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Applying The ‘Catch All’ General Control Volume And The Reynolds Transport Equation To Improve Thermodynamics Instruction.

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In the instruction of Thermodynamics it is usual practice in most courses and textbooks to introduce applications of the First and Second Laws of Thermodynamics via closed systems. As students progress the introduction of open systems then follows. In the author’s experience this method often leads to a perceptual disconnect in the ‘flow’ of the material and can be a cause of considerable confusion among students. This paper describes a teaching approach whereupon a ‘catch all’ general control volume is introduced as the primary tool of the subject from day one of the course. The accumulation or reduction of a generic property within the control volume is shown to occur as a result of three possible processes; direct transfer across a boundary, direct transfer in conjunction with some ‘carrier’ flow, or finally from spontaneous generation or destruction within the control volume itself. The generalized Reynolds Transport Equation is then formulized from this scenario. First applications of the Reynolds Equation are then introduced. For the First Law of Thermodynamics the property of ‘energy’ must of course be considered. Heat, work and mass transfer across the boundary, as well as the possibility of work done by a moving boundary and internal sources of ‘energy generation’ must all be described and included within the derivation. The recognition that a closed system is a simplification of the more general control volume now makes the traditional requirement for such a distinction trivial. It is stressed throughout the course that the value of the Reynolds Transport Equation and the general control volume are their generality and aid to the visualization of fundamental physical processes. This rather than the mathematical rigor of their application is the primary focus of class instruction. Finally the paper gives some consideration to the conceptually more challenging property of entropy. By describing it as a measure of “energy degradation” it is then included as just another property in the Reynolds Transport Equation. Its subsequent passage through, and generation within, the control volume then also become rather uneventful academic challenges. Ultimately this approach to the teaching of Thermodynamics has been found very beneficial. Personal observations and student feedback reinforces the belief that a typical student would rather learn one, more complicated, generally applicable model than learn several simpler models which become more elaborate and have more ‘additions’ as problems become more complex.

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Foley, A. (2006, June), Applying The 'catch All' General Control Volume And The Reynolds Transport Equation To Improve Thermodynamics Instruction Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--492