This work describes the development and validation of a computational model for vertical borehole heat exchangers in residential ground-source heat pump energy systems. Due to the size and shape of vertical borehole heat exchangers, their operation thermally impacts a large volume of surrounding soil and thus discretized models have largely been confined to short-term transient simulations, such as the case of a thermal response test. The proposed model employs a computationally efficient physics-based models at variable spatial dimensions which can be used for long-time simulation of the ground heat transfer. The model can generally be considered as a composition of three separate domains: the borehole domain, which combines one-dimensional, three-dimensional and equations-based physics, the near-field soil domain, which resolves three-dimensional transient heat conduction and the far-field soil domain which is modelled as one-dimensional axisymmetric transient heat conduction. The main purpose of this work is to present each component of the model and validate their behaviours and assumptions through a combination of comparison to experimental data, highly cited published works, and well-known analytical models. The complete composite model ignores the three-dimensional effects of fluid heat transfer, and the axial heat transfer in the far-field in order to reduce the computational effort, and the level of uncertainty introduced by each simplification is explored. Finally, to support the composite model, a new method determining the thermal impact of the borehole operation mentioned previously was devised and presented alongside the model development and validations. This method, based on the previously defined thermal impacting radius, improves the consistency and theoretical foundation of the value’s definition based on a system energy balance, rather than local temperature conditions. / Thesis / Master of Applied Science (MASc)

No description available.

Understanding the mechanisms that serve to increase heat transfer provides valuable knowledge to minimize the size and maximize the performance of compact heat exchangers. This document presents a detailed experimental heat transfer study of six scaled up louvered fin geometries that are typical of those found in modern louvered fin compact heat exchangers. Heat transfer measurements were performed over a range of Reynolds numbers and with two different boundary conditions. A fully heated boundary condition allowed the effects of the thermal field to be observed while an adiabatic boundary condition allowed the effects of the flow field to be observed. The results indicated that the complex thermal and flow field patterns that developed within the louvered fin geometries strongly affected the heat transfer of individual louvers. In the entrance region of the louvered array, the effects of the flow field were dominant while in the fully developed region of the louvered arrays, the effects of the thermal field were dominant. A companion two-dimensional CFD study indicated that the heat transfer trends of the louvers resulting from both the thermal and flow fields were well predicted. Based on heat transfer performance, it was determined that the theta = 27°, Fp/Lp = 1.52 geometry performed the best at Re = 230 and Re = 370, while the theta = 39°, Fp/Lp = 0.91 geometry performed best at Re = 1016. / Master of Science

A compact heat exchanger is a device used to transfer thermal energy between two or more fluids. The most extensive use of compact heat exchangers occurs in the commercial trucking industry. Most compact heat exchanger designs contain tubes carrying one fluid and external fins through which passes another fluid. To enhance the fin-side heat transfer in a compact heat exchanger, which is typically the air side of the heat exchanger, louvers are manufactured into the fins. Louvered fins initiate the growth of new boundary layers such that the average convective heat transfer coefficient is higher than that which would occur for a continuous fin. Approximately 85% of the total thermal resistance occurs on the air side of the heat exchanger. To design more space and weight efficient heat exchangers, it is imperative to gain a fundamental understanding of the mechanisms that serve to increase the heat transfer on the air side. This thesis presents the heat transfer results of three scaled-up louvered fin geometries and compares these results to six additional models in which the louver angle, fin pitch and Reynolds number were varied. Two experiments were performed to determine the reference temperature used for the calculation of the heat transfer coefficients. The use of two reference temperatures allowed the effects of the flow field and thermal field to be separated. This thesis also presents details of an optimization study performed for a louvered fin array. The results of the experimental study showed that the hot thermal wakes formed at the entrance louver have an adverse effect on the heat transfer of downstream louvers. Measuring the adiabatic wall temperature of the louvers in the array showed the effect of these thermal wakes. The experimental study showed that the optimal louver geometry was Reynolds number dependent. For the lower two Reynolds numbers of ReLp = 230 and 370, the Fp/Lp = 1.52, q = 27° model was found to be the best performer, which does not agree with previous studies. For ReLp = 1016, the Fp/Lp = 0.91, q = 39° model was shown to have optimal heat transfer performance, which is in agreement with a previous study performed by Chang and Wang (1996). / Master of Science

