Viscosity and Surface Tension Explained

As influenced by the temperature and pressure variations of viscosity: Mainly, the viscosity varies with pressure and temperature. Although the effects of pressure are almost negligible with respect to temperature effects, which are much more pronounced. An increase in pressure in both liquid and gas leads to an increase in dynamic viscosity. An increase in temperature leads to a decrease of dynamic viscosity in liquids, whereas the opposite is true for gases. Fluid Viscosity Lubricants (IVLUB): The viscosity index is a dimensionless number that describes the behavior of a lubricating fluid against a temperature variation. IVLUB To obtain a trial, it is done at 100 ºF and 210 ºF by comparing the values of the viscosity with the viscosity of reference lubricants. The formula is IV = (AB / AC) * 100. A (100 °F viscosity of an oil of IV = 0). B (viscosity of the sample at 100 ºF in VSS). C (100 °F viscosity of an olive oil - IV = 100). From A and C, we obtain tables. The concept of surface tension: When a liquid expands, it does not do so freely but forms an interphase with a second fluid (liquid or gas) or a solid surface. Molecules immersed in the liquid mass will be attracted or repelled in the same magnitude in all directions; however, the molecules located at the free surface are unbalanced because they are attracted or repelled differently. This causes shear stresses to appear in the phase separation, behaving like a membrane. This membrane behaves like an elastic membrane whose surface tension coefficient is: s = F / L = Energy / Area (N / M). It is the tension strength per unit length and coplanar with the interphase that can withstand this. It is also defined as the energy stored per unit area in the interphase. Capillary pressure: If the phase is between a curved surface, the equilibrium condition states that there must be a pressure difference between both sides, with the highest pressure on the concave side. The surface tension is balanced by the pressure difference. A) Increased pressure in a cylinder does not affect the phase, and hence there is no surface tension. Ap = F / SF = S = Ap Ap · · 2RL, s = F / LF = s x L • 2 Ap · 2RL = s x L • 2 = Ap = s / R. B) Increase of pressure in a spherical drop: F = S = Ap Ap · · II · R ², F = s x L = s · 2IIR Ap · II · R ² = s · 2IIR = Ap = 2 s / R.