• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 33
  • 16
  • 12
  • 7
  • 1
  • 1
  • Tagged with
  • 89
  • 89
  • 26
  • 25
  • 25
  • 20
  • 15
  • 15
  • 9
  • 8
  • 7
  • 7
  • 7
  • 7
  • 7
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Testing of a repaired micro-concrete model of a cooling tower shell

Mozaffarian, Hossein January 2011 (has links)
Typescript (photocopy). / Digitized by Kansas Correctional Industries
32

Environmental impact: a critical review of implementing evaporative cooling system in Hong Kong

何美儉, Ho, Mei-kim. January 2002 (has links)
published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management
33

Analysis, synthesis and optimization of complex cooling water systems

Gololo, Khunedi Vincent January 2013 (has links)
Cooling water systems are used to remove excess heat from a chemical process to the atmosphere. The primary components of these systems are the cooling tower and the heat exchanger network. There is a strong interaction between these individual components, thus their performances are interrelated. Most published research in this area has focused mainly on optimization of the individual components i.e. optimization of heat exchanger network or optimization of the cooling towers. This approach does not optimize the cooling water system as a whole. Previous research work in which a holistic approach was used is limited to cooling water systems with single cooling water source. This work presents a technique for integrated optimization of complex cooling water systems. The system under consideration consists of multiple cooling towers each supplying a set of heat exchangers. A superstructural approach is employed to explore all possible combinations between the heat exchangers and the cooling towers. The cooling water reuse opportunities within the heat exchanger networks are also explored. A detailed mathematical model consisting of the cooling towers and the heat exchanger networks model is developed. Two practical scenarios are considered and the mathematical formulations for Case I and II yield nonlinear programing (NLP) and mixed integer nonlinear programming (MINLP) structure respectively. Although the reuse/recycle philosophy offers a good debottlenecking opportunity, the topology of the associated cooling water network is more complex, hence prone to higher pressure drop than the conventional parallel design. This is due to an increased network pressure drop associated with additional reuse/recycle streams. Therefore, it is essential to consider pressure drop during the synthesis of cooling water networks where the reuse/recycle philosophy is employed. The on-going research in this area is only limited to cooling water networks consisting of a single cooling water source. The common technique used is mathematical optimization using either superstructural or non superstructural approach. This work further presents a mathematical technique for pressure drop optimization in cooling water systems consisting of multiple cooling towers. The proposed technique is based on the Critical Path Algorithm and the superstructural approach. The Critical Path Algorithm is used to select the cooling water network with minimum pressure drop whilst the superstructural approach allows for cooling water reuse. The technique which was previously used in a cooling water network with single source is modified and applied in a cooling water network with multiple sources. The mathematical formulation is developed considering two cases. Both cases yield mixed integer nonlinear programming (MINLP) models. The cooling tower model is also used to predict the exit condition of the cooling tower given the inlet conditions from the cooling water network model. The results show up to 29% decrease in total circulating cooling water flowrate when the cooling water system is debottlenecked without considering pressure drop. Consequently, the overall cooling towers effectiveness was improved by up to 5%. When considering pressure drop the results showed up to 26% decrease in total circulating water flowrate. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Chemical Engineering / unrestricted
34

Investigation of performance enhancing devices for the rain zones of wet-cooling towers

