353 research outputs found
Performance characteristics of a centrifugal pump impeller with running tip clearance pumping solid-liquid mixtures
No full textThis paper presents extensive results on the performance of an unshrouded centrifugal pump impeller handling solid-liquid mixtures. The effect of the clearance between the impeller tip and the casing and of the solid concentration, density and mean diameter on the pump performance characteristics is investigated. The results are discussed and utilized, together with data available in the literature, to establish a correlation allowing the prediction of the head reduction factor for sit shrouded/unshrouded impeller centrifugal punips handling solid-liquid mixtures. The predictions made with the proposed correlation show a better agreement with experimental results than previous ones
Comparative evaluation of some existing correlations to predict head degradation of centrifugal slurry pumps
No full textIn order to optimally design a slurry transportation system, it is necessary to know how the presence of solids will change the performance of the slurry pump to be installed. This paper makes the comparison of some existing correlations available in the literature to predict the head reduction factors of such centrifugal pumps handling slurries. For this purpose, a large number of published data for various centrifugal slurry pump tests in the literature have been used to develop a new correlation and then this correlation and all others have been tested against the data. For the proposed correlation, the mean and average deviations between the calculated and measured head reduction factor is 8.378 and 0.620%, respectively, for all data of mostly handling commercial slurries. It also produces 12.441 % mean deviation in the prediction of efficiency ratio for 216 data points. Overall, the new correlation that can be applied to both metal and rubber lined pumps with impeller diameter up to 850 mm, gives remarkably closer fit to the published data of both head and efficiency ratios than all existing correlations
Effects of tip clearance and impeller geometry on the performance of semi-open ceramic centrifugal fan impellers at elevated temperatures
No full textCentrifugal fans are being widely used in many industrial applications. However, when handling gases with temperatures exceeding 800 degrees C, the use of centrifugal fan impellers are of particular interest since the conventional steel impellers would not be operated at such elevated temperatures. In the present experimental study, three semi-open centrifugal fan impellers have been designed and fabricated using ceramic materials to provide high resistance to temperature. Experiments have been conducted to investigate the performance characteristics of these impellers and the deteriorations in their performance due to varying tip clearance. Factors have been determined to estimate the tip clearance losses. Results showed that the simple impeller geometries of ceramic materials were less sensitive to the varying tip clearance. In addition, the gas temperature has been found to have almost no influence on the performance degradation due to the tip leakage flow. (C) 2005 Elsevier Inc. All rights reserved
Exergy analysis of laminar fluid flow in stainless steel microtubes
No full textIn the study, exergy analysis of steady laminar fluid flow in stainless steel microtubes with diameters between 103 mu m and 179 mu m were conducted in the adiabatic conditions experimentally. The exergy losses were obtained for deionised water flowing in rough microtubes with the surface relative roughness of 2-6%. Results indicated that the exergy loss was in a good agreement with the conventional theory and the increasing in relative roughness leads to increasing exergy loss. As Re increases, measured exergy losses were found to be significantly higher than that of the predicted values
Second law analysis of water flow through smooth microtubes under adiabatic conditions
No full textIn the study, a second law analysis for a steady-laminar flow of water in adiabatic microtubes has been conducted. Smooth microtubes with the diameters between 50 and 150 mu m made of fused silica were used in the experiments. Considerable temperature rises due to viscous dissipation and relatively high pressure losses of flow were observed in experiments. To identify irreversibility of flow, rate of entropy generation from the experiments have been determined in the laminar flow range of Re = 20-2200. The second law of thermodynamics was applied to predict the entropy generation. The results of model taken from the literature, proposed to predict the temperature rise caused by viscous heating, correspond well with the experimental data. The second law analysis results showed that the flow characteristics in the smooth microtubes distinguish substantially from the conventional theory for flow in the larger tubes with respect to viscous heating/dissipation (temperature rise of flow) total entropy generation rate and lost work. (C) 2010 Elsevier Inc. All rights reserved
EXPERIMENTAL VALIDATION OF LMTD METHOD FOR MICROSCALE HEAT TRANSFER
No full textThe single phase fluid flow and heat transfer characteristic has been investigated experimentally. Experiments were conducted to cover transition zone for the Reynolds numbers ranging from 100 to 4800 by fused silica and stainless steel microtubes having diameters of 103-180 mu m. The applicability of the Logarithmic Mean Temperature Difference (LMTD) method was revealed and an experimental method was developed to calculate the heat transfer coefficient. Moreover the scaling effects in micro scale such as axial conduction, viscous heating and entrance effects were discussed. The heat transfer coefficients were compared with data obtained by the correlations available in the literature in the study. The Nusselt numbers of microtube flows do not accord with the conventional results when the Reynolds number was lower than 1000. After that, the Nusselt number approaches the conventional theory prediction. On the aspect of fluid characteristics, the friction factor was well predicted with conventional theory and the conventional friction prediction was valid for water flow through microtube with a relative surface roughness less than about 4 %
INVESTIGATION OF THE VISCOUS HEATING EFFECT AT SINGLE-PHASE LAMINER WATER FLOW IN MICROTUBES
No full textIn the study, experimental and numerical study have been conducted with microtubes having diameters range between 50 and 150 mu m to investigate viscous heating effects on the single-phase water flow. In the experiments temperature rises due to viscous heating have been measured under adiabatic conditions. Numeric analysis of flow through the adiabatic microtubes was performed by taking into account viscous heating effects using by computational fluid dynamic (CFD) code ANSYS CFX 12.0. CFD results were compared both experimental and analytical model results
Performance improvements for unplanned high density wireless LANs
No full textChaotic unplanned IEEE 802.11 WLAN deployments are becoming the norm and such residential deployments have many nearby access points (APs) and stations on the same channel, either due to lack of coordination or insufficient available channels. Thus, inter-cell interference in these high-density settings is common but not well-understood. Our evaluations for such interfering deployments reveal that up-to two-thirds of the WLAN system capacity may be lost in a typical large-apartment building with 50 interfering WLANs In this thesis, we first report on our analysis of high-density unplanned WLANs' performance under realistic scenarios. We find that with a typical TCP-dominant workload, cumulative system throughput is characterized by the number of actively interfering APs rather than the number of clients. We verify that due to TCP flow control, the number of backlogged stations in such a network equals twice the number of active APs. Thus, a single AP network proves very robust even with over one hundred clients, while multiple interfering APs lead to a significant increase in collisions that reduces throughput and affects multimedia traffic. Based on our analysis, we suggest a practical contention window adaptation technique, WiPhi, using information on the number of nearby APs rather than clients. We also point out the need for collision-resilient rate adaptation in such a setting. Together these techniques can largely recover the loss in cumulative throughput in a setting with strongly interfering APs. We then propose an alternative ISP-level solution, HeedNet, recovering lost performance by scheduling the IP packets of the bulk traffic at the ISP edge-router towards interfering APs. It requires no changes to the MAC protocol and the APs of the network, making it a viable solution for ISPs. We evaluate HeedNet via simulations and an actual deployment to show that a significant portion of the lost system capacity can be regained (more than 2.2X improvement compared to legacy). HeedNet also increases the fairness, reducing starvation among WLANs. Additionally, we show that HeedNet improves the performance of the non-scheduled (i.e., non-bulk) traffic considerably, such as VoIP, due to the reduced-collision rate environment it creates.Ph.D.Includes bibliographical referencesIncludes vitaby Mesut Ali Ergi
Measuring the service quality of student affairs at higher education and an examplary application of it
No full textKumru, Mesut (Dogus Author) -- Yıldız Kumru, Pınar (Dogus Author)Due to its main characteristics of intangibility, inseparability, heterogeneity andperishability, it is quite difficult to describe and measure the service quality in general. A number of methods have been developed to measure service quality in the application areas. As one of these methods, SERVQUAL is to be used in this study to measure the service quality of student affairs at higher education and the gaps between expected service and perceived performance for the service beneficiaries are derived.Hacettepe Üniversitesi, Valör Kongre Organizasyonlar
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