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Reynolds average Navier-Stokes (RANS) modeling has established itself as a critical design tool in many engineering applications, thanks to its superior computational efficiency. The drawbacks of RANS models are well known, but not necessarily well understood: poor prediction of transition, non-equilibrium flows, mixing and heat transfer, to name the ones relevant to our study. In the present study, we use a direct numerical simulation (DNS) of a reciprocating channel flow driven by an oscillating pressure gradient to test several low- and high-Reynolds' RANS models. Temperature is introduced as a passive scalar to study heat transfer modeling. Low-Reynolds' models manage to capture the overall physics of wall shear and heat flux well, yet with some phase discrepancies, whereas high-Reynolds' models fail. We have derived an integral method for wall shear and wall heat flux analysis, which reveals the contributing terms for both metrics. This method shows that the qualitative agreement appears more serendipitous than driven by the ability of the models to capture the correct physics. The integral method is shown to be more insightful in the benchmarking of RANS models than the typical comparisons of statistical quantities. This method enables the identification of the sources of discrepancies in energy budget equations. For instance, in the wall heat flux, one model is shown to have an out of phase dynamic behavior when compared to the benchmark results, demonstrating a significant issue in the physics predicted by this model. Our study demonstrates that the integral method applied to RANS modeling yields information not previously available that should guide the derivation of physically more accurate models.

The main objective of this study is to propose and to validate simplified models to simulate the performance of refrigeration systems. The proposed modelling approach of the system is modular: the compressor is modelled by a simple and physical model that takes into account the heat transfers and the un-matching of internal and external pressure ratio for the scroll compressors. The evaporator is modelled as a two zones heat exchanger on the refrigeration side (one for the two phases zone and the other one for superheated gas) and finally the condenser is assumed to be divided into three zones (de-superheating, two-phase and the sub-cooling). The compressor model was already developed by other author; here it is only validated using three scroll compressors and two reciprocating ones. The main differences are the conditions at which these compressors are tested: 20 bar at the supply and 40 at the exhaust. The condenser and evaporator models are the main contribution of this study. These models use the geometry and the correlation from the literature to calculate the global heat transfer coefficient on each zone. In the case of the condenser, a mean void fraction model is used to determinate the condenser subcooling as function of the refrigerant charge or vice-versa. The refrigeration system model is validated with experimental results obtained on each component and the whole system in five different test benches. The results show a very good agreement between the measured and predicted main outputs of the system.

Die Dissertation besteht aus Textteil (1) und Bildteil (2).

Shape Memory Alloys (SMA) are a group of metallic alloys that have the ability to return to some previously defined shape or size when subjected to an appropriate thermal cycling procedure. In recent years there has been a lot of research on the development of small, light and, yet, powerful actuators for use in areas like robotics, prosthetics, biomimetics, shape control and grippers. Many of the miniaturized conventional actuators do not have sufficient power output to be useful and SMAs can be used advantageously here. The widespread use of SMAs in actuators is limited by their low bandwidth. Use of SMAs in two-way actuators requires that they undergo thermal cycling (heating and cooling). While SMAs can be heated quickly by resistive heating, conventional convection cooling mechanisms are much slower as the exothermic austenitic to martensitic phase transformation is accompanied by the release of significant amount of latent heat. While a number of cooling mechanisms have been studied in SMA actuator literature, most of the cooling mechanisms involve unidirectional forced convection. This may not be the most effective method. Oscillating flow in a channel can sometimes enhance heat transfer over a unidirectional flow. One possible explanation for this heat transfer enhancement is that the oscillatory flow creates a very thin Stokes viscous boundary-layer and hence a large time-dependent transverse temperature gradient at the heated wall. Therefore heat transfer takes place at a large temperature difference, thereby enhancing the heat transfer. In this work, the heat transfer from an SMA actuator under an oscillating channel is investigated and is compared to steady, unidirectional flow heat transfer. Oscillating flow is simulated using a finite volume based method. The resulting velocity field is made use of in solving the heat transfer problem using a finite difference scheme. A parametric study is undertaken to identify the optimal flow conditions required to produce the maximum output for a given geometry of the SMA actuator. The latent heat of transformation of the SMA is accounted for by means of a temperature dependent specific heat.

