8/17/2023 0 Comments Foss viscosity meter![]() Also, the viscosity of a gas does not depend in its density! These mysteries can only be unraveled at the molecular level, but there the explanations turn out to be quite simple.Īs will become clear later, the coefficient of viscosity \( \eta \) can be viewed in two rather different (but of course consistent) ways: it is a measure of how much heat is generated when faster fluid is flowing by slower fluid, but it is also a measure of the rate of transfer of momentum from the faster stream to the slower stream. Going on to fluids, we’ll give the definition of the coefficient of viscosity for liquids and gases, give some values for different fluids and temperatures, and demonstrate how the microscopic picture can give at least a qualitative understanding of how these values vary: for example, on raising the temperature, the viscosity of liquids decreases, that of gases increases. To begin with, we’ll review the molecular picture of friction between solid surfaces, and the significance of the coefficient of friction \( \mu \) in the familiar equation \( F = \mu N \). Heat is energy of random motion at the molecular level, so to have any understanding of how this energy transfer takes place, it is essential to have some picture, however crude, of solids and/or liquids sliding past each other as seen on the molecular scale. Like friction between moving solids, viscosity transforms kinetic energy of (macroscopic) motion into heat energy. Viscosity is, essentially, fluid friction. The RCT estimated by the OPT was the only milk coagulation property to show good agreement with the FRM-derived value, although this was not true for the data from late-coagulating samples.Ĭopyright © 2012 American Dairy Science Association. The relative influence of days in milk on k(20) and a(45) varied, as did the effect of parity on a(45) and that of the measuring unit of coagulation meter on k(20) and a(30). The correlations between k(20) and a(45), and milk yield varied among instruments, as did the correlations between k(20), a(30), and a(45) and milk composition, and the correlations between a(45) and pH. The between-instrument correlation coefficients were either moderate (0.48 for a(30)) or low (0.24 and 0.17 for k(20) and a(45), respectively) when the same traits were compared. The proportion of noncoagulating samples for which k(20) could be estimated differed between instruments, being less for the OPT. 33.66 mm for the OPT and the FRM, respectively). 5.36 min for the OPT and the FRM, respectively), as did the a(45) figures (41.49 vs. The average k(20) values varied greatly (8.16 vs. ![]() Milk coagulation properties measured using the OPT differed considerably from those obtained using the FRM. ![]() ![]() Extending the analysis by either instrument to 90 min permitted RCT and k(20) values to be obtained even for late-coagulating milk samples. The trial was performed in the same laboratory, by the same technician, and following the same procedures. Individual milk samples of 913 Brown Swiss cows from 63 herds located in Trento Province (Italy) were analyzed for rennet coagulation time (RCT, min), curd-firming time (k(20), min), and 2 measures of curd firmness (a(30) and a(45),mm) using the 2 instruments and under identical conditions. The aim of the present study was to compare milk coagulation properties measured through a traditional mechanical device, the Formagraph (FRM Foss Electric A/S, Hillerød, Denmark), and a near-infrared optical device, the Optigraph (OPT Ysebaert SA, Frépillon, France). ![]()
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