Dissertations / Theses on the topic 'Effects of heat'

Since the invention of the laser in 1960, its use has been growing steadily. New laser sources with high beam power and high beam quality provide potential for further growth. High quality beams can be shaped by optical tools, such as scanners or Diffractive Optical Elements, DOE, to almost any beam shape, enabling innovative laser process solutions. For welding in particular, a tailored beam can be used to control the melt pool and to optimise the temperature field and cycle. For example, joining of electrical components like battery cells becomes more common due to the shift to electrical vehicles. This is a field of applications where laser welding with a tailored beam has high potential due to the need of tightly controlled design tolerances or processing temperatures and in turn electrical and mechanical properties. The research presented in the thesis encompasses the heat flow generated from tailored laser beams, the thermal effects on the weld shape and on other quality criteria, the generated residual stress and its influence on fatigue crack propagation. For the sake of simplicity, melt flow was not considered in the calculations, which was discussed, too. The first three papers apply predictive mathematical modelling for the temperature field while the fourth paper experimentally derives the thermally induced residual stress distribution back from measured fatigue crack propagation.Paper I contains a FEM-based numerical heat flow study of a conduction mode laser welding case where a C-shaped overlap joint is desired. The quality criteria demand the welding process to be tightly controlled in terms of laser power and pulse time. Contrary to expectations, the joint geometry can significantly deviate from the laser beam C shape. As a continuation, in Paper II various quantitative indicators were derived and studied as part of the numerical simulation, in order to identify a suitable beam shape and in turn a DOE-design.Paper III presents a semi-analytical mathematical model that was developed for the heat flow in pulsed conduction mode welding for spatially and temporally shaped laser beams. As an alternative to FEM, the model is fast due to its analytical nature, which enables iterative beam shape optimization and DOE-design. By studying different beam shapes and the induced temperature fields, the potential and limits of the model were demonstrated and discussed. Paper IV is a study on residual stress that is thermally induced during the heating and cooling cycle of laser keyhole welding. Acceleration measurement of the crack propagating across the weld during fatigue testing turned out to be a suitable method to derive the residual stress distribution along the crack, including its alteration during the cracking. Comparisons with FEM-based stress analysis provide a link back to the temperature field induced by the laser, which enables optimization, e.g. by beam shaping.
Godkänd; 2015; 20150911 (jessun); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Jesper Sundqvist Ämne: Produktionsutveckling/Manufacturing System Engineering Uppsats: Heat Conduction Effects During Laser Welding Examinator: Professor Alexander Kaplan, Institutionen för teknikvetenskap och matematik, Avdelning: Produkt- och produktionsutveckling, Luleå tekniska universitet Diskutant: Professor Lars Pejryd, Örebro universitet, Örebro Tid: Tisdag 10 november, 2015 kl 12.30 Plats: E632, Luleå tekniska universitet

The impact of thermal stress on psychological performance has been the subject of considerable research attention. However, the effects of heat on performance are poorly understood. The literature yields inconsistent results, reflecting methodological shortcomings in previous research, particularly with regard to the definition of the independent variable. Investigators have focused on heat stress per se to the neglect of the participants' thermal physiological response. In addition, investigators have typically tested small samples, and have relied on a limited range of performance measures of unknown sensitivity. Few theoretical accounts of performance during thermal stress have been proposed, and these are poorly elaborated. The principal aim of this research programme was to elucidate the effects of heat on psychological performance. Emphasis was placed on defining the independent variable in terms of physiological strain. Performance was measured using a comprehensive range of sensitive tasks. In the first and second experiments, an innovative water immersion technique was used to control thermal strain precisely. The principal effect of heat strain observed in these experiments was an increase in the speed of performance, without variation in accuracy. This effect was attributed to an increase in nerve conduction velocity associated with raised body temperature. The duration of immersion in the second experiment was fifty percent longer than that in the first, but little variation in performance with the duration of heat strain was evident. In light of the limited external validity of the immersion experiments, subsequent investigation focused on the effects of more realistic sources of thermal strain. A survey of military personnel indicated that occupational exposure to thermal stress is perceived to impair some cognitive and psychomotor functions. The final experiment measured performance during prolonged exposure to heat stress in a climatic chamber. The results indicate that the performance changes observed in the immersion experiments generalize to conditions involving exposure to more realistic sources of heat strain

Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, March 1994.
Thesis advisor(s): Morris Driels. "March 1994." Includes bibliographical references. Also available online. Mode of access: World Wide Web. System requirements: Adobe Acrobat Reader.

Passive and active heat loading causes cardiovascular strain, which can have diverse and substantial effects. Thus, cardiovascular function is integral to work and heat stress tolerance, but recent hyperthermia and exercise literature has not emphasised this relationship, instead focusing on the roles of upper �critical� core temperature or rate of heat storage as primary mechanisms of fatigue. Therefore, the aim of this thesis was to examine some potential causes and effects of cardiovascular strain under heat stress, including potential strategies for attenuating that strain. Body precooling before exercise increases heat storage capacity; the primary mechanism by which attenuations in thermal and cardiovascular strain, and improved work capacity is thought to occur. However, no precooling study has utilised realistic airflow in the laboratory, possibly inflating its purported benefits. Therefore, Study One examined the cardiovascular, thermal, psychophysical and ergogenic effects of precooling with and without airflow in the heat (30�C, 50% rh). Ten males completed four trials in balanced order, comprising 60- min immersion in thermoneutral (35�C) or cool (24�C) water before cycling at 95% ventilatory threshold with airflow (~4.8 m�s⁻�) or no airflow, until exhaustion. Heart rate and mean core, body, and skin temperatures were attenuated for 15 min into cycling after precooling. Endurance time was extended by 30 � 23 min with airflow, and 16 � 15 min with precooling relative to control (28 � 12 min) but not further extended with strategies combined (29 � 21 min). Precooling removed 784 � 223 kJ�m⁻� (calorimetrically); less than the effect of airflow alone (1323 � 1128 kJ�m⁻�). Competition for blood between tissues is pronounced during exercise in the heat: skin and gut have marked increases and decreases, respectively. Gut ischemia affects epithelial tight junction integrity, allowing lippopolysaccharide ingress and immune responses. Bovine colostrum may attenuate gut permeability. Study Two (double-blind, placebo controlled) investigated the effects of aerobic fitness (7 highly fit, 8 moderately fit) and bovine colostrum on physiological and perceived strain, and performance during mixed-mode exercise; cycle 15 min at 50% maximal heart rate range (HRR), run 30 min at 80% HRR then 30 min self-selected paced before another 15 min cycle at the same work-rate. Airflow was graded to running speed. During the last cycle, blood pressure, stroke volume and total peripheral resistance were lower, heart rate and skin blood flow increased, and skin temperature was unchanged compared to the first cycle. Indices of fever response (IL-1β, TNF-α) were not evident during exercise, nor were those of blood-brain barrier permeability (S100β) or cognitive impairment (Stroop test). Neither bovine colostrum, nor higher fitness modified these measures. Moving to upright posture is orthostatically stressful and can initially decrease cerebral perfusion. Compression garments are used to assist venous return; while their effectiveness is unknown, they could reduce heat or orthostatic-induced hypoperfusion. Study Three investigated the cardiovascular and cerebrovascular responses to orthostatic stress with and without passive heating (+0.5�C). Fifteen participants completed two trials (compression v placebo garments) in balanced order. Cerebral autoregulation was assessed via 3-min stand, and via thigh cuff inflation. All participants experienced initial orthostatic hypotension upon standing in one or more trials, with 4/15 individuals experiencing presyncopal symptoms, aborting the standing protocol. In those who "fainted", reductions in blood pressure and partial pressure of end-tidal CO₂ reduced middle cerebral artery velocity. Neither training status nor compression trousers modified the responses. Collectively, cardiovascular strain to heat stress is attenuated when realistic airflow is provided. Increased cardiovascular strain does not inevitably result in clinical outcomes to heat stress. Higher fitness does not necessarily attenuate cardiovascular responses or higher tolerance to heat stress.

