Hidrodinamičke pojave u centrifugalno vrtložnoj pumpi

Konstrukcija i određivanje radnih karakteristika pumpi je i dalje složen zadatak, prvenstveno zbog velikog broja slobodnih geometrijskih parametara čiji se utjecaj ne može direktno procijeniti. Značajna cijena koštanja konstruiranja pumpi na temelju eksperimentalnih istraživanja, tj. mjerenjima na prototipovima čini računalne simulacije temeljene na računalnoj mehanici fluida (engl. Computational fluid dynamics - CFD) najprihvatljivijim alatom pri konstruiranju i analizi radnih karakteristika pumpi. Međutim, nestacionarne pojave pri međudjelovanju rotora i statora, te nestabilnosti strujanja i dalje nužno zahtijevaju validaciju i verifikaciju dobivenih rezultata eksperimentalnim putem. Istraživanje energetske pretvorbe u centrifugalno vrtložnoj pumpi u ovom radu je provedeno numeričkim simulacijama strujanja u centrifugalnoj pumpi, centrifugalno vrtložnoj pumpi i vrtložnom dijelu centrifugalno vrtložne pumpe, te mjerenjima relevantnih parametara koji opisuju radne karakteristike pumpi na njihovim fizikalnim modelima. Rezultati mjerenja poslužili su kao eksperimentalna validacija numeričkih simulacija, ali i obrnuto, vizualizacija strujanja proizašla iz numeričke simulacije korištena je za interpretaciju mjerenja. Validacija numeričkog modela provedena je usporedbom dobivenih integralnih veličina, (protoka, visine dobave i snage) s izmjerenima na istovjetnim fizikalnim modelima. Također je provedena usporedba dobivenih veličina kod centrifugalne, centrifugalno vrtložne pumpe i vrtložnog dijela u cilju njihove usporedbe. Za potrebe provođenja eksperimentalnih istraživanja, u Laboratoriju za hidrodinamiku i hidrauličke strojeve Fakulteta strojarstva i brodogradnje u Zagrebu, izrađeni su fizikalni modeli centrifugalne i centrifugalno vrtložne pumpe koji odgovaraju numeričkim te eksperimentalna linija s pripadajućom opremom koja je omogućila promjenu broja okretaja, odabir radne točke te mjerenje trenutnog protoka, prirasta tlaka i snage pogonskog elektromotora. Numerička simulacija nestacionarnog strujanja u centrifugalnoj pumpi i centrifugalno vrtložnoj pumpi provedena je korištenjem aplikacijskog komercijalnog programskog paketa ANSYS Fluent za računalnu dinamiku fluida koji se temelji na metodi konačnih volumena. IV Provedena istraživanja su pridonijela pojašnjenju mehanizama energetske pretvorbe u centrifugalno vrtložnoj pumpi te potvrdila povoljni utjecaj vrtložnog vijenca na karakteristike iste (protok, tlak, iskoristivost, kavitacijska karakteristika)

Research of the Design Feasibility of a 3-Wheel Electric Vehicle with a Simplified Control System

The need for a simple, customised electric vehicle (EV) has inspired the research of the possibility to build a simple EV tailored for the specific needs of the buyer. This paper is focused on the concept of an EV with no conventional control mechanism. In this paper, a research of user needs, vehicle dynamics, vehicle aerodynamics, type of drive and batteries was carried out. EV aerodynamics characteristics were simulated by using the Computational Fluid Dynamics (CFD) software. The control system was designed in correlations with the maximal safe velocity and the radius of EV turning on a circular path. The stability of the EV, concerning the vehicle turning over and wheels slipping while driving in the curves, was the main concern of this paper. The steering wheel and brake pad were replaced with a control stick. Using the Finite Element Method (FEM) analysis, key parts of the construction were constructed

Experimental and Numerical Investigation of Centrifugal Vortex Pump Operating Benefits for Energy Efficient Systems

One of the ways to improve the performance of centrifugal pumps, proposed and experimentally validated by our research, is the method of creating so-called coherent structures, vortices and turbulence in the peripheral area of the centrifugal stage by adding a vortex rim to the back side of centrifugal rotor. A new construction of the pump, so called centrifugal vortex pump (CV), combines the good sides of these two types of pumps: high head of the vortex pump and high efficiency of the centrifugal pump. In addition, centrifugal pumps deliver higher flow rates with lower pressures, vortex pumps deliver higher pressures but with lower flow rates. For centrifugal vortex pumps, the vortex blades are located at the rear of the centrifugal rotor. The outer diameter of the vortex rim (VR) is smaller than the outer diameter of the centrifugal rotor (CR). The vortex rim induces vorticity to a portion of the flow that has passed through the centrifugal rotor. This vortexed flow is then reunited with the rest of the flow that has not been pulled down by vortex rotor. The vortex energy of that additional stream transfers some of its kinetic energy to the main stream. This added kinetic energy is converted to a pressure that accumulates the pressure exerted by the centrifugal rotor, and thus the vortex rim improves the overall pump performance. An intense process of gas dispersion occurs in the vortex region, which increases the stability of the pump when pumping a mixture of liquids and gases. The process of energy conversion in a centrifugal vortex pump, i.e., flow visualisation of mixing streams from a centrifugal rotor and a vortex rotor, and the quantization and superpositions have been shown in this paper

