DETC2006-99487 ON DESIGN AND PERFORMANCE OF INTERNAL EPITROCHOIDAL PUMPS

ABSTRACT In this study an analysis of rotor profiles geometry in internal epitrochoidal pumps and a systematic study of their performance as a function of the geometrical parameters are introduced. Internal pumps are used in various fields, like automotive, alimentary, or medical-scientific. This machines consist of two rotors: generally the inner rotor has epitrochoidal profile and the profile of the outer rotor is determined as conjugate to the inner one. The rotor geometry and the final performance of the whole machine has been studied by many researchers, using different methods. In this paper the construction of the profiles is performed by the theory of gearing, in order to calculate performance indexes. In particular the pump type with epitrochoidal outer rotor has been considered. Even if it is impossible to establish an optimal profile valid for every application, the analysis of the results obtained allows to choose the design parameters, in order to optimize the shape of the rotors for any particular application. INTRODUCTION Internal lobe pumps, usually called gerotors, have been widely studied in the last decades. These machines are constituted by a cylindrical housing and two rotors rotating at different angular velocities with a fixed ratio. The inner rotor transmits the motion to the outer one by a number of contact points equal to the number of lobes of the inner rotor plus one. The chambers in which the fluid is elaborated are enclosed by the same contact points, so that their volume varies during rotary motion. In order to separate the high and low pressure zones, a common solution consists in realizing suitable inlet and discharge ports in the housing plates (se

Differentiation of Mesenchymal Stem Cells towards an insulin-releasing phenotype after co-culture with Pancreatic Islets

Transplantation of pancreatic islets has become a promising clinical option to treat patients with type 1 diabetes, alternative to the standard therapy with insulin injections. Islet transplantation is a minimally invasive therapeutic approach, and it allows a better metabolic control and a long-term insulin independence in more than 80% of patients (Ryan et al., 2002). However this therapeutic treatment has some side effects, such as the poor yield of pancreatic islet explants and even more the immune graft rejection, which have as a consequence the very limited lifespan of transplanted pancreatic islets. To avoid these side effects several strategies have been proposed and, besides the treatment with immunosuppressive drugs, promising results have been obtained with the use of Mesenchymal Stem cells (MSCs), already known in literature to be able to support the survival of many cell types (Scuteri et al., 2006). Several in vivo studies have demonstrated that the concurrent transplantation of pancreatic islets with MSCs reduces the number of islets required to achieve glycemic control in diabetic rats, but the mechanisms of these encouraging results are still unknown (Figliuzzi et al., 2009). For these reasons in this in vitro study we characterized the effect of co-culture of rat MSC on survival and functioning of rat pancreatic islets, by evaluating for 4 weeks: i) MSC adhesion to pancreatic islets; ii) viability of pancreatic islets co-cultured with MSCs; iii) the expression of insulin after co-culture; iv) the ability of co-cultured pancreatic islets to correctly adjust insulin release after variation of glucose concentration. Our results demonstrated that MSCs are able to adhere to pancreatic islets, but to increase only partly the pancreatic islet survival, which retain the ability to express and correctly release insulin after glucose variation in medium culture. Noteworthy that the insulin level in the medium of co-cultured pancreatic islets is always higher with respect to medium of pancreatic islets alone. The immunofluorescence analysis reveals that also MSCs (and not only pancreatic islets) are able to express insulin, but only in co-culture. These results, which justify the in vivo observation reported above, suggest that MSCs undergo to differentiation into a insulin-releasing phenotype after co-culture with pancreatic islets. We are now evaluating the molecular mechanisms which drive this effect, by analyzing the role of soluble factors and of proteins able to induce insulin expression. This study was granted by MIUR – FIRB Futuro in Ricerca 2008 RBFR08VSVI_001

Theoretical Analysis of an Innovative Volumetric Rotary Machine

In this paper a study of an innovative volumetric rotary machine is presented . The machine consists in a stator and a number of pistons rotating inside the stator and attached to a crank. The mechanism realizes for every piston a chamber that varies its volume during crank rotation, and consequently it can be used to design a volumetric rotary machine. In order to obtain the analytical equation of the stator profile the geometrical constraints that characterize the mechanism are analyzed. Once the stator profile is determined and suitable design parameters settled, the profile of the rolling pistons is obtained numerically, considering their relative motion in respect to the stator. In order to evaluate the performance of the machine, the specific displacement and the maximum compression ratio are calculated as a function of the design parameters. Finally a basic dynamic analysis of the machine is presented. The results obtained permit to choose the design parameters for a particular application, showing that the mechanism can be particularly suitable for pumps, compressors and pneumatic engines

