Master of Science / Department of Mechanical and Nuclear Engineering / Steven J. Eckels, Bruce R. Babin / This project studied the pool boiling of R-134a and R-123 on smooth and enhanced tubes. This is the 1st phase of ASHRAE project RP-1316 "Experimental Evaluation of The Heat Transfer Impacts of Tube Pitch in a Highly Enhanced Surface Tube Bundle". A Turbo BII-HP and a Turbo BII-LP enhanced tubes were used in this study. These tubes were manufactured and donated by Wolverine Tube, Inc. Four different boiling cases were tested, R-134a on smooth tube, R-123 on smooth tube, R-134a on Turbo BII-HP tube, and R-123 on Turbo BII-LP tube. The first step in this study was performing a modified Wilson plot analysis, once completed, the average and local refrigerant heat transfer coefficients were determined. This thesis also presents the enthalpy-based heat transfer analysis (EBHT), a new method for determining the heat exchanger's overall heat transfer coefficient as a function of the enthalpy change of incompressible fluids. The test tubes' outer diameter is 19.05 mm and length is 1 m. Tests were conducted in a single tube test section, in which the test tube was water heated. All tests were conducted at a saturation temperature of 4.44 °C. The heat flux range is 9.2-126.6 kW/m[superscript]2 for testing with R-134a on smooth tube, 9.2-58 kW/m[superscript]2 for R-123 on smooth tube, 4.1-135.1 kW/m[superscript]2 for R-134a on Turbo BII-HP tube and 4.7-59.8 kW/m[superscript]2 for R-123 on Turbo BII-LP tube. Results show that the heat transfer coefficient increases with heat flux for all cases except the case of R-134a on Turbo BII-HP tube, where it experiences a trend change. Part of this study was comparing the smooth and enhanced tubes performances. R-134a Turbo BII-HP tube to smooth tube heat transfer coefficient ratio changes from 4 at low heat flux to 1.7 at high heat flux. R-123 Turbo BII-LP tube to smooth tube heat transfer coefficient ratio changes from 24 at low heat flux to 7 at high heat flux. The performance of Turbo BII-HP and Turbo BII-LP was found to be very similar over the tested heat flux range of the Turbo BII-LP tube. Comparison plots with available literature are presented.

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Vapor generation is central to the flow dynamics within fuel injector nozzles. Because the degree of atomization affects engine emissions and spray characteristics, quantification of phase change within diesel fuel injectors is a topic of design interest. Within the nozzle, the large pressure gradient between the upstream and downstream plena induce large velocities, creating separation and further pressure drop at the inlet corner. When local pressure in the throat drops below the fluid vapor pressure, phase change can occur with sufficient time. At the elevated temperatures present in diesel engines, this process can be dependent upon the degree of superheat, motivating the modeling of heat transfer from the wall. By modeling cavitation and flash boiling phenomena as a departure from equilibrium conditions, the HRMFoam model accurately reproduces canonical adiabatic flows. An experimentally determined relaxation time controls the rate at which vapor is generated, and includes model constants tuned for water and a diesel fuel surrogate. The model is shown to perform well for several benchmark experimental cases, including the work of Reitz, Lichtarowicz, and Nurick. With the implementation of the Farve-averaged energy equation, the present work examines and validates the transport of enthalpy through the fixed heat flux and fixed wall temperature boundary conditions. The pipe heat transfer experiments of Boelter and Allen are replicated using the kEpsilon, Realizable kEpsilon, and Spalart-Allmaras models. With proper turbulence model selection, Allen's heat transfer coefficient data is reproduced within 2.9%. Best-case bulk temperature rise prediction is within 0.05%. Boelter's bulk temperature rise is reproduced within 16.7%. Turbulent diffusivity is shown to determine radial enthalpy distribution.

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The Abraham Solvation Parameter Model (ASPM) is a linear, free-energy relationship that can be used to predict various solute properties based on solute-solvent interactions. The ASPM has been used to predict log (K or Cs,organic/Cs,gas) values, as well as log (P or Cs,organic/Cs,water) values for solute transfer into the following organic solvents: 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, 2-isopropoxyethanol and 2-butoxyethanol. The derived log (K or Cs,organic/Cs,gas) correlations describe the experimental data to within 0.14 log units (or less). The derived log (P or Cs,organic/Cs,water) correlations describe the experimental data to within 0.16 log units (or less). The ASPM has also been used to predict the enthalpies of solvation of organic solutes dissolved in the following solvents: acetic acid, dimethyl carbonate, diethyl carbonate, 1-butanol, 1-pentanol, 1-hexanol. The derived enthalpy of solvation correlations, using the L solute descriptor, describe the experimental data to within 2.50 log units (or less). The derived enthalpy of solvation correlations, using the V solute descriptor, describe the experimental data to within 3.10 log units (or less). Validation analyses have been performed on several of the correlations; and, as long as the solute descriptors fall within the given ranges as reported, the original correlations show good predictive ability for determining 1) solute transfer into, and 2) enthalpy of solvation for the aforementioned solvents.

