Müller I. A history of thermodynamics. The doctrine of energy and entropy (Müller I. A history of thermodynamics. The doctrine of energy and entropy.pdf), страница 13

Asimov: “Biographies …” loc. cit. p. 614.Except in those unfortunate countries with a virulent green, or environmentalist party,which, more often than not, is also anti-nuclear.84 Actually, the difficulty is not so much to reach the high temperatures, but it is difficult tocontain the hot gas. All conventional container walls would melt and, in fact vaporize.83462 EnergyAlthough extremely unlikely, this is conceivable in a general way.85 In theevent, however, it turned out to be an error, or a fake.

Anyway, the coldfusion-experiment could not be repeated. Actually, however, before thebubble burst, several laboratories worldwide jumped on the bandwagon andreported having seen cold fusion as well. Among ordinary non-nuclearphysicists there was some furtive malicious gloating over the simplicity ofthe process, because for years they had seen the funding of their ownprojects refused, while a near infinite amount of money was poured intoineffective fusion research, – hot fusion naturally. Their world turned greyagain after the truth emerged. But controlled fusion seems still a long wayoff.85It is true that chemical reactions can sometimes be catalysed by contact with a metal, butthe energy barriers to be overcome in such cases are much, much smaller than the nuclearones.3 EntropyIt may seem strange that the entropy – which is one of the most subtleconcepts of theoretical physics, or natural philosophy – first emerged in thecontext of an engineering proposition.

Namely the question of how toimprove the efficiency of heat engines. We shall see how that came about.Actually the entropy has never shed its hybrid position between physicsand engineering: The students of mechanical engineering keep a(temperature-entropy)-diagram among their files, which they are taught touse for the lay-out of power plants and jet nozzles. The chemical engineersare familiar with the entropy of mixing which they use to construct phasediagrams, and all physicists know that nature strikes a compromise betweenentropy and energy when it drives the sap into the tree-tops by osmosis.Heat EnginesIt was Denis Papin (1647–1712) – a student of Christaan Huygens (1629–1695) – who first condensed water and lifted a weight by doing so.1 Papinowned a long brass tube of diameter 5cm.

Some water at the bottom wasevaporated, and thus lifted a piston, which was then fixed by a bolt. Afterwards the tube was taken from the fire, the vapor condensed and a Torricellivacuum formed inside, i.e. a low pressure equal to the vapor pressureappropriate to the extant temperature. When the bolt was removed, the airpressure drove the piston downward and was thus able to lift a weight ofsixty pounds. This in a nutshell is the manner in which the motive power ofsteam works: by creating a vacuum through condensation.Denis Papin knew the properties of saturated vapor well, so that he also knew thatwater under pressures beyond 1atm boils at a higher temperature than 100°C. Hemade use of this phenomenon in a pressure cooker: In a closed vessel some toughmeat is heated in water. The accumulating steam raises the pressure and thus theboiling point of water, so that the meat finds itself immersed in water as hot as150°C (say).

Thus it becomes sufficiently cooked in a short time. Papin was invited1We shall not enter into speculations about whether and how Hero of Alexandria – in thefirst century A.D. – employed steam power in the automatic working of doors and statues,which priests used to impose on gullible worshippers, cf. I. Asimov: ‘‘Biographies…”loc.cit. p. 38.483 Entropyto demonstrate his digester for the Royal Society of London and he cooked animpressive meal for King Charles II.2However, Papin’s brass tube was not a steam engine yet; it did only onestroke at a time.

Proper steam engines were developed later when a pressingneed arose in England in the early 18th century. England was suffering akind of energy crisis: The country was deforested and what trees remainedwere needed for the navy and could not be used for fuel.3 At the same timethe output from the coal mines was in decline, and threatened to ceasealtogether, because of difficulties with drainage at the depth where the pitshad arrived. That situation provided a strong incentive for inventors, and sothe steam engine came just in time.

It was developed by the engineerThomas Savery (1650–1715) and by Thomas Newcomen (1663–1729), aclever and skilful blacksmith. The machine was at first exclusively used topump water from mines, so that coal could be brought up from a greaterdepth, previously inaccessible. Therefore it may not have mattered so much,that a good part of the coal was used to heat the boiler of the engine. IndeedNewcomen’s engine was quite wasteful of fuel.4In due time, however, the steam engine was employed by the ironindustry to power bellows, and hammers for crushing the ore.

Thus coalbecame a commodity to be paid for by the owners of the iron works, andtherefore the efficiency of the engine had to be improved.The Newcomen machine worked by injection of cold water into thecylinder, cf. Fig. 3.1. Thus the steam was condensed and a good vacuumwas developed, which pulled down the piston in a powerful stroke.Afterwards new steam from the boiler pushed the piston back up, beforewater was injected again, etc.James Watt (1736–1819) recognized the reason for the wastefulness ofthe process: A good part of the precious new hot steam condensed whilereheating cylinder and piston, which had just been cooled by the injectedwater. Watt improved the machine by inventing a separate cooler, orcondenser, into which the steam was pushed before condensation.

Thecondensed water was then pumped back into the boiler. Watt also introduced other improvements, likex keeping the cylinder wall warm by heating it with the incoming steam,x introducing an ingenious system of valves so that the piston could workin both the down-stroke and the up-stroke,2According to I. Asimov: ‘‘Biographies…” loc.cit. p. 204.According to I. Asimov: ibidem p.

145.4 Yet the machines were successful. By 1775 sixty of them had been erected in Cornwallalone and there were about one hundred in the Tyne basin. According to R.J. Law: ‘‘TheSteam Engine”. A Science Museum booklet. Her Majesty’s Stationary Office, London(1965) p. 10.3Heat Engines49Fig. 3.1. The Newcomen enginex closing the steam valve before the end of the stroke; it is true thatthis provided less work per cycle, but it was an efficient measurenevertheless, because still less steam was consumed.Above all, however, Watt has made the steam engine into more than apump.

He converted the up- and down-movement of the piston into therotation of a wheel in his famous rotative engine with a sun-and-planettransmission gear. This extended the efficacy of the engine greatly, becauseit could now be used to drive lathes, drills, spinning wheels and looms, –then ships and locomotives. Thus Watt’s machine became the motor of theindustrial revolution.James Watt was born in Glasgow. He received an abbreviated educationas an instrument maker in London, whereupon he became a laboratoryassistant at the University of Glasgow.

He repaired and improved a modelof the Newcomen machine which had broken down, and was thus able toattract the attention of Joseph Black, the discoverer of the latent heat, seeabove. Black became Watt’s first mentor and financier, and he introducedhim to an industrialist, Dr. John Roebuck, with whom Watt went into a1 223 , 3 partnership, – one third for Watt. Later the 3 share was taken over byMatthew Boulton, and the two partners started a successful business sellingsteam engines. Law writes 5 … the customer paid for all the materials andfound the labour for erection. The firm sent drawings and an erector. Theyalso supplied important parts like the valves and the valve gear… As5R.J.