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.

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

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In our study, the Finite Volume Method (FVM) is successfully implemented to simulate thermal process of polymerization. This application is verified based on the obtained plots compared with those from other two methods as well as experimental data. After the verification, a method is developed to optimize heat history in order to reduce processing time and in the meantime to maintain the uniformity of cure state. Also sensitivities of cure state to different parameters are examined. Besides, a correlation between temperature and the degree of polymerization profile on sample surface is found using on-line monitoring method.

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The need and demand for propulsion devices on nanosatellites has grown over the last decade due to interest in expanding nanosatellite mission abilities, such as attitude control, station-keeping, and collision avoidance. One potential micro-propulsion device suitable for nanosatellites is an electrothermal plasma thruster called Pocket Rocket. Pocket Rocket is a low-power, low-cost propulsion platform specifically designed for use in nanosatellites such as CubeSats. Due to difficulties associated with integrating propulsion devices onto spacecraft such as volume constraints and heat dissipation limitations, a characterization of the heat generation and heat transfer properties of Pocket Rocket is necessary. Several heat-transfer models of Pocket Rocket were considered as a part of this analysis to determine viability and complexity of the analysis, including a lumped thermal model, a finite-element model written in MATLAB, and a finite-volume model constructed using ANSYS Fluent and environmental conditions to closely reflect the experimental environment, both steady-state and transient. Results were validated experimentally. A Pocket Rocket thruster was manufactured for this purpose, and data regressed against model predictions to compare the validity of predicted models. Thermal models compared favorably to experimental measurements, accurately predicting the temperatures obtained at the surface of the thruster within 10 Kelvin after 1.5 hours of operation as well as the temporally-dependent temperature increases during the duration of operation within a standard error of ±6 Kelvin. Mission and integration viability is found to be favorable and within the realm of practicality for use of Pocket Rocket on nanosatellites.

The transient thermal response of a 15-cell, 48 volt, lithium-ion battery pack for an unmanned ground vehicle was simulated with ANSYS Fluent. Heat generation rates and specific heat capacity of a single cell were experimentally measured and used as input to the thermal model. A heat generation load was applied to each battery and natural convection film boundary conditions were applied to the exterior of the enclosure. The buoyancy-driven natural convection inside the enclosure was modeled along with the radiation heat transfer between internal components. The maximum temperature of the batteries reached 65.6 °C after 630 seconds of usage at a simulated peak power draw of 3,600 watts or roughly 85 amps. This exceeds the manufacturer's maximum recommended operating temperature of 60 °C. The pack was redesigned to incorporate a passive thermal management system consisting of a composite expanded graphite matrix infiltrated with a phase-changing paraffin wax. The redesigned battery pack was similarly modeled, showing a decrease in the maximum temperature to 50.3 °C after 630 seconds at the same power draw. The proposed passive thermal management system kept the batteries within their recommended operating temperature range.

Heat transfer is a critical part of engineering design, from the cooling of rocket engines to the thermal management of the increasingly dense packaging of electronic circuits. Even for the most fundamental modes of heat transfer, a topic of research is devoted to finding novel ways to improve it. In recent decades, investigators experimented with the idea of exposing systems to acoustic waves with the hope of enhancing thermal transfer at the surface of a body. Ultrasound has been applied with some success to systems undergoing nucleate boiling and in single-phase forced and free convection heat transfer in water. However, little research has been done into the use of sound waves to improve heat transfer in air. In this thesis the impact of acoustic waves on natural convection heat transfer from a horizontal cylinder in air is explored. An experimental apparatus was constructed to measure natural convection from a heated horizontal cylinder. Verification tests were conducted to confirm that the heat transfer could be described using traditional free convection heat transfer theory. The design and verification testing of the apparatus is presented in this work. Using the apparatus, experiments were conducted to identify if the addition of acoustic waves affected the heat transfer. For the first set of experiments, a 40 kHz standing wave was created along the length of the heated horizontal cylinder. While our expectation was that our results would mirror those found in the literature related to cooling enhancement using ultrasound in water (cited in the body of this thesis), they did not. When a 40 kHz signal was used to actuate the air surrounding the heated cylinder assembly, no measurable enhancement of heat transfer was detected. Experiments were also performed in the audible range using a loudspeaker at 200 Hz, 300 Hz, 400 Hz, 500 Hz, and 2,000 Hz. Interestingly, we found that a 200 Hz acoustic wave causes a significant, measurable impact on natural convection heat transfer in air from a horizontal cylinder. The steady-state surface temperature of the cylinder dropped by approximately 12℃ when a 200 Hz wave was applied to the system.

This report details an approach to using metal foam heat exchangers inside an integrated thermal management system on a variable cycle engine. The propulsion system of interest is a variable cycle engine with an auxiliary, variable flow rate fan. The feasibility of utilizing an open-celled metallic foam heat exchanger in the ducting between the constant and variable-fans on this variable cycle engine to cool the avionics was explored using an experimental approach. Two heat exchangers, 6.3 inch width by 6.3 inch length by 0.5 inch thickness, were constructed from 20 and 40 pores per inch (PPI) metal foam and tested. Both were constructed using 6061-T6 aluminum open-cell metal foam with a relative density of 8% and brazed using 4047 aluminum braze to 0.02 inch thick sheet metal made of 6061-T6 aluminum. Both models were subjected to internal forced convection using heated air with flow rates of 4, 8, 12, 16, and 20 standard cubic feet per minute (SCFM). They were also subjected to external forced convection using blowers to supply cooling air to simulate the variable cycle engine’s fans. One duct was supplied with a constant 34 ft/s cooling flow, while the other cooling flow velocity was varied between 0% and 100% of this 34 ft/s, in 25% increments. The temperature and pressure of the flow internal to the metal foam, as well as the heat exchanger external surface and cold flow temperatures, were recorded. A hot-flow Reynolds number range of 1,300 to 6,400 was tested. Results showed expected trends for the hydraulic performance of both heat exchangers. The form factors were 50.4 and 54.8 ft^-1 and the permeabilities were 9.11E-7 and 6.32E-7 ft^2 for the 20 and 40 PPI heat exchangers, respectively. Due to a defect on one side of the 40 PPI heat exchanger, the thermal results are based only on the 20 PPI heat exchanger. While the present study examines a different metal foam heat transfer configuration than most other studies, the metal foam Nusselt numbers were comparable to past studies. In addition, the pumping power required was not excessive and would allow the thermal management system to be realized without an unreasonable energy input. Therefore, a metal foam heat exchanger integrated within the ducting of a variable cycle engine is deemed feasible. The pumping power and thermal resistance were used to create a performance predicting model of the 20 PPI heat exchanger. From this model, the optimized 20 PPI heat exchanger has a hot-flow rate of 10.5 SCFM. The resulting pumping power and thermal resistance are estimated to be 6.7 BTU/hr and 0.036 °R/(BTU/hr), respectively.

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