Over the last decade, rapidly growing world energy consumption is leading to supply difficulties, exhaustion of fossil energy resources, and global environmental deterioration. More than one-third of energy expenditure is attributable to buildings. Urbanization is intensifying these trends with tighter spatial interrelationships among buildings. This is escalating building energy consumption due to the mutual impact of buildings on each other and, as a result, exacerbating Urban Heat Island (UHI) effects. I sought solutions to this significant engineering issue from nature, and discovered a similar heat island effect in flowers, namely the micro-greenhouse effect. However, a special cooling effect has been observed in a peculiar temperate flower, Galanthus nivalis, which generates cooler intrafloral temperatures. In this research, I studied the special retro-reflectance of the flower petals, which has been suggested as a possible contributor to this cooling effect, and implemented a bio-inspired retro-reflective pattern for building envelopes. I conducted cross-regional energy simulation of building networks in a dynamic simulation environment in order to examine its thermal-energy impact. I found that building surface temperatures dropped considerably when neighboring buildings were retrofitted with my bio-inspired retro-reflective facade. I concluded that my bio-inspired retro-reflective pattern for building envelopes; (1) lessens the reflected heat of solar radiation in spatially-proximal buildings leading to reduced UHI, and (2) reduces the energy required for cooling and, therefore, energy consumption. The research has further implications and contributions on building design, urban planning, development of retro-reflective technology, and environmental conservation.
Master of Science

Studies show that vasomotor and sudomotor activity is compromised in individuals with Type 1 Diabetes (T1DM) which could lead to altered thermoregulatory function. However, recent work suggests that the impairments may only be evidenced beyond a certain level of heat stress. We therefore examined T1DM-related differences in heat loss responses of sweating and skin blood flow (SkBF) during exercise performed at progressive increases in the requirement for heat loss. Participants were matched for age, sex, body surface area and fitness cycled at fixed rates of metabolic heat production of 200, 250, and 300 W•m-2 of body surface area, each rate being performed sequentially for 30 min. Local sweat rate (LSR), sweat gland activation (SGA), and sweat gland output (SGO) were measured on the upper back, chest and forearm while SkBF (laser-Doppler) was measured on the forearm and upper back only. We found that despite a similar requirement for heat loss, LSR was lower in T1DM on the chest and forearm only, relative to Control and only different at the end of the second and third exercise periods. Differences in chest LSR were due to reduced SGA whereas the decreased forearm LSR was the result of a decrease in SGO. SkBF did not differ between groups. The reduction in the sweating response in the T1DM group was paralleled by a greater increase in core temperature. We show that T1DM impairs heat dissipation as evidenced by reductions in LSR and not SkBF. A compromised thermoregulatory response during and following physical exertion is of considerable concern due to the associated increased risk of post-exertion heat-related injury.

Six elite wheelchair shooters undertook a simulated competition of 2 hr duration under three different conditions: 1. 24-26 °C and 40% humidity (C), 2. 36 °C and 60% humidity (H), and 3. the H condition whilst using simple head, neck and torso cooling devices (HC). The trials were undertaken at the same time on consecutive days in a counter-balanced, randomised order. Two shooters were removed from the H trial at t=75 and t=105 min, respectively, due to tympanic temperature elevations above 39 °C, but were able to complete the full 2 hr of competition during the C and HC conditions. Heart rates were significantly elevated for the group during the H condition compared to C and HC (106 ± ll, 80 ± 10, 90 ± 7 beats.min-' respectively at t=90 min, p<0.05) as were perceptions of thermal discomfort (6.4 ± 0.7, 3.5 ± 0.4, 4.8 ± 1.0 respectively at t=90 min, p<0.05). These responses were at least partially alleviated by the use of the simple, yet practical, cooling devices. Practically, this may improve performance in shooting competitions as it allows more time to fire a shot between heart beats, and enables shooters to concentrate more easily on the task required of them. Responses to heat exposure were more pronounced in athletes with a higher level of disability (CS versus T4 versus cerebral palsy), and those who wore heavy leather shooting jackets (rifle versus pistol shooters). Although further research is recommended, it would appear that the rules governing shooting attire and prolonging exposure to heat should be reconsidered for events in which wheelchair athletes compete.

High oil corn (HOC) is essentially dent corn that has been selected for high oil content in the scutellum. It is a value-added crop that can potentially offer a premium price for producers. Though southeastern U.S. producers have not had problems achieving sufficient yields, the oil content necessary for premium prices has been elusive. One of the most evident differences between these growers and their northern counterparts is the climate. Temperatures during the reproductive growth and grain fill periods are higher in southern latitudes. A two-part research project was conducted to further investigate the significance of temperature on oil content. The field project consisted of three different plantings; the first being planted May 11th, 2000, the second three weeks later on June 1st, 2000, and the third three weeks after the second, on June 22nd, 2000. The intention of the three plantings was to force the reproductive period and grain fill to occur during different times in the growing season. Ambient temperature data was supplied by the WKU Weather Center. Each planting was harvested and analyzed for oil content. The project resulted in a significant difference in oil content between the first planting and the last two plantings. The laboratory project began in the field. Sixteen ears per planting were hand pollinated and then harvested ten days after pollination. Six to twelve kernels, still attached to the cob, were removed from each ear. These pieces were placed on growth media in petri dishes and divided into two groups. One group was placed in an incubator set at 25°C, an optimum temperature for grain fill. The other group was placed in an incubator set at 35°C, a temperature representing heat stress during grain fill. There was no significant difference in oil content between the two different temperatures.

