It is shown that, by using dimensionless variables for representation of relationships among thermodynamic properties, the functional relations can be simplified and made more concise.  Consider, for example, states that can be reached one from the other by changing the volume and/or entropy – that is, states where u = u(s,v), and the classical equation du = T ds – p dv is applicable.  With appropriate definitions of dimensionless internal energy i , entropy σ, and volume γ: di = τ dσ – π dγ and i = i(σ,γ).  It will be claimed that this innovation will have vast relevance. 

One significant effect is that in the case of exergy, the dimensionless property relations become independent of the ‘dead state’ properties – such as T0, p0, μi0.  That is to say, for example, when i = i(σ,γ) then dimensionless exergy x satisfies dx = ϑ dσ – φ dγ  and x = x(σ,γ). 

This opens the door to employing exergy balances in lieu of energy balances in the mathematical modeling of processes.  Examples are presented in a companion paper, “An Assertive Statement of the 2nd Law of Thermodynamics – Updated”. 

An Assertive Statement of the 2nd Law of Thermodynamics - Updated

This presentation will summarize and update an approach to Thermodynamics that invokes a statement of the 2nd Law proposed at ECOS2017 and published in Reference 1.  The key point of that 2nd Law statement is this: Exergy is the ‘driving force’ that impels all processes – the ‘driving force’ of the kinetics.  In turn, using 3 examples that modeled processes – simple ones – Reference 1 presented evidence supporting the asserted statement.  The evidence consisted of (a) showing the consistency of results with traditional models and (b) that a single kinetic relation provided by the 2nd Law sufficed when more than one is required in the traditional models.  (Indeed, the examples support the common contention, held by many, that the traditional kinetic relations follow from the fact that exergy is annihilated by kinetic processes.)

Importantly, this paper goes a step further.  It will be shown herein, with two or more examples, that the processes can be modeled without invoking energy balances among the governing equations – i.e. without invoking the ‘The 1st Law of Thermodynamics’.  The key is the use of property relations for exergy, presented in the companion presentation entitled “Dimensionless Property Relations.”

(On the basis of teaching experience, the author contends that the approach to Thermodynamics presented in Reference 2 makes the subject more easily understood, less ‘mysterious’.  Having said that, it is suggested that Thermodynamics could be made significantly less ‘strange’ – more in accord with common sense – by debunking the conclusions that were drawn from Joule’s experiments.  And it could be hoped that the subject will become more fruitful, for humanity).

1 Energy 157 (2018) 503-515

2 Energy 35 (2010) 1047–1056