Measuring tube/flask and balance to obtain a volume and mass for the calculation of densities.įor this investigation, I am not expecting to obtain perfect results as there are a number of errors that are likely to occur due to the limitations of our apparatus and judgement.Glycerol and set of different sized balls (densities assumed to be the same and constant through the balls and fluid).Metre ruler, stopwatches and micrometer.Rubber bands/tape for marking start and stop distances.Cylindrical tubing (blocked off at bottom).The only variables that will be changed for us to gain a range of results will be the size of the balls.read more. To observe and record the terminal velocities of different sized balls falling through Glycerol, and hence calculate the viscosity of Glycerol. One method of calculating the viscous drag (also the method I will be using) is by subtracting the upthrust exerted by the fluid on an object (ball) from the weight of the object as it is dropped through the fluid, assuming that the object has reached it’s terminal velocity and therefore has equal forces acting on it. The viscosity of a fluid can be calculated by using Stroke’s Law, which relates the viscosity of a fluid to the viscous drag (opposing force) and velocity at which it is travelling. The higher the viscosity of a fluid, the less easily it can flow. Viscosity is a measure of the resistance against the flow of a substance (fluid). Nagi (Alicante, Spain, 1993).Calculating the viscosity of Glycerol Introduction: Wolf, in Second International Discussion Meeting on Relaxations in Complex Systems, edited by K. Cohen, in Advances in Chemical Physics, edited by I. thesis, Massachusetts Institute of Technology, 1969. Samara (Colorado Springs, Colorado, 1993). The slope, dT g/ dP, is positive with the pressure dependence for glycerol being considerably smaller than for DBP both are nonlinear, tending to saturate in temperature at high pressures. The P‐dependence of the glass transition is also determined over a wide range of T. For glycerol, the trends towards increased fragility at elevated pressure and temperature are consistent with diminished hydrogen bonding under those conditions. Glycerol, however, becomes more fragile over the same temperature range. Using this, DBP shows a trend common to several liquids, a decrease in fragility with increasing temperature. For the isothermal model, we derive a new measure of fragility. This is dramatic for DBP, which goes from a strong to an intermediate‐strength liquid. Under isochoric conditions, the fragility for both glycerol and DBP increases with increasing density. For glycerol and (less conclusively) DBP under isobaric conditions, the fragility increases markedly at high pressure. Fragility parameters are evaluated for these three isometric conditions. These data provide an assessment of the T‐dependence of an isothermal model (free volume), the P‐dependence of an isobaric model (Vogel–Tammann–Fulcher) and by extension that for isochoric conditions. The T‐dependence of viscosity is larger for glycerol than DBP but the P‐dependence smaller for glycerol than for DBP, whereas the T‐dependence is much more pressure sensitive for DBP. This level of precision allows us to define a viscosity surface which can then be extrapolated to the glass transition along both temperature and pressure cuts. The overall precision of the data are approximately 10% or better throughout. The majority of the results extend up to viscosities of 10 7 cP, with those at 22.5 ☌ going to 10 10 cP. These studies were made using a combination of a rolling‐ball and a centrifugal‐force diamond anvil cell viscometer. The pressure and temperature dependent viscosities of two glass forming liquids, glycerol and dibutyl phthalate (DBP), have been studied in the range P=0–3 GPa, T=0–125 ☌, and η=10 1–10 10 cP.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |