With the current development of the computer industry, CFD simulations have become the widespread standard in the industry, forming a baseline tool for numerous designs and safety procedures. This extensive dependence on the CFD codes rather than experiments raises the issue of the reliability of the results obtained from these codes. This thesis is intended to study the dependence of the CFD results on the grid types, numerical schemes and turbulence models. Additionally, comparisons between a general purpose commercial code STAR-CCM+ and a specialized code FDS are presented towards the end of this thesis. To study the numerical errors introduced by the grids and schemes, a laminar flow induced by natural convection inside a square cavity was considered first. Using Richardson’s extrapolation, a grid independent solution was calculated and compared with the results obtained from different grid types and schemes for Rayleigh (Ra) numbers , and . Comparison plots showed a higher dependence of the accuracy of the results on the cell shapes along with the order of the scheme and the cell size. Additionally, with the same cavity a grid dependence study for the and model has been done at .To test the reliability of the Quasi-DNS performed by an Unstructured Finite Volume (FV) CFD code, Turbulent Kinetic Energy (TKE) budgets should be calculated. User subroutines were developed to calculate the budgets of the TKE and to verify the user subroutines, prior to coaxial cylinder test case, a Q-DNS of the channel flow at has been performed using different grid configurations and numerical schemes. Results obtained from the Q-DNS of the channel flow on the polyhedral cells with the bounded central differencing scheme were found to be in good agreement with the reference DNS data. After the validation test case, a Q-DNS of the buoyancy driven turbulent flow inside a horizontal annular cavity at a high Rayleigh number, Ra = 1.18x109 with outer to inner cylinder ratio of 4.85 was carried out using a commercial code. Comparisons of Q-DNS results with low-Re URANS models, and model, showed that the latter models are able to capture the general flow features but fail to predict the large unsteadiness and high turbulence levels in the plume. However, local heat transfer rates along the inner and outer cylinder walls are on average of acceptable accuracy for engineering purposes. Finally, a full scale industrial test case of a fire in a compartment has been simulated. Both URANS ( model) and LES (Smagorinsky model) approaches are applied to model the turbulence with and without incorporating the combustion modelling. A comparison of the CFD results with the experimental data showed that for building fire simulations, accuracy of the results is more sensitive to the correlations used in the combustion modelling rather than the type of the turbulence model.

abstract: Granular material can be found in many industries and undergo process steps like drying, transportation, coating, chemical, and physical conversions. Understanding and optimizing such processes can save energy as well as material costs, leading to improved products. Silica beads are one such granular material encountered in many industries as a catalyst support material. The present research aims to obtain a fundamental understanding of the hydrodynamics and heat transfer mechanisms in silica beads. Studies are carried out using a hopper discharge bin and a rotary drum, which are some of the most common process equipment found in various industries. Two types of micro-glass beads with distinct size distributions are used to fill the hopper in two possible packing arrangements with varying mass ratios. For the well-mixed configuration, the fine particles clustered at the hopper bottom towards the end of the discharge. For the layered configuration, the coarse particles packed at the hopper bottom discharge first, opening a channel for the fine particles on the top. Also, parameters such as wall roughness (WR) and particle roughness (PR) are studied by etching the particles. The discharge rate is found to increase with WR, and found to be proportional to (Root mean square of PR)^(-0.58). Furthermore, the drum is used to study the conduction and convection heat transfer behavior of the particle bed with varying process conditions. A new non-invasive temperature measurement technique is developed using infrared thermography, which replaced the traditional thermocouples, to record the temperatures of the particles and the drum wall. This setup is used to understand the flow regimes of the particle bed inside the drum and the heat transfer mechanisms with varying process conditions. The conduction heat transfer rate is found to increase with decreasing particle size, decreasing fill level, and increasing rotation speed. The convection heat transfer rate increased with increasing fill level and decreasing particle size, and rotation speed had no significant effect. Due to the complexities in these systems, it is not always possible to conduct experiments, therefore, heat transfer models in Discrete Element Method codes (MFIX-DEM: open-source code, and EDEM: commercial code) are adopted, validated, and the effects of model parameters are studied using these codes. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2020

<p> An experimental study of free convection heat transfer from a heated horizontal plate facing downwards in air is reported in this thesis. The results of this study are in good agreement with the results obtained by Fishenden and Saunders. This study also investigates the effects of restraining the development of the thermal boundary layer with 1/2" and 1" edge strips around the edges of the test plate. This study led to the conclusion that edge restrains tended to decrease the heat transfer from the plate. </p> <p> The range of Grashof Prandtl Number product investigated is between 4 x 10⁸ and 8 x 10⁹ resulting in the heat flux range of 0.7 Btu/hrft² to 102 Btu/hrft². Correlations are presented relating heat flux and temperature difference between plate surface temperature and ambient temperature. </p> / Thesis / Master of Engineering (ME)

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.

