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Sivanantharaja, G. (Geethanchali). "Effect of surface roughness on heat transfer in heat exchanger." Bachelor's thesis, University of Oulu, 2017. http://urn.fi/URN:NBN:fi:oulu-201712143310.
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The heat exchanger is a device that transfers heat from one fluid to another or between fluid and the environment. Over the last few decades, the role of heat exchangers has increased in the process of heat recovery and introduction of new energy sources. Surface roughness of heat exchanger wall plays a vital role in the efficiency of heat transfer. Therefore, significance of surface roughness is examined by many researchers applying different shapes of roughness. Roughness is the variation in the height of a surface. It could be either a part of the geometry or due to deposition of undesired materials (which decreases the thermal function of the heat exchanger, increases the pressure drop and could cause corrosion). Dimensionless heat transfer correlations such as Nusselt number provides a clear view about the effect of heat transfer by surface roughness. This thesis combines different Nusselt correlations for distinct shapes of surface roughness and investigates the suitability of them on a test experiment by comparing the values gotten. From this investigation it was clear that the value of Nunner correlation delivers the most reasonable results for a fouled layer formed by means of crystallization. Also the Nusselt correlation by Saini et al. could be more suitable for artificial surface roughness than for a fouled surfaceLämmönvaihdin on laite, joka siirtää lämpöä fluidista toiseen tai fluidin ja ympäristön välillä. Viimeisimpien vuosikymmenten aikana lämmönvaihtimien rooli on kasvanut lämmön talteenottoprosesseissa ja uusien energialähteiden käyttöönotossa. Lämmönvaihtimien pinnankarheudella, jolla tarkoitetaan seinämän pintakuvion korkeuden muutosta verrattuna tasaiseen pintaan, on merkittävä rooli lämmönvaihtimen tehokkuudessa. Pinnankarheuden vaikutusta lämmönsiirtoon onkin tarkasteltu useissa tutkimuksissa. Pinnankarheus voi olla osa lämmönvaihdinrakennetta tai johtua ei haluttujen materiaalien kerrostumisesta pinnalle. Tällöin puhutaan likaantumisesta, joka heikentää lämmönvaihtimen lämmönsiirtoa, lisää painehäviötä ja voi aiheuttaa korroosiota. Dimensiottomat korrelaatiot, kuten Nusseltin luku antavat tietoa pinnankarheuden aiheuttamasta vaikutuksen lämmönsiirtoon. Tässä kandidaatintyössä on tarkasteltu kirjallisuudessa esitettyjä Nusseltin luvun korrelaatioita ja niiden soveltuvuutta eri pinnankarheuden muotoihin sekä tutkittu niiden soveltuvuutta todellisen lämmönvaihtimen tapauksessa. Tästä tutkimuksessa tarkastelluista korrelaatioista Nunnerin korrelaatio soveltui parhaiten likaantuneen lämmönvaihtimen lämmönsiirron tarkasteluun. Sainin ym. korrelaatio arvioitiin soveltuvan paremmin keinotekoisen pinnankarheuden kuin likaantuneen pinnan lämmönsiirron tarkasteluun
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Arjona, Anibal Augusto. "Molecular responses of neonatally heat stressed broilers exposed to acute heat stress." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39965.
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Exposure of broiler cockerels to between 35.0 to 37.8 C for 24 hr at 5 days of age increases their survival when exposed to a heat challenge at 6 weeks of age (35.0-37.8 C; RH 50% ). This' phenomenon does not resemble acclimation since the physiological changes known to occur in acclimated birds exposed to heat have not been observed in the neonatally stressed birds. A series of experiments were conducted to elucidate the mechanisms of neonatally induced thermotolerance. In Experiment 1, the erythrocyte protein profile of control and 5 days heated birds prior to and during exposure to acute heat were determined. Prior to juvenile heat exposure no differences in the erythrocytic protein profile of neonatally stressed and control birds were observed at any age (10, 17, 24, 31 and 38 days of age) when maintained under control conditions. However, upon exposure to an acute heat challenge (40.5 C; 52 days of age) temporal and differential expressions of proteins similar in molecular weight to heat shock proteins (HSPs) were observed between the neonatally stressed and control birds. In Experiment 2, the effects of neonatal heat stress at various ages (5, 8, 12, 16 days of age) on the protein synthesis profile of heart, brain (telencephalon, diencephalon, brain stem, cerebellum) and liver tissues during exposure to an acute heat challenge were studied. In addition, body temperature during neonatal heat exposure was monitored. A significant increase in body temperature was observed during neonatal heat stress. A steady increase in the magnitude of the temperature change was noticed up to 12 days of age. Body temperature of birds exposed to neonatal heat at 16 days of age was similar to that of birds heated at 5 days of age.Ph. D.
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Poirier, Martin. "The Effect of Progressive Heat Acclimation on Change in Body Heat Content." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26219.
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Heat acclimation increases the local heat loss responses of sweating and skin blood flow which is thought to persist for up to 3 weeks post-acclimation. However, the extent to which increases in local heat loss affect whole-body heat loss as a function of increasing levels of heat stress remains unresolved. Using direct calorimetry, we examined changes in whole-body evaporative heat loss (EHL) during progressive increases in metabolic heat production 1) prior to (Day 0), during (Day 7) and following a 14-day heat acclimation protocol (Day 14) – Induction phase, and; 2) at the end of a 1-week (Day 21) and 2-week decay period (Day 28) – Decay phase. Ten males performed intermittent exercise (3 x 30-min (min) bouts of cycling at 300 (Ex1), 350 (Ex2), and 400 watts•meters2 (W•m2) (Ex3) separated by 10 and 20 min rest periods, respectively). During the induction period, EHL at Day 7 was increased at each of the three exercise bouts (Ex1: + 6%; Ex2 +8%; Ex3: +13%, all p≤0.05) relative to Day 0 (EHL at Ex1: 529 W; Ex2: 625 W; Ex3: 666 W). At Day 14, EHL was increased for all three exercise bouts compared to Day 0 (Ex1: 9%; Ex2: 12%; Ex3: 18%, all p≤0.05). As a result, a lower cumulative change in body heat content (ΔHb) was measured at Day 7 (-30%, p≤0.001) and Day 14 (-47%, p≤0.001). During the decay phase, EHL at Day 21 and 28 was only reduced in Ex 3 (p≤0.05) compared to Day 14. In parallel, ΔHb increased by 39% (p=0.003) and 57% (p≤0.001) on Day 21 and Day 28 relative to Day 14, respectively. When Day 28 was compared to Day 0, EHL remained elevated in each of the exercise bouts (p≤0.05). As such, ΔHb remained significantly lower on Day 28 compared to Day 0 (-16%, p=0.042). We show that 14 days of heat acclimation increases whole-body EHL during exercise in the heat which is maintained 14 days post-acclimation.
