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The present paper and part 2 (adjacent) study the sound field produced by a convected point quadrupole embedded in and moving along the axis of a round plug-flow jet. Only subsonic eddy convection velocities are considered. We examine cold jets here and hot jets in part 2. A principal feature of the study is extensive comparison with jet-noise data. It appears that this simple model problem succeeds in explaining all the major interesting features of jet-noise data, on both hot and cold jets, for jet exit velocities in the low supersonic range. Particular success is achieved in explaining aspects of the data not explainable by the Lighthill acoustic-analogy approach. The picture of jet-noise generation that emerges (at least for jet velocities in the low supersonic regime) is in many respects a striking reaffirmation of the Lighthill point of view. It appears that there is an intrinsic or universal distribution of compact quadrupoles, whose strength and frequency distribution scale with the jet velocity and nozzle diameter as would be expected from simple dimensional reasoning, responsible for jet-noise generation. These quadrupoles are of course convected by the mean flow and satisfactory agreement with the data is obtained by assuming that they are devoid of any intrinsic directionality. There appears to be no significant jet Mach number (compressibility) or jet temperature effect on the scaling of this intrinsic distribution. The essential improvement over the Lighthill analysis is the incorporation of mean-flow shrouding effects on the radiation of the convected quadrupoles. It is perhaps no exaggeration to claim that, with the incorporation of such a shrouding effect, the problem of scaling jet noise with regard to the jet velocity, jet temperature, jet size and the angle from the jet axis appears to be completely resolved. (The ‘scaling’ principle cannot of course be very simply expressed and in fact needs calculations of the sort contained in the present paper to implement it.)

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The effect of standing waves of controlled amplitude and frequency on the steady state rate of mass transfer through thin horizontal liquid layers is studied experimentally. The variables studied are the film thickness, the amplitude and frequency of the waves, and the spacing between the probes generating the waves. A bulk motion of complicated pattern known as drift is caused by the finite amplitude of the waves. The rate of mass transfer in the absence of imposed vibration is two to three times greater than that expected by molecular diffusion alone. Vibration increases the rate up to an order of magnitude or more, depending on the hydrodynamic conditions. The data at low frequencies are correlated by an expression of the form (i-io)/idiff = KAf3hhYzL-Yz.It is well known that liquid phase mass transfer rates in gas-liquid contacting may be significantly increased when waves appear on the interface. The increase is often very much more than can be accounted for by the increase in surface area alone. The increase in rate is to be sought, rather, in the interaction of the velocity and concentration fields, for if the instantaneous flux of a species in a fluctuating velocity and concentration field is given by . l = -DVc + uc, then the averaged flux is given by r= -DVc + uc + ?c/ If the fluctuating velocity and fluctuating concentration have a component in phase the averaged flux will be increased by the convective terms even if the mean velocity is zero. Due to the smallness of the molecular diff usivity in liquids, the convectiveeddy flux may be quite important in determining the overall transfer rate. A rigorous theory for the increase in mass transfer rate should be based on the convective diffusion equation using the velocity field set up by the waves, but due to the mathematical complexities of this problem and in computing the velocity field itself no adequate solution to the differential equation has been given yet. Instead, mass transfer across gas-liquid interfaces has been treated by idealized models such as surface renewals or eddy diffusion.It would seem that experimental data on mass transfer rates in liquid films with waves of controlled amplitude and frequency would aid in the development of a more rigorous theory and in the evaluation of the various models. The only work known to the authors, however, where mass transfer was studied under the influence of waves of controlled frequency is that of Muenz and Marchello ( 8 ) , who examined the unsteady state absorption of several gases into a horizontal layer of water on whose surface traveling waves of controlled frequency were generated. In their experiments reported so far, they made no attempt to vary the amplitude of the waves -_ -or the depth of the liquid layer. They expressed their experimental results in terms of an effective diffusivity which they found to vary as the 7/6 power of the molecular diffusivity and the 1/3 power of the frequency. Two closely related problems are mass transfer into agitated pools (2, 5 ) and to falling liquid film...