G. Raush

Bio: G. Raush is an academic researcher from Polytechnic University of Catalonia. The author has contributed to research in topics: Gear pump & Gas compressor. The author has an hindex of 11, co-authored 30 publications receiving 340 citations.

Three-Dimensional Numerical Simulation of an External Gear Pump With Decompression Slot and Meshing Contact Point

Abstract: Recently several works have been published on numerical simulation of an external gear pump (EGP). Such kinds of pumps are simple and relatively inexpensive, and are frequently used in fluid power applications, such as fluid power in aeronautical, mechanical, and civil engineering. Nevertheless, considerable effort is being undertaken to improve efficiency and reduce noise and vibration produced by the flow and pressure pulsations. Numerical simulation of an EGP is not straightforward principally for two main reasons. First, the gearing mechanism between gears makes it difficult to handle a dynamic mesh without a considerable deterioration of mesh quality. Second, the dynamic metal-metal contact simulation is important when high pressure outflow has to be reproduced. The numerical studies published so far are based on a two-dimensional (2D) approximation. The aim of the present work is to contribute to the understanding of the fluid flow inside an EGP by means of a complete three-dimensional (3D) parallel simulation on a cluster. The 3D flow is simulated in a LINUX cluster with a solver developed with the OPENFOAM Toolbox. The hexahedral mesh quality is maintained by periodically replacing the mesh and interpolating the physical magnitudes fields. The meshing contact point is simulated with the viscous wall approach, using a viscosity model based on wall proximity. The results for the flow rate ripples show a similar behavior to that obtained with 2D simulations. However, the flow presents important differences inside the suction and the discharge chambers, principally in the regions of the pipes' connection. Moreover, the decompression slot below the gearing zone, which can not be simulated with a 2D approximation, enables a more realistic simulation of a contact ratio greater than 1. The results are compared with experimental measurements recently published.

Numerical simulation and experimental validation of vapour compression refrigeration systems. Special emphasis on CO2 trans-critical cycles

Abstract: A numerical and experimental comparative study of a carbon dioxide trans-critical refrigerating system and a conventional subcritical refrigerating cycle is presented. Attention is focussed not only on the whole refrigeration cycle, but also on the behaviour of the hermetic reciprocating compressors used in these systems. The comparative cases presented have been specially designed for small cooling capacity units with an evaporation temperature around 0 8C. A detailed numerical simulation model for hermetic reciprocating compressors performance, widely validated under conventional fluid refrigerants, has been extended to numerically obtain the CO2 compressor prototypes behaviour. Two CO2 compressor prototypes working with CO2 have been experimentally tested in a specific unit, specially designed and built to analyse high-pressure single stage vapour compression trans-critical refrigerating equipments. This set-up has allowed validating a detailed numerical simulation code for the thermal and fluid-dynamic behaviour of single stage vapour compression refrigeration system working with CO2 as fluid refrigerant. The numerical results and the experimental data obtained to validate compressors, heat exchangers and whole cycle behaviour have shown a really good agreement. Finally, the numerical and experimental comparison between the carbon dioxide system and the sub-critical conventional cycle has shown the possibility of CO2 as fluid refrigerant under the studied working conditions. q 2005 Elsevier Ltd and IIR. All rights reserved.

Influence of the interteeth clearances on the flow ripple in a gerotor pump for engine lubrication

Abstract: A gerotor pump, which is widely used in the automotive industry for engine oil lubrication, produces an instantaneous flow fluctuation and the estimation of this is fundamental in order to evaluate the pump quality for silent and smooth operation. The intricate aspects of the pumping process of a gerotor pump make computational fluid dynamics the appropriate tool for modelling and simulation to provide insights into its flow characteristics. Because the instantaneous flow is rather dependent on the teeth contact, a new boundary condition of a virtual wall was developed, which allows simulation of the teeth contact in the interteeth radial clearances. This new boundary condition is utilized in a three-dimensional model of the gerotor pump with mesh deformation and remeshing at every time step by means of a home-made ad-hoc code programmed by the present authors and named viscous wall cell. The code has been integrated into the computational fluid dynamics solver. The interteeth clearances are studied under the following different operating conditions (working pressures and rotational velocities): first, no contact points (no teeth contact is studied in order to prove that, even if the interteeth radial clearance is sufficiently small, the leakage cannot be negligible); second, all contact points (the ideal approach is considered with zero interteeth radial clearances used to model zero manufacturing tolerances); third, one contact point at different locations (the existence of manufacturing tolerances and the teeth contact approach make the pump’s operation and its pumping mechanism more realistic in the simulation). The numerical instantaneous flow is compared with the analytical instantaneous flow, with the instantaneous flow modelled by using the bond graph technique, and with the experimental determination of the flow ripple for a specific unit. The results obtained show the importance of simulating the teeth contact and prove to be an excellent estimation of the instantaneous flow behaviour to obtain the dynamic properties of a gerotor pump under more realistic conditions than its design.

