An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

Summary

An experimentally accessible analog method for studying molecular hydrodynamic processes in dense fluids is presented. The technique uses particle image velocimetry of vibrated, high-restitution grain piles and allows direct, macroscopic observation of dynamical processes known and predicted to exist in strongly interacting, high density gases and liquids.

Abstract

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

Introduction

Molecular hydrodynamics studies the dynamics and statistical mechanics of individual molecules and collections of molecules within fluids. Among the many experimental techniques developed for studying molecular hydrodynamic systems^1,2, light scattering^1,2,3, molecular dynamic simulations^4,5,6,7 and, to a lesser extent, inelastic neutron scattering⁸ have been most comm....

Protocol

1. Preparation of Vibratory System

1. Set up the vibratory system as shown in Figure 1. This system consists of an annular polyurethane bowl (having an outer diameter of 600 mm), attached to a single-speed (1740 rpm), unbalanced motor, where the latter generates process vibrations. This is attached to a weighted base and separated by a group of eight springs (the bowl and weighted base are purchased assembled as one piece). Attach the bowl assembly to its stand and secure with two supplied rubber hooks. Place peristaltic pump on a table near the bowl and attach pump outlet hose to bowl lubrication inlet point. <....

Results

In presenting representative results, we refer to continuum-time-scale processes as those observed and predicted over time-scales, that are long relative to the characteristic grain collision time scale,

Discussion

In order to use vibrated grain piles as macroscopic analogs for investigating molecular hydrodynamic processes, an experimentalist must, on one hand, learn and use four basic measurements, and on the other, master a few basic elements of equilibrium and non-equilibrium statistical mechanics. Focusing first on experimental measurements, these include: i) measurement of individual grain dynamics through measurement of the single-particle velocity autocorrelation function, ii) measurement of time-average/long-time-scale sur.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Vibratory Polishing Bowl	Raytech	AV-75
Flow Meter	Peristaltic Pumps	913 Mity Flex
Scale	Pelouze	4040
Triaxial Accelerometer	PCB Piezotronics	PCB 356B11	Accelerometer with Sensor Signal Conditioner
Data Acquisition Computer	IBM	Thinkpad	Used with high speed camera
High Speed Camera	Redlake	Motionxtra HG-XR
Zoom Lens	Tamron	Model A18	18-250mm F/3.5-6.3
High intensity Light	ARRI	EB 400/575 D
Data Processing Computer	Dell	Dell Precision Tower 7910
PIV Software	Dantec Dynamics	Dynamic Studio 2013	version 3.41.38
Data Acquisition Hardware	National Instruments	SCXI	SCXI-1000 Chasis with SCXI 1100 Card and SCXI 1303 Adapter
Data Acquisition Software	National Instruments	LabVIEW 2012
Data Processing Software	MATHWORKS	MATLAB
Polishing Media	Rosler	RSG 10/10S	Multiple media types used (mixed, spherical, triangular)
Polishing Solution	Rosler	FC KFL (3%)	3% soap solution with water
Ruled Scale	Swiss Precision Instruments	13-911-3
Graduated Cylinder	Global Scientific	601082