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The measurement of temperature in hot gases plays an important role in many engineering applications, such as the efficiency and performance of an engine. As such, understanding the accuracy of these temperature measurements is also important. One of the common ways in which temperature is measured is through the use of total temperature probes. Previous research both at Virginia Tech and in outside studies has been performed to quantify the errors associated with total temperature probe measurements. This work has led to the development of low-order models which can be used to calculate the performance of a total temperature probe as a first-order estimate. These low-order models require knowledge of the heat transfer to the total temperature sensor in order to calculate the probe performance. However, the heat transfer to the sensor is a difficult quantity to calculate and has only been quantified over a set range of operating conditions for a single probe design. This research seeks to expand the range of applicability of the Virginia Tech low-order model by quantifying the heat transfer to the sensor of a total temperature probe over a range of probe geometries through the use of computational models. Key geometry parameters were altered to understand how altering these geometry features would impact the heat transfer to the sensor. In order to quantify the heat transfer to the sensor for varied probe geometries, a new method of characterizing the flow conditions about the sensor was also developed. By characterizing the flow conditions about the sensor, a better quantification of the heat transfer can be obtained. This thesis presents the correlation that was developed to quantify the changes in the flow about the sensor caused by varying the key geometry parameters. The flow conditions encompassed total temperatures from 294 K to 727 K at a Mach number of 0.4. The changes in the flow conditions about the sensor are then used to develop a heat transfer correlation to allow the heat transfer to the sensor to be calculated based off the changes in the flow conditions. The heat transfer to the sensor can then be substituted into the low-order model and used to calculate the performance of a total temperature probe. / Master of Science / The measurement of temperature in hot gases plays an important role in many engineering applications, such as the efficiency and performance of an engine. As such, understanding the accuracy of these temperature measurements is also important. One of the common ways in which temperature is measured is through the use of total temperature probes. Previous research has been performed to quantify the errors associated with total temperature probe measurements. This work has led to the development of low-order models which can be used to calculate probe errors. These low-order models require knowledge of the heat transfer to the total temperature sensor in order to calculate the probe errors. However, the heat transfer to the sensor is a difficult quantity to calculate and has only been quantified over a set range of flow conditions for a single probe design. This research seeks to quantify how the heat transfer to the sensor of a total temperature probe changes for different probe designs. Key geometry parameters were altered to understand how changing these geometry features would impact the heat transfer to the sensor. This thesis presents how the heat transfer to the total temperature sensor can be calculated over a range of different probe designs. The heat transfer to the sensor can then be substituted into the low-order model and used to calculate the performance of a total temperature probe.

Electromagnetic and heat transfer analysis is used to determine possibility of selective heating of nanometer-sized, metallic catalyst particles attached to a ceramic support through microwave irradiation. This analysis is incorporated into a macroscopic heat transfer model of a packed and fluidized catalyst bed heated by a microwave field to predict thermal effects associated with selective heating of the catalyst sites. The model shows a dependence on particle size and microwave frequency on the selective heating of the catalyst sites. The macroscopic thermal effects are shown to be small for a typical experiment. However, changing the support material and catalyst particle size are shown to distinguish the thermal effects associated with selective heating of the metallic catalysts. / Master of Science

Graphite foams have high bulk thermal conductivity and low density, making them an excellent material for heat exchanger applications. This research focused on the characterization of graphite foams under various processing conditions (different foaming pressures and particle additions), specifically studying the effects of porosity on the thermal properties. The characterization of the foams included measuring cell sizes, percent open porosity, number of cells per square inch, bulk density, Archimedes density, compression strength, thermal conductivity, thermal resistance, and permeability. Several relationships between the structure and properties were established, and a recommendation for the processing conditions of graphite foams for the use in heat exchangers was determined. / Master of Science

A dynamic phantom for use in investigating hyperthermia heating systems has been designed, constructed, and tested. A computer controlled the flow rate of 80% Ethanol to each of 4 preserved in vitro canine kidneys which acted as the phantom material. The flow rates were regulated with stepper motor controlled valves and measured with flow meters by the computer. This provided a flexible system for adjusting the perfusion as desired. The system was tested with step and ramp changes in perfusion under constant power ultrasound and with a temperature controlled perfusion algorithm, all of which yielded repeatable results. The dynamic phantom developed in this work shows potential for expediting investigations of hyperthermia controllers, temporal blood flow patterns, and inverse problems. Its computer based nature gives it great flexibility which would lend itself well to automated testing procedures.