Terblanche, Riaan 03 1900 (has links)
Thesis (MScEng)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: The performance of a natural draught wet-cooling tower can be improved by reducing the average drop size in the rain zone. In this thesis, the effect of installing different horizontal grids below the fill on drop size in the rain zone is investigated experimentally and theoretically. A specially designed horizontal grid consisting of evenly spaced slats and a grid made from expanded metal sheeting are tested. Drop size distribution measurements are taken below different cooling tower fills to determine the respective Sauter mean drop sizes and also below different configurations of splash grids to determine the reduction in drop size. Drop break-up through a grid of horizontally placed slats is modelled and compared to measured data to determine the optimum configuration in terms of spacing between the grid and fill, slat width and slat spacing. A cross flow rain zone is modelled under different air and water flow combinations with CFD for two distributions that represent the rain with and without splash grids and the results are compared. The Merkel transfer characteristic for all the flow conditions using both distributions are determined using a Lagrangian, Merkel, Poppe and e- NTU method in order to quantify the increase in rain zone Merkel number. Pressure drop over the cross flow rain zone is also determined and compared for the two distributions under considerations. / AFRIKAANSE OPSOMMING: Die verkoelingsvermoë van ‘n reënsone van ‘n natuurlike trek nat koeltoring kan verbeter word deur die verkleining van die gemiddelde druppelgrootte. In hierdie tesis word die effek wat horisontale roosters op die druppelgrootte het, wanneer dit onder die pakking geïnstalleer is, eksperimenteel en teoreties ondersoek. ‘n Spesiaal ontwerpte rooster bestaande uit horisontaal gepakte latte en ‘n gerolde metaal rooster word onderskeidelik vir hierdie doel gebruik. Druppelgrootte metings word geneem onder verskillende koeltoring pakkingsmateriaal om die Sauter gemiddelde diameter te bepaal, asook onder die verskillende rooster opstellings om die verkleinde druppelgrootte te bepaal wat die rooster veroorsaak. Druppelopbreking deur ‘n laag horisontaal gepakte latte word gemodelleer en vergelyk met gemete data om sodoende die beste kombinasie tussen die afstand onder die pakkingsmateriaal, latwydte en latspasiëring te bepaal. ‘n Kruisvloei reënsone word gemodelleer met CFD onder verkillende lug- en watervoeikombinasies vir twee druppelverdelings wat die reënsone met en sonder roosters verteenwoordig. Die Merkel oordragskoëffisiënt vir die twee verdelings word bereken en vergelyk deur van ‘n Lagrange- , Merkel- , Poppe- en e-NTU metode gebruik te maak om sodoende die verbetering in reënsone Merkelgetal te kwantifiseer. Drukvalle oor die reënsone word ook bereken en vergelyk vir die twee verdelings wat beskou is.
35

Evaluation of natural draught wet-cooling tower performance uncertainties

Van Der Merwe, Daniel 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2007. / ENGLISH ABSTRACT: A natural draught wet-cooling tower (NDWCT) was modelled using the Merkel method with an improved energy equation as recommended by Kloppers and Kroger (2005a) - referred to as the Improved Merkel method. The improved energy equation is used for calculating the heat rejection rate of the tower and includes the energy associated with water evaporation. The sensitivity indexes of a NDWCT were calculated numerically with the Improved Merkel method model. It was found that the perfonnance of a NDWCT is most sensitive to the fill Merkel number. The "Natklos" fill test facility at Stellenbosch University was used to estimate typical uncertainties found in fill performance characteristics. The zeroth order uncertainty for the Merkel number and loss coefficient was calculated to be 0.2100 m-1 and 0.4248 m- 1 , respectively, while the first order uncertainty for the Merkel number and loss coefficient was calculated to be 0.1933 m- 1 and 0.2008 m-1 , respectively. ASME requires that the uncertainty in tower capability has to be less than 6 % for a NDWCT perfonnance test to be deemed ASME approved. Propagating typical measurement uncertainties found in NDWCT test standards and experimental data into the tower capability showed that the 6 % uncertainty limit imposed by ASME is unrealistic and too stringent. Performance curve generator (PCG) is a software package developed that generates NDWCT perfonnance curves. With these performance curves it is possible to easily and effectively adjust the off-design test results in order to detennine whether the NDWCT has met its guarantee or not. / AFRIKAANSE OPSOMMING: Die werksverrigting van 'n natuurlike trek nat koeltoring (NTNT) is gemodelleer deur gebruik te maak van die Merkel metode met 'n verbeterde energie vergelyking, soos aanbeveel deur Kloppers en Kroger (2005a) - Verbeterde Merkel metode. Die energie vergelyking word gebruik om die toring se tempo van warmteoordrag te bereken en sluit die energieverlies as gevolg van verdamping in. Die Verbeterde Merkel metode model was gebruik om die sensitiwiteits-indekse van 'n NTNT te bepaal. Die analise toon dat die toring se werksverrigting die sensitiefste is vir die pakking se Merkel getal. Die Natklos pakkingstoetsfasiliteit aan die Universiteit van Stellenbosch was gebruik om tipiese onsekerheid in die pakkingsprestasiekarakteristieke te bepaal. Die zero-orde onsekerheid in die Merkel getal en verlieskoeffisient was bereken as 0.2100 m· 1 en 0.4248 m· 1 , onderskeidelik, terwyl die eerste-orde onsekerhede bereken was as 0.1933 m·1 en 0.2008 m· 1 , onderskeidelik. Die toelaatbare onsekerheid in toringvennoe vir 'n NTNT aanvaardingstoes volgens ASME is 6 %. Deur tipes meetonsekerhede, soos gegee deur NTNT aanvaardings-toesstandaarde sowel as eksperimentele data, deur te propageer, word 'n onsekerheid veel groter as die toelaatbare 6 % gegenereer. 'n Renekaarpakket, genaamd Performance Curve Generator (PCG), is ontwikkel om werksverrigtinskurwes vir 'n NTNT te genereer. PCG se werksverrigtinskurwes maak dit moonltik om maklik te bepaal of a NTNT sy ontwerpskriterea bereik het of nie.
36