El objetivo principal de esta tesis es el estudio de los efectos de las altas temperaturas en el desarrollo gamético y cómo el uso de agentes antioxidantes suplementados a los medios de maduración o mantenimiento/congelación de espermatozoides podría contrarrestar los efectos negativos del estrés térmico y/o de la excesiva producción de radicales libres de oxígeno (ROS), con la finalidad de encontrar métodos adicionales que mejoren la fertilidad durante la época cálida del año. En el capítulo 1 se ha evaluado la influencia del estrés térmico sobre la maduración de ovocitos bovinos en comparación con ovocitos sobremadurados. Los ovocitos estresados térmicamente (41.5ºC, entre las 18-21h de maduración; HSO) y sobremadurados (28h de maduración; OMO) tienen 17.1 y 18 veces más probabilidades de presentar maduración ovocitaria anómala en comparación con los ovocitos madurados bajo condiciones fisiológicas (38.5ºC). Así pues, el estrés térmico produce un envejecimiento ovocitario mediante la aceleración de los procesos nucleares y citoplasmáticos de una forma similar a los que se producen durante la sobremaduración. El objetivo del segundo capítulo fue comparar los efectos del estrés térmico en la maduración ovocitaria según si estos son obtenidos en la época fría (Febrero-Marzo) o cálida (Mayo-Junio) del año. Sólo pudo detectarse la interacción entre la época del año y el tratamiento al que fueron expuestos los ovocitos en cuanto a maduración citoplasmática, siendo los ovocitos obtenidos durante la época fría 25.96 veces más probables de mostrar una maduración anómala cuando se someten a estrés térmico. Así pues, existe una mayor tolerancia al estrés térmico cuando los ovocitos provienen de la época cálida del año en comparación con los obtenidos en la época fría. En el capítulo 3, se evaluó el supuesto efecto protector de agentes antioxidantes suplementados en el medio de maduración de HSO bovinos. El retinol mejoró la progresión de los ovocitos a MII (P = 0.031), aunque retinyl y ácido oleico no pudieron contrarrestar los efectos del estrés térmico. Así, el retinol parece ser válido protegiendo la maduración nuclear en ovocitos estresados térmicamente. El objetivo del capítulo 4 fue evaluar el efecto de una exposición prolongada a ciclos circadianos de estrés térmico (31ºC, 3 horas/día) sobre los espermatozoides epididimarios de conejo. La motilidad total y la progresividad se vieron afectadas negativamente por las altas temperaturas (P < 0.05). Además, el estrés térmico incrementó la ratio de subpoblaciones menos mótiles aunque manteniendo los porcentajes de subpoblaciones más mótiles. En el capítulo 5, se evaluó el efecto del suplemento de agentes antioxidantes (albúmina sérica bovina, retinol y retinyl) en un medio de congelación comercial como método para mejorar la calidad de los espermatozoides descongelados de conejo, ya que la congelación produce un incremento de los niveles de ROS. El hecho de añadir agentes antioxidantes no mejoró la calidad espermática post-congelación, aunque el suplemento con retinyl parece ser tóxico. Por todo ello, es necesario realizar más estudios con el fin de encontrar el antioxidante apropiado y la concentración más efectiva con la cual pueda mejorarse la calidad espermática post-congelación. El objetivo del último capítulo fue evaluar el efecto de las altas temperaturas sobre los espermatozoides epididmarios de toro y cómo suplementar retinol al medio de mantenimiento como agente antioxidante podría mejorar los parámetros de calidad espermática. Retinol en el medio de mantenimiento no mostró ningún efecto sobre los parámetros de calidad espermática con excepción del porcentaje de acrosomías, el cual se redujo. Así pues, el retinol podría estabilizar la membrana acrosomal de los espermatozoides en situaciones de estrés oxidativo debido a las altas temperaturas.
The general aim of this thesis has been the study of the effects of high temperatures on gamete development and how the use of antioxidant agents supplemented to the maturation medium and sperm storage/freezing extenders could counteract the negative effects of heat stress and/or the excessive production of reactive oxygen species (ROS), in order to find additional methods to improve fertility during the warm season of the year. In chapter 1, the influence of heat stress on bovine oocyte maturation was evaluated and compared with overmatured oocytes. Based on the odds ratio, heat-stressed (41.5ºC, 18-21h of maturation; HSO) and overmatured (28h of maturation; OMO) oocytes were, 17.1 and 18 times more likely to show anomalous oocyte maturation, respectively, than control oocytes (38.5ºC; CO). Hence, heat stress proved to be valuable in aging oocytes by advancing nuclear and cytoplasmic processes in a similar form to that of oocyte overmaturation. The aim of chapter 2 was to compare the effects of heat stress on bovine oocyte maturation from oocytes collected during the cold (February-March) or warm (May-June) periods of the year. Only a significant interaction between season of collection and treatment was found in terms of cytoplasmic maturation, being oocytes collected during the cold season 25.96 times more likely to show an anomalous maturation when exposed to the heat treatment. From this chapter, it can be concluded that exists a higher tolerance to heat stress from oocytes harvested in the warm season compared to those collected in the cold period of the year. In chapter 3, the presumptive protective effects of antioxidant agents (retinol, retinyl and oleic acid) on maturation medium were evaluated on bovine HSO. Retinol allowed to improve the oocyte MII progression under heat stress conditions (P = 0.031), although retinyl and oleic acid, at the concentrations used in this study, could not counteract adverse effects of HS. Hence, retinol proved to be valuable in heat-stressed oocytes protecting nuclear maturation. Chapter 4 aimed to assess the effect of long exposure to summer circadian heat stress cycles (31ºC, 3 hours/day) on epididymal sperm cells from rabbit bucks. Sperm total motility and progressivity were negatively affected by high temperatures (P < 0.05). According to motile sperm-subpopulations, heat stress significantly increased ratio of less motile subpopulations, although maintaining percentage of the high motile subpopulation. Hence, the induced changes in sperm motility produced by environmental heat stress are linked to concomitant changes in the proportion of motile sperm-subpopulations of the epididymis, although these changes did not affect the subpopulation with the highest motile epididymal sperm cells. In the chapter 5, the effect of antioxidant agents (bovine serum albumin, retinol and retinyl) supplemented at different concentrations into a commercial freezing extender was evaluated in order to improve post-thaw rabbit sperm quality since cryopreservation increases ROS levels. The addition of antioxidant agents did not improve thaw-sperm quality, although retinyl supplementation seems to be toxic. More studies are required in order to find the appropriate antioxidants and their most effective concentrations, which will improve rabbit post-thaw sperm quality. The aim of the last chapter was assess the effect of high temperatures on bull epididymal sperm cells and how the addition of retinol as antioxidant agent in the storage extender could improve sperm quality parameters. Sperm quality parameters are mainly affected by high temperatures (41.5ºC) and the addition of retinol to the storage extender did not show any effect on sperm quality parameters with an exemption of the percentage of altered acrosomes, which was reduced in presence of retinol. Thus, retinol may stabilize sperm acrosomal membrane in situations of oxidative stress due to high temperatures.

