Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: A 1.5 x 1.5 m2 counter-flow fill performance test facility is described in detail. Instrumentation was selected and installed in the cooling tower fill test facility and calibrated to ensure measurement accuracy. A facility control program was written to simplify the operation of the test facility via a user interface. The program calculates automatically the Merkel number and loss coefficients as measures of fill thermal and flow performance respectively. A spray frame was designed and manufactured to ensure uniform water distribution to the fill. The water distribution through different fills with varying fill heights and different water flow rates was measured. The water attached to the walls of the test facility was examined. Film, trickle and splash fills are tested in the upgraded test facility. The film and trickle fill performance determined during testing is deemed acceptable as these fills have minimal migration effects. Fills with poor distribution effects and large migration of water towards the walls of the test facility, like the splash fill tested, cannot to be tested accurately in a 1.5 x 1.5 m2 test section as the results do not represent the performance of the fill in a relatively large cooling tower. Other aspects examined were: • air flow uniformity • air fill bypass effects • location of water inlet and outlet temperature measurement points • location of pressure measurement probes. It was determined that, in the current test facility: • air uniformity is suitable for performance testing • air bypass effects can be ignored for open fills and can be minimised for dense fills by packing sponge between the fill and walls • water inlet and outlet temperatures should be measured in the pipe-work, resulting in a measurement method that is not influenced by the relative weightings of each thermocouple • pressure difference over the fill height measured by the pressure measurement tap is independent of its location on the fill outlet plane provided the pressure measurement points are perpendicular to the air stream and are not against the walls. / AFRIKAANSE OPSOMMING: 'n 1.5 x 1.5 m² Teenvloei pakking werkverrigting toetsfasiliteit word in detail beskryf. Instrumentasie is gekies en geïnstalleer in die koeltoring pakking toetsfasiliteit en gekalibreer om akkuraatheid te verseker. 'n Fasiliteit beheer program is geskryf om die gebruik van die toetsfasiliteit te vereenvoudig. Die program het ‘n vriendelike gebruikers intervalk. Die program bereken outomaties die Merkel-getal en verlies koëffisiënte as mate van pakking termiese- en vloeiwerksverrigting. 'n Sproeiraam is ontwerp en vervaardig om uniforme water verspreiding aan die pakking te verseker. Die water verspreiding deur verskillende pakkings met verskillende pakking hoogtes en water vloei snelhede is gemeet. Die water aangeheg aan die mure van die toetsfasiliteit is ook ondersoek. Film, druppel en spat pakkings word in die opgegradeerde toetsfasiliteit getoets. Die film- en druppelpakking werksverrigting bepaal tydens die toetse is aanvaarbaar, aangesien hierdie pakkings minimale migrasie effekte het. Pakking met swak verspreiding effekte en 'n groot migrasie van water na die wande van die toetsfasiliteit, soos gevind met die spatpakking toetse, kan nie met akkuraatheid in 'n 1.5 x 1.5 m² toets seksie getoets word nie omdat die resultate nie die werkverrigting van die pakking verteenwoordig in 'n relatief groot koeltoring. Ander aspekte wat ondersoek was: • lugvloei uniformiteit • lug omleiding effeckte • die posisie van water in- en uitlaat temperatuur meetpunte • posisie van die drukmeetapparaat. Dit is vasgestel dat, in die huidige toetsfasiliteit • lugvloei eenvormigheid geskik is vir prestasietoetsing • lug omleiding effekte kan geïgnoreer word vir oop pakkings en kan verklein word vir digte pakkings deur spons tussen die pakking en mure te pak • water inlaat- en uitlaattemperature behoort gemeet te word in die pypwerk en lei tot 'n metings metode wat nie beïnvloed word deur die relatiewe gewigte van elke thermokoppel nie • die druk verskil gemeet deur die drupmeetpunte oor die pakkinghoogte is onafhanklik van hul posisie op die pakkinguitlaatvlak op voorwaarde dat die drukmeetpunte loodreg is teen die lugstroom en nie teen die mure nie.