Thermal energy storage based solar drying systems: a review.

Abstract: Solar dryer based on thermal energy storage materials is quite effective for continuously drying agriculture and food products at steady state in the temperature range (40 °C–60 °C). Such dryers have globally become a potential viable substitute to the solar dryers based on fossil fuel, due to the utilization of clean energy resources and cost-effectiveness. Storage materials utilized in these dryers can store energy during the sunshine hour and deliver the stored energy during off-sunshine. It reduces the existing load on the gap between energy demand and supply, hence plays a vital role in energy sustainability. A number of studies have been done in last few decades for drying agriculture and food products with a solar dryer based on thermal energy storage concept. This paper mainly presents a review on the important contributions made so far in the field of solar drying systems based on the thermal energy storage medium, with a focus on recent updates in thermal energy storage technology available in terms of materials capable of storing heat as sensible and latent heat.

Models for Flow Rate Simulation in Gear Pumps: A Review

Abstract: Gear pumps represent the majority of the fixed displacement machines used for flow generation in fluid power systems. In this context, the paper presents a review of the different methodologies used in the last years for the simulation of the flow rates generated by gerotor, external gear and crescent pumps. As far as the lumped parameter models are concerned, different ways of selecting the control volumes into which the pump is split are analyzed and the main governing equations are presented. The principles and the applications of distributed models from 1D to 3D are reported. A specific section is dedicated to the methods for the evaluation of the necessary geometric quantities: analytic, numerical and Computer-Aided Design (CAD)-based. The more recent studies taking into account the influence on leakages of the interactions between the fluid and the mechanical parts are explained. Finally the models for the simulation of the fluid aeration are described. The review brings to evidence the increasing effort for improving the simulation models used for the design and the optimization of the gear machines.

Detailed thermodynamic characterization of hermetic reciprocating compressors

Abstract: The aim of this paper is the detailed analysis of different well-known thermodynamic efficiencies usually used to characterize hermetic compressors. Attention is focussed on the volumetric efficiency, the isentropic efficiency, and the combined mechanical–electrical efficiency. A procedure is presented to detach these efficiencies into their main components (physical sub-processes) to get deeper insight on the overall behavior. The volumetric efficiency is split into partial efficiencies related to pressure drop and heat transfer effects, supercharging effects, superdischarging effects, leakages, etc. The isentropic efficiency is detached using two different points of view: the work associated to the individual sub-processes (compression, discharge, expansion, suction), and the work associated to the underpressures, overpressures, and between the inlet and outlet mean compressor pressures. Finally, the combined mechanical–electrical efficiency is related to the heat transfer losses/gains, and to the exergy transfers and exergy destroyed. Even though some of the concepts introduced in the paper can be applied to different kinds of compressors, the discussion is specially focussed on hermetic reciprocating compressors. An advanced simulation model developed by the authors has been used to generate data to illustrate the possibilities of the detailed thermodynamic characterization proposed. The criteria developed are useful tools for comparison purposes, to characterize compressors, and to assist designers during the optimization process.

Applications of software in solar drying systems: A review

Abstract: This review paper is focused on the application of software in solar drying systems. The application of software is very important to develop and analyze the mathematical models and predicting the performance of different kinds of solar drying systems. It is also useful for predicting the crop temperature, moisture content and drying rate, drying kinetics, and color of the crop. Computational fluid dynamics can be used for the analysis and investigation of air flow and temperature distribution pattern through appropriate simulation with the help ANSYS and FLUENT. MATLAB and FORTRAN are very useful tools to develop mathematical models for prediction the crop temperature, air temperature, the moisture evaporated. It is also very useful for training and testing of various models. For statistical data analysis, statistical software SPSS, Sigma Plot V and Statistica. All recent employed software and their utility in solar drying systems are emphasized in this communication. This comprehensive review of the various software applications in different solar drying systems is useful for academician, scientist and researchers.