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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.

Mine cooling system components are an integral part of a mine‟s ventilation system. A mine‟s reliance on these capital intensive components are set to increase as mines deepen. Mine cooling systems consume up to a quarter of the electricity used on mines. Component efficiency should be monitored to ensure optimum utilisation. Downtime should be minimised so that production is not negatively influenced. Replacing expensive components in an age of severe economic pressure should be avoided altogether. In this study, the performance of mine cooling system components was monitored. The effects of various operational and maintenance interventions on component performance have been quantified. Quantifying the effects of management decisions led to the refining of operational procedures, the optimisation of future maintenance, and the subsequent identification of electrical energy savings potential without the need for expensive modifications. Investigations show that a mine could realise a saving of up to nine hundred thousand rand annually by optimising the maintenance schedule of chillers. Extrapolated results estimate an electrical energy saving of 52 127 MWh per year if the strategy were implemented on twenty of South Africa‟s biggest mines. In addition, a monetary saving in excess of five hundred thousand rand could be saved through refining operational procedures. These strategies will be possible without the need for expensive installations or complicated modifications. Monitoring cooling system performance allows management to identify trends in performance, to understand component inter-dependence, and to allow for informed decision-making. In addition, performance monitoring allows for the identification of component and instrumentation faults. Statistical control charts and simulation modelling are some of the tools that have been employed in this study. These tools assist management formulate strategies and decisions with a higher degree of confidence. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

Today nucleate boiling is widely used in numerous industrial applications such as cooling processes because of the high achieved heat transfer rates for low temperature differences. It remains a possible cooling solution for the next generation of central processing units (CPU), which dissipate heat fluxes exceeding the capabilities of today’s conventional forced air cooling. However, nucleate boiling is a very complex and elusive process involving many mechanisms which are not fully understood yet and a comprehensive model is still missing. For this study a new experimental setup was designed, constructed and commissioned to investigate bubble nucleation, growth, departure and interaction during nucleate pool boiling from a silicon device fully immersed in fluorinert FC-72. The location of bubble nucleation is controlled by artificial cavities etched into the silicon substrate. Boiling is initiated with a heater integrated on the back and micro-sensors indicate the wall temperature at the bubble nucleation site. During this work three different silicon test section designs were fabricated and boiling experiments on these substrates successfully conducted. Bubble growth, bubble departure frequencies and bubble departure diameters for different dimensioned artificial cavities, varied pressure and increasing wall temperature were measured from high-speed imaging sequences. Bubble interactions like vertical and horizontal coalescence were visualised and their impact on the boiling heat transfer investigated. The influence of spacing between two neighbouring artificial cavities on bubble nucleation and departure frequencies, vertical coalescence frequencies and departure diameters was analysed. The acquired data are used as input for a numerical code developed by our collaborators (Brunel University, UK and Los Alamos National Laboratories, USA) and are a first step to validate the code. The code studies the interactions between bubble nucleation sites on solid surfaces as a network. The simulations will help design boiling substrates utilised for chip cooling applications with optimal artificial cavity distribution to maximise the cooling heat transfer.

CIVINS / Carbon nanotubes (CNTs) exhibit exceptional electrical, thermal, and mechanical properties that could potentially transform such diverse fields as composites, electronics, cooling, energy storage, and biological sensing. For the United States Navy, composites potentially provide a significant decrease in lifetime maintenance costs of ships by eliminating hull corrosion. A stronger composite could also improve naval ship survivability or increase combat payloads by reducing the hull weight of ships and submarines. Further, cooling requirements of ship borne electronics have grown exponentially and represent a significant weight penalty for advanced ship designs. Any improvement in thermal transport could significantly improve future naval ship designs. In order to realize these benefits, methods must be discovered to fully characterize CNT growth mechanisms, consistently produce CUTs in manufacturable quantities, and to integrate CUTs into macroscale structures which reflect the properties of individual CUTs. While growth of CNTs in laboratory scale chemical vapor deposition (CVD) tube furnaces has shown great promise, existing low cost tube furnace designs limit the researcher's ability to fully separate critical reaction parameter such as temperature and flow profiles and limit the rate of temperature change during the growth process. Conventional tube furnace designs also provide limited mechanical access to the growth Site and prevent optical monitoring of the growth site, removing the ability to observe and interact in situ during growth. This thesis presents the SabreTube, a low-cost desktop cvD apparatus that decouples temperature and flow variables, provides mechanical and optical access to the reaction site during growth, and provides modular fixturing to enable versatile experimentation with and characterization of CUT growth mechanisms. This thesis also presents the Nanosled, a device designed to translate a substrate through a CVD furnace. / Contract number: N62271-97-G-0026. / CIVINS

