Master of Science / Department of Mechanical and Nuclear Engineering / Amy R. Betz / The purpose of this research was to test if biphilic surfaces mitigate frost and ice formation. Frost, which forms when humid air comes into contact with a surface that is below the dew point and freezing temperature of water, hinders engineering systems such as aeronautics, refrigeration systems, and wind turbines. Most previous research has investigated increasingly superhydrophobic materials to delay frost formation; however, these materials are dependent on fluctuating operating conditions and surface roughness. Therefore, the hypothesis for this research was that a biphilic surface would slow the frost formation process and create a less dense frost layer, and water vapor would preferentially condense on hydrophilic areas, thus controlling where nucleation initially occurs. Preferential nucleation can control the size, shape, and location of frost nucleation. To fabricate biphilic surfaces, a hydrophobic material was coated on a silicon wafer, and a pattern of hydrophobic material was removed using photolithography to reveal hydrophilic silicon-oxide. Circles were patterned at various pitches and diameters. The heat sink was comprised of two parts: a solid bottom half and a finned upper half. Half of the heat sink was placed inside a polyethylene base for insulation. Tests were conducted in quiescent air at room temperature, 22 °C, and two relative humidities, 30% and 60%. Substrate temperatures were held constant throughout all tests. All tests showed a trend that biphilic surfaces suppress freezing temperature more effectively than plain hydrophilic or hydrophobic surfaces; however, no difference between pattern orientation or size was noticed for maximum freezing temperature. However, the biphilic patterns did affect other aspects such as time to freezing and volume of water on the surface. These effects are from the patterns altering the nucleation and coalescence behavior of condensation.

During flight missions, fighter pilots are in general exposed to vast amounts of stress including mild hypoxia, vibrations, high accelerations, and thermal discomfort. It is interesting to predict potential risks with a certain mission or flight case due to these stresses to increase safety for fighter pilots. The most predominant risk is typically thermal discomfort which can lead to serious health concerns. Extensive exposure to high or low temperature in combination with a demanding work situation weakens the physical and mental state of the pilot and can eventually lead to life-threatening conditions. One method to estimate the physical and mental state of a person is to measure the body core temperature. The body core temperature cannot be measured continuously during flight and needs to be estimated by using for instance a human thermoregulatory model. In this study, a model of the human thermoregulatory system and the cockpit environment is developed. Current thermoregulatory models are not customized for fighter pilots but a model developed by Fiala et al. in 2001, which has previously shown good performance in both cold and warm environments as well as for various activation levels for the studied person, is used as a theoretical foundation. Clothing layers are implemented in the model corresponding to clothes used by pilots in the Swedish air force flying the fighter aircraft Gripen E in warm outside conditions. Cooling garments and air conditioning systems as well as avionics, canopy, and cockpit air are included in the model to get a realistic description of the cockpit environment. Input to the model is a flight case containing data with altitude and velocity of the fighter during a mission. human heat transfer; body temperature regulation; physiological model;cooling garment; cockpit modeling

Master of Science / Department of Mechanical and Nuclear Engineering / Bruce R. Babin / A significant body of literature exists for experiments in spray cooling applications that utilize one-dimensional heat transfer through a metal ingot to determine the average surface heat flux. Due to inherent non-uniformities in spray distributions, measurements that account for the two-dimensional effects are required. In this study, an infrared (IR) camera was used to capture the two-dimensional temperature distribution formed when spraying an electrically heated NiChrome surface with three different fluids. IR thermography captured the thermal response of the un-sprayed side of a 0.005-inch (0.125mm) think strip of NiChrome exposed to spray from a 90° full-cone nozzle at low mass fluxes (0.025 – 0.045 lb/ft[superscript]2-s / 0.122 – 0.220 kg/m[superscript]2-s) from a distance of approximately 5 to 11 inches (13 to 28cm). Results were measured for surface average temperatures ranging from 150 to 600°F (65 – 315°C).