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Yang, Jun. "Effect of non-uniform axial heat-flux distribution on critical heat flux." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26816.
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An experimental study of the effect of axial flux distribution (AFD) on critical heat flux (CHF) was conducted in directly heated tubes at the Freon-equivalent CANDU reactor conditions of interest. CHF measurements were obtained on test sections with four nonuniform AFD profiles as well as a uniform AFD profile using HFC-134a as a test fluid. Each of the non-uniform AFD test sections had a stepped cosine heat flux profile with approximately 16 heat flux steps. The test conditions covered a pressure range of 1662 to 2389 kPa, a mass flux range of 2827 to 4648 kg m-2 s -1 and an inlet quality range of -0.909 to -0.002.
The results showed that the AFD has a strong effect on CHF at high dryout qualities. (Abstract shortened by UMI.)
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Zhang, Ji. "Geometry effect on post-dryout heat transfer." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0013/MQ28469.pdf.
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Bhatti, A. R. "Effect of heat treatment on metallic glasses." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236306.
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Williams, Winifred Elizabeth. "HEAT TRANSFER IN THE MICROCIRCULATION." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275277.
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Morrison, Shawnda A., and n/a. "Causes and effects of cardiovascular strain in the heat." University of Otago. School of Physical Education, 2008. http://adt.otago.ac.nz./public/adt-NZDU20080404.162058.
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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.
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Sazama, Matt. "The effect of vapor permeable versus non-vapor permeable shirts on heat stress." Online version, 2001. http://www.uwstout.edu/lib/thesis/2001/2001sazamam.pdf.
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Martin, David E. "The effect of heat stress on excess post exercise oxygen consumption." Virtual Press, 1992. http://liblink.bsu.edu/uhtbin/catkey/834623.
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While a great deal of research has been directed towards the phenomena of excess post exercise oxygen consumption (EPOC), the effect of thermal stress on EPOC is not well defined. To assess the effect of heat stress on EPOC, seven healthy, active subjects (4 female, 3 male; 23.9 ± 2.0 years of age) performed 4 trials: one control (quiet rest) and one exercise (45 minutes of cycling at 65% VO2max workload) trial in moderate (23° C, 50% humidity) and hot (35° C, 50% humidity) environments. Oxygen consumption (V02), heart rate (HR) and rectal temperature (RT) were assessed pre, during and post control or exercise. Subjects were monitored until post exercise VO2 had returned to within ±2% of baseline. EPOC was determined by subtracting baseline VO2 from total V02 during the post exercise period. During the first 15 minutes (acute) post exercise, a significant EPOC (p = 0.0019) was seen in both exercise conditions over both control conditions. During the slow phase (> 15 minutes post exercise to baseline), there was no significant difference between the hot control (HC), moderate exercise (ME), or hot exercise (HE) EPOC. Total time post exercise until baseline was achieved was 35, 44, and 51 minutes for HC, ME, and HE respectively. HR was significantly elevated in both exercise conditions. During the acute post exercise period, HR in HE was elevated above MC, ME and HC (p < 0.05). RT was elevated in both exercise conditions during and post exercise. The present data indicate that heat stress does not have a significant effect on the magnitude or duration of EPOC.School of Physical Education
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Chao, Sheng-Hao. "Heat Shock Proteins in Ascaris suum." Thesis, University of North Texas, 1995. https://digital.library.unt.edu/ark:/67531/metadc279311/.
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Ascaris suum were exposed to a number of stressors, including heavy metals and both high (40°C) and low (18°C) temperatures. The 70kD and 90kD heat shock proteins (HSPs) in the different A. suum tissues were analyzed by Western blot and quantitated by Macintosh Image Program.
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Picton, S. "The effect of heat-stress on tomato ripening." Thesis, University of Nottingham, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233614.
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Wagstaff, Marcus James Dermot. "The neuroprotective effect of the heat shock proteins." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267150.
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Ivester, David Newell. "Heat exchanger modeling and optimization in the triple-effect absorption cycle." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/16076.
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Cassel, Stanley David. "The effect of increasing length on the overall conductance and capacitance of long heat pipes." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/19589.
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Alm, David Michael. "Comparison and interaction of heat and salt stress in cultured tobacco cells." Virtual Press, 1986. http://liblink.bsu.edu/uhtbin/catkey/445616.
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Cultured tobacco cells (Nicotiana tabacum L., cv Wisconsin-38) were subjected to temporary sub-lethal heat and salt shock treatments to determine the effects of these treatments on various physiological parameters after subsequent lethal heat or salt stresses. Tobacco cells developed a tolerance to a non-permissive temperature stress (54C for 14 min) when pretreated with heat shock of 38C for 2h but not when pretreated at 42C for 2h. Cells pretreated at 38 (2h) exhibited less than 30% normal growth when the 54C stress came immediately after the 38C treatment. Tolerance to the 54C stress developed with increased interval between shock and stress with cells exhibiting 95% normal regrowth when the 54C stress was administered 8h after the 38C shock. The developement of heat tolerance was inhibited if heat shock was done in the presence of a non-injuring level of EGTA (.0.5mM). Cells treated with EGTA during heat shock grew normally at 23C but not after a 54C heat stress. EDTA (0.5mM) had little effect on the acquisition of tolerance to heat stress.Wisconsin-38 cells developed a tolerance to a non-permissive salt stress (2% NaCl for 16h) when pretreated at a lower salt level (1.2% NaCl) for 3h. Cells heat shocked at 38C exhibited increased tolerance of the lethal salt stress up to 8h. Conversely, cells heat shocked at 42C exhibited immediate tolerance to lethal salt stress and this tolerance decayed over eight hours. The heat shock-induced acquisition of salt tolerance was inhibited by both EGTA and EDTA.Proteins synthesized during heat and salt stress treatments were labeled with [35S]-methionine and/or [3H]-leucine and separated using Sodium dodecylsulfate polyacrylamide gel electrophoresis. Fluorographic analysis of the gels indicate that a number of proteins are produced in response to heat shock. Similar analysis of proteins from salt shocked cells indicates that no salt shock proteins are produced in response to a brief low-level sodium chloride shock.
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Gidugu, Praveen. "Effect of adding a regenerator to Kornhauser's MIT "two-space" test rig." Cleveland, Ohio : Cleveland State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1212595450.
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Thesis (M.S.)--Cleveland State University, 2008.Abstract. Title from PDF t.p. (viewed on July 9, 2008). Includes bibliographical references (p. 100-103). Available online via the OhioLINK ETD Center. Also available in print.
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Kiflemariam, Robel. "Heat-Driven Self-Cooling System Based On Thermoelectric Generation Effect." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2281.
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This research entails the first comprehensive and systematic study on a heat-driven, self-cooling application based on the thermoelectric generation effect. The system was studied using the first and second laws of thermodynamics to provide a solid and basic understanding of the physical principles governing the system. Multiphysics equations that relate heat transfer, fluid dynamics and thermoelectric generation are derived. The equations are developed with increasing complexity, from the basic Carnot heat engine to externally and internally irreversible engines. A computational algorithm to systematically use the fundamental equations has been presented and computer code is implemented based on the algorithm.
Experiments were conducted to analyze the geometric and system parameters affecting the application of thermoelectric based self-cooling in devices. Experimental results show that for the highest heat input studied, the temperature of the device has been reduced by 20-40% as compared to the natural convection case. In addition, it has been found that in the self-cooling cases studied, convection thermal resistance could account for up to 60% of the total thermal resistance.
A general numerical methodology was developed to predict steady as well as transient thermal and electrical behavior of a thermoelectric generation-based self-cooling system. The methodology is implemented by using equation modeling capabilities to capture the thermo-electric coupled interaction in TEG elements, enabling the simulation of major heating effects as well as temperature and spatial dependent properties. An alternative methodology was also presented, which integrates specialized ANSI-C code to integrate thermoelectric effects, temperature-dependent properties and transient boundary conditions. It has been shown that the computational model is able to predict the experimental data with good accuracy (within 5% error). A parametric study has been done using the model to study the effect of heat sink geometry on device temperature and power produced by TEG arrays.
In addition, a dynamic model suited for integration in control systems is developed. Therefore, the study has shown the potential for a heat driven self-cooling system and provides a comprehensive set of tools for analysis and design of thermoelectric generation.
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WIDELITZ, RANDALL BRUCE. "HEAT SHOCK PROTEIN SYNTHESIS AND THERMOTOLERANCE EXPRESSION IN RAT EMBRYONIC FIBROBLASTS (HYPERTHERMIA, GENE REGULATION)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183851.
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In response to a variety of hyperthermic treatments, rat embryonic fibroblasts synthesize heat shock proteins (hsps), including those with molecular weights of 68,000 (hsp 68), 70,000 (hsp 70) and 89,000 (hsp 89). Hyperthermic stresses, which produce the hsps, also cause expression of thermotolerance. The dependence of thermotolerance expression on hsp synthesis was investigated in this mammalian cell line under different heating conditions. Temperature shift experiments showed that hsp synthesis and thermotolerance expression were dependent not only on the absolute hyperthermic temperature, but also on the difference between the initial incubation temperature and the hyperthermic temperature. Small temperature differences which produced no cell killing did not cause detectable synthesis of hsp 68. Increasing the difference of the initial and hyperthermic temperatures reduced cell survival and increased the synthesis of hsp 68. Thermotolerance could be expressed by surviving cells following an initial heat stress even when both heat shock and general protein synthesis were inhibited. Cells exposed to cycloheximide were heated, incubated at their initial temperature for six hours and reheated in the presence of the drug. The inhibitor was then removed and the cells plated for colony formation. The hsps were expressed during this latter incubation period. The regulation of hsp 70 in rat fibroblasts was investigated next. Hsp 70 synthesis rates correlated with the amount of hsp 70 encoding mRNA. The time course of heat shock synthesis and general protein synthesis recovery were each dependent on the duration of the heat stress. Inhibiting protein synthesis with cycloheximide resulted initially in the accumulation of the RNA encoding hsp 70 but did not effect the normal turnover of this RNA species. The conclusions based on these findings are that thermal survival adaptation can be expressed in the absence of hsp 68 synthesis. Hsp 68 is expressed by cells that will ultimately die (see Chapter 2). The hsps do not appear to protect cells against subsequent heat stress. They may function in a repair capacity (see Chapter 3). Hsp 70 expression is primarily regulated by transcription in Rat-1 cells. Hsp 70 does not act to regulate its own turnover (see Chapter 4).
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Turgay, Metin Bilgehan. "Effect Of Surface Roughness In Microchannels On Heat Transfer." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610253/index.pdf.
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In this study, effect of surface roughness on convective heat transfer and fluid flow in two dimensional parallel plate microchannels is analyzed by numerically. For this purpose, single-phase, developing, laminar fluid flow at steady state and
in the slip flow regime is considered. The continuity, momentum, and energy equations for Newtonian fluids are solved numerically for constant wall temperature boundary condition. Slip velocity and temperature jump at wall boundaries are imposed to observe the rarefaction effect. Effect of axial
conduction inside the fluid and viscous dissipation also considered separately. Roughness elements on the surfaces are simulated by triangular geometrical obstructions. Then, the effect of these roughness elements on the velocity field and Nusselt number are compared to the results obtained from the analyses of flows in microchannels with smooth surfaces. It is found that increasing surface roughness reduces the heat transfer at continuum conditions. However in slip flow regime, increase in Nusselt number with increasing roughness height is observed. Moreover, this increase is found to be more obvious at low rarefied flows. It is also found that presence of axial conduction and viscous dissipation has increasing effect on heat transfer in smooth and rough channels.
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Ferizaj, Drilon, and Mohamad Kassem. "Effect of nanofluids on thermal performance of heat pipes." Thesis, KTH, Energiteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-148074.
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A relatively new way for utilizing the thermal performance of heat pipes is to use nanofluids as working fluids in the heat pipes. Heat pipes are effective heat transfer devices in which the nanofluid operates in the two phases, evaporation and condensation. The heat pipe transfers the heat supplied in e.g. a laptop, from the evaporator to condenser part. Nanofluids are mixtures consisting of nanoparticles (e.g. nano-sized silver particles) and a base fluid (e.g. water). The aim of this bachelor’s thesis has been to examine the effect of nanofluids on heat pipes on the subject of temperature parameters and thermal resistance in the heat pies, through findings in literature and an applied model. The study, based on literature and an applied model, found that higher particle conductivity and higher concentration of nanoparticles consequently decrease the thermal resistance in the heat pipes, resulting in an enhanced thermal performance of the heat pipes with nanofluids as working fluids. It is however concluded that difficulties in finding the optimal synthesis of nanofluids, the concentration level of nanoparticles and the filling ratio of nanofluids in heat pipes, set bounds to the commercial use of nanofluids in heat pipes. It is suggested that, in order to enhance the heat transfer performance of nanofluids in heat pipes, to conduct further research concerning e.g. synthesis of nanofluids and concentration level of nanoparticles in nanofluids.
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Kleiven, Thomas J. (Thomas John). "Effect of gas path heat transfer on turbine loss." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112466.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 117-118).
This thesis presents an assessment of the impact of gas path, i.e., streamtube-to-streamtube, heat transfer on aero engine turbine loss and efficiency. The assessment, based on the concept of mechanical work potential [19], was carried out for two model problems to introduce the ideas. Three-dimensional RANS calculations were also conducted to show the application to realistic configurations. The first model problem, a constant area mixing duct, demonstrates the importance of selecting a fluid component loss metric appropriate to the purpose of the overall system in which the component resides. The phenomenon of thrust increase due to mixing is analyzed to show that system performance can increase even though there is a loss of thermodynamic availability. Gas path heat transfer affects mechanical work potential, and thus turbine loss, through a mechanism called thermal creation [19]. The second model problem, an inviscid heat exchanger, illustrates how thermal creation is due to enthalpy redistribution between flow regions with different local Brayton efficiency. Heat transfer across a static pressure difference, or between gases with different specific heat ratios, can cause turbine efficiency to increase or decrease depending on the direction of the heat flow. Three-dimensional RANS calculations have also been interrogated to define and determine the thermal creation, and thus the losses, in a modern two-stage cooled high pressure turbine. At representative engine operating conditions the effect of thermal creation was a 0.1% decrease in efficiency, with the thermal creation accounting for 1% of the overall lost work. Introducing coolant flow into the main gas path increased the loss from thermal creation in the first stage by 84% and decreased the loss from thermal creation in the second stage by 8%.
by Thomas J. Kleiven.
S.M.
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Underwood, David Scott. "Effect of heat release on streamwise vorticity enhanced mixing." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/47390.
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Kim, Jun-Pill. "LAND-USE PLANNING AND THE URBAN HEAT ISLAND EFFECT." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1253215365.
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Joober, Khaled. "The effect of flow geometry on critical heat flux." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6544.
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An extensive and systematic literature review on the effect of flow geometry on the Critical Heat Flux (CHF) has been performed. This review covers most of the flow geometries such as tubes, concentric and eccentric annuli, rectangular channels, irregular-shaped channels and bundles. The following geometric parameters have been found to strongly influence the CHF: (i) hydraulic-equivalent diameter, (ii) heated-equivalent diameter, (iii) gap size, (iv) unheated adjacent surface, (v) heated adjacent surface, (vi) curvature, (vii) eccentricity (including bowing), and (viii) channel shape. It is found that some of the geometric effects on CHF depend on the flow conditions and the CHF type. For each geometry the parametric trends have been described, whenever sufficient experimental results are available. A review and assessment of the available prediction methods is conducted. The following trends have been identified in this study: (i) in general the CHF in annuli (concentric and eccentric) is lower than that in tubes, especially for high quality and narrow gaps; (ii) for rectangular channels and irregular-shaped channels, corners can cause a large CHF reduction; (iii) the CHF for concave surface is significantly higher than the CHF for a convex surface; (iv) the effect of gap size in concentric annuli is different for a departure from nucleate boiling (DNB) type CHF and CHF type for the annular flow regime. For the first CHF type reduction in gap size results in a CHF decrease, while for the second CHF type it results in CHF enhancement; and (v) heating the adjacent surface results in a CHF increase. Based on the observed trends, CHF correction factors have been derived for each geometry. Finally, an interim CHF prediction method for subchannels and flow conditions of interest to CANDU$\sp*$ reactors has been proposed. ftn$\sp*$CANDU--CANada Deuterium Uranium, a registered trademark.
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Stapleton, Jill. "The effect of physical training on body heat regulation." Thesis, University of Ottawa (Canada), 2009. http://hdl.handle.net/10393/28141.
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Purpose. We evaluated the effects of an eight-week aerobic exercise training program in previously sedentary individuals on whole-body heat balance. Whole-body evaporative (H˙E) and dry (H˙ D) heat loss as well as changes in body heat content (DeltaH b) were measured using simultaneous direct whole-body and indirect calorimetry. It was hypothesized that following the 8-week exercise training program, a more rapid increase in the rate of whole-body heat loss would occur during exercise resulting in a decrease in the change of body heat content by the end of exercise. It was further hypothesized that the rate of decay of whole-body heat loss during recovery would be greater following the exercise training program.
Methods. Ten previously sedentary young adults (7 males, 3 females) underwent an 8-week exercise program. Participants exercised at a university based facilities 4-5 times per week, 30-90 minutes per session, supervised by personnel. Prior to, and after the 8-week training program, subjects underwent an incremental treadmill test to measure their maximal aerobic capacity (V˙O2max). On a subsequent day, they performed 60-90 minutes of cycling at a constant rate of heat production (∼450 W) followed by 60 minutes of recovery, in a calorimeter at 30°C and 15% relative humidity. Core temperature [esophageal; (Tes), rectal (Tre ) and aural canal (Tau)], mean skin temperature, skin blood flow (SkBF), local sweat rate (LSR), mean arterial pressure (MAP), and heart rate (HR) were measure at baseline and at 2 min, 5 min, 8 min, 12 min, 15 min, 30 min, 45 min, 60 min, and 90 min intervals for the exercise and post-exercise recovery periods.
Results. No significant difference in the rate of total heat loss (H˙L=H˙E+H˙D) was observed during exercise. As a result, the average DeltaHb was similar for the pre- (+441+/-89 kJ) and post-training (+430+/-118 kJ) 60-min exercise bout (p=0.385). Although the absolute changes in Tes (p=0.060), Tre (p5≤0.05) and Tau (p≤0.05) were lower at rest post-training, no differences in the relative change from baseline was measured during exercise. Local sweat rate and SkBF were elevated during exercise however the relative changes from baseline were similar pre- to post-training. A 12% increase in V˙O2max was measured after the 8-week training program (p≤0.05). This was paralleled by a decrease in heart rate throughout exercise (p=0.004).
