Joule-Kelvin experiment

The Joule-Kelvin experiment has recently (1909) been repeated by J. P. Dalton, who finds, for the plug effect in air ... 

In an idealized Joule-Thomson experiment (also called the Joule-Kelvin experiment) a gas is confined by pistons in a cylinder that is divided into two parts by, a rigid porous membrane (see Fig. 7.3). The gas, starting at pressure P, and temperature 7, is expanded adiabatically and quasi-statically through the membrane to pressure P2 and temperature T2. The two pressures are kept constant during the experiment. If V1 is the initial volume of the number of moles of gas that pass through the membrane and V2 is the final volume of this quantity of gas, then the work done by the gas... 

For further cooling of a fluid, a common procedure is to use a continuous throttling process in which the fluid is forced to flow through a porous plug, valve, or other constriction that causes an abrupt drop in pressure. A slow continuous adiabatic throttling of a gas is called the Joule-Thomson experiment, or Joule-Kelvin experiment, after the two scientists who collaborated between 1852 and 1862 to design and analyze this procedure. ... 

Jochmann s equation, 164 Joule, 31 experiments with gases, 137 Kelvin effect, 164, 225 researches, 28, 51 theorem, 136... 

The temperatures T and T can be measured directly. When values of T" versus p" are plotted for a series of Joule-Thomson experiments having the same values of T and p and different values of p", the curve drawn through the points is a curve of constant enthalpy. The slope at any point on this curve is equal to the Joule-Thomson coefficient (or Joule-Kelvin coefficient) defined by... 

The method in use previous to Berthelot s depended on the results of the Porus Plug experiments of Joule and Kelvin. 

Lord Kelvin s close associate, the expert experimentalist J. P. Joule, set about to test the former s theoretical relationship and in 1859 published an extensive paper on the thermoelastic properties of various solids—metals, woods of different kinds, and, most prominent of all, natural rubber. In the half century between Gough and Joule not only was a suitable theoretical formula made available through establishment of the second law of thermodynamics, but as a result of the discovery of vulcanization (Goodyear, 1839) Joule had at his disposal a more perfectly elastic substance, vulcanized rubber, and most of his experiments were carried out on samples which had been vulcanized. He confirmed Gough s first two observations but contested the third. On stretching vulcanized rubber to twice its initial length. Joule ob-... 

It must be borne in mind, however, that the above definition of a perfect gas, though true as fai as it goes, is not a complete thermodynamical definition The complete definition will be given after we have considered the porous plug experiment of Joule and Thomson (afterwards Lord Kelvin)... 

The experiment conceived by Joule and Thomson (Kelvin) demonstrated that on adiabatic expansion, without performing additional work, the enthalpy of a gas (ideal or real) remains constant. From this it follows that the internal energy U of an ideal gas is independent of the volume and is, thus, determined by the temperature alone. 

The basic problem is that the thermal units and the mechanical units were different at this time. We do not use the old units, but restrict to the MKS system for the mechanical units and to calories and Kelvin for the thermal units. In the experiment, all the numerical values are known. Say a weight of 1 kg was used that fell down 1 m and 1 kg of water was used. An increase of temperature of 2.34 mK was observed. Note that in fact Joule used a much more heavy machinery, probably a very expensive device at this time. We insert now the numbers in the equation ... 

A typical experiment performed by Joule is described in Prob. 3.10 on page 99. His results for the mechanical equivalent of heat, based on 40 such experiments at average temperatures in the range 13 °C-16 °C and expressed as the work needed to increase the temperature of one gram of water by one kelvin, was 4.165J. This value is close to the modern value of 4.1855 J for the 15 °C calorie, the energy needed to raise the temperature... 

You can use the previous equation to obtain the entropy change for a phase change. Consider the melting of ice. The heat absorbed is the heat of fusion, AHfus, which is known from experiment to be 6.0 kJ for 1 mol of ice. You get the entropy change for melting by dividing by the absolute temperature of the phase transition, 273 K (0°C). Because entropy changes are usually expressed in joules per kelvin, you convert AT j to 6.0 X 10 J. 

Joule won the battle but the war was not over, by far. No other than the very sympathetic to Joule - as we have seen - Kelvin, in his 1849 paper on Account of Carnot s Theory of the Motive Power of Heat with Numerical Results derived from Regnault s Experiments on Steam still has very strong doubts. Cardwell writes ... 

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