Special Bicycle Ergometer for Optimum Rider Position

This paper presents an original 7-degrees of freedom device to adjust, test and optimize different positions of a bicycle rider. The system allows data acquisitions of forces, angles and velocities during cycling performance. An overall of eight forces and three angles are simultaneously measured. An efficient position enables the rider to reduce the muscular effort for a given power produced. Basically good bike position presents three general parameters: saddle height, saddle-to-bar distance, and fore/aft saddle position. Determining the correct horizontal saddle position is of relevant importance in finding the correct fit for a road cyclist and the final frame geometry. Moreover saddle position determines seat tube angle as well as the top tube/stem length dimension. The traditional method consists of positioning the rider's saddle so that the knee (the tibial tuberosity) is over the pedal spindle with the crank in horizontal position. But this method does not consider the relation between the positions of arms and torso for different physiques. This special device, actuated with hydraulic cylinders, allows to achieve optimum horizontal saddle position by measuring horizontal forces on saddle and handlebar. Pedals, with three axial load cells, measure the effective pedaling force in three orthogonal directions exerted by the rider. The aim of the research is to determine a quantitative method to establish the optimum rider position in order to minimize the muscular efforts

Toward Computerized Determination of Envelope to Family of Parametric Planar Curves

This paper introduces an original analytical procedure for the computation of the planar curve in meshing with a general two dimensional curve. Considering a planar gear mechanism with a constant transmission ratio, in this work a general expression of the explicit solution of the equation of meshing is presented. Besides, an original method to evaluate the undercutting conditions, based on the explicit solution of the equation of meshing, is shown. Taking into account a generating curve in homogeneous coordinates and the transformation matrixes which define the relative motion between the profiles, the solution of the equation of meshing and consequently the profile conjugated to the generating curve can be directly found, by a simple coordinate transformation. The explicit solution is expressed with the general conventions of the theory of gearing. Once the equation of the conjugated curve is obtained, a direct method for the evaluation of the undercutting condition can be applied. The proposed method allows to implement effective and affordable computer codes for the computation of conjugate planar profiles

On Twin Screw Compressors Design

Twin screw compressors are widely used in many applications, such as compressing air, refrigerating, industrial gas processing, engines supercharging, etc. In the last quarter of the twentieth century the number of units manufactured registered an extraordinary increase: in fact the development of advanced manufacturing techniques permitted to exploit the basic advantages of these machines in respect to the other types of compressors. In particular twin screw compressors are characterized by the ability to satisfy varying load demands, reliability in service, high efficiency, simple maintenance. Despite the diffusion of this type of machines in many industrial fields, the available literature about them is still limited, in particular regarding the rotor profile geometry. In fact, almost every industrial profile of the rotors is protected by patents, and the companies that hold them seldom diffuse information about the generating methods. In this paper a general description of this type of machine is presented, focusing on the mechanical aspects and in particular on the shape of the rotors. The first part of the paper introduces the main advantages and disadvantages in respect to the other compressor types and the state of the art of this type of machine. Then a deep mathematical analysis of a method for the profiling of screw compressor rotors, based on the theory of gearing, and typical aspects related to the machine design, such as the rotor flow area, the sealing line on the cross-sectional plane and on the rotors and the blow-hole area, are discussed. In the second part of the work the theory above presented is applied to three different geometries of the rotors, and other possible more complex profiles are introduced

Theoretical Analysis of Internal Epitrochoidal and Hypotrochoidal Machines

In this article, a complete and original method to analyse both the epitrochoidal and the hypotrochoidal rotary machines is presented. The internal trochoidal machines consist of two rotors: the first rotor is an envelope of a trochoid, the second rotor is its conjugate. In particular, in this article, the profiles of the trochoidal rotor and its conjugate are expressed by original and particularly synthetic equations using a method based on the theory of gearing. Then the geometry of these machines is completely defined by the choice of four non-dimensional parameters. Once these parameters are selected, the geometric and kinematic characteristics of the rotor profiles are obtained in an original analytic form; hence, the main theoretical performance indexes are computed by a proper method. The results of the analysis allow us to choose the best geometric configuration for a specific application

Theoretical Analysis of Internal Lobe Pumps

In this work a theoretical study of the performance of internal epitrochoidal pumps, as a function of the geometrical parameters, is achieved. The machines considered are constituted by two rotors: one rotor has an epitrochoidal profile, and the other rotor is shaped by arcs of circumference and by a limit profile. In this paper the construction of the profiles is performed by the theory of gearing, in order to calculate some selected performance indexes. By choosing three non-dimensional parameters, all the possible geometries of this type of pumps can be examined: in particular, the used approach permits to consider the pump type with epitrochoidal outer rotor too. Finally, a general analysis of the calculated performance and operational indexes is presented