Studies conducted for this dissertation utilized a rodent model exposed to single or multiple short duration heat loads in an effort to: 1) elucidate the changes in energy metabolism occurring at the tissue and whole-body level in response to hyperthermia, 2) characterize specific aspects of glucose utilization and hepatic glucose production following a heat load and 3) determine if aspects of mitochondrial function and/or dysfunction might play a role in the metabolic changes that occur in response to heat stress. Study 1 was conducted to determine if rodents exposed to heat stress shared similarities using a bovine heat stress model. Specifically, we were interested in identifying changes in blood metabolites and hormones, as well as gene expression and protein abundance of enzymes associated with energy metabolism in skeletal muscle (type I and type II), liver and adipose tissue. Previous bovine data indicates glucose may be preferentially utilized during heat stress, suggesting alterations in energy metabolism. This study provided evidence that tissue-specific changes occur in response to a heat load and that full glucose oxidation might be reduced, specifically in skeletal muscle where abundance of PDK4 mRNA was increased. Within skeletal muscle, glucose transporters (GLUTs 1 and 4) also tended to be increased in rats exposed to a heat load. Increases in skeletal muscle AMPK-α and PGC-1α as well as increased expression of energy substrate transporters suggests heat stress may impose a cellular energy deficit and/or increased energy demands which subsequently leads to changes in energy metabolism. Few changes were noted in either hepatic or adipose tissue in response to acute heat stress in this pilot study. Study aim of Chapter 3 was to further characterize the effects of heat stress on energy metabolism at the tissue and whole-body level in rats exposed to either 1 or 2 bouts of heat. Rats exposed to a 6 h heat load tended to have higher plasma glucose but reduced insulin levels, compared to thermal neutral controls, suggesting decreased glucose uptake or increased hepatic glucose output. Additionally, although heat stress likely increases whole-body energy demand, plasma NEFA levels were blunted in the early hours following onset of heat, suggesting increased adipocyte insulin sensitivity. Gene expression of enzymes associated with oxidative energy metabolism were increased in the TA (which is comprised primarily of glycolytic muscle fibers) following 2 bouts and in liver following a single bout of heat, while expression of oxidative enzymes were decreased within the soleus (a primarily oxidative muscle type). AMPK mRNA was increased following a single bout of heat in hepatic tissue and after 2 bouts of heat in type I skeletal muscle. AMPK mRNA abundance remained the same following 1 bout but was reduced following 2 bouts of heat within type II skeletal muscle. In the TA, phosphorylated AMPK protein abundance was reduced by HS. Abundance of PGC-1α mRNA was increased in types I and II skeletal muscle but was only numerically increased in liver following heat exposure. These data suggest differences at the transcription level in how heat effects energy metabolism within types I and II skeletal muscle as well as between muscle and hepatic tissue and also suggests a cellular attempt to increase energy production (by all mechanisms) in response to heat exposure. Study 3 (Chapter 4) focused on the effect of a heat load on glucose utilization in skeletal muscle and hepatic glucose production capacity. Similar to study 1, PDK4 expression was increased in types I and II skeletal muscle, while PDK2 expression was increased in hepatic tissue. Within skeletal muscle, increases in PDK expression paralled the increased protein abundance of PDHE1α following heat exposure, implying a decrease in oxidative glucose metabolism. Within the liver, protein abundance of PDH-E1α was reduced following a single heat load, but returned to TN levels after a 2nd heat exposure, suggesting that glucose oxidative metabolism is increased above normal levels after an initial heat exposure, but reduced following multiple heat bouts. Hepatic mRNA abundance for gluconeogenic enzymes were increased, implying an increase in hepatic glucose output capacity. The purpose of Study 4 (Chapter 5) was to determine if heat stress elicits changes on mitochondrial function/dysfunction (i.e. oxidative stress), that may account for changes observed in energy metabolism. Expression of genes associated with antioxidant defense were increased by heat stress, but differed between types I and II skeletal muscle as well as between muscle, hepatic tissue and WBCs. The abundance of mRNA for antioxidant enzymes was increased the greatest, and expression of DNA repair enzymes were also upregulated the most within hepatic tissue due to heat exposure, suggesting either increased damage at the level of hepatocytes or greater defensive capacity following an environmental insult. Taken together, this data provides evidence that heat alters energy metabolism, but these changes are tissue-specific and may be reflective of where damage is occurring, or which tissues are able to adapt and/or compensate for increased energy demands imposed by an environmental insult.

The second used a pre-heated flat plate in a transient wind tunnel to determine heat transfer rates with freestream turbulence generated by a number of parallel bar grids. Both liquid crystals and thin film gauges were used for heat-flux studies. A correlation has been derived that defines the heat transfer enhancement in terms of turbulence intensity and integral scale, as well as extending the conclusions of previous workers to apply at high intensities and with severe anisotropy.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 148-156).
Nanofluids, engineered colloidal dispersions of nanoparticles in fluid, have been shown to enhance pool and flow boiling CHF. The CHF enhancement was due to nanoparticle deposited on the heater surface, which was verified in pool boiling. However, no such work has been done for flow boiling. Using a cylindrical tube pre-coated with Alumina nanoparticles coated via boiling induced deposition, CHF of water was found to enhance up to 40% compared to that of the bare tube. This confirms that nanoparticles on the surface is responsible for CHF enhancement for flow boiling. However, existing theories failed to predict the CHF enhancement and the exact surface parameters attributed to the enhancement cannot be determined. Surface modifications to enhance critical heat flux (CHF) and Leidenfrost point (LFP) have been shown successful in previous studies. However, the enhancement mechanisms are not well understood, partly due to many surface parameters being altered at the same time, as in the case for nanofluids. Therefore, the remaining objective of this work is to evaluate separate surface effect on different boiling heat transfer phenomena. In the second part of this study, surface roughness, wettability and nanoporosity were altered one by one and respective effect on quenching LFP with water droplet was determined. Increase in surface roughness and wettability enhanced LFP; however, nanoporosity was most effective in raising LFP, almost up to 100°C. The combination of the micro posts and nanoporous coating layer proved optimal. The nanoporous layer destabilizes the vapor film via heterogeneous bubble nucleation, and the micro posts provides intermittent liquid-surface contacts; both mechanisms increase LFP. In the last part, separate effect of nanoporosity and surface roughness on pool boiling CHF of a well-wetting fluid, FC-72, was investigated. Nanoporosity or surface roughness alone had no effect on pool boiling CHF of FC-72. Data obtained in the literature mostly for microporous coatings showed CHF enhancement for well wetting fluids, and existing CHF models are unable to predict the enhancement.
by Bao Hoai Truong.
Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008.
Includes bibliographical references (p. 82-86).
Ocean heat content change (ocean heat uptake) has an important role in variability of the Earth's heat balance. The understanding of which methods and physical processes control ocean heat uptake needs improvement in order to better understand variability in the Earth's heat balance, improve the simulation of present-day climate, and improve the understanding and projection of future climate. Wind stress can play a strong role in ocean heat uptake on all timescales, and short timescale wind stress effects have not been well studied in the literature. This study for the first time examines short timescale spatial and temporal patterns of global variable wind stress datasets in a coupled atmosphere-ocean climate model. NCEP wind stress dataset was characterized for years 1978 to 2007. NCEP monthly means and monthly standard deviations are of the same magnitude, and strong wind stress events (tropical cyclones) are observed. A variety of metrics cannot reliably identify significant timescales or spatial patterns of the variable wind stress. Model behavior with and without variable wind stress is studied. This study uses the MIT IGSM, a 4°x 11 vertical level zonal atmospheric model coupled at the four hour timestep to a 20x2.50x22 vertical level ocean model with the K profile parameterization. Ocean properties in a no forcing scenario are sensitive to variable wind stress. In a weak forcing scenario (observed forcing over the last century), ocean properties are sensitive to variable wind stress, and internal modes of variability (such as an equatorial Pacific oscillation) are observed. In a global warming scenario (1% CO2 rise per year or a business as usual emissions scenario), the strong forcing overwhelms the more subtle responses due to the differences in variable wind stress forcing. Regardless of forcing, the high frequency variable wind stress (monthly or less) variable wind stresses can force a low frequency response. Hence the major source of annual variability of the MOC in this coarse resolution model is surface wind variability.
by Kelly Klima.
S.M.

