9/22/2023 0 Comments Dynamic viscosity air surface![]() When temperature increases, kinetic energy of liquid molecules increases, resulting a decrease in intermolecular forces. Moreover, a change in temperature ( T in☌ or K) causes a change in surface tension of a liquid. water strider, some spider species) to walk on the liquid and causes capillary action. ![]() 2, 3 Because of this effect, the surface layer of the liquid behaves like a stretched elastic membrane that allows the insects (e.g. ![]() Surface tension ( σ sin N/m or kgf/m in meter-kilogram-second (MKS) unit system) 1 is resulted from the attraction effect between the molecules of the liquid due to various intermolecular forces. Keywords: fluid mechanics, surface tension, specific weight, kinematic viscosity, water, temperature, nonlinear regression, statistical analysis Introduction The computational analysis yielded simple mathematical structures to be easily used for educational and practical purposes. The statistical results clearly corroborated that the proposed equations were accurate enough to be used in estimation of the present fluid mechanics-related parameters. Moreover, illustrative examples and relevant MATLAB ® scripts were presented to demonstrate the applicability of the present equations. The proposed formulations were developed using a total of 155 data points and compared against different equations from the literature. The estimations were proven to be satisfactory with very high determination coefficients above 0.999. The formulations were derived within the framework of the nonlinear regression analysis based on the Richardson’s extrapolation method and the Levenberg–Marquardt algorithm. Viscosity is the measure of a fluid's resistance to flow.Three simple empirical models were proposed to predict surface tension, specific weight, and kinematic viscosity of water as a function of temperature. The higher the viscosity of a fluid (liquid or gas), the slower it traverses across a surface. Imagine dripping maple syrup on your waffles for your breakfast. Maple syrup, a very viscous fluid, would pour slower than when you pour milk on your cereal as milk's viscosity is much lower. We can also express viscosity as the internal friction of a fluid in motion. The attraction between the molecules of a viscous fluid is much higher than that of a less viscous fluid. However, when we apply heat or additional thermal energy to our fluids, their molecules start moving faster. ![]() As a result, in gases, molecules experience more friction against each other, making them flow slower and become viscous. In liquids, when molecules start to move faster, their attraction from each other weakens. This weakening results in liquid molecules to move more freely and, therefore, with a lower viscosity. In this article, we'll focus more on the viscosity of liquids, specifically on the kinematic viscosity and the dynamic viscosity of water. Dynamic viscosity, or the absolute viscosity of water, or any fluid, is proportional to the tangential shear stress per unit area needed to move one plate at a constant speed over another plate at a maintained fluid thickness between these two plates, like in a Couette flow, as shown below: When dealing with viscosities, when we mention "viscosity," we actually mean dynamic viscosity. The larger the force or stress needed to move the plate, the more viscous the fluid is. ![]()
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