Tag Archives: Thermodynamics

Rhapsody in Blue

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118-1841_IMGLast Saturday we went to a fantastic concert at the Liverpool Philharmonic Hall.  It featured the pianist Michel Camilo playing the UK premier of one of his own compositions, Piano Concert No. 2 ‘Tenerife’ and Gershwin’s Rhapsody in Blue with the Royal Liverpool Philharmonic Orchestra.  He was fabulous – there are a couple clips on YouTube of him playing Rhapsody in Blue so you can some idea of what we experienced on Saturday evening.  I cannot play the piano and so his virtuosity was all the more impressive to me.  The applause at the end was ecstatic and followed by an even more spectacular encore, Caribe.

As we applauded for what seemed like a couple of minutes, I was reminded of an example that I had worked through in class last term for my first year undergraduate course in Thermodynamics.  The worked example is attached and involves estimating the temperature rise in palms of your hands as a consequence of vigorously clapping during which kinetic energy is converted into internal energy in the flesh of your palms and causes the temperature rise, ignoring the energy converted into sound.  The emphasis was on estimating by creating a model using a set of identified assumptions and, once we had an answer, I discussed the influence of those assumptions and introduced the idea of sensitivity analysis – this is not included in the worked example attached.

For twenty enthusiastic claps we found a temperature rise of a quarter of a degree Celsius, which we would probably notice since the hairless skin on the palm at the base of thumb is sensitive to changes as small as a twentieth of a degree, according to Dr Lynette Jones of MIT [doi:10.4249/scholarpedia.7955].

Zen and entropy

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Picture1Last weekend I went to a performance of Handel’s Messiah in our local cathedral.  The atmosphere in the vast cathedral was wonderful and for part of the performance I was transformed into a zen-like state by the music.

However, there were quite of lot of disturbances during the performance including some that went beyond the usual coughing and sneezing.  It is interesting that a sneeze in the quiet environment of a cathedral or library causes a large disturbance while the same sneeze in a busy street goes unnoticed.  Of course, it is about the change in the noise level, and as a percentage, the added noise of a sneeze is much greater in the quiet library than the busy street.  Noise is a form of energy that becomes dispersed and dissipated as it propagates and so it is easy to equate it to heat which exhibits the same behaviour.  Heat transfers from hot to cold places while noise propagates from loud to quiet places, and neither does the reverse, which was Clausius’ observation that lead to the Second Law of Thermodynamics.  Clausius also defined change in entropy as the heat transfered divided by the temperature at which it occurs.  So the same heat transfer creates more entropy at low than at high temperatures, just as a sneeze causes more disorder/disruption in a quiet than a loud environment.  We can equate entropy to the level of disorder present in any system or environment.

And the second law of thermodynamics states that the entropy of an isolated system will always increase until it reaches a maximum at equilibrium.

Clean fossil fuel?

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The amount of energy stored in methane hydrate could be twice that of all other fossil fuel reserves based on data from the US Geological Survey, the New Scientist reported on 31st August, 2013 in an article entitled ‘Buried Treasure’.  At this point, most of you are probably wondering what methane hydrate is and where it is stored.  Microbes on the seabed eating organic matter produce methane molecules that at high pressure and low temperature combine with the water to form a hydrate, which is white crystal.  Large deposits of methane hydrate deposits are believed to lie along continental margins, mostly in ocean sediments.

Natural gas and shale gas (‘Fracking’ on August 28th, 2013) are also methane, which releases less carbon dioxide when it is burned than coal or gas and hence is regarded as cleaner.  However, methane hydrate deposits might have an additional advantage because some research has shown that the methane molecule trapped in the hydrate crystal can be replaced by a carbon dioxide one.  So we might be able to extract methane and simultaneously store carbon dioxide.  Sounds too good to be true and the second law of thermodynamics will ensure that there is a price to be paid somewhere and somehow (see post entitled ‘Sonic Screwdriver’ on April 17th, 2013 for more the 2nd law).

http://www.newscientist.com/article/mg21929320.800-frozen-fuel-the-giant-methane-bonanza.html

https://www.llnl.gov/str/Durham.html

http://www.jogmec.go.jp/english/oil/technology_015.html?recommend=1

On the beach

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beachMaybe you are lying on the beach reading this, or if not dreaming about lying on the beach.  We enjoy lying on the beach, or next to a swimming pool, in part because it involves doing nothing and in part because of the heat transfer.  Heat transfer is transfer of energy from a high to a lower temperature zone.  It can occur in four ways: conduction, free convection, forced convection and radiation; and all of them occur on the beach on a hot day.

Conduction occurs as a flow of kinetic energy from one molecule to the next by direct contact.  When you are lying on the beach it occurs between you and the surface that you are lying on.  When you first lie down on hot sand, then the energy flows from the hot sand to your cooler body by conduction.

Free or natural convection is heat transfer carried by a rising current of fluid due to buoyancy effects created by the hotter fluid being less dense.  This tends to happen above your warm body after you have been lying in the sun for a while.  It also happens above the hot sand and you can sometimes see a heat haze caused by the rising hot air that has a lower density and thus different refractive index compared to the surrounding air.

Forced convection also involves heat transfer by a moving current of fluid but in this case the flow is caused by an external source.  So if there is breeze across the beach then you will be cooled by forced convection as you lie on the beach.

Radiation consists of electromagnetic waves in the infrared spectrum travelling away from a source in all directions.  This is the heat from the sun that makes it so pleasant to lie on the beach on a sunny day.

Ok, shut your eyes and go back to sleep.  The heat transfer lesson is over – though some of you might want to think about whether that breeze is really forced convection since it is probably caused by natural convection on a climatic scale.