By Grossi M.

Similar physics books

Additional resources for Asymptotic behaviour of the Kazdan-Warner solution in the annulus

Example text

In addition, convection causes the rate of evaporation in a still medium, which is essential for these experiments and must he known accurately, to be determined in a different apparatus, namely a vessel with absorbing walls. e. with wind constant close to unity. In this case it is therefore best to use the method of free drops. Strictly speaking the experiments with Millikan's condenser described in § 10 refer to drops moving freely with respect to the medium but with such small radii (~ 1-2μ) and correspondingly small Re (of the order of 10~5-10"4) that the effect of movement on the rate of evaporation is vanishingly small.

E. approximating to the real value, were, as expected, lower than those shown "by the thermocouple to (exp. ). The relative error is paricularly great in the case of water. ) « 3-9° h = 0·4°; at 20<>, 11·Ie QUASISTATIONARY PROCESSES OF MOTIONLESS DROPLETS 27 and 7-4°; at 40°,24·Θ and 16·6? Using the theory on p. 16 we can calculate the ratios of external to internal temperature change to he 1·75, 2·4 and 1·85 respectively. This wide variation is prohahly due to the lack of geometrical similarity "between the experiments, which were also carried out at different temperatures.

1-10) for which there is still no theory of e vaporation. All the above applies equally well to the heat transfer from a spherical body in a stream, for which Nu = 2(1 + ßRe^Pr1'·). (il. 25) The term f in brackets in eg. 25) denotes the increase in rate of evaporation or heat transfer due to the relative movement of the medium and is usually called the wind constant. ♦Note, however, that a second approximation leading to eg. 20) gives c = — . when φ « 0 and p = oo # QUASISTATIONARY PROCESSES OP MOVING DROPLETS 45 For the fall in temperature of an evaporating drop we have instead of eq.