Analysis of Surface Curvature Influence on 3D Scanning Accuracy of Dental Castings

The main goal of this study is determining the influence of surface curvature on 3D scanning accuracy of dental castings. The hypothesis is that 3D scanning errors occur on the geometry (surfaces) of a higher curvature on the dental anatomy. Ten dental castings (five mandibular and five maxillar) were 3D scanned with four different dental 3D scanners. As a reference device Atos Core industrial 3D scanner was used. Using a qualitative-quantitative approach of dividing every tooth in three areas (OS – occlusal surface, CSB – crown surface buccal side, CSP – crown surface palatal side) and observing the frequency of maximal deviation for each area a deviation map was obtained, which shows on what area, are the biggest deviations and in which frequency they emerge. In total 160 teeth were analysed. To conclude, 3D scanning errors occur more frequently on the geometry (surfaces) of a higher curvature on the dental anatomy. Future work suggests conducting a full numerical analysis to find a correlation between the accuracy of 3D scanned teeth surface and a surface curvature. Comparing the 3D scanning deviation to the calculated curvature of the surface could unveil which curvature is hard to 3D scan and generates errors

Application of ecological principles in machining

Većina tekućina za obradu metala koje se primjenjuju za hlađenje i podmazivanje pri različitim postupcima obrade metala odvajanjem čestica formulirana je iz mineralnih ulja koja se izdvajaju iz sirove nafte. Zbrinjavanje otpadnih tekućina otvara brojna ekološka pitanja osobito kada se uzme u obzir da se radi o jednom od najsloženijih i najopasnijih vrsta otpada. Razvoj ekološke svijesti uz istovremeno donošenje novih, strožih zakonskih regulativa u svrhu zaštite prirodnih dobara kao i razvoj sustava za upravljanje zdravljem i sigurnošću osoba na radu sve više usmjeravaju proizvodnu industriju prema razvoju i implementaciji alternativnih tehnika hlađenja i podmazivanja u obradi metala te u konačnici suhoj obradi. Tako se danas već govori o posebno prilagođenoj obradi odnosno proizvodnji koristeći nazive "ekološki prihvatljiva obrada", "održiva proizvodnja", "zelena proizvodnja" i sl. U ovome radu istražuju se mogućnosti i prednosti primjene alternativnih tehnika hlađenja i podmazivanja, a posebno hlađenje vrtložnom cijevi. Također, evaluacija obrade obuhvaćena je eksperimentalnom studijom u svrhu razumijevanja vjerojatnih utjecaja korištenja hlađenja vrtložnom cijevi na troškove proizvodnje. Studija slučaja odnosi se na obradu martenzitnog nehrđajućeg čelika. Pokazano je da troškovi alata predstavljaju glavni doprinos ukupnom trošku proizvodnje i da u usporedbi s emulzijom za obradu metala hlađenje vrtložnom cijevi nudi ekonomično rješenje na putu prema održivoj obradi.Most metalworking fluids used for cooling and lubrication in various machining processes are formulated from mineral oils separated from crude oil. Disposal of waste fluids opens numerous ecological issues, especially considering that it is one of the most complex and hazardous waste types. Developing environmental awareness while at the same time adopting new, stricter legal regulations for the protection of natural assets as well as developing health and safety management systems for people at work are increasingly directing the manufacturing industry towards the development and implementation of alternative cooling and lubrication techniques in machining and ultimately dry machining. Thus, today it is already talking about specially adapted machining or manufacturing using the terms "environmentally friendly machining", "sustainable manufacturing", "green manufacturing" and the like. In this paper, the possibilities and advantages of using alternative cooling and lubrication techniques, especially cooling with a vortex tube, are explored. In addition, the machining evaluation was covered by an experimental study in order to understand the likely effects of the use of cooling with the vortex tube on the production costs. The case study concerns the machining of martensitic stainless steel. It is shown that tool costs represent a major contribution to the total production cost and that in comparison with the metalworking emulsion the cooling with the vortex tube offers an economical solution on the route to sustainable machining