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: A passive night-sky radiation cooling system consists of a radiation panel and a cold water storage tank. The stored cold water may be used to cool a room during the day time, particularly in summer. In this thesis a theoretical and mathematically sound simulation model is developed. An experimental set-up was constructed and subsequently used to show that the theoretical model effectively simulates the transient heating or cooling response of the system. It is shown that under South African conditions the typical heat emitting rate during the night is 55 W/m2. After the heat has been removed from the water, it is stored in a cold water tank from where it is circulated through a natural convector during the day time to absorb heat from the room. The experiment extracted a minimum of 102 W/m3 of heat from a 1.87 m3 galvanized steel room while a brick room with a volume of 120 m3 requires 22.7 W/m3. Additional to cooling, the system during the day, absorbed an average of 362 W of energy and heated 68 l of water from 24 °C to 62 °C within an 8-hour period. The system achieved similar results during winter conditions and the experiment confirms that the system is capable of operating without a control system. Therefore it is recommended that renewable energy-conscious designers pay more attention to the use of night-sky radiation cooling in future. / AFRIKKANSE OPSOMMING: en ’n koue water tenk. Die sisteem kan gebruik word om ’n vertrek gedurende die dag te verkoel, veral in die somer, deur gebruik te maak van die gestoorde verkoelde water. In hierdie tesis word ’n teoretiese en sinvolle wiskundige simulasie model ontwikkel. ’n Eksperimentele stelsel is gebou en vervolgens gebruik om te bewys dat die teoretiese model die veranderende verkoeling en verwarming van die stelsel effektief simuleer. Die tesis dui aan dat onder Suid Afrikaanse toestande daar ’n hitte vrystellings tempo van 55 W/m2 is gedurende die nag. Nadat die water verkoel is, word dit gestoor in die koue water tenk vanwaar dit deur ’n natuurlike konvektor sirkuleer en gedurende die dag warmte vanuit die vertrek onttrek. Die eksperiment het ’n minimum van 102 W/m3 warmte vanuit die galvaniseerde 1.87 m3 vertrek geabsorbeer, terwyl ’n baksteen vertrek van 120 m3, 22.7 W/m3 verkoeling benodig. Bykomstig tot die verkoelingstelsel verhit die sisteem 68 l water vanaf 24 °C to 62 °C gedurende ’n 8-uur periode in die dag, dus word 362Wenergie geabsorbeer. Die sisteem is ook getoets tydens winter toestande, die resultate was dieselfde as wat in die somer verkry is. Verder is daar ook bewys dat die sisteem sonder enige beheerstelsel kan funksioneer. Verder word daar aanbeveel dat hernubare energie bewuste ontwerpers in die toekoms meer aandag aan ruimte straling verkoeling skenk.

Denna studie är utförd på uppdrag av DGL AB. Syftet var att utreda varför temperaturen inte sjunker till önskad nivå i två olika kylrum vilka används för nedkylning och förvaring av färdigförpackade livsmedel. Arbetet genomfördes med hjälp av förlustberäkningar samt temperaturmätningar för att kunna identifiera och uppskatta storlek samt procentuella skillnader på olika förlustfaktorer. Praktiska mätningar på plats utgjorde underlag för de resultat som redovisas i arbetet. Kyleffektbehov har beräknats och baserats på företagets maximala produktion av färdig vara per dygn. I resultaten framkom att kylmaskinens effekt var väl dimensionerad men att kylelementens kapacitet i kylrummen var för låg med tanke på mängden förluster. Studien resulterade i förslag på minskning av transmissionsförluster genom isolering av väggar och tak i respektive kylrum samt även isolering av kylvattentanken belägen i kylrum 2. Rengöring av kylelementens flänsar, komplettering eller byte till andra mer effektavgivande kylelement var ytterligare förslag på åtgärder. / This study is conducted on behalf of DGL AB. The purpose was to investigate why the temperature does not drop to the desired level in two different cooling storages whom are used for cooling and storing of prepackaged groceries. The project was carried out with the help of loss calculations and temperature measurements to identify and estimate size as well as percentage differences in different loss factors. The sites measurements outlined the basis for this project. The cooling effect requirement is calculated based on the company's actual maximum production amount per day. The results showed that the effect of the cooling unit is oversized, however the cooling radiators capacity was too low considering the amount of losses. The outcome of the study suggest a decrease in thermal transmission losses through isolation of walls and ceilings in each of the cooling storages as well as isolation of the cooling water tank located in cooling storage 2. Cleaning of the cooling radiators flanges, supplementing or replacing with other cooling radiators that has more power output was additional suggestions to the result.