Losses in the inlet section of counterflow wet-cooling towers

De Villiers, Eugene 12 1900 (has links)
One copy microfiche. / Thesis (MEng)--Stellenbosch University, 1998. / ENGLISH ABSTRACT: The flow resistances in the inlet sections of counterflow wet-cooling towers are investigated and correlations are derived for inclusion in a one-dimensional tower performance model. The rain zone loss is modelled using analytical-numerical methods. Experimental verification of the model produces satisfactory confirmation of the method's general validity. Semi-empirical correlations are produced to predict the loss coefficient as a function of six dimensionless variables for both rectangular and circular cooling towers. In addition, a study is made of the heat and mass transfer in the rain zone and its influence on tower performance. The inlet loss coefficients for dry, isotropically packed, circular and rectangular counterflow cooling towers are determined experimentally and empirical correlations are formulated to fit this data. The inlet losses for isotropic-resistance-fill towers are found to be higher than those for orthotropic-resistance-fill towers. Computational fluid dynamics is used to investigate the dependence of the inlet loss coefficient on the rain zone characteristics. The rain zone loss generally dampens the inlet loss, but this coupling is indirect and necessitates a large amount of dependent variables. The numerical model is validated by means of experimental data for dry towers and it is found that the degree of accuracy achieved for circular towers exceeds that for rectangular towers. Consequently, the correlation derived to predict this occurrence for circular towers, can be applied more confidently than its rectangular counterpart. An example is presented wherein the improved accuracy iQ tower performance prediction, when applying this correlation, is shown. Additional measures for tower performance enhancement are also explored. / AFRIKAANSE OPSOMMING: 'n Studie is gemaak van vloeiweerstande in die inlaat seksie van nat teenvloei koeltorings met die oog op die afleiding van korrelasies om die verskynsels, vir gebruik in puntmodel koeltoring simulasies, te voorspel. Die reensone verlies is gemodelleer met behulp van 'n analities-numeriese metode. Die model is geverifieer met behulp van eksperimentele toetse. Semi-empiriese korrelasies word afgelei wat die verlies, as 'n funksie van ses dimensielose veranderlikes, vir beide ronde en reghoekige koeltorings, voorspel. Daar word ook 'n studie gemaak van die hitte en massa oordrag in die reensone en hoe dit koeltorings se termiese oordrags vermoe be'invloed. Die inlaat verlies vir droe, isotropies gepakte, ronde en reghoekige koeltorings is eksperimenteel bepaal en empiriese korrelasies is geformuleer om die data te pas. Daar is gevind dat die inlaat verlies vir isotropies gepakte torings hoer is as die vir ortotropies gepakte torings. Numeriese vloei dinamika is gebruik om die afuanklikheid van die inlaat verlies se grootte op die reensone se eienskappe te ondersoek. Die algemene tendens is vir die reensone om die inlaat verlies te demp, maar die afuanklikheid is indirek sodat 'n groot aantal veranderlikes benodig word om die demping te karakteriseer. Die numeriese model word geverifieer deur middel van eksperimentele data vir droe koeltorings en daar word tot die gevolgtrekking gekom dat ronde torings heelwat meer akuraat gemodelleer word as reghoekige torings. Dit veroorsaak dat die korrelasie wat afgelei is om die demping te voorspel vir ronde torings, met baie meer vertroue toegepas kan word as sy reghoekige eweknie. 'n Voorbeeld word gedoen om die verbeterde akuraatheid in koeltoring modellering, wat verkry kan word met behulp van die vergelyking, te wys. Bykomende matrieels, om torings se verkoelings vermoe te verbeter, word ook ondersoek.
37