The current study focuses on improving and testing the CTF thermalhydraulics computer code. CTF is a thermalhydraulic code used for subchannel analysis of nuclear power reactors developed as part of the US DOE CASL program and distributed by North Carolina State University. Subchannel analyses are used to predict the local fuel temperatures and coolant conditions inside a complex nuclear fuel assembly. Such calculations are used to improve designs of nuclear fuel, improve operating margins, or perform safety analysis. An important part of the code development process is the verification and validation for its intended use. In this work validation activities are performed using the RISO experiments are modeled in CTF for adiabatic and diabatic cases in annular flow regimes and a limited set of tests in CANDU geometries. The CTF predictions significantly overpredicted the pressure drop for cases involving annular flow conditions. Depending on the application, such overprediction can result in significant errors in the computation of fuel element dryout and other figures of merit. For example, an analysis using fixed pressure boundary conditions CTF predicts much lower subchannel flows and hence fuel element temperatures may be overestimated. On the other hand, for a scenario with mass flux and inlet pressure as boundary conditions, the impact of pressure drop discrepancies on dryout predictions may be lower. Therefore, there is a particular focus in this thesis on the two-phase pressure drop models and the RISO experiment specifically, since the RISO tests involve a range of annular flow conditions which is prototypical of many CANDU accident analysis conditions. In addition to the RISO experiments, 28-element CANDU full scale rod bundle experiments are modeled in CTF for single-phase and two-phase flow conditions. Cases are modeled for crept and uncrept conditions with different bearing pad heights i.e., 1.17 mm and 1.35mm. Pressure drop predictions are compared with the experimental results where single-phase comparisons are in good agreement while an overprediction of ~25% is observed for two-phase conditions. The effect of bearing pads on the subchannel local parameters, like mass flow rate, are also studied. Furthermore, the effect of turbulent mixing rate on subchannel enthalpy distribution in the bundle and CHF in different subchannels is also analyzed. Based on the comparison to the RISO and CANDU 28 element test databases, the overprediction of pressure drop in the annular flow regime needs improvement in the current version of CTF. This overprediction of the frictional pressure drop results from either wall drag or interfacial shear stress phenomena. In this study, it is demonstrated that the issue occurs mostly as a result of interfacial friction factor modelling this work examines several alternative approaches. The results show the Ju’s and Sun’s interfacial friction factor better predicts the results among all the other six correlations implemented in CTF. The major impediment in further testing of CTF is that it lacks the capability to simulate R-134a fluids. Given there is a large database of R-134a two-phase tests, another aspect of this thesis is to extend CTF for application and validation using refrigerants. The current CTF version only supports fluid properties for water and FLiBe salts. By adding R-134a fluid properties the testing and validation range of CTF is broadened for different experiments performed using R-134a fluids. CHF experiments are modeled in CTF and results are compared with experimental data. For local conditions correlation, 2006 water LUT are used to predict CHF and DNBR. The fluid-to-fluid scaling method is applied in CTF when using CTF with R-134a fluid properties for CHF and DNBR predictions to account for the difference in fluid properties between R-134a and the CHF look-up table. / Thesis / Master of Applied Science (MASc) / COBRA-TF (CTF) is a thermalhydraulic code, based on the historical code COBRA-TF, used for subchannel analysis of nuclear power reactors. Subchannel analysis can be used to predict the local fuel temperatures and coolant conditions inside a complex nuclear fuel assembly. CTF is a transient code that simultaneously solves conservation equations for mass, momentum, and energy for the three coolant phases present, i.e. vapor, continuous liquid, and entrained liquid droplet phases. The scope of the current study includes 1) testing the code for conditions relevant to CANDU accident analysis, 2) refinement of the models that are used in two-phase interfacial friction calculations, and 3) inclusion of alternate fluid properties. The testing of CTF is performed with different experimental databases covering CANDU thermalhydraulic conditions. The refinement is done by improving the pressure drop prediction in the annular flow regime by using different interfacial friction factor correlations from earlier studies in the literature. The current CTF version includes water and liquid salt properties (FLiBe) for coolant fluids. Freon (R-134a) fluid properties have been added in CTF in order to broaden the testing range of CTF for different experimental database using R-134a as working fluid.