An experimental investigation of the flow boiling of water at atmospheric pressure was undertaken, including a high—speed cine photographic study of the flow structure near the Critical Heat Flux (CHF). Experimental tests from single-phase forced convection to burnout were conducted at different flow velocities and inlet subcoolings for water flowing upwards through a vertical channel of rectangular cross—section electrically heated on one wall with a glass window forming the opposite wall. The test surfaces were stainless steel strips of constant dimensions, except that wall thickness ranged from 0.08 mm to 0.20 mm. Quantitative measurements of the bubble parameters for the same heating surface under the same operating conditions with varying levels of heat flux (70% to 95% of CHF) were carried out. A nucleation site deactivation/reactivation process was observed with increasing heat flux. A proposed site deactivation mechanism explained this behaviour. A nucleate boiling heat transfer model was proposed for the fully— developed nucleate boiling region, with allowance made for the overlapping areas of bubble influence. It compared favourably with the experimental data. The effect of wall thickness on CHF was investigated: increases in CHF as between the 0.08 mm and the 0.20 mm wall thickness ranging from 38% to 57% were observed. An empirical expression for CHF, including wall thickness as a parameter was developed, correlating the experimental data to within 15% and indicating a limiting value for wall thickness affecting CHF. The flow regimes near burnout were identified as bubbly and slug, these being independent of wall thickness. Other models proposed for the CHF mechanism were tested against the detailed experimental observations at high subcoolings. They were found to be inconsistent with the experimental evidence. A possible alternative for the CHF mechanism points towards stabilisation/ growth of a vapour patch following bubble coalescence as a most likely cause for burnout.

Thesis (Ph.D. (Applied Mathematics)) -- University of Limpopo, 2020 / The flow of electrically conducting fluids in the presence of a magnetic field has wide applications in science, engineering and technology. Examples of the applications include industrial processes such as the cooling of reactors, extrusion of plastics, purification of crude oil, medical applications, aerodynamics and many more. The induced magnetic field usually act as a flow control mechanism, especially under intense heat. In this study a couple stress fluid in a channel will be used as the working fluid. Channel flow and heat transfer characteristics of couple stress fluids find applications in processes such as the extrusion of polymer fluids, solidification of liquid crystals, cooling of metallic plates in a bath, tribology of thrust bearings and lubrication of engine rod bearings. One major characteristic that distinguishes the couple stress fluid from other non-Newtonian fluids is the inclusion of size-dependent microstructure that is of mechanical significance. As such, the couple stress constitutive model is capable of describing the couple stresses, the effect of body couples and the nonsymmetric tensors manifested in several real fluids of technological importance. A fully developed laminar magnetohydrodynamic (MHD) flow of an incompressible couple stress fluid through a vertical channel due to a steady-periodic temperature on the channel plates is investigated. Specifically, the effects of couple stresses and internal heat generation on MHD natural convection flow with steady-periodic heat input, the impact of magnetic field induction on the buoyancy-induced oscillatory flow of couple stress fluid with varying heating and a mixed convective two dimensional flow of unsteady MHD couple stress fluid through a channel field with porous medium are studied. Analytical methods and the semi-analytic Adomian decomposition method will be used to solve the resulting non-linear differential equations governing the flow systems. Useful results for velocity, temperature, skin friction and Nusselt number are obtained and discussed quantitatively. The effects of the various flow governing parameters on the flow field are investigated.