Conclusion. Although physical training resulted in improvements in cardiorespiratory function as evidenced by increases in V˙O2max and reduced HR response during exercise, these adaptations did not result in an improvement in the capacity for heat dissipation during exercise.
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Hayes, Mark. "The effect of progressive heat acclimation on games players performing intermittent-sprint exercise in the heat." Thesis, University of Brighton, 2014. https://research.brighton.ac.uk/en/studentTheses/5d460be8-1826-4a96-ac35-9c07c6943e6d.
Full textAbstract:
Intermittent-sprint performance is reduced in hot environments and the impairment occurs without significant difference in metabolic responses to exercise. Reductions in cerebral blood flow and voluntary activation occur with hyperthermia and neuromuscular impairment has been posited to explain decreased performance in the heat. Heat acclimation is used to minimise heat mediated performance impairment, yet traditional protocols may limit adaptation. The purpose of this thesis was to examine the efficacy of a novel progressive heat acclimation model for games players performing intermittent-sprint exercise in the heat and to examine if this method can ameliorate neuromuscular fatigue following exercise of this type.
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Al-Waaly, Ahmed. "The effect of heat transfer on temperature measurement and its applications to study microchannel heat sinks." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6781/.
Full textAbstract:
Analytical, numerical and experimental analyses have been performed to investigate the effects of thermocouple wire electrical insulation on the temperature measurement of a reference surface. Two diameters of K-type thermocouple, 80μm and 200μm, with different exposed stripped wire lengths (0 mm, 5mm, 10mm, 15mm and 20mm) were used to measure various surface temperatures (4oC, 8oC, 15oC, 25oC and 35oC). Measurements were made when the thermocouple probe is in direct contact with the surface and the wires are extended vertically and exposed to natural convection from outside environment. Experimental results confirmed that the thermal effect from the electrical insulation on temperature measurement was within -0.5oC and therefore it can be neglected. Moreover, the experimental results agree well with those obtained by both the analytical and numerical methods and further confirm that the diameter of the thermocouple has an impact on the temperature measurement. Analytical results of the thermocouple wire with insulation confirm that there is no specific value for the critical radius and the rate of heat flux around the thermocouple wire continuously increases with the wire radius even when this is larger than the critical radius. Experimental and numerical analyses have been performed to investigate the heating impact of using thermocouples for the temperature measurement of small volumes of cold water. Two sizes of K-type thermocouple have been used: 80μm and 315μm to measure the temperature of the cold water inside a small chamber while the thermocouple wires were extended vertically in the outside environment. For this study, the chamber temperature was adjusted to 4oC. The results show that the heating effect of the thermocouple decreases for the greater depth measurements and this effect is eliminated when the thermocouple junction is close to the chamber bottom surface. The increase in the thermal resistance between the bottom surface and the thermocouple junction raises the heating effect of the thermocouple impact. Moreover, the exposed length of thermocouple wires to the environment has no effect over a specific length where the wire end temperature is equal to that of the environment. Experimental and numerical analyses have been carried out to study the effect of using subchannels in heat sink to minimise the effect of hotspots generated on a chip circuit. Two devices of heat sink – with and without subchannels – were fabricated in order to investigate this effect. The first device was manufactured with a normal parallel channel while the second one was designed to extract more heat by dividing the main channels above the hotspot into two subchannels. A hotspot heat flux (16.7×104 [W/m2]) was applied at the centre of the channels while a uniform heat flux (4.45×104 [W/m2]) was applied at upstream and downstream of the channels. Five mass flow rates have generated under gravity force to investigate the performance of devices under different operating conditions. The results showed the maximum surface temperature was reduced by 4oC the temperature uniformity was improved. Moreover, thermal resistance was reduced by 25% but the pumping power was increased as a result of the presence of the subchannels.
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Zahlan, Hussam. "Flow obstacle effect on film boiling heat transfer with uniform and non-uniform axial heat flux." Thesis, University of Ottawa (Canada), 2009. http://hdl.handle.net/10393/28143.
Full textAbstract:
An experimental investigation of the effects of axial flux distribution (AFD) and obstacles on film-boiling heat transfer was performed in a vertical tube using HFC-134a as coolant. The following parameters were examined: (1) Axial flux profiles (uniform, inlet-peak and outlet-peak), (2) Flow-blockage ratios (12% and 24%), (3) Obstacle pitches (150 mm and 300 mm), (4) Obstacle shapes (blunt and round).
Test conditions covered the pressure 1665 and 2389 kPa (water-equivalent value: 10 and 14 MPa), a mass-flux range from 1395 to 3575 kg.m-2.s -1 (water-equivalent value: 2000 to 5000 kg.m-2.s -1) and an inlet-fluid temperature range from 30 to 70°C (water-equivalent value: 229 to 324°C). Film-boiling temperature measurements were recorded for all possible heat-flux levels, up to a limiting surface temperature of 240°C to avoid Freon decomposition. Inside wall temperature distributions of the obstacle-equipped test sections were compared against those of a reference bare tube at similar flow conditions.
Flow obstacles were found to have a significant influence on film-boiling heat-transfer. Film-boiling wall temperatures along the test section were reduced significantly by decreasing the obstacle pitch, by increasing the obstacle size and by using a blunt instead of streamline-shaped obstacle.
The effect of AFD on film-boiling heat transfer is noticeable in the developing film-boiling region and can be attributed mainly to the variation in critical heat flux (CHF) occurrence. However, the AFD effect appears to be less obvious in the fully developed film-boiling region.
Since the literature suggested that the single-phase pressure-loss coefficient of the flow obstructions could be an important parameter in correlating the film-boiling heat-transfer enhancement, this parameter was also measured and correlated.
Previously derived prediction methods for obstacle-enhanced film-boiling heat transfer did not provide satisfactorily agreement with the data; therefore, a new prediction method was derived to predict the film-boiling heat-transfer augmentation for uniform AFD tubes. The new equation accounts for the enhancement in film-boiling heat transfer due to turbulence generated by (i) liquid-film termination at the dryout point and (ii) the upstream flow obstructions. The new correlation was applied to non-uniform AFD data. It was concluded that (i) this new prediction method is also applicable to non-uniform AFD tubes, (ii) the new prediction method has the correct asymptotic trends and (iii) single-phase pressure-loss coefficients cannot be used directly to predict the heat-transfer enhancement for both blunt and rounded obstacles.