Advancements in the networking and routing industry have created higher power electronic systems which dissipate large amounts of heat while cooling technology for these electronic systems has remained relatively unchanged. This report illustrates the development and testing of a hybrid liquid-air cooling system prototype implemented on Cisco’s 7609s router. Water was the working fluid through cold plates removing heat from line card components. The water was cooled by a compact liquid-air heat exchanger and circulated by two pumps. The testing results show that junction temperatures were maintained well below the 105°C limit for ambient conditions around 30°C at sea level. The estimated junction temperatures for Cisco’s standard ambient conditions of 50°C at 6,000 feet and 40°C at 10,000 feet were 104°C and 96°C respectively. Adjustments to the test data for Cisco’s two standard ambient conditions with expected device characteristics suggested the hybrid liquid-air cooling design could meet the projected heat load.

During this investigation, vibration induced droplet generation from a liquid layer was examined as a means for achieving high heat flux evaporative cooling. Experiments were performed in which droplets were generated from a liquid layer using a submerged vibrating piezoelectric driver. Parameters determined during this investigation of droplet generation were droplet mass flow rate, droplet size, driver frequency, driver voltage, and liquid layer thickness. The results showed that as the liquid layer thickness was increased, the frequencies and frequency ranges at which droplet generation occurred decreased. Droplet mass flow rates were varied by adjustment of the liquid layer thickness, driver frequency, and driver voltage. The dependence of the drivers displacement, velocity, and acceleration on frequency and voltage was determined, and the drivers frequency response was related to the occurrence of droplet generation. As a result, a frequency-dependent dimensionless parameter was proposed as a method for predicting droplet generation from the surface of the liquid layer. The dimensionless parameter is a combination of the Froude number and the dimensionless driver acceleration. The measurements have shown that droplet generation occurs when the parameter is between distinct upper and lower bounds. An analytical heat transfer model of a droplet cooling heat transfer cell was developed to simulate the performance of such a cell for thermal management applications. Using droplet flow rates determined as functions of driver voltage, driver frequency, liquid layer thickness, and interception distance, the heat transfer rate of a droplet cooling heat transfer cell was predicted for varied heat source temperatures and cell conditions. The heat transfer model was formulated in such a way as to accommodate a number of parameter variations that can be used for the design of a simple heat transfer cell. The model was used to determine the effect of droplet cooling on the heat transfer rate from a heated surface, but it can also be used to determine the influence of any of the other embodied parameters that may be of interest for thermal management applications.

High combustion temperatures and long operation durations require the use of cooling techniques in liquid propellant rocket engines. For high-pressure and high-thrust rocket engines, regenerative cooling is the most preferred cooling method. In regenerative cooling, a coolant flows through passages formed either by constructing the chamber liner from tubes or by milling channels in a solid liner. Traditionally, approximately square cross sectional channels have been used. However, recent studies have shown that by increasing the coolant channel height-to-width aspect ratio and changing the cross sectional area in non-critical regions for heat flux, the rocket combustion chamber gas side wall temperature can be reduced significantly without an increase in the coolant pressure drop. In this study, the regenerative cooling of a liquid propellant rocket engine has been numerically simulated. The engine has been modeled to operate on a LOX/Kerosene mixture at a chamber pressure of 60 bar with 300 kN thrust and kerosene is considered as the coolant. A numerical investigation was performed to determine the effect of different aspect ratio cooling channels and different number of cooling channels on gas-side wall and coolant temperature and pressure drop in cooling channel.

