Multicomponent nucleation and droplet growth in natural gas

The first quantitative experimental results are presented on homogeneous nucleation and droplet growth in a multicomponent gas-vapor mixture. Using the pulse-expansion wave tube technique, we investigated the condensation behavior of natural gas consisting of over 30 components. Data were obtained in the pressure range between 6 and 24 bar and at temperatures ranging from 221 to 237 K. The observed droplet growth rates are quantitatively explained using a multicomponent model for diffusion controlled growth. The nucleation rate data are for the moment mainly presented as a challenge to theoreticians, although some qualitative arguments are presented that could be helpful in the interpretation. The data appear to agree at least qualitatively with theoretical values (according to the revised binary classical nucleation theory) for a mixture of n-octane and methane, a model mixture which also shows the same macroscopic phase behavior as natural gas. ©1998 American Institute of Physics

Unsteady entrance flow in a 90 degrees curved tube

A numerical model enabling the prediction of the axial and secondary velocity fields in three-dimensional configurations at moderate Reynolds numbers and Womersley parameters is presented. Steady and unsteady entrance flows in a 90° curve tube (d = [fraction one-sixth]) under various flow conditions are analysed. The good quality agreement between axial and secondary velocities for a sinusoidally varying flow rate at a Womersley parameter of a = 7.8, obtained from a finite-element calculation, and those obtained from laser-Doppler measurements justify the use of the numerical model. Halfway into the deceleration phase for a sinusoidally varying flow rate (200 <Re <800, a = 7.8) a strong resemblance is found to the steady flow case (Re = 700). In contrast with steady flow, near the inner wall reversed axial flow regions are found halfway into and at the end of the deceleration phase. Throughout the flow cycle the Dean-type secondary flow field highly influences axial flow resulting in a shift of the maximal axial velocity towards the outer wall, C-shaped axial isovelocity lines and an axial velocity plateau near the inner wall. Further downstream in the curved tube the Dean-type secondary vortex near the plane of symmetry is deflected towards the sidewall (’tail’–formation), as is also found for steady flow. An increase of the Womersley parameter (a = 24.7) results in a constant secondary flow field which is probably mainly determined by the steady component of the flow rate. A study on the flow phenomena occurring for a physiologically varying flow rate suggests that the diastolic phase is only of minor importance for the flow phenomena occurring in the systolic phase. Elimination of the steady flow component (- 300 <Re <300) results in a pure Dean-type secondary flow field (no ‘tail’-formation) for a = 7.8 and in a Lyne-type secondary flow field for a = 24.7. The magnitude of the secondary velocities for a = 24.7 are of O(10-2) as compared to the secondary velocities for a = 7.8

Learning outcomes of a group behavioral modification program to prevent urinary incontinence

This study describes acquisition of knowledge and motor skill in bladder training (BT) and pelvic floor muscle training (PFMT) and adherence following a behavioral modification program (BMP). Essentially continent (0–5 episodes in past year) community-dwelling older women ( n =359) were randomized to treatment ( n =164), a 2-h group education session supplemented by one brief individualized session of approximately 10 min, or control ( n =195), no instruction, and followed for 12 months. Knowledge, motor skill, and adherence to the BMP were documented. Changes in pelvic muscle function and voiding interval were used to validate self-reported adherence. Following group instruction, mean BT and PFMT knowledge was 90 and 86%, respectively; 68% demonstrated correct PFMT technique without additional instruction, 29% required brief instruction, and 3% were unable to learn PFMT technique. Adherence ranged from 63 to 82% for PFMT and 58 to 67% for BT. Group instruction supplemented with brief individual instruction as needed is an effective teaching method for BT and PFMT.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45894/1/192_2005_Article_1284.pd