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North, Travis. "Experimental and analytical study of time varying electrical fields and their effect on convective boiling heat transfer /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1426090.
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Awuah, George Brobbey. "Heat transfer and kinetic studies of particulates under aseptic processing conditions." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28419.
Full textAbstract:
Fluid-to-particle heat transfer coefficients (h$ rm sb{fp}$) associated with food and model particles under simulated aseptic processing conditions were experimentally evaluated, and verified using measured inactivation kinetic parameters of the enzyme trypsin. Convective heat transfer coefficients were determined initially using two methods: a rate method based on evaluated heating/cooling rate indices (f$ rm sb c$/f$ rm sb h$) and a ratio method based on the ratio of temperature difference between the medium and particle locations.Carrot and potato tissue in the form of finite cylinders of different lengths (0.02-0.04 m) and diameters (0.016-0.023 m) were used for evaluating h$ rm sb{fp}$ associated with aqueous CMC solutions (0-1.0% w/w) at temperatures ranging from 50 to 80$ sp circ$C and at relatively low fluid flow (0.2 to $0.7 times10 sp{-3}$ m/s) conditions. Carrots generally gave higher h$ rm sb{fp}$ values (100-550 W/m$ sp2$C) compared to potatoes (80-450 W/m$ sp2$C). Laminar flow natural convection dominated the flow regime. Hence, the Nusselt number was modeled as a function of Rayleigh's number which resulted in coefficients of determination (R$ sp2$) greater than 0.80.
A pilot scale holding tube simulator was designed and fabricated for routine/rapid gathering of heat penetration data which may be experienced in high temperature short time processing conditions.
Using the simulator under conditions comparable to industrial applications, and a full factorial experimental design, h$ rm sb{fp}$ values were estimated using finite cylinders of Teflon and potato tissue of different sizes (length: 0.020-0.0254 m; diameter: 0.0159-0.0254 m), and spherical Teflon particles (diameter 0.0191 m) in food grade CMC solutions (0-1.0% w/w). Operating temperatures were 90, 100 and 110$ sp circ$C, and flow rate was varied from 1.0-$1.9 rm times10 sp{-4} m sp3$/s. Average h$ rm sb{fp}$ values ranged from 56 to 966 W/m$ sp2$C depending on size, shape, fluid concentration, particle orientation, and tube diameter. Differences caused by different particle materials were accounted for by introducing a thermal diffusivity ratio in developed dimensionless correlations for both mixed and forced convective heat transfer to spherical and finite cylindrical particles under simulated aseptic processing conditions.
Thermal inactivation of trypsin (bovine pancreas type III) in low and high pH media was studied at temperatures ranging from 90-130$ sp circ$C. Comparative studies of its kinetic data with other bioindicators indicated the enzyme to be suitable for HTST verification/validation purposes. Further studies revealed, probably depending on pH, that trypsin was more susceptible to thermal inactivation at temperatures around 70$ sp circ$C. (Abstract shortened by UMI.)
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Arambakam, Raghu. "MODELING EFFECT OF MICROSTRUCTURE ON THE PERFORMANCE OF FIBROUS HEAT INSULATION." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3212.
Full textAbstract:
Heat insulation is the process of blocking the transfer of thermal energy between objects at different temperatures. Heat transfer occurs due to conduction, convection, or radiation, as well as any combination of these three mechanisms. Fibrous insulations can completely suppress the convective mode of heat transfer for most applications, and also help to reduce the conductive and radiative modes to some extent. In this study, an attempt has been made to computationally predict the effects of microstructural parameters (e.g., fiber diameter, fiber orientation and porosity) on the insulation performance of fibrous materials. The flexible simulation method developed in this work can potentially be used to custom-design optimal multi-component fibrous insulation media for different applications. With regards to modeling conductive heat transfer, a computationally-feasible simulation method is developed that allows one to predict the effects of each microstructural parameter on the transfer of heat across a fibrous insulation. This was achieved by combining analytical calculations for conduction through interstitial fluid (e.g., air) with numerical simulations for conduction through fibrous structures. With regards to modeling radiative heat transfer, both Monte Carlo Ray Tracing and Electromagnetic Wave Theory were implemented for our simulations. The modeling methods developed in this work are flexible to allow simulating the performance of media made up of different combinations of fibers with different materials or dimensions at different operating temperatures. For example, our simulations demonstrate that fiber diameter plays an important role in blocking radiation heat transfer. In particular, it was shown that there exists an optimum fiber diameter for which maximum insulation against radiative transfer is achieved. The optimum fiber diameter is different for fibers made of different materials and also depends on the mean temperature of the media. The contributions of conduction and radiation heat transfer predicted using the above techniques are combined to define a total thermal resistance value for media with different microstructures. Such a capability can be of great interest for design and optimization of the overall performance of fibrous media for different applications.
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Houmard, Joseph A. "Rate of heat acclimation : effects of exercise intensity and duration." Virtual Press, 1988. http://liblink.bsu.edu/uhtbin/catkey/533882.
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Johnsen, Suzanne Louise 1960. "Early embryos of dams of heat stress." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277034.
Full textAbstract:
Increased environmental heat causes early embryonic death before implantation. This study was designed to examine tissues of dams exposed to environmental temperatures of 36°C and to examine 72 hour old embryos from these dams. Results showed adult mice exposed to heat stress had significant changes in liver morphology with hepatocyte swelling and vacuolization of the cytoplasm, organelles in the hepatocytes were displaced next to the cell membrane. After 48 hours of recovery from heat stress, liver morphology appeared normal. Embryos from heat stressed dams had delayed development indicated by increased 2alpha helical cellular inclusions. Embryos responded differently to different fixation techniques indicated permeability changes in either the zona pellucida or cellular membranes. Litter size or pup survivability from heat stressed dams allowed to recover indicated changes seen at this point were reversible
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Machate, Malgorzata S. "Joule heat effects on reliability of RF MEMS switches." Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-1007103-115232/.
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Vaitekunas, David A. "An investigation of the effect of flow obstructions on critical heat flux, pressure drop and heat transfer." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0020/NQ57073.pdf.
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Davis, Jacqueline A. "The hypertensive response to repeated days of heat-exercise exposure." Virtual Press, 1989. http://liblink.bsu.edu/uhtbin/catkey/562777.