The reduction or elimination of leakage of hydraulic fluid from fluid power systems is considered a fundamental prerequisite for the expanded use of fluid power. There is also a need to reduce seal friction to both reduce energy dissipation and eliminate control problems. These seals are developed through empirical means at the present time, since the fundamental physics of seal operation has been unclear. This research develops numerical models for analyzing reciprocating hydraulic rod seals with various rod surfaces. These models consist of coupled fluid mechanics, contact mechanics and deformation analyses. Both flooded and starved lubrication boundary conditions are applied. For seals with a smooth rod and a plunge-ground rod, the model combines a 1-D finite volume Reynolds equation solver with a 2-D axisymmetric finite element deformation and static contact mechanics analyses, and a Greenwood-Williamson contact mechanics analysis with rod motion. Leakage and friction, along with sealing zone details with the plunge-ground rod are compared with those with the smooth rod. The influence of rod surface finish on seal performance is investigated and explained, under both flooded and starved conditions For seals with a micro-patterned rod, the model consists of finite volume Reynolds equation solver, finite element deformation and static contact mechanics analyses and a Greenwood-Williamson dynamic contact mechanics analysis. This model is able to handle rod surface pattern with 3-dimensional geometrics. Simulations with different micro-pattern geometries are performed to analyze the fundamental mechanism of surface pattern effects on seal operation. Again, both flooded and starved conditions are applied and the results for both cases are compared and analyzed.

Submitted by Diogo Barreiros (diogo.barreiros@ufba.br) on 2017-02-17T16:41:33Z No. of bitstreams: 9 Capitulo I.pdf: 29639 bytes, checksum: 8007a2f7dfe2a8a68371ae454ff21265 (MD5) Capitulo II.pdf: 2398618 bytes, checksum: 67ec1b928bbd365a7a6ebc67b63a0cc3 (MD5) Capitulo III.pdf: 729546 bytes, checksum: 7778ce88975d7784a5c831e8af33cc12 (MD5) Capitulo IV.pdf: 39255 bytes, checksum: f005a001f7b707ab00d207d6718633b3 (MD5) Capitulo V.pdf: 424609 bytes, checksum: c070a2136bd33f21641c2d67d3b860d5 (MD5) Capitulo VI.pdf: 656297 bytes, checksum: 72bcce0a93526c29edd43b88091f3b94 (MD5) Capitulo VII.pdf: 1134199 bytes, checksum: 7fa6475029a4659167bab63ca25d6a37 (MD5) Capitulo VIII.pdf: 28984 bytes, checksum: 1c011016b6a3107609e9ebc952e018b4 (MD5) Elementos Pre-textuais.pdf: 78941 bytes, checksum: 38125074504363e58154371d872e9499 (MD5) / Approved for entry into archive by Vanessa Reis (vanessa.jamile@ufba.br) on 2017-02-21T11:56:14Z (GMT) No. of bitstreams: 9 Capitulo I.pdf: 29639 bytes, checksum: 8007a2f7dfe2a8a68371ae454ff21265 (MD5) Capitulo II.pdf: 2398618 bytes, checksum: 67ec1b928bbd365a7a6ebc67b63a0cc3 (MD5) Capitulo III.pdf: 729546 bytes, checksum: 7778ce88975d7784a5c831e8af33cc12 (MD5) Capitulo IV.pdf: 39255 bytes, checksum: f005a001f7b707ab00d207d6718633b3 (MD5) Capitulo V.pdf: 424609 bytes, checksum: c070a2136bd33f21641c2d67d3b860d5 (MD5) Capitulo VI.pdf: 656297 bytes, checksum: 72bcce0a93526c29edd43b88091f3b94 (MD5) Capitulo VII.pdf: 1134199 bytes, checksum: 7fa6475029a4659167bab63ca25d6a37 (MD5) Capitulo VIII.pdf: 28984 bytes, checksum: 1c011016b6a3107609e9ebc952e018b4 (MD5) Elementos Pre-textuais.pdf: 78941 bytes, checksum: 38125074504363e58154371d872e9499 (MD5) / Made available in DSpace on 2017-02-21T11:56:14Z (GMT). No. of bitstreams: 9 Capitulo I.pdf: 29639 bytes, checksum: 8007a2f7dfe2a8a68371ae454ff21265 (MD5) Capitulo II.pdf: 2398618 bytes, checksum: 67ec1b928bbd365a7a6ebc67b63a0cc3 (MD5) Capitulo III.pdf: 729546 bytes, checksum: 7778ce88975d7784a5c831e8af33cc12 (MD5) Capitulo IV.pdf: 39255 bytes, checksum: f005a001f7b707ab00d207d6718633b3 (MD5) Capitulo V.pdf: 424609 bytes, checksum: c070a2136bd33f21641c2d67d3b860d5 (MD5) Capitulo VI.pdf: 656297 bytes, checksum: 72bcce0a93526c29edd43b88091f3b94 (MD5) Capitulo VII.pdf: 1134199 bytes, checksum: 7fa6475029a4659167bab63ca25d6a37 (MD5) Capitulo VIII.pdf: 28984 bytes, checksum: 1c011016b6a3107609e9ebc952e018b4 (MD5) Elementos Pre-textuais.pdf: 78941 bytes, checksum: 38125074504363e58154371d872e9499 (MD5) / A necessidade de novas metodologias para análise e monitoramento de compressores alternativos motivou o desenvolvimento de um sistema digital multicanal com capacidade de medir diferentes grandezas simultaneamente. Como base para este trabalho escolheu-se medir pressão dinâmica, vibração e deslocamento do pistão. O desenvolvimento deste trabalho dentro de um curso de Mecatrônica produziu um sistema simples e eficiente cujos resultados experimentais, apresentados sob a forma de gráficos e dados de desempenho, confirmaram os defeitos introduzidos artificialmente. Isto permitiu validar o Sistema de Diagnóstico de Compressores Alternativos (SDCA) e demonstrou o quanto este recurso é poderoso para o diagnóstico de defeitos, tanto nos componentes da parte de compressão (fluid end) quanto nos de acionamento (power end). Estas informações, transformadas em recomendações de reparo, serão a base para uma atuação preditiva dos setores de Planejamento de Manutenção.

