Numerical simulations of the flow in the elbow draft tube of a Kaplan turbine were carried out in order to elucidate the effects of tail water level on draft tube performance and flow stability. The influence of the tail water level is explored considering the correct boundary condition at the inlet of the draft tube. It is found that the increasing tail water level affects the inlet boundary condition of the draft tube, the flow rate through the turbine, and draft tube. Thus, head recovery, efficiency and the possibility of cavitation phenomena decreases. However, the head loss increases, and the flow rate through the turbine and draft tube decreases.

Microfiltration is an important process in the pharmaceutical industry. Filter selection and validation is a time-consuming and expensive process. Quality by design approach is important for product safety. The article covers the instrumentalization and process control of a laboratory-scale dead-end microfiltration layout. The layout is a downscale model of the actual production line, and the goal is filter validation and analysis of process parameters, which may influence filter operation. Filter size, fluid pressure, valve plunger speed, and timing issues were considered. The focus is on the identification of the most influential process parameters and their influence on the repeatability of pressure oscillations caused by valve opening. The goal was to find the worst-case scenario regarding pressure oscillations and, consequently, filter energy intake. The layout was designed as compact as possible to reduce pressure losses between the filter and valve. Valve-induced pressure oscillations proved to be prevailing over the water hammer effect. Several filters in sizes between 3.5 cm2 and 6900 cm2 were tested, and some recommendations were suggested for the reduction of energy intake of the filter and to improve the repeatability of the process.

This paper presents experimentally obtained flow characteristics inside the vane passage of a vented brake disc and at the brake disc exit. The flow conditions of three different brake discs were compared: a basic design with straight vanes and two prototypes with different vane heights, shapes (airfoil shape) and numbers. The possible effect on brake disc cooling performance was studies. Hot-wire anemometry was applied to measure the pumping performance of different discs, and particle imaging velocimetry was used to map the velocity field. All three discs were tested on a brake disc dynamometer according to the SAE J2522 standard, and the maximum temperature was measured during the thermal capacity test. No prototype outperformed the original brake disc. Moreover, the brake disc with the increased vane thickness and reduced vane height (prototype C) performed significantly worse, whereas prototype B, designed with an increased vane height and increased number of vanes, performed similarly to the original brake disc. A comparison of the flow characteristics of the three discs indicated that the significant decrease in the cooling airflow rate deteriorated the cooling performance of prototype C the most. On the other hand, the improved pumping performance did not improve the cooling performance of prototype B. Only the comparison of the internal cooling air flow pattern of the original and prototype B brake discs revealed the reason. While the characteristic jet-wake flow structure formed within the vane passage of the original brake disc, the inter-vane channel flow within brake disc B was distributed much more uniformly in a circumferential direction, with significantly lower flow velocities near the pressure vane side. This reduced the convective heat transfer on the brake disc vanes, which number, as well as the heat transfer surface area increased without the desired cooling effect.

In filling lines equipped with membrane separation devices in the form of filters energy, consumption is only one of the important working parameters, the other being sustainable filter performance in terms of separation efficiency. As the filling line is typically equipped with a valve, intermittent operation of the filter is an important form of its use. Whereas the overall energy consumption of the filtration process is governed by the continuous operation mode, the intermittent mode, characterised by opening/closing of the valve, contributes most to problems of filter failure, i.e., the breakthrough of filtered particles through the membrane. A model for determination of the energy intake of a microfiltration membrane during the opening and closing of a valve is presented in this work. The model is based on computational analysis of the pressure wave signals recorded during the opening/closing of the valve using Fourier transform, and expressed in a nondimensional filter area specific energy intake form. The model is applied to a case of constant pressure dead-end microfiltration with three filter types: a single membrane filter, a stacked filter and a pleated filter with filtration surface areas ranging from 17.7 cm2 to 2000 cm2. Both clean filters, as well as partially clogged filter cases are taken into account. Second order polynomial models of the energy intake are developed and evaluated based on extensive analysis of the experimental data. The analysis of energy intake results show that the largest energy intake was observed for the clean filter case. When membrane fouling occurs at the constant flow rate values it leads to larger energy intake, however, due to a decreasing specific flow rate during fouling these values do not exceed the clean filter case.

The objective of this study was to determine the density of anaerobic granules on different heights of a full-scale Upflow Anaerobic Sludge Bed reactor. The density was defined through the settling velocities of anaerobic granules, measured in a full-scale Upflow Anaerobic Sludge Bed reactor. In this study, granular density was calculated with the measured settling velocities and developed mathematical model. The developed mathematical model is based on the Stokes model. In the experiment, granules were taken from different heights of an Upflow Anaerobic Sludge Bed reactor, from 0.6 to 7.6 m. The granules' diameters varied between 1 and 5 mm. The granules were taken from six different heights through the reactor. The settling velocity of the active granules (with gas in the granule pore and on the surface of the granule) was measured first. After the active granules' settling velocity measurement, the granules were placed in a vortex to obtain degassed granules (granules without any gas in the pores or on the surface), for which the settling velocities were also measured later. It is shown that granules' densities at different heights are independent of the reactor height.