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Получены композиции на основе альгината натрия и фторкаучука СКФ-26, наполненные частицами магнитных материалов: Ni, Fe, Fe3O4, SrFe12O19, MQP-Системы изучены методами изотермической микрокалориметрии, механического динамического анализа и магнитометрии. Методом микрокалориметрии измерены энтальпии смешения компонентов композитных пленок и рассчитаны значения предельной энтальпии адгезии полимерных матриц к поверхности магнитных порошков. Показано, что для систем на основе СКФ-26 энтальпия адгезии является отрицательной величиной, абсолютные значения которой увеличиваются в ряду Ni-Fe-Fe3O4. В системах альгинат натрия/Ni и альгинат натрия/Fe реализуется атермическое смешение, а в системах альгинат натрия/ФС и альгинат натрия/ Fe3O4 – экзотермическое. С помощью метода ДМА получены концентрационные зависимости динамических модулей потерь и упругости, а также угла сдвига для систем на основе раствора альгината натрия и магнитных порошков Fe, Fe3O4 и SrFe12O19 при частоте 1 Гц и напряжении 1 Па. Обнаружено, что с увеличением концентрации частиц неорганического вещества в суспензиях наблюдается увеличение динамических модулей и уменьшение угла сдвига, причем для суспензии, содержащей магнетит, характер течения не меняется. При течении суспензий, содержащих порошки Fe или SrFe12O19 начинают преобладать упругие свойства. Методом магнитометрии для систем СКФ-26/Ni и CКФ-26/Fe были получены петли магнитного гистерезиса в диапазоне напряженности магнитного поля от -15 кЭ до 15 кЭ. Показано, что с ростом содержания порошка в композите остаточная намагниченность и намагниченность насыщения не меняются, а коэрцитивная сила уменьшается, т. е. на размагничивание магнитного материала требуется меньше энергии. Методом магнитометрии получены данные для систем на основе альгината натрия, содержащих 30% Fe или Fe3O4. Обнаружено, что для системы альгинат натрия/Fe значения намагниченности насыщения для композита больше, чем для индивидуального порошка Fe, что может быть обусловлено упорядочением спинов на поверхности магнитных частиц при формировании композита. / Compositions based on sodium alginate and SKF-26 fluoro-rubber filled with particles of magnetic materials: Ni, Fe, Fe3O4, SrFe12O19, MQP-systems were studied by isothermal microcalorimetry, mechanical dynamic analysis and magnetometry. The enthalpy of mixing of composite film components was measured by microcalorimetry and the values of the limiting enthalpy of adhesion of polymer matrices to the surface of magnetic powders were calculated. It is shown that for systems based on SKF-26, the enthalpy of adhesion is a negative value, the absolute values of which increase in the series Ni-Fe-Fe3O4. In the sodium alginate/Ni and sodium alginate/Fe systems, athermic mixing is realized, and in the sodium alginate/FS and sodium alginate/ Fe3O4 systems, exothermic mixing is realized. The DMA method is used to obtain the concentration dependences of the dynamic loss and elasticity modulus, as well as the shear angle, for systems based on a solution of sodium alginate and magnetic powders Fe, Fe3O4, and SrFe12O19 at a frequency of 1 Hz and a voltage of 1 Pa. It is found that with an increase in the concentration of inorganic matter particles in the suspensions, an increase in the dynamic modules and a decrease in the shear angle are observed, and for a suspension containing magnetite, the flow pattern does not change. During the course of suspensions containing Fe or SrFe12O19 powders, elastic properties begin to prevail. Magnetic hysteresis loops in the magnetic field strength range from -15 kE to 15 kE were obtained by magnetometry for the SKF-26/Ni and SKF-26/Fe systems. It is shown that with an increase in the powder content in the composite, the residual magnetization and saturation magnetization do not change, and the coercive force decreases, i.e., less energy is required to demagnetize the magnetic material. Data for systems based on sodium alginate containing 30% Fe or Fe3O4 were obtained by magnetometry. It is found that for the sodium alginate/Fe system, the saturation magnetization values for the composite are greater than for the individual Fe powder, which may be due to the ordering of spins on the surface of magnetic particles during the formation of the composite.

No description available.