The results provided by this study include (a) temperature fileds in the interior and surface of the heater (b) determination of the heat transfer coefficient on the surface of the heater (c) the effects of different dimensionless working parameters

A detailed analysis of the heat transfers and fluid flows within a direct thermosyphonic solar-energy water-heater has been undertaken. The collector energy equations when cast in a two-dimensional form enabled heat transfer and thermal capacitance effects to be simulated accurately at the small flow rates encountered commonly in such systems. An investigation of thermocline relaxation processes within the store indicated negligible mixing at the store inlet over a wide range of Richardsons numbers (43,608 < Ri < 729,016). Thermal relaxation under conditions of no flow was shown to be due predominantly to axial conduction along the store wall. The use of an appropriate non-isothermal friction factor correlation when calculating frictional losses in the collector's riser pipes, produced predicted steady-state flow rates which were corroborated experimentally to within 2%. An indoor test facility, monitored and controlled by a microcomputer, enabled 'real' operating conditions to be simulated. The predicted responses of the system to identical conditions showed good agreement with the corresponding experimental observations, the predicted heat delivery being within 2.8% of the measured value. A technique for correlating the daily performances of thermosyphon solar-energy water-heaters has been developed. The five dimensionless groups which form the basis of the correlations and the functional relationships between these groups were derived from an analytical solution of a linear first-order differential transient heat balance carried out on a generic system. Thermal performance data used in the correlations was generated by the numerical simulation using representative U. K. hourly weather data and operating conditions. The minimum amount of data required to establish a characteristic curve for an individual system was found to be thirty days. Using such a curve, the total annual solar fraction agreed with that predicted by the high level model to within 3%. Two universal curves were determined in which the gradients of characteristic curves were correlated against the derived dimensionless groups. The accuracy of the resulting two-stage algorithm in determining annual solar fractions was established as ranging from 5.5% for predominantly multiple-pass systems to a mean of 10.5% for single-pass systems.

Este trabalho propõe um método com objetivo de avaliar a eficiência energética de aquecedores de água residenciais de acumulação elétricos. Os aquecedores foram submetidos a um ciclo de operação simulando uma condição de uso para o cálculo da eficiência. Este ciclo de duração de um dia é composto pelas fases: produção de água quente, reaquecimento e manutenção da temperatura interna. O método foi aplicado no programa experimental e permitiu a identificação de diversos parâmetros referentes ao funcionamento dos aquecedores, tais como: perda passiva por 24 horas, produção de água quente, tempo de reaquecimento, variação da temperatura interna da água e a sua eficiência energética. / This work proposes a method with objective of evaluating the energy efficiency of electrical residential storage water heaters. The heaters were submitted to an operation cycle simulating a use condition for the calculation of the efficiency. This cycle with duration of one day is composed by the phases: hot water withdrawal, temperature recovery and standby thermal loss. The method was applied in the experimental program and it allowed the identification of several parameters regarding the operation of such heaters as: standby thermal loss per 24 hours, hot water rate output, reheating time, cyclic variation of the temperature and its energy efficiency.

Este trabalho propõe um método com objetivo de avaliar a eficiência energética de aquecedores de água residenciais de acumulação elétricos. Os aquecedores foram submetidos a um ciclo de operação simulando uma condição de uso para o cálculo da eficiência. Este ciclo de duração de um dia é composto pelas fases: produção de água quente, reaquecimento e manutenção da temperatura interna. O método foi aplicado no programa experimental e permitiu a identificação de diversos parâmetros referentes ao funcionamento dos aquecedores, tais como: perda passiva por 24 horas, produção de água quente, tempo de reaquecimento, variação da temperatura interna da água e a sua eficiência energética. / This work proposes a method with objective of evaluating the energy efficiency of electrical residential storage water heaters. The heaters were submitted to an operation cycle simulating a use condition for the calculation of the efficiency. This cycle with duration of one day is composed by the phases: hot water withdrawal, temperature recovery and standby thermal loss. The method was applied in the experimental program and it allowed the identification of several parameters regarding the operation of such heaters as: standby thermal loss per 24 hours, hot water rate output, reheating time, cyclic variation of the temperature and its energy efficiency.

Micro-channels are very important in bio-medical and cooler research. Although many research have been conducted with micro-channels, few results have been contributed to discuss the properties of fluids inside a micro-channel. For example, the thermal distribution of the fluid in a micro-channel is only simulated with numerical analysis approach. In our research, we aim to design a device that can measure real thermal data within a micro-channel. We first applied excimer laser lithography on a PMMA substrate to fabricate a micro-channel with 20 mm length, 200£gm width and 200£gm depth. Micro-heater and micro-thermal sensor is than fabricated by sputtering pt thin-thim with PVD process on a glass substrate. Finally, these devices were assembled with UV-curing and than applied for further testing. According to our experiment, lift-off process cannot be easily applied to fabricate micro-heater and micro-thermal sensor since the architecture of these devices were fragile in metal line sidewalls. Wet-lithography is than used to conquer this problem. Our primary test on this micro-thermal sensor shows that its resistance varies with thermal changes. Such mechanism can be applied to measuring thermal field in a micro-channel.

Electronically monitoring whether or not your car block heater is connected to a mains outlet might at first seem like an arbitrary task. A device installed in the comfort of the car seating area, which tells the user at every startup whether or not his/her car is connected to a mains outlet, could have market appeal though. But in order for it to be a worthwhile idea to pursuit, a certain requirement has to be met. It has to be able to be able to accurately detect whether or not the car is connected, through a single connection; the car ground. A certain part of the voltage in the phase of the mains will be capacitively coupled upon the safety ground. By exploiting the fact that the car ground will be connected to the mains safety ground when the block heater cable is in use, a device which can detect that coupled voltage could possibly be developed. In other words, a cable monitoring unit which in actuality detects a connection to the mains safety ground through capacitive coupling, hence the title of this dissertation. This work sets out to taking appropriate measurements to find out whether or not this proposed method of safety ground detection is valid, with heavy emphasis on whether or not it is applicable to a cable monitoring unit. According to the measurement results, an appropriate device is developed. A device which can fill the function described in the previous paragraph. Development of such a device involves; proper method of supplying power which upholds a galvanically isolated floating ground, signal processing, reliable detection mechanism, and considerations to how unintentional capacitive coupling behaves. A theoretical model of the device is put forth, as well as an actual rough prototype to in practice try to prove that the concept and method is valid. Downsides and problems with the device are discussed, such as upholding an effective detection system without making the device hard and cumbersome to use. Possible solutions to these problems are also proposed. The possible future of the concept of this device is also touched upon.

Polymerase Chain Reaction (PCR) detection paves the way to reliable and rapid diagnosis of diseases and has been used extensively since its introduction. Many miniaturized PCR systems were presented by microfluidics and lab-on-a-chip community. However, most of the developed systems did not employ real-time detection and thus required post-PCR processes to obtain results. Among the few real-time PCR systems, almost all of them aimed for medical applications and those for plant pathogen diagnosis systems are almost non-existent in the literature. In this work, we are presenting a portable system that employs microfluidics PCR system with integrated optical systems to accomplish real-time quantitative PCR for plant pathogen diagnosis. The system is comprised of a PCR chip that has a chamber for PCR sample with integrated metal heaters fabricated by standard microfabrication procedures, an optical system that includes lenses, filters, a dichroic mirror and a photomultiplier tube (PMT) to achieve sensitive fluorescence measurement capability and a computer control system for Proportional Integral Derivative (PID) control and data acquisition. The optical detection system employs portable components and has a size of 3.9 x 5.9 x 11.9 cm which makes it possible to be used in field settings. On the device side, two different designs are used. The first design includes a single chamber in a 25.4 x 25.4 mm device and the capacity of the chamber is 9 micro-liters which is sufficient to do gel electrophoresis verification. The second design has three 2.2 micro-liter chambers squeezed in the same size device while having smaller volume to increase high throughput of the system. The operation of the system was demonstrated using Fusarium oxysporum spf. lycopersici which is a fungal plant pathogen that affects crops in the USA. In the presence of the plant pathogen, noticeable increases in the photomultiplier tube output were observed which means successful amplifications and detections occurred. The results were confirmed using gel electrophoresis which is a conventional post-PCR process to determine the existence and length of the amplified DNA. Clear bands located in the expected position were observed following the gel electrophoresis. Overall, we have presented a portable PCR system that has the capability of detecting plant pathogens.

Feed water heaters are large shell and tube heat exchangers. They from part of the Rankine cycle used in coal fired power plants with the main purpose being the improvement of the overall cycle efficiency. Like most heat exchangers, feed water heaters suffer from fouling. Fouling is defined as “any undesirable deposit on heat exchanger surfaces that increases resistance to heat transmission”. In the design of heat exchangers, fouling is accommodated by adding additional surface area to the heat exchanger. The amount of additional area is determined by the use of fouling factors. Although this is the only wide-spread method accepted in industry, the fouling factors in use are outdated, generally considered conservative and lead to oversized heat exchangers. The purpose of this study was to design and build a test rig that can accurately measure fouling factors of feed water heater tubes that has been in service for a full life cycle. A comprehensive literature study was performed to decide on the most effective test method, as well as the required instrument type and accuracy. The best method was found to be where the overall heat transfer coefficient for a fouled tube, outside cleaned tube (half clean) and clean tube was measured. The measured values are then converted to the internal, external and overall fouling factors. Validation test were done on the test rig. These included energy balance tests, theoretical comparison tests and repeatability tests. The results of all tests were acceptable and within measurement uncertainty limits. Five sample test tubes, obtained from a 30 year old LP heater at an Eskom power station, were tested. The results indicated that the average measured fouling factors were less than 20% of the commonly used HEI fouling factors. This is significantly lower and confirms that the fouling factors in use for this specific case are conservative. The test rig proved to be accurate and effective in measuring the fouling factors. Although the tests shows promising results, the small amount of tubes tested from only one heat exchanger are not sufficient to make meaningful conclusions. The test rig is now ready for a future study where a large sample of tubes can be tested.

<p> CHF and Post-CHF tests were performed in water at 9.7 MPa using two vertical test assemblies having identical, internally heated annular flow channels, one heated directly, the other indirectly. Experiments were conducted to determine the effect of these methods of heating on CHF and Post-CHF heat transfer. </p> <p> For the range of the test conditions investigated, the results show that the direct and indirect heaters have similar CHF performance. At heat fluxes above CHF and mass fluxes of 2.0 and 3.5 Mg.s^-1 .m^-2 , the indicated maximum wall temperatures of the heaters were similar, but at the highest mass flux for the tests, 5.0 Mg.s^-1 .m^-2 , the indirect heater had lower indicated maximum wall temperatures than the direct heater for a given heat flux above CHF. </p> <p> A multi-fluid model, of the type used previously in the prediction of CHF, was derived and tested against the experimental data. The model, which considers droplet entrainment, deposition and evaporation in the annular flow regime, assumes dryout to occur when the liquid film flow on the inner rod approaches zero. The CHF predictions were in fairly good agreement with the experimental results. In general, the model under-predicted CHF at low inlet subcoolings and over-predicted CHF at high inlet subcooling. The error trend is consistent with that of the CHF prediction models of other researchers. </p> <p> In addition to the CHF prediction model, a Post-CHF model to predict the vapour temperatures, and hence, the heated wall temperature is also presented in the report. The theory is based on a physical model of heat transfer in the liquid deficient regime. In the model, heat in the dry region is assumed to transfer from the heated wall to superheat the steam and some of this heat, in turn, is used to evaporate the droplets which are entrained in the vapour core. Droplet entrainment and deposition at the shroud (outer tube) film-vapour interface are modelled. Heat transfer enhancement due to increased turbulence downstream of the rod centering spacers is incorporated through an empirical correlation. The predicted results were compared to the direct heater experiments. In general, the predicted wall temperatures were in agreement with those in the experiments. </p> / Thesis / Master of Engineering (MEngr)

A facility was designed to provide high-enthalpy, hypersonic flow to a detonation chamber. Preliminary investigation identified 1300 K and Mach 5 as the total temperature and Mach number require to stabilize an oblique detonation wave inside the detonation chamber. Vitiated-air heating was the preheating method chosen to meet these capabilities. The vitiator facility heats compressed air while still retaining about 50% of the original oxygen content. Schlieren flow visualization and conventional photography was performed at the exit plane of a choke plate, which simulated the throat of a converging-diverging nozzle. A shock diamond formation was observed within the jet exhausting out of the choke hole. This is a clear indication that the facility is capable of producing hypersonic flow. A stoichiometric propane-air mixture was burned inside the combustion chamber. A thermocouple survey measured an average temperature of 1099 K at the exit plane of the mixing chamber; however, the actual temperature is likely higher than this, because cool, ambient air could be seen mixing with the hot, vitiated air near the exit plane. Because the adiabatic flame temperature of propane-air is lower than that of hydrogen-air, if hydrogen is used to vitiate the air, the facility is capable of meeting the 1300-K objective.