The investment decision support tool was developed, which can be applied to check the technical feasibility and economic viability of an Organic Rankine Cycle system, and to select the appropriate working fluid, based only on basic information on the waste heat source, i.e. source temperature and mass (heat) flow rate.Two profitability criteria, Net Present Value and Payback Period, were introduced for economic evaluation, while an Organic Rankine Cycle design correlations-based model was developed, and applied for prediction of technical parameters and components' design estimation.Validation performed with the previously published data confirmed model accuracy in spite of its simplicity.The model gave quick answers, and was incorporated successfully into a decision algorithm, which was supported by a set of system component design and cost functions, and could serve as an effective tool for preliminary feasibility evaluation of any proposed Organic Rankine Cycle based waste heat recovery system.An example of model application over the broad range of waste heat source temperatures is presented and the results discussed in order to show its basic capabilities.

A trash rack is applied in front of the turbine to restrict the entrance of significantly sized material present in the water. It obstructs the free flow, and produces energy-losses by generating eddies induced partially by the trash rack bars and partially by the debris collected on it. While the additional static forces due to debris accumulation are considered in the trash rack design process, the debris caused energy losses taking place during plant operation are usually neglected, although a rather simple model was developed to account for them. However, the long term application of this model demands an extensive set of trash rack clogging data and, therefore, no such application has been documented so far. Thus, an analysis was performed to acquire the debris accumulation intensity with time and to evaluate the extra energy losses they caused. Data on one year operation of a hydropower plant aggregate i.e. flow rate and trash rack head losses measured at 15 minute intervals, were acquired and used to build a rack clogging model. Using this model, it was possible to distinguish clearly between debris and rack structure caused head losses. and to analyse different cleaning strategies. It was shown that cumulative debris contributed to almost one half of head losses although the rack was cleaned frequently. This shows clearly that debris caused head losses may not be neglected, moreover, debris removal has to be planned carefully and carried out efficiently. Analyses of acquired data confirmed that incomplete debris removal increased head losses by 18 %, and proved how important regular and thorough rake cleaning is. Moreover, it was found out that the actually applied periodical rake cleaning was not optimal, and that the circumstances required cleaning strategy performed much better. It resulted in similar head losses, while the number of rack cleanings was reduced by 60 %.

In this study angle-resolved flow-fields within the rotor passage of an axial fan operating under rotating stall conditions were measured with the use of Particle Imaging Velocimetry (PIV) and the application of phase-resolved visualisation. More than 1000 random PIV images of the observed blade's passing were obtained during the first step. These were then phase-locked averaged, and a sequence composed of angle-resolved flow-fields. The successive PIV images represented the evolution of a flow field within the blade passage influenced by the rotating stall cell. This paper reports on the phase-locked averaging procedure. The influence of the reference signal, i.e. dynamic pressure time-history ahead of the rotor, was studied on composed flow-fields and their measurement uncertainties. Three averaging procedures were developed and compared using the criteria of minimal velocity variation along the selected flow-path. Measurement uncertainty improved substantially when the characteristic shape and not the frequency of the reference signal was used for the phase-shift averaging.

The electrical losses during hydroelectric generator operation may account for 1 to 2% of electricity production, and represent an interesting heat potential. The generator cooling water temperature is low, and application of a mechanically driven heat pump represents, therefore, a reasonable solution when, however, it is also economically viable. A simplified techno-economic model was built in order to check the economic viability of such waste heat recovery system. The model enables the source and sink heat temperature, as well as, heat flow rate to be variated and the basic heat pump parameters estimated including its COP and investment cost. An oil boiler system is assumed as a waste heat recovery system alternative. It serves for economical comparison and evaluation of the net present value and payback period of any proposed low temperature waste heat recovery system configuration.

