VIRTUAL INSTRUMENTATION SOFTWARE FOR THE RHEOLOGICAL PROPERTIES OF THE NON-NEWTONIAN FLUIDS

Transcription

1 VIRTUAL INSTRUMENTATION SOFTWARE FOR THE RHEOLOGICAL PROPERTIES OF THE NON-NEWTONIAN FLUIDS Eng. Irina Radulescu, S.C. I.C.T.C.M. S.A. Bucharest, ROMANIA Dr. eng. Alexandru V. Radulescu, University POLITEHNICA Bucharest, ROMANIA Dr.eng. Tom Savu, University POLITEHNICA Bucharest, ROMANIA 1. Introduction The most important activity direction of these researches is to offer high quality information services for the academic and research community from Romania and other countries. This activity is also oriented through the projects realized for the industrial and commercial partners. The idea of our project is to realize some applications with didactic purpose, being used in the virtual space of the instrumentation laboratories. In a modern way and for easier and faster obtaining of the information - we offer the possibility to realise a virtual instrumentation laboratory for the simulation and the optimisation of the non-newtonian fluids flow processus, because the study of the fluids flow processes is very important for many domains such as: the oil industry, greasing centralized installations from syderurgical factories, the machine-tools construction industry, thermal motors and vehicles, the biolubrication domain, [1], [2]. Today, Internet is a work instrument. Using the means offered by Internet - it becomes possible the cooperation between the persons, which belong to different organizations. That's how are quickly made very performed specialists teams, which cooperate only for a small time, during the project. From this point of view, the virtual instrumentation laboratory is an educational multimedia modulus for learning and exploring, fitting in a knowledge theoretical base enriched with programmable objects, on-line tests, possibilities to evaluate and to record the users performance, [3], [4]. The virtual laboratory will be a project for equipment and software achievement and also a material, informational, methodological and knowledge resourses system, with the purpose of scientifical reaserch developing. It can be developed only using the international experience and it follows a better contact between the roumanian research and education and the international values circuit.

2 2. Rheology of lubricating greases The American Society for Testing and Materials (ASTM) defined lubricating grease as a solid or semi-fluid lubricant consisting of a thickening agent in a liquid lubricant. To improve certain properties and functions, additional components are sometimes included, called as additives, [5]. Lubricating grease properties depend on both its composition and the manufacturing process used. More investigation to find a way of really measuring and monitoring the physical structure of lubricating grease is needed before any conclusions about the physical shape and form of the structure can be correlated to the chemical and physical behaviour of lubricating grease. Since these properties are most important for actual service behaviour of lubricating grease, such research must be given a high priority by manufacturers and customers, preferably involving universities or other institues with experience of microscopy techniques. Rheology is practised and well established in many other business areas, with products not unlike greases, at least from a consistency viewpoint. Molecular weight distribution, texture, ability to be spread and even taste can be estimated or measured by the use of now classical rheological tests, [6]. In order to describe the main properties of the greases, several theoretical rheological models are used, such as [6] : The Bingham model: u τ = τ 0 ± µ (1) y The Herschel Bulkley model: n 1 u u τ = τ 0 + m (2) y y The Casson model: 1 n 1 1 n n u τ = τ 0 + µ (3) y The rheological parameters of the non-newtonian fluids can be usually determined using a rheometer. The rheology of lubricating greases is almost exclusively based on the viscometric motions. A viscometric motion is a onedimensional shear flow. The velocity has one single component, which is function only of the normal direction to the motion and the time. There are two types of viscometric motions used in rheometry: 1. Couette motion is generated by the relative motion between two surfaces in the absence of a pressure gradient ; this motion is modelled in rotational rheometers (double cylinders geometry, cone and plate, plate and plate, as Figure 1a). 2. Poiseuille motion is generated by a constant pressure gradient ; this kind of motion is specific for the capillary rheometers, as Figure 1b.

3 a) Rotational rheometers b) Capillary rheometers Figure 1: Geometry of rheometers, [7] The rheological tests based on a viscometric motion are divided into two categories: 1. Controlled strain experiments; the input is the shear strain rate γ (angular velocity or the flow rate) expressed in units of s -1 and the measured output is the shear stress σ (the torque or the pressure gradient), expressed in units of Pa. 2. Controlled stress experiments; the input is the shear stress σ and the output is the shear strain rate γ. Two typical flow curves for these rheological experiments are presented in Figure 2a and 2b, [7] τ, Pa "Strain control" t = 20 C τ, Pa "Stress control" t = 20 C du/dy, s -1 du/dy, s -1 a) Strain control test b) Stress control test Figure 2: Flow curves for the rheological tests, [7] Table 1 presents the rheological parameters of the non-newtonian fluids (lubricating greases), modelled as Herschel-Bulkley fluids. For each of the 11 lubricating greases, the parameters have been determined based on stress control and strain control rheological tests. The results were interpreted using the regression analysis method.