Published Article / The simulation of an exhaust manifold's thermal behaviour is an important concern for various reasons. Amongst them is the need to minimise catalyst light-offtime as significant exhaust emissions are generated within this period. Modelling such behaviour is not simplistic as it is governed by complex interactions between exhaust gas flow and the manifold itself. Computational fluid dynamics (CFD) is a powerful tool for such simulations. However its applicability for transient simulations is limited by high central processing unit (CPU) demands. The present study proposes an alternative computational method to assess and rank the relative impact of the manifold's thermal properties on its exterior temperature. The results show that stainless steel manifolds potentially minimise heat loss from the exhaust gas when compared with their cast iron counterparts. This may result in an increase in thermal energy being available to heat the catalyst.

Heat management in high thermal-density systems such as CPU chips, nuclear reactors and compact heat exchangers is confronting rising challenges due to ever more miniaturized and intensified processes. While searching for heat transfer enhancement, micro-channel flow boiling and the usage of high thermal potential fluids such as nanofluids are found to be efficient heat removal approaches. However, the limited understanding of micro-scale multiphase flows impedes wider applications of these techniques. In this thesis work, liquid-vapour phase change and multiphase flow heat transfer in micro-channels were experimentally investigated. Included are studies on the single phase friction, vapour dynamics, liquid meniscus evaporation, two-phase flow instabilities and heat transfer. An experimental system was built. Rectangular microchannels with different hydraulic diameters (571 μm, 762 μm and 1454 μm) and crosssectional aspect ratios were selected. Transparent heating was utilised by coating the micro-channels with a layer of tantalum on the outer surfaces. FC-72, n-pentane, ethanol, and ethanol-based Al2O3 nanofluids were used as working fluids. Pressures and temperatures at micro-channel inlet and outlet were acquired. Simultaneous visualisation and thermographic profiles were monitored. Single phase friction of pure liquids and nanofluids mostly showed good agreement with the conventional theory. The discrepancies were associated with hydrodynamic developing flow and the early transition to turbulent flow, but nanoparticle concentration showed minor impact. After boiling incipient, the single vapour bubble growth and flow regimes were investigated, exploring the influences of flow and thermal conditions as well as the micro-channel geometry on vapour dynamics. In addition, liquid meniscus evaporation as the main heat transfer approach at thin liquid films in micro-channels was studied particularly. Nanoparticles largely enhanced meniscus stability. Besides, flow instabilities were analyzed based on the pressure drop and channel surface temperature fluctuations as well as the synchronous visualization results. Moreover, study on flow boiling heat transfer was undertaken, the corresponding heat transfer characteristics were presented and the heat transfer mechanisms were elucidated. Furthermore, ten existing heat transfer correlations were assessed. A modified heat transfer correlation for high aspect ratio micro-channel flow boiling was proposed. The crucial role of liquid property and microchannel aspect-ratio on flow boiling heat transfer was highlighted.

The following paper presents a one-dimensional numerical model for simulating transient thermohydraulic pipe flow based on the Method of Characteristics. In addition to mass and momentum conservation, the proposed scheme also guarantees compliance with the laws of thermodynamics by solving the energy equation. The model covers transient changes in fluid properties due to pressure changes, heat transfer and dissipation. The presented methodology also allows the computation of the transient temperature distribution in the pipe wall through an additional ordinary finite difference scheme. The numerical procedure is implemented in the commercial simulation software DSHplus. The capability of the code is examined by comparing the simulation results with theoretical solutions and experimental data.

Controlling the thermo-elastic behavior of tooling machines can only be achieved by systematic analysis, characterization and design of their fluidic system. In the first stage of this project, fundamental work was done to develop simulation methods for the calculation of the thermodynamic behavior of a representative example of a milling machine and each of its components. With experimental and numerical data it was proven, that significant improvement can be achieved by a proper design of heat transfer conditions of the fluidic system. To correct and counterbalance thermo-energetic effects, it will be necessary to develop new structures of the tooling machines systems which ensure the temperature-control of local subsystems in dependence of the actual working process. The work which is documented in this paper deals with the thermodynamic behavior of the motor spindle.

