Some Physics Demonstrations

Abstract

A theory relating to the viscous,flow of stable suspensoid sols, and briefly outlined in earlier papers is extended in the present work.It suggests (i) that concentration patterns are developed within suspensoid sols as a result of shearing, (ii) that these patterns arise through the operation of 'least action forces'. (The existence of such forces is required in order that the principle of least action shall be applicable to those changes in the configuration of the system of particles comprising the disperse phase of the sol which accompany shearing), (iii) that the velocity distribution pattern within such a sol is related in any given case to the concentration pattern, (iv) that the anomalous properties of suspensoid sols under shear arise in consequence of the development of these patterns, and (v) that changes in these properties are due to changes in the parameters dejning these patterns, and these, in turn lead to variations in the magnitudes of the least action forces with changes in the shearing conditions. It leads, in the case of flow through capillary tubes to the following conclusions:(1) Shear dependence of viscosity is a universal characteristic of such sols. (2) The overall mean sol concentration within a tube during.flow is always less than the concentration in the reservoir from which it is supplied.(3) The mean concentration over any cross section diminishes systematically along a tube from a maximum value equal to the reservoir concentration (near to the entrance) to a minimum value at points nearer to the exit. (4) The overall mean sol concentration varies with flow rate from a maximum value (equal to the reservoir concentration) at zero rate of flow to a minimum value (alwaysgreater than one half of the reservoir concentration) at the highest rate,for non-turbulent Pow. (5) The velocity profile, as defined by the ratio of mean to maximum streaming velocity, is also shear dependent, the ratio varying systematically between limits of one harf and one. (6) The ratios of mean to maximum velocity and of mean tube concentration to reservoir concentration are equal to one another .for sols showing no appreciable Brownian movement and flowing in very long tubes. (7) These velocity and concentration ratios can under the conditions mentioned in (6), be expressed as a simple function of the relative viscosity of the sol. (8) The axial sol concentration increases systematically along the tube from a minimum value (equal to the reservoir concentration), near the tube entrance, to a maximum value which may be many times as great at points nearer to the exit. (This hyperconcentration will under appropriate conditions lead to the formation of a thrombus.)Experiments designed for the investigation of the conclusions numbered (1)) (2), (4), (5) and (7) are also described. The results yielded by these experiments support the conclusions mentioned.