This thesis investigates the refrigerant (R-134a) flow in three minichannels having different geometries experimentally. During the last 40 years heat transfer in small scales has been a very attractive research area. Improvements in heat transfer in the refrigeration applications by means of usage of micro/minichannels provide significant developments in this area. Also it is known that experimental studies are very important to constitute a database which is beneficial for new developments and research. During the two-phase flow experiments conducted in the minichannels, low mass flow rates and constant wall temperature approach, which are the conditions in the evaporators of the refrigerator applications were applied because one of the purposes of this study is to determine the most ideal minichannel among the tested minichannels for usage in the evaporator section of the refrigerators. Two-phase flow experiments were made with refrigerant R134a in the three minichannels having hydraulic diameters of 1.69, 3.85 and 1.69 mm respectively. As distinct from the others, the third minichannel has a rough inner surface. Comparison of the experimental results of the three minichannels was made in terms of forced convection heat transfer coefficients and pressure drop at constant quality and mass flux values. As a result of the experiments, the most ideal minichannel among the tested minichannels was determined for the evaporator applications in the refrigerators.

The work presents investigations into the development of a fuel-powered compact SMA actuator system. For the final SMA actuator, the K-alloy SMA strip (0.9 mm x 2.5 mm), actuated by a forced convection heat transfer mechanism, was embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, ran along the strip and was utilized to prevent mixing between the hot and the cold fluid in order to increase the energy density of the system. The fuel, such as propane, was utilized as main energy source in order to achieve high energy and power densities of the SMA actuator system. Numerical analysis was carried out to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency. Multi-channel combustor/heat exchanger and micro-tube heat exchanger were designed and tested to achieve high heat transfer rate and high compactness. The final SMA actuator system was composed of pumps, valves, bellows, multi-channel combustor/heat exchanger, micro-tube heat exchanger and control unit. The experimental tests of the final system resulted in 250 N force with 2 mm displacement and 1.0 Hz actuation frequency in closed-loop operation, in which the hot and the cold fluid were re-circulated by pumps.

In this thesis a numerical study has been undertaken to investigate turbulent flow and heat transfer in a number of flow problems, representing the gas-cooled reactor core flows. The first part of the research consisted of a meticulous assessment of various advanced RANS models of fluid turbulence against experimental and numerical data for buoyancy-modified mixed convection flows, such flows being representative of low-flow-rate flows in the cores of nuclear reactors, both presently-operating Advanced Gas-cooled Reactors (AGRs) and proposed ‘Generation IV’ designs. For this part of the project, an in-house code (‘CONVERT’), a commercial CFD package (‘STAR-CD’) and an industrial code (‘Code_Saturne’) were used to generate results. Wide variations in turbulence model performance were identified. Comparison with the DNS data showed that the Launder-Sharma model best captures the phenomenon of heat transfer impairment that occurs in the ascending flow case; v^2-f formulations also performed well. The k-omega-SST model was found to be in the poorest agreement with the data. Cross-code comparison was also carried out and satisfactory agreement was found between the results.The research described above concerned flow in smooth passages; a second distinct contribution made in this thesis concerned the thermal-hydraulic performance of rib-roughened surfaces, these being representative of the fuel elements employed in the UK fleet of AGRs. All computations in this part of the study were undertaken using STAR-CD. This part of the research took four continuous and four discrete design factors into consideration including the effects of rib profile, rib height-to-channel height ratio, rib width-to-height ratio, rib pitch-to-height ratio, and Reynolds number. For each design factor, the optimum configuration was identified using the ‘efficiency index’. Through comparison with experimental data, the performance of different RANS turbulence models was also assessed. Of the four models, the v^2-f was found to be in the best agreement with the experimental data as, to a somewhat lesser degree were the results of the k-omega-SST model. The k-epsilon and Suga models, however, performed poorly. Structured and unstructured meshes were also compared, where some discrepancies were found, especially in the heat transfer results. The final stage of the study involved a simulation of a simplified 3-dimensional representation of an AGR fuel element using a 30 degree sector configuration. The v^2-f model was employed and comparison was made against the results of a 2D rib-roughened channel in order to assess the validity and relevance of the precursor 2D simulations of rib-roughened channels. It was shown that although a 2D approach is extremely useful and economical for ‘parametric studies’, it does not provide an accurate representation of a 3D fuel element configuration, especially for the velocity and pressure coefficient distributions, where large discrepancies were found between the results of the 2D channel and azimuthal planes of the 3D configuration.