The first Molten Salt Reactor (MSR) was designed and tested at Oak Ridge National Laboratory (ORNL) in the 1960's, but recent technological advancements now allow for new components, such as heat exchangers, to be created for the next generation of MSR's and molten salt-cooled reactors. The primary (fuel salt-to-secondary salt) heat exchanger (PHX) design is shown here to make dramatic improvements over traditional shell-and-tube heat exchangers when changed to a compact heat exchanger design. While this paper focuses on the application of compact heat exchangers on a Molten Salt Reactor, many of the analyses and results are similarly applicable to other fluid-to-fluid heat xchangers. The heat exchanger design in this study seeks to find a middle-ground between shell- and-tube designs and new ultra-efficient, ultra-compact designs. Complex channel geometries and microscale dimensions in modern compact heat exchangers do not allow routine maintenance to be performed by standard procedures, so extended surfaces will be omitted and hydraulic diameters will be kept in the minichannel regime (minimum channel dimension between 200 μm and 3 mm) to allow for high-frequency eddy current inspection methods to be developed. High aspect ratio rectangular channel cross-sections are used. Various plant layouts of smaller heat exchanger banks in a "modular" design are introduced. FLUENT was used within ANSYS Workbench to find optimized heat transfer and hydrodynamic performance. With similar boundary conditions to ORNL's Molten Salt Breeder Reactor's shell-and-tube design, the compact heat exchanger interest in this thesis will lessen volume requirements, lower fuel salt volume, and decrease material usage. / Master of Science

Lubricants and liquid cooling are used in many industrial applications to ensure reliability and longevity of machinery. Oil cooling of both electrical and mechanical applications is of interest since oil is better suited for electrical applications than water and already available in the system as a lubricant. Brazed plate heat exchangers (BPHEs) have many advantages compared to other heat exchanger types commonly used in oil cooling applications. Flow maldistribution inside BPHEs can arise with highly viscous fluids like oil. Since flow is hard to measure when plate heat exchangers are brazed together, Computational Fluid Dynamics (CFD) can be used instead. This study investigates parameters that could affect flow distribution inside BPHEs with the CFD-tool COMSOL Multiphysics. The study is made on three different geometries at different detail levels. The purpose of the study is to expand the knowledge about fluid behavior in BPHEs and how it affects efficiency. It was proved from the Bernoulli equation that flow velocity, gravity and Reynolds number were some parameters that could affect flow distribution inside BPHEs. Two simplified models were built for evaluation of viscosity, gravity and Reynolds number. A more detailed model was provided by SWEP representing the fluid domain of a full-size distribution zone model. Model validation and mesh independence study were made with expressions due to the lack of experimental data. Investigations of viscosity, gravity and Reynolds number were made through isolation and alteration of the respective parameter. The validation and mesh independence study proved the models trustworthy and detailed enough to capture the physical behavior. Small deviations from expected validation results can be explained with the assumptions and simplifications made in the process. Results show that flow maldistribution increases with viscosity differences between channels. Viscosity maldistribution is greater for oil than for water. It is important to consider how the fluid viscosity changes with temperature under the respective working conditions. Gravity has no effect on flow distribution as long as it acts along or opposite the main flow direction. As plate heat exchangers are generally placed vertically, gravity will not affect flow distribution. Gravity has a significant effect on flow distribution if plate packages are places horizontally. High Reynolds numbers have a positive effect on flow distribution and reduce the difference between highest and lowest velocities across the outlet. Very low flow velocities should therefore be avoided since it increases flow maldistribution.

A microwave heat exchanger (MHE) is a device which converts microwave (MW) energy into usable form of heat energy. The working principle of the MHE is based on a collective effect of electromagnetic wave propagation, heat transfer and fluid flow, so the development of an efficient device requires complicated experimentation with processes of different physical nature. A peculiar phenomenon making the design of MHE even more challenging is extit{thermal runaway}, a nonlinear phenomenon in which a small increase in the input power gives rise to a large increase in temperature. Such high temperature may result in material damage through excessive thermal expansion, cracking, or melting. In this Thesis, we report on an initial phase in the development of a computational model which may help clarify complicated interaction between nonlinear phenomena that might be difficult to comprehend and control experimentally. We present a 2D multiphysics model mimicking operation of a layered MHE that simulates the nonlinear interaction between MW, thermal, and fluid flow phenomena involved in the operation of the MHE. The model is built for a triple layered (fluid-ceramic-fluid) MHE and is capable of capturing the S- and SS-profiles of power response curve which determines steady-state temperature solution as a function of incident power. The model is implemented on the platform of the COMSOL Multiphysics modeling software. We show that a MHE with particular thickness and dielectric properties of the layers can operate efficiently by keeping temperatures during thermal runaway under control. Overall temperatures increase rapidly as soon as the local maximum temperature reaches a critical value. This condition is held true both in absence and in presence of fluid flow. It is demonstrated that the efficiency of the MHE dramatically increases when thermal runaway is achieved. As the amount of heat energy, which is being transferred to the fluid from the heated dielectric, increases, incident power required to achieve thermal runaway also increases. It is also shown that, with appropriate length of the layered MHE, thermal runaway can be achieved at a lower power level. While the model developed in this Thesis studies the basic operation of a three layered MHE, it can further be developed to investigate optimum design parameters of the MHE of other structures so that maximum thermal efficiency is achieved.