Full textAbstract:
The physiological responses of hypertensive subjects to a single bout of exercise in a hot environment have been investigated. It was the purpose of this study to compare the effect of successive days of exercise in the heat on borderline hypertensive and normotensive individuals, with particular interest being paid to the positive relationship that exists between plasma volume and blood pressure. Eight hypertensive subjects (HT) and 8 normotensive controls (NT) performed a standardized work task, (walking for 60 minutes at 3.5 mph on a 5% grade), in dry heat, (40C, 257. RH), on 7 successive days. Working capacity and acclimatization were compared during two, 90 minute heat tolerance tests (HTT), one prior to, and the other following the acclimation period.Both groups demonstrated a similar degree of heat acclimation, as reflected in significantly lower HTT2 core temperatures, (P< 0.05), and heart rates, (p< 0.01). Plasma volume expansion over the 9 days was also equal for both groups (+77.), but appeared to have no effect on their resting or exercising blood pressures. No differences were observed in the ability of either group to complete the work task, although the HT group exercised at a significantly higher percentage of their maximal oxygen uptake, (p< 0.05), than the NTs.These results indicate that no abbreviation in working capacity is experienced by borderline HT'% during exercise in the heat as a consequence of their high blood pressure. The anticipated elevation in blood pressure as a result of an expansion i n plasma volume did not occur. Consequently, these individuals show the same positive acclimation to exercise in the heat as their NT counterparts.School of Physical Education
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Sarikaya, Onur Turgay. "Analysis Of Heat Treatment Effect On Springback In V-bending." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610182/index.pdf.
Full textAbstract:
Aluminum based alloys have wide area of usage in automotive and defense industry and bending processes are frequently applied during production. One of the most important design criteria of bending processes is springback, which can be basically defined as elastic recovery of the part during unloading. To overcome this problem, heat treatment is generally applied to the workpiece material to refine tensile properties.
In this study, the effect of heat treatment on springback characteristics of aluminum studied both numerically by using finite element analysis and experimentally. For this purpose, two different materials are selected and various heat treatment procedures are considered. The aluminum sheets having thickness of 1.6 mm, 2 mm and 2.5 mm are bent to 60˚
, 90&
#730
and 120&
#730
. The von Mises stress distributions, plastic strain values and punch load values and comparison of the numerical and experimental results are also given.
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Churi, Asawari Shreeniwas. "Effect of heat shock on hilA expression in Salmonella Typhimurium." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1490.
Full textAbstract:
The effect of heat shock was observed on the expression of hilA in Salmonella
Typhimurium by creating a fluorescence-based reporter strain of Salmonella and by realtime
reverse transcriptase polymerase chain reaction (RT-PCR).
The hilA gene in Salmonella is known to play an important role in its pathogenesis.
hilA is known to be activated when the bacteria encounter stress-inducing conditions. A
number of factors have been identified that affect hilA expression, such as, pH,
osmolarity, oxygen tension. When Salmonella enter their warm-blooded hosts, they
encounter an increase in temperature. Therefore, heat is another stressor that is
encountered by Salmonella during infection of their hosts.
A fluorescence-based strain of Salmonella was created to study the effect of heat
shock. The gene for green fluorescent protein (gfp) was placed under the control of the
promoter of hilA on a plasmid. This plasmid was used to transform Salmonella cells to
create a fluorescent strain. In this strain, when the hilA promoter is activated, gfp is
transcribed, which encodes the green fluorescent protein. This protein can be measured
by a fluorescence assay. The results of this study indicated that at 45ºC, hilA is activated.
RT-PCR was used to look at hilA expression at different temperature. The results of this
study indicated that, compared to 37ºC, higher temperatures like 45ºC and 55ºC
significantly activate hilA.
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Balci, Hamza. "Specific heat and nernst effect of electron-doped cuprate superconductors." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/217.
Full textAbstract:
Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Shahin, Gus A. "The effect of pulsating flow on forced convective heat transfer." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ39881.pdf.
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Shurkian, Omer M. "The effect of laundering and heat exposure on apparel fabrics." Thesis, University of Manchester, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488300.
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Jackson, D. O. "The effect of plate geometry upon plate heat exchanger perormance." Thesis, University of Bradford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376714.
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Rokan, Mohammad. "Effect of heat on the properties of automotive airbag materials." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/effect-of-heat-on-the-properties-of-automotive-airbag-materials(afa7fe9e-4c3f-46df-ab95-ee744c6fda05).html.
Full textAbstract:
Automotive airbags are subjected to extreme temperatures (up to 900°C) during deployment which is achieved by using pyrotechnic inflators. Although the airbag fully inflates within a few milliseconds, the heat often causes physical damage to the airbags fabric and seams in this short period of time. In this study, the effects of heat on airbag yarns (highly drawn Nylon 6,6) and airbag fabrics were investigated with the goal of understanding whether or not high heat causes the internal structure of the material to change. The degree of crystallinity of the material was found to increase as the delta H values of the material increased with heat and heating rate in a Differential Scanning Calorimeter (DSC) for both unheated and heated fibres (extracted from airbag yarns) as well as unfired and fired airbag fabrics. The storage modulus of the material was also found to drop gradually as the material was heated from sub-zero temperature to melting point in a Dynamic Mechanical Analyzer (DMA) with sharp drops in the glass-transition and melting regions. The initial stiffness and the breaking strength of the material were found to decrease in a tensile tester as the temperature and heating rate at which the material was heated increased. This unusual behaviour, i.e. a reduction in stiffness and strength with a rise in the degree of crystallinity was found to be due to a reduction in the molecular orientation of the fibres as high levels of shrinkage were observed for both yarns and fabrics when the material was heated. The shrinkage increased with increasing temperature and heating rate which caused the diameter of the fibre to increase. Upon correlation with shrinkage, the initial stiffness and breaking strength of the material were found to be inversely proportional to shrinkage while the breaking strain was proportional to shrinkage.
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Merkin, Ryan 1974. "The Urban Heat Island's Effect on the diurnal temperature range." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28612.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004."June 2004."
Includes bibliographical references (p. 59-61).
(cont.) representing Phoenix and its rural equivalent is presented through a comparison with estimated energy fluxes for Houston, TX.
