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Search Publications by: Robert F. Berg (Assoc)

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Displaying 26 - 50 of 60

Viscosity

December 1, 2005
Author(s)
Robert F. Berg
This article summarizes the role of viscosity in describing the properties and flow of fluids. Its measurement, dependences on temperature and density, and deviations from Newtonian behavior are discussed. Example plots and a bibliography are included.

Simple flow meter and viscometer of high accuracy for gases

January 6, 2005
Author(s)
Robert F. Berg
A model and supporting measurements are presented for the laminar flow of gases through a long capillary with a circular cross section. Using the model with a coil of quartz capillary of known dimensions yields the flow rates of a gas of known viscosity

Development of a Microfluidic Rheometer for Complex Fluids

January 1, 2005
Author(s)
Jai A. Pathak, Robert F. Berg, Kathryn Beers
Our group has recently published a report of a combinatorial rheometer/viscometer developed in our lab, based on the princinple of a damped harmonic oscillator. In this paper, we describe a modification of this approach to scale down this viscometer to the

Multi-Sample Couette Viscometer for Polymer Formulations

January 1, 2005
Author(s)
H J. Walls, Robert F. Berg, Eric J. Amis
We describe a prototype scalable viscometer aimed at facilitating rapid measurements of multiple samples. The device simultaneously measures the viscosity of four samples in an array of Couette cells. Each cell contains a rotor with an embedded permanent

Quartz capillary flow meter for gases

March 1, 2004
Author(s)
Robert F. Berg
This article describes an accurate meter for gas flow rates below 1000 micromol/s. (~1 micromol/s  1.3 cm3/min at 0 °C and 1 atm.) Two gauges measure the input and output pressures as the gas flows through a flow element consisting of either a single

Development of a Combinatorial Rheometer for Polymer Formulations

February 1, 2004
Author(s)
H J. Walls, Robert F. Berg, Kathryn L. Beers, Eric J. Amis
Finding the best formulation for a new application, or fine-tuning an existing formulation to meet various customer needs, requires extensive sample preparation and testing. Our goal is to make this exploration more efficient for the property of viscosity

NIST-IMGC Comparison of Gas Flows Below 1 Liter per Minute

June 13, 2003
Author(s)
Robert F. Berg, G Cignolo
We compared the IMGC and NIST standards for small gas flows at the IMGC. The IMGC standard is a recently developed primary flow meter that extracts a large piston out of a temperature-controlled chamber. Controlling the piston's speed holds the pressure in

Two Primary Standards for Low Flows of Gases

September 1, 2002
Author(s)
Robert F. Berg, S A. Tison
We describe two primary standards for gas flow in the range from 0.1 to 1000 mol/s. (1 mol/s =1.3448 standard cubic centimeters per minute.) The first standard is a volumetric technique in which measurements of pressure, volume, temperature, and time are

Mass Flow Research and Standards: NIST Workshop Results

July 1, 2001
Author(s)
Robert F. Berg, David S. Green, G E. Mattingly
A recent workshop at the National Institute of Standards and Technology (NIST) identified research and standards that will benefit users and manufacturers of mass flow controllers and related equipment. The workshop identified problems with flow

Laminar Flow of Four Gases Through a Helical Rectangular Duct

February 1, 2001
Author(s)
Robert F. Berg, S A. Tison
We report measurements and a model of gas flow through a helical duct of rectangular cross section. The measurements on helium, nitrogen, argon, and sulfur hexafluoride yielded molar flow rates from observations of the rate of rise of pressure in a known

Frequency-Dependent Viscosity of Xenon Near the Critical Point

October 1, 1999
Author(s)
Robert F. Berg, Michael R. Moldover, G A. Zimmerli
We used a novel, overdamped oscillator aboard the Space Shuttle to measure the viscosity Η of xenon near its critical density ρ c and temperature T c. In microgravity, useful data were obtained within 0.1 mK of T c, corresponding to a reduced temperature t

Viscoelasticity of Xenon Near the Critical Point

February 1, 1999
Author(s)
Robert F. Berg, Michael R. Moldover, G A. Zimmerli
Using a novel, overdamped, oscillator flown aboard the Space Shuttle, we measured the viscosity of xenon near the liquid-vapor critical point in the frequency range 2 Hz [less than or equal to} f {less than or equal to} 12 Hz. The measured viscosity

Critical Viscosity of Xenon: Surprises and Scientific Results

October 1, 1998
Author(s)
Robert F. Berg, Michael R. Moldover, G A. Zimmerli
The Critical Viscosity of Xenon (CVX) experiment, which flew on board Space Shuttle flight STS-85 in August 1997, measured the viscosity of xenon near the liquid-vapor critical point. Very close to the critical temperature (T c = 290 K), the viscosity Η of

Internal waves in xenon near the critical point

June 1, 1996
Author(s)
Robert F. Berg, Margaret J. Lyell, Geoffrey B. McFadden, Ronald G. Rehm
Just above the liquid-vapor critical point, a fluid’s large compressibility causes a stable stratification in which the density varies by as much as 10% in 1 cm. This stratification supports internal gravity waves which we observed with an oscillator

Hydrodynamic similarity in an oscillating body viscometer

September 1, 1995
Author(s)
Robert F. Berg
Hydrodynamic similarity can be used to calibrate simply and accurately an oscillating-body viscometer of arbitrarily complicated geometry. Usually, an explicit hydrodynamic model based on a simple geometry is required to deduce viscosity from the transfer

Temperature and frequency dependence of anelasticity in a nickel oscillator

September 1, 1995
Author(s)
Robert F. Berg
The frequency dependence of the real and imaginary parts of a nickel oscillator’s transfer function is described over 3 decades in frequency by the use of simple expressions. These expressions incorporate only the resonance frequency omega0, the quality

Remarkably small critical exponent for the viscosity of a polymer solution

July 15, 1994
Author(s)
Robert F. Berg, Karen Gruner
We have measured the apparent critical exponent y characterizing the divergence of the viscosity eta  (T- Tc)^-y near the liquid-liquid critical point of the mixture polystyrene in diethyl malonate. The data span the range in reduced temperature of 10-4