Efficiency improvement in turbomachines is an important aspect in reducing the use of fossil-based fuel and thereby reducing carbon dioxide emissions in order to achieve a sustainable future. Gas turbines are mainly fossil-based turbomachines powering aviation and land-based power plants. In line with the present situation and the vision for the future, gas turbine engines will retain their central importance in coming decades. Though the world has made significant advancements in gas turbine technology development over past few decades, there are yet many design features remaining unexplored or worth further improvement. These features might have a great potential to increase efficiency. The high pressure turbine (HPT) stage is one of the most important elements of the engine where the increased efficiency has a significant influence on the overall efficiency as downstream losses are substantially affected by the prehistory. The overall objective of the thesis is to contribute to the development of gas turbine efficiency improvements in relation to the HPT stage.   Hence, this study has been incorporated into a research project that investigates leading edge contouring near endwall by fillet and external cooling on a nozzle guide vane with a common goal to contribute to the development of the HPT stage. In the search for HPT stage efficiency gains, leading edge contouring near the endwall is one of the methods found in the published literature that showed a potential to increase the efficiency by decreasing the amount of secondary losses. However, more attention is necessary regarding the realistic use of the leading edge fillet. On the other hand, external cooling has a significant influence on the HPT stage efficiency and more attention is needed regarding the aerodynamic implication of the external cooling. Therefore, the aerodynamic influence of a leading edge fillet and external cooling, here film cooling at profile and endwall as well as TE cooling, on losses and flow field have been investigated in the present work. The keystone of this research project has been an experimental investigation of a modern nozzle guide vane using a transonic annular sector cascade. Detailed investigations of the annular sector cascade have been presented using a geometric replica of a three dimensional gas turbine nozzle guide vane. Results from this investigation have led to a number of new important findings and also confirmed some conclusions established in previous investigations to enhance the understanding of complex turbine flows and associated losses.   The experimental investigations of the leading edge contouring by fillet indicate a unique outcome which is that the leading edge fillet has no significant effect on the flow and secondary losses of the investigated nozzle guide vane. The reason why the leading edge fillet does not affect the losses is due to the use of a three-dimensional vane with an existing typical fillet over the full hub and tip profile. Findings also reveal that the complex secondary flow depends heavily on the incoming boundary layer. The investigation of the external cooling indicates that a coolant discharge leads to an increase of profile losses compared to the uncooled case. Discharges on the profile suction side and through the trailing edge slot are most prone to the increase in profile losses. Results also reveal that individual film cooling rows have a weak mutual effect. A superposition principle of these influences is followed in the midspan region. An important finding is that the discharge through the trailing edge leads to an increase in the exit flow angle in line with an increase of losses and a mixture mass flow. Results also indicate that secondary losses can be reduced by the influence of the coolant discharge. In general, the exit flow angle increases considerably in the secondary flow zone compared to the midspan zone in all cases. Regarding the cooling influence, the distinct change in exit flow angle in the area of secondary flows is not noticeable at any cooling configuration compared to the uncooled case. This interesting zone requires an additional, accurate study. The investigation of a cooled vane, using a tracer gas carbon dioxide (CO2), reveals that the upstream platform film coolant is concentrated along the suction surfaces and does not reach the pressure side of the hub surface, leaving it less protected from the hot gas. This indicates a strong interaction of the secondary flow and cooling showing that the influence of the secondary flow cannot be easily influenced.   