Design of medium pressure nozzles for cooling towers

Thacker, John Edward 05 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 1997. / One copy microfiche. / ENGLISH ABSTRACT: This project concerns the investigation of parameters controlling the behaviour of full-cone spray nozzles of the type used in cooling towers. In the present study large medium pressure hollow and full cone nozzles were investigated. A literature survey provided insight into the relationships between the nozzle dimensions and their spray characteristics, while equations found in the literature were used to correlate the experimental data. It was found that the spray cone angle of hollow cone nozzles could be manipulated by using rounded orifice outlets and this finding lead to the development of a uniquely profiled outlet that actually produces a square spray pattern. More experimental work was done to determine the relationship between the central jet of a full-cone nozzle and the other major nozzle dimensions. These results were then correlated and formulated into a set of guidelines for designing full-cone nozzles. / Digitized at 300 dpi Colour PDF format (OCR), using ,KODAK i 1220 PLUS scanner. Digitised, Ricardo Davids on request from Corinna 01 October 2014 / AFRIKAANSE OPSOMMING: Hierdie projek behels 'n studie van belangrike parameters in volkegel sproeimondstukke soos gebruik in koeltorings. In die huidige studie word groot mediumdruk holkegel en volkegel sproeimondstukke ondersoek. 'n Literatuurstudie het die nodige insig verskaf omtrent die verwantskap tussen mondstuk dimensies en hul spuitkarakteristieke, terwyl vergelykings uit die literatuur gebruik is om die eksperimentele data te korreleer. Dit was gevind dat die sproeir kegelhoek van die holkegelmondstuk verander kon word deur gebruik te maak van geronde uitlate. Afleidings wat gemaak is het gely tot die ontwikkeling van 'n unieke geprofielde uitlaat wat 'n vierkantige sproeipatroon gelewer het. Bykomstige eksperimentele werk is gedoen om die verwantskap tussen die sentralestraal van 'n volkegelmondstuk en die ander hoof mondstukdimensies te bepaal. Die reultate is verwerk om riglyne vir die ontwerp van vierkantige patroon volkegel mondstukke daar te stel.
38

Numerical analysis of flow around infinite and finite cylinders at trans-critical Reynolds numbers with and without surface roughness