Rezultati raziskav vpliva biodizla in njegovih mešanic z gorivom D2 na delovanje dizelskih motorjev so si pogosto nasprotujoči. Medtem ko velja glede emisij splošna ugotovitev o zmanjšanju koncentracije saj ter zvečanju NOx, pa so si ugotovitve o emisijah nezgorelih oglikovodikov in CO pogosto nasprotujoče. Tudi poročanje o zmanjšanju emisij NOx ni redko. Vzrok za tako različne ugotovitve tiči najverjetneje v različnih razmerah raziskovanja, motorjih z različno obliko zgorevalnega prostora, različnih sistemih za vbrizg goriva in podobno. Da bi analizirali mogoče vplive, smo opravili raziskave na dveh različnih dizelskih motorjih. Izmerili smo obratovalne in emisijske značilke pri delovanju z biodizlom in gorivom D2 ter posneli indikatorske diagrame, s katerimi smo lahko analizirali potek zgorevanja. Rezultati so pokazali, da ugotovitev o vplivu biodizla na potek zgorevanja in emisijske značilke ne smemo posploševati, saj se za oba obravnavana motorja pomembno razlikujejo. © 2007 Strojniški vestnik. Vse pravice pridržane. (Ključne besede: bio-goriva, zgorevanje, dizelski motorji)

The losses caused by the debris accumulated on the trash rack of a 20 MW hydropower plant aggregate were obtained and analyzed experimentally. Data for one year of operations was collected and processed. Using a simple temperaturecompensated model, it was possible to distinguish clearly between the losses caused by the trash rack itself and by the debris collected on the trash rack. This made it possible to examine the seasonal effect of the debris on the head losses and to predict the optimal frequency of trash rack cleaning, as well as annual losses during electricity production and power plant economics in general. The analysis showed that the annual losses could be reduced significantly by applying an optimal cleaning strategy. However, an optimal strategy is difficult to predict, because of the stochastic nature of the amount of debris drifting daily in the river. It is much easier to perform cleaning as circumstances require by determining an optimal upper limit of head loss above which the trash rack should be cleaned. Using this approach, the total number of trash rack cleanings per year was reduced, while the extra energy losses due to debris remains unchanged.

V gradivu so opisane osnovne metode merjenja pomembnejših fizikalnih veličin na področju strojništva. V uvodnem poglavju je podana obravnava posplošenega merilnega sistema, definirani so njegovi funkcionalni elementi in opisani načini delovanja ter postopki merjenja. Prikazan je tudi vpliv interferenčnih in modifikatorskih vhodnih veličin na rezultate merjenja, poleg tega so podane metode za zmanjšanje tega vpliva. Karakteristike merilnih inštrumentov so opisane v drugem poglavju. Začenjajo ga statične karakteristike, ki so v večjem delu posvečene pogreškom in merilni negotovosti. V nadaljevanju pa so opisane dinamične karakteristike in kot primer sta predstavljena merilna sistema prvega in drugega reda. Merjenje temperature je obravnavano v tretjem poglavju. Uvodoma sta predstavljeni termodinamična in mednarodna temperaturna lestvica. Sledi opis postopkov merjenja temperature, ki ga začenjajo klasične in nato še električne metode kontaktnega merjenja temperature, zaključuje pa ga brezkontaktno merjenje s sevalnimi termometri. V četrtem poglavju je obravnavano merjenje pomika z analognimi električnimi merilnimi sistemi ter z optičnimi digitalnimi merilniki. Merjenje hitrosti in pospeška v petem poglavju je omejeno na merjenje vibracij in vrtilne frekvence. Prikazano je delovanje mehanskih, električnih, optičnih in digitalnih elektronskih merilnih sistemov. V šestem poglavju je predstavljeno merjenje deformacij z merilnimi trakovi. Prikazane so najpogostejše električne vezave merilnih trakov in obravnavani so osnovni eno- in dvoosni obremenitveni primeri. Analizirani so vzroki za nastanek pogreškov, razloženi pa so tudi postopki za njihovo zmanjšanje. Merjenje tlaka v sedmem poglavju je razdeljeno na merjenje statičnih tlakov z različnimi kapljevinskimi manometri in mehanskimi merilniki z elastičnimi pretvorniki, merjenje nizkodinamičnih tlakov z električnimi manometri ter visokodinamičnih tlakov s piezoelektričnimi senzorji. V osmem poglavju so predstavljeni postopki merjenja pretoka tekočin z dušilnimi elementi, volumetričnimi merilniki in različnimi električnimi merilniki. Prikazane so tudi osnovne metode za merjenje hitrosti tekočine z ultrazvočnimi in laserskimi metodami.

This paper compares the vapour ejector and electric vacuum pump power consumptions with machine learning algorithms by using real process data and presents some novelty guideline for the selection of an appropriate condenser vacuum pump system of a steam turbine power plant. The machine learning algorithms are made by using the supervised machine learning methods such as artificial neural network model and local linear neuro-fuzzy models. The proposed non-linear models are designed by using a wide range of real process operation data sets from the CHP system in the thermal power plant. The novelty guideline for the selection of an appropriate condenser vacuum pumps system is expressed in the comparative analysis of the energy consumption and use of specific energy capable of work. Furthermore, the novelty is expressed in the economic efficiency analysis of the investment taking into consideration the operating costs of the vacuum pump systems and may serve as basic guidelines for the selection of an appropriate condenser vacuum pump system of a steam turbine. (C) 2016 Elsevier Ltd. All rights reserved.

