Whether Convergent Nozzles Can Help In Decreasing Power Consumption Of Compresso

Energy of the fluid = potential (eg pressure) + kinetic (like flow)

Please go through the basics of fluid flow- the available head - which defines the available energy.

You convert one form into another.

Any additional component in the hydraulic line is going to increase the losses and definitely a passive component can not generate (or inject) energy.

The nozzles (I have not seen the article but can guess) must be to concentrate the air flow (and thereby increase the energy density) at the Wind Turbine and that is not increasing energy- it is focusing it into the area (and thereby reducing it elsewhere- in the wake of the nozzle)

But since that is free energy (sorry about the name- it is not exactly FE in the sense of the PMM - but it is in the sense that that energy is not available to do the required work that we want to extract from it) we don't mid line losses increase in the nozzle as far as we can get a bit more.

That is like you forcus the sun rays onto heater but in turn create shade eleswhere.

UD15

Have you gone through the article that I have mentioned in my post? Prof Williams thinks just the opposite.

The motto behind the use of convergent nozzle is using the enthalpy of the gas/steam itself to compress it to higher pressure or create effect like higher pressure. Remember that the gas/steam already has sufficient enthalpy stored in it.

I would not put a whole lot of faith in the referenced literature...

Dr Alan Williams, a scientist and former Member of Parliament

Appears to be of the opinion that only the First Law of Thermodynamics is applicable in this particular case("The author asserts that all the changes involved are subject only to the first law of thermodynamics and could allow the conversion of solar energy into electricity with an overall efficiency of over 50%."), and seems to be of the opinion that the Second Law is not applicable. I also have the distinct impression that he may be of the opinion that there is either significantly more thermal energy available from the sun than actually exists, or that his machines have significantly less inertia than the illustrations would suggest.

A key warning phrase that should raise eyebrows is "No experimental work has been conducted.".

Proceed with caution, and do NOT invest heavily into this scheme. Perhaps Dr. Williams could encourage his former associates in Parliament to pony up the money necessary to develop his ideas further...

Just tell me, is there anything you found that can violate 2nd law of thermodynamics? If so, then kindly point it out.

The individual that finds anything that violates any of the Laws of Thermodynamics is mistaken. Despite that, many still persist with perpetual motion machines, over unity devices and the other codswallop that accompanies them. Some even have the audacity to ask for assistance in this forum!

Problem with many here is that they think that they can speak the last words of thermodynamics and though they can not prove, but just saying is enough. Those people just forgot the history of science that there are so many "impossibles" later proved possible, like flying machines heavier than air.

You're so right, pranabjyoti. Embittered cynics, whose default position is scorn, enforce a wrong orthodoxy even without understanding anything. "Oh, no, not another one of those ..." and maybe with some derision to add flavor to spite. Anyone, like you, who has the gumption to start a discussion deserves a sincere and thoughtful answer, and if he/she is mistaken, a kind explanation. I learn something good at CR4 just about every day.

Thank you Wilmot. What I want is a proper answer to my question with proper explanation. If you think some machine is violating 1st law of thermodynamics then ask for the source of energy and do the energy balance, if that's negative then it's a perpetual motion of 1st kind. If you doubt that any machine violate 2nd law of thermodynamics, calculate entropy and show that entropy of universe decrease at the end of the process. But without that just foul crying like it violates laws of thermodynamics is too much irritating. I think such people should be banned form posting so that others time and energy can be saved. If you don't have sufficient logic and theory and fact in favor to place, don't take part in any scientific discussion. That means waste of time to you and others.

I remember in long back thermodynamics text book there was an PMM (to discuss about PMMs) - that was about the warm water of the sea and cold water on surface and how it can be used to drive a turbine.

The article looks surprisingly similar to it (Instead of the water it is air as medium)

The steam turbine efficiency claimed is around 82% but is it?

As I remember carnot cycle efficiency (which is the ideal) reaches about 75% or so. The author must be assuming the isentropic efficiency to be the actual efficiency?

Of course here the exact thermodynamic steam cycle can not be used. It is brayton cycle (of Gas Turbine) than the carnot cycle.

Transmission of the solar energy through glass is another exaggarated assumption (Did the author assumed the visible spectrum or the infrared spectrum?)

As per the literatures the maximum insolation is about 1KW/sq meter maximum and 250 KW/sq meter average (ie on no cloudy summer days) and out of this the lion's part is the visible spectrum, which of course is not being used by the device.

