Ventilation as a dynamical problem : a paper read before the Annual Meeting of the Medical Officers of Schools Association, on February 6th, 1902 / by W.N. Shaw ; with the subsequent discussion.

  • Shaw, Napier, 1854-1945.
Date:
1902
Catalogue details

Licence: In copyright

Credit: Ventilation as a dynamical problem : a paper read before the Annual Meeting of the Medical Officers of Schools Association, on February 6th, 1902 / by W.N. Shaw ; with the subsequent discussion. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    for drawing attention to the analogy ; you will tind it of immense assistance in all j)ractical applications. 'riie analogy can he built u}) from the 6imi)le8t exainj>les. A simple electrical circuit consists of a battery, which has an electromotive force and resistance, external r€*sistance and connecting wires. A simple ventilation circuit (for a single room) consists of the moving ag^mt (e.^., a chimney and tire), which has aeromotive force and resistance, external resistance (the resistance (d inlets) and connecting spaces (the room and the external air). A second independent ventilation circuit (for a second room) can in like manner be resolved into a second aeromotive force, resistance and connecting si)aces, and be represented by a second electric circuit with its electromotive force, re- sistances and connecting wires. The two ventilation circuits are connected because one of the analogues of connecting wires—the external air—is common to both circuits. If the rooms are adjoining rooms with a door between them they have a st‘Cond connexion. The law of relation between ath-omotive force, flow and resistance, A = V-H, is dilferent from the electrical law (Ohm’s law), E = (’ H, in that the pneumatic flow (V) enters as a squared quantity, while the electric current (C) enters in the lirst power ; but otherwise the analogy can be followed to any of its conse(|uenccs. If we work out the analogy for a house of several floors, we get a very complicated and intricate problem; ath-omotive forces exist wherever there are tires, wherever there are open- ings ex})osed to wind, and wherever there are fans. There are also subsidiary aeromotive forces between rooms on dilferent floors, owing to dilferences of temperature between the inside and outside of the house. Resistances exist for all channels of entry, ventilation openings, window or door openings, chinks, “coM” open chimneys, c(c., and for all channels of exit. In an ordinary house the latter are generally limited to the chimneys that have fires in their grates, unless there are ()})enings on o])iK)site sides ami wind enough to make use of them ; but, just as, with a conq)licated electrical network, we can follow along with the current all round a complete circuit, and taken the sum of the products of current and resistance to be ecpial to the algebraic sum of ;ill the electro- motive forces in the circuit; so we can follow along the venti- lation circuit into the building by any ])racticable i)ath and out again, and takt* the sum of tin* })roducts of the resistance and tile S(juare of the flow in each ])art to l)e equal to the algebraic sum of the ai’-romotivt* forc(‘s; or, in other words, to the ('ffective “ head” for that circuit. 'J'he comj)lication thus indicated when a building of many