Some properties depend on temperature, pressure, and composition, while others also depend on length and velocity scales characteristic of the system under study. The governing equations are solved separately in each domain, subject to the boundary conditions imposed at the free surface as well as the boundaries of each. In fancy terms, all the dimensionless groups are formed from one independent dimensionless group. Generally n k equals the number of different dimensions sometimes called basic or prichapter 5 dimensional analysis and similarity 277. Throughout the rest of this book or any such book dimensionless groups are used to generalize data. Dimensional analysis university of california, san diego. The dimensionless nondimensional numbers criteria, groups, products, quantities, ratios, terms posses the followingfeatures.
Dimensionless groups dimensionless groups flat plate. Dimensionless groups for understanding free surface flows of complex fluids. For example, the biot number and the peclet number have forms for both mass and heat transfer. In recent years the dimensionless groups, as demonstrated in detail here, have grown in significance and importance in contemporary mathematical and computer modeling as well as the traditional fields of physical modeling. Dimensionless groups are frequently encountered in engineering studies of complicated processes or as similarity criteria in model studies. Each dimensionless group is expressed as a natural logarithm of the dimensionless group in order to keep the values of the dimensionless groups from getting excessively large, and to facilitate the visualization of the surface fitting procedure described in the next subsection. Lewis number is a dimensionless number which is the ratio of thermal diffusivity to mass diffusivity or schmidt number to prandtl number. Dimensionless groups article about dimensionless groups. It tells us whether the flow is laminar or turbulent.
The scaling variables must not form a dimensionless group among themselves, but adding one more variable will form a dimensionless quantity. Dimensionless numbers in fluid mechanics are a set of dimensionless quantities that have an important role in analyzing the behavior of fluids. These three dimensionless groups can now be used as the primary variables to define the system behavior in place of the original six variables i. Dimensionless groups sometimes the dimensionless group is describing heat transfer and sometimes mass transfer. Dimensionless group an overview sciencedirect topics. The number of dimensionless groups is always equal to the number of variables minus the number of repeat variables. What combination to use for that one group is up to you, but you need only one group. Pdf dimensionless characteristics of centrifugal pump. Dimensionless groups for understanding free surface flows of complex fluids article pdf available june 2005 with 478 reads how we measure reads.
Dimensionless characteristics of centrifugal pump article pdf available in chemical papers slovak academy of sciences january 2005 with 5,544 reads how we measure reads. Dimensionless numbers are of key importance in parametric analysis of engineering problems. The utility of dimensionless groups in newtonian fluid mechanics is well known, since the pioneering work of reynolds 1883b. Dimensionless groups flat platestraight pipe increments r 1 1.
Dimensionless groups can be divided into two types. Definitions and symbols for physical and chemical dimensionless quantities, with areas of application of the different numbers. Select a number of repeating variables, where the number required is equal to the number of reference dimensions notes. These nondimensional numbers are helpful tools in heat transfer. Add the engineering toolbox extension to your sketchup from the sketchup pro sketchup extension warehouse. Dimensionless groups are useful in arriving at key basic relations among system variables that are valid for various fluids under various operating conditions. View dimensionless groups from chee 3363 at university of houston. Why are dimensionless numbers used in heat transfer and. These equations reveal a total of four dimensionless parameters, one in the momentum equation and three in the freesurfacepressure boundary condition. Dimensionless group article about dimensionless group by.
Dimensionless groups reynolds number example youtube. Dimensionless numbers are of very high importance in mechanical engineering and chemical engineering including thermodynamics, fluid mechanics, mass transfer, heat transfer, solid mechanics, momentum transfer and chemical reaction engineering. Dimensionless time in temperature curves, used in explicit. Do not choose the dependent variable as one of the repeating variables, since the repeating variables will generally appear in more than one pi term. It is a matter of expertise, and partly of taste, to determine a. The above groups can be written in the form of dimensionless equation represent the. Common examples include the reynolds or the mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, flow speed, etc. The value of dimensionless groups for generalizing experiemental data has been long recognized. The reynolds number is always important, with or without a free surface, and can be neglected only in flow regions away from high. Dimensionless definition at, a free online dictionary with pronunciation, synonyms and translation.