Foot note summarises

This paper gives a qualitative and descriptive indication of principles by which it may be possible to convert solar energy into electricity with good efficiency using sealed ground level structures. The author has limitations in background expertise and needs people to develop the theoretical framework

BTW: There has been work on in this field for example in this paper http://www.cognizance.org.in/main/pages/technovision/Dr_Garud_Teri.pdf

But except the parabolic collectors using the normal (but low temperature) steam turbines none look efficient enough to be cost effective

Well, use of temperature gradient to generate electricity is well researched and at least scientifically (not commercially) successful.

You are also mixing turbine efficiency with Carnot's efficiency. Turbine efficiency means what % of Carnot's efficiency can be achieved by the Turbine and that actually means the output = Carnot's efficiencyX82%. And I also want to tell you that I am not interested in other features of the paper but rather use of convergent nozzle shaped structures for increasing output with a smaller turbine. As per the author, the convergent nozzle shaped structure will convert the enthalpy of hot gas into motion and that means more output from the turbine. Actually this thought is the backbone of this whole project and have you find any flaw in it from the viewpoint of thermodynamics?

Sorry, but it was not I who was mixing up (The isentropic Efficiency of 82%) but the author of the paper referred in the link.

The convergent nozzle as I mentioned in my earlier link (at least just a bit of it) is already in use as I mentioned in my earlier post to convert the energy of hot gas into kinetic Energy (Gas Turbines - do it where the combustion chamber section narrows a bit into the transition pieces before it hits the buckets (ie the turbine blades)

Any of the impulse turbines will use this principle includying Hydro (Impulse type-eg pelton wheels).

As I mentioned earlier also - it is the changing of head (pressure into flow)- keep it as a pressure head and you would be running a reaction turbine and in velocity head an impulse. Both can be housed in the same size housing (or almost)

Many years ago (the early 1980's) I worked on a design analysis for an Ocean Thermal Energy Conversion (OTEC) system, which utilizes the naturally-occurring temperature difference between deep sea water and surface seawater- this sounds like what you are describing. There have been a number of demonstration units of this technology over the years (I believe one based on the research in which I was involved was actually built and operated off Hawaii several years ago), and the US Navy is still pursuing research in this area.

However, several things llimit the commercial viability of this technology, the first being that the temperature difference is pretty small (even at "ideal sites"), which pretty much limits how much energy you can get for a given installation- and which basically says that, in order to be commercially viable, such installations must be huge (i.e., expensive). A second limitation I remember is that the "ideal" sites (deep, deep water near a population center) are very few and far between- if you don't have a market close to where you are generating the electricity, your costs will escalate exponentially.

By the way, one of the potential byproducts of certain styles of OTEC systems is potable water...

I have my own thoughts in this regard, specially for open-cycle OTEC. What will happen if a heat pump is added to increase the temperature difference? In open-cycle OTEC, water is evaporated i.e. the latent heat of vaporization of water is collected from warm seawater. Now, if we introduce a heat pump to heat up the vapor coming from Evaporator, the temperature difference between the Boiler and the Condenser will increase and that will convert a larger share of the latent heat of vaporization in addition to the heat added to vapor by the heat pump into electricity and that means increased output. Now, the question arises how to increase the vapor pressure of the steam coming from the Evaporator. Whether simple heating up is enough or some extra measures like putting a convergent nozzle is necessary to increase the vapor pressure in the turbine.

Actually, what kills the commercial potential for the OTEC process is the fact that one must have some pretty extensive (and expensive) piping infrastructure to bring the water from two different depths together. Adding additional equipment like a heat pump of sufficient magnitude to have any effect at all increases the cost of the equipment and reduces the net energy output.

The Wikipedia page for OTEC gives some pretty good updated information on the current state of the art for this technology, and discusses some of the engineering limitations- limitations that are not going to go away no matter how much wishful thinking we chose to employ...

How can net energy output will decrease while the efficiency will increase?

Actually we are probably missing a fact that "pressure" is a force, not energy and there is no such law as "conservation of pressure". Convergent nozzles can be used to increase pressure of low pressure (but high enthalpy) gas/steam like hydrolics and that doesn't violate any law of thermodynamics. And thus can be helpful in injecting low pressure gas/steam in higher pressure vessels/Boilers.

The author says: "if the diameter of the solar collector is about 5-10 times the diameter of the throat of the nozzle, then it is possible to convert ALL the enthalpy above ambient of the rising warm air into kinetic energy in the throat of the nozzle." I don't understand.

I also wonder about the heat rejection (the "energy sink" box in Fig. 2) being sufficient to sustain mass flow through the turbine. The author seems to be of the opinion that heat rejection is optional.

