and handling of ultra low heads.
Bulb Turbines have a horizontal axis and their runners are directly connected to the generators which are located in water tight enclosures called bulbs. These turbines carry the advantage of having a straight flow resulting in higher velocity and thus higher discharge for a given runner diameter. They have higher specific speed and runner diameter is about 15% lesser than Vertical Kaplan turbines. That is why these are increasingly being preferred. However, the hydraulic losses in these turbines are more in comparison to other turbines. Another minus point of bulb turbines is that their machine failure rate is higher. This is because the thrust of axles on bearings is excessive in this type of turbines. This is the reason that many of these turbines are found under-performing these days.
In Vertical Kaplan Turbines, the axis is vertical and thus there is hardly any pressure on bearings. Therefore, their failure rate is low. Their cost is also comparable to that of Horizontal turbines. Their minus point is that they need a spiral development and direction of flow changes many times thus resulting in slightly higher diameter of the runner. Vertical Turbines installed at Mukerian, UBDC and Anandpur Sahib Hydel Project are performing better than Horizontal turbines installed elsewhere in the state. The table given below shows some guidelines for the selection of turbines.
The above table shows some overlapping of head ranges. This range enables us to choose better of the two turbines after analysing other related factors.
Bulb Turbines and Vertical Kaplan Turbines are thus always carrying a neck to neck fight and choice between them rests on individual site conditions. In addition to cost, efficiency and output, an important point that should be kept in view is the post installation performance of these turbines.
Coming to the modern Tubular Turbines, these are integrated with the generators as water tight modules for direct installation in the waterway. Very little space is required for their installation. Entire machine module can be placed underground and only a small building for switching equipment and automation needs to be erected above the ground. The wicket gates and propeller blades are fixed type. For generation up to 500 KW, turbine and generator are linked to the same shaft and no gear box is used. The cost of civil works is minimal. For higher generation, several gear driven generators are grouped around the turbine.
In Switzerland, a small size plant of just 12 KW with an ultra low head of only 1.4 metres and water flow of 1.5 cumec has been commissioned. In Finland, five compact units, each of only 33 KW operating at a head of only two metres have been installed. The message is clear that these countries are determined to make use of every small fall and discharge by using tubular turbines which are perfectly suitable for such small heads.
India has so far shown much
inclination towards Bulb or Vertical Kaplan turbines only. Reason for
this is that mere data projection by the turbine manufacturers lends
no confidence to the end users. It is the ‘proven track record’
that clicks to the mind and transforms the thinking process. Another
reason is that our cash strapped developers and hydro station owners
can’t afford to take chances or bear experimentation costs.
Sometimes this slow adoption of technology has carried a blessing in
disguise as the teething troubles are overcome by the foreigners and
technology is perfected by the time India adopts it.
Prof Norman Myers, the eminent British environmentalist, who recently visited India and lectured in a few cities has presented a grim picture of the effects of global warming with the mean temperature of the earth having increased by about 1.6 degree C. If global warming continues, "an increase of 3 to 4 degree C in the equatorial regions or a drop of a few degrees at the poles will lead to receding mountain glaciers and melting of the polar ice caps and a rise in the sea level".
Myers has predicted that there is a growing risk that the climate will change in ways that seriously disrupt our lives. While the globe will get warmer and receive more precipitation, individual regions will experience different climatic changes and environmental impacts.
According to the British environmentalist, not only will there be a faster rise in sea levels, one would also witness frequent hurricanes and storms, more heat waves and droughts, resulting in more and more conflicts for water resources, and a greater increase in heat-related illness and wider spread of infectious diseases.
The rise in sea levels will also affect India. It is estimated that around 23 million Indians in the East Coast (comprising West Bengal, Orissa and parts of Andhra Pradesh) may have to abandon their homes because of the rise in sea levels, said Prof Myers. Global warming may threaten our health, our farms and forests, beaches and wetlands and other natural habitats.
The question arises whether we can slow global warming. Since the formulation of the Kyoto Protocol there have been discussions on reducing emissions but not much headway has possibly been made. The IPCC Report (1994) has pointed out that the damaging effects of greenhouse gas concentrations in the atmosphere could cost on the order of 1 to 1.5 per cent of GDP for developing countries and 2 to 9 per cent of GDP for developed countries.
As is well known, the industrialised nations constitute only 20 per cent of the entire global population but produce 80 per cent of the global carbon dioxide emissions in the atmosphere. Burning of fossil fuels and emission of greenhouse gases like carbon-dioxide were in defiance of the Kyoto protocol.
In fact, Myers asserted that "to stabilise the amount of carbon-dioxide in the atmosphere, the emission of carbon-dioxide needs to be cut down by as much as 60 per cent. The use of alternative sources of energy like wind and solar energy could cut down on the emission of COs".
The eighth session of the Conference of Parties to the Framework Convention on Climate Change (October 2002) in its declaration pointed out: "Actions are required to diversify energy supply by developing advanced, cleaner, more efficient, affordable and cost-effective energy technologies, including fossil fuel technologies and renewable energy technologies, hydro included, and their transfer to developing countries on concessional terms as mutually agreed".
Coming to the case of India, one may refer to a report on global warming which has been prepared by the School of Environmental Sciences of Jawaharlal Nehru University. The report has predicted that the Sunderbans and other parts of South 24 Parganas in West Bengal as well as large parts of coastal India, including Goa, Orissa, Mumbai, the southern States and Island will be affected if global warming raises sea levels.
Around 0.16 per cent of the country’s land area or 0.41 per cent of the coastal regions (around 5763 sq km) are likely to be lost in the process. It has been estimated that 1.68 per cent of the population (according to the 1991 census) or 7.1 million will suffer and the financial loss would be around Rs 1.85 crores.