The heat transfer characteristics through arrays of pin fins were studied for the further development of internal cooling methods for turbine airfoils. Low aspect ratio pin fin arrays were tested through a range of Reynolds numbers between 5000 and 30,000 to determine the effects of pin spacing as well as aspect ratio on pin and endwall heat transfer. Experiments were also conducted to determine the independent effects of pin spacing and aspect ratio on arrays with different flow incidence angles. The pin Nusselt numbers showed almost no dependence on pin spacing or flow incidence angle. Using an infrared thermogaphy technique, spatially-resolved Nusselt numbers were measured along the endwalls of each array. The endwall results showed that streamwise spacing had a larger effect than spanwise spacing on array-averaged Nusselt numbers. Endwall heat transfer patterns showed that arrays with flow incidence angles experienced less wake interaction between pins than arrays with perpendicular flow, which caused a slight decrease in heat transfer in arrays with flow incidence angles. The effect of flow incidence angle on array-average Nusselt number was greater at tighter pin spacings. Even though the pin Nusselt number was independent of pin spacing, the ratio of pin-to-endwall Nusselt number was dependent on flow conditions as well as pin spacing. The pin aspect ratio had little effect on the array-average Nusselt number for arrays with perpendicular flow; however, the effect of flow incidence angle on array-average Nusselt number increased as aspect ratio decreased. / Master of Science

This study describes a detailed investigation on the effects that upstream step misalignment and upstream purge film cooling have on the endwall heat transfer for nozzle guide vanes in a land based power generation gas turbine at transonic conditions. Endwall Nusselt Number and adiabatic film cooling effectiveness distributions were experimentally calculated and compared with qualitative data gathered via oil paint flow visualization which also depicts endwall flow physics. Tests were conducted in a transonic linear cascade blowdown facility. Data were gathered at an exit Mach number of 0.85 with a freestream turbulence intensity of 16% at a Re = 1.5 x 106 based on axial chord. Varied upstream purge blowing ratios and a no blowing case were tested for 3 different upstream step geometries, one of which was the baseline (no step). The other two geometries are a backward step geometry and a forward step geometry, which comprised of a span-wise upstream step of +4.86% span and -4.86% span respectively. Experimentation shows that the addition of upstream purge film cooling increases the Nusselt Number at injection upwards of 50% but lowers it in the throat of the passage by approximately 20%. The addition of a backward facing step induces more turbulent mixing between the coolant and mainstream flows, thus reducing film effectiveness coverage and increasing Nusselt number by nearly 40% in the passage throat. In contrast, the presence of a forward step creates a more stable boundary layer for the coolant flow, thus aiding to help keep the film attached to the endwall at higher blowing ratios. Increasing the blowing ratio increases film cooling effectiveness and endwall coverage up to a certain point, beyond which, the high momentum of the coolant results in poor cooling performance due to jet liftoff. Near endwall streamlines without purge cooling generated by Li et al. [1] for the same geometries were compared to the experimental data. It was shown that even with the addition of upstream purge cooling, the near endwall streamlines as they moved downstream matched strikingly well with the experimental data. This discovery indicates that while the coolant flow will likely affect the flow streamlines three dimensionally, they are minimally effected by the coolant flow near the endwall as the flow moves downstream. / Master of Science / Gas turbine engines are commonly used for power production by burning natural gas. This leads to exceedingly hot temperatures through several stages of the engine. These temperatures often exceed the melting points of the metal components, especially in the region immediately following the combustion zone. Relatively cooler air from the compressor stage of the engine is used to cool these hot regions using sophisticated cooling schemes (external/internal cooling). The performance of these schemes can be severely influenced by unintentional but unavoidable geometric discrepancies caused by non-uniform thermal expansion and manufacturing tolerances of the engine components. This study investigates the impact of these geometric variations (specifically: combustor line/nozzle guide vane platform misalignment) on a commonly employed external cooling scheme (purge cooling) where the cooler air creates a protective layer between the metal and the hot gases. The geometric variation is found to make significant impact to the performance of the cooling scheme. The misalignment in one direction is found to be detrimental to the purge cooling effectiveness, while the other geometric misalignment helps the cooling scheme. In addition, increasing the amount of cooling does not necessarily mean better cooling because the increased amount of coolant can jet off of the surface before it can protect it from the hot gas. Quantitative results explaining the effects geometric misalignment and purge cooling are presented in the research herein.