This study has found significant evidence of the Urban Heat Island Effect (UHIE) in Phoenix, AZ using historic and recent (up to 2002) temperature records. First, an explicit indicator of UHIE was identified by the -0.148⁰F per year decrease of the diurnal temperature range (DTR). This was explained by an increasing trend of 0.190⁰F per year in mean minimum temperature while the mean maximum increased at a much slower pace of 0.042⁰F per year. This has manifested itself in a significant nighttime heat island. Second, the UHIE for Phoenix was estimated to contribute about 15 [plus-minus] 5% of total climate variability for this city. That is, only about, 85% of the DTR for Phoenix can be accounted for by natural variability. This was established by comparing the average historical climate record for Phoenix Sky Harbor International Airport and several nearby rural sites. In this analysis, Casa Grande National Monument, a national park 40 miles southeast of Phoenix, was chosen as the most appropriate rural site for application of a method to assess the Phoenix UHIE by trading space-for-time. Finally, the basic concepts for the development of an urban heat island model were outlined. Land use changes and the materials used to build infrastructure were determined to be the most significant factors in determining the magnitude of the Phoenix (and similar cities) UHIE. These materials effectively reduce surface albedo and emissivity, decrease latent heat release by lowering the water permeability of surfaces, and increase the storage heat flux due to greater surface area density and much larger thermal mass offsetting the lower specific heat capacity. Anthropogenic heat release is also a factor, but mainly in dense urban cities. The energy balance
by Ryan Merkin.
S.M.
46
Neal, Rebecca Anne. "Effect of combined stressors on heat acclimation and temperate exercise." Thesis, University of Portsmouth, 2017. https://researchportal.port.ac.uk/portal/en/theses/effect-of-combined-stressors-on-heat-acclimation-and-temperate-exercise(7873a797-3d32-40b6-ba6e-0bbf034e1493).html.
Full textAbstract:
Recent evidence suggests heat acclimation (HA) may improve exercise performance under cooler conditions and that combined-stressor approaches might optimise HA. Accordingly, the studies presented in this thesis examined strategies for optimising HA in well-trained athletes through the use of combined-stressor approaches and the subsequent effects on exercise in a temperate environment (cross-stressor). The first two studies examined the effect of dehydration in combination with exercise-heat stress on HA over the short- and longer-term and its subsequent decay, as well as investigating thermoregulation, parameters related to endurance performance and performance, in temperate conditions. Study three examined the addition of an overnight hypoxic stressor on short- and longer-term HA and endurance exercise performance in a temperate environment, after HA and following a 2-week decay. The final study comprehensively explored the ergogenic potential of heat acclimation for endurance performance in a temperate environment, relative to a cool exercise control group. Together these studies demonstrated that the majority of the alterations associated with HA are rapidly induced (5-days) but longer programmes (10-days) are necessary to optimise these adaptations; they are well maintained over a short decay period (7-days). Combined stressor approaches (addition of dehydration or hypoxia) did not meaningfully affect the rate or magnitude of the induction of HA. Finally, HA did not induce any greater ergogenic benefit than a cool exertion matched exercise programme in a temperate environment. In conclusion, HA is rapidly induced, robust, and the HA phenotype is minimally influenced by combined stressors (dehydration or hypoxia) when thermal strain is clamped. Moreover, when compared to an ecologically valid control, HA does not notably influence endurance performance or its related parameters in a temperate environment. These extensive findings provide useful guidance for athletes utilising environmental stressors in preparation for competition in various conditions.
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Morrison, Graham K. "The effect of stabilization heat treatment on AA5182 aluminium alloy." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/4961.
Full textAbstract:
Includes abstract.Includes bibliographical references.
AA5182 aluminium alloy is used for the manufacturing of can ends for beverage cans. The alloy selection for this part is based on the formability of the material and its resistance to softening over time. Owing to the intricate design of the can end opening tab, it is vital that the material maintains its strength during its shelf life. The mechanical properties of the AA5182 aluminium alloy are dependent on the microstructural evolution of the alloy during processing and forming. Al-Mg alloys, like AA5182, can undergo a low temperature heat treatment, which has the effect of stabilizing the microstructure and minimizing the subsequent recovery processes during and after coil coating. The effects of these heat treatments have been investigated in order to understand the effectiveness of the stabilization heat treatment on the AA5182 alloy. This study investigates various stabilization heat treatment temperature profiles, and then aims to characterize the microstructural evolution of the material during a simulation of the coil coating practice that the material is exposed to as the final step in the rolling mill operation.
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Nguyen, Duc-Khuyen, and 阮德勸. "Heat Transfer Characteristics of a Spiral Heat Exchanger with Solid Heat Conduction Effect." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/57129099195631040753.
Full textAbstract:
博士國立中興大學
機械工程學系所
104
The effect of radial and spiral-direction solid heat conduction on the heat transfer effectiveness of a counter-current spiral heat exchanger constructed by four Archimedes spirals was investigated. The heat transfer effectiveness ( ) is a function of number of transfer units (NTU1 and NTU2), ratio of flow capacity rates (C), dimensionless wall thickness ( ), Biot number (Bi1 or Bi2), number of spiral turns (Nt) and dimensionless start-point angle of spiral ( ). By comparing to the effectiveness of the heat exchanger without the solid heat conduction effect ( ), a performance evaluation factor called the decrement in heat transfer effectiveness ( ) was defined and numerically evaluated. The and the values are weakly dependent on the value, but moderately increase with the Nt value. Either at the balanced-flow operation or at the unbalanced-flow operation, the heat exchanger has an optimum Bi1 value and an optimum Bi2 value ranging from 10-4 to 10-2. At the optimum Bi1 or Bi2 values, the value is a maximum and the value nears zero. In the thermodynamic second-law analysis, an optimum hot flow-to-cold flow capacity-rate ratio was found. For obtaining a large net recovered exergy rate, the spiral heat exchanger needs to possess a large number of transfer units (greater than 2.0) and be operated at a near balanced-flow condition. For gas-to-gas, liquid-to-liquid and gas-to-liquid waste heat recovery applications, the maximum possible values of the spiral heat exchanger at balanced-flow operation were estimated. In the experiment, a gas-to-liquid spiral heat exchanger was manufactured and used for measuring the heat transfer and pressure drop data in the gas channel. Empirical equations for the Nusselt number (Nu) and Darcy friction factor (f) were established for the Reynolds number (Re) in the range of 4447 to 32017.
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ZHONG, CHONG-YI, and 仲崇毅. "Numerical simulation on heat island effect." Thesis, 1989. http://ndltd.ncl.edu.tw/handle/57074683349728899973.
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LIN, XU-KUN, and 林許坤. "Pressure effect on boiling heat transfer." Thesis, 1986. http://ndltd.ncl.edu.tw/handle/30731719930983729682.
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