While thermoelectric technology has developed steadily over the last 50 years, transverse thermoelectrics have generally been ignored in the industrial and commercial uses of thermoelectric devices to date. This project focuses on investigating transverse thermoelectric effects for localized cooling and heat flux sensing. Thermoelectric cooling devices are useful when their advantages (small size, solid state, active temperature control) outweigh their relatively poor efficiency. Transverse heat flux sensors, which generate an electric field in a direction orthogonal to the heat flow, have the advantage that the signal depends on the length of the device rather than the thickness. Thus, they can be made very thin for fast response times while maintaining a large signal. A prototype transverse device was built out of bulk samples of bismuth and bismuth telluride, which are common thermoelectric materials. The device was constructed of alternating layers of the constituent materials to simulate the effects of an intrinsically anisotropic material. The device was tested for its cooling and heat flux sensing capabilities, and the results of this testing were compared to predicted values. Although the device failed to demonstrate cooling, its heat flux sensing capabilities were promising. The device was tilted to several angles of inclination between 44° and 84° from horizontal, and the output voltage was recorded for several values of heat flux. The signal strength varied between 190.2 and 2321.6 ìV/(W/cm2), at inclination angles of 84° and 44°, respectively. The results followed the trend of the predicted values well, but the magnitude of the output voltage was significantly lower than expected. An uncertainty analysis was performed, and it was determined that the most likely source of error was the uncertainty in the amount of heat flux that went through the device during testing. This thesis outlines the process of building and testing the device, and the analysis of the results. Recommendations for future work are also given.
Master of Science

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 97-99).
Predicting the conditions of critical heat flux (CHF) is of considerable importance for safety and economic reasons in heat transfer units, such as in nuclear power plants. It is greatly advantageous to increase this thermal limit and much effort has been devoted to studying the effects of surface characteristics on it. In particular, recent work carried out by O'Hanley demonstrated the separate effects of surface wettability, porosity, and roughness on CHF, and found that porous hydrophilic surface coatings provided the largest CHF increase, with a 50-60% enhancement over the base case. In the present study, a systematic investigation of the effects that the physical characteristics of the hydrophilic layers have on heat transfer was conducted. Parameters experimentally explored include porous layer thickness, pore size, and void fraction (pore volume fraction). The surface characteristics are created by depositing layer-by-layer (LbL) thin compact coatings made of hydrophilic SiO₂ nanoparticles of various sizes. A new coating was developed to reduce the void fraction by using polymers to partially fill the voids in the porous layers. All test surfaces are prepared on indium tin oxide - sapphire heaters and tested in a pool boiling facility at atmospheric pressure in MIT's Thermal-Hydraulics Laboratory. Results indicate that CHF follows a trend with respect to each parameter studied and clear CHF maxima reaching up to 114% enhancement are observed for specific thickness and pore size values. ZnO₂ nanofluid-generated coatings are also prepared and their boiling performance is compared to the boiling performance of the engineered LbL coatings. The results highlight the dependence of CHF on capillary wicking and are expected to allow further optimization of the nanoengineered surfaces.
by Melanie Tetreault-Friend.
S.M.

It is well established that older adults display marked impairments in the heat loss responses of sweating and skin blood flow relative to young adults which can exacerbate body heat storage by compromising whole-body heat loss (evaporative + dry heat exchange). Similarly, young women display reductions in whole-body heat loss relative to young men during exercise in dry heat. As such, it is possible that the age-related decline in whole-body heat loss will be greater among women relative to men. To examine whether the age-related decline in whole-body heat loss would be greater in women relative to men during exercise in dry heat, and whether this response would be more pronounced with a greater elevation in the level of heat stress, whole-body heat loss (evaporative ± dry heat exchange) was evaluated in 80 individuals (46 men, 34 women) aged between 18-70 years. Participants completed an incremental exercise model involving three, 30-min bouts of semi-recumbent cycling at fixed rates of metabolic heat production (150, 200, 250 W/m2), each separated by a 15-min recovery period in hot-dry conditions (40˚C, ~15% relative humidity). Whole-body heat loss was measured using direct calorimetry whereas metabolic heat production was measured using indirect calorimetry. Whole-body heat loss declined with age (across men and women) during moderate- and vigorous-intensity exercise by 4.2 and 6.6 W/m2 (both P < 0.050), respectively, however, these relationships were not modified by sex (both P > 0.050). Nonetheless, whole-body heat loss was lower in women relative to men during moderate- and vigorous-intensity exercise by 8.4 and 12.1 W/m2 (both P < 0.05), respectively. Therefore, the results of this thesis demonstrate that the age-related decline in whole-body heat loss is not dependent on sex.

Thesis (Ph. D.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains xii, 145 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 143-145).

Nanomechanical resonators have extremely low masses (~ 10−15 kg) and frequencies from a few megahertz all the way up to the gigahertz range. These properties along with a small damping rate make them very useful or ultrasensitive detection applications, now pushing into the realm of zeptonewtons (10−21 N) and zeptograms (10−21 g). On a more fundamental level, nanomechanical resonators are expected to display quantum mechanical effects when cooled down to millikelvin temperatures. The understanding of dissipation in nanomechanical resonators is important for device applications and to study quantum mechanical effects in such systems. However, despite a range of experiments on semiconducting and metallic devices, dissipation in nanomechanical resonators at low temperatures is not yet well understood. Although mechanical resonators have traditionally been operated in the linear regime, exploiting their nonlinearities can prove advantageous for industrial applications as well as opening up new experimental windows into the fundamental study of the nonlinear dynamics of mesoscopic systems. In this thesis, we present results from low temperature dissipation studies on pure gold and on gold-coated high-stress silicon nitride nanomechanical resonators. A theory, which predicts the existence of tunnelling two-level systems (TLS) in bulk disordered solids at low temperatures, is used as a framework to describe the data. The nonlinear interactions between different flexural modes of a single silicon nitride device, are explored experimentally and theoretically. The resonators were fabricated as doubly-clamped beams using a combination of optical lithography, electron-beam lithography, dry and wet etching techniques. The motion of the resonators was actuated and detected using the magnetomotive scheme. At low temperatures, all the beams had resonant frequencies between 3 and 60 MHz and quality factors in the range 105 − 106. The strong variation observed in dissipation and resonant frequency at the lowest temperatures (below 1 K) indicates the presence of tunnelling TLS in nanomechanical resonators.