The study has projected three broad
possibilities by the year 2100. The "high" estimate shows
waters rising to about a metre, the "best" estimate is a
rise of about 60 cms and the "low" estimate of 30 cms. The
one-metre level rise is being called unlikely and the "low"
estimate may be considered rational, based on the revised projections
in the last one decade. INFA
Oxygen is necessary for getting fire. But sun also spits out fire. That means in sun also oxygen exists. Is it right?
You have to realise that the importance of oxygen for supporting a fire is due to the fact that we have an abundance of materials that have carbon and hydrogen as their components. These elements are found in all vegetation, in wood, in coal and in oil. Oxygen is abundant in the atmosphere. When temperature is raised, through lighting a matchstick, a lightning strike, a spark or any other means these material and oxygen combine to produce energy. If such materials were absent oxygen itself will not produce fire. But we know that energy is produced in other reactions, chemical and not chemical. Solar energy is not produced chemically but through nuclear reactions in which lighter elements combine to produce heavier elements. In fact it is now known that elements like carbon nitrogen and oxygen are also produced in the solar furnace, deep inside the sun. This is also true of all other elements. Sun-like stars are responsible for the production of most of the elements we know. This happens in various phases of evolution of the stars. Most of the reactions that do this are exothermic, in the sense that they also produce energy. Yes, oxygen exists in the sun but is not primarily responsible for the solar flares that emanate from its surface. These fires have a different origin and a different nature.
Why the fruits and flowers are losing fragrance while we keep them in our fridge?
I congratulate you for discovering this question. I am using the word discovering because it did not occur to me till now. It is quite possible that lot of people have already discovered it and most of them even know the answer. The extent to which we become used to accepting the world without ever asking why is truly amazing. I will try guessing the answer to your query. There might be some other considerations that come in. If you think of something let me know. I will also think a little more about it.
We smell things because actual molecules
travel out and reach the receptors in our nose. These receptors are like locks
that accept only specific keys. They are very particular. When a reception
occurs a signal travels out to our brain giving us the feeling of a specific
smell. There are a thousand or more types of receptors, each giving a slightly
different sense of smell. In addition there might be smell we sense through
combinations of different sets of receptors firing. Let me not go on talking
about this amazing capability we have to enjoy this world and return to your
question. Now the basic answer is easy. Molecules can diffuse out if they
belong to a material that is volatile. The number of molecules coming out would
depend on the vapour pressure. Vapour pressure increases with temperature. (We
know this because we can dry our wet clothes faster if we hang them out in the
sun). So at low temperature the volatiles of the fruit or the flower would come
out at a lower rate. Smell is nothing but sensing of volatiles. Hence it would
be reduced if the fruit or the flower were cold.
NEW PRODUCTS & DISCOVERIES
Super fabric from
The superior mechanical and electrical properties of carbon nanotubes have intrigued materials scientists for a decade. But they’ve struggled to take advantage of the hollow tubes, just nanometers wide, for macroscopic projects.
Now, researchers have spun the tubes into composite fibres that are tougher than steel, Kevlar, or spider silk. The new fibres appear to be tougher than any other synthetic or natural material, says Ray Baughman of the University of Texas at Dallas in Richardson. Toughness indicates how much energy a material can absorb before breaking.
By modifying a process developed by French researchers , Baughman’s team spins fibres made of carbon nanotubes and polyvinyl alcohol, a common industrial polymer. In the June 12 Nature, Baughman and his colleagues describe the finished threads, which are the width of a human hair and 100 to 200 meters long.
The achievement is "very good news for the field of nanotubes," says Philippe Poulin of the Paul Pascal Research Center in Passac, France, one of the researchers who developed the technique that Baughman’s team modified.
Brain’s image of body
Physical therapy changes the way body parts are represented in the brain, a finding researchers hope will lead to improved therapies.
A team of researchers in Germany and the US studied 10 musicians suffering from focal hand dystonia, which causes the hands to cramp into abnormal positions and make uncoordinated movements.
The musicians underwent therapy in which parts of their hands were immobilised with a splint while they exercised. The magnetic currents in the patients’ brains were measured before therapy and after it had been under way for eight days.
Before the therapy the brains had an abnormal representation of the hand, according to the team led by Victor Candia of the University of Konstanz, Germany.
After treatment of the hand, manual dexterity was improved and the brain representation of the affected hand became more like that of the normal hand.
The study "demonstrates that in the case of motor disorders, but
also for other brain disorders — for example after brain injury —
highly specific therapeutic plans have to be developed," Candia
With due respect to Prof Yashpal, may I dare to add something to the article "What is the reason for magnetic energy and gravitation force" (May 1):
Einstein’s General Theory of Relativity explains the difference between accelerated and non-accelerated systems and the nature of the force acting in both.
If a person is there in deep space where there is no object around, then he is not subject to any gravitational pull.
Now if the craft were spinning in its track, he would be pressed against the walls of the craft and would consider that he had weight. No difference is there between this force created in the craft and the force of gravitational pull of earth.
An outside observer thinks that this force is due to his (A’s) tendency to continue in his previous state (his inertia).
Above considerations led Einstein to the principle of Equivalence which tells that inertial forces and gravitational forces are equivalent.
He also concluded that gravitation can be explained by the geometrical properties of space.
Einstein visualised a four-dimensional space-time continuum. Presence of mass in this continuum changes the geometry of this space i.e. makes it curved due to which there is gravitation. Similar geometrical properties may sometime explain the phenomena of electromagnetic force.