The purpose of this developmental project was to design and fabricate a vertical reciprocating conveyor in order to eliminate the process of manually carrying 27 pound containers of plastic resin up and down a flight of offset space saver stairs. This project took place and was built for Phoenix Closures Incorporated. The conveyor was designed and built in house because there are no commercially available vertical reciprocating conveyors available that meet the necessary requirements. The capabilities of the proposed vertical reciprocating conveyor are not limited to the carrying of the containers but designed to carry vacuum cleaners, tool boxes, and spare parts to the mezzanine. The vertical reciprocating conveyor is designed for a greater capacity then the 27 pounds the container of plastic resin weighs, but the safety systems are not designed in a way that would allow the conveyor to lift a greater amount of weight.

In-cylinder heat transfer is important to the performance of many reciprocating energy conversion machines. It is particularly important to the performance of Stirling machines. For cylinder spaces without inflow, heat transfer and related power losses can be predicted using an analytical model which neglects turbulence. In actual engine cylinders, where significant turbulence levels can be generated by high velocity inflow, a model which neglects inflow may not be adequate. Several models have been proposed for in-cylinder heat transfer with inflow-produced turbulence. Existing models are based on the assumption that turbulence levels remain constant over the cycle. In the current work, experiments were performed to measure the effects of inflow produced turbulence on in-cylinder heat transfer. Experiments were conducted for two different inflow configurations. These experiments have shown that turbulence levels can change significantly over the course of the cycle, invalidating one of the major assumptions common to existing models. In response to the experimental results, a new model was proposed to predict the effects of variations in the turbulence level throughout the cycle. Based on the I-D energy equation, it extends an existing heat transfer model by replacing the laminar thermal conductivity with a time varying effective turbulent thermal conductivity. The varying component of the effective thermal conductivity is assumed to be small relative to the mean component, allowing the use of a perturbation method. Two Nusselt numbers were formulated based on the model results. The first was a complex valued Nusselt number. Previous work had demonstrated that a constant complex Nusselt number could effectively predict heat transfer throughout the cycle in cylinder spaces without inflow. For cylinders with inflow, the current model predicts a complex Nusselt number that varies over the cycle. The second Nusselt number was formed using the steady components of the second order temperature profiles. F or this steady Nusselt number, including the effects of thermal conductivity variations throughout the cycle resulted in a heat transfer coefficient that was larger than that predicted using a mean effective conductivity alone. / Master of Science

This research involves the study of a one- and two-cylinder convertible reciprocating Freon compressor for air conditioning or refrigeration purposes. The main concern is the reduction of the vibration (noise) caused during the operation of the compressor. Vibration is a main concern when the compressor is shifted from the one-cylinder operation to the two-cylinder operation mode and the reverse of this shift. The objectives for this research are (1) to investigate the shaking force due to the reciprocating mass at high frequencies, which are up to 4600 Hz (80w) in this research; (2) to determine the dominant force for compressor vibration among the three possible sources of shaking force due to reciprocating mass, impact forces due to clearance at the connecting rod - piston joint, and the z-axis force from the motor torque due to the rotor's conductor rods being skewed at an angle; (3) to minimize the difference in change of kinetic energies when switching between the one- and two-cylinder operating modes of the compressor. The properties of the vibration in one- and two-cylinder operation have been studied and results have been analyzed in terms of kinetic energies generated in different setting of operation of the compressor. Dynamic simulation for the impact force is computed using SIMULINK. The Z-axis force due to the motor is computed. Results indicated that shaking force due to the reciprocating mass is the dominant force for only the first two harmonics (w, 2w). An optimization routine based on Hooke and Jeeves pattern search method is developed and an optimized setting of angle, force, and torque for balancing of the crankshaft to achieve objective (3) is determined. / Master of Science