Due to good energy-efficiency of electrohydraulic compact drives a cooling aggregate often is not installed. The operating temperature is governed by the complex interaction between dissipative heat input and passive heat output. This paper targets the simulation of the thermo-energetic behaviour of an electrohydraulic compact drive by means of a lumped parameter model in order to predict the operating temperature. The developed thermo-hydraulic model is validated against measurements utilising thermocouples and a thermographic camera to capture temperatures. The results show, that the presented methodology enables a satisfying accurate prediction of the thermo-energetic behaviour of electrohydraulic compact drives. A further analysis of simulation results is given, highlighting the power losses and heat rejection capabilities of different components. Finally, measures for the improvement of the heat rejection capabilities are studied.

Wetting and spreading of liquid systems on solid substrates under transient conditions, driven by surface tension and viscous forces along with the interface interactions (e.g., a substrate dissolution or diffusion and/or chemical reaction) is a complex problem, still waiting to be fully understood. In this study we have performed an extensive experimental investigation of liquid aluminum alloy spreading over aluminum substrate along with corroboration with theoretical modeling, performed in separate but coordinate study. Wetting and spreading to be considered take place during a transient formation of the free liquid surface in both sessile drop and wedge-tee mating surfaces’ configurations. The AA3003 is used as a substrate and a novel self-fluxing material called TrilliumTM is considered as the filler metal. In addition, benchmark, non-reactive cases of spreading of water and silicon oil over quartz glass are considered. The study is performed experimentally by a high temperature optical dynamic contact angle measuring system and a standard and high speed visible light camera, as well as with infra read imaging. Benchmark tests of non-reactive systems are conducted under ambient environment’s conditions. Molten metal experiment series featured aluminum and silicone alloys under controlled atmosphere at elevated temperatures. The chamber atmosphere is maintained by the ultra-high purity nitrogen gas purge process with the temperature monitored in real time in situ. Different configurations of the wedge-tee joints are designed to explore different parameters impacting the kinetics of the triple line movement process. Different power law relationships are identified, supporting subsequent theoretical analysis and simulation. Under ambient temperature conditions, the non-reactive liquid wetting and spreading experiments (water and oil systems) were studied to verify the equilibrium triple line location relationships. The kinetics relationship between the dynamic contact angle and the triple line location is identified. Additional simulation and theoretical analysis of the triple line movement is conducted using the commercial computer software platform Comsol in a collaboration with a team from Washington State University within the NSF sponsored Grant #1235759 and # 1234581. The experimental work conducted here has been complemented by a verification of the Comsol phase-field modeling. Both segments of work (experimental and numerical) are parts of the collaborative NSF sponsored project involving the University of Kentucky and Washington State University. The phase field modeling used in this work was developed at the Washington State University and data are corroborated with experimental results obtained within the scope of this Thesis.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: The thermal regulation response of a neonate has to maintain temperature homeostasis, thus resisting the changes to core temperature caused by the unstable external environment. In this thesis a theoretical thermal regulation response model for human infants subject to a well-defined environment is presented. This model will aid in understanding the influences of environmental effects on core and skin temperature. The respiratory system was also included in the thermal regulation response model. A literature study was undertaken emphasising thermal regulation of neonates. The blood circulation system, skin tissue physiology and the respiratory system physiology were reviewed and helped to provide a better understanding of the thermal regulation mechanisms and how heat transfer theory can be used to analyse heat loss in neonates. The thermal heat transfer properties of skin tissue was specified and used in the development of the theoretical simulation model. The bioheat equation developed by Pennes was reviewed as well as a mathematical model developed by Fiala et al. The theoretical model was developed by applying the conservation of energy and the applicable properties to one dimensional layers to generate a set of time dependent differential equations. The set of equations was solved using an explicit numerical finite