Experimental and Numerical Analysis of a Non-Newtonian Fluids Processing Pump

Abstract Centrifugal pumps are used in many applications in which non-Newtonian fluids are involved: food processing industry, pharmaceutical and oil/gas applications. In addition to pressure and temperature, the viscosity of a non-Newtonian fluid depends on the shear rate and usually is several orders of magnitude higher than water. High values of viscosity cause a derating of pump performance with respect to water. Nowadays, pumping and mixing non-Newtonian fluids is a matter of increasing interest, but there is still lack of a detailed analysis of the fluid-dynamic phenomena occurring within these machines. A specific design process should take into account these effects in order to define the proper pump geometry, able to operate with non-Newtonian fluids with specific characteristics. Only few approaches are available for correcting the pump performance based on the Hydraulic Institute method. In this work, an experimental and numerical campaign is presented for a semi–open impeller centrifugal pump elaborating non-Newtonian fluids. An on-purpose test bench was built and used to investigate the influence on pump performance of three different non-Newtonian fluids. Each pump performance test was accompanied by the rheological characterization of the fluid, in order to detect modifications of the rheological phenomena and allow a proper Computation Fluid Dynamics (CFD) modeling. The performance of the machine handling both Newtonian and non-Newtonian fluids are highlighted in relation with the internal flow field

Termofluidodinamica applicata ai processi industriali di pastorizzazione e raffreddamento

Nel campo delle tecnologie alimentari, sempre di più le problematiche di scambio termico stanno evidenziandosi come una frontiera di studi e analisi in quanto poco o per niente considerate fino ad oggi. In particolare, lo scambio termico tra sistemi di condizionamento degli alimenti (refrigerazione, essicazione, pastorizzazione, abbattimento della temperatura) ed alimenti stessi presenta livelli di difficoltà molto elevati a causa delle proprietà dei materiali, della modalità di scambio termico e della presenza contemporanea di più fasi di processamento. Uno dei settori a maggiore interesse è quello dei liquidi imbottigliati. Questi, al loro interno scambiano calore tramite il fenomeno della convezione naturale ma all’esterno scambiano calore tramite convezione forzata. L’influenza sul processo di questi fenomeni viene condizionata dalla natura del fluido stesso che può presentare comportamento diverso se si dovesse trattare di fluidi con caratteristiche del tutto simili all’acqua, fluido dal comportamento noto in molte condizioni diverse, o di fluidi alimentari ottenuti come soluzioni acquose di polpe di frutti diversi. Essendo nell’ambito alimentare, tutti i trattamenti devono rispettare le condizioni igienico sanitare richieste dalle normative che richiedono anche la verifica sperimentale della realizzazione del trattamento termico come ad esempio la verifica delle unità di pastorizzazione dopo il trattamento di pastorizzazione in uno dei prodotti più consumati al mondo, la birra. Il progetto intende affrontare le principali problematiche legate ai trattamenti di pastorizzazione degli alimenti tramite macchine a tunnel con strumenti analitici (VEM) e numerici (CFD) e con prove sperimentali condotte presso un laboratorio esterno all’Università degli Studi di Ferrara dove si svolge il corso del Dottorato. Il progetto, infatti, è il frutto della collaborazione tra l’università e una azienda leader mondiale nella produzione di macchina a tunnel per il trattamento termico di prodotti alimentari di nome Sidel che ha sede a Verona e che mette a disposizione i laboratori e tutta la conoscenza sviluppata e accumulata nel corso degli anni.In the field of food technologies, heat exchange problems are increasingly emerging as a frontier of studies and analyzes as they are little or not considered to date. In particular, the heat exchange between food conditioning systems (refrigeration, drying, pasteurization, temperature reduction) and food itself presents very high levels of difficulty due to the properties of the materials, the heat exchange method and the simultaneous presence of more processing phases. One of the sectors of greatest interest is that of bottled liquids. These, inside them exchange heat through the phenomenon of natural convection but outside they exchange heat through forced convection. The influence on the process of these phenomena is conditioned by the nature of the fluid itself which can exhibit different behavior if it were to deal with fluids with characteristics very similar to water, fluid with a behavior known in many different conditions, or food fluids obtained as aqueous solutions of pulps of different fruits. Being in the food sector, all treatments must comply with the sanitary conditions required by the regulations which also require experimental verification of the realization of the heat treatment such as the verification of the pasteurization units after the pasteurization treatment in one of the most consumed products at the world, beer. The project aims to address the main problems related to food pasteurization treatments using tunnel machines with analytical (VEM) and numerical (CFD) instruments and with experimental tests conducted at a laboratory outside the University of Ferrara where the course takes place of the Doctorate. The project, in fact, is the result of the collaboration between the university and a world leader in the production of tunnel machines for the heat treatment of food products named Sidel which is based in Verona and which provides the laboratories and the whole knowledge developed and accumulated over the years

The effects of third substances at the particle/surface interface in compressor fouling