En esta tesis, se estudiaron los efectos del estrés por calor (EC) sobre la producción de ovejas lecheras Lacaune (Exp.1), así como la respuesta de cabras lecheras Murciano-Granadina bajo condiciones de EC a la L-carnitina (Exp. 2) y la metionina (Exp. 3). En los 3 Exp., los animales fueron alimentados con una ración única mezclada y se ordeñaron x2 al día. Las condiciones ambientales fueron: termo-neutralidad (TN; THI = 59-65) y EC (día, THI = 83; noche, THI = 75). El fotoperíodo (día-noche) fue constante (12-12 h). La temperatura rectal (TR), el ritmo respiratorio (RR), la IMS, el consumo de agua (CA) y la producción de leche (PL) se registraron diariamente, mientras que la leche para la composición se muestreó semanalmente y se registró el peso vivo (PV) al inicio y al final de cada período. En el Exp.1, las ovejas (n = 8) fueron expuestas a TN o EC en un diseño cruzado de 2 períodos (21 días cada uno). Además, a las ovejas se les administró glucosa, insulina y epinefrina para evaluar sus respuestas metabólicas. EC aumentó la TR, RR, CA y la pérdida de PV, pero redujo la IMS y el contenido de grasa y proteína de la leche sin afectar a PL. A pesar de la reducción de IMS por EC, los AGNE en sangre no cambiaron, y sin embargo los valores de creatinina aumentaron. La respuesta a los desafíos metabólicos indicó que las ovejas EC presentaban una rápida absorción de glucosa y una mayor resistencia a las señales lipolíticas en comparación con las ovejas TN. En los Exp.2 y 3 con cabras lecheras, el diseño fue un cuadrado latino 4 × 4, ya que se agregaron 2 factores dietéticos a las 2 condiciones ambientales. Las 2 condiciones dietéticas fueron control (CON) sin suplementación, versus L-carnitina protegida del rumen (CAR, Exp. 2) o metionina protegida del rumen (Met, Exp. 3). En Exp. 2, las cabras EC experimentaron un aumento de TR y RR. Además, las cabras EC sufrieron una pérdida del 26% en IMS, pero tendieron a comer partículas de tamaño más largo. La CAR aumentó drásticamente las concentraciones de carnitina libre, acetilo y total en sangre. A pesar de esta absorción eficiente, CAR no tuvo efecto sobre IMS, producción de leche o metabolitos en sangre en condiciones TN o EC. En el Exp.3, la IMS de las cabras TN se limitó a 2.0 kg/d, mientras que las cabras de EC se alimentaron ad libitum. Así pues, las cabras EC presentaron sólo un 9.8% menos IMS que TN, aunque significativo. En consecuencia, no se detectaron cambios en PL. Se observaron incrementos esperables en TR y RR debido al EC, pero Met redujo el RR por la mañana y RT en la tarde. Además, Met evitó la pérdida típica de PV en condiciones de EC. El perfil de aminoácidos en sangre (AA) reveló una menor concentración basal de Met, a pesar de los niveles comparables de IMS. Además, las cabras EC tenían poco glutamato, lo que podría estar relacionado con una inflamación y respuesta inmune a nivel gastrointestinal. La suplementación con Met ahorró glutamato, independientemente de la temperatura ambiente. En general, el EC afectó negativamente la producción de las ovejas lecheras. La adaptación metabólica de las ovejas lecheras al EC incluyó una reducción de la movilización de grasa corporal y el aumento de la degradación de las proteínas musculares. La metionina, pero no la L-carnitina, tuvo algunos efectos beneficiosos sobre el rendimiento de las cabras lecheras estresadas por el calor. Probablemente un poco más AA además de la metionina deberían ser suplementados en condiciones de EC.
In the current thesis the effects of heat stress (HS) on performance of Lacaune dairy ewes (Exp.1) as well as the response of HS Murciano-Granadina dairy goats to dietary L-carnitine (Exp. 2) and methionine (Exp. 3) were evaluated. In the 3 Exp., animals were fed a total mixed ration and milked x2 daily. The environmental conditions were: thermal neutral (TN; THI = 59-65) and HS (day, THI = 83; night, THI = 75). Photoperiod (light- dark) was constant (12-12 h). Rectal temperature (RT), respiratory rate (RR), DMI, water intake (WI) and milk yield (MY) were recorded daily, whereas milk for composition was sampled weekly and BW was registered at the start and the end of each period. In Exp.1, ewes (n = 8) were exposed to TN or HS in a crossover design with 2 periods (21 d each). Further, ewes were administered with glucose, insulin and epinephrine to evaluate the metabolic responses. HS increased RT, RR, WI and BW loss, but reduced DMI, and milk fat and protein contents without affecting MY. Despite the reduced DMI by HS, blood NEFA did not change, but creatinine values increased. Response to the metabolic challenges indicated that HS ewes had faster uptake of glucose and greater resistance to lipolytic signals compared to TN ewes. In Exp.2 & 3 with dairy goats, the design was 4 × 4 Latin square as 2 dietary factors were added to the 2 environmental conditions. The 2 dietary conditions were control (CON) without supplementation vs. rumen protected L-carnitine (CAR, Exp. 2) or rumen protected methionine (Met, Exp. 3). In Exp. 2, HS goats experienced increased RT and RR. Additionally, HS goats suffered 26% loss in DMI, but they tended to eat longer particle sizes. CAR dramatically increased blood free-, acetyl, and total-carnitine concentrations. Despite this efficient absorption, CAR had no effect on DMI, milk production or blood metabolites in TN or HS conditions. In Exp.3, DMI for TN goats was limited to 2.0 kg/d, whereas HS goats were kept feeding ad libitum. Consequently, HS goats had only 9.8% (although significant) less DMI than TN. Consequently, no changes in MY were detected. Expected increments in RT and RR due to HS were detected but Met resulted in less RR in the morning and lower RT in the afternoon. In addition, Met avoided the typical BW loss under HS conditions. The profile of blood amino acids (AA) revealed less basal Met concentration, despite the comparable DMI levels. Additionally, HS goats were in shortage of glutamate, which could be related to the inflammation and immune response at the gastrointestinal level. Met supplementation spared glutamate regardless the ambient temperature. Overall, HS negatively affected the performance of dairy ewes. Metabolic adaptations of dairy ewes to HS included reduced body fat mobilization and increased muscle protein breakdown. Methionine, but not L-carnitine, had some beneficial effects on the performance of heat-stressed dairy goats. Probably some more AA in addition to methionine should be supplemented under HS conditions.
Cette thèse, étude les effets du stress thermique (ST) sur les performances des brebis laitières Lacaune (Exp.1) ainsi que la réponse des chèvres laitières Murciano-Granadina à la L-carnitine (Exp.2) et à la méthionine (Exp. 3) sous conditions de ST. Dans les 3 Exp, les animaux ont reçu une ration totale mélangée et traitent x2 par jours. Les conditions environnementales étaient : thermoneutralité (TN; THI = 59-65) et ST (jour, THI = 83; nuit, THI = 75). La photopériode (jour-nuit) était constante (12-12 h). La température rectale (TR), le rythme respiratoire (RR), la MSI, la prise d’eau (PE) et la production de lait (PL) ont été enregistrés quotidiennement, tandis que le lait pour la composition a été échantillonné chaque semaine et PV a été enregistré au début et à la fin de chaque période. Dans Exp.1, les brebis (n = 8) ont été exposées au TN ou au ST avec permutation de 2 périodes (21 j chacune). En plus, les brebis ont été administrées avec du glucose, de l’insuline et de l’épinéphrine pour évaluer la réponse métabolique. Le ST a augmenté le TR, RR, PE et a réduit le PV, mais a réduit l’IMS et le contenu en matières grasses et en protéines du lait sans affecter la PL. Malgré la réduction de l’IMS par le ST, le AGNE sanguin n’a pas changé, mais les valeurs de créatinine ont augmenté. La réponse aux défis métaboliques a indiqué que les brebis ST avaient une absorption plus rapide du glucose et une plus grande résistance aux signaux lipolytiques que les brebis TN. Dans Exp.2 & 3 avec des chèvres laitières, le design expérimental était un carré latin 4 × 4 car 2 facteurs alimentaires ont été ajoutés aux 2 conditions environnementales. Les 2 conditions alimentaires étaient control (CON) sans supplémentation et une supplémentation avec la L-carnitine protégée du rumen (CAR, Exp. 2) ou avec la méthionine protégée du rumen (Met, Exp. 3). Dans Exp. 2, les chèvres ST ont demontré une augmentation du TR et RR accrues. De plus, les chèvres ST ont réduit de 26% l’IMS, mais elles avaient tendance à manger des particules plus longues. La CAR a considérablement augmenté les concentrations libres, d’acétyle et carnitine totale de sang. Malgré cette absorption efficace, la CAR n’a eu aucun effet sur l’IMS, la PL ou les métabolites sanguins dans les conditions TN ou ST. Dans Exp.3, l’IMS pour les chèvres TN était limité à 2,0 kg/j, tandis que les chèvres ST étaient nourries ad libitum. Par conséquent, les chèvres ST avaient seulement 9,8% (bien que significatif) de moins d’IMS que TN. Par conséquent, aucun changement dans PL n’a été détecté. Des augmentations attendues de la TR et du RR dues au ST ont été détectées, mais la Met a entraîné une diminution du RR le matin et une TR plus basse l’après-midi. De plus, Met a évité la perte de PV typique dans les conditions ST. Le profil des acides aminés du sang (AA) a révélé une concentration en Met basale inférieure, malgré des niveaux de DMI comparables. De plus, les chèvres ST manquaient de glutamate, ce qui pourrait être lié à l’inflammation et à la réponse immunitaire au niveau gastro-intestinal. La supplémentation rencontrée a épargné le glutamate quelle que soit la température ambiante. Globalement, le ST a affecté négativement la performance des brebis laitières. Les adaptations métaboliques des brebis laitières au ST comprenaient une mobilisation réduite des graisses corporelles et une dégradation accrue des protéines musculaires. La méthionine, mais pas la L-carnitine, a eu certains effets bénéfiques sur les performances des chèvres laitières soumises à un ST. Probablement un peu plus d’AA en plus de la méthionine devrait être supplémenté dans les conditions ST.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, June 2003.
"August 2002."
Includes bibliographical references (p. 73-77).
As commercial and military aircraft engines approach higher total temperatures and increasing overall fuel-to-air ratios, there exists a potential for significant heat release to occur in the turbine if energetic species emitted from the combustor are further oxidized during interaction with film-cooling flows. Currently there is little basis for understanding the effects on aero-performance and durability due to such secondary reactions. To study surface heat flux augmentation due to near-wall reactions, a shock tube experiment was employed to generate short duration, high temperature (1000-2800 K) and pressure (6 atm.) fuel-rich flows over a film-cooled flat plate. The relative increase in surface heat flux due to near-wall reactions was investigated over a range of fuel levels, mass blowing ratios (0.5-2.0), and Damkohler numbers (ratio of flow to chemical time scales) from near zero to 30. It was shown that significant increases in surface heat flux can be produced due to chemical reactions in the film-cooling layer. Under some conditions, the heat flux exceeded that obtained when no film-cooling layer was present on the surface. A numerical tool was developed and showed good agreement with the experimental results for predicting changes in surface heat flux and film effectiveness in the presence of local reactions. Off-surface effects and changes in convective heat transfer coefficient were also evaluated. Realistic turbine and cooling flows were examined to ascertain the robustness of various cooling configurations to near-wall reactions. The result of this work is a set of tools based on a group of parameters that can be used to assess changes in heat load due to near-wall reactions. The non-dimensional parameters are the Damkohler
(cont.) number (Da), mass and momentum blowing ratios (B and I), freestream energetic heat release potential (H*), and scaled heat flux ratio (Qs). The scaled heat flux ratio always increases with Damk6hler number and depends on the structure of the cooling jet, but is not a function of the freestream fuel energy content.
by Daniel Robert Kirk.
Ph.D.

