Thesis. 1976. Sc.D.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Microfiche copy available in Archives and Engineering. / Vita. / Bibliography: leaves 122-128. / Sc.D.

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The ironmaking blast furnace (BF) remains the most significant and important process for the production of liquid iron. For the achievement of stable furnace operation and good performance, mathematical modellings at different levels increasingly become a powerful tool in developing better understanding of this multiphase flow system, in particular the gas-solid flow. This thesis represents an effort in this area. A simplified and continuum-based mathematical model is proposed and tested to predict the BF gas-solid flow at a macroscopic level. The results show that the simple model is able to predict the general features of the solid flow, including the effects of gas and solid flowrates, and materials properties. The simplified model can be readily implemented in a full process model that needs to have a quick response to change for the purpose of control and optimization. To overcome the difficulties encountered in continuum modelling, i.e. determination of constitutive correlations, and particularly the description of the stagnant zone when related to BF, a discrete model based on the coupling approach of discrete element method (DEM) and computational fluid dynamics (CFD) is then employed to investigate the gas-solid flow in a model BF at a microscopic level. The results confirm the effects of variables such as gas flow rate, solid flow rate, particle properties, and model types. More importantly, such an approach can generate abundant microscopic information such as flow structure (particle velocity, porosity, coordination number) and force structure, which are of paramount importance to elucidate the gas-solid flow mechanisms, and develop a more comprehensive understanding of BF gas-solid flow, such as the formation mechanism of the stagnant zone. Further, the transient gas-solid flow phenomena, together with the considerations of cohesive zones and hearth liquid, can be predicted. Further, in order to develop understanding of thermal behaviour and elucidate the heat transfer mechanisms occurring in particle-fluid flow system, a new model is proposed by extending the DEM-CFD, and then tested in gas fluidization. The model considers the three heat transfer modes, and demonstrates its ability in investigating the heat transfer mechanisms, and offers an effective method to elucidate the mechanisms governing the heat transfer in particle-fluid systems at a particle scale. It is recommended to apply to the study of BF thermal behaviour.

A miniature reciprocating expander is being developed as part of a larger program to develop a heat actuated heat pump for portable applications. By utilizing the higher energy density of liquid hydrocarbon fuels relative to batteries, a heat actuated heat pump would be able to provide cooling for much longer than motor driven units of equal weight. A prototype expander has been constructed and demonstrated to produce up to 22 W of shaft power at 2500 rpm using 60 psig, room temperature nitrogen as the input. Assuming adiabatic conditions, the expander appears to operate at up to 80% isentropic efficiency. However, when heat inflow to the expander is accounted for, the resulting polytropic efficiency is about 10% lower. In addition to experimental results, models of expander performance with different loss mechanisms are presented. These mechanisms include over- and under-expansion, in-cylinder heat transfer, clearance volume, friction, and valve pressure drop. / Graduation date: 2005

The effects of the orifice geometry and the surface boundary condition on the heat transfer distribution to a flat surface of an impinging jet array were investigated. The jet array impinged normally onto the surface which was either isothermal or had a uniform heat flux. The experiments were performed for the flow rate range from 0.0039 to 0.0070 m��/s corresponding to jet Reynolds numbers of 5000 to 11000. The jet-to-surface spacings varied from 1 to 4 jet diameters. After impinging, the air jet was constraine4 to exit in one direction creating a "crossflow". condition. The isothermal surface results are presented in terms of the average heat transfer coefficient. For the uniform heat flux surface, both average and local values are presented. The average and local heat transfer distributions were mapped using thermochromic liquid crystals. Results are presented for two jet geometries: circular and cusped ellipse. The cusped ellipse jets show better heat transfer performance compared to the circular jets for both surface boundary conditions. This is thought to be a result of increased turbulence and the axis-switching phenomenon. Results for the uniform heat flux surface boundary higher than for the isothermal surface boundary condition. This result can be explained by the difference between the surface temperature and the jet temperature for both surface boundary conditions. Correlations of Nusselt versus Reynolds numbers are presented for both jet geometries and surface boundary conditions. / Graduation date: 2000

Miniature energy and chemical systems (MECS) are miniature thermal, fluid, and chemical devices in the mesoscale size range between a sugar cube and a human fist. MECS take advantage of improved rates of mass and heat transfer that have been observed at the microscale. There are many potential applications for MECS, including manportable cooling and decentralized chemical processing. However, this potential has not been realized due to limitations in microfabrication. MECS devices require: 1) the fabrication of complex geometries incorporating microscale features; and 2) the thermal, mechanical and chemical properties of engineering metals. This thesis centers on developing a process for producing high-aspect-ratio, MECS devices in stainless steel. In order to achieve this goal, laser ablation and diffusion bonding were employed in a metal microlamination (MML) process. The process involves stacking and bonding a series of laminates with low-aspect-ratio features to produce a composite device with high-aspect-ratio features (20:1). Laser ablation was used to form many laminates of 0.003" 302 stainless steel. These laminates were then joined via diffusion bonding. The process developed in this thesis is unique in that it: 1) permits the MECS designer greater freedom in specifying microchannel widths; and 2) has produced microscale features in excess of 20:1 aspect ratio. Microchannels and microfins in excess of 20:1 aspect ratio were fabricated in stainless steel using this method. Resultant microchannels were tested by flowing air through them at various flow rates and measuring the resulting pressure drop. Experimental results were compared with theoretical calculations and other technical literature. Findings suggest that the preliminary efforts to build a MECS device resulted in significant air blockage in the microchannel passageways. Sources of this blockage include bent fins, warpage and misalignment among others. Further process refinements are needed to prove the economic viability of this process. / Graduation date: 1998