An unsteady flow field with rotating stall cells in an axial flow fan has been investigated experimentally. In order to capture the behaviour of the rotating stall cell, measurements of the flow field at the rotor inlet and velocity field within the rotor blade passage at an 80 % span were carried out with the PIV system. Those data were processed by socalled “phase-locked averaging” technique, which enabled to capture the flow field of the rotating stall cell in the reference co-ordinate system fixed to the rotor. As a result, a sequence of 18 images was composed at the three different flow rates and the behaviour of the rotating stall cell has been analysed.

The description of the combustion process in internal combustion engines is typically performed through so-called combustion parameters, such as: the maximum combustion pressure, maximum temperature of the cycle, crankshaft angle of the start of combustion, the angular interval of duration of combustion, the heat release characteristics, thee increment of the total amount of heat developed, the angular interval of combustion delay, the heat transfer etc. Due to the complexity of the combustion process in internal combustion engines to this day there are still no models that could efficiently and above all in a reliable way predict the heat release characteristics for a wide range of different types of IC engines. Phenomenological, empirical and CFD models for specific constructive characters of the engine and fuel applied are targeted explored. The paper presents a procedure for determining the heat release characteristics through approximate functions of combustion, using the example of a very specific way of preparing a mixture of fuel and air in the diesel engine, so-called M-procedure. The applied approximate function is validated through experimental test results on a specific IC engine.

Currently, conventional energy sources i.e. fossil fuels represent the main segment as regards electricity generation. Thus, their contribution to global CO2 emissions is considerable. This study considers carbon capture and storage (CCS) as a promising solution for the environmental problems we are now facing. Based on previous research, post-combustion capture (PCC) has been recognized as being the more appropriate technology for CO2 capturing from the existing power plants. The main purpose of our study was to investigate the correlation between the efficiency of carbon dioxide capturing and its influence on the reduction of electricity production efficiency and levelized cost of electricity at the new unit VI of the thermal power plant of TE Sostanj, Slovenia. A zero-dimensional model was used for appropriately considering the flows of mass and energy within the PCC system as a function of carbon dioxide capture efficiency and a rather simple cost model was applied for predicting the additional levelized electricity cost due to PCC system implementation. By changing the efficiency of the capture system, as well as the evaluated prices of carbon emission coupons, our results show the possible economic eligibilities of the PCC system in the future.

The presented paper introduces a performed study into the possibility of replacing mineral diesel fuel with pure biodiesel fuel or their blends with diesel fuel. The presented work was carried out experimentally and numerically on a heavy-duty bus diesel engine using mineral diesel fuel, neat biodiesel fuel made from rapeseed oil and their 25% (B25), 50% (B50) and 75% (B75) blends. The influence of biodiesel fuel and blends on engine combustion, performance and emission characteristics was studied experimentally on an engine test-bed and numerically using an AVL BOOST simulation program. A new empirical sub-model for determining a combustion model parameters was proposed within a BOOST program. All the model's parameters were determined regarding the properties of the tested fuel and engine speed. The obtained results show a reduction in engine power and torque when increasing the percentage of biodiesel fuel in the fuel blends due to lower calorific value of biodiesel fuel. Higher oxygen content in the biodiesel and blends contributed to a better oxidation process within the combustion chamber, which resulted in a reduction of carbon oxides (CO) and nitrogen oxides (NOx) at three different engine speeds (1360, 1700 and 2000 min(-1)) and full throttle position. Both the experimental and numerical results indicated that neat biodiesel or biodiesel-diesel blends can be used within a heavy-duty diesel engine with modified static fuel delivery angle (injection pump timing) of the mechanically-controlled injection system. (C) 2014 Elsevier Ltd. All rights reserved.

Visualisation of a flow field was performed within the rotor blade passage of an axial flow fan operating under rotating stall conditions. A PIV system was used to capture the velocity field at an 80% span of the rotor blade. PIV triggering was synchronized with the observed blades' passing, and over 1000 PIV images were obtained. These were then phase-locked averaged, and a sequence of 36 images was composed. The successive images represented the evolution of a flow field within the blade passage with 10 angular steps and made it possible for the structure and behaviour of the flow within the rotor blade passage to be analysed under rotating stall conditions. The initiation and development of flow distortion were clearly shown to be influenced by the advance of the rotating stall cell and the restoration of normal flow with the rotating stall cell moving away. (C) 2014 Elsevier Inc. All rights reserved.