We have come a long way in the 63 years since we have gained independence. Yet, there are a number of challenges for us lying ahead which seek immediate attention. One of them being our dearth for alternative energy sources owing to the inefficiency of the current energy supply for the billion population.

India has an estimated power requirement between 800,000 MW and 950,000MW by 2030. To help India meet its gigantic future energy requirements, the Prime Minister has expressed the need to develop public private partnerships in ways and means to meet the estimated Rs.60, 000 billion ($1.2 trillion) investment required over next 25 years to provide electricity to consumers at affordable cost.

Solution: CAPP

The limited supplies, uneven distribution, and rising costs of fossil fuels, such as oil and gas, create a need to change to more sustainable energy sources in the foreseeable future. Pointing out that India is short of energy resources like oil, gas and uranium and even coal is not as abundant as is generally believed, there is a high focus on search for alternative sources and their efficient usage and supply. Hence over the coming decades one of India’s greatest challenge will be to secure diversified sources of energy and harnessing them as CAPP (Cheap and Portable Power).

The Ordinary

Conserve: We need to conserve the non-renewable resources such that they last longer, or get time to be replenished for future availability.

Sun, Wind, Water: There is a high focus for abundant renewable sources like solar, biomass, wind, hydro, and so forth. In a country like India with extreme summers, the potential for harnessing solar energy is great. If only the cost of the photovoltaic (PV) units get more lessened, solar power will become more widespread. Though not as abundant as the solar, the wind energy is also viable in India. Innovations are required such that these abundant sources are better utilized.

The Extraordinary

Sonoluminescence: A strange word, indeed, but can emerge to be very promising if only we could come by a way to use it out. This is the process of using ultrasonic sound (sono) to excite bubbles in a liquid such that they implode and produce small bursts

Long exposure image of multi-bubble sonoluminescence created by a high-intensity ultrasonic horn immersed in a beaker of liquidscuss the mechanism for Single-Bubble Sonoluminescence (SBSL), see the figure.

of light (luminescence).This fascinating process needs to be explored a bit in detail.

Sonoluminescence can occur when a sound wave of sufficient intensity induces a gaseous cavity within a liquid to collapse quickly. This cavity may take the form of a pre-existing bubble, or may be generated through a process known as cavitation. Sonoluminescence in the laboratory can be made to be stable, so that a single bubble will expand and collapse over and over again in a periodic fashion, emitting a burst of light each time it collapses. For this to occur, a standing acoustic wave is set up within a liquid, and the bubble will sit at a pressure anti-node of the standing wave. The frequencies of resonance depend on the shape and size of the container in which the bubble is contained.

The Mechanism

The mechanism of this phenomenon is still unsettled. Theories include: hotspot, bremsstrahlung radiation, collision-induced radiation and corona discharges, nonclassical light, proton tunnelling, electrodynamic jets and fractoluminescent jets (now largely discredited due to contrary experimental evidence).

•           During the tensile portion of the pressure variation, induced by the sound wave, the bubbles grow

•          Subsequent compression forces the bubbles to rapidly collapse and emit light.

An important factor is that the bubble contains mainly inert noble gas such as argon or xenon (air contains about 1% argon, and the amount dissolved in water is too great; for sonoluminescence to occur, the concentration must be reduced to 20–40% of its equilibrium value) and varying amounts of water vapour. Chemical reactions cause nitrogen and oxygen to be removed from the bubble after about one hundred expansion-collapse cycles.

During bubble collapse, the inertia of the surrounding water causes high pressure and high temperature, reaching around 10,000 Kelvin in the interior of the bubble, causing the ionization of a small fraction of the noble gas present. The centre of such a bubble may be even more astonishingly hot. This description is simplified from the original literature, which details various steps of differing duration from 15 microseconds (expansion) to 100 picoseconds (emission).

From Left to Right : apparition of bubble, slow expansion, quick and sudden contraction, emission of light

What makes the bubbles light up?

As for predictive models there are several models that predict many different aspects of sonoluminescence including bubble geometry, temperature distribution within the bubble, and the spectra of the light emitted from the bubble.

The concentration of energy is justified as below, the average acoustic energy given to an atom of the liquid is

where ρ is the density of the liquid and v is the velocity amplitude produced by the sound wave. If the wavelength of the sonoluminescence is 200 nm the energy of a photon is

which is about 12 orders of magnitude larger than the acoustic energy afforded an atom.

Sonoluminescence is poorly understood because the spatial extent of the event is on the order of a micron and the time scale is only a few nanoseconds. MBSL (multi-bubble sonoluminescence) makes this even more difficult because of the large number of randomly growing and collapsing bubbles.

The Conclusion

It might not sound like much, but the process used can theoretically solve the cold fusion problem. In a nutshell, if you pass high frequency sound wave (between 20 and 40 kHz) through a liquid that has air bubbles, the sound waves causes the bubbles to contract suddenly, and briefly produce temperatures hotter than the surface of the sun at the centre of the bubbles. That’s hot enough to start a ”fusion” reaction, and is contained in a relatively ”cold” surrounding.