It's not enough to collect solar energy and then channel the convective mass flow of air through a convergent nozzle within a sealed container and through a turbine; you must also have sufficient heat rejection, to dump the accumulated solar energy into the environment. Without heat rejection I don't see how to sustain the mass flow through the turbine.

Heat flux (watts per square centimeter of surface) through the container end and into ambient air, without any forcing by blowers, will be small. So you will need a lot of surface area. And since this apparatus is outside, in the sunshine, that large surface for heat rejection will be heated by the sun and there might not be any heat rejection at all.

You may be interested in this patent application for a Vapor Vortex Heat Sink, a hermetically sealed container for collecting the waste heat from computer chips or other low temperature sources by forced convection boiling to drive an organic Rankine cycle for power generation. We just got notice of allowance so this will be issuing as a U.S. patent.

Did any of the respondant thought about whether convergent nozzle can be used to increase the pressure ?

In an incompressible fluid definitely not - maintaining the flow constant, the convergent nozzle will increase the velocity(here the OP is right) but that will reduce the pressure (Bernoulli)

Even in compressible fluid this effect will be predominant.

The compressor (or any pump for that matter) will generate a total head and that head is the energy of the output. Whether it is in form of potential head (pressure) or kinetic head (flow)

Assuming the compressor outlet head is required (and hence constant), it's power consumption can be reduced by

- Increasing the suction head (so that it has to generate less head)

- By reducing the losses (that are not getting transferred to the medium and increasing it's energy content)

No passive device (including convergent mozzle) can increase the suction head, it can only reduce through losses.

- Nozzles can of course reduce the losses by

a) Directing the flow to the most preferred direction (or optimum direction) as is done in inlet guide vanes

b) Converting the head to velocity head / pressure head/ mixed head depending upon the type of compressor.

Just google with convergent nozzle and you will see that "nozzles can help to convert enthalpy of fluids" into velocity. Even you can see that in wikipedia too. And as per physics, velocity is motion. Therefore, kindly explain me in more detail that whether that can help to increase the pressure in the particular direction at the expense of enthalpy of the fluid, to be more specific hot gas having sufficient enthalpy embedded in it.

Velocity and pressure are not synonym - in hydraulic sense

Pressure is static - It is the potential head

velocity is dynamic - it is the kinetic head.

At the molecular level, pressure is nothing but expression of random motion of particles of gas when the gas is static. But what nozzles do is to increase the velocity of the gas (its molecules too) along a specific direction and thus increasing the pressure along the direction.

Turbines/ any real life equipment of a reasonable size do not run on quantum mechanics. The statistical agglomeration of the individual molecular activities is what makes a matter behave the way they do.

Look at ths link to undestand the pressure distribution

http://www.engapplets.vt.edu/fluids/CDnozzle/cdinfo.html

• When the flow accelerates (sub or supersonically) the pressure drops
• The pressure rises instantaneously across a shock
• The pressure throughout the jet is always the same as the ambient (i.e. the back pressure) unless the jet is supersonic and there are shocks or expansion waves in the jet to produce pressure differences.
• The pressure falls across an expansion wave.

BTW this discussion is not going anywhere and as far as engineers are concerned pressure and velocity are entirely different features. Convertible yes but same no.

What I have said is related to classical mechanics, not quantum. Quantum mechanics deals with sub-atomic particles.

Wiki

In physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces. The study of the motion of bodies is an ancient one, making classical mechanics one of the oldest and largest subjects in science, engineering and technology.

Classical mechanics describes the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies. Besides this, many specializations within the subject deal with gases, liquids, solids, and other specific sub-topics. Classical mechanics provides extremely accurate results as long as the domain of study is restricted to large objects and the speeds involved do not approach the speed of light. When the objects being dealt with become sufficiently small, it becomes necessary to introduce the other major sub-field of mechanics, quantum mechanics, which reconciles the macroscopic laws of physics with the atomic nature of matter and handles the wave-particle duality of atoms and molecules. In the case of high velocity objects approaching the speed of light, classical mechanics is enhanced by special relativity. General relativity unifies special relativity with the Newton's law of universal gravitation, allowing physicists to handle gravitation at a deeper level.

Of course there is another Statistical Mechanics dealing with the molecular level statistically.

I differ with this wiki definition, because James Clerk Maxwell and others, who formulated equations and formulas related to molecular movement of gas molecules were considered to be classical physicists. Quantum mechanics started with scientists like Max Planck, Niels Bohr, Einstein and t he laws of molecular motion is well established then and Maxwell was dead. Maxwell did his scientific work in the later part of 19th century.