The overall outcome enhances the understanding of complex turbine flows, loss behaviour of cooled blade, secondary flow and interaction of cooling and secondary flow and provides recommendations to the turbine designers regarding the leading edge contouring and external cooling. Additionally, this study has provided to a number of new significant results and a vast amount of data, especially on profile and secondary losses and exit flow angles, which are believed to be helpful for the gas turbine community and for the validation of analytical and numerical calculations. / Ökad verkningsgrad i turbomaskiner är en viktig del i strävan att minska användningen av fossila bränslen och därmed minska växthuseffekten för att uppnå en hållbar framtid. Gasturbinen är huvudsakligen fossilbränslebaserad, och driver luftfart samt landbaserad kraftproduktion. Enligt rådande läge och framtidsutsikter bibehåller gasturbinen denna centrala roll under kommande decennier. Trots betydande framsteg inom gasturbinteknik under de senaste årtionden finns fortfarande många designaspekter kvar att utforska och vidareutveckla. Dessa designaspekter kan ha stor potential till ökad verkningsgrad. Högtrycksturbinsteget är en av de viktigaste delarna av gasturbinen, där verkningsgraden har betydande inverkan på den totala verkningsgraden eftersom förluster kraftigt påverkas av tidigare förlopp. Huvudsyftet med denna studie är att bidra till verkningsgradsförbättringar i högtrycksturbinsteget.   Studien är del i ett forskningsprojekt som undersöker ledskenans framkantskontur vid ändväggarna samt extern kylning, i jakten på dessa förbättringar. Den aerodynamiska inverkan av en förändrad geometri vid ledskenans ändväggar har i tidigare studier visat potential för ökad verkningsgrad genom minskade sekundärförluster. Ytterligare fokus krävs dock, med användning av en rimlig hålkälsradie. Samtidigt har extern kylning i form av filmkylning stor inverkan på verkningsgraden hos högtrycksturbinsteget och forskning behövs med fokus på den aerodynamiska inverkan. Av denna anledning studeras här inverkan både av ändrad hålkälsradie vid ledskenans framkant samt extern kylning i form av filmkylning av skovel, ändvägg och bakkant på aerodynamiska förluster och strömningsfält. Huvudpelaren i detta forskningsprojekt har varit en experimentell undersökning av en geometrisk replika av en modern tredimensionell gasturbinstator i en transonisk annulärkaskad. Detaljerade undersökningar i annulärkaskaden har gett betydande resultat, och bekräftat vissa tidigare studier. Detta har lett till ökad förståelsen för de komplexa flöden och förluster som karakteriserar gasturbiner.   De experimentella undersökningarna av förändrad framkantsgeometri leder till den unika slutsatsen att den modifierade hålkälsradien inte har någon betydande inverkan på strömningsfältet eller sekundärförluster av den undersökta ledskenan. Anledningen till att förändringen inte påverkar förlusterna är i detta fall den tredimensionella karaktären hos ledskenan med en redan existerande typisk framkantsgeometri. Undersökningarna visar också att de komplexa sekundärströmningarna är kraftigt beroende av det inkommande gränsskiktet. Undersökning av extern kylning visar att kylflödet leder till en ökad profilförlust. Kylflöde på sugsidan samt bakkanten har störst inverkan på profilförlusten. Resultaten visar också att individuella filmkylningsrader har liten påverkan sinsemellan och kan behandlas genom en superpositionsprincip längs mittsnittet. En viktig slutsats är att kylflöde vid bakkanten leder till ökad utloppsvinkel tillsammans med ökade förluster och massflöde. Resultat tuder på att sekundärströmning kan minskas genom ökad kylning. Generellt ökar utloppsvinkeln markant i den sekundära flödeszonen jämfört med mittsnittet för alla undersökta fall. Den kraftiga förändringen i utloppsvinkel är dock inte märkbar i den sekundära flödeszonen i något av kylfallen jämfört med de okylda referensfallet. Denna zon fordrar ytterligare studier. Spårgasundersökning av ledskenan med koldioxid (CO2) visar att plattformskylning uppströms ledskenan koncentreras till skovelns sugsida, och når inte trycksidan som därmed lämnas mer utsatt för het gas. Detta påvisar den kraftiga interaktionen mellan sekundärströmning och kylflöden, och att inverkan från sekundärströmningen ej enkelt kan påverkas. De generella resultaten från undersökningen ökar förståelsen av komplexa turbinflöden, förlustbeteenden för kylda ledskenor, interaktionen mellan sekundärströmning och kylflöden, och ger rekommendationer för turbinkonstruktörer kring förändrad framkantsgeometri i kombination med extern kylning. Dessutom har studien gett betydande resultat och en stor mängd data, särskilt rörande profil- och sekundärförluster och utloppsvinkel, vilket tros kunna vara till stor hjälp för gasturbinssamfundet vid validering av analytiska och numeriska beräkningar. / <p>QC 20140909</p> / Turbopower, Sector rig

