Viscosity temperature coefficient

Although the viscosity index is useful for characterizing petroleum oils, other viscosity—temperature parameters are employed periodically. Viscosity temperature coefficients (VTCs) give the fractional drop in viscosity as temperature increases from 40 to 100°C and is useful in characterizing behavior of siHcones and some other synthetics. With petroleum base stocks, VTC tends to remain constant as increasing amounts of VI improvers are added. Constant B in equation 9, the slope of the line on the ASTM viscosity—temperature chart, also describes viscosity variation with temperature. 

T[ at 25°C, mm /s(=cSt) viscosity—temperature coefficient density, g/mL refractive index pour point, °C... 

Since the viscosity-temperature coefficient of high-boiling fractions, such as lubricating oil, is an important expression of its suitability, a convenient number... 

Caffyn, J. E. 1951. The viscosity temperature coefficient of homogenized milk. J. Dairy Res. 18, 95-105. 

Since the viscosity-temperature coefficient of lubricating oil is an important expression of its suitability, a convenient number to express this property is very useful, and hence, a viscosity index (ASTM D-2270) was derived. It is established that naphthenic oils have higher viscosity-temperature coefficients than do paraffinic oils at equal viscosity and temperatures. The Dean and Davis scale was based on the assignment of a zero value to a typical naphthenic crude oil and that of 100 to a typical paraffinic crude oil intermediate oils were rated by the formula ... 

Viscosity index, the customary basis for comparison of change of viscosity in hydrocarbon oils, becomes less satisfactory when applied to silicone oils, because the viscosity index varies with viscosity as well as with the temperature coefficient. In silicone oils the variation of viscosity with temperature is too small in relation to the viscosity itself. A true viscosity-temperature coefficient (VTC) has been proposed as a more satisfactory criterion [see Wilcock, Mechanical Engineering 66, 739 (1944)1. 

Taking into account the well-known WLF-equation relating the viscosity-temperature coefficient of a polymer to its glass temperature they obtained Eqs. (5) and (6)... 

D. F. Wilcox, Viscosity-Temperature Coefficient, Mechanical Engineering 66 739 (1944). 

Compared with petroleum-based fluids, silicone oils show relatively small changes in viscosity as a result of temperature change (59,328). A common measure of the viscosity change with temperature is the viscosity—temperature coefficient (VTC) (341). Typical dimethylsilicone VTC is 0.6 or less. Phenylsilicones are slightly higher. Organic oils are typically 0.8 or greater. The viscosity—temperature curves follow equations 27 and 28, where a, b, and c are constants. 

Electrical properties are of interest. The dielectric constant varies from 2.2-2.S, depending on viscosity. Power factor is in the order of 0.0005 up to frequencies of 10. They maintain an unusually constant viscosity with change of temperature. Whereas the viscosity-temperature coefficient... 

Linear short-chain polysiloxanes Me3Si(OSiMe2)nOSiMe3 are used as silicone oils. Such oils are characterized by their high thermal stability and low viscosity temperature coefficient (VTC). A low VTC implies a small change in viscosity vis-a-vis temperature. Thus, many modem silicone oils retain their fluid-like characteristics even at temperatures as low as -80 °C. 

Figure 6.7 The viscosity temperature coefficient, fir = r[ dr /dT)px, of H2O + NaBr solution and pure water as a function of concentration and temperature at atmospheric pressure, (a) , Abdulagatov and Azizov (2006a) O, Isono (1984) x, pure water (lAPWS, Kestrn et al, 1984a) (h) , 2.961 mol kg O, 0.049 mol-kg (--------), pure water (lAPWS, Kestin et al., 1984a) (------), smoothed...

Because of their thermal stability and low viscosity-temperature coefficient, silicone fluids find use as hydraulic fluids, lubricants and greases. Other applications include textile finishes, mould release agents and anti-foaming agents where water repellency, non-stick characteristics and surface activity respectively are utilized. 

---