![]() ![]() 4–7 The use of computational techniques for various aims (e.g. The surface tension, specific weight, and kinematic viscosity of water are important parameters for many biological or industrial processes. This relationship can be mostly expressed in the form of an Arrhenius-type formulation. The behaviour of liquids is noticeably different from gases, and the viscosity decreases with increasing temperature for the liquids. 4, 5 It is noted that models for estimating liquid viscosities are much less derived than for gases, and their implementation is restricted to a qualitative definition. For convenience, this ratio is given the name kinematic viscosity ( ν) and is expressed as ν= μ/ ρ. 2–5 In fluid mechanics, the ratio of dynamic viscosity ( μ) to density ( ρ) appears frequently. Therefore, viscosity ( μ in kgf.s/m 2 or ν in m 2/s, respectively, for dynamic and kinematic viscosity) can be described as a magnitude of the resistance of a fluid to deformation under shear stress. two parallel layers moving in a liquid) provide a resistance to this flow. Although the liquid flows when a shear force is applied, however, the frictional forces between the fluid layers (e.g. 6A liquid can be considered to consist of molecular layers superimposed on one another. Other factors influence water's density such as whether it is tap or fresh water or saltwater, and these variations of water changes its density. Water has the maximum density only when it is pure water. When the temperature changes from either greater or less than 4☌, the density will become less than this value. 4, 5 In MKS unit system, the specific weight of water at 4☌ is approximately 1000kgf/m 3, and the density (mass density or specific mass) is about 2/m 4. 2 The weight per unit volume of a substance is called the specific weight γ (in kgf/m 3) and is determined from γ= ρg, where g is the acceleration of gravity (9.807m/s 2) and ρ (in kgf.s 2/m 4) is density. Thus, surface tension decreases with increase in temperature. 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. This inversion between \(\xi =0.55\) and 0.65 roughly coincides with the peritectic point at \(\xi =0.Three simple empirical models were proposed to predict surface tension, specific weight, and kinematic viscosity of water as a function of temperature. In the isosteric group for \(\xi =0.65\) the slope is clearly inverted. The extension of the operation range of absorption heat pumps and chillers with aqueous lithium bromide as working pair to evaporator temperatures below \(0\,^\), resulting in different gradients with respect to temperature. ![]()
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