Jorge Parrondo

Steady and Unsteady Radial Forces for a Centrifugal Pump With Impeller to Tongue Gap Variation

Experimental and numerical studies are presented on the steady and unsteady radial forces produced in a single volute vaneless centrifugal pump. Experimentally, the unsteady pressure distributions were obtained using fast response pressure transducers. These measurements were compared with equivalent numerical results from a URANS calculation, using the commercial code FLUENT. Two impellers with different outlet diameters were tested for the same volute, with radial gaps between the blade and tongue of 10.0% and 15.8% of the impeller radius, for the bigger and smaller impeller diameters, respectively. Very often, pump manufacturers apply the similarity laws to this situation, but the measured specific speeds in this case were found to be slightly different. The steady radial forces for the two impellers were calculated from both the measured average pressure field and the model over a wide range of flow rates in order to fully characterize the pump behavior. The data from the pressure fluctuation measurements were processed to obtain the dynamic forces at the blade passing frequency, also over a wide range of flow rates

Performance of a centrifugal pump running in inverse mode

Abstract This paper presents the functional characterization of a centrifugal pump used as a turbine. It shows the characteristics of the machine involved at several rotational speeds, comparing the respective flows and heads. In this way, it is possible to observe the influence of the rotational speed on efficiency, as well as obtaining the characteristics at constant head and runaway speed. Also, the forces actuating on the impeller were studied. An uncertainty analysis was made to assess the accuracy of the results. The research results indicate that the turbine characteristics can be predicted to some extent from the pump characteristics, that water flows out of the runner free of swirl flow at the best efficiency point, and that radial stresses are lower than in pump mode.

The Effect of Impeller Cutback on the Fluid-Dynamic Pulsations and Load at the Blade-Passing Frequency in a Centrifugal Pump

A study is presented on the fluid-dynamic pulsations and the corresponding dynamic forces generated in a centrifugal pump with single suction and vaneless volute due to blade-volute interaction. Four impellers with different outlet diameters, obtained from progressive cutbacks (trimmings) of the greatest one, were successively considered in the test pump, so that the radial gap between the impeller and the volute ranged from 8.8% to 23.2% of the impeller radius. The study was based on the numerical computation of the unsteady flow through the machine for a number of flow rates by means of the FLUENT code, solving the 3D unsteady Reynolds-averaged Navier-Stokes equations. Additionally, an experimental series of tests was conducted for the pump with one of the impellers, in order to obtain pressure fluctuation data along the volute front wall that allowed contrasting the numerical predictions. The data collected from the numerical computations were used to estimate the dynamic radial forces and torque at the blade-passing frequency, as a function of flow rate and blade-tongue radial gap. As expected, for a given impeller diameter, the dynamic load increases for off-design conditions, especially for the low range of flow rates, whereas the progressive reduction of the impeller-tongue gap brings about corresponding increments in dynamic load. In particular, varying the blade-tongue gap within the limits of this study resulted in multiplying the maximum magnitude of the blade-passing frequency radial force by a factor of about 4 for low flow rates (i.e., below the nominal flow rate) and 3 for high flow rates.

Waste-to-energy technologies in continuous process industries

A range of new waste-to-energy (WtE) technologies in continuous process industries have been analyzed in terms of conversion, energy saving, heat recovery, electricity generation, transportation fuel, storing energy and fuel, environmental emissions, and recycling management. This new group of WtE technologies is an emerging technology group for energy-intensive industries apart from the wide concept of “clean energy technologies”. The current state of WtE technologies has been examined for five representative sectors in continuous industrial processes: iron and steel, cement, primary aluminum production, metal casting, and glass industry. The purpose of the study was to seek synergetic interactions between continuous process industries, with special emphasis on the case of the iron and steel industry. For the purpose of a comparative analysis, waste heat recovery (WHR) technology has been included. A case study in the steel sector is illustrated as a real-world example for solid recovery using WHR in sintering process.

Development of a predictive maintenance system for a centrifugal pump

An approach is presented for the development of a predictive maintenance system for rotor‐dynamic pumps, which focuses on the diagnosis of abnormal events related to fluid‐dynamic operating conditions. This methodology is based on an experimental characterization of the dynamic response of the pump under different loads and operation anomalies. The procedure has been put into practice on a medium‐sized centrifugal pump. The results obtained show that a simple spectral analysis of the pressure signals captured at either the inlet or the outlet of the pump can provide sufficient decision criteria to constitute the basis for a diagnostic system. This was not true however when analyzing signals of acceleration at the pump casing.

Performance characteristics and internal flow patterns in a reverse-running pump–turbine

Vaneless centrifugal pumps are reversible turbomachines that can operate also as centripetal turbines in low and very low-head power plants. However, the general performance in reverse mode is difficult to predict since the internal flow patterns are different from pump mode and the performance characteristics are not usually provided by manufacturers. This article presents numerical and experimental investigations on the operation of a reverse-running pump–turbine. The numerical calculations were carried out by solving the full unsteady Reynolds-averaged Navier–Stokes equations with the commercial code Fluent for several flowrates between 20 per cent and 160 per cent of rated conditions and both modes of operation. A complementary series of experimental measurements were performed in a test rig in order to obtain the general characteristics of the machine in pump and turbine modes, with the purpose of validating the numerical predictions. Once validated, the numerical model was used to investigate the flow patterns at some significant locations by means of pressure and velocity contours, and also by vector maps. Additionally, the model allowed the estimation of the steady load on the impeller as a function of flowrate in both modes of operation. It was concluded that, while the radial load in reverse mode is three times smaller than in pump mode, the axial load can be up to 1.6 times larger.

Numerical investigation of a centrifugal pump running in reverse mode

Abstract This article reports a work on the three-dimensional flow simulation in a centrifugal pump operating in reverse mode. The simulations were carried out with the commercial code Fluent using unsteady flow calculations together with a sliding mesh technique. Hence, it was possible to account for the effect of blade—tongue interactions on the local flow. The numerical predictions were compared with the experimentally determined performance characteristics and also with the static pressure distribution obtained around the periphery of the impeller. Once validated, the numerical model was used to investigate the global flow. Additionally, the total radial force (steady and unsteady components) on the impeller for a number of flowrates was estimated. It was found that the unsteady radial force (peak to peak) varied between 24 and 54.3 per cent of the steady value within the considered flow interval. The maximum force amplitude was reached when the trailing edge of one blade (pressure side) was located 3° downstream of the tongue tip.

A Numerical and Experimental Analysis of Flow in a Centrifugal Pump

Computational fluid dynamics (CFD) analysis has been used to solve the unsteady three-dimensional viscous flow in the entire impeller and volute casing of a centrifugal pump. The results of the calculations are used to predict the impeller/volute interaction and to obtain the unsteady pressure distribution in the impeller and volute casing. The calculated unsteady pressure distribution is used to determine the unsteady blade loading. The calculations at the design point and at two off-design points are carried out with a multiple frame of reference and a sliding mesh technique is applied to consider the impeller/volute interaction.

Measurements in the Dynamic Pressure Field of the Volute of a Centrifugal Pump

This paper presents an experimental investigation into the dynamic pressure field existing in the volute of an industrial centrifugal pump in order to characterize the interaction phenomena between impeller and volute. For that purpose, pressure signals were obtained simultaneously at different points of the volute casing by means of two miniature fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the passing blade frequency, regarding both amplitude and phase delay relative to a reference point. The analysis of the dependence of the pressure fluctuations on both flow-rate and position along the volute clearly indicates the leading role played by the tongue in the impeller-volute interaction and the increase of the amplitude of the dynamic forces in off-design conditions.

Fluidelastic instability in multispan heat exchanger tube arrays

An experimental study of fluidelastic instability in multispan heat exchanger tube arrays is presented. The experiments were conducted in a wind tunnel using a parallel triangular array of brass tubes with pitch ratio of 1·47. A variety of configurations were studied with up to four support plates, such that the spans between supports were of different lengths. Of particular concern were those configurations for which the conventional theory predicted instability in modes higher than the first. It is shown unequivocally for a number of cases that the conventional theory not only fails to predict the correct mode of instability but may also be substantially unconservative in predicting the critical velocity for fluidelastic instability. An alternative semi-empirical model is presented which predicted the observed critical model of instability and gave a conservative estimate of the critical velocity for all seven of the different configurations studied.