Automotive components are tested extensively in wind tunnels by automotive manufacturers and race teams. This is usually achieved using an accurate scale model representation of the component within the wind tunnel. Automotive heat exchangers, however, are comprised of numerous intricate geometries and are therefore impractical to produce at model scale. Instead they are simply modelled as pressure drops, achieved using a thin mesh or honeycomb of known porosity. Most commercial computational fluid dynamics solvers ignore the geometry of the heat exchanger and instead model it as a discontinuity with a known pressure drop and heat transfer. The pressure drop across an automotive heat exchanger, however, was found to vary with both the coolant temperature and the angle of inclination of the heat exchanger. This thesis initially presents a relationship between the pressure drop coefficient and the inclination angle for varying media porosities. Mathematical relationships for inclination angles of 0°, 15°, 30° and 45°. were derived relating this pressure drop coefficient to the porosity of the media. Weighted least squares is proposed over ordinary least squares when obtaining the Forchheimer equation coefficients from experimental measurements. Investigation extends into the thermo-fluid effects on a full scale automotive heat exchanger when inclined at 0 °, 15°, 30° and 45°. It was found, depending on the angle, that there was a difference in the pressure drop of up to 10% between the unheated and heated (100 C) heat exchanger. Based on the proposed mathematical relationship, this correlated to a 4% decrease in porosity in order to accurately model the automotive heat exchanger at subscale. The thesis concludes with experimental and numerical investigation into the heat transfer on a hydrodynamically and thermally developing ow within a radiator channel. Laser doppler anemometry measurements recorded a 1.5% increase in the centreline velocity compared to 0.8% obtained from numerical simulation.