The Cu-Cl thermochemical cycle is a promising method to generate hydrogen as a clean fuel for human use in the future. The cycle can be coupled to nuclear reactors to supply its heat requirements. The cycle generates hydrogen by splitting water molecules through a series of chemical reactions. Thermal management within the cycle is crucial for improving its thermal efficiency. The cycle has an average theoretical efficiency of around 46% without any heat recovery. The efficiency may increase up to 74%, if all heat associated with the products of the cycle’s steps is recycled internally. The products of the different processes that transfer heat are; oxygen, hydrogen, and molten CuCl. The heat carried by oxygen and hydrogen can be recovered by the use of conventional heat exchangers. However, recovering heat from molten CuCl is very challenging due to the phase transformations that molten CuCl undergoes, as it cools down from liquid to solid states. This thesis presents a new model that predicts the fluid flow and heat transfer in a direct contact heat exchanger, designed to recover the heat from molten CuCl, through the physical interaction between CuCl droplets and air. Numerical results for the variations of temperature, velocity, heat transfer rate, and so forth, are given for two cases of CuCl flow. The predicted dimensions of the heat exchanger were found to be a diameter of 0.13 m, and a height of 0.6 and 0.8 m for 1 and 0.5 mm droplet diameters, respectively. The results obtained provide valuable insights for the equipment design and scale-up of the Cu-Cl cycle. / UOIT

For the evaluation of non-ferrous heat exchanger tube, there are many non-destructive testing methods; however, the eddy current testing (ECT) method is the most popular one. By using of ECT, you may find out the defects existing inside or outside the tube wall, diagnose the heat exchanger system and find out the latent problems. The problem is that an improper signal analysis will result in error in the range of 15〜25% of the tube wall thickness, or even over 40% error. This is a great discouragement to the ECT inspectors, and will reduce the confidence of the proprietors of power plants or petro-chemical industries to the use of ECT. Therefore, in this thesis, the study is mainly focus on the problems of the aluminum brass tubes in condenser using ECT method. This thesis will analyze the causes of error of aluminum brass tubes when using ECT, prepare calibration and reference tubes, and test them using eddy current instruments. The relationship among the raw data with volts, phase angle and depth has been found. Two data evaluation methods are developed, one is the defect depth modification equation and the other is the auxiliary evaluation curve. The new methods are proved to be more accurate and practical in the evaluation of heat exchanger tube after more than one year of verification by field testing in the power plant. The results obtained in this thesis are very helpful to reduce the probability of tube failure.

In adult cardiomyocytes, the established mechanism of excitation-contraction coupling is calcium-induced calcium release (CICR) mediated by L-type Ca2+ channels (Cav1.2). Briefly, membrane depolarization opens voltage-gated Cav1.2 to allow for the influx of extracellular Ca2+ into the cytosol. This small sarcolemmal (SL) Ca2+ influx is necessary for triggering a larger release of Ca2+ from the intracellular Ca2+ storage site, the sarcoplasmic reticulum (SR), through the SR Ca2+ release channel also known as the ryanodine receptor (RyR). RyR-mediated release of SR Ca2+ effectively raises the cytosolic free Ca2+ concentration, allowing for Ca2+ binding to troponin C on the troponin-tropomysin complex, leading to cross-bridge formation and cell contraction. However, previous functional data suggests an additional CICR modality involving reverse mode Na+-Ca2+ exchanger (NCX) activity also exists in neonate cardiomyocytes. To further our understanding of how CICR changes occur during development, we investigated the spatial arrangement of caveolin-3 (cav-3), the principle structural protein of small membrane invaginations named caveolae, and NCX in developing rabbit ventricular myocytes. Using traditional as well as novel image processing and analysis techniques, both qualitative and quantitative findings firmly establish the highly robust and organized nature of NCX and cav-3 distributions during development. Specifically, our results show that NCX and cav-3 are distributed on the peripheral membrane as discrete clusters and are not highly colocalized throughout development. 3D distance analysis revealed that NCX and cav-3 clusters are organized with a distinct longitudinal and transverse periodicity of 1-1.5 μm and that NCX and cav-3 cluster have a pronounced tendency to be mutually exclusive on the cell periphery. Although these findings do not support the original hypothesis that caveolae is the structuring element for a restricted microdomain facilitating NCX-CICR, our results cannot rule out the existence of such microdomain organized by other anchoring proteins. The developmentally stable distributions of NCX and cav-3 imply that the observed developmental CICR changes are achieved by the spatial re-organization of other protein partners of NCX or non-spatial modifications. In addition, the newly developed image processing and analysis techniques can have wide applicability to the investigations on the spatial distribution of other proteins and cellular structures.