Denna studie undersöker absorptionstekniken i syfte att ta reda på förutsättningarna för absorptionskyla i Härnösand. En investeringskalkyl har genomförts för att bedöma lönsamheten. I huvudsak har en litteraturstudie genomförts och för investeringskalkylen har nuvärdesmetoden använts samt att produktspecifikationer har efterfrågats från de största leverantörerna i världen. Resultatet visar att det finns två typer av kommersialiserade absorptionskylmaskiner på marknaden, varav den ena är tillämpbar för decentraliserad kylproduktion i fjärrvärmenät vid temperaturer kring 75 °C, och den andra för högre temperaturer kring 120-150 °C och lämpar sig därmed inte för decentraliserad kylproduktion. Det forskas och utvecklas kring andra mer avancerade tekniker och investeringskalkylen visar att en investering är lönsam beroende på storleken på absorptionskylmaskinen och försäljningspriset på kylan som levereras till kunden. Slutsatsen är att säljargument och en motivering måste tas fram varför kunden ska välja att få sin kyla levererad via en absorptionskylmaskin istället för en kompressorkylmaskin. / This study examines the absorption cooling technology in order to find the prerequisites of absorption cooling in Härnösand. An investment appraisal has been completed to ensure profitability. Mainly, a literature review has been conducted and the net present value decision rule has been used for the investment appraisal and product specifications have been requested from the main global suppliers. The result shows that there are essentially two absorption chillers commercialized in the market, one of which is applicable for decentralized cooling production in a district heating network at temperatures around 75 °C, and the second which is applicable for temperatures in the range of 120-150 °C and thus not suitable for decentralized cooling production. Research and development for more advanced techniques is ongoing and the investment appraisal shows that the profitability is depending on the size of the chiller unit and the selling price for the cooling energy. The conclusion is that a sale proposal and a motivation are needed on why the customer should choose to have their cooling delivered from an absorption chiller instead of a compressor chiller.

Proton Exchange Membrane Fuel Cells (PEMFCs) present a promising alternative to the conventional internal combustion engine for automotive applications because of zero harmful exhaust emissions, fast refuelling times and possibility to be powered by hydrogen generated through renewable energy. However, several issues need to be addressed before the widespread adoption of PEMFCs, one such problem is the removal of waste heat from the fuel cell electrochemical reaction at high ambient temperatures. Automotive scale fuel cells are most commonly liquid cooled, evaporative cooling is an alternative cooling method where liquid water is added directly into the fuel cell flow channels. The liquid water evaporates within the flow channel, both cooling and humidifying the cell. The evaporated water, along with some of the product water, is then condensed from the fuel cell exhaust, stored, and re-used in cooling the fuel cell. This work produces a system level model of an evaporatively cooled fuel cell vehicle suitable for the study of water balance and heat exchanger requirements across steady state operation and transient drive cycles. Modelling results demonstrate the ability of evaporatively cooled fuel cells to self regulate temperature within a narrow region (±2°C) across a wide operating range, provided humidity is maintained within the flow channels through sufficient liquid water addition. The heat exchanger requirements to maintain a self sufficient water supply are investigated, demonstrating that overall heat exchange area can be reduced up to 40% compared to a liquid cooled system due to the presence of phase change within the vehicle radiator improving heat transfer coefficients. For evaporative cooling to remain beneficial in terms of heat exchange area, over 90% of the condensed liquid water needs to be extracted from the exhaust stream. Experimental tests are conducted to investigate the condensation of water vapour from a saturated air stream in a compact plate heat exchanger with chevron flow enhancements. Thermocouples placed within the condensing flow allow the local heat transfer coefficient to be determined and an empirical correlation obtained. The corresponding correlation is used to produce a heat exchanger model and study the influence different heat exchanger layouts have on the overall required heat transfer area for an evaporatively cooled fuel cell vehicle. A one-dimensional, non-isothermal model is also developed to study the distribution of species, current density and temperature along the flow channel of an evaporatively cooled fuel cell using different methods of liquid water addition. Results show that good performance can be achieved with cathode inlet humidities as low as 20%, although some anode liquid water addition may be required at high current densities due to increased electro-osmotic drag. It is also demonstrated that both good membrane hydration and temperature regulation can be managed by uniform addition of liquid water across the cell to maintain a target exhaust relative humidity.

Master of Science / Department of Mechanical Engineering / Donald Fenton / The need to store and access electronic information is growing on a daily basis as more and more people conduct business and personal affairs through email and the internet. To meet these demands, high energy density data centers have sprung up across the United States and around world. To ensure that vital data centers run constantly, proper cooling must be maintained to prevent overheating and possible server damage from occurring. Emergency cooling systems for such systems typically utilize traditional batteries, backup generator, or a combination thereof. The electrical backup provides enough power to support cooling for essential components within the data centers. While this method has shown to be reliable and effective, there are several other methods that provide reliable emergency cooling at a fraction of the cost. This paper address the lack of information regarding the initial, operation, and maintenance costs of using Thermal Energy Storage (TES) tanks for emergency cooling. From research and various field examples, five emergency cooling system layouts were designed for various peak cooling loads. Looking at the different cooling loads, components, and system operations an economic evaluation of the system over a 20 year period was conducted. The economic analysis included the initial and maintenance costs of each system. In an effort to better understand power consumption of such systems and to help designer’s better estimate the long term costs of TES tanks systems, five layouts were simulated through a program called TRNSYS developed for thermal systems. To compare against current systems in place, a benefit to cost ratio was done to analyze TES versus a comparable UPS. The five simulated systems were one parallel pressurized tank, one parallel and one series atmospheric tank, one parallel low temperature chilled water, and one series ice storage tank. From the analysis, the ice storage and pressurized systems were the most cost effective for 1 MW peak cooling loads. For 5 MW peak cooling loads the ice storage and chilled water systems were the most cost effective. For 15 MW peak loads the chilled water atmospheric TES tanks were the most cost effective. From the simulations we concluded that the pressurized and atmospheric systems consumed the least amount of power over a 24 hour period during a discharge and recharge cycle of the TES tank. From the TRNSYS simulations, the ice storage system consumed 22 – 25% more energy than a comparable chilled water system, while the low temperature storage system consumed 6 – 8% more energy than the chilled water system. From the benefit-cost-ratio analysis, it was observed that all systems were more cost effective than a traditional battery UPS system of comparable size. For the smaller systems at 1 MW the benefit-cost-ratio ranged between 0.25 to 0.55, while for larger systems (15 MW) the ratio was between 1.0 to 3.5 making TES tanks a feasible option for providing emergency cooling for large and small systems.

M.Phil. / The aim of this research is to study the underhood airflow thermal behaviour of the extra low profile (XLP) dozer due to the excessive heat dissipated and observed during testing sessions executed at ground level, using computational fluid dynamics (CFD). The motivation of this project is to identify the reasons of poor cooling performance of this equipment, to develop and to demonstrate the capabilities of CFD in thermal research by validating the CFD result with experiments using a scaled model, prior to analyzing the full-scale dozer ...

Numerical simulation is progressively taking importance in the design of an aero- nautical engine. However, concerning the particular case of cooling devices, the high number of sub-millimetric cooling holes is an obstacle for computational sim- ulations. A classical approach goes through the modelling of the effusion cooling by homogenisation. It allows to simulate a full combustor but failsin representing the jet penetration and mixing. A new approach named thickened-hole model was developed during this thesis to overcome this issue. A work on improving the mesh resolution onkey areas thanks to an automatic adaptive method is also presented, leading to a clear breakthrough. In parallel, as the flame tube temperature is a cornerstone for the combustor durability,a low-cost approach is proposed to predict it. To meet the time-constraints of design, it is based on thermal modelling instead of a direct thermal resolution.