Distributionsförluster är en viktig faktor i fjärrenergisystem. Genom att optimera förluster i sådana system, kan både ekonomiska och miljömässiga aspekter uppfyllas. Tyvärr finns det ringa information om rörförluster i fjärrkylasystem. Föreliggande studie fokuserar på förluster i ett fjärrkylanät genom att både använda ett R-nätverk och FEM simuleringsmodeller. Ett R-nätverksmodell bestående av termiska konduktanser har utvecklats genom analytiska ekvationer och simuleringar med FEM har utfört för validering av modellen. Därefter har ett fjärrkylanätverk som konstrueras i Gävle, analyserats. Undersökningen omfattar 15 olika rördiametrar i tre utföranden (dubbelrör med två symmetriska och en osymmetrisk värmeisolering) och i tre förläggningsdjup (0,8; 2 och 4 meter) för en säsong om 7 månader (April t o m Oktober). Särskilt utreds ökningen av temperaturen hos framledningsmediet, där matningsrören förlagts i en å mitt i staden om en sträcka av 1 km. Den maximala förlusten under säsongen, bland alla rörkonfigurationer, motsvarar 2 % av den totala levererade energin. Slutligen konstateras att kombinationen av isolerad framledningsrör och oisolerade returrör verkar som en gångbar investering, ekonomiskt och tekniskt, men kan inte användas i hela nätet eftersom stora delar har redan byggts med oisolerade plaströr. R-nätverksmodellen, som visades vara effektiv och pålitlig i undersökningen, kan som beräkningsverktyg, framförallt för dimensionering och för att uppskatta energiförluster. / Distribution losses are a very important factor in district energy systems. By optimizing the losses in such a system, both economical and environmental aspects can be fulfilled. Unfortunately, there is few information regarding losses for district cooling systems. This study focuses on losses in district cooling networks by using both R-network and FEM simulation models. A R-network model composed of thermal conductances has been developed through analytical equations and simulations have been performed for validation. Afterwards, an in-progress construction project of a district cooling network from the city of Gävle, Sweden, is analyzed. The assessment consists of 15 pipe diameters in three configurations (two symmetric cases and one asymmetric), at three ground laying depths (0.8, 2 and 4 meters) for a duration of 7 months (April to October). A particular case in which the main distribution pipes from and to the plant are submerged in the city’s river for a distance of 1 km is investigated in order to estimate the temperature increase of the supply water. A maximum cooling loss below 2% of the total delivered energy during the season for any network configuration resulted from the calculation. Finally, the mixed pipes array seems to be a feasible investment both economically and technically but it cannot be used for the entire network spread since a part of the network has been already built with the non-insulated plastic pipes. The R-network model proved to be effective and reliable in the analysis which provides confidence that it can serve as a solid foundation for a calculation tool - primarily for design purposes and also for estimating energy loss.

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted

The diploma thesis aims to prepare a study of the cooling system of a multifunctional building with regard to climate change predicted until the middle of the 21st century. The work includes determining the heat load of refrigerated rooms and designing measures to reduce heat gains in the summer. Diploma thesis includes design of a cooling system with fan-coil units as end appliances with the necessary hydraulic calculations. A single-stage absorption cooling unit is used as the considered cooling source, to which a free cooling heat exchanger is assigned. The design of the cooling source includes the necessary hydraulic calculations and dimensioning of the system ensuring its functional operation. Part of the diploma thesis is drawing documentation of cooling technology and connection of fan-coil units.