4 Table 1: Rheological parameters of the lubricating greases, [7] No. Grease Standard NLGI No. τ 0, Pa m, Pa.s n 1 UM 160 Li 0 EP STAS UM 185 Li 0 STAS UM 165 Li Ca STAS UM 170 Li Ca 2 STAS / U 90 Ca 1 STAS / L 90 Ca 1 G NTR / U 85 Ca 3 STAS UM 185 Li 2 STAS UM 175 Li Ca 3 STAS U 90 Ca 3 STAS Rul 145 Na 3 STAS n 3. Structure of the virtual instrumentation software The virtual instrumentation software is based on a datas bank concerning the non-newtonian fluids reological properties and it is a demonstrative modulus for the reological tests. Using the LabVIEW facilities is the most modern way in the field. It is a graphical schedule medium developed by National Instruments Corporation and it is useful for dates acquisition, analyze and presentation, industrial processes control and command, systems dynamic behavior analyze, [8]. Using a graphical schedule named "G" we realized executable applications, called virtual instruments, which can be used in any field. The schedule is realized by using block diagrams, which are compiled as computer code. The components of the virtual instruments are a frontal panel (PF), which simulates the measure device mask and a block diagram (DB), which is the real executable software. The frontal panel (Figure 3) contains icons, which represent different push buttons, switches, screens and other component elements of a measurement device. On the frontal panel we have included dates and we have visualized the outside dates. The application gives some control elements - for entrance values introduction- and indicators - for results listing. There are used: a switch for the establishment of the type test ( Stress or Strain ) and the simulation domain limits, a list with the greases types, 4 push buttons for the simulation configuration,

5 measurement simulation, regression calculus and stop the application. There is also an element for the graphic representation of simulated values and of the regressioncalculated curves and a table for the listing of the regression curves coefficients. Figure 3: Consumer interface The block diagram is composed by interconnected icons, with the information wave transmission purpose (dates). Figure 4 presents the logical schema for the application entitled measurement, and Figure 5 shows another schema for the application grease selection. Figure 4: Measurement logical schema Figure 5: Grease selection logical schema

6 4. Conclusions 1. The virtual instrumentation software created is not only an equipment and software project, but they are also - a material, informational, methodological and knwoledge resourses system, with the purpose of scientifical reaserch developing. It can be developed only using the international experience and it follows a better contact between the roumanian research and education and the international values circuit. 2. Virtual instrumentation software will influence the research developing for the friction couples projection field, demanding the real function conditions. 3. It is a modern and efficient way to replace a complex and expensive laboratory apparatus, which costs are between Euro to Euro. 4. Virtual instrumentation software will be an aide in the fundamental or application research and also it will give the documentation, the high level instruction and consulting for different beneficiaries. 5. The viability and the virtual instrumentation software success are guaranteed by the novelty of the non-newtonian fluids flow processus simulation problems, those can be possible, last time, owing to achievement of specialized software from this research area. REFERENCES 1. Encarnacão, J.L., Lindner, R. Computer Aided Design-Fundamentals and System Arhitecture, Berlin: Springer-Verlag, Pratt, M. J., Virtual prototypes and product models in mechanical engineering, London, Chapman&Hall, Shimoda, H., Yoshikawa, H. An Experimental Study on a Virtual Collaborator as a New Human Interface, Control Engineering Practice, Vol. 5, No. 3, pp *** Virtual Prototypying Virtual environments and product design process, Proceedings of the IFIP workshop on virtual environments and their applications and virtual prototyping, London, Chapman&Hall, *** Lubricating Grease Guide, National Lubricating Grease Institute, 4 th Edition, Balan, C., Hamnelid, L., Franco, J.M., Britton, M., Callaghan, P.T., Bonneau, D., Radulescu, Al.V., Marin, Al., The Rheology of Lubricating Grease, European Lubricating Grease Institute Publications, Radulescu, Al.V., Contribution to the study of journal bearings lubricated with non-newtonian fluids, PhD Thesis, University POLITEHNICA Bucharest, 1997 (in Romanian) 8. Radulescu, Al.V., Ioanid, P., Radulescu, I., Virtual instrumentation laboratory for the simulation and the optimisation of the non-newtonian fluids flow processus, Tha Annals of University Dunarea de Jos of Galati, Fascicle VIII, Tribology, 2003, pp