Thesis (Ph. D.)--West Virginia University, 2007.
Title from document title page. Document formatted into pages; contains xiii, 131 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 129-130).

Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, December 1990.
Thesis Advisor(s): Atchley, Anthony A. ; Hofler, Thomas J. "December 1990." Description based on title screen as viewed on March 31, 2010. DTIC Descriptor(s): Heat Transfer, Coupling (Interaction), Peak Values, Ratios, Temperature, Thermodynamics, Edges, Isolation, Sensitivity, Regions, Short Range (Time), Profiles, Plates, Internal, Acoustic Arrays, Pressure, Drives, Leading Edges, Mean, Amplitude, Sound Pressure, Stacking, Thermopiles. DTIC Identifier(s): Heat Pumps, Energy Conversion, Energy Storage, Heat Transfer, Thermoacoustic Couples, Theses Author(s) subject terms: Acoustics, Thermoacoustics, Thermoacoustic Heat Transport. Includes bibliographical references (p. 34). Also available in print.

CCI Valve Technology AB is a company located in Säffle, Sweden, that manufactures and installs bypass valves. Due to requirements outside normal standards on the valve's hardness values, some measurements have had difficulties meeting such requirements. During this thesis work, tests were carried out to determine how to overcome the difficulties. The experiments focused on five different areas that may affect the components hardness, welding method, soaking temperature during post weld heat treatment, measuring procedure, component thickness and number of heat treatment cycles. The Grade 91 steel specimens that were examined consisted of five solid cylinders and three various pipes that were welded together by using shielded metal arc welding (SMAW) or gas tungsten arc welding (GTAW). Each pipe was sawed apart into three equal parts. All specimens were hardness tested and eight of the specimens' microstructure was studied with an optical microscope. The hardness measurement instruments used, LECO V-100-C2 and GE-MIC 10, are Vickers hardness testers, one stationary and the other one portable. The measuring results contain a vast number of different hardness measurement data. From the analyzed data, the conclusions were drawn that the most suitable soaking temperature during post weld heat treatment were 750° C, that the SMAW method creates a more stable hardness profile than the GTAW method, and that one heat treatment cycle is more beneficial than two or more.

Heat shock protein 70 (HSPA/HSP70) gene expression is induced by a wide range of cellular stress conditions. This study investigated HSPA/HSP70 expression in human cell lines exposed to hypoxic conditions, in cancerous and non-cancerous brain tissue specimens from 18 patients (gliomas and normal conditions), and in post mortem rat brain samples exposed to heat shock. Three human glioma cell lines were chosen for this study, each representing various types of glioma: (astrocytoma, oligodendroglioma and glioblastoma), with a normal human astrocyte cell line used as a control. In addition, 18 clinical brain tissue samples were also examined. HSPA RNA transcripts and proteins were examined in these samples using qRT-PCR, immunofluorescence and flow cytometry techniques. The average HSPA mRNA copy numbers detected in glioblastoma tissue were 1.8 and 8.8 fold higher respectively than in lower grade glioma and control tissues, which is suggestive of a grade related transcription profile. Similar patterns of grade related expression were also observed in corresponding cell lines. The percentage of cells showing positive for HSPA protein in normal cell lines increased from 0 to 33% immediately after exposure to hypoxia, and gradually declined to 11% 24 h after treatment. However, the effects of hypoxia were marginal in glioma cells, due to the already elevated levels of HSPA. Although hypoxia induced HSPA expression in normal cells, it did not achieve the same level of induction in cancer cells, suggesting that there are other factors which contribute to the induction of HSPA. These results suggest that HSPA is induced in cancer cells, not only by hypoxia, but also by other factors. In addition, this study indicated for the first time that HSPA expression in glioma cells may possibly be grade related, and thus may have value as a prognostic marker. However a greater sample size is needed to validate such findings. This study showed that HSPA is expressed at low levels in normal brain tissue, but was more highly expressed in brain tissue subjected to mild heat shock. The levels of HSPA transcripts in heat shocked post mortem brain tissue showed a marked increase in HSPA expression. GAPDH was used as a control gene for these studies, and exhibited a consistent level of expression in normal and tumourous cell lines and tissue samples under normal and hypoxic conditions, and also in post mortem tissues exposed to heat shock. For Homo sapiens GAPDH, the average transcript numbers for normal and tumourous cell lines and brain tissue samples were approximately 145,000 copies per sample. For Rattus norvegicus GAPDH, levels were higher than for human samples, at an average of 268,300 copies per sample. The consistency of these results confirms that GAPDH was a suitable candidate gene for the purpose of this study. Early in the post-mortem period, HSPA is expressed more highly in tissues subjected to single and multiple heat shocks compared to controls. However, later post-mortem intervals of between 3 - 24 h demonstrated inconsistent and irregular results, with no predictive or reproducible patterns. Therefore, although there is demonstrable de novo expression of HSPA in post mortem brain tissue in response to heat shock, it is difficult to predict the full parameters of this induction, probably as a result of other forms of cellular stress affecting these tissues under our experimental methodology. These initial studies indicate that the use of HSPA with the methodologies employed here are not suitable as an accurate indicator of post-mortem interval.

There are several different types of compact heat exchangers used in applications where small size and weight are required. One particular type of compact heat exchanger, the louvered fin heat exchanger, has been used heavily in the automotive and air conditioning industries. Over the last several decades, the majority of the work towards improving louvered fin exchanger efficiency has focused on designing more efficient fins by optimizing fin parameters like louver angle, fin pitch, louver pitch, and louver length. At this point in time, many improvements to standard louver geometry have been made, so other surfaces and methods of enhancing exchanger performance need to be studied if any significant future efficiency gains are to be expected. This thesis presents a detailed experimental study that has two major foci relative to the performance of the louvered fin compact heat exchanger. The first is to determine the effect of louver length on pressure drop and tube wall heat transfer, which is the primary heat transfer surface in the heat exchanger. The second is to augment tube wall heat transfer with the use of delta winglets placed on the fins near the tube wall. These studies were completed on a 20X scale model of a louvered fin exchanger with a fin pitch to louver pitch ratio of 0.76 and a louver angle of 27°, over a Reynolds number range based on louver pitch of 230 < ReLp < 1016. The three louver lengths evaluated were 100%, 82%, and 70% of the fin height and delta winglet experiments were performed for louver length to fin pitch ratios of 100% and 70%. Heat transfer results for the louver length tests show that decreasing louver length leads to increases in tube wall heat transfer of 0% to 50% depending on Reynolds number. Also, delta winglets placed on the fins near the tube wall have been shown to produce average tube wall heat transfer augmentations of up to 52%.
Master of Science