The grashof number is used to determine the heat transfer coefficient under free convection. Many correlations in heat transfer are based on dimensionless numbers, which are used to establish similitude among cases which might seem very different. I say more about the formation and use of dimensionless groups in section 4. Sometimes the dimensionless group is describing heat transfer and sometimes mass transfer. Dimensionless groups for understanding free surface flows of complex fluids gareth h. Often, factors of 2 or 12 are included in the standard pi groups. Dimensionless groups in free convection our previous treatment forced convection, assumed. Cramprn where ra gr pr c depends on geometry, orientation, type of. To form a dimensionless combination of parameters we assume 1 et. In problems involving free interfaces, if the reynolds number is low, inertial. Example of unit conversion for a dimensionless group by showing the reynolds number, a number describing how a fluid flows through a pipe. Chapter 5 dimensional analysis and similarity pmtusp. Pdf submitted to bulletin of the society of rheology, may 2005 no abstract. Dimensionless groups for understanding free surface flows.
Reynolds number, gives the information, whether the flow is inertial or viscous force dominant. Mckinley director, hatsopoulos microfluids laboratory dept. Therefore, we can expect to form three dimensionless groups in this problem. Convection heat transfer microelectronics heat transfer. Taylor 19501 estimated the yield of the 1945 bomb to be 16. Just upload files you want to join together, reorder them with draganddrop if you need and click join files button to merge the documents. Dimensionless quantities are widely used in many fields, such as mathematics, physics, chemistry. Dimensionless numbers, abbreviated as dn, are nondimensional quantity of dimension one and can not be measured on a scale of physical units. Some terms, such as reaction rate and gaseous mass transfer coefficient, can be. To deal with complex freeconvection problems, we desire to nondimensionalize the equation of motion eom. It is a pure number, thus always having a dimension of 1. Dimensionless groups this spreadsheet will calculate dimensionless groups that commonly appear in nonisothermal, reacting gas flows.
Nondimensional scaling provides a method for developing dimensionless groups that can provide physical insight into the importance of. Theyarealgebraicexpressions,namelyfractions, where in both the numerator and denominator are powers of physical quantities with the total physical dimension equal to unity. If lewis number is greater than one item explains the predominance of concentration boundary layer. Dimensionless numbers free online course materials. Dimensionless numbers in fluid mechanics wikipedia. So any true statement about the period can be written just using kt2m. In a system of coherent units, it can therefore be represented by a pure number. Pdf joiner allows you to merge multiple pdf documents and images into a single pdf file, free of charge.
Four significant dimensionless numbers in heat transfer course are discussed in this article. Natural convection heat transfer correlations the general form of the nusselt number for natural convection is as follows. Each repeating variable must be dimensionally independent of the others. Find the relationship between variables affecting a phenomenon. Ratio of gas molecule mean free path to process lengthscale indicates validity of lineofsight 1 or continuum dimensionless group is a combination of dimensional or dimensionless quantities having zero overall dimension. Pdf dimensionless groups for understanding free surface. This is used to characterize flows in which there is simultaneous heat and mass by convection transfer. Dimensionless numbers in heat transfer me mechanical. List of all important dimensionless numbers and their. The governing equations for elastic liquids are far more complex than the navierstokes equations and accordingly more non dimensionless groups are required in rheology. A dimensionless group is any combination of dimensional or dimensionless quantities possessing zero overall dimensions. Fundamentals of fluid mechanics chapter 7 dimensional analysis modeling, and similitude jyhcherng shieh.884 1523 1221 638 310 888 581 285 289 1433 1651 1562 684 234 182 1069 1229 569 1086 1414 427 807 1401 1426 905 1311 1638 1372 1612 1275 837 1129 910 1125 632 351 868 426 1375 553 918