Viscosity can also be defined as the property of a fluid due to which it offers resistance to the movement of one layer of fluid over another adjacent layer. Viscosity increases with increase in temperature in case of gases whereas it decreases in case of liquid.Ĭonsider, a plate is placed at a distance of ‘Y’ from the fixed surface. The space in between is filled with a fluid. The plate moves with a velocity U by a force F as shown in fig 1.2. A fluid layer at a distance of y from surface moves with a velocity of `u’ and a layer at a distance of dy from y moves with a velocity of u+du.Īccording to Newton’s law of viscosity the shear force, F acting between two layers of fluid is proportional to difference in their velocities du and area A of the plate and inversely proportional to the distance dy between them. Μ (Mu) is the constant of proportionality or co-efficient of dynamic viscosity or Viscosity Unit. Its unit can be derived asĭu/dy – is the rate of shear deformation or rate of shear strain. Dynamic Viscosity (μ):Īs explained earlier, the dynamic viscosity (μ) is defined as the shear stress required causing unit rate of shear deformation. The kinematic viscosity ( v) viscosity is defined as the ratio of dynamic viscosity to mass density. It has dimensions (mass / (length × time)), and the corresponding SI unit is the pascal -second (Pas). The name kinematic viscosity has been given to the ratio (µ/p) because kinematics is defined as the study of motion without regard to the cause of motion and it concerned with length and time only. Volume viscosity (also called bulk viscosity, or dilatational viscosity) is a material property relevant for characterizing fluid flow. Gravity Viscosity at 20☌/68☏ and 50☌/122☏ for more than 120 crudes is shown as function of specific gravity15☌/60☏. Likewise kinematic viscosity also involves the magnitudes of length and rime only. Online calculators, figures and tables with dynamic and kinematic viscosity of liquid and gaseous butane, C 4 H 10, at varying temperarure and pressure, SI and Imperial units. In case of liquids, kinematic viscosity decreases with increase in temperature. In case of gases, it increases with increase in temperature. Relative or Specific viscosity is the ratio of dynamic viscosity of any fluid to the dynamic viscosity of water at 20☌. Since, water has a viscosity of 1, it is taken as standard substance for relative viscosity. It states that the shear stress τ on fluid element, layer is directly proportional to the rate of shear strain. The constant of proportionality is called coefficient of viscosity. The fluids which follow this law is known as Newtonian, fluids otherwise, it is known as Non-Newtonian fluids. Variation of Viscosity Unit with respect o temperature for some common fluids are given in fig 1.2(b). In case of liquids, when the temperature increases the distance between molecules increases and the cohesive force decreases. So, viscosity of liquids decreases when the temperature increases.Measurement is the most important aspect of our life. We use measurement in science, engineering, business trading, personal life, education, and more other fields. As technology is growing day by day so we need a highly accurate and easy convenient global measuring system in each and every field. It is essential to use standard measurement in every field that everyone to be sure that they not get cheated. In history for measurement people used the human body as a tool. In Table 2, we present most common units for viscosity and the conversion factors between them. Note that 1 cm2/s is equivalent to 100 cSt. However, due to the viscosity values of most common fluids, square centimeters per second (cm2/s) is used more often. For measuring length used forearm, hand, foot & finger as a unit. The SI unit for kinematic viscosity is square meters per second (m2/s). The foot, finger is a subdivided shorter unit of a length. This type of measurement is not accurate cause different in size of the arm & finger for different people & some of the countries still using it. In history, there were lots of measuring systems developed but mostly used imperial, the metric system of measurement. Dimensional formula for some Physical quantities Coefficient of viscosity, dimension, M1L1T1 Planck s constant, h mv ML2T1 Thermal resistance. Where u is the average fluid velocity within the pipe and d is the inside diameter of the pipe.Īpplication of dynamic forces (and the Reynolds number) to the real world: sky-diving, where friction forces equal the falling body's weight.We use these systems for measure distances, volume, weight, speed, area etc. The density of a fluid, is generally designated by the Greek symbol ρ
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