Category Archives: Soapbox

Something for nothing?

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Let’s try a thought experiment, following on from my previous post (Beyond Zero on 20th February, 2013).  Imagine two equal amounts of matter, A and B at -350 Kelvin and 350 Kelvin respectively.  We would expect heat to flow from the hot one, that’s B to A, the cold one.  This would cause the internal energy of B to decrease with a corresponding rise in the internal energy of A so that B gets colder while A gets hotter, i.e. they both move closer to absolute zero with corresponding decreases in entropy.  The Second Law of Thermodynamics does not allow this to happen and in fact the reverse would occur, i.e. heat would flow from the cold one A to B, lowering the temperature of A and raising the temperature of B so that they both move away from absolute zero with corresponding increases in entropy.coldgraph2

IF we could actually make this happen then we would able to design engines with efficiencies higher that 100%.  One corollary of the Second Law of Thermodynamics is that heat cannot be converted into work without some of the heat being wasted or lost as entropy.  In a power station, heat is taken from a hot source (e.g. a nuclear reactor, solar concentrator or gas furnace) and some of it converted into shaft work, which turns a generator to produce electricity, while the remainder is dumped into a cold sink usually the environment via cooling towers.  However, if our cold sink was at a negative temperature on the Kelvin scale then we could take heat from the cold sink and the hot source at the same time!  Why aren’t we doing this?  Well, we don’t have any naturally occurring cold sinks at below zero Kelvin and to create one uses more energy than we would gain in our super-efficient power station – that’s the Second Law kicking in again.  So you can’t have something for nothing.

Lincoln on equality

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I watched Steven Spielberg’s movie ‘Lincoln’ recently.  Lincoln is portrayed as quoting Euclid on equality: ‘Things that are equal to the same things are equal to each other’.  This is from Euclid’s book ‘Elements’ which was in common use until modern times as a mathematics textbook and is believed to have sold more copies than any other book besides the Bible.  In the movie Lincoln extends the meaning of this first of Euclid’s ten axioms from mathematics to embrace the equality of men.  Since I am teaching thermodynamics at the moment, I was struck by its similarity to the zeroth law of thermodynamics, which states that ‘two systems in thermal equilibrium with a third system  are also in thermal equilibrium with each other’.  The concept of the zeroth law is sometimes accredited to Rankine who lived in the middle of the 19th century, or more than two thousand years after Euclid (380BC – 260BC).  It is reputed to be called the zeroth law because it was only recognised as being of fundamental importance to thermodynamics after the first and second laws were well-established and to rename them would have caused confusion.  The zeroth law allows temperature and temperature scales to be defined.  It seems to me to be a special case of Euclid’s first axiom ‘Things that are equal to the same things are equal to each other’, and that it is remarkable that it took the fathers of thermodynamics so long to recognise it, especially when they were probably brought up on Euclid’s ‘Elements’ as their mathematics textbook at school.

Food waste

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korea cafeteriaIt has been reported recently that there are more people suffering from obesity in the world than from malnutrition (http://www.ifrc.org/en/publications-and-reports/world-disasters-report/wdr2011/).  This might suggest that global society has a major distribution problem to solve and that current approaches are failing.  This is a tentative conclusion supported by another recent report which estimates that half of global food production is wasted (http://www.imeche.org/knowledge/themes/environment/global-food).  Some agricultural production never reaches the distribution system and rots in the fields, while some is disposed of untouched by end-purchasers.  Presumably end-purchasers throwing away uneaten food are not starving and probably a high proportion of them are obese.

The second law of thermodynamics demands that there must be waste in all processes, so we can never reduce the wasted food production to zero but 50% wastage seems high and perhaps implies we some way to go before population growth is limited by food production (see post on ‘Two Earths’ in August 13th, 2012 or ‘Population crunch’ on September 15th, 2012).  Of course, if the majority of current food production is unsustainable then we are in trouble already.

Unavoidable junk

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167-6734_IMGThe laws of thermodynamics are physical laws whose relevance extend beyond the study of engines and heat plants.  We can restate the first law of thermodynamics (conservation of energy) as ‘the quantity of matter is constant and finite’.  Matter changes both in nature and as it moves through the economic system; and as it does so, its intrinsic properties change rendering it less useful and usable, thus requiring more and more resources to make it useful again.  This last sentence is a form of the second law of thermodynamics.  Very useful (low entropy) goods, such as iron ore and fossil fuels, eventually produce less useful (high entropy) matter, such as piles of junk cars in scrap-metal yards and greenhouse gases, as they move through the economic system.  In our current western life-style, we are all contributing to the generation of vast piles of junk; we are hooked on it; we are all ‘junkies’.

In the paragraph above, I have plagiarised the 2009 report entitled ‘The New Sustainable Frontier’ mentioned in the previous posting on this blog [http://www.gsa.gov/graphics/ogp/2009_New_Sustainable_Frontier_Complete_Guide.pdf ].  However, similar ideas were expressed by Handscombe and Patterson in their 2004 book entitled the ‘Entropy Vector’ [http://www.worldscientific.com/worldscibooks/10.1142/5365 ].  They paraphrased the first and second laws of thermodynamics as ‘you can’t have something nothing’ and ‘you can’t have it just anyway you like it’.