Solid-fluid thermal interactions during unsteady flow in porous media play an important role in the regenerators of pulse tube cryocoolers. Pore-level thermal processes in porous media under unsteady flow conditions are poorly understood. The objective of this investigation is to study the pore-level thermal phenomena during pulsating flow through a generic, two-dimensional porous medium by numerical analysis. Furthermore, an examination of the effects of flow pulsations on the thermal dispersion and heat transfer coefficient that are encountered in the standard, volume-average energy equations for porous media are carried out. The investigated porous media are periodic arrays of square cylinders. Detailed numerical data for the porosity range of 0.64 to 0.84, with flow Reynold's numbers from 0-1000 are obtained. Based on these numerical data, the instantaneous as well as cycle-average thermal dispersion and heat transfer coefficients, to be used in the standard unsteady volume-average energy conservation equations for flow in porous media, are derived. Also, the adequacy of current applied cycle-average correlations for heat transfer coefficients and the inclusion of the thermal dispersion in the definition of an effective fluid thermal conductivity are investigated.

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This work presents the development of a novel and non-invasive method that measures fluid flow rate and temperature in pipes. While current non-invasive flow meters are able to measure pipe flow rate, they cannot simultaneously measure the internal temperature of the fluid flow, which limits their widespread application. Moreover, devices that are able to determine flow temperature are primarily intrusive and require constant maintenance, which can shut down operation, resulting in downtime and economic loss. Consequently, non-invasive flow rate and temperature measurement systems are becoming increasingly attractive for a variety of operations, including for use in leak detection, energy metering, energy optimization, and oil and gas production, to name a few. In this work, a new solution method and parameter estimation scheme are developed and deployed to non-invasively determine fluid flow rate and temperature in a pipe. This new method is utilized in conjunction with a sensor-based apparatus--"namely, the Combined Heat Flux and Temperature Sensor (CHFT+), which employs simultaneous heat flux and temperature measurements for non-invasive thermal interrogation (NITI). In this work, the CHFT+ sensor embodiment is referred to as the British Thermal Unit (BTU) Meter. The fluid's flow rate and temperature are determined by estimating the fluid's convection heat transfer coefficient and the sensor-pipe thermal contact resistance. The new solution method and parameter estimation scheme were validated using both simulated and experimental data. The experimental data was validated for accuracy using a commercially available FR1118P10 Inline Flowmeter by Sotera Systems (Fort Wayne, IN) and a ThermaGate sensor by ThermaSENSE Corp. (Roanoke, VA). This study's experimental results displayed excellent agreement with values estimated from the aforementioned methods. Once tested in conjunction with the non-invasive BTU Meter, the proposed solution and parameter estimation scheme displayed an excellent level of validity and reliability in the results. Given the proposed BTU Meter's non-invasive design and experimental results, the developed solution and parameter estimation scheme shows promise for use in a variety of different residential, commercial, and industrial applications. / MS / This work documents the development of a novel and non-invasive method that measures fluid flow rate and temperature in pipes. While current non-invasive flow meters are able to measure pipe flow rate, they cannot simultaneously measure the internal temperature of the fluid flow, which limits their widespread application. Moreover, devices that are able to determine flow temperature are primarily intrusive and require constant maintenance, which can shut down operation, resulting in downtime and economic loss. Consequently, non-invasive flow rate and temperature measurement systems are becoming increasingly attractive for a variety of operations, including for use in leak detection, energy metering, energy optimization, and oil and gas production, to name a few. This paper presents a new method that utilizes a non-invasive British Thermal Unit (BTU) Meter based on Combined Heat Flux and Temperature Sensor (CHFT+) technology to determine fluid flow rate and temperature in pipes. The non-invasive BTU Meter uses thermal interrogation to determine different flow parameters, which are used to determine the fluid flow rate and temperature inside a pipe. The method was tested and validated for accuracy and reliability through simulations and experiments. Given the proposed BTU Meter’s noninvasive design and excellent experimental results, the developed novel sensing method shows promise for use in a variety of different residential, commercial, and industrial applications.