Since the beginning of the 1950s, manufacturers and operators have struggled to understand, reduce and eliminate compressor fouling and its effects on gas turbine operation. Several devices (inertial separators, barriers, filters, etc.) and strategies (on-line and off-line washing, manual cleaning, etc.) have been adopted in order to limit and/or eliminate the foulants which stick to the compressor blade and vane surfaces. The state of the power plant design and installation and environmental conditions determine the rate of fouling and, in turn, gas turbine performance losses. The types of contaminant (organic or inorganic), their concentration and their ability to stick are variable depending on the weather conditions. Desert, tropical, rural, and off-shore conditions are characterized by different foulants with different characteristics which determine compressor fouling. In this paper, an analysis of the influence of third substances at the particle/surface interface is presented. The analysis is carried out on two different compressor rotors, transonic and subsonic. Firstly, a sensitivity analysis is proposed related to the particle diameter and foulant mixture in order to highlight the influence of air humidity due to environmental conditions or the pressure drop after the filtration stages. The effects of a water electrolytic solution (generated by the presence of inorganic matter) and a water surfactant solution (used in the case of washing) are also considered. In this case, the properties of the mixture substance (solid particles bound by a liquid film) are considered. Secondly, using previous numerical analyses (particle-laden flow with a Eulerian-Lagrangian approach) as a starting point, the variation in particle sticking ability is evaluated against the presence of third substances (water solutions and oily substances) and the particle kinematic characteristics using a sticking model based on an energy balance equation. The results show the influence of the third substance on particle sticking capability using a susceptibility-to-fouling criterion. Particularly in the presence of humid conditions, sticking capability increases with respect to dry conditions, even though the major effects are due to the mixture viscosity and not only to the presence of liquid water. The sticking capability of the mixture varies according to particle diameter as a function of the particle normal velocity. The results are presented in order to easily quantify the effects of the presence of a third substance at the particle/surface interface according to the type of liquid phase involved in the sticking process

Quantitative CFD analyses of particle deposition in a heavy-duty subsonic axial compressor

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the microparticles not captured by the air filtration system can cause deposits on blading and, consequently, result in a decrease in compressor performance. In literature there are some studies related to the fouling phenomena in transonic compressors, but in industrial applications (heavy-duty compressors, pump stations, etc.) the subsonic compressors are widespread. It is highly important for the manufacturer to gather information about the fouling phenomenon related to this type of compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion (0.15 μm - 1.50 μm) in a multistage (i.e. eight stage) subsonic axial compressor, carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The adopted computational strategy allows the evaluation of particle deposition in a multistage axial compressor thanks to the use of a mixing plane approach to model the rotor/stator interaction. The compressor numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in literature. The number of particles and sizes are specified in order to perform a quantitative analysis of the particle impacts on the blade surface. The blade zones affected by particle impacts and the kinematic characteristics (velocity and angle) of the impact of micrometric and sub-micrometric particles with the blade surface are shown. Both blade zones affected by particle impact and deposition are analyzed. The particle deposition is established by using the quantity called sticking probability, adopted from literature. The sticking probability links the kinematic characteristics of particle impact on the blade with the fouling phenomenon. The results show that micro-particles tend to follow the flow by impacting on the compressor blades at full span. The suction side of the blade is only affected by the impacts of the smallest particles. Particular fluid dynamic phenomena, such as corner separations and clearance vortices, strongly influence the impact location of the particles. The impact and deposition trends decrease according to the stages. The front stages appear more affected by particle impact and deposition than the rear ones

Quantitative computational fluid dynamics analyses of particle deposition in a heavy-duty subsonic axial compressor

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the microparticles not captured by the air filtration system can cause deposits on blading and, consequently, result in a decrease in compressor performance. In the literature, there are some studies related to the fouling phenomena in transonic compressors, but in industrial applications (heavy-duty compressors, pump stations, etc.), the subsonic compressors are widespread. It is highly important for the manufacturer to gather information about the fouling phenomenon related to this type of compressor. This paper presents three-dimensional (3D) numerical simulations of the microparticle ingestion (0.15–1.50 lm) in a multistage (i.e., eight stage) subsonic axial compressor, carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The adopted computational strategy allows the evaluation of particle deposition in a multistage axial compressor thanks to the use of a mixing plane approach to model the rotor/stator interaction. The compressor numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in the literature. The number of particles and sizes is specified in order to perform a quantitative analysis of the particle impacts on the blade surface. The blade zones affected by particle impacts and the kinematic characteristics (velocity and angle) of the impact of micrometric and submicrometric particles with the blade surface are shown. Both blade zones affected by particle impact and deposition are analyzed. The particle deposition is established by using the quantity called sticking probability (SP), adopted from the literature. The SP links the kinematic characteristics of particle impact on the blade with the fouling phenomenon. The results show that microparticles tend to follow the flow by impacting on the compressor blades at full span. The suction side (SS) of the blade is only affected by the impacts of the smallest particles. Particular fluid dynamic phenomena, such as corner separations and clearance vortices, strongly influence the impact location of the particles. The impact and deposition trends decrease according to the stages. The front stages appear more affected by particle impact and deposition than the rear ones