difference method, given the initial conditions. The mathematical model included heat loss through the skin, heat loss through the respiratory system, as well as the effect of environments (in incubator or in a bassinette) with different temperatures, relative humidity’s and air velocities. Clothing was also incorporated. A clinical trial was conducted to facilitate a better understanding of thermal stability in neonates. The data acquired during the clinical trial was also used to verify/validate the theoretical simulation model. The results from the simulation temperatures were compared with the average outer skin layer temperature measured during the clinical trial and an average deviation of only 0.22 °C was found, thereby proving that the simulation model gives realistic results. An experimental respiratory model was designed to simulate the respiratory system and illustrate the functioning thereof with regards to heat transfer. This was done by designing an experimental mechanical lung apparatus. The apparatus was tested and successfully imitated the respiratory system with regards to heat transfer. The results obtained from this experiment indicated that the trachea must be moistened continuously in order to condition inhaled air. The outcome of this project identified two possible applications. For the first application it can be used as a test tool for quickly evaluating the influence of different environmental conditions in the transient temperature distribution of neonates. The second application would be to enable medical professionals to monitor the influence of the thermal environment, including the temperature, relative humidity and air velocity, on the neonate’s temperature change to allow for a speedier thermal intervention strategy. / AFRIKKANSE OPSOMMING: Die hitte regulering reaksie van 'n pasgebore baba moet temperatuur homeostase handhaaf, en sodoende die veranderinge aan die kern temperatuur weerstaan wat veroorsaak word deur ‘n onstabiele eksterne omgewing. In hierdie tesis word 'n teoretiese hitte regulerings reaksie model vir menslike babas, onderhewig aan 'n goed-gedefinieerde omgewing, aangebied. Hierdie model sal help met die verstaan van die invloed wat omgewings effekte het op die kern en vel temperatuur. Die respiratoriese sisteem is ook ingesluit in die hitte regulering reaksie model. 'n Literatuurstudie is onderneem met die klem op hitte regulering van pasgebore babas. Die bloed sirkulasie sisteem, vel weefsel fisiologie en die respiratoriese sisteem fisiologie is hersien en help met beter begrip van die hitte regulering meganismes en hoe hitteoordrag teorie kan gebruik word om hitte verlies in pasgebore babas te analiseer. Die hitte-oordrag eienskappe van vel weefsel is gespesifiseer en word gebruik in die ontwikkeling van die teoretiese simulasie model. Die ‘bioheat’ vergelyking ontwikkel deur Pennes is hersien asook 'n wiskundige model wat ontwikkel is deur Fiala et al. Die teoretiese model is ontwikkel deur die toepassing van die behoud van energie tesame met die gebruik van toepaslike eienskappe en een dimensionele lae om 'n stel tyd afhanklike differensiaalvergelykings op te wek. Die stel vergelykings is opgelos met behulp van 'n eksplisiete numeriese eindige verskil metode, gegewe die aanvanklike toestande. Die wiskundige model sluit in die hitte verlies deur die vel, hitte verlies deur die respiratoriese stelsel, sowel as die effek van die omgewing (broeikas of in 'n bassinette) met verskillende temperature, relatiewe humiditeit en lug snelhede. Klere is ook in ag geneem. 'n Kliniese proef is gedoen om 'n beter begrip van termiese stabiliteit in pasgebore babas te fasiliteer. Die data wat tydens die kliniese proef verhaal is, is ook gebruik om die die teoretiese simulasie model te verifieer. Die resultate van die simulasie temperature is vergelyk met die gemiddelde buitenste vel laag temperatuur gemeet tydens die kliniese proef en 'n gemiddelde afwyking van slegs 0.22 °C is gevind, wat dus bewys dat die simulasie model realistiese resultate gee. 'n Eksperimentele respiratoriese model is ontwerp om die respiratoriese stelsel te simuleer en die funksionering daarvan te illustreer met betrekking tot hitte-oordrag. Dit is gedoen deur die ontwerp van 'n eksperimentele meganiese long apparaat. Die apparaat is getoets en slaag daarin om die respiratoriese stelsel suksesvol na te boots met betrekking tot hitteoordrag. Die resultate verkry uit hierdie eksperiment het aangedui dat die tragea kostant klam gemaak moet word om ingeasemde lug te kondisioneer. Die uitkoms van hierdie projek het twee moontlike toepassings geïdentifiseer. Die eerste is dat dit as 'n toets instrument vir die vinnige evaluering van die invloed van verskillende omgewingsfaktore in die temperatuur verspreiding van pasgebore babas gebruik kan word. Die tweede toepassing sal wees om medici in staat te stel om die invloed van die termiese omgewing te monitor, insluitend die temperatuur, relatiewe humiditeit en lug snelheid, om die neonaat se temperatuur verandering te monitor en voorsiening te maak vir 'n vinniger verwarmings intervensiestrategie.