Burger, Abri Andre Spies 03 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This thesis investigates the flow field and pressure distributions around cylinders at trans-critical Reynolds numbers using the k-ε Realizable turbulence model. A steady state 2-D and 3-D Fluent® model is successfully developed to evaluate the effects of changing various modelling parameters on the static pressure distribution around an infinite and finite cylinder. These parameters include surface roughness, cylinder rotation and air viscosity at the cylinder surface. The subsequent results obtained are compared to each other and to data trends from literature as well as measured experimental results and are found to be in good agreement. In addition a method for calibrating all developed methods based on their shear stress curves over a flat plate model is also successfully developed. The main objective is to find an appropriate single parameter which can be used for the rigorous adjustment of the pressure distribution around a cooling tower, which will allow for improved sensitivity analysis and modelling of cooling tower performance under wind conditions with and without meridional ribs located on the outer shell surface. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die vloeiveld en druk verdelings rondom silinders by trans-kritiese Reynolds getalle deur gebruik te maak van die k-ε Realizable turbulensie model. ‘n Bestendige toestand 2-D en 3-D Fluent® model is suksesvol ontwikkel om die uitwerking van die verandering van verskeie model parameters op die statiese druk verdeling rondom ‘n oneindige en eindige silinder te evalueer. Die laasgenoemde parameters sluit in oppervlak grofheid, silinder rotasie en lug viskositeit by die silinder wand. Die daaropeenvolgende resultate wat verkry word, word met data tendense uit die literatuur asook gemete data vanuit eksperimente vergelyk en goeie ooreenkoms i.t.v die data tendense is gevind. Verder is ‘n metode vir die suksesvolle kalibrasie van die ontwikkelde numeriese tegnieke ontwikkel. Die laasgenoemde kalibrasie metode is gebaseer op die vergelyking van skuifspanning kurwes vir vloei oor ‘n plat plaat model. Die hoofdoel van die navorsing is om ‘n geskikte enkele parameter te vind wat gebruik kan word vir die effektiewe aanpassing van die druk verdeling rondom ‘n koeltoring wat sal lei tot verbeterde sensitiwiteits analise en modellering van koeltoring verrigting onder wind toestande met en sonder meridionale ribbes geleë op die buitenste dop oppervlak.
39

The effects of dissolved solids in process cooling water and mine water on concrete corrosion.

Xulu, B. A. January 1998 (has links)
An investigation has been carried out to determine the effects of the dissolved solids in process cooling water (pcw) and mine water (mw) on concrete corrosion. An experimental set up was designed to simulate the process in the cooling towers of Sasol (Pty) Ltd at Secunda. The investigation was carried out using Ordinary Portland Cement (OPC) and Portland Blastfurnace Cement (PBFC). The corrosion process was monitored as a function of time by determining the concentrations of the ions left in solution. This was done using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Ion Chromatography (lC). The observation, identification and characterization of the secondary phases formed during the corrosion process were analyzed using the Scanning Electron Microscopy(SEM). Energy Dispersive X-ray Microanalysis (EDX) made it possible to identify the various microstructures and quantify their elemental composition. This made it possible to monitor the penetration of sulphate ions in the mortar. Powder X-ray Diffraction (XRD) qualitative analysis was also performed on the test mortar specimens. The organic constituents in process cooling water were determined using Gas Chromatography coupled with a Mass Spectrometer (GC-MS). The corrosion indices which measures the aggressiveness of water solutions towards cement and concrete were calculated for both process cooling water and mine water. The results of the investigation showed that mine water is more corrosive than process cooling water. This observation has been linked to the presence of the organic compounds in process cooling water. The results also indicated that PBFC was mores resistant to chemical attack than ope. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.
40

Re-inhabiting the void

Athienides, Despina 18 May 2005 (has links)
The challenge of this project is to turn a large residual empty space into a public place, a truly relational space. The site was decided upon first, and within its vastness the spirit of the surroundings arose which in turn gave birth to the development programme. At the stage where a site was chosen, no particular functional theme other than that of “adaptive reuse” existed. Located in the industrial sector of Pretoria West, the site was chosen for its ability to stun the visitor to silence with its scale and grandeur. Currently housing the Pretoria West Power Station, the visitor is confronted by structures which appear to be beyond the realm of human interaction. The dissertation explored the transformation of “urban void” to a public place where events can be held. This proposed events centre thrusts the landscape into the intervention, blurring the thresholds between inside and outside. The building itself has little regard for the boundaries imposed on it by the site. Purposely ignoring these limitations, the building extends its boundaries over the lake, creating space above untouched territory. The design aims to fragment the intervention into smaller experiences, which allows the visitor to engage more intimately with the intervention. This project addressed the issues of visual contact. / Dissertation (MArch(Prof))--University of Pretoria, 2